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1.  Similar Health Benefits of Endurance and High-Intensity Interval Training in Obese Children 
PLoS ONE  2012;7(8):e42747.
Purpose
To compare two modalities of exercise training (i.e., Endurance Training [ET] and High-Intensity Interval Training [HIT]) on health-related parameters in obese children aged between 8 and 12 years.
Methods
Thirty obese children were randomly allocated into either the ET or HIT group. The ET group performed a 30 to 60-minute continuous exercise at 80% of the peak heart rate (HR). The HIT group training performed 3 to 6 sets of 60-s sprint at 100% of the peak velocity interspersed by a 3-min active recovery period at 50% of the exercise velocity. HIT sessions last ∼70% less than ET sessions. At baseline and after 12 weeks of intervention, aerobic fitness, body composition and metabolic parameters were assessed.
Results
Both the absolute (ET: 26.0%; HIT: 19.0%) and the relative VO2 peak (ET: 13.1%; HIT: 14.6%) were significantly increased in both groups after the intervention. Additionally, the total time of exercise (ET: 19.5%; HIT: 16.4%) and the peak velocity during the maximal graded cardiorespiratory test (ET: 16.9%; HIT: 13.4%) were significantly improved across interventions. Insulinemia (ET: 29.4%; HIT: 30.5%) and HOMA-index (ET: 42.8%; HIT: 37.0%) were significantly lower for both groups at POST when compared to PRE. Body mass was significantly reduced in the HIT (2.6%), but not in the ET group (1.2%). A significant reduction in BMI was observed for both groups after the intervention (ET: 3.0%; HIT: 5.0%). The responsiveness analysis revealed a very similar pattern of the most responsive variables among groups.
Conclusion
HIT and ET were equally effective in improving important health related parameters in obese youth.
doi:10.1371/journal.pone.0042747
PMCID: PMC3412799  PMID: 22880097
2.  High Intensity Training Improves Health and Physical Function in Middle Aged Adults 
Biology  2014;3(2):333-344.
High intensity training (HIT) is effective at improving health; however, it is unknown whether HIT also improves physical function. This study aimed to determine whether HIT improves metabolic health and physical function in untrained middle aged individuals. Fourteen (three male and eleven female) untrained individuals were recruited (control group n = 6: age 42 ± 8 y, weight 64 ± 10 kg, BMI 24 ± 2 kg·m−2 or HIT group n = 8: age 43 ± 8 y, weight 80 ± 8 kg, BMI 29 ± 5 kg·m−2). Training was performed twice weekly, consisting of 10 × 6-second sprints with a one minute recovery between each sprint. Metabolic health (oral glucose tolerance test), aerobic capacity (incremental time to exhaustion on a cycle ergometer) and physical function (get up and go test, sit to stand test and loaded 50 m walk) were determined before and after training. Following eight weeks of HIT there was a significant improvement in aerobic capacity (8% increase in VO2 peak; p < 0.001), physical function (11%–27% respectively; p < 0.05) and a reduction in blood glucose area under the curve (6% reduction; p < 0.05). This study demonstrates for the first time the potential of HIT as a training intervention to improve skeletal muscle function and glucose clearance as we age.
doi:10.3390/biology3020333
PMCID: PMC4085611  PMID: 24833513
VO2 peak; oral glucose tolerance; functional capacity; middle age
3.  The impact of brief high-intensity exercise on blood glucose levels 
Background
Moderate-intensity exercise improves blood glucose (BG), but most people fail to achieve the required exercise volume. High-intensity exercise (HIE) protocols vary. Maximal cycle ergometer sprint interval training typically requires only 2.5 minutes of HIE and a total training time commitment (including rest and warm up) of 25 minutes per session. The effect of brief high-intensity exercise on blood glucose levels of people with and without diabetes is reviewed.
Methods
HIE (≥80% maximal oxygen uptake, VO2max) studies with ≤15 minutes HIE per session were reviewed.
Results
Six studies of nondiabetics (51 males, 14 females) requiring 7.5 to 20 minutes/week of HIE are reviewed. Two weeks of sprint interval training increased insulin sensitivity up to 3 days postintervention. Twelve weeks near maximal interval running (total exercise time 40 minutes/week) improved BG to a similar extent as running at 65% VO2max for 150 minutes/week. Eight studies of diabetics (41 type 1 and 22 type 2 subjects) were reviewed. Six were of a single exercise session with 44 seconds to 13 minutes of HIE, and the others were 2 and 7 weeks duration with 20 and 2 minutes/week HIE, respectively. With type 1 and 2 diabetes, BG was generally higher during and up to 2 hours after HIE compared to controls. With type 1 diabetics, BG decreased from midnight to 6 AM following HIE the previous morning. With type 2 diabetes, a single session improved postprandial BG for 24 hours, while a 2-week program reduced the average BG by 13% at 48 to 72 hours after exercise and also increased GLUT4 by 369%.
Conclusion
Very brief HIE improves BG 1 to 3 days postexercise in both diabetics and non-diabetics. HIE is unlikely to cause hypoglycemia during and immediately after exercise. Larger and longer randomized studies are needed to determine the safety, acceptability, long-term efficacy, and optimal exercise intensity and duration.
Video abstract
doi:10.2147/DMSO.S29222
PMCID: PMC3587394  PMID: 23467903
high-intensity interval training; sprint interval training; diabetes; glucose
4.  Comparing Fat Oxidation in an Exercise Test with Moderate-Intensity Interval Training 
This study compared fat oxidation rate from a graded exercise test (GXT) with a moderate-intensity interval training session (MIIT) in obese men. Twelve sedentary obese males (age 29 ± 4.1 years; BMI 29.1 ± 2.4 kg·m-2; fat mass 31.7 ± 4.4 %body mass) completed two exercise sessions: GXT to determine maximal fat oxidation (MFO) and maximal aerobic power (VO2max), and an interval cycling session during which respiratory gases were measured. The 30-min MIIT involved 5-min repetitions of workloads 20% below and 20% above the MFO intensity. VO2max was 31.8 ± 5.5 ml·kg-1·min-1 and all participants achieved ≥ 3 of the designated VO2max test criteria. The MFO identified during the GXT was not significantly different compared with the average fat oxidation rate in the MIIT session. During the MIIT session, fat oxidation rate increased with time; the highest rate (0.18 ± 0.11 g·min- 1) in minute 25 was significantly higher than the rate at minute 5 and 15 (p ≤ 0.01 and 0.05 respectively). In this cohort with low aerobic fitness, fat oxidation during the MIIT session was comparable with the MFO determined during a GXT. Future research may consider if the varying workload in moderate-intensity interval training helps adherence to exercise without compromising fat oxidation.
Key PointsFat oxidation during interval exercise is not com-promised by the undulating exercise intensityPhysiological measures corresponding with the MFO measured during the GXT correlated well to the MIITThe validity of exercise intensity markers derived from a GXT to reflect the physiological responses during MIIT.
PMCID: PMC3918567  PMID: 24570605
Interval exercise; FATmax; maximal fat oxidation; obesity
5.  A Practical Model of Low-Volume High-Intensity Interval Training Induces Performance and Metabolic Adaptations That Resemble ‘All-Out’ Sprint Interval Training 
Recently, a novel type of high-intensity interval training known as sprint interval training has demonstrated increases in aerobic and anaerobic performance with very low time commitment. However, this type of training program is unpractical for general populations. The present study compared the impact of a low-volume high-intensity interval training to a "all-out" sprint interval training. Twenty-four active young males were recruited and randomized into three groups: (G1: 3-5 cycling bouts ˟ 30-s all-out with 4 min recovery; G2: 6- 10 cycling bouts ˟ 125% Pmax with 2 min recovery) and a non-trained control group. They all performed a VO2max test, a time to exhaustion at Pmax (Tmax) and a Wingate test before and after the intervention. Capillary blood lactate was taken at rest, 3, and 20 min after the Wingate trial. Training was performed 3 sessions per week for 4 weeks. In G1, significant improvements (p < 0.05) following training were found in VO2max (9.6%), power at VO2max (12.8%), Tmax (48.4%), peak power output (10.3%) and mean power output (17.1%). In G2, significant improvements following training were found in VO2max (9.7%), power at VO2max (16.1%), Tmax (54.2%), peak power output (7.4%; p < 0.05), but mean power output did not change significantly. Blood lactate recovery (20th min) significantly decreased in G1 and G2 when compared with pre-testing and the CON group (p < 0.05). In conclusion, the results of the current study agree with earlier work demonstrating the effectiveness of 30-s all-out training program to aerobic and anaerobic adaptations. Of substantial interest is that the low volume high intensity training provides similar results but involves only half the intensity with double the repetitions.
Key pointsGiven the markedly lower training volume in the training groups, our results suggest that intense interval training is indeed a time-efficient strategy to induce rapid metabolic and performance adaptations.The results demonstrate that a practical low-volume HIT program is effective for improving metabolic and performance adaptations that resemble many of the same performance gains occurred in all-out SIT protocol.
PMCID: PMC3737829  PMID: 24150635
Wingate test; repeated sprints; blood lactate; training adaptations.
6.  Cardiorespiratory fitness level correlates inversely with excess post-exercise oxygen consumption after aerobic-type interval training 
BMC Research Notes  2012;5:646.
Background
The purpose of this study was to reveal any association between cardiorespiratory fitness level and excess post-exercise oxygen consumption (EPOC) using three cycling protocols with varying degrees of exercise intensity, i.e., sprint interval training (SIT), high-intensity interval aerobic training (HIAT), and continuous aerobic training (CAT).
Findings
Ten healthy men, aged 20 to 31 years, attended a cross-over experiment and completed three exercise sessions: SIT consisting of 7 sets of 30-s cycling at 120% VO2max with a 15-s rest between sets; HIAT consisting of 3 sets of 3-min cycling at 80~90% VO2max with a 2-min active rest at 50% VO2max between sets; and CAT consisting of 40 min of cycling at 60~65% VO2max. During each session, resting VO2, exercise VO2, and a 180-min post-exercise VO2 were measured. The net exercise VO2 during the SIT, HIAT, and CAT averaged 14.7 ± 1.5, 31.8 ± 4.1, and 71.1 ± 10.0 L, and the EPOCs averaged 6.8 ± 4.0, 4.5 ± 3.3, and 2.9 ± 2.8 L, respectively. The EPOC with SIT was greater than with CAT (P < 0.01) and HIAT (P = 0.12). Correlation coefficients obtained between subjects’ VO2max and the ratio of EPOC to net exercise VO2 for SIT, HIAT, and CAT were −0.61 (P = 0.06), -0.79 (P < 0.01), and −0.42 (P = 0.23), respectively.
Conclusions
Our data suggest that cardiorespiratory fitness level correlates negatively with the magnitude of EPOC, especially when performing aerobic-type interval training.
doi:10.1186/1756-0500-5-646
PMCID: PMC3527216  PMID: 23171610
Aerobic fitness; Maximal oxygen consumption; Cycling; Energy expenditure; Exercise physiology
7.  High- and Moderate-Intensity Training Normalizes Ventricular Function and Mechanoenergetics in Mice With Diet-Induced Obesity 
Diabetes  2013;62(7):2287-2294.
Although exercise reduces several cardiovascular risk factors associated with obesity/diabetes, the metabolic effects of exercise on the heart are not well-known. This study was designed to investigate whether high-intensity interval training (HIT) is superior to moderate-intensity training (MIT) in counteracting obesity-induced impairment of left ventricular (LV) mechanoenergetics and function. C57BL/6J mice with diet-induced obesity (DIO mice) displaying a cardiac phenotype with altered substrate utilization and impaired mechanoenergetics were subjected to a sedentary lifestyle or 8–10 weeks of isocaloric HIT or MIT. Although both modes of exercise equally improved aerobic capacity and reduced obesity, only HIT improved glucose tolerance. Hearts from sedentary DIO mice developed concentric LV remodeling with diastolic and systolic dysfunction, which was prevented by both HIT and MIT. Both modes of exercise also normalized LV mechanical efficiency and mechanoenergetics. These changes were associated with altered myocardial substrate utilization and improved mitochondrial capacity and efficiency, as well as reduced oxidative stress, fibrosis, and intracellular matrix metalloproteinase 2 content. As both modes of exercise equally ameliorated the development of diabetic cardiomyopathy by preventing LV remodeling and mechanoenergetic impairment, this study advocates the therapeutic potential of physical activity in obesity-related cardiac disorders.
doi:10.2337/db12-1580
PMCID: PMC3712042  PMID: 23493573
8.  High-intensity interval training and hypertension: maximizing the benefits of exercise? 
Essential arterial hypertension is the most common risk factor for cardiovascular morbidity and mortality. Regular exercise is a well-established intervention for the prevention and treatment of hypertension. Continuous moderate-intensity exercise training (CMT) that can be sustained for 30 min or more has been traditionally recommended for hypertension prevention and treatment. On the other hand, several studies have shown that high-intensity interval training (HIT), which consists of several bouts of high-intensity exercise (~85% to 95% of HRMAX and/or VO2MAX lasting 1 to 4 min interspersed with intervals of rest or active recovery, is superior to CMT for improving cardiorespiratory fitness, endothelial function and its markers, insulin sensitivity, markers of sympathetic activity and arterial stiffness in hypertensive and normotensive at high familial risk for hypertension subjects. This compelling evidence suggesting larger beneficial effects of HIT for several factors involved in the pathophysiology of hypertension raises the hypothesis that HIT may be more effective for preventing and controlling hypertension.
PMCID: PMC3371620  PMID: 22720199
Exercise; hypertension; autonomic nervous system; endothelial function; arterial stiffness
9.  Fibre-Specific Responses to Endurance and Low Volume High Intensity Interval Training: Striking Similarities in Acute and Chronic Adaptation 
PLoS ONE  2014;9(6):e98119.
The current study involved the completion of two distinct experiments. Experiment 1 compared fibre specific and whole muscle responses to acute bouts of either low-volume high-intensity interval training (LV-HIT) or moderate-intensity continuous endurance exercise (END) in a randomized crossover design. Experiment 2 examined the impact of a six-week training intervention (END or LV-HIT; 4 days/week), on whole body and skeletal muscle fibre specific markers of aerobic and anaerobic capacity. Six recreationally active men (Age: 20.7±3.8 yrs; VO2peak: 51.9±5.1 mL/kg/min) reported to the lab on two separate occasions for experiment 1. Following a muscle biopsy taken in a fasted state, participants completed an acute bout of each exercise protocol (LV-HIT: 8, 20-second intervals at ∼170% of VO2peak separated by 10 seconds of rest; END: 30 minutes at ∼65% of VO2peak), immediately followed by a muscle biopsy. Glycogen content of type I and IIA fibres was significantly (p<0.05) reduced, while p-ACC was significantly increased (p<0.05) following both protocols. Nineteen recreationally active males (n = 16) and females (n = 3) were VO2peak-matched and assigned to either the LV-HIT (n = 10; 21±2 yrs) or END (n = 9; 20.7±3.8 yrs) group for experiment 2. After 6 weeks, both training protocols induced comparable increases in aerobic capacity (END: Pre: 48.3±6.0, Mid: 51.8±6.0, Post: 55.0±6.3 mL/kg/min LV-HIT: Pre: 47.9±8.1, Mid: 50.4±7.4, Post: 54.7±7.6 mL/kg/min), fibre-type specific oxidative and glycolytic capacity, glycogen and IMTG stores, and whole-muscle capillary density. Interestingly, only LV-HIT induced greater improvements in anaerobic performance and estimated whole-muscle glycolytic capacity. These results suggest that 30 minutes of END exercise at ∼65% VO2peak or 4 minutes of LV-HIT at ∼170% VO2peak induce comparable changes in the intra-myocellular environment (glycogen content and signaling activation); correspondingly, training-induced adaptations resulting for these protocols, and other HIT and END protocols are strikingly similar.
doi:10.1371/journal.pone.0098119
PMCID: PMC4047011  PMID: 24901767
10.  Effects of high aerobic intensity training in patients with schizophrenia—A controlled trial 
Nordic Journal of Psychiatry  2011;65(4):269-275.
Background: Patients with schizophrenia have a high risk of cardiovascular disease (CVD). High aerobic intensity training (HIT) improve peak oxygen uptake (VO2peak), net mechanical efficiency of walking and risk factors for CVD but has not been investigated in patients with schizophrenia. Aims: To investigate effects from HIT on VO2peak, net mechanical efficiency of walking and risk factors for CVD in patients with schizophrenia. Methods: 25 inpatients (F20-29, ICD-10) were allocated to either HIT or playing computer games (CG), 3 days per week for 8 weeks. HIT consisted of 4 × 4-min intervals with 3-min break periods, at 85-95% and 70% of peak heart rate, respectively. Results: 12 and seven patients completed HIT and CG, respectively. The baseline VO2peak in both groups combined (n = 19) was 36.8 ± 8.2 ml/kg/min and 3.12 ± 0.55 1/min. The HIT group improved VO2peak by 12% from 3.17 ± 0.59 to 3.56 ± 0.68 1/min (P < 0.001), more than the CG group (P = 0.014). Net mechanical efficiency of walking improved by 12% in the HIT group from 19.8 ± 3.0% to 22.2 ± 4.5% (P = 0.005), more than the CG group (P = 0.031). The psychiatric symptoms, expressed as the Positive and Negative Syndrome Scale (PANSS) and the Calgary Depression Scale for Schizophrenia (CDSS), did not improve in either group. Conclusions: VO2peak and net mechanical efficiency of walking improved significantly by 8 weeks of HIT. HIT should be included in rehabilitation in order to improve physical capacity and contribute risk reduction of CVD.
doi:10.3109/08039488.2011.560278
PMCID: PMC3169036  PMID: 21332297
Cardiovascular disease; Exercise; Oxygen consumption; Schizophrenia
11.  Physiological adaptations to soccer specific endurance training in professional youth soccer players 
Background: Improved oxygen uptake improves soccer performance as regards distance covered, involvements with the ball, and number of sprints. Large improvements in oxygen uptake have been shown using interval running. A similar physiological load arising from interval running could be obtained using the soccer ball in training.
Objectives: The main aim was to study physiological adaptations to a 10 week high intensity aerobic interval training program performed by professional youth soccer players, using a soccer specific ball dribbling track.
Methods: Eleven youth soccer players with a mean (SD) age of 16.9 (0.4) years performed high intensity aerobic interval training sessions twice per week for 10 weeks in addition to normal soccer training. The specific aerobic training consisted of four sets of 4 min work periods dribbling a soccer ball around a specially designed track at 90–95% of maximal heart frequency, with a 3 min recovery jog at 70% of maximal heart frequency between intervals.
Results: Mean Vo2max improved significantly from 63.4 (5.6) to 69.8 (6.6) ml kg–1 min–1, or 183.3 (13.2) to 201.5 (16.2) ml kg–0.75 min–1 (p<0.001). Squat jump and counter movement jump height increased significantly from 37.7 (6.2) to 40.3 (6.1) cm and 52.0 (4.0) to 53.4 (4.2) cm, respectively (p<0.05). No significant changes in body mass, running economy, rate of force development, or 10 m sprint times occurred.
Conclusion: Performing high intensity 4 min intervals dribbling a soccer ball around a specially designed track together with regular soccer training is effective for improving the Vo2max of soccer players, with no negative interference effects on strength, jumping ability, and sprinting performance.
doi:10.1136/bjsm.2004.012526
PMCID: PMC1725215  PMID: 15849290
12.  Reducing the Intensity and Volume of Interval Training Diminishes Cardiovascular Adaptation but Not Mitochondrial Biogenesis in Overweight/Obese Men 
PLoS ONE  2013;8(7):e68091.
Objective
The purpose of this research was to determine if the adaptations to high intensity interval training (HIT) are mitigated when both intensity and training volume (i.e. exercise energy expenditure) are reduced.
Methods
19 overweight/obese, sedentary males (Age: 22.7±3.9 yrs, Body Mass Index: 31.4±2.6 kg/m2, Waist Circumference: 106.5±6.6 cm) performed 9 sessions of interval training using a 1-min on, 1-min off protocol on a cycle ergometer over three weeks at either 70% (LO) or 100% (HI) peak work rate.
Results
Cytochrome oxidase I protein content, cytochrome oxidase IV protein content, and citrate synthase maximal activity all demonstrated similar increases between groups with a significant effect of training for each. β-hydroxyacyl-CoA dehydrogenase maximal activity tended to increase with training but did not reach statistical significance (p = 0.07). Peroxisome proliferator-activated receptor gamma coactivator-1α and silent mating type information regulator 2 homolog 1 protein contents also increased significantly (p = 0.047), while AMP-activated protein kinase protein content decreased following the intervention (p = 0.019). VO2peak increased by 11.0±7.4% and 27.7±4.4% in the LO and HI groups respectively with significant effects of both training (p<0.001) and interaction (p = 0.027). Exercise performance improved by 8.6±7.6% in the LO group and 14.1±4.3% in the HI group with a significant effect of training and a significant difference in the improvement between groups. There were no differences in perceived enjoyment or self-efficacy between groups despite significantly lower affect scores during training in the HI group.
Conclusions
While improvements in aerobic capacity and exercise performance were different between groups, changes in oxidative capacity were similar despite reductions in both training intensity and volume.
doi:10.1371/journal.pone.0068091
PMCID: PMC3702554  PMID: 23861854
13.  Intensity Thresholds for Aerobic Exercise–Induced Hypoalgesia 
Despite many studies investigating exercise-induced hypoalgesia, there is limited understanding of the optimal intensity of aerobic exercise in producing hypoalgesic effects across different types of pain stimuli. Given that not all individuals are willing or capable of engaging in high intensity aerobic exercise, whether moderate intensity aerobic exercise is associated with a hypoalgesic response and whether this response generalizes to multiple pain induction techniques needs to be substantiated.
Purpose
This study’s purpose is to test for differences in the magnitude of pressure and heat pain modulation induced by moderate (MAE) and vigorous (VAE) intensity aerobic exercise.
Methods
Twelve healthy young males and 15 females completed one training session and three testing sessions consisting of 25 minutes of either 1) stationary cycling at 70% heart rate reserve (HRR), 2) stationary cycling at 50% HRR, or 3) quiet rest (control). Pain testing was conducted on both forearms prior to and immediately following each condition and included the following tests: pressure pain thresholds (PPT), suprathreshold pressure pain test, static continuous heat test, and repetitive pulse heat pain test. Repeated measures ANOVAs were conducted on each pain measure.
Results
VAE and MAE reduced pain ratings during static continuous heat stimuli and repetitive heat pulse stimuli, with VAE producing larger effects. VAE also increased PPTs, while neither exercise influenced suprathreshold pressure pain ratings.
Conclusion
These results suggest that MAE is capable of producing a hypoalgesic effect using continuous and repetitive pulse heat stimuli. However, a dose-response effect was evident as VAE produced larger effects than MAE.
doi:10.1249/MSS.0000000000000143
PMCID: PMC4056570  PMID: 24002342
aerobic exercise; exercise-induced analgesia; pressure pain; thermal pain; temporal summation of pain
14.  Continuous and High-Intensity Interval Training: Which Promotes Higher Pleasure? 
PLoS ONE  2013;8(11):e79965.
Objectives
To compare the psychological responses to continuous (CT) and high-intensity interval training (HIT) sessions.
Methods
Fifteen men attended one CT session and one HIT session. During the first visit, the maximum heart rate, VO2Peak and respiratory compensation point (RCP) were determined through a maximal cardiopulmonary exercise test. The HIT stimulus intensity corresponded to 100% of VO2Peak, and the average intensity of both sessions was maintained at 15% below the RCP. The order of the sessions was randomized. Psychological and physiological variables were recorded before, during and after each session.
Results
There were no significant differences between the average percentages of VO2 during the two exercise sessions (HIT: 73.3% vs. CT: 71.8%; p = 0.779). Lower responses on the feeling scale (p≤0.01) and higher responses on the felt arousal scale (p≤0.001) and the rating of perceived exertion were obtained during the HIT session. Despite the more negative feeling scale responses observed during HIT and a greater feeling of fatigue (measured by Profile of Mood States) afterwards (p<0.01), the physical activity enjoyment scale was not significantly different between the two conditions (p = 0.779).
Conclusion
Despite the same average intensity for both conditions, similar psychological responses under HIT and CT conditions were not observed, suggesting that the higher dependence on anaerobic metabolism during HIT negatively influenced the feeling scale responses.
doi:10.1371/journal.pone.0079965
PMCID: PMC3841165  PMID: 24302993
15.  The Positive Effects of Priming Exercise on Oxygen Uptake Kinetics and High-Intensity Exercise Performance Are Not Magnified by a Fast-Start Pacing Strategy in Trained Cyclists 
PLoS ONE  2014;9(4):e95202.
The purpose of this study was to determine both the independent and additive effects of prior heavy-intensity exercise and pacing strategies on the VO2 kinetics and performance during high-intensity exercise. Fourteen endurance cyclists (VO2max  = 62.8±8.5 mL.kg−1.min−1) volunteered to participate in the present study with the following protocols: 1) incremental test to determine lactate threshold and VO2max; 2) four maximal constant-load tests to estimate critical power; 3) six bouts of exercise, using a fast-start (FS), even-start (ES) or slow-start (SS) pacing strategy, with and without a preceding heavy-intensity exercise session (i.e., 90% critical power). In all conditions, the subjects completed an all-out sprint during the final 60 s of the test as a measure of the performance. For the control condition, the mean response time was significantly shorter (p<0.001) for FS (27±4 s) than for ES (32±5 s) and SS (32±6 s). After the prior exercise, the mean response time was not significantly different among the paced conditions (FS = 24±5 s; ES = 25±5 s; SS = 26±5 s). The end-sprint performance (i.e., mean power output) was only improved (∼3.2%, p<0.01) by prior exercise. Thus, in trained endurance cyclists, an FS pacing strategy does not magnify the positive effects of priming exercise on the overall VO2 kinetics and short-term high-intensity performance.
doi:10.1371/journal.pone.0095202
PMCID: PMC3989295  PMID: 24740278
16.  Individual Responses to Completion of Short-Term and Chronic Interval Training: A Retrospective Study 
PLoS ONE  2014;9(5):e97638.
Alterations in maximal oxygen uptake (VO2max), heart rate (HR), and fat oxidation occur in response to chronic endurance training. However, many studies report frequent incidence of “non-responders” who do not adapt to continuous moderate exercise. Whether this is the case in response to high intensity interval training (HIT), which elicits similar adaptations as endurance training, is unknown. The aim of this retrospective study was to examine individual responses to two paradigms of interval training. In the first study (study 1), twenty active men and women (age and baseline VO2max = 24.0±4.6 yr and 42.8±4.8 mL/kg/min) performed 6 d of sprint interval training (SIT) consisting of 4–6 Wingate tests per day, while in a separate study (study 2), 20 sedentary women (age and baseline VO2max = 23.7±6.2 yr and 30.0±4.9 mL/kg/min) performed 12 wk of high-volume HIT at workloads ranging from 60–90% maximal workload. Individual changes in VO2max, HR, and fat oxidation were examined in each study, and multiple regression analysis was used to identify predictors of training adaptations to SIT and HIT. Data showed high frequency of increased VO2max (95%) and attenuated exercise HR (85%) in response to HIT, and low frequency of response for VO2max (65%) and exercise HR (55%) via SIT. Frequency of improved fat oxidation was similar (60–65%) across regimens. Only one participant across both interventions showed non-response for all variables. Baseline values of VO2max, exercise HR, respiratory exchange ratio, and body fat were significant predictors of adaptations to interval training. Frequency of positive responses to interval training seems to be greater in response to prolonged, higher volume interval training compared to similar durations of endurance training.
doi:10.1371/journal.pone.0097638
PMCID: PMC4029621  PMID: 24847797
17.  The impact of aerobic exercise training on novel adipokines, apelin and ghrelin, in patients with type 2 diabetes 
Summary
Background
Accumulating data support the atheroprotective role of the novel adipokines, apelin and ghrelin. The aim of the present randomized study was to investigate the effects of aerobic exercise training on these adipokines in patients with type 2 diabetes mellitus (T2DM).
Material/Methods
Fifty-four overweight (BMI >25 kg/m2) patients with T2DM, but without vascular complications, were randomized to either the aerobic exercise training group (EG, N=27), 4 times/week, 45–60 min/session; or to the control group (CG, N=27), orally instructed to increase physical activity. Clinical glycemic and lipid parameters, exercise capacity (VO2peak), insulin, HOMA-IR, and serum levels of apelin and ghrelin were assessed at baseline and after 12 weeks.
Results
Aerobic exercise significantly improved lipid and glycemic profile and insulin sensitivity compared to CG (p<0.05). Furthermore, between-groups comparison showed a considerable exercise-induced upregulation in apelin (p=0.007) and VO2peak (p<0.001) levels. Negligible changes in body-weight, waist-hip ratio and ghrelin concentrations were detected within and between groups after the completion of the study (p>0.05). However, subgroup analysis revealed a considerable increment in ghrelin levels only in the exercise-treated women compared to their control counterparts (p=0.038). LDL and HOMA-IR reduction were found to be independent predictors of apelin increment in multiple regression analysis (R2=0.391, p=0.011).
Conclusions
In patients with T2DM, systemic, long-term, aerobic exercise exerts positive effects on apelin and ghrelin (only in women), even in the absence of significant weight loss, suggesting its pleiotropic effects.
doi:10.12659/MSM.882734
PMCID: PMC3560628  PMID: 22534708
exercise; apelin; ghrelin; adipokines; type 2 diabetes
18.  High Intensity Interval Training in a Real World Setting: A Randomized Controlled Feasibility Study in Overweight Inactive Adults, Measuring Change in Maximal Oxygen Uptake 
PLoS ONE  2014;9(1):e83256.
Background
In research clinic settings, overweight adults undertaking HIIT (high intensity interval training) improve their fitness as effectively as those undertaking conventional walking programs but can do so within a shorter time spent exercising. We undertook a randomized controlled feasibility (pilot) study aimed at extending HIIT into a real world setting by recruiting overweight/obese, inactive adults into a group based activity program, held in a community park.
Methods
Participants were allocated into one of three groups. The two interventions, aerobic interval training and maximal volitional interval training, were compared with an active control group undertaking walking based exercise. Supervised group sessions (36 per intervention) were held outdoors. Cardiorespiratory fitness was measured using VO2max (maximal oxygen uptake, results expressed in ml/min/kg), before and after the 12 week interventions.
Results
On ITT (intention to treat) analyses, baseline (N = 49) and exit (N = 39) O2 was 25.3±4.5 and 25.3±3.9, respectively. Participant allocation and baseline/exit VO2max by group was as follows: Aerobic interval training N =  16, 24.2±4.8/25.6±4.8; maximal volitional interval training N = 16, 25.0±2.8/25.2±3.4; walking N = 17, 26.5±5.3/25.2±3.6. The post intervention change in VO2max was +1.01 in the aerobic interval training, −0.06 in the maximal volitional interval training and −1.03 in the walking subgroups. The aerobic interval training subgroup increased VO2max compared to walking (p = 0.03). The actual (observed, rather than prescribed) time spent exercising (minutes per week, ITT analysis) was 74 for aerobic interval training, 45 for maximal volitional interval training and 116 for walking (p =  0.001). On descriptive analysis, the walking subgroup had the fewest adverse events.
Conclusions
In contrast to earlier studies, the improvement in cardiorespiratory fitness in a cohort of overweight/obese participants undertaking aerobic interval training in a real world setting was modest. The most likely reason for this finding relates to reduced adherence to the exercise program, when moving beyond the research clinic setting.
Trial Registration
ACTR.org.au ACTRN12610000295044
doi:10.1371/journal.pone.0083256
PMCID: PMC3890270  PMID: 24454698
19.  Effect of Exercise Intensity on Differentiated and Undifferentiated Ratings of Perceived Exertion During Cycle and Treadmill Exercise in Recreationally Active and Trained Women 
The purpose of the study is to examine the effect of aerobic exercise intensity on components of the differentiated perceived exertion model in young women performing weight bearing and non-weight bearing aerobic exercise. Subjects were 18-25 yr old women who were recreationally active (n = 19; VO2max = 33.40 ml·kg-1·min-1) and trained (N = 22; VO2max = 43.3 ml·kg-1·min-1). Subjects underwent two graded exercise tests (GXT) on a treadmill and bike which were separated by 48 hours. RPE-Overall, -Legs, and -Chest, as well as oxygen uptake (VO2) and heart rate were recorded each minute. Individual regression analyses were used to identify RPE-Overall,-Legs, and -Chest at 40, 60, 80% VO2max/peak. Separate two factor (site (3) x intensity (3)) ANOVAs with repeated measures on site and intensity were computed for each training status. Furthermore, RPE responses were also examined with a one factor (site (3)) within subject ANOVA with repeated measure on site at the ventilatory breakpoint. For both the recreationally active and trained groups no significant differences were observed for RPE-Overall, -Legs, and -Chest during treadmill exercise. However, for cycling exercise results indicated that RPE-Legs was significantly greater at all exercise intensities than RPE-Overall and RPE-Chest for trained subjects while for recreationally active subjects RPE-Legs was only significantly higher at the highest exercise intensity. Responses at the ventilatory breakpoint during cycle exercise indicated that RPE-Legs was significantly greater than RPE-Chest and RPE-Overall for trained subjects but not for recreationally active subjects. Signal dominance was not observed at an intensity equivalent to the ventilatory breakpoint during treadmill exercise in either of the groups. In recreationally active and trained females signal dominance was demonstrated only during cycling exercise, but not during treadmill exercise. Signal integration could not be demonstrated during cycling and treadmill exercise at various intensities.
Key pointsRPE is a valid tool to track relative exercise intensity and can be applied as differentiated and undifferentiated responses regardless of training status.RPE-Legs dominated the signal response in trained women during cycling exercise.RPE-Legs, -Chest, and -Overall did not differ significantly in trained and recreationally active women during treadmill exercise.RPE-Legs and -Chest contribute equally to the formation of RPE-Overall during cycling and treadmill exercise.
PMCID: PMC3761819  PMID: 24149781
Aerobic exercise; physical exertion; oxygen consumption; physical fitness
20.  Effects of 12 Weeks High-Intensity & Reduced-Volume Training in Elite Athletes 
PLoS ONE  2014;9(4):e95025.
It was investigated if high-intensity interval training (HIT) at the expense of total training volume improves performance, maximal oxygen uptake and swimming economy. 41 elite swimmers were randomly allocated to a control (CON) or HIT group. For 12 weeks both groups trained ∼12 h per week. HIT comprised ∼5 h vs. 1 h and total distance was ∼17 km vs. 35 km per week for HIT and CON, respectively. HIT was performed as 6-10×10-30 s maximal effort interspersed by 2–4 minutes of rest. Performance of 100 m all-out freestyle and 200 m freestyle was similar before and after the intervention in both HIT (60.4±4.0 vs. 60.3±4.0 s; n = 13 and 133.2±6.4 vs. 132.6±7.7 s; n = 14) and CON (60.2±3.7 vs. 60.6±3.8 s; n = 15 and 133.5±7.0 vs. 133.3±7.6 s; n = 15). Maximal oxygen uptake during swimming was similar before and after the intervention in both the HIT (4.0±0.9 vs. 3.8±1.0 l O2×min−1; n = 14) and CON (3.8±0.7 vs. 3.8±0.7 l O2×min−1; n = 11) group. Oxygen uptake determined at fixed submaximal speed was not significantly affected in either group by the intervention. Body fat % tended to increase (P = 0.09) in the HIT group (15.4±1.6% vs. 16.3±1.6%; P = 0.09; n = 16) and increased (P<0.05) in the CON group (13.9±1.5% vs. 14.9±1.5%; n = 17). A distance reduction of 50% and a more than doubled HIT amount for 12 weeks did neither improve nor compromise performance or physiological capacity in elite swimmers.
doi:10.1371/journal.pone.0095025
PMCID: PMC3988165  PMID: 24736598
21.  Low- and High-Volume of Intensive Endurance Training Significantly Improves Maximal Oxygen Uptake after 10-Weeks of Training in Healthy Men 
PLoS ONE  2013;8(5):e65382.
Regular exercise training improves maximal oxygen uptake (VO2max), but the optimal intensity and volume necessary to obtain maximal benefit remains to be defined. A growing body of evidence suggests that exercise training with low-volume but high-intensity may be a time-efficient means to achieve health benefits. In the present study, we measured changes in VO2max and traditional cardiovascular risk factors after a 10 wk. training protocol that involved three weekly high-intensity interval sessions. One group followed a protocol which consisted of 4×4 min at 90% of maximal heart rate (HRmax) interspersed with 3 min active recovery at 70% HRmax (4-AIT), the other group performed a single bout protocol that consisted of 1×4 min at 90% HRmax (1-AIT). Twenty-six inactive but otherwise healthy overweight men (BMI: 25–30, age: 35–45 y) were randomized to either 1-AIT (n = 11) or 4-AIT (n = 13). After training, VO2max increased by 10% (∼5.0 mL⋅kg−1⋅min−1) and 13% (∼6.5 mL⋅kg−1⋅min−1) after 1-AIT and 4-AIT, respectively (group difference, p = 0.08). Oxygen cost during running at a sub-maximal workload was reduced by 14% and 13% after 1-AIT and 4-AIT, respectively. Systolic blood pressure decreased by 7.1 and 2.6 mmHg after 1-AIT and 4-AIT respectively, while diastolic pressure decreased by 7.7 and 6.1 mmHg (group difference, p = 0.84). Both groups had a similar ∼5% decrease in fasting glucose. Body fat, total cholesterol, LDL-cholesterol, and ox-LDL cholesterol only were significantly reduced after 4-AIT. Our data suggest that a single bout of AIT performed three times per week may be a time-efficient strategy to improve VO2max and reduce blood pressure and fasting glucose in previously inactive but otherwise healthy middle-aged individuals. The 1-AIT type of exercise training may be readily implemented as part of activities of daily living and could easily be translated into programs designed to improve public health.
Trial Registration
ClinicalTrials.gov NCT00839579
doi:10.1371/journal.pone.0065382
PMCID: PMC3667025  PMID: 23734250
22.  Effect of Traditional Aerobic Exercises Versus Sprint Interval Training on Pulmonary Function Tests In Young Sedentary Males: A Randomised Controlled Trial 
Background: Physical inactivity is now a global non-communicable disease. Current recommendations from American College of Sports Medicine, American Heart Association and UK medical officers for physical activity are difficult to implement, due to time constraints and hence, they have less compliance.
Purpose: To compare Sprint Interval Training (SIT) and traditional aerobic exercise (AE) with respect to changes in Vital capacity (VC), Maximum Voluntary Ventilation (MVV) and Physical Fitness Index (PFI) in young sedentary males.
Study Design: This was a randomised, controlled trial.
Methods: Fourteen young, sedentary, healthy males who were aged 18-25 years were randomly allocated to SIT group and AE group for 3 weeks. SIT group exercised at high intensity for 10 minutes a day, three days a week. AE group exercised at moderate intensity for 30 minutes a day, five days a week.
Results: Improvement in FVC (litres) in AE group was 0.31 ± 0.11 and that in SIT group was 0.48 ± 0.17. The improvement in MVV (litres) in AE Group was 21.5 ± 11.6 and that in SIT group was 27.77 ± 7.03. Thus, SIT showed a better improvement in primary outcome i.e. FVC and MVV, although difference in improvement was statistically not significant (p= 0.09 and 0.29 respectively). Secondary outcome i.e. PFI improved by 5.57 ± 1.71% in AE group and by 10.28 ± 3.03% in SIT group. The difference in improvement was statistically significant (p= 0.003).
Conclusions: SIT can be suggested as a time efficient option for improving cardiorespiratory fitness and hence, it can be used as a health promotion strategy.
doi:10.7860/JCDR/2013/5797.3343
PMCID: PMC3809629  PMID: 24179890
Exercise; Vital capacity; Physical fitness; Time
23.  Effect of Exercise Intensity on Unfolded Protein Response in Skeletal Muscle of Rat 
Endoplasmic reticulum (ER) stress, unfolded protein response (UPR), and mitochondrial biogenesis were assessed following varying intensities of exercise training. The animals were randomly assigned to receive either low- (LIT, n=7) or high intensity training (HIT, n=7), or were assigned to a control group (n=7). Over 5 weeks, the animals in the LIT were exercised on a treadmill with a 10° incline for 60 min at a speed of 20 m/min group, and in the HIT group at a speed of 34 m/min for 5 days a week. No statistically significant differences were found in the body weight, plasma triglyceride, and total cholesterol levels across the three groups, but fasting glucose and insulin levels were significantly lower in the exercise-trained groups. Additionally, no statistically significant differences were observed in the levels of PERK phosphorylation in skeletal muscles between the three groups. However, compared to the control and LIT groups, the level of BiP was lower in the HIT group. Compared to the control group, the levels of ATF4 in skeletal muscles and CHOP were significantly lower in the HIT group. The HIT group also showed increased PGC-1α mRNA expression in comparison with the control group. Furthermore, both of the trained groups showed higher levels of mitochondrial UCP3 than the control group. In summary, we found that a 5-week high-intensity exercise training routine resulted in increased mitochondrial biogenesis and decreased ER stress and apoptotic signaling in the skeletal muscle tissue of rats.
doi:10.4196/kjpp.2014.18.3.211
PMCID: PMC4071173  PMID: 24976760
ER stress; Exercise; Mitochondria; Skeletal muscle; Unfolded protein responses
24.  The Effects of Intermittent Exercise on Physiological Outcomes in an Obese Population: Continuous Versus Interval Walking 
This study compared the effects of 12 weeks of caloric restriction and interval exercise (INT) and caloric restriction and continuous aerobic exercise (CON) on physiological outcomes in an obese population. Forty-four individuals (BMI ≥ 30 kg·m-2) were randomised into the INT or CON group. Participant withdrawal resulted in 12 and 14 participants in the INT and CON groups, respectively. All participants were on a strict monitored diet. Exercise involved two 15-min bouts of walking performed on five days per week. Interval exercise consisted of a 2:1 min ratio of low-intensity (40-45% VO2peak) and high- intensity (70-75% VO2peak) exercise, while the CON group exercised between 50-55% VO2peak. Exercise duration and average intensity (%VO2peak) were similar between groups. There were no significant differences (p > 0.05) between the two groups for any variable assessed apart from very low density lipoprotein (VLDL-C), which significantly decreased over time in the INT group only (p < 0.05, d = 1.03). Caloric restriction and interval exercise compared to caloric restriction and continuous aerobic exercise resulted in similar outcome measures apart from VLDL-C levels, which significantly improved in the INT group only.
Key pointsTwelve weeks of interval exercise and caloric restriction resulted in significant improvement in very low density lipoprotein cholesterol in an obese population, as compared to continuous aerobic exercise and caloric restriction.Twelve weeks of either interval exercise or continuous exercise resulted in similar improvements in aerobic fitness in an obese population.
PMCID: PMC3737972  PMID: 24149382
Interval training; body fat; fitness; metabolism
25.  Sprint-Interval Training Induces Heat Shock Protein 72 in Rat Skeletal Muscles 
Previous studies have demonstrated that endurance exercise training increases the level of heat shock proteins (HSPs) in skeletal muscles. However, little attention has been drawn to the effects of high intensity-short duration exercise, or sprint- interval training (SIT) on HSP72 level in rat skeletal muscles. This study performed to test the hypothesis that the SIT would induce the HSP72 in fast and slow skeletal muscles of rats. Young male Wistar rats (8 weeks old) were randomly assigned to a control (CON) or a SIT group (n = 8/group). Animals in the SIT group were trained (1 min/sprint, 6~10 sets/day and 5~6 days/week) on a treadmill for 9 weeks. After the training period, HSP72 levels in the plantaris (fast) and soleus (slow) muscles were analyzed by Western blotting method. Enzyme activities (hexokinase, phosphofructokinase and citrate synthase) and histochemical properties (muscle fiber type compositions and cross sectional area) in both muscles were also determined. The SIT resulted in significantly (p < 0.05) higher levels of HSP72 in both the plantaris and soleus muscles compared to the CON group, with the plantaris producing a greater HSP72 increase than the soleus (plantaris; 550 ± 116%, soleus; 26 ± 8%, p < 0.05). Further, there were bioenergetic improvements, fast-to-slow shift of muscle fiber composition and hypertrophy in the type IIA fiber only in the plantaris muscle. These findings indicate that the SIT program increases HSP72 level of the rat hindlimb muscles, and the SIT-induced accumulation of HSP72 differs between fast and slow muscles.
Key PointsThere is no study about the effects of high intensity but short duration exercise, or sprint-interval training (SIT) on heat shock protein 72 (HSP72) level in skeletal muscles.The SIT program (≤ 10 min·day-1) accumulated HSP72 in rat skeletal muscles.The SIT-induced accumulation of HSP72 in the plantaris (fast) muscle was drastic compared to the soleus (slow) muscle and accompanied with the improvements of enzyme activities, fast-to-slow shift within fast muscle fiber type and muscle hypertrophy.
PMCID: PMC3827560  PMID: 24259991
Hindlimb; treadmill running; enzyme activity; fiber type shift; hypertrophy

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