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1.  Peak Fat Oxidation Rate During Walking in Sedentary Overweight Men and Women 
The aim of this study was to determine the relative exercise intensity that elicits maximal fat oxidation during walking in inactive and overweight men and women and evaluate any possible sex differences. Forty six healthy, sedentary, overweight men (age: 36.3 ± 1.3 years, body fat: 28.8 ± 0.8%, n = 28, mean ± SE) and women (age: 36.6 ± 1.8 years, body fat: 37.1 ± 0.8%, n = 18) participated in the study. Fat oxidation was calculated from expired air analysis using indirect calorimetry during an incremental treadmill walking test. Peak fat oxidation rate (PFO) was higher in men compared to women (0.31 ± 0.02 vs. 0.20 ± 0.02 g.min-1; p < 0.001), but this difference disappeared when PFO was scaled per kg fat-free mass (4. 36 ± 0.23 vs. 3.99 ± 0.37 fat free mass-1.min-1). Also, the relative exercise intensity at which PFO occurred was similar for men and women and corresponded to 40.1 ± 1.8 and 39. 5 ± 2.3% of maximal oxygen uptake (VO2max) and 60.0 ± 1.4 and 57.8 ± 1.4% of maximal heart rate, respectively. The walking speed corresponding to PFO was 5.5 ± 0.2 and 5.0 ± 0.1 km·h-1 for men and women, respectively. Regression analysis showed that sex, FFM and VO2max were significant predictors of PFO expressed in g.min-1 (adjusted R2 = 0.48, p = 0.01). However when PFO was scaled per kg FFM, only a small part of the variance was explained by VO2max (adjusted R2 = 0.12, p < 0.05). In conclusion, peak fat oxidation rate and the corresponding relative exercise intensity were similar in male and female overweight and sedentary individuals, but lower compared to those reported for leaner and/or physically active persons. Walking at a moderate speed (5.0-5.5 km·h-1) may be used as a convenient way to exercise at an intensity eliciting peak fat oxidation in overweight individuals.
Key pointsPeak fat oxidation rate scaled per kg fat-free mass and the corresponding relative exercise intensity are similar in male and female overweight and sedentary individuals, but lower compared to those reported for leaner and/or physically active persons.Walking at a moderate speed (5.0-5.5 km.h-1) may be used as a convenient way to exercise at an intensity eliciting peak fat oxidation in overweight individuals.The relationship between %HRmax and %VO2max in overweight individuals is different from that reported for normal-weight adults and should be taken into account to optimize exercise intensity using heart rate in obese individuals.Due to the low intensity corresponding to peak fat oxidation in overweight and sedentary persons and the inter-individual differences, exercise intensity for health benefits should be prescribed following individual testing.
PMCID: PMC3761910  PMID: 24149961
Exercise intensity; calorimetry; substrate utilisation
2.  Gender differences in injuries among rural youth. 
Injury Prevention  1995;1(1):15-20.
GOAL: This paper presents injury data from the first year of a three year longitudinal study of risk taking behaviors among adolescents. SAMPLE: Study subjects were a cohort of 758 rural students from Maryland's Eastern Shore who were in the eighth grade in 1987. METHODS: Students completed a 45 minute, self administered survey in which they reported numbers of injuries experienced in the past year, risk taking behaviors, anger expression, delinquency, alcohol and drug use, physical exercise, work experience, and level of parental supervision. In addition, students had their height and weight measurements taken by trained research staff and completed a self rating of pubertal development using Tanner drawings. RESULTS: Slightly more than half (53.2%) of the boys and over one third (37.7%) of the girls reported experiencing one or more medically attended injuries during the last year. Poisson regression analyses were conducted to estimate the extent to which gender differences in injuries could be accounted for by adolescent behaviors. Gender effects became non-significant when adjustments were made for risk taking, school discipline problems, and exercise frequency. Gender differences in injuries were reduced but remained significant when substance use, employment, and anger were controlled. Poisson regression analyses were conducted separately for males and females to assess whether factors associated with injuries were similar across genders. For boys, risk taking, anger, and school discipline problems were significantly related to number of injuries. Boys with a low body mass index and late pubertal development (mean ratio 3.09), as well as those with high body mass index and early pubertal development (mean ratio 2.16), reported greater numbers of injuries than average boys. For girls, substance use, cruising, risk taking, anger, and exercise frequency were significantly associated with injuries. Girls with an early onset of menses reported, on average, twice the number of injuries than those who were on time. Girls with high body mass index who were late in their pubertal development reported, on average, five times more injuries than other girls. CONCLUSIONS: Although gender is a significant risk factor for injuries, certain behaviors like risk taking, school related delinquency, and physical exercise partially explain the higher number of injuries among adolescent males in this study. For both males and females, indicators of pubertal and physical development are important factors to consider in studies of injuries during early adolescence.
PMCID: PMC1067535  PMID: 9345987
3.  Cardiorespiratory Characteristics and Cholesterol Responses to a Single Session of Heavy Leg Press Exercise 
The effect of resistance exercise on blood lipids is not clear yet. The purpose of this study was to examine the cholesterol responses to a heavy resistance leg press exercise emphasizing on the eccentric movement 24 and 48 hours following exercise and to quantify the cardiorespiratory responses of the exercise bout in an attempt to clarify the exercise characteristics that may be responsible for the effects of heavy resistance exercise on blood lipids. Nine healthy, untrained male volunteers aged 27.2 ± 1.1 yrs (76.2 ± 2.5 kg, 1.79 ± 0.02 m) performed a session of heavy RE emphasizing on the eccentric movement consisting of eight sets of inclined leg presses at six repetition maximum with 3-min rest intervals. Venous blood samples were obtained at rest (control) and 24 and 48 hours following exercise. Average VO2 at rest was 4.0 ± 0.4 ml·min−1·kg−1, during exercise 19.6 ± 0.2 ml·min−1·kg−1 and during the 180 sec recovery period between sets 12.5 ± 0.2 ml·min−1·kg−1. RER values decreased with the progression of the exercise and were significantly lower during the last four sets compared with the first four sets of the exercise session. Resting heart rate was 67 ± 2 bpm, and maximum heart rate during exercise was 168 ± 1 bpm. Serum creatine kinase was significantly elevated on day 1 (1090 ± 272 U·L−1, p < 0.03) and peaked on day 2 (1230 ± 440 U·L−1 p < 0. 01). Total cholesterol, HDL cholesterol and calculated LDL cholesterol concentration did not change significantly following with exercise. This protocol of heavy resistance exercise has no effect on TC or cholesterol sub-fraction concentration 24 and 48 hours following exercise which may be due to the low energy expenditure of the exercise and/or to the gender of the participants.
Key pointsRepeated sets of heavy resistance exercise significantly increase oxygen uptake both during exercise and the following recovery period.Even though exercise was of low volume (8 sets x 6 repetitions) the elevated oxygen uptake during the rest intervals in combination with the total exercise session duration (26 min) resulted in aerobic energy expenditure that is equivalent to low to moderate intensity cycling.Leg press resistance exercise emphasizing on the eccentric movement that caused muscle damage had no effect on total cholesterol, HDL-C and LDL-C during the two days following exercise in young healthy male subjects.
PMCID: PMC3761812  PMID: 24149784
Muscle damage; energy expenditure; total cholesterol; HDL; oxygen uptake.
4.  Acute Physiological Responses to Short- and Long-Stage High-Intensity Interval Exercise in Cardiac Rehabilitation: A Pilot Study 
Despite described benefits of aerobic high-intensity interval exercise (HIIE), the acute responses during different HIIE modes and associated health risks have only been sparsely discovered in heart disease patients. Therefore, the aim of this study was to investigate the acute responses for physiological parameters, cardiovascular and inflammatory biomarkers, and catecholamines yielded by two different aerobic HIIE protocols compared to continuous exercise (CE) in phase III cardiac rehabilitation. Eight cardiac patients (7 with coronary heart disease, 1 with myocarditis; 7 males, 1 female; age: 63.0 ± 9.4 years; height: 1.74 ± 0.05 m; weight: 83.6 ± 8.7 kg), all but one treated with ß-blocking agents, performed a maximal symptom-limited incremental exercise test (IET) and three different exercise tests matched for mean load (Pmean) and total duration: 1) short HIIE with a peak workload duration (tpeak) of 20 s and a peak workload (Ppeak) equal to the maximum power output (Pmax) from IET; 2) long HIIE with a tpeak of 4 min, Ppeak was corresponding to the power output at 85 % of maximal heart rate (HRmax) from IET; 3) CE with a target workload equal to Pmean of both HIIE modes. Acute metabolic and peak cardiorespiratory responses were significantly higher during long HIIE compared to short HIIE and CE (p < 0.05) except HRpeak which tended to be higher in long HIIE than in short HIIE (p = 0.08). Between short HIIE and CE, no significant difference was found for any parameter. Acute responses of cardiovascular and inflammatory biomarkers and catecholamines didn’t show any significant difference between tests (p > 0.05). All health-related variables remained in a normal range in any test except NT-proBNP, which was already elevated at baseline. Despite a high Ppeak particularly in short HIIE, both HIIE modes were as safe and as well tolerated as moderate CE in cardiac patients by using our methodological approach.
Key pointsHigh-intensity interval exercise (HIIE) with short peak workload durations (tpeak) induce a lower acute metabolic and peak cardiorespiratory response compared to intervals with long tpeak despite higher peak workload intensities and identical mean load. No significant difference for any physiological parameter was found between short HIIE and CE.Between short HIIE, long HIIE, and CE, no significant difference was found in the increase (or decrease, respectively,) of health related markers such as cardiovascular biomarkers, catecholamines, or inflammatory parameters during exercise.During all exercise modes, all risk markers remained in a normal range except for NT-proBNP which was, however, already elevated at baseline.Short HIIE, long HIIE, and CE were safely performed by patients with CHD or myocarditis in cardiac rehabilitation by using our methodological approach to exercise prescription. This approach included the prescription of exercise intensities with respect to LTP1, LTP2, and Pmax as well as a conscious setting of Pmean at a moderate level (80 % of PLTP2). Importantly, all exercise modes were matched for Pmean and exercise duration in order to enable a comparison of the three protocols.
PMCID: PMC4763850  PMID: 26957930
intermittent exercise; exercise prescription; acute effects; health-related markers; heart disease patients
5.  Comparison of rehydration regimens for rehabilitation of firefighters performing heavy exercise in thermal protective clothing: A report from the Fireground Rehab Evaluation (FIRE) trial 
Fire suppression activities results in cardiovascular stress, hyperthermia, and hypohydration. Fireground rehabilitation (rehab) is recommended to blunt the deleterious effects of these conditions.
We tested the hypothesis that three rehydration fluids provided after exercise in thermal protective clothing (TPC) would produce different heart rate or core temperature responses during a second bout of exercise in TPC.
On three occasions, 18 euhydrated firefighters (16 males, 2 females) wearing TPC completed a standardized, 50-minute bout of upper and lower body exercise in a hot room that mimicked the National Fire Protection Association (NFPA) rehabilitation guidelines of “two cylinders before rehab” (20 min work, 10 min recovery, 20 min work). After an initial bout of exercise, subjects were randomly assigned water, sport drink, or an intravenous (IV) infusion of normal saline equal to the amount of body mass lost during exercise. After rehydration, the subject performed a second bout of exercise. Heart rate, core and skin temperature, and exercise duration were compared with a two-way ANOVA.
Subjects were firefighters aged 28.2±11.3 years with a VO2peak of 37.4±3.4 ml/kg/min. 527±302 mL of fluid were provided during the rehabilitation period. No subject could complete either the pre- or post-rehydration 50-minute bout of exercise. Mean (SD) time to exhaustion (min) was longer (p<0.001) in bout 1 (25.9±12.9 min. water, 28.0±14.1 min. sport drink, 27.4±13.8 min. IV) compared to bout 2 (15.6±9.6 min. water, 14.7±8.6 min. sport drink, 15.7±8.0 min. IV) for all groups but did not differ by intervention. All subjects approached age predicted maximum heart rate at the end of bout 1 (180±11 bpm) and bout 2 (176±13 bpm). Core temperature rose 1.1±0.7°C during bout 1 and 0.5±0.4°C during bout 2. Core temperature, heart rate, and exercise time during bout 2 did not differ between rehydration fluids.
Performance during a second bout of exercise in TPC did not differ when firefighters were rehydrated with water, sport drink, or IV normal saline when full rehydration is provided. Of concern was the inability of all subjects to complete two consecutive periods of heavy exercise in TPC suggesting the NFPA “two cylinders before rehab” guideline may not be appropriate in continuous heavy work scenarios.
PMCID: PMC2867093  PMID: 20095824
Cardiovascular strain; Thermal Stress; Performance; Hydration
6.  How to Regulate the Acute Physiological Response to “Aerobic” High-Intensity Interval Exercise 
The acute physiological processes during “aerobic” high-intensity interval exercise (HIIE) and their regulation are inadequately studied. The main goal of this study was to investigate the acute metabolic and cardiorespiratory response to long and short HIIE compared to continuous exercise (CE) as well as its regulation and predictability. Six healthy well-trained sport students (5 males, 1 female; age: 25.7 ± 3.1 years; height: 1.80 ± 0.04 m; weight: 76.7 ± 6.4 kg; VO2max: 4.33 ± 0.7 l·min-1) performed a maximal incremental exercise test (IET) and subsequently three different exercise sessions matched for mean load (Pmean) and exercise duration (28 min): 1) long HIIE with submaximal peak workloads (Ppeak = power output at 95 % of maximum heart rate), peak workload durations (tpeak) of 4 min, and recovery durations (trec) of 3 min, 2) short HIIE with Ppeak according to the maximum power output (Pmax) from IET, tpeak of 20 s, and individually calculated trec (26.7 ± 13.4 s), and 3) CE with a target workload (Ptarget) equating to Pmean of HIIE. In short HIIE, mean lactate (Lamean) (5.22 ± 1.41 mmol·l-1), peak La (7.14 ± 2.48 mmol·l-1), and peak heart rate (HRpeak) (181.00 ± 6.66 b·min-1) were significantly lower compared to long HIIE (Lamean: 9.83 ± 2.78 mmol·l-1; Lapeak: 12.37 ± 4.17 mmol·l-1, HRpeak: 187.67 ± 5.72 b·min-1). No significant differences in any parameters were found between short HIIE and CE despite considerably higher peak workloads in short HIIE. The acute metabolic and peak cardiorespiratory demand during “aerobic” short HIIE was significantly lower compared to long HIIE and regulable via Pmean. Consequently, short HIIE allows a consciously aimed triggering of specific and desired or required acute physiological responses.
Key pointsHigh-intensity interval exercise (HIIE) with short peak workload durations (tpeak) induce a lower acute metabolic and peak cardiorespiratory response compared to intervals with long tpeak despite higher peak workload intensities (Ppeak) and identical mean load (Pmean).Short HIIE response is the same as in continuous exercise (CE) matched for Pmean.It is possible to regulate and predict the acute physiological response by means of Pmean for short HIIE but not for long HIIE.The use of fixed percentages of maximal heart rate (HRmax) for exercise intensity prescription yields heterogeneous exercise stimuli across subjects. Therefore, objective individual markers such as the first and the second lactate turn point are recommend prescribing exercise intensity not only for continuous but also for intermittent exercise.
PMCID: PMC4306779  PMID: 25729286
Intermittent exercise; exercise prescription; acute physiological demand; mean load; peak workload duration
7.  Abnormal haemodynamic response to exercise in heart failure with preserved ejection fraction 
European Journal of Heart Failure  2011;13(12):1296-1304.
Peak oxygen uptake (VO2) is diminished in patients with heart failure with preserved ejection fraction (HFpEF) suggesting impaired cardiac reserve. To test this hypothesis, we assessed the haemodynamic response to exercise in HFpEF patients.
Methods and results
Eleven HFpEF patients (73 ± 7 years, 7 females/4 males) and 13 healthy controls (70 ± 4 years, 6 females/7 males) were studied during submaximal and maximal exercise. The cardiac output (Qc, acetylene rebreathing) response to exercise was determined from linear regression of Qc and VO2 (Douglas bags) at rest, ∼30% and ∼60% of peak VO2, and maximal exercise. Peak VO2 was lower in HFpEF patients than in controls (13.7 ± 3.4 vs. 21.6 ± 3.6 mL/kg/min; P < 0.001), while indices of cardiac reserve were not statistically different: peak cardiac power output [CPO = Qc × mean arterial pressure (MAP); HFpEF 1790 ± 509 vs. controls 2119 ± 581 L/mmHg/min; P = 0.20]; peak stroke work [SW = stroke volume (SV) × MAP; HFpEF 13 429 ± 2269 vs. controls 13 200 ± 3610 mL/mmHg; P = 0.80]. The ΔQc/ΔVO2 slope was abnormally elevated in HFpEF patients vs. controls (11.2 ±3.6 vs. 8.3 ± 1.5; P = 0.015).
Contrary to our hypothesis, cardiac reserve is not significantly impaired in well-compensated outpatients with HFpEF. The abnormal haemodynamic response to exercise (decreased peak VO2, increased ΔQc/ΔVO2 slope) is similar to that observed in patients with mitochondrial myopathies, suggesting an element of impaired skeletal muscle oxidative metabolism. This impairment may limit functional capacity by two mechanisms: (i) premature skeletal muscle fatigue and (ii) metabolic signals to increase the cardiac output response to exercise which may be poorly tolerated by a left ventricle with impaired diastolic function.
PMCID: PMC3220394  PMID: 21979991
Cardiac output response to exercise; Haemodynamic response to exercise; Heart failure with preserved ejection fraction; Exercise capacity; Myocardial contractile reserve; Oxygen consumption
8.  The Effect of High Intensity Interval Exercise in High / Low Temperatures on Exercise-Induced Bronchoconstriction (EIB) in Trained Adolescent Males 
Tanaffos  2013;12(3):29-43.
Exercise-induced bronchoconstriction (EIB) describes airway narrowing that occurs in association with exercise. Exercise in hot and cold environments has been reported to increase exercise-induced bronchoconstriction (EIB) in subjects with asthma. However, to our knowledge, the effect of hot and cold environment on pulmonary function and EIB in trained males has not been previously studied. The main goal of this research was to examine the influence of environmental temperature and high intensity interval exercise on pulmonary function in trained teenage males. Also, this study sought to assess the influence of exercise and environmental temperature on EIB.
Materials and Methods
Thirty trained subjects (mean age 16.56±0.89 yrs, all males) underwent high intensity interval exercise testing (22 minutes) by running on a treadmill in hot and cold environments under standardized conditions (10 °C and 45 °C with almost 50% relative humidity in random order in winter and summer). Lung function (flow volume loops) was measured before and 1, 5, 15, 30 and 60 min after the exercise by digital spirometer. Data was analyzed using SPSS software and P < 0.05 was considered significant. The diagnosis of EIB was made by 10% fall in FEV1 post-exercise.
The post-exercise maximal reduction in forced expiratory volume in 1s (FEV1), peak expiratory flow (PEF) and average forced expiratory flow rate over the middle 50% of the FVC (FEF25-75) increased significantly compared to pre-exercise at 10 °C with almost 50% relative humidity (cold air). The obtained values were: -15.93(15min post-exercise), -22.53 (1 min post-exercise) and -18.25%(5min post-exercise). Post-exercise maximal reduction in FEV1, PEF and FEF25-75 increased significantly compared to pre-exercise value at 45 °C with almost 50% relative humidity (hot air). Obtained values were: -10.35 (1 min post-exercise), -9.16 (1 min post-exercise) and -7.39 (5 min post-exercise). Changes in FEV1, PEF and FEF25-75 reduction in cold air was significantly greater than in hot air (P < 0.05). Maximal prevalence of exercise-induced bronchoconstriction (EIB) in cold and hot air was 60% (18 of 30 subjects) and 40% (12 of 30 subjects), respectively.
This study demonstrated that pulmonary function in hot and cold air was influenced by temperature (in the same relative humidity (50%) and also high intensity interval exercise. Prevalence of EIB after high intensity exercise in hot and cold air increased in trained adolescent males; however, these changes in cold air were greater than in hot air among trained adolescent males. Therefore, results of this study suggest that adolescents (although trained) should avoid high intensity (95% maximal heart rate) exercise in winter (extremely low temperature) and summer (extremely high temperature) to prevent EIB.
PMCID: PMC4153253  PMID: 25191471
Temperature; Exercise-Induced Bronchoconstriction; Exercise
9.  Ventilatory response to exercise in adolescents with cystic fibrosis and mild-to-moderate airway obstruction 
SpringerPlus  2014;3:696.
Data regarding the ventilatory response to exercise in adolescents with mild-to-moderate cystic fibrosis (CF) are equivocal. This study aimed to describe the ventilatory response during a progressive cardiopulmonary exercise test (CPET) up to maximal exertion, as well as to assess the adequacy of the ventilatory response for carbon dioxide (CO2) exhalation. Twenty-two adolescents with CF (12 boys and 10 girls; mean ± SD age: 14.3 ± 1.3 years; FEV1: 78.6 ± 17.3% of predicted) performed a maximal CPET. For each patient, data of a sex- and age matched healthy control was included (12 boys and 10 girls; mean ± SD age: 14.3 ± 1.4 years). At different relative exercise intensities of 25%, 50%, 75%, and 100% of peak oxygen uptake (VO2peak), breathing pattern, estimated ventilatory dead space ventilation (VD/VT ratio), minute ventilation (VE) to CO2 production relationship (VE/VCO2-slope), partial end-tidal CO2 tension (PETCO2), and the VE to the work rate (VE/WR) ratio were examined. VO2peak was significantly reduced in CF patients (P = 0.01). We found no differences in breathing pattern between both groups, except for a significantly higher VE at rest and a trend towards a lower VE at peak exercise in patients with CF. Significantly higher values were found for the estimated VD/VT ratio throughout the CPET in CF patients (P < 0.01). VE/VCO2-slope and PETCO2 values differed not between the two groups throughout the CPET. VE/WR ratio values were significantly higher in CF during the entire range of the CPET (P < 0.01). This study found an exaggerated ventilatory response (high VE/WR ratio values), which was adequate for CO2 exhalation (normal VE/VCO2-slope and PETCO2 values) during progressive exercise up to maximal exhaustion in CF patients with mild-to-moderate airway obstruction.
PMCID: PMC4254890  PMID: 25512888
Pulmonary physiology; Ventilation; Breathing pattern; Children
10.  Inspiratory Muscle Fatigue Following Moderate-Intensity Exercise in the Heat 
Heavy exercise has been shown to elicit reductions in inspiratory muscle strength in healthy subjects. Our purpose was to determine the combined effects of moderate-intensity endurance exercise and a thermal load on inspiratory muscle strength in active subjects. Eight active, non heat-acclimatized female subjects (23.5 ± 1.4 yr; VO2max = 39.8 ± 2.4 randomly performed two 40 min endurance exercise bouts (60% VO2max) in either a thermo-neutral (22°C/21% RH) or hot (37°C/33% RH) environment on separate days. Maximal sustained inspiratory mouth pressure (PImax) was obtained pre and post exercise as an index of inspiratory muscle strength. Additional variables obtained every 10 min during the endurance exercise bouts included: rectal temperature (TRE), heart rate (HR), minute ventilation (VE), oxygen uptake (VO2), tidal volume (VT), breathing frequency (Fb), and ratings of perceived exertion and dyspnea (RPE/RPD). Data were analyzed with repeated measures ANOVA. PImax was significantly reduced (p < 0.05) after exercise in the hot environment when compared to baseline and when compared to post exercise values in the thermo-neutral environment. PImax was unchanged from baseline following exercise in the thermo-neutral environment. HR and TRE were significantly higher (p < 0.05) in the hot compared to the thermo-neutral environment. VE and VO2 were not significantly different between conditions. VT was unchanged between conditions whereas Fb was higher (p < 0.05) in the hot condition compared to thermo-neutral. RPE was not significantly different between conditions. RPD was significantly higher (p < 0.05) in the hot compared to the thermo-neutral environment. We conclude that moderate-intensity endurance exercise (60% VO2max) in a hot environment elicits significant reductions in inspiratory muscle strength in unfit females. This finding is novel in that previous studies conducted in a thermo-neutral environment have shown that an exercise intensity of >80% VO2max is required to elicit reductions in inspiratory muscle strength. In addition, dyspnea perception during exercise is greater in a hot environment, compared to thermo-neutral, at a similar level of VE and VO2.
Key PointsThe combined effects of a heat load and exercise on inspiratory muscle strength were investigated in untrained female subjects.Previous studies have shown that a very high exercise intensity (> 80% VO2max) is required to elicit reductions in inspiratory muscle strength.Prolonged submaximal exercise (40-min/60% VO2max) in a hot environment significantly reduced inspiratory muscle strength in untrained females whereas the same intensity in a thermo-neutral environment had no effect on inspiratory muscle function.These reductions in inspiratory muscle strength may be related to competition for blood flow among the locomotor, inspiratory, and cutaneous circulations.
PMCID: PMC3887326  PMID: 24453527
Control of breathing; endurance; respiratory function; thermal load
11.  Continuous low- to moderate-intensity exercise training is as effective as moderate- to high-intensity exercise training at lowering blood HbA1c in obese type 2 diabetes patients 
Diabetologia  2009;52(9):1789-1797.
Exercise represents an effective interventional strategy to improve glycaemic control in type 2 diabetes patients. However, the impact of exercise intensity on the benefits of exercise training remains to be established. In the present study, we compared the clinical benefits of 6 months of continuous low- to moderate-intensity exercise training with those of continuous moderate- to high-intensity exercise training, matched for energy expenditure, in obese type 2 diabetes patients.
Fifty male obese type 2 diabetes patients (age 59 ± 8 years, BMI 32 ± 4 kg/m2) participated in a 6 month continuous endurance-type exercise training programme. All participants performed three supervised exercise sessions per week, either 55 min at 50% of whole body peak oxygen uptake \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \left( {\mathop V\limits^{ \cdot } {\text{O}}_{{2{\text{peak}}}} } \right) $$\end{document} (low to moderate intensity) or 40 min at 75% of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \mathop V\limits^{ \cdot } {\text{O}}_{{2{\text{peak}}}} $$\end{document} (moderate to high intensity). Oral glucose tolerance, blood glycated haemoglobin, lipid profile, body composition, maximal workload capacity, whole body and skeletal muscle oxidative capacity and skeletal muscle fibre type composition were assessed before and after 2 and 6 months of intervention.
The entire 6 month intervention programme was completed by 37 participants. Continuous endurance-type exercise training reduced blood glycated haemoglobin levels, LDL-cholesterol concentrations, body weight and leg fat mass, and increased \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \mathop V\limits^{ \cdot } {\text{O}}_{{2{\text{peak}}}} $$\end{document}, lean muscle mass and skeletal muscle cytochrome c oxidase and citrate synthase activity (p < 0.05). No differences were observed between the groups training at low to moderate or moderate to high intensity.
When matched for energy cost, prolonged continuous low- to moderate-intensity endurance-type exercise training is equally effective as continuous moderate- to high-intensity training in lowering blood glycated haemoglobin and increasing whole body and skeletal muscle oxidative capacity in obese type 2 diabetes patients.
Trial registration:
PMCID: PMC2723667  PMID: 19370339
Diabetes; Glycaemic control; Lifestyle intervention; Training modalities
12.  Male Circumcision at Different Ages in Rwanda: A Cost-Effectiveness Study 
PLoS Medicine  2010;7(1):e1000211.
Agnes Binagwaho and colleagues predict that circumcision of newborn boys would be effective and cost-saving as a long-term strategy to prevent HIV in Rwanda.
There is strong evidence showing that male circumcision (MC) reduces HIV infection and other sexually transmitted infections (STIs). In Rwanda, where adult HIV prevalence is 3%, MC is not a traditional practice. The Rwanda National AIDS Commission modelled cost and effects of MC at different ages to inform policy and programmatic decisions in relation to introducing MC. This study was necessary because the MC debate in Southern Africa has focused primarily on MC for adults. Further, this is the first time, to our knowledge, that a cost-effectiveness study on MC has been carried out in a country where HIV prevalence is below 5%.
Methods and Findings
A cost-effectiveness model was developed and applied to three hypothetical cohorts in Rwanda: newborns, adolescents, and adult men. Effectiveness was defined as the number of HIV infections averted, and was calculated as the product of the number of people susceptible to HIV infection in the cohort, the HIV incidence rate at different ages, and the protective effect of MC; discounted back to the year of circumcision and summed over the life expectancy of the circumcised person. Direct costs were based on interviews with experienced health care providers to determine inputs involved in the procedure (from consumables to staff time) and related prices. Other costs included training, patient counselling, treatment of adverse events, and promotion campaigns, and they were adjusted for the averted lifetime cost of health care (antiretroviral therapy [ART], opportunistic infection [OI], laboratory tests). One-way sensitivity analysis was performed by varying the main inputs of the model, and thresholds were calculated at which each intervention is no longer cost-saving and at which an intervention costs more than one gross domestic product (GDP) per capita per life-year gained. Results: Neonatal MC is less expensive than adolescent and adult MC (US$15 instead of US$59 per procedure) and is cost-saving (the cost-effectiveness ratio is negative), even though savings from infant circumcision will be realized later in time. The cost per infection averted is US$3,932 for adolescent MC and US$4,949 for adult MC. Results for infant MC appear robust. Infant MC remains highly cost-effective across a reasonable range of variation in the base case scenario. Adolescent MC is highly cost-effective for the base case scenario but this high cost-effectiveness is not robust to small changes in the input variables. Adult MC is neither cost-saving nor highly cost-effective when considering only the direct benefit for the circumcised man.
The study suggests that Rwanda should be simultaneously scaling up circumcision across a broad range of age groups, with high priority to the very young. Infant MC can be integrated into existing health services (i.e., neonatal visits and vaccination sessions) and over time has better potential than adolescent and adult circumcision to achieve the very high coverage of the population required for maximal reduction of HIV incidence. In the presence of infant MC, adolescent and adult MC would evolve into a “catch-up” campaign that would be needed at the start of the program but would eventually become superfluous.
Please see later in the article for the Editors' Summary
Editors' Summary
Acquired immunodeficiency syndrome (AIDS) has killed more than 25 million people since 1981 and more than 31 million people (22 million in sub-Saharan Africa alone) are now infected with the human immunodeficiency virus (HIV), which causes AIDS. There is no cure for HIV/AIDS and no vaccine against HIV infection. Consequently, prevention of HIV transmission is extremely important. HIV is most often spread through unprotected sex with an infected partner. Individuals can reduce their risk of HIV infection, therefore, by abstaining from sex, by having one or a few sexual partners, and by always using a male or female condom. In addition, male circumcision—the removal of the foreskin, the loose fold of skin that covers the head of penis—can halve HIV transmission rates to men resulting from sex with women. Thus, as part of its HIV prevention strategy, the World Health Organization (WHO) recommends that male circumcision programs be scaled up in countries where there is a generalized HIV epidemic and where few men are circumcised.
Why Was This Study Done?
One such country is Rwanda. Here, 3% of the adult population is infected with HIV but only 15% of men are circumcised—worldwide, about 30% of men are circumcised. Demand for circumcision is increasing in Rwanda but, before policy makers introduce a country-wide male circumcision program, they need to identify the most cost-effective way to increase circumcision rates. In particular, they need to decide the age at which circumcision should be offered. Circumcision soon after birth (neonatal circumcision) is quick and simple and rarely causes any complications. Circumcision of adolescents and adults is more complex and has a higher complication rate. Although several studies have investigated the cost-effectiveness (the balance between the clinical and financial costs of a medical intervention and its benefits) of circumcision in adult men, little is known about its cost-effectiveness in newborn boys. In this study, which is one of several studies on male circumcision being organized by the National AIDS Control Commission in Rwanda, the researchers model the cost-effectiveness of circumcision at different ages.
What Did the Researchers Do and Find?
The researchers developed a simple cost-effectiveness model and applied it to three hypothetical groups of Rwandans: newborn boys, adolescent boys, and adult men. For their model, the researchers calculated the effectiveness of male circumcision (the number of HIV infections averted) by estimating the reduction in the annual number of new HIV infections over time. They obtained estimates of the costs of circumcision (including the costs of consumables, staff time, and treatment of complications) from health care providers and adjusted these costs for the money saved through not needing to treat HIV in males in whom circumcision prevented infection. Using their model, the researchers estimate that each neonatal male circumcision would cost US$15 whereas each adolescent or adult male circumcision would cost US$59. Neonatal male circumcision, they report, would be cost-saving. That is, over a lifetime, neonatal male circumcision would save more money than it costs. Finally, using the WHO definition of cost-effectiveness (for a cost-effective intervention, the additional cost incurred to gain one year of life must be less than a country's per capita gross domestic product), the researchers estimate that, although adolescent circumcision would be highly cost-effective, circumcision of adult men would only be potentially cost-effective (but would likely prove cost-effective if the additional infections that would occur from men to their partners without a circumcision program were also taken into account).
What Do These Findings Mean?
As with all modeling studies, the accuracy of these findings depends on the many assumptions included in the model. However, the findings suggest that male circumcision for infants for the prevention of HIV infection later in life is highly cost-effective and likely to be cost-saving and that circumcision for adolescents is cost-effective. The researchers suggest, therefore, that policy makers in Rwanda and in countries with similar HIV infection and circumcision rates should scale up male circumcision programs across all age groups, with high priority being given to the very young. If infants are routinely circumcised, they suggest, circumcision of adolescent and adult males would become a “catch-up” campaign that would be needed at the start of the program but that would become superfluous over time. Such an approach would represent a switch from managing the HIV epidemic as an emergency towards focusing on sustainable, long-term solutions to this major public-health problem.
Additional Information
Please access these Web sites via the online version of this summary at
This study is further discussed in a PLoS Medicine Perspective by Seth Kalichman
Information is available from the US National Institute of Allergy and Infectious Diseases on HIV infection and AIDS
Information is available from the Joint United Nations Programme on HIV/AIDS (UNAIDS) on HIV infection and AIDS and on male circumcision in relation to HIV and AIDS
HIV InSite has comprehensive information on all aspects of HIV/AIDS
Information is available from Avert, an international AIDS charity on many aspects of HIV/AIDS, including information on HIV and AIDS in Africa, and on circumcision and HIV (some information in English and Spanish)
More information about male circumcision is available from the Clearinghouse on Male Circumcision
The National AIDS Control Commission of Rwanda provides detailed information about HIV/AIDS in Rwanda (in English and French)
PMCID: PMC2808207  PMID: 20098721
13.  Effect of Intermittent Sub-Maximal Exercise on Percent Body Fat Using Leg-To-Leg Bioelectrical Impedance Analysis in Children 
The purpose of this investigation was to determine the effect of intermittent sub-maximal exercise on percent body fat (%BF) estimated by leg-to-leg bioelectrical impedance analysis (LBIA) in children. Fifty-nine children (29 girls; 30 boys) mean age 9.0 ± 1.3 years participated in this study. LBIA measured %BF values were obtained immediately before and within five minutes after completing an intermittent exercise protocol consisting of three 8-minute sub-maximal exercise bouts (2.74 km·hr-1, 0% grade; 4.03 km·hr-1, 0% grade; and 5.47 km·hr-1, 0% grade) each separated by a 5-min seated rest period. The three exercise bouts corresponded to 56%, 61% and 71% of maximal heart rate. Significant differences (p < 0.001) were observed for fat mass, fat free mass, total body water, and body weight, post-exercise in both groups. Significant reductions (p < 0.001) in %BF were observed post-exercise in the female (23.1 ± 9.9 vs. 21.8 ± 9. 9 %) and male (23.3 ± 10.5 vs. 21.8 ± 10.2 %) children when compared to pre-exercise values. However, for the majority of the subjects (females = 86%; males = 73%) the decrease in %BF post- exercise was less than 2.0 %BF. These data indicate that sub-maximal intermittent exercise, that may be representative of daily free-form activities in children, will most likely have a limited impact on %BF estimates when the assessment is performed immediately post-exercise.
Key PointsLBIA measures of body weight, percent body fat, fat mass, fat free mass and total body water were significantly lower after the intermittent sub-maximal exercise.The reductions in percent body fat for girls (1.4%) and boys (1.5%) compare favorably to previous investigations.Intermittent exercise, that may be representative of daily free-form activities in children, will most likely have a limited impact on LBIA percent body fat estimates
PMCID: PMC3842143  PMID: 24353460
Bioelectrical impedance analysis; body fat; sub-maximal exercise; children
14.  Gender Differences in Adolescent Premarital Sexual Permissiveness in Three Asian Cities: Effects of Gender-Role Attitudes 
Gender is an important factor in understanding premarital sexual attitudes and behaviors. Many studies indicate that males are more likely to initiate sexual intercourse and have more permissive perceptions about sex than females. Yet few studies have explored possible reasons for these gender differences. With samples of unmarried adolescents in three Asian cities influenced by Confucian cultures, this paper investigates the relationship between underlying gender norms and these differences in adolescents’ premarital sexual permissiveness.
16,554 unmarried participants aged 15–24 were recruited in the Three-City Asian Study of Adolescents and Youth, a collaborative survey conducted in 2006–2007 in urban and rural areas of Hanoi, Shanghai and Taipei, with 6204, 6023 and 4327 from each city respectively. All of the adolescents were administered face-to-face interviews, coupled with Computer Assisted Self Interview (CASI) for sensitive questions. Scales on gender-role attitudes and on premarital sexual permissiveness for both male and female respondents were developed and applied to our analysis of the data. Multi-linear regression was used to analyze the relationship between gender-role attitudes and sexual permissiveness.
Male respondents in each city held more permissive attitudes towards premarital sex than did females with both boys and girls expressing greater permissiveness to male premarital sexual behaviors. Boys also expressed more traditional attitudes to gender roles (condoning greater inequality) than did girls in each city. Adolescents’ gender-role attitudes and permissiveness to premarital sex varied considerably across the three cities, with the Vietnamese the most traditional, the Taiwanese the least traditional, and the adolescents in Shanghai in the middle. A negative association between traditional gender roles and premarital sexual permissiveness was only found among girls in Shanghai and Taipei. In Shanghai, female respondents who held more traditional gender role attitudes were more likely to exercise a double standard with respect to male as opposed to female premarital sex (OR=1.18). This relationship also applied to attitudes of both girls and boys in Taipei (OR=1.20 and OR=1.22, respectively).
Although with variation across sites, gender differences in premarital sexual permissiveness and attitudes to gender roles among adolescents were very significant in each of the three Asian cities influenced by Confucian-based values. Traditional gender norms may still be deeply rooted in the three cities, especially among females, while it is important to advocate gender equity in adolescent reproductive health programs, the pathway of traditional gender norms in influencing adolescent reproductive health outcomes must be understood, as must differences and similarities across regions.
PMCID: PMC4235609  PMID: 22340852
Gender role; Premarital sex; Attitudes; Asian; Confucian
15.  Differential Impact of Acute High-Intensity Exercise on Circulating Endothelial Microparticles and Insulin Resistance between Overweight/Obese Males and Females 
PLoS ONE  2015;10(2):e0115860.
An acute bout of exercise can improve endothelial function and insulin sensitivity when measured on the day following exercise. Our aim was to compare acute high-intensity continuous exercise (HICE) to high-intensity interval exercise (HIIE) on circulating endothelial microparticles (EMPs) and insulin sensitivity in overweight/obese men and women.
Inactive males (BMI = 30 ± 3, 25 ± 6 yr, n = 6) and females (BMI = 28 ± 2, 21 ± 3 yr, n = 7) participated in three experimental trials in a randomized counterbalanced crossover design: 1) No exercise control (Control); 2) HICE (20 min cycling @ just above ventilatory threshold); 3) HIIE (10 X 1-min @ ∼90% peak aerobic power). Exercise conditions were matched for external work and diet was controlled post-exercise. Fasting blood samples were obtained ∼18 hr after each condition. CD62E+ and CD31+/CD42b- EMPs were assessed by flow cytometry and insulin resistance (IR) was estimated by homeostasis model assessment (HOMA-IR).
There was a significant sex X exercise interaction for CD62E+ EMPs, CD31+/CD42b- EMPs, and HOMA-IR (all P<0.05). In males, both HICE and HIIE reduced EMPs compared to Control (P≤0.05). In females, HICE increased CD62E+ EMPs (P<0.05 vs. Control) whereas CD31+/CD42b- EMPs were unaltered by either exercise type. There was a significant increase in HOMA-IR in males but a decrease in females following HIIE compared to Control (P<0.05).
Overweight/obese males and females appear to respond differently to acute bouts of high-intensity exercise. A single session of HICE and HIIE reduced circulating EMPs measured on the morning following exercise in males but in females CD62E+ EMPs were increased following HICE. Next day HOMA-IR paradoxically increased in males but was reduced in females following HIIE. Future research is needed to investigate mechanisms responsible for potential differential responses between males and females.
PMCID: PMC4339732  PMID: 25710559
16.  Sex differences in cardiovascular function during submaximal exercise in humans 
SpringerPlus  2014;3:445.
Differences in cardiovascular function between sexes have been documented at rest and maximal exercise. The purpose of this study was to examine the sex differences in cardiovascular function during submaximal constant-load exercise, which is not well understood.
Thirty-one male and 33 female subjects completed nine minutes moderate and nine minutes vigorous intensity submaximal exercise (40 and 75% of peak watts determined by maximal exercise test). Measurements included: intra-arterial blood pressure (SBP and DBP), cardiac index (QI), heart rate (HR), oxygen consumption (VO2) and arterial catecholamines (epinephrine = EPI and norepinephrine = NE), and blood gases. Mean arterial pressure (MAP), stroke volume index (SVI), systemic vascular resistance index (SVRI), arterial oxygen content (CaO2), arterial to venous O2 difference (AVO2) and systemic oxygen transport (SOT) were calculated.
At rest and during submaximal exercise QI, SVI, SBP, MAP, NE, CaO2, and SOT were lower in females compared to males. VO2, AVO2, EPI were lower in females throughout exercise. When corrected for wattage, females had a higher Q, HR, SV, VO2 and AVO2 despite lower energy expenditure and higher mechanical efficiency.
This study demonstrates sex differences in the cardiovascular response to constant-load submaximal exercise. Specifically, females presented limitations in cardiac performance in which they are unable to compensate for reductions in stroke volume through increases in HR, potentially a consequence of a female’s blunted sympathetic response and higher vasodilatory state. Females demonstrated greater cardiac work needed to meet the same external work demand, and relied on increased peripheral oxygen extraction, lower energy expenditure and improvements in mechanical efficiency as compensatory mechanisms.
PMCID: PMC4153874  PMID: 25191635
Cardiac output; Arterial pressure; Systemic vascular resistance; Catecholamines; Energy expenditure
17.  Association between heart rate at rest and myocardial perfusion in patients with acute myocardial infarction undergoing cardiac rehabilitation – a pilot study 
This study was conducted to determine if there was a link among heart rate at rest (rHR), muscle volume changes, and single photon emission computed tomography (SPECT) parameters after 6-month cardiac rehabilitation in patients with acute myocardial infarction (AMI).
Material and methods
Twenty-nine consecutive AMI patients (mean age: 63.0 ±9.1 years) who received appropriate percutaneous coronary intervention on admission were enrolled. 99mTc-Sestamibi myocardial SPECT images were obtained at the early (30 min) and delayed (4 h) phases after tracer injection at 2 weeks (0M) and 6 months (6M) after the onset of AMI. Within a few days of SPECT, all patients underwent cardiopulmonary exercise test for evaluation of cardiac rehabilitation effects. Before the initiation of exercise test, leg muscle volume was measured. All patients were stratified into the ≥ 70 beats per minute (bpm) (n = 15) or < 70 bpm (n = 14) group based on rHR at 6M.
There were no significant differences in the recanalization time, peak cardiac enzyme, or initial left ventricular ejection fraction between the two groups. After the 6-month training, the muscle volume changes in the lower limbs (< 70 bpm, 0.23 ±0.22; ≥ 70 bpm, –0.07 ±0.26, p < 0.05) were significantly greater in the < 70 bpm group than the ≥ 70 bpm group. The decreased rate of rHR had a significant correlation with the improved global severity (r = 0.62, p = 0.001) and extent (r = 0.48, p = 0.017) of left ventricle evaluated by 99mTc-Sestamibi myocardial SPECT delayed phase.
The result of this preliminary study demonstrated that improved myocardial perfusion was closely related to decreased rHR after cardiac rehabilitation.
PMCID: PMC3460498  PMID: 23056072
cardiac rehabilitation; exercise capacity; myocardial infarction; skeletal muscle; single photon emission computed tomography
18.  Sex Differences in Pulmonary Oxygen Uptake Kinetics in Obese Adolescents 
The Journal of pediatrics  2014;165(6):1161-1165.
To determine if sex differences exist in the pulmonary oxygen uptake (VO2) uptake on-kinetic response to moderate exercise in obese adolescents. Additionally, we examined if a relationship exists between the VO2 on-transient response to moderate intensity exercise, steady state VO2, and peak VO2 between obese male and female adolescents.
Study design
Male (n=12) and female (n=28) adolescents completed a graded exercise test to exhaustion on a treadmill. Data from the initial 4-min of treadmill walking were used to determine the time constant.
The time constant was significantly different (P=0.001) between obese male and female adolescents (15.17±8.45 s vs. 23.07±8.91 s, respectively). No significant relationships were observed between the time constant and variables of interest in either sex.
Sex differences exist in VO2 uptake on-kinetics during moderate exercise in obese adolescents, indicating an enhanced potential for males to deliver and/or utilize oxygen. It may be advantageous for females to engage in a longer warm-up period prior to initiation of an exercise regimen, preventing an early termination of the exercise session.
PMCID: PMC4253596  PMID: 25241180
Aerobic Fitness/VO2 Max; Assessing Physiological Demands of Physical Activity; Gas Exchange Kinetics in Laboratory and Field
19.  Bronchial lability and skin reactivity in siblings of asthmatic children. 
Archives of Disease in Childhood  1984;59(9):871-876.
Seventy five children with asthma (42 boys and 33 girls; age range 4 years 2 months to 15 years) and 75 of their siblings (37 boys and 38 girls; age range 4 years 3 months to 17 years 8 months) were studied to elucidate the mechanisms involved in the increased prevalence of asthma in boys, a prevalence that tends to disappear after puberty. Immediate cutaneous hypersensitivity to five allergens and maximum fall in peak expiratory flow rate after six minutes of treadmill running (bronchial lability) were determined in patients and siblings. There was no significant difference between boys and girls in skin test reactivity to single or multiple allergens in the sibling group. The percentage fall in peak expiratory flow rate after exercise was significantly greater in male than in female siblings and when a positive test was defined as a fall after exercise of either 10% or 15% of the rate before exercise the number of positive tests was significantly greater in boys. The results suggest that more boys than girls in this age group have asthma because their bronchial lability is greater, and not because more boys are atopic.
PMCID: PMC1628713  PMID: 6486865
20.  Lactate Kinetics After Intermittent and Continuous Exercise Training 
The purpose of this study was to assess, the effects of continuous and intermittent exercise training on lactate kinetic parameters and maximal aerobic speed (MAS) using field tests. Twenty-four male sport students were equally divided into continuous (CT) and intermittent (IT) physically trained groups. Another six participants acted as non-trained controls (CG). The trained participants practiced 6-days per week for 6 weeks. Before and after training, all participants completed an incremental exercise test to assess their MAS, and a 30- second supra-maximal exercise followed by 30 minutes of active recovery to determine the individual blood lactate recovery curve. It was found that exercise training has significantly increased MAS (p < 0.001), the lactate exchange and removal abilities as well as the lactate concentrations at the beginning of the recovery ([La]-(0)); for both CT and IT groups; this was accompanied by a significant reduction of the time to lactate-peak. Nevertheless, the improvement in MAS was significantly higher (p < 0.001) post-intermittent (15.1 % ± 2.4) than post-continuous (10.3 % ± 3.2) training. The lactate-exchange and removal abilities were also significantly higher for IT than for CT-group (P<0.05). Moreover, IT-group showed a significantly shorter half-time of the blood lactate (t-½-[La]) than CT-group (7.2 ± 0.5 min vs 7.7 ± 0.3 min, respectively) (p < 0.05). However, no significant differences were observed in peak blood lactate concentration ([La]peak), time to reach [La]peak (t-[La]peak), and [La]-(0) between the two physically-trained groups. We conclude that both continuous and intermittent training exercises were equally effective in improving t-[La]peak and [La]peak, although intermittent training was more beneficial in elevating MAS and in raising the lactate exchange (γ1) and removal (γ2) indexes.
Key pointsCoaches and athletes need to be aware of the potentiality positive effects of exercise intensity.Improvements in physical fitness are associated with a concomitant increase in the lactate removal ability.In order to reduce lactate accumulation and increase maximal aerobic speed maximally, interval training method, with work speeds equal to 90% - 100% of MAS, may be the effective way when compared with continuous training method.
PMCID: PMC3761459  PMID: 24149461
Biexponential mathematical model; recovery; supra-maximal exercise.
21.  Ischemic preconditioning accelerates muscle deoxygenation dynamics and enhances exercise endurance during the work-to-work test 
Physiological Reports  2015;3(5):e12395.
Ischemic preconditioning (IPC) improves maximal exercise performance. However, the potential mechanism(s) underlying the beneficial effects of IPC remain unknown. The dynamics of pulmonary oxygen uptake (VO2) and muscle deoxygenation during exercise is frequently used for assessing O2 supply and extraction. Thus, this study examined the effects of IPC on systemic and local O2 dynamics during the incremental step transitions from low- to moderate- and from moderate- to severe-intensity exercise. Fifteen healthy, male subjects were instructed to perform the work-to-work cycling exercise test, which was preceded by the control (no occlusion) or IPC (3 × 5 min, bilateral leg occlusion at >300 mmHg) treatments. The work-to-work test was performed by gradually increasing the exercise intensity as follows: low intensity at 30 W for 3 min, moderate intensity at 90% of the gas exchange threshold (GET) for 4 min, and severe intensity at 70% of the difference between the GET and VO2 peak until exhaustion. During the exercise test, the breath-by-breath pulmonary VO2 and near-infrared spectroscopy-derived muscle deoxygenation were continuously recorded. Exercise endurance during severe-intensity exercise was significantly enhanced by IPC. There were no significant differences in pulmonary VO2 dynamics between treatments. In contrast, muscle deoxygenation dynamics in the step transition from low- to moderate-intensity was significantly faster in IPC than in CON (27.2 ± 2.9 vs. 19.8 ± 0.9 sec, P < 0.05). The present findings showed that IPC accelerated muscle deoxygenation dynamics in moderate-intensity exercise and enhanced severe-intensity exercise endurance during work-to-work test. The IPC-induced effects may result from mitochondrial activation in skeletal muscle, as indicated by the accelerated O2 extraction.
PMCID: PMC4463825  PMID: 25952936
Exercise; mitochondria; near-infrared spectroscopy; nitric oxide; skeletal muscle
22.  Effects of a 4-Week Eccentric Training Program on the Repeated Bout Effect in Young Active Women 
The aim of this study was to analyze the responses of women to the repeated bout effect (RBE) and to a short eccentric training program. Twenty-four young females were randomly assigned to a training group (TG, n = 14) or a control group (CG, n = 10). They performed two identical acute eccentric bouts (120 repetitions at 70% of 1RM) in a leg-press device in an 8 weeks interval. TG followed a 4-week-eccentric-training program between the bouts. Maximal isometric contraction, range of motion, peak power and quadriceps muscle soreness were compared between and within groups before and after the two acute eccentric bouts. TG and CG presented significant losses of isometric strength and peak power, and an increment in soreness after the first bout. Isometric strength and peak power were recovered faster in CG after the second bout (p < 0.05) compared with TG, which showed a similar recovery of these parameters after the second bout compared with the first one. A decrease in soreness and a faster recovery of range of motion were found in TG (p < 0.05) following the second bout compared with the first one, but not in CG. Data indicate that a 4-week eccentric training program may prevent the RBE over those adaptations related with muscle damage (e.g. strength loss), but it may increase RBE impact on inflammatory processes (e.g. soreness).
Key pointsAn acute bout of eccentric exercise induces losses of strength, peak power and range of motion, and increases muscle soreness in young active women.When the acute eccentric bout is repeated by young women, the losses of strength and power are smaller, indicating less muscle damage. However, muscle pain and range of motion do not present any difference with the results obtained after the first bout, which would indicate that the repeated bout effect does not affect inflammatory response after acute eccentric exercise.Four weeks of eccentric training is enough to increase maximal isometric strength, but not dynamic strength (1RM) or peak power. Furthermore, this training seems to prevent those adaptations provided by the repeated bout effect related with muscle damage. On the other hand, the eccentric training seems to be a positive tool to decrease muscle soreness, and thus the inflammatory response, associated to a repeated acute eccentric bout.
PMCID: PMC3761500  PMID: 24149560
Lengthening contraction; strength; peak power
23.  Child Mortality Estimation: Estimating Sex Differences in Childhood Mortality since the 1970s 
PLoS Medicine  2012;9(8):e1001287.
Cheryl Sawyer uses new methods to generate estimates of sex differences in child mortality which can be used to pinpoint areas where these differences in mortality merit closer examination.
Producing estimates of infant (under age 1 y), child (age 1–4 y), and under-five (under age 5 y) mortality rates disaggregated by sex is complicated by problems with data quality and availability. Interpretation of sex differences requires nuanced analysis: girls have a biological advantage against many causes of death that may be eroded if they are disadvantaged in access to resources. Earlier studies found that girls in some regions were not experiencing the survival advantage expected at given levels of mortality. In this paper I generate new estimates of sex differences for the 1970s to the 2000s.
Methods and Findings
Simple fitting methods were applied to male-to-female ratios of infant and under-five mortality rates from vital registration, surveys, and censuses. The sex ratio estimates were used to disaggregate published series of both-sexes mortality rates that were based on a larger number of sources. In many developing countries, I found that sex ratios of mortality have changed in the same direction as historically occurred in developed countries, but typically had a lower degree of female advantage for a given level of mortality. Regional average sex ratios weighted by numbers of births were found to be highly influenced by China and India, the only countries where both infant mortality and overall under-five mortality were estimated to be higher for girls than for boys in the 2000s. For the less developed regions (comprising Africa, Asia excluding Japan, Latin America/Caribbean, and Oceania excluding Australia and New Zealand), on average, boys' under-five mortality in the 2000s was about 2% higher than girls'. A number of countries were found to still experience higher mortality for girls than boys in the 1–4-y age group, with concentrations in southern Asia, northern Africa/western Asia, and western Africa. In the more developed regions (comprising Europe, northern America, Japan, Australia, and New Zealand), I found that the sex ratio of infant mortality peaked in the 1970s or 1980s and declined thereafter.
The methods developed here pinpoint regions and countries where sex differences in mortality merit closer examination to ensure that both sexes are sharing equally in access to health resources. Further study of the distribution of causes of death in different settings will aid the interpretation of differences in survival for boys and girls.
Please see later in the article for the Editors' Summary.
Editors' Summary
In 2000, world leaders agreed to eradicate extreme poverty by 2015. To help track progress towards this global commitment, eight Millennium Development Goals (MDGs) were set. MDG 4, which aims to reduce child mortality, calls for a reduction in under-five mortality (the number of children who die before their fifth birthday) to a third of its 1990 level of 12 million by 2015. The under-five mortality rate is also denoted in the literature as U5MR and 5q0. Progress towards MDG 4 has been substantial, but with only three years left to reach it, efforts to strengthen child survival programs are intensifying. Reliable estimates of trends in childhood mortality are pivotal to these efforts. So, since 2004, the United Nations Inter-agency Group for Child Mortality Estimation (UN IGME) has used statistical regression models to produce estimates of trends in under-five mortality and infant mortality (death before age one year) from data about childbearing and child survival collected by vital registration systems (records of all births and deaths), household surveys, and censuses.
Why Was This Study Done?
In addition to estimates of overall childhood mortality trends, information about sex-specific childhood mortality trends is desirable to monitor progress towards MDG 4, although the interpretation of trends in the relative mortality of girls and boys is not straightforward. Newborn girls survive better than newborn boys because they are less vulnerable to birth complications and infections and have fewer inherited abnormalities. Thus, the ratio of infant mortality among boys to infant mortality among girls is greater than one, provided both sexes have equal access to food and medical care. Beyond early infancy, girls and boys are similarly vulnerable to infections, so the sex ratio of deaths in the 1–4-year age group is generally lower than that of infant mortality. Notably, as living conditions improve in developing countries, infectious diseases become less important as causes of death. Thus, in the absence of sex-specific differences in the treatment of children, the sex ratio of childhood mortality is expected be greater than one and to increase as overall under-five mortality rates in developing countries decrease. In this study, the researcher evaluated national and regional changes in the sex ratios of childhood mortality since the 1970s to investigate whether girls and boys have equal access to medical care and other resources.
What Did the Researcher Do and Find?
The researcher developed new statistical fitting methods to estimate trends in the sex ratio of mortality for infants and young children for individual countries and world regions. When considering individual countries, the researcher found that for 92 countries in less developed regions, the median sex ratio of under-five mortality increased between the 1970s and the 2000s, in line with the expected changes just described. However, the average sex ratio of under-five mortality for less developed regions, weighted according to the number of births in each country, did not increase between the 1970s and 2000s, at which time the average under-five mortality rate of boys was about 2% higher than that of girls. This discrepancy resulted from India and China—the two most populous developing countries—having sex ratios for both infant and under-five mortality that remained constant or declined over the study period and were below one in the 2000s, a result that indicates excess female mortality. In China, for example, infant mortality was found to be 12% higher for boys than for girls in the 1970s, but 24% lower for boys than for girls in the 2000s. Finally, although in the less developed regions (excluding India and China) girls went from having a slight survival disadvantage at ages 1–4 years in the 1970s, on average, to having a slight advantage in the 2000s, girls remained more likely to die than boys in this age group in several Asian and African countries.
What Do These Findings Mean?
Although the quality of the available data is likely to affect the accuracy of these findings, in most developing countries the ratio of male to female under-five mortality has increased since the 1970s, in parallel with the decrease in overall childhood mortality. Notably, however, in a number of developing countries—including several each in sub-Saharan Africa, northern Africa/western Asia, and southern Asia—girls have higher mortality than boys at ages 1–4 years, and in India and China girls have higher mortality in infancy. Thus, girls are benefitting less than boys from the overall decline in childhood mortality in India, China, and some other developing countries. Further studies are needed to determine the underlying reasons for this observation. Nevertheless, the methods developed here to estimate trends in sex-specific childhood mortality pinpoint countries and regions where greater efforts should be made to ensure that both sexes have equal access to health care and other important resources during early life.
Additional Information
Please access these websites via the online version of this summary at
This paper is part of a collection of papers on Child Mortality Estimation Methods published in PLOS Medicine
The United Nations Childrens Fund works for children's rights, survival, development, and protection around the world; it provides information on Millennium Development Goal 4, and its Childinfo website provides detailed statistics about child survival and health, including a description of the United Nations Inter-agency Group for Child Mortality Estimation; the 2011 UN IGME report Levels & Trends in Child Mortality is available
The World Health Organization also has information about Millennium Development Goal 4 and provides estimates of child mortality rates (some information in several languages)
Further information about the Millennium Development Goals is available
A 2011 report by the United Nations Department of Economic and Social Affairs entitled Sex Differentials in Childhood Mortality is available
PMCID: PMC3429399  PMID: 22952433
24.  Neuromuscular and Blood Lactate Responses to Squat Power Training with Different Rest Intervals Between Sets 
Studies investigating the effect of rest interval length (RI) between sets on neuromuscular performance and metabolic response during power training are scarce. Therefore, the purpose of this study was to compare maximal power output, muscular activity and blood lactate concentration following 1, 2 or 3 minutes RI between sets during a squat power training protocol. Twelve resistance-trained men (22.7 ± 3.2 years; 1.79 ± 0.08 cm; 81.8 ± 11.3 kg) performed 6 sets of 6 repetitions of squat exercise at 60% of their 1 repetition maximum. Peak and average power were obtained for each repetition and set using a linear position transducer. Muscular activity and blood lactate were measured pre and post-exercise session. There was no significant difference between RI on peak power and average power. However, peak power decreased 5.6%, 1.9%, and 5.9% after 6 sets using 1, 2 and 3 minutes of RI, respectively. Average power also decreased 10.5% (1 min), 2.6% (2 min), and 4.3% (3 min) after 6 sets. Blood lactate increased similarly during the three training sessions (1-min: 5.5 mMol, 2-min: 4.3 mMol, and 3-min: 4.0 mMol) and no significant changes were observed in the muscle activity after multiple sets, independent of RI length (pooled ES for 1-min: 0.47, 2-min: 0.65, and 3-min: 1.39). From a practical point of view, the results suggest that 1 to 2 minute of RI between sets during squat exercise may be sufficient to recover power output in a designed power training protocol. However, if training duration is malleable, we recommend 2 min of RI for optimal recovery and power output maintenance during the subsequent exercise sets.
Key pointsThis study demonstrates that 1 minute of RI between sets is sufficient to maintain maximal power output during multiple sets of a power-based exercise when it is composed of few repetitions and the sets are not performed until failure. Therefore, a short RI should be considered when designing training programs for the development of muscular power.Short RI may be more practical for strength coaches under time constraints (i.e. 1 minute of RI required only 7 minutes to complete an exercise session, while with 2 minutes take 12 minutes, and 17 minutes with 3 minutes of RI).Future research is needed to examine the longitudinal effects of interval rest in training programs designed for the development of muscular power.
PMCID: PMC4424454  PMID: 25983574
Power development; muscle recovery; power training; strength training
25.  The oxygen delivery response to acute hypoxia during incremental knee extension exercise differs in active and trained males 
It is well known that hypoxic exercise in healthy individuals increases limb blood flow, leg oxygen extraction and limb vascular conductance during knee extension exercise. However, the effect of hypoxia on cardiac output, and total vascular conductance is less clear. Furthermore, the oxygen delivery response to hypoxic exercise in well trained individuals is not well known. Therefore our aim was to determine the cardiac output (Doppler echocardiography), vascular conductance, limb blood flow (Doppler echocardiography) and muscle oxygenation response during hypoxic knee extension in normally active and endurance-trained males.
Ten normally active and nine endurance-trained males (VO2max = 46.1 and 65.5 mL/kg/min, respectively) performed 2 leg knee extension at 25, 50, 75 and 100% of their maximum intensity in both normoxic and hypoxic conditions (FIO2 = 15%; randomized order). Results were analyzed with a 2-way mixed model ANOVA (group × intensity).
The main finding was that in normally active individuals hypoxic sub-maximal exercise (25 – 75% of maximum intensity) brought about a 3 fold increase in limb blood flow but decreased stroke volume compared to normoxia. In the trained group there were no significant changes in stroke volume, cardiac output and limb blood flow at sub-maximal intensities (compared to normoxia). During maximal intensity hypoxic exercise limb blood flow increased approximately 300 mL/min compared to maximal intensity normoxic exercise.
Cardiorespiratory fitness likely influences the oxygen delivery response to hypoxic exercise both at a systemic and limb level. The increase in limb blood flow during maximal exercise in hypoxia (both active and trained individuals) suggests a hypoxic stimulus that is not present in normoxic conditions.
PMCID: PMC2526084  PMID: 18700024

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