To assess performance of existing wear/nonwear time classification algorithms for accelerometry data collected in the free-living environment using a wrist-worn triaxial accelerometer and a waist-worn uniaxial accelerometer in older adults.
Twenty-nine adults aged 76 to 96 years wore wrist accelerometers for ~24-h per day and waist accelerometers during waking for ~7 days of free-living. Wear and nonwear times were classified by existing algorithms (Alg[Actilife], Alg[Troiano] and Alg[Choi]) and compared with wear and nonwear times identified by data plots and diary records. Using bias and probability of correct classification, performance of the algorithms, two time-windows (60- and 90-min), and vector magnitude (VM) vs. vertical axis (V) counts from a triaxial accelerometer, were compared.
Automated algorithms (Alg[Choi] and Alg[Troiano]) classified wear/nonwear time intervals more accurately from VM than V counts. The use of 90-min time window improved wear/nonwear classification accuracy when compared with the 60-min window. The Alg[Choi] and Alg[Troiano] performed better than the manufacturer-provided algorithm (Alg[Actilife]), and Alg[Choi] performed better than Alg[Troiano] for wear/nonwear time classification using data collected by both accelerometers.
Triaxial wrist-worn accelerometer can be used for an accurate wear/nonwear time classification in free-living older adults. The use of 90-min window and VM counts improves performance of commonly used algorithms for wear/nonwear classification for both uniaxial and triaxial accelerometers.
nonwear categorization; physical activity assessment; accelerometry; sedentary behavior
Although studies have shown health benefits for moderate-intensity physical activity, there is limited evidence to support beneficial effects for high amounts of vigorous activity among middle-aged and older men. The objective of this study was to examine the relationship between vigorous-intensity physical activity, compared to moderate-intensity activity, and risk of major chronic disease in men.
We prospectively examined the associations between vigorous- and moderate-intensity physical activity and risk of major chronic disease among 44,551 men aged 40–75 years in 1986. Leisure-time physical activity was assessed biennially by questionnaire. During 22 years of follow-up, we documented 14,162 incident cases of major chronic disease, including 4769 cardiovascular events, 6449 cancer events, and 2944 deaths from other causes.
The hazard ratio (HR) of major chronic disease comparing ≥ 21 to 0 MET-hours/week of exercise was 0.86 (95% CI: 0.81, 0.91) for vigorous-intensity activity and 0.85 (95% CI: 0.80, 0.90) for moderate activity. For CVD, the corresponding HR were 0.78 (95% CI: 0.70, 0.86) and 0.80 (95% CI: 0.72, 0.88), respectively. When examined separately, running, tennis, and brisk walking were inversely associated with CVD risk. Furthermore, more vigorous activity was associated with lower disease risk; the HR comparing >70 to 0 MET-hours/week of vigorous-intensity exercise was 0.79 (95% CI: 0.68, 0.92; P <0.0001 for trend) for major chronic disease and 0.73 (95% CI: 0.56, 0.96; P <0.0001 for trend) for CVD.
Vigorous- and moderate-intensity physical activity were associated with lower risk of major chronic disease and cardiovascular disease. Increasing amounts of vigorous activity remained inversely associated with disease risk, even among men in the highest categories of exercise.
exercise; epidemiology; cardiovascular disease; cancer; risk factors
The United States Department of Health and Human Services disseminated physical activity guidelines for Americans in 2008. The guidelines are based on appropriate quantities of moderate-to-vigorous aerobic physical activity and resistance exercise associated with decreased morbidity and mortality risk and increased health benefits. However, increases in physical activity levels are associated with increased risk of musculoskeletal injuries. We related the amount and type of physical activity conducted on a weekly basis with the risk of musculoskeletal injury.
Prospective, observational study using weekly Internet tracking of moderate-to-vigorous physical activity and resistance exercise behaviors and musculoskeletal injuries in 909 community-dwelling women for up to 3 years. Primary outcome was self-reported musculoskeletal injuries (total, physical activity-related, and non physical activity-related) interrupting typical daily work and/or exercise behaviors for ≥2 days or necessitating health care provider visit.
Meeting versus not meeting physical activity guidelines was associated with more musculoskeletal injuries during physical activity (hazard ratio [HR] = 1.39, 95% confidence interval [CI] = 1.05 – 1.85, P = 0.02), but was not associated with musculoskeletal injuries unrelated to physical activity (HR = 0.99, 95% CI = 0.75 – 1.29, P = 0.92), or with musculoskeletal injuries overall (HR = 1.15, 95% CI = 0.95 – 1.39, P = 0.14).
Results illustrate the risk of musculoskeletal injury with physical activity. Musculoskeletal injury risk rises with increasing physical activity. Despite this modest increase in musculoskeletal injuries, the known benefits of aerobic and resistance physical activities should not hinder physicians from encouraging patients to meet current physical activity guidelines for both moderate-to-vigorous exercise and resistance exercise behaviors with the intent of achieving health benefits.
MODERATE; PREVALENCE; STRENGTHENING; VIGOROUS
The aim of this study was to investigate the relative influence of genetic and environmental factors on children’s leisure time exercise behavior, through the classical twin design.
Data were taken from the Netherlands Twin Register. The twins were 7 (N=3,966 subjects), 10 (N=3,562) and 12 years old (N=8,687), with longitudinal data for 27% of the sample. Parents were asked to indicate the children’s regular participation in leisure time exercise activities, including frequency and duration. Resemblance between monozygotic and dizygotic twins for weekly MET hours spent on exercise activities was analyzed as a function of their genetic relatedness.
Average weekly MET hours increased with age for both boys [age 7: 14.0 (SD=11.8); age 10: 22.6 (SD=18.7); age 12: 28.4 (SD=24.9)] and girls [age 7: 9.7 (SD=9.5); age 10: 15.3 (SD=15.1); age 12: 19.3 (SD=19.8)]. Around 13% of boys and girls across all age groups did not participate in any regular leisure time exercise activities. Tracking of exercise behavior from age 7 to age 12 was modest (.168 < r < .534). For boys, genetic effects accounted for 24% (CI: 18–30%) of the variance at age 7, 66% (53–81%) at age 10 and 38% (32–46%) at age 12. For girls, this was 22% (15–30%), 16% (9–24%), and 36% (30–43%), respectively. Environmental influences shared by children from the same family explained 71%, 25% and 50% of the variance in boys (aged 7, 10, 12) and 67%, 72% and 53% in girls. The shared environment influencing exercise behavior was partially different between boys and girls.
Our results stress the important role of shared environment for exercise behavior in young children.
Twin design; physical activity; heritability; genes; tracking; childhood
Our study characterizes food and energy intake responses to long-term aerobic (AT) and resistance training (RT) during a controlled 8-month trial.
In the STRRIDE AT/RT trial, overweight/obese sedentary dyslipidemic men and women were randomized to AT (n = 39), RT (n = 38), or a combined treatment (AT/RT; n = 40) without any advice to change their food intakes. Quantitative food intake assessments (QDI) and food frequency questionnaires (FFQ) were collected at baseline (BEF) and after 8 mo. training (END); body mass (BM) and fat free mass (FFM) were also assessed.
In AT and AT/RT, respectively, meaningful decreases in reported energy intake (REI) (−217 and −202 kcal; p < 0.001) and in intakes of fat (−14.9 and −14.9 g; p < 0.001, p = 0.004), protein (−8.3 and −10.7 g; p = 0.002, p < 0.001), and carbohydrate (−28.1 and −14.7 g; p = 0.001, p = 0.030) were found by FFQ. REI relative to FFM decreased (p < 0.001 and p=0.002) as did intakes of fat (−0.2 and −0.3 g; p = 0.003 and p = 0.014) and protein (−0.1 and −0.2 g; p = 0.005 and p < 0.001) in AT and AT/RT and carbohydrate (−0.5 g; p<0.003) in AT only. For RT, REI by QDI decreased (−3.0 kcal/kg FFM; p=0.046), as did fat intake (−0.2 g; p = 0.033). BM decreased in AT (−1.3 kg, p=0.006) and AT/RT (−1.5 kg, p = 0.001) but was unchanged (0.6 kg, p = 0.176) in RT.
Previously sedentary subjects completing 8 months of AT or AT/RT reduced their intakes of kcal and macronutrients and BM. In RT, fat intakes and REI (when expressed per FFM) decreased, BM was unchanged, and FFM increased.
aerobic exercise; resistance training; energy intake; body mass; obesity
Physical activity recommendations are defined in terms of time spent being physically active (e.g., 30 minutes brisk walking, five days a week). However, walking volume may be more naturally assessed by distance than time. Analyses were therefore performed to test whether time or distance provide the best metric for relating walking volume to estimated total and regional adiposity.
Linear and logistic regression analyses were used to relate exercise dose to body mass index (BMI), body circumferences, and obesity in a cross-sectional sample of 12,384 female and 3,434 male walkers who reported both usual distance walked and time spent walking per week on survey questionnaires. Metabolic equivalent hours per day (METhr/d, 1 MET=3.5 ml O2•kg−1•min−1) were calculated from the time and pace, or distance and pace, using published compendium values. Results: Average METhr/d walked was 37% greater when calculated from time spent walking vs. usual distance in women, and 31% greater in men. Per METhr/d, declines in BMI and circumferences (slope±SE) were nearly twice as great, or greater, for distance- vs. time-derived estimates for kg/m2 of BMI (females: −0.58±0.03 vs. −0.31±0.02; males: −0.35±0.04 vs. −0.15±0.02), cm of waist circumference (females: −1.42±0.07 vs. −0.72±0.04; males: −0.96±0.10 vs. −0.45±0.07), and reductions in the odds for total obesity (odds ratio, females: 0.72 vs. 0.84; males: 0.84 vs. 0.92), and abdominal obesity (females: 0.74 vs. 0.85; males: 0.79 vs. 0.91, all comparisons significant).
Distance walked may provide a better metric of walking volume for epidemiologic obesity research, and better public health targets for weight control, than walking duration. Additional research is required to determine whether these results, derived in a sample that regularly walks for exercise, apply more generally.
obesity; energy; physical activity; exercise volume; guidelines
Physical activity may protect against breast cancer. Few prospective studies have evaluated breast cancer mortality in relation to cardiorespiratory fitness, an objective marker of physiologic response to physical activity habits.
We examined the association between cardiorespiratory fitness and risk of death from breast cancer in the Aerobics Center Longitudinal Study. Women (N=14,811), aged 20 to 83 years with no prior breast cancer history, received a preventive medical examination at the Cooper Clinic in Dallas, TX, between 1970 and 2001. Mortality surveillance was completed through December 31, 2003. Cardiorespiratory fitness was quantified as maximal treadmill exercise test duration and was categorized for analysis as low (lowest 20% of exercise duration), moderate (middle 40%), and high (upper 40%). At baseline, all participants were able to complete the exercise test to at least 85% of their age-predicted maximal heart rate.
A total of 68 breast cancer deaths occurred during follow-up (mean=16 years). Age-adjusted breast cancer mortality rates per 10,000 woman-years were 4.4, 3.2, and 1.8 for low, moderate, and high cardiorespiratory fitness groups, respectively (trend P = 0.008). After further controlling for body mass index, smoking, drinking, chronic conditions, abnormal exercise electrocardiogram responses, family history of breast cancer, oral contraceptive use, and estrogen use, hazard ratios (95% CI) for breast cancer mortality across incremental cardiorespiratory fitness categories were 1.00 (referent), 0.67 (0.35–1.26), 0.45 (0.22–0.95); trend P = 0.04.
These results indicate that cardiorespiratory fitness is associated with a reduced risk of dying from breast cancer in women.
Epidemiology; Prevention; Death from breast cancer; Physical activity
An active lifestyle is widely recognized as having a beneficial effect on cardiovascular health. However, no clear consensus exists as to whether exercise training increases overall physical activity energy expenditure (PAEE) or whether individuals participating in regular exercise compensate by reducing their off-exercise physical activity. The purpose of this study was to evaluate changes in PAEE in response to aerobic training (AT), resistance training (RT), or combined aerobic and resistance training (AT/RT).
Data are from 82 participants in the Studies of Targeted Risk Reduction Interventions through Defined Exercise—Aerobic Training versus Resistance Training study, a randomized trial of overweight (body mass index = 25–35 kg·m−2) adults, in which participants were randomized to receive 8 months of AT, RT, or AT/RT. All subjects completed a 4-month control period before randomization. PAEE was measured using triaxial RT3 accelerometers, which subjects wore for a 5- to 7-d period before and after the exercise intervention. Data reduction was performed with a previously published computer-based algorithm.
There was no significant change in off-exercise PAEE in any of the exercise training groups. We observed a significant increase in total PAEE that included the exercise training, in both AT and AT/RT but not in RT.
Eight months of exercise training was not associated with a compensatory reduction in off-exercise physical activity, regardless of exercise modality. The absence of compensation is particularly notable for AT/RT subjects, who performed a larger volume of exercise than did AT or RT subjects. We believe that the extended duration of our exercise training program was the key factor in allowing subjects to reach a new steady-state level of physical activity within their daily lives.
ACCELEROMETER; CALORIC EXPENDITURE; AEROBIC TRAINING; RESISTANCE TRAINING; COMPENSATION
It has been well established in mammals that circadian behavior as well as the molecular clockwork can be synchronized to the light-dark (LD) cycle via the suprachiasmatic nucleus of the hypothalamus (SCN). In addition to light, it has been demonstrated that non-photic time cues, such as restricting the time of food availability, can alter circadian behavior and clock gene expression in selected peripheral tissues such as liver. Studies have also suggested that scheduled physical activity (exercise) can alter circadian rhythms in behavior and clock gene expression, however currently the effects of exercise alone are largely unknown and have not been explored in skeletal muscle.
Period2∷Luciferase (Per2∷Luc) mice were maintained under 12 hours of light followed by 12 hours of darkness (12L:12D) then exposed to 2 hours of voluntary or involuntary exercise during the light phase for 4 weeks. Control mice were left in home cages or moved to the exercise environment (sham). A second group of mice had restricted access to food (4 hours per day for 2 weeks) in order to compare the effects of two non-photic cues on PER2∷LUC bioluminescence. Skeletal muscles, lung and SCN tissue explants were cultured for 5-6 days to study molecular rhythms.
In the exercised mice, the phase of peak PER2∷LUC bioluminescence was shifted in the skeletal muscle and lung explants but not the SCN suggesting a specific synchronizing effect of exercise on the molecular clockwork in peripheral tissues.
These data provide evidence that the molecular circadian clock in peripheral tissues can respond to the time of exercise suggesting that physical activity contributes important timing information for synchronization of circadian clocks throughout the body.
PERIOD2∷LUCIFERASE; CIRCADIAN; NON-PHOTIC; TIME CUE
The ability of female sex steroids to regulate tissue function has long been appreciated, however their role in the regulation of striated muscle function has received considerably less attention. The purpose of this symposium review is to document recent evidence indicating the role female sex steroids have in defining the functional characteristics of striated muscle. The presentations provide substantial evidence indicating that estrogens are critical to the physiological and metabolic regulation of striated muscle, thus when considering women’s health issues striated muscle must included as an important target tissue along with other classically thought of estrogen sensitive tissues.
estrogens; muscle; metabolism; cardiac; sex; exercise
Previous studies have demonstrated that pattern recognition approaches to accelerometer data reduction are feasible and moderately accurate in classifying activity type in children. Whether pattern recognition techniques can be used to provide valid estimates of physical activity energy expenditure in youth remains unexplored in the research literature.
To develop and test artificial neural networks (ANNs) to predict physical activity (PA) type and energy expenditure (PAEE) from processed accelerometer data collected in children and adolescents.
100 participants between the ages of 5 and 15 y completed 12 activity trials that were categorized into 5 PA types: sedentary, walking, running, light intensity household activities or games, and moderate-to-vigorous intensity games or sports. During each trial, participants wore an ActiGraph GT1M on the right hip and VO2 was measured using the Oxycon Mobile portable metabolic system. ANNs to predict PA type and PAEE (METs) were developed using the following features: 10th, 25th, 50th, 75th, and 90th percentiles and the lag one autocorrelation. To determine the highest time resolution achievable, features were extracted from 10, 15, 20, 30, and 60 s windows. Accuracy was assessed by calculating the percentage of windows correctly classified and root mean square error (RMSE).
As window size increased from 10 to 60 s, accuracy for the PA type ANN increased from 81.3% to 88.4%. RMSE for the MET prediction ANN decreased from 1.1 METs to 0.9 METs. At any given window size, RMSE values for the MET prediction ANN were 30–40% lower than conventional regression-based approaches.
ANNs can be used to predict both PA type and PAEE in children and adolescents using count data from a single waist mounted accelerometer.
objective assessment; validity; children; adolescents; pattern recognition
We tested the hypothesis that low intensity exercise in mdx mice improves plantarflexor muscle contractile function, resistance to fatigue, and mitochondrial adaptations without exacerbating muscular dystrophy.
We subjected mdx mice to 12 wk of voluntary, low-resistance wheel running (Run, n=17) or normal cage activities (sedentary; Sed, n=16) followed by in vivo analyses for plantarflexor torque generation and fatigue resistance, or running capacity on a treadmill. Gastrocnemius muscles were further evaluated for exercise-induced mitochondrial adaptations and fiber type distribution and central nuclei. T-tests were used to determine differences between the Sed and Run groups.
Plantarflexor submaximal isometric torques and maximal isometric torque at multiple ankle joint angles, and resistance to fatigue were greater in Run compared to Sed mdx mice (P<0.05). Citrate synthase and β-HAD enzyme activities and COX IV protein expression in gastrocnemius muscles were greater in Run than Sed mdx mice (P≤0.04), along with a trend of fiber type transformation from type IIb to type 2x fibers. Exercise training in mdx mice did not elevate serum creatine kinase levels, but led to a significant reduction of centrally-nucleated myofibers.
Voluntary, low-resistance wheel running in mdx mice can result in skeletal muscle adaptation, leading to improved contractile function and reduced fatigability, with no indication that exercise was detrimental. This study supports the need for further investigation of low intensity exercise as an early therapeutic intervention in ambulatory boys with DMD.
Duchenne muscular dystrophy; fatigue; mitochondria; physical activity; skeletal muscle; strength
Standards for estimating maximal heart rate (HR) are important when interpreting adequacy of physiologic stress during exercise testing, assessing chronotropic response, and prescribing an exercise training regimen. The equation 220 – age is used to estimate maximum HR; however, it over-estimates measured maximal HR in patients taking beta-adrenergic blockade (βB) therapy. This study developed and validated a practical equation to predict maximal HR in patients with heart failure (HF) taking βB therapy.
Data from symptom-limited exercise tests completed on patients with systolic HF participating in the Heart Failure and A Controlled Trial Investigating Outcomes of Exercise Training (HF-ACTION) trial and taking a βB agent were used to develop a simplified equation, which was validated using bootstrapping.
The simplified derived equation was [119 + 0.5(resting HR) − 0.5(age) − (0, if test was completed using a treadmill; 5, if stationary bike)]. The R2 and standard error of the estimate (SEE) were 0.28 and 18 beats·min−1, respectively. Validation of this equation yielded a mean R2 and SEE of 0.28 and 18 beats·min−1, respectively. For the equation 220-age, the R2 was −2.93 and the SEE was 43 beats·min−1.
We report a valid and simple population-specific equation for estimating peak HR in patients with HF taking βB therapy. An equation that should be helpful when evaluating chronotropic response or assessing if a maximum effort was provided during exercise testing. We caution, however, that the magnitude of the variation (SEE=18 beats·min−1) associated with this prediction equation may make it impractical when prescribing exercise intensity.
Chronotropic incompetence; exercise; left ventricular systolic dysfunction; testing
To investigate the effect of posterior cruciate ligament (PCL) deficiency on the kinematics and the cartilage contact characteristics of the patellofemoral joint during an in vivo single-leg lunge.
Ten patients with an isolated PCL injury in one knee and the contralateral side intact participated in the study. Magnetic resonance and dual fluoroscopic imaging techniques were used to analyze the patellofemoral kinematics and cartilage contact of the intact and the PCL-deficient knee during a quasi-static single-leg lunge from 0° to 120° of flexion.
PCL deficiency significantly changed the patellofemoral kinematics between 90° and 120° of knee flexion (P < 0.007): an increased patellar flexion angle by 10.7< on average and a decreased lateral shift (on average −1.9 mm), patellar tilt (approximately −2.7°), and valgus rotation (approximately −1.8°) were observed in the PCL-deficient knee compared with the intact contralateral joint. The changes in patellofemoral kinematics resulted in significant changes in patellofemoral cartilage contact (P < 0.007). PCL deficiency caused a distal (approximately −3.3 mm) and medial (approximately + 2.7 mm) shift of cartilage contact from 75° to 120° of flexion.
The altered tibiofemoral kinematics that were previously described in PCL deficiency resulted in changes in patellofemoral joint function at flexion angles greater than 75°. This abnormal loading of the patellofemoral joint might predispose the patellofemoral cartilage to degenerative changes. Because we did not detect differences in the patellofemoral joint behavior of the intact and the PCL-deficient knee between 0° and 60° of flexion, rehabilitation exercises might be safely performed in this range of flexion. On the other hand, repetitive deep knee squats should be avoided in PCL-deficient patients, so as not to excessively disturb the patellofemoral cartilage contact kinematics.
DUAL FLUOROSCOPIC IMAGING; PATELLOFEMORAL COMPLICATIONS; PATELLAR TRACKING; PATELLOFEMORAL CARTILAGE CONTACT; SINGLE-LEG LUNGE
To assess the cardiovascular responses during constant load walking and to identify predictors of this response in peripheral artery disease (PAD) patients.
Seventy-nine patients with PAD performed a constant load treadmill test (2 mph, 0% grade). During the test, systolic blood pressure (BP), diastolic BP, and heart rate (HR) were obtained at the fourth minute to the last minute of exercise. Patients were also characterized on demographic measures, cardiovascular risk factors, baseline exercise performance and vascular measures.
During constant load walking, there was a significant increase (p<0.01) in systolic BP (+12 ± 10 mmHg), diastolic BP (+6 ± 9 mmHg), and HR (+5 ± 5 bpm). The HR responses was negatively correlated with ischemic window (r= −0.23; p<0.05), expressed as an area under the curve of the resting ankle systolic BP and its recovery from maximal graded treadmill test, and positively correlated with the HR during the first minute of recovery from maximal graded treadmill test (r= 0.27; p<0.05). The increase in cardiovascular variables during constant load walking was greater in subjects with higher body mass index and in men (p<0.05).
Patients with PAD had an increased cardiovascular response during constant load walking, and these responses were greater in obese patients and in men. The clinical implication is that PAD patients engaged in walking training programs, particularly men and those with obesity, require frequent assessment of cardiovascular parameters to avoid exaggerated increases in BP and HR during constant load walking.
Peripheral Vascular Disease; Intermittent Claudication; Exercise; Blood Pressure
The purpose of this study was to examine the ability of the YMCA submaximal exercise test protocol using a total body recumbent stepper (TBRS) to predict VO2 peak.
Out of 112 individuals initially screened, one-hundred ten individuals with low to moderate cardiovascular disease risk met the inclusion criteria for participation in the study. The maximal exercise test used a motorized treadmill and the Bruce or modified Bruce protocol. Oxygen uptake was measured and analyzed through collection of expired gases using a metabolic measurement system. The submaximal exercise test was performed at least 24 hours later but no more than 5 days post maximal exercise testing. Participants were instructed to keep a pace of 100 steps per minute and the resistance increase every 3 minutes according to the protocol until fatigue, or 85% of HR max was achieved. A cross validation study was also performed to determine the accuracy of the prediction equation.
Using a stepwise regression, we report that VO2 peak can be predicted using a five element model including age, weight, sex, watts_endsubmax and HR_endsubmax (F5,69 = 70.31, p <0.001). We report a strong correlation between the predicted VO2 peak to the actual VO2 peak.
These data suggest the YMCA submaximal exercise test can be used with the TBRS to predict VO2 peak in healthy adults.
aerobic fitness; rehabilitation; prediction model; exercise; cardiopulmonary; cross validation
The decreased internal knee extensor moment is a significant gait asymmetry among patients with anterior cruciate ligament (ACL) deficiency, yet the muscular strategy driving this altered moment for the injured limb is unclear.
To determine whether patients with ACL deficiency and characteristic knee instability would demonstrate normal extensor and increased flexor muscle force to generate a decreased internal extensor moment (i.e. employ a hamstring facilitation strategy).
Gait analysis was performed on 31 athletes with acute ACL rupture who exhibited characteristic knee instability after injury. Peak internal knee extensor moment was calculated using inverse dynamics and muscle forces were estimated using an EMG-driven modeling approach. Comparisons were made between the injured and contralateral limbs.
As expected, patients demonstrated decreased peak knee flexion (p=0.028) and internal knee extensor moment (p=0.0004) for their injured limb, but exhibited neither an isolated decrease in extensor force (quadriceps avoidance), nor an isolated increase in flexor force (hamstring facilitation) at peak knee moment. Instead, they exhibited decreased muscle force from both flexor (p=0.0001) and extensor (p=0.0103) groups. This strategy of decreased muscle force may be explained in part by muscle weakness which frequently accompanies ACL injury, or by apprehension, low confidence and fear of further injury.
This is the first study to estimate muscle forces in the ACL-deficient knee using an EMG-driven approach. These results affirm the existence of neuromuscular asymmetries in the individuals with ACL deficiency and characteristic knee instability.
Knee Moment; Muscle Force; Quadriceps Avoidance; Hamstring Facilitation; Instability
Females have been reported to have a 3-5 times greater incidence of non-contact ACL injury when compared to their male counterparts. Previous research suggests that physical maturation is one factor that is associated with the development of potentially injurious lower extremity biomechanics in female athletes.
To determine if lower extremity biomechanics differ between male and female soccer athletes during a cutting maneuver across different stages of maturational development.
One hundred and fifty six soccer players (76 male and 80 females) between the ages of 9 and 23 participated. Subjects were classified based on maturation as pre-pubertal, pubertal, post-pubertal or young adult. Lower extremity kinematics, kinetics and ground reaction forces (GRF) were obtained during a 45 degree side-step cutting maneuver. Differences between sex and maturation were assessed for peak knee valgus angle, knee adductor moments and GRF's (vertical, posterior and lateral) during weight acceptance using a 2 factor ANCOVA (controlling for approach velocity).
No sex × maturation interactions were found for any variable of interest. On average, females exhibited greater knee abduction and adductor moments than males. Pre-pubertal athletes demonstrated greater knee adductor moments and GRFs than all other groups.
Biomechanical differences between males and females were evident across all stages of maturation. On average, less mature athletes exhibit biomechanical patterns during cutting that may place them at greater risk for injury than their more mature counterparts.
puberty; cutting; locomotor skills; kinematics; kinetics
Research examined joint physical activity and sedentary behavior among 291 parent-child pairs who both wore an accelerometer and global positioning systems (GPS) device over the same 7-day period.
Children were 52.2% female, 8-14 years, and 43.0% Hispanic. Parents were 87.6% female. An Actigraph GT2M accelerometer and GlobalSat BT-335 GPS device collected activity and global positioning data, respectively. Linear distance between the parent and child for each 30-sec. epoch was calculated using geographic coordinates from the GPS. Joint behavior was defined as a separation distance less than 50m between parents and children.
On average during non-school waking hours, parents and children spent 2.4 min. (SD = 4.1) per day performing moderate-to-vigorous physical activity (MVPA) together and 92.9 min. (SD = 40.1) per day in sedentary behavior together. Children engaged in an average of 10 min. per day of MVPA during non-school waking hours when their parent was nearby but not engaging in MVPA. During this same period, parents engaged in 4.6 min. per day of MVPA when their child was nearby but not engaging in MVPA. Household income level and the child’s age were negatively associated with joint MVPA. Girls engaged in a greater percentage of their total MVPA together with their parent than boys. Girls and older children engaged in more sedentary behavior together with their parent than boys and younger children. Older parents engaged in a greater percentage of their sedentary behavior together with their children than younger parents.
Replacing the time that parents and children spend together in sedentary pursuits with joint physical activity could have health benefits, especially for girls, older children, older parents, and higher income families.
moderate-to-vigorous physical activity; accelerometer; global positioning systems; age; sex
A maximal exercise respiratory exchange ratio (RERmax) ≥1.10 is commonly used as a criterion to determine if a “true” maximal oxygen uptake (VO2max) has been attained during maximal-effort exercise testing. Because RERmax is heavily influenced by CO2 production from acid buffering during maximal exercise, we postulated that dietary acid load, which affects acid-base regulation, might contribute to variability in RERmax.
To determine if a habitual dietary intake that promotes systemic alkalinity results in higher RERmax during VO2max testing.
Sedentary men and women (47-63y, n=57) with no evidence of cardiovascular disease underwent maximal graded treadmill exercise tests. VO2max and RERmax were measured with indirect calorimetry. Habitual diet was assessed for its long-term effect on systemic acid-base status by performing nutrient analysis of food diaries and using this information to calculate the potential renal acid load (PRAL). Participants were grouped into tertiles based on PRAL.
The lowest PRAL tertile (alkaline PRAL) had higher RERmax values (1.21±0.01, p≤0.05) than the middle tertile (1.17±0.01) and highest PRAL tertile (1.15±0.01). There were no significant differences (all p≥0.30) among PRAL tertiles for RER at submaximal exercise intensities of 70%, 80%, or 90% VO2max. After controlling for age, sex, VO2max, and maximal heart rate (HRmax), regression analysis demonstrated that 19% of the variability in RERmax was attributed to PRAL (r=−0.43, p=0.001). Unexpectedly, HRmax was lower (p≤0.05) in the low PRAL tertile (164±3 beats/min) versus the highest PRAL tertile (173±3 beats/min).
These results suggest that individuals on a diet that promotes systemic alkalinity may more easily achieve the RERmax criterion of ≥1.10 which might lead to false-positive conclusions about achieving maximal effort and VO2max during graded exercise testing.
maximal oxygen uptake; stress test; renal acid load; alkaline diet; ash diet
The purposes of this study were to suppress estradiol levels in adolescent (postpubertal rats) using gonadotropin-releasing hormone antagonist (GnRH-a) injections and to determine the changes in bone structure and mechanical strength.
In an Institutional Animal Care and Use Committee–approved study, female rats at 23 d of age were assigned to a baseline group (BL65; n = 10) sacrificed on day 65, a control group (Control; n = 15) sacrificed on day 90, or an experimental group (AMEN; n = 9) sacrificed on day 90 that received daily injections of GnRH-a for a 25-d period from 65 to 90 d of age (2.5 mg·kg−1 per dose).
Body weights were similar on day 65; however, the AMEN group was significantly heavier than the Control group (17%, P = 0.001) on day 90. In the AMEN rats relative to the Control group, plasma estradiol levels were reduced by 36% (P = 0.0001) and plasma insulin-like growth factor 1 levels were 24% higher (P = 0.003). In the femur, there was no change in periosteal bone apposition or total cross-sectional area. The marrow area increased by 13.7% (P = 0.05) resulting in a 7.8% decrease in relative cortical area (P = 0.012), and endocortical bone formation rate increased by 39.4% (P = 0.04). Trabecular volume and number decreased by 51.5% (P = 0.0003) and 49.5% (P = 0.0003), respectively. The absolute peak moments of the tibiae and femurs were unchanged in the AMEN group relative to the Control group, but these were reduced by 8.8% (P = 0.03) and 7.5% (P = 0.09), respectively, when normalized by body weight.
Suppression of estradiol by 25 d of GnRH-a administration to 65-d-old (postpubertal) rats reduced trabecular volume and number by about 50%, increased endocortical bone turnover, and reduced relative cortical thickness without changing tibial and femoral total area. These changes in bone structure were associated with no change in absolute mechanical strength possibly because of increases in body weight or in insulin-like growth factor 1 concentrations.
BONE HISTOMORPHOMETRY; BIOMECHANICS; GONADOTROPIN-RELEASING HORMONE; ESTROGEN; CORTICAL BONE
Physical activity is frequently a component of interventions designed to diminish weight gain in children. It is essential to determine whether the energy expenditure (EE) elicited by these interventions is sufficient to reduce the rate of weight gain.
To quantify the EE of the Physical Activity across the Curriculum (PAAC) intervention. This intervention involved two 10-min physically active academic lessons per day, taught by classroom teachers.
We assessed EE of PAAC in 19 males and 19 females using both an indirect calorimeter (IC) (COSMED K4b2) and an accelerometer (ActiGraph) (AC). Independent t-tests were used to evaluate gender differences. Dependent t-tests were used to examine the difference between EE assessed by IC and AC. The agreement between EE measured by IC and estimated by AC was evaluated using a Bland-Altman plot. A Pearson correlation between EE measured by IC and estimated by AC was calculated.
There were no significant gender differences for age, BMI, or EE; therefore, analyses by gender were not performed. The mean EE measured by IC was 3.1 ± 1.0 kcal/min(3.4 METs). Mean EE estimated by AC (1.8 ± 0.9 kcal/min) was significantly lower (P < 0.05) than EE measured by IC (mean underestimation = 1.3 kcal/min). The Bland-Altman plot suggested increased underestimation with increased levels of EE. The 95% limits of agreement were large (-2.8 to +0.3 kcal/min). The correlation between EE measured by IC and estimated by AC was r = 0.68 (P < 0.001).
PAAC elicited a level of EE that may prevent excessive weight gain in children. AC significantly underestimated the EE of PAAC lessons and may not provide useful EE estimates in this context.
Indirect Calorimeter; Accelerometer; Classroom; School-Based
Despite intense interest in understanding how old age may alter skeletal muscle fatigability, a quantitative examination of the impact of study design on age-related differences in muscle fatigue does not exist.
The purpose of this study was to conduct a systematic review of the differences in muscle fatigue between young and older adults, with specific examination of moderator variables suggested to contribute to discrepancies across studies: contraction intensity, contraction mode, duty cycle, fatigue index, sex, muscle group, and contraction type.
The standardized effect of age on muscle fatigue was computed for 37 studies (60 standardized effects). Standardized effects were coded as positive when less fatigue was reported in older individuals compared with young individuals.
The overall standardized effect of age on muscle fatigue was positive (0.56). In studies using dynamic contractions or using muscle power as the index of fatigue, the standardized effect was negative (–0.12 and –2.5, respectively). The standardized effect for all other moderator categories was positive (range = 0.09–0.90), indicating less fatigue in older adults under all other methodological conditions.
This review provides the first quantitative analysis of the effect of study design on age-related differences in muscle fatigue. The results indicate that older individuals develop less muscle fatigue than young individuals, particularly during isometric contractions of the elbow flexor and knee extensor muscles. However, the results also suggest that older adults develop greater fatigue during dynamic contractions, particularly when the decline in power is assessed. Studies that verify this latter outcome are needed, as are studies designed to elucidate the mechanisms of fatigue.
AGING; CONTRACTION; QUANTITATIVE REVIEW; ISOMETRIC; POWER
Maximal or peak aerobic capacity (VO2peak) during a maximal effort graded exercise test (GXT) is considered by many to be the “gold standard” outcome for assessing the impact of exercise training on cardiorespiratory fitness. The reliability of this measure in Parkinson Disease (PD) has not been established, where the degree of motor impairment can vary greatly and is influenced by medications. This study examined the reliability of VO2peak during maximal effort GXT in subjects with PD.
Seventy healthy middle-aged and older subjects with PD, Hoehn and Yahr stage 1.5 to 3 underwent a screening/acclimatization maximal effort treadmill test followed by 2 additional maximal effort treadmill tests with repeated measurements of VO2peak. A third VO2peak test was performed in a subset of 21 subjects.
The mean VO2peak measurement was 2.4% higher in the second test compared to the first test (21.42 ± 4.3 ml/kg/min versus 21.93 ± 4.50 ml/kg/min, mean ± SD, p=0.03). The intraclass correlation coefficients (ICC) for VO2peak expressed either as ml/kg/min or L/min was highly reliable, with ICC of 0.90 and 0.94 respectively. The maximum heart rate (ICC of 0.91), and final speed achieved during the tests (ICC of 0.94) were also highly reliable, with the respiratory quotient (RQ) being the least reliable of the parameters measured (ICC of 0.65).
Our results demonstrate that measurement of VO2peak is reliable and repeatable in subjects with mild to moderate PD, thereby validating use of this parameter for assessing the effects of exercise interventions on cardiorespiratory fitness.
graded exercise test; reliability; cardiorespiratory fitness; maximal oxygen uptake; Parkinson Disease
Accurate and reliable measurement of physical activity plays an important role in assessing effective lifestyle interventions for obesity. This study examined reliability of accelerometer-based estimates of physical activity levels of overweight and obese adults before and after a lifestyle weight loss program.
Participants were overweight and obese (BMI 25–45 kg/m2) members (n=1592; 67% female, 42% African American) of the multi-center Weight Loss Maintenance trial. They wore RT3 accelerometers during waking hours for 7 days at baseline and after a 6-month weight loss intervention that included diet and physical activity recommendations. Moderate to vigorous physical activity (MVPA) and MVPA occurring in bouts ≥ 10 minutes (bout MVPA) were assessed.
At baseline, wear time minimums of 10 and 6 hours/day resulted in similar average minutes·day−1 of MVPA (18.3 and 18.0 minutes) and MVPA bout minutes·day−1 (6.9 and 6.7 minutes). Similar wear times occurred after the weight loss intervention for MVPA (27.0 and 26.8 minutes) and bout MVPA (15.1 and 15.0 minutes). Reliability measurements by Intra Class Correlation (ICC) were larger for 4 versus 2 days·week−1 minimum wear time for both MVPA and bout MVPA (4 day ICCs .27–.44 and 2 day ICCs .19–.38), but there was little increase in ICC comparing 4 (ICCs.27–.44) and 7 days·week−1 (ICCs .30–.46).
Longer wear time requirements did not result in significant increases in reliability. Using 4 days of data with ≥ 6 hours·day−1 of wear time optimized the balance between ICC and participant burden in overweight and obese adults before and after a weight loss intervention. Future investigations using accelerometers to estimate MVPA in overweight and obese samples can consider requiring less monitor wear time.
Physical Activity; Exercise; Bouts; Ambulatory Monitoring; Measurement