Test the relationship of change in body mass index (BMI) percentile score group (from 6th to 8th grade) with change in cardiovascular fitness (CVF), baseline BMIz-score and CVF.
3,998 (92%) children in the HEALTHY trial provided complete data at the beginning of 6th and end of 8th grades. Height and weight were assessed according to standardized protocol. CVF was measured using the 20 meter shuttle run. Changes in BMI percentile were categorized into five groups: increased a BMI category, stayed obese, stayed overweight, stayed healthy weight, and decreased a BMI category. Data were analyzed separately by gender, controlling for race, parental education, change in pubertal stage, and baseline BMIz-score and CVF.
Youth (males and females) who lowered their BMI group or remained in the healthy or overweight groups had significantly larger increases in CVF, than the stayed obese or increased a BMI category groups. But these relationships accounted for a small percentage of variance (i.e. weak relationship). Staying obese was associated with the highest baseline BMIz-score, with the second highest among those who decreased a BMI category. BMI category change accounted for the most variance in baseline BMIz-score.
Changes in BMI categories were substantially more strongly related to 6th grade values of BMIz-score than to CVF changes. Since pre-existing adiposity may inhibit adiposity change, changes in CVF and adiposity should be attempted prior to middle school.
Obesity; Overweight; Longitudinal; Children
There is evidence that physical activity may reduce the risk of developing Alzheimer’s disease and dementia. However, few reports have examined the physical activity-dementia association with objective measures of physical activity. Cardiorespiratory fitness (hereafter called fitness) is an objective reproducible measure of recent physical activity habits.
We sought to determine whether fitness is associated with lower risk for dementia mortality in women and men.
We followed 14,811 women and 45,078 men, ages 20-88 at baseline, for an average of 17 years. All participants completed a preventive health examination at the Cooper Clinic in Dallas, Texas during 1970-2001. Fitness was measured with a maximal treadmill exercise test, with results expressed in maximal metabolic equivalents (METs). The National Death Index identified deaths through 2003. Cox proportional hazards models were used to examine the association between baseline fitness and dementia mortality, adjusting for age, sex, examination year, body mass index, smoking, alcohol use, abnormal ECGs, and health status.
There were 164 deaths with dementia listed as the cause during 1,012,125 person-years of exposure. Each 1-MET increase in fitness was associated with a 14% lower adjusted risk of dementia mortality (95% confidence interval, CI 6%-22%). With fitness expressed in tertiles, adjusted hazard ratios (HRs) for those in the middle and high fitness groups suggest their risk of dementia mortality was less than half that of those in the lowest fitness group (respectively: HR 0.44, CI 0.26-0.74; HR 0.49, CI 0.26-0.90).
Greater fitness was associated with lower risk of mortality from dementia in a large cohort of men and women.
physical fitness; cognitive function; Alzheimer’s disease; vascular dementia; metabolic equivalents (METs)
Month-to-month variation in physical activity levels in a cohort of post-menopausal women participating in a single site clinical trial undergoing lifestyle intervention was investigated prior to and after lifestyle intervention.
Participants were Caucasian and African-American women (mean age 57.0 ± 3.0) from the Women On the Move through Activity and Nutrition (WOMAN) study. Physical activity was measured subjectively by questionnaire and objectively by pedometer at baseline and at the 18-month follow-up.
At baseline, prior to intervention, pedometer steps were highest in the summer months (7,616 steps/day), lower in the fall (6,293 steps/day), lowest in winter (5,304 steps/day), and then rebounded in the spring (5,850 steps/day). Physical activity estimates from the past-week subjective measure followed the same seasonal pattern. After 18-months, the lifestyle change group significantly increased their pedometer step counts when compared to the health education group (p<0.0001). At 18-months, pedometer step counts for the health education group followed a pattern similar to that found in the entire group prior to intervention, whereas, month-to-month step counts for the lifestyle change group appeared to remain consistent throughout the year.
These results confirm previous reports that suggest physical activity levels fluctuate throughout the year. Lifestyle intervention, which includes a physical activity component, not only increases step counts, but appears to reduce some of variation in physical activity levels over the course of a year in post-menopausal women.
pedometer; seasonality; post-menopause; lifestyle intervention
To compare daily ambulatory measures in children, adolescents, and young adults with and without metabolic syndrome, and to assess which metabolic syndrome components, demographic measures, and body composition measures are associated with daily ambulatory measures.
Two-hundred fifty subjects between the ages of 10 and 30 years were assessed on metabolic syndrome components, demographic and clinical measures, body fat percentage, and daily ambulatory strides, durations, and cadences during seven consecutive days. Forty-five of the 250 subjects had metabolic syndrome, as defined by the International Diabetes Federation.
Subjects with metabolic syndrome ambulated at a slower daily average cadence than those without metabolic syndrome (13.6 ± 2.2 strides/min vs. 14.9 ± 3.2 strides/min; p=0.012), and they had slower cadences for continuous durations of 60 minutes (p=0.006), 30 minutes (p=0.005), 20 minutes (p=0.003), 5 minutes (p=0.002), and 1 minute (p=0.001). However, the total amount of time spent ambulating each day was not different (p=0.077). After adjustment for metabolic syndrome status, average cadence is linearly associated with body fat percentage (p<0.001) and fat mass (p<0.01). Group difference in average cadence was no longer significant after adjusting for body fat percentage (p=0.683) and fat mass (p=0.973).
Children, adolescents, and young adults with metabolic syndrome ambulate more slowly and take fewer strides throughout the day than those without metabolic syndrome, even though the total amount of time spent ambulating is not different. Furthermore, the detrimental influence of metabolic syndrome on ambulatory cadence is primarily a function of body fatness.
Ambulation; body fat; children; metabolic syndrome; physical activity
The purpose of the study was to examine the relationship between serum 25-hydroxy vitamin D (25(OH)D) levels and muscle strength in 419 healthy men and women over a broad age range (20-76 years of age).
Isometric and isokinetic strength of the arms and legs was measured using computerized dynamometry and its relation to vitamin D was tested in multivariate models controlling for age, gender, resting heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), body mass index (BMI), maximal oxygen uptake (VO2max,), physical activity counts, and season of vitamin D measurement.
Vitamin D was significantly associated with arm and leg muscle strength when controlling for age and gender. When controlling for other covariates listed above, vitamin D remained directly related to both isometric and isokinetic arm strength but only to isometric leg strength.
These data suggests that there may be a differential effect of vitamin D on upper and lower body strength. The mechanism for this difference remains unclear but could be related to differences in androgenic effects or to differences in vitamin D receptor expression. Our study supports a direct relationship between vitamin D and muscle strength and suggests that vitamin D supplementation be evaluated to determine if it is an effective therapy to preserve muscle strength in adults.
25-Hydroxyvitamin D; Dynamometry; Androgen; VDR
BORCHERS, J. R., K. L. CLEM, D. L. HABASH, H. N. NAGARAJA, L. M. STOKLEY, and T. M. BEST. Metabolic Syndrome and Insulin Resistance in Division 1 Collegiate Football Players. Med. Sci. Sports Exerc., Vol. 41, No. 12, pp. 2105–2110, 2009.
To estimate the prevalence of metabolic syndrome and insulin resistance in a cohort of Division 1 collegiate football players.
Ninety football players were evaluated in a cross-sectional study to estimate the prevalence of metabolic syndrome, insulin resistance, and associated risk factors. Obesity was defined as a body fat ≥25% determined by BOD POD measurements. The National Cholesterol Education Program Adult Treatment Panel III criteria were used to estimate prevalence of metabolic syndrome. Quantitative insulin sensitivity check index calculations were performed to estimate prevalence of insulin resistance. Linear regression techniques were used to determine association between body fat percentage and other measured continuous parameters. Fisher exact test was used to determine association between nominal variables, and one-way ANOVA compared the three groups defined by position.
Summary measures showed a small prevalence of abnormal individual measurements. There was an association between body fat percentage and most evaluated parameters (P < 0.05). The prevalence of obesity, insulin resistance, and metabolic syndrome was 21%, 21%, and 9%, respectively. Obesity is closely associated with metabolic syndrome (P < 0.0001) and insulin resistance (P < 0.0001) in this population. All subjects with metabolic syndrome were obese, and the odds for insulin resistance in the obese group are 10.6 times the odds for the nonobese group. Linemen (n = 29) had 19 of the 19 obese subjects, 13 of the 19 subjects with insulin resistance, and all subjects with metabolic syndrome.
There is a strong association between obesity and both metabolic syndrome and insulin resistance in Division 1 collegiate football players. Linemen are at significant risk for metabolic syndrome and insulin resistance compared with other positions. This may be predictive of future health problems in Division 1 collegiate football players, especially linemen.
Obesity; Cardiovascular Risk Factors; Exercise; Diet
To investigate the effect of a yearlong moderate-intensity aerobic exercise intervention on C-reactive protein (CRP), serum amyloid A (SAA), and interleukin 6 (IL-6) among overweight or obese postmenopausal women.
In a randomized controlled trial, 115 postmenopausal, overweight or obese, sedentary women, aged 50-75 years were randomized to an aerobic exercise intervention of moderate-intensity (60-75% observed maximal heart rate), for ≥45 min/day, 5 days/week (n=53), or to a 1 day/week stretching control (n=62), on an intent-to-treat basis. CRP, SAA, and IL-6 were measured at baseline, 3-months, and 12-months.
From baseline to 12-months, CRP decreased 10% in exercisers and increased 12% in controls (p=0.01); no effects were observed for SAA and IL-6. Among participants at baseline who were obese (BMI≥30kg/m2) or had abdominal obesity (waist circumference (WC)≥88cm), exercise resulted in a more pronounced reduction in CRP (BMI≥30kg/m2: p=0.002; WC≥88cm: p<0.0001), borderline for SAA (BMI≥30kg/m2: p=0.08; WC≥88cm: p=0.04); no intervention effects were observed among women who did not have these characteristics. Overall, weight loss was minimal in the exercise intervention (~1.8kg). Linear trends were observed between CRP and 12-month changes in: aerobic fitness (ptrend = 0.006), exercise adherence (ptrend = 0.004), percentage body fat (ptrend = 0.002), body weight (ptrend = 0.002), waist circumference (ptrend = 0.02), and intra-abdominal fat (ptrend = 0.03).
A moderate-intensity exercise intervention reduced CRP over 12-months among women who were obese at baseline. These findings support the role of exercise in modulating inflammatory processes that are related to increased risk of chronic disease among obese women.
overweight; inflammation; C-reactive protein; physical activity; randomized controlled trial; serum amyloid A
Epithelial Na+ Channels (ENaC) play a crucial role in ion and fluid regulation in the lung. In cystic fibrosis (CF) Na+ hyperabsorption results from ENaC over activity, leading to airway dehydration. Previous work has demonstrated functional genetic variation of SCNN1A (the gene encoding the ENaC α-subunit), manifesting as an alanine (A) to threonine (T) substitution at amino acid 663, with the αT663 variant resulting in a more active channel.
We assessed the influence of genetic variation of SCNN1A on the diffusing capacity of the lungs for carbon monoxide (DLCO) and nitric oxide (DLNO), together with alveolar capillary membrane conductance (DM), pulmonary capillary blood volume (VC), and alveolar volume (VA) at rest and during peak exercise in 18 patients with CF [10 homozygous for αA663 (AA group) and 8 with at least one T663 allele (AT/TT group)]. Due to the more active channel we hypothesized that the AT/TT group would show a greater increase in DLCO, DLNO, and DM with exercise due to exercise-mediated ENaC inhibition and subsequent attenuation of Na+ hyperabsorption.
The AT/TT group had significantly lower pulmonary function, weight and BMI than the AA group. Both groups had similar peak workloads, relative peak oxygen consumptions, and cardiopulmonary responses to exercise. The AT/TT group demonstrated a greater increase in DLNO, DLNO/VA, and DM in response to exercise (% increases: DLNO= 18±11vs.41±38; DLNO/VA= 14±21vs.40±37; DM= 15±11vs.41±38, AAvs.AT/TT, respectively). There were no differences between groups in absolute diffusing capacity measures at peak exercise.
These results suggest that genetic variation of the alpha-subunit of ENaC differentially affects the diffusing capacity response to exercise in patients with CF.
exercise; cystic fibrosis; diffusing capacity; DLNO; DLCO; ENaC polymorphism
To determine the effect of body mass index (BMI) on level of agreement between six previously established prediction equations for three commonly used accelerometers to predict summary measures of energy expenditure (EE) in youth.
One hundred thirty-one youth between the ages of 10–17 years and BMI from 15 to 44 kg/m2 were outfitted with hip-worn ActiGraph GT1M, Actical, and RT3 accelerometers and spent approximately 24 hours in a whole-room indirect calorimeter while performing structured and self-selected activities. Five commonly used regression and one propriety equations for each device were used to predict the minute-to-minute EE (normalized to metabolic equivalents, METs), daily physical activity level (PAL), and time spent in sedentary, light, moderate, and vigorous physical activity intensity categories. The calculated values were compared with criterion measurements obtained from the room calorimeter.
All predictive equations, except RT3, significantly over- or under-predicted daily PAL (p < 0.001), with large discrepancies observed in the estimate of sedentary and light activity. Discrepancies between actual and estimated PAL ranged from 0.05 to 0.68. In addition, BMI represented a modifier for two ActiGraph predictive equations (AG1 and AG2), affecting the accuracy of physical activity-related EE (PAEE) predictions.
ActiGraph (AG3) and the RT3 closely predicted overall PAL (within 4.2 and 6.8%, respectively) as a group. When adjusting for age, sex, and ethnicity, Actical (AC1 and AC2) and ActiGraph (AG3) were not influenced by BMI. However, a gap between some hip-worn accelerometer predictive and regression equations was demonstrated compared to both criterion measurement and each other, which poses a potential difficulty for inter-study (e.g. different accelerometers) and intra-study (e.g., BMI, adiposity) comparisons.
Energy prediction; Adiposity; Actical; ActiGraph; RT3
To investigate the effect of changes in expiratory intrathoracic pressure (ITP) on stroke volume (SV) at rest and during moderate exercise in patients with heart failure vs. healthy individuals.
SV was obtained by echocardiography during spontaneous breathing and during expiratory loads of 5 and 10 cm H2O produced by a ventilator in 11 patients with heart failure (61±9 years, EF: 32±4%, NYHA class I-II) and 11 age-matched healthy individuals at rest and during exercise at 60% of aerobic capacity on a semi-recumbent cycle ergometer.
At rest, expiratory loading did not change heart rate, SV index (SVI) or cardiac index (CI) in either group. During moderate exercise, expiratory loading increased SVI and CI in patients with heart failure, but decreased SVI and CI in healthy individuals. There was a negative correlation between changes in gastric pressure and SVI (r=−0.51, p<0.05) in healthy individuals, while there was a positive correlation between changes in gastric pressure accompanying expiratory loading and CI (r=0.83, p<0.01) in patients with heart failure.
Expiratory loading during moderate exercise elicited increases in SVI and CI in patients with heart failure but decreased SVI and CI in healthy individuals. Improvements in cardiac function during submaximal exercise in patients with heart failure may be caused by a beneficial reduction in LV preload.
preload; cardiorespiratory; exercise tolerance; stroke volume
This study explored the environmental and psychological correlates of active commuting in a sample of adults from the European Prospective Investigation into Cancer (EPIC) Norfolk cohort.
Members of the cohort who were in employment, lived within 10km of work, and did not report a limitation that precluded walking were included in this analysis. Psychological factors, perceptions of the neighbourhood environment and travel mode to work were reported using questionnaires. Neighbourhood and route environmental characteristics were estimated objectively using a Geographical Information System. The mediating effects of psychological factors were assessed using a series of regression models.
1279 adults (mean age of 60.4 years SD=5.4) were included in this analysis, of which, 25% actively commuted to work. In multivariable regression analyses, those who reported strong habits for walking or cycling were more likely to actively commute, whilst those living 4-10km from work were less likely to actively commute. In addition, living in a rural area was associated with a decreased likelihood of men’s active commuting and in women, living in a neighbourhood with high road density and having a route to work which was not on a main or secondary road was associated with an increased likelihood of active commuting. There was weak evidence that habit acted to partly mediate the associations between environmental correlates and active commuting in both sexes.
The findings suggest that interventions designed to encourage the development of habitual behaviours for active commuting may be effective, especially amongst those living close to work.
walking; cycling; EPIC-Norfolk; neighbourhood; route
Slow heart rate recovery (HRR) from a graded exercise treadmill test (GXT) is a marker of impaired parasympathetic reactivation that is associated with elevated mortality. Our objective was to test whether demographic, behavioral or coronary heart disease (CHD) risk factors during young adulthood were associated with the development of slow HRR.
Participants from the Coronary Artery Risk Development in Young Adults study underwent symptom-limited maximal GXT using a modified Balke protocol at baseline (1985–86) and 20-year follow-up (2005–06) examinations. HRR was calculated as the difference between peak heart rate (HR) and HR two-minutes following cessation of the GXT. Slow HRR was defined as 2-minute HRR < 22 beats·min−1.
In 2,730 participants who did not have slow HRR at baseline, mean HRR was 44 beats*min−1 (SD = 11) at baseline and declined to 40 beats·min−1 (SD=12) in 2005–06; slow HRR developed in 5% (n=135) of the sample by 2005–06. Female sex, black race, fewer years of education, obesity, cigarette smoking, higher depressive symptoms, higher fasting glucose, hypertension, metabolic syndrome and physical inactivity and low fitness were each associated with incident slow HRR. In a multivariable model higher BMI, larger waist, low education, fasting glucose and current smoking remained significantly associated with incident slow HRR. Increasing BMI (per SD higher) over follow-up and incident hypertension, diabetes and metabolic syndrome (in the subsets of participants who were free from those conditions at baseline), were each associated with a significantly elevated odds of incident slow HRR.
On average, HRR declines with aging; however, the odds of having slow HRR in early middle age is significantly associated with traditional CHD risk factors.
Epidemiology; Cardiovascular Disease; Exercise; Autonomic Nervous System
Fat contained within skeletal muscle is strongly associated with obesity, type 2 diabetes mellitus, and metabolic syndrome. Physical inactivity may be a risk factor for greater fat infiltration within skeletal muscle during growth.
We sought to examine the relationship between physical activity and skeletal muscle fat content of the calf and thigh in girls.
Data from 464 girls, aged 8–13 years, was used to examine the relationship between physical activity and skeletal muscle fat content of the calf and thigh. Calf and thigh muscle density (mg/cm3), an index of skeletal muscle fat content, was assessed at the 66% tibia and 20% femur sites relative to the respective distal growth plates of the non-dominant limb using peripheral quantitative computed tomography (pQCT). Physical activity level was classified by past year physical activity questionnaire (PYPAQ) score.
Muscle densities of the calf and thigh were inversely correlated with percent total body fat (r =−0.37 and−0.48, P values < 0.001) and total body fat mass (r =−0.33 and−0.40, P values < 0.001). Multiple linear regression with physical activity, ethnicity, maturity offset, and muscle cross-sectional area as independent variables showed that physical activity was independently associated with muscle densities of the calf (β = 0.14, P = 0.002) and thigh (β = 0.15, P < 0.001). Thus, lower physical activity was associated with higher skeletal muscle fat content.
Our results suggest that a lower level of physical activity may lead to excess skeletal muscle fat content of the calf and thigh in girls.
MUSCLE QUALITY; EXERCISE; FEMALE; YOUTH; PQCT
Genetic factors account for 40%–70% of the population variation in body mass index (BMI), suggesting that genetic predisposition is a major risk factor for excess weight. The purpose of this study was to test whether exercise attenuates the inherited risk for excess body weight.
Survey questionnaires of exercise (usual running distance) and BMI were obtained from a national sample of 582 female and 344 male self-identified monozygotic (MZ) twins. Regression analyses were used to test whether running disparity diminished the inheritance of BMI when adjusted for age, education, cigarette use, and selected dietary variables.
The active twins ran between 0 and 10.7 km/d more than their less active twins if female (mean±SD:1.61±1.50 km/d) and between 0 and 13.7 km/d more if male (1.88 ± 1.78 km/d). Average BMIs of the less active twins were 22.38±3.56 and 24.59±3.08 kg/m2 in females and males, respectively. Within-twin correlations were significant (P <0.0001) for usual distance run (females: r = 0.64; males: r = 0.61) and BMI (females: r = 0.67; males: r = 0.71). Greater running differences (∆km/d) attenuated the effect of the less active twins’ BMIs on their active MZ twins’ BMI (females: −14.3% per Δkm/d, P<10−7; males: −7.4% per Δkm/d, P=0.004), such that by 4 Δkm/d, the inherited risk was reduced by 58.8% in females and 29.6% in males.
These results are consistent with the attenuation of the inherited risk of excess body weight by running, which is remarkable because BMI regulation is assumed to be multifactorial, its genetic inheritance is polygenic, and no single genetic polymorphism currently explains >1% of the BMI variance.
The aim of the research was to determine how knee extensor strength asymmetry influences gait asymmetry and variability since these gait parameters have been related to mobility and falls in older adults.
Strength of the knee extensors was measured in 24 older women (65 – 80 yr). Subjects were separated into symmetrical strength (SS, n = 13) and asymmetrical strength (SA, n = 11) groups using an asymmetry cutoff of 20%. Subjects walked at a standard speed of 0.8 m s−1 and at maximal speed on an instrumented treadmill while kinetic and spatiotemporal gait variables were measured. Gait and strength asymmetry were calculated as the percent difference between legs and gait variability as the coefficient of variation over twenty sequential steps.
SA had greater strength asymmetry (27.4 ± 5.5%) than SS (11.7 ± 5.4%, P < 0.001). Averaged across speeds, SA had greater single (7.1% vs. 2.5%) and double-limb support time asymmetry (7.0 vs. 4.3%) than SS and greater single-limb support time variability (9.7% vs. 6.6%, all P < 0.05). Group × speed interactions occurred for weight acceptance force variability (P = 0.02) and weight acceptance force asymmetry (P = 0.017) with greater variability at the maximal speed in SA (5.0 ± 2.4% vs. 3.7 ± 1.2%) and greater asymmetry at the maximal speed in SA (6.4 ± 5.3% vs. 2.5 ± 2.3%).
Gait variability and asymmetry are greater in older women with strength asymmetry and increase when they walk near their maximal capacities. The maintenance of strength symmetry, or development of symmetry through unilateral exercise, may be beneficial in reducing gait asymmetry, gait variability, and fall risk in older adults.
Elderly; Mobility Limitation; Walking; Quadriceps Muscle; Aging
Patellofemoral pain (PFP) has often been attributed to abnormal hip and knee mechanics in females. To date, there have been few investigations of the hip and knee mechanics of males with PFP. The purpose of this study was to compare the lower extremity mechanics and alignment of male runners with PFP with healthy male runners and female runners with PFP. We hypothesized that males with PFP would move with greater varus knee mechanics compared with male controls and compared with females with PFP. Further, it was hypothesized that males with PFP would demonstrate greater varus alignment.
A gait and single leg squat analysis was conducted on each group (18 runners per group). Measurement of each runner’s tibial mechanical axis was also recorded. Motion data were processed using Visual 3D (CMotion, Bethesda, Md., USA). Analyses of Variance were used to analyze the data.
Males with PFP ran and squatted in greater peak knee adduction and demonstrated greater peak knee external adduction moment compared with healthy male controls. In addition, males with PFP ran and squatted with less peak hip adduction and greater peak knee adduction compared with females with PFP. The static measure of mechanical axis of the tibial was not different between groups. However, a post-hoc analysis revealed that males with PFP ran with greater peak tibial segmental adduction.
Males with PFP demonstrated different mechanics during running and during a single leg squat compared with females with PFP and with healthy males. Based upon the results of this study, therapies for PFP may need to be sex-specific.
Patellofemoral Pain; Running; Biomechanics; Sex Differences
Accurate and reliable methods for assessing human physical activity energy expenditure (PAEE) are informative and essential for understanding individual behaviors and quantifying the impact of physical activity (PA) on disease, PA surveillance and for examining determinants of PA in different populations. This paper reviews recent advances in the estimation of PAEE, in three interrelated areas: 1) types of sensors worn by human subjects, 2) features extracted from the measured sensor signals, and 3) modeling techniques to estimate the PAEE using these features. The review illustrates three directions in the PAEE studies, and provides recommendations for future research, with the aim to produce valid, reliable, and accurate assessment of PAEE from wearable sensors.
Physical activity; energy expenditure; body-worn sensors; computational methodology
To prospectively examine the independent and joint effects of alcohol consumption and cardiorespiratory fitness on the incidence of metabolic syndrome in a cohort of men.
A prospective examination of 3,411 apparently healthy men at baseline, who came to the Cooper Clinic (Dallas, Texas) for at least 2 preventive visits (1979–2010). Primary exposure variables were cardiorespiratory fitness and alcohol intake; the outcome measure was metabolic syndrome (MetS) and the components thereof. Cox proportional hazard models were computed to assess the relationship between the exposure variables and the incidence of MetS while adjusting for confounders.
Over a mean follow-up period of 9 years (SD=7.8), 276 men developed MetS. In multivariable analysis, a dose-response relationship was observed between increased levels of fitness and reduced MetS risk (moderate fitness: HR=0.60, 95%CI 0.43–0.82; high fitness: HR=0.49, 95%CI 0.35–0.69). When examining the independent effects of alcohol, light drinking increased the risk for MetS by 66% (HR=1.66, 95%CI 1.11–2.48). No statistically significant interaction effect was observed between alcohol and fitness in relation to MetS (P = 0.32). When assessing the relation between each exposure and the components of MetS, higher fitness consistently reduced the risk of all components; whereas lower alcohol intake reduced the risk of elevated glucose and blood pressure and increased the risk for low HDL-c.
Among this cohort of men, higher fitness levels reduced the risk for MetS and its components. The relation between alcohol intake levels and metabolic risk was more complex and not reflected when examining MetS as a whole.
CARDIORESPIRATORY FITNESS; ALCOHOL INTAKE; METABOLIC SYNDROME; COHORT STUDY
Investigations employing wearable monitors have begun to examine how sedentary time behaviors influence health.
To demonstrate the utility of a measure of sedentary behavior and to validate the activPAL and ActiGraph GT3X for estimating measures of sedentary behavior: absolute number of breaks and break-rate.
Thirteen participants completed two, 10-hour conditions. During the baseline condition, participants performed normal daily activity and during the treatment condition, participants were asked to reduce and break-up their sedentary time. In each condition, participants wore two ActiGraph GT3X monitors and one activPAL. The ActiGraph was tested using the low frequency extension filter (AG-LFE) and the normal filter (AG-Norm). For both ActiGraph monitors two count cut-points to estimate sedentary time were examined: 100 and 150 counts∙min−1. Direct observation served as the criterion measure of total sedentary time, absolute number of breaks from sedentary time and break-rate (number of breaks per sedentary hour [brks.sed-hr−1]).
Break-rate was the only metric sensitive to changes in behavior between baseline (5.1 [3.3 to 6.8] brks.sed-hr−1) and treatment conditions (7.3 [4.7 to 9.8] brks.sed-hr−1) (mean [95% CI]). The activPAL produced valid estimates of all sedentary behavior measures and was sensitive to changes in break-rate between conditions (baseline: 5.1 [2.8 to 7.1] brks.sed-hr−1, treatment: 8.0 [5.8 to 10.2] brks.sed-hr−1). In general, the AG-LFE and AG-Norm were not accurate in estimating break-rate or absolute number of breaks and were not sensitive to changes between conditions.
This study demonstrates the utility of expressing breaks from sedentary time as a rate per sedentary hour, a metric specifically relevant to free-living behavior, and provides further evidence that the activPAL is a valid tool to measure components of sedentary behavior in free-living environments.
Sedentary behavior; Breaks; Activity monitors; activPAL; ActiGraph
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