Shelby L. Francis

Sustained effects of physical activity on bone health: Iowa Bone Development Study

Studies of youth athletics and interventions have shown some maintenance of bone mineral content (BMC; g) after cessation of training, but less is known about sustained effects of everyday physical activity (PA). Using a prospective cohort, this report examined potential effects of childhood PA on adolescent BMC. Participants (N=156 boys, 170 girls) had exams at ages 5, 13, and 15. Body size and maturity were determined using anthropometry. Moderate-to-vigorous-intensity PA (MVPA) and vigorous-intensity PA (Vigorous PA) were measured using accelerometry. BMC of the spine and hip was measured using dual-energy X-ray absorptiometry. Mixed regression models tested whether PA at age 5 affected BMC at ages 13 and 15 after adjustment for age (year), height (cm), weight (kg), maturity (pre-peak height velocity or post), and activity level (min/day). Analysis was repeated to control for age 5 BMC. On average, boys participated in 59, 52, and 38 min of MVPA and 13, 17, and 11 min of Vigorous PA at ages 5, 13, and 15, respectively. MVPA (β=0.799) and Vigorous PA (β=1.338) at age 5 predicted later spine BMC (p<0.05). MVPA (β=0.480) at age 5 predicted hip BMC. Girls participated in 47, 33, and 26 min of MVPA and 10, 9 and 7 min of Vigorous PA at ages 5, 13, and 15, respectively. Neither MVPA nor Vigorous PA predicted later spine BMC. MVPA (β=0.302) at age 5 predicted hip BMC. After controlling for BMC at age 5 as well as the other covariates, the effect of MVPA (β=0.695) and Vigorous PA (β=1.079) at age 5 remained significant for boys at the spine. For girls, neither MVPA nor Vigorous PA at age 5 predicted spine or hip BMC. Childrens early PA appears to have a modest effect on adolescent BMC at the critical regions of spine and hip; benefits may be greater for geometric changes, which future studies should include.

Objectively measured physical activity predicts hip and spine bone mineral content in children and adolescents ages 5-15 years: iowa bone development study.

This study examined the association between physical activity (PA) and bone mineral content (BMC; gram) from middle childhood to middle adolescence and compared the impact of vigorous-intensity PA (VPA) over moderate- to vigorous-intensity PA (MVPA). Participants from the Iowa bone development study were examined at ages 5, 8, 11, 13, and 15 years (n = 369, 449, 452, 410, and 307, respectively). MVPA and VPA (minutes per day) were measured using ActiGraph accelerometers. Anthropometry was used to measure body size and somatic maturity. Spine BMC and hip BMC were measured via dual-energy x-ray absorptiometry. Sex-specific multi-level linear models were fit for spine BMC and hip BMC, adjusted for weight (kilogram), height (centimeter), linear age (year), non-linear age (year2), and maturity (pre peak height velocity vs. at/post peak height velocity). The interaction effects of PA × maturity and PA × age were tested. We also examined differences in spine BMC and hip BMC between the least (10th percentile) and most (90th percentile) active participants at each examination period. Results indicated that PA added to prediction of BMC throughout the 10-year follow-up, except MVPA, did not predict spine BMC in females. Maturity and age neither modify the PA effect for males nor females. At age 5, the males at the 90th percentile for VPA had 8.5% more hip BMC than males in the 10th percentile for VPA. At age 15, this difference was 2.0%. Females at age 5 in the 90th percentile for VPA had 6.1% more hip BMC than those in the 10th percentile for VPA. The age 15 difference was 1.8%. VPA was associated with BMC at weight-bearing skeletal sites from childhood to adolescence, and the effect was not modified by maturity or age. Our findings indicate the importance of early and sustained interventions that focus on VPA. Approaches focused on MVPA may be inadequate for optimal bone health, particularly for females.

Muscle Power Predicts Adolescent Bone Strength: Iowa Bone Development Study

PURPOSE To assess association between lower body muscle power and bone strength as well as the mediating effect of muscle cross-sectional area (MCSA) on that association. METHODS Participants (141 males and 162 females) were approximately 17 yr. Muscle power was predicted using vertical jump and the Sayers equation. Using peripheral quantitative computed tomography (pQCT), bone strength indices were obtained at two locations of the tibia, corresponding to primary stressors acting upon each site: bone strength index for compression (BSI) at the distal 4% site; density-weighted polar section modulus strength-strain index (SSIp) and cortical bone area (CoA) at the 66% midshaft site for torsion. Muscle cross-sectional area was measured at the 66% site. Pearson bivariate and partial correlation coefficients were estimated to quantify the strength of the associations among variables. Direct and indirect mediation model effects were estimated, and 95% bootstrap confidence intervals were constructed to test the causal hypothesis. Height and maturity were examined as covariates. RESULTS Pearson correlation coefficients among muscle power, MCSA, and bone strength were statistically significant (P < 0.01) and ranged from r = 0.54 to r = 0.78. After adjustment for covariates, associations were reduced (r = 0.37 to 0.69) (P < 0.01). Mediation models for males for BSI, SSIp, and CoA accounted for 38%, 66%, and 54% of the variance in bone strength, respectively. Models for females for BSI, SSIp, and CoA accounted for 46%, 77%, and 66% of the variance, respectively. CONCLUSIONS We found strong and consistent associations as well as direct and indirect pathways, among muscle power, MCSA, and tibia strength. These results support the use of muscle power as a component of health-related fitness in bone health interventions for older adolescents.

Changes in Gait over a 30-min Walking Session in Obese Females.

Purpose This study assessed the biomechanical gait changes in obese and normal-weight female adult subjects after a commonly recommended 30-min walking session. Hip and knee adduction and extensor moments, which are the primary modulators of frontal and sagittal plane load distribution, were hypothesized to increase in obese females after a 30-min walking period, resulting in more stress across the hip and knee joint. Methods Ten obese (37.7 ± 4.8 yr of age, body mass index [BMI] = 36.1 ± 4.2 kg·m−2) and 10 normal-weight control female subjects (38.1 ± 4.5 yr of age, BMI = 22.6 ± 2.3 kg·m−2) walked 30 min continuously on the treadmill at their self-selected speed. V˙O2max was estimated using Ebbeling protocol. A three-dimensional pre- and posttreadmill gait analysis was conducted using infrared markers and force plates to calculate hip and knee moments. Results Knee extensor moments increased in both obese, pretreadmill (0.54 ± 0.28 N·m·kg−1) to posttreadmill (0.78 ± 0.43 N·m·kg−1) (P = 0.01), and control subjects, pretreadmill (0.57 ± 0.34 N·m·kg−1) to posttreadmill (0.80 ± 0.49 N·m·kg−1) (P = 0.02). Hip extensor moments decreased for both obese and control subjects. Knee adduction moments did not change in either obese or control subjects. Knee extensor and adductor moments showed good to moderate relationships with V˙O2max, but not BMI or waist circumference. Conclusion Obese and normal-weight subjects experienced an increase in knee extensor moments after 30 min of walking similarly; therefore, clinicians do not need special consideration for obese individuals when recommending 30-min walking sessions. Fitness may be the important factor in judging the implications of exercise on joint mechanics and parameters of a walking program.

Calibration of the global physical activity questionnaire to Accelerometry measured physical activity and sedentary behavior

BackgroundSelf-report questionnaires are a valuable method of physical activity measurement in public health research; however, accuracy is often lacking. The purpose of this study is to improve the validity of the Global Physical Activity Questionnaire by calibrating it to 7 days of accelerometer measured physical activity and sedentary behavior.MethodsParticipants (n = 108) wore an ActiGraph GT9X Link on their non-dominant wrist for 7 days. Following the accelerometer wear period, participants completed a telephone Global Physical Activity Questionnaire with a research assistant. Data were split into training and testing samples, and multivariable linear regression models built using functions of the GPAQ self-report data to predict ActiGraph measured physical activity and sedentary behavior. Models were evaluated with the testing sample and an independent validation sample (n = 120) using Mean Squared Prediction Errors.ResultsThe prediction models utilized sedentary behavior, and moderate- and vigorous-intensity physical activity self-reported scores from the questionnaire, and participant age. Transformations of each variable, as well as break point analysis were considered. Prediction errors were reduced by 77.7–80.6% for sedentary behavior and 61.3–98.6% for physical activity by using the multivariable linear regression models over raw questionnaire scores.ConclusionsThis research demonstrates the utility of calibrating self-report questionnaire data to objective measures to improve estimates of physical activity and sedentary behavior. It provides an understanding of the divide between objective and subjective measures, and provides a means to utilize the two methods as a unified measure.

Do fitness and fatigue affect gait biomechanics in overweight and obese children

The purpose of this study was to determine how an overweight or obese childs cardiorespiratory fitness level and a state of fatigue affect gait biomechanics. METHODS Using a three-dimensional motion analysis system, twenty-nine (female and male) overweight and obese children aged 8-11 years walked on force plates before and after being fatigued from the Progressive Aerobic Cardiovascular Endurance Run (PACER) protocol. Joint moments were calculated for the knee and hip in the frontal and sagittal planes. RESULTS In a non-fatigued state, peak hip and knee adductor moments showed a negative relationship with cardiorespiratory fitness level (R2=0.26, 0.26). After the subjects were fatigued, peak hip extensor (p=0.02), peak knee extensor moments (p=0.02) and peak knee adductor moments (p=0.01) showed a significant increase. CONCLUSION This trend illustrates that as an overweight or obese individuals fitness improves, the lower limb joint moments in the frontal plane decrease when walking. However, with the introduction of cardiorespiratory fatigue, lower limb joint moments tend to increase in the frontal and sagittal planes. Increased joint stress may have potential implications for obese children performing physical activity, as well as for clinicians who are attempting to intervene in the cycle of obesity.

Cross-Validation of Single-Stage Treadmill Tests for Predicting Aerobic Fitness in Adolescents With Type I Diabetes

PURPOSE Determining fitness is important when assessing adolescents with type 1 diabetes mellitus (T1DM). Submaximal tests estimate fitness, but none have been validated in this population. This study cross-validates the Ebbeling and Nemeth equations to predict fitness (VO2max (ml/kg/min)) in adolescents with T1DM. METHODS Adolescents with T1DM (n = 20) completed a maximal treadmill test using indirect calorimetry. Participants completed one 4-min stage between 2.0 and 4.5 mph and 5% grade (Ebbeling/Nemeth protocol). Speed and grade were then increased until exhaustion. Predicted VO2max was calculated using the Ebbeling and Nemeth equations and compared with observed VO2max using paired t tests. Pearson correlation coefficients, 95% confidence intervals, coefficients of determination (R²), and total error (TE) were calculated. RESULTS The mean observed VO2max was 47.0 ml/kg/min (SD = 6.9); the Ebbeling and Nemeth mean predictions were 42.4 (SD = 9.4) and 43.5 ml/kg/min (SD = 6.9), respectively. Paired t tests resulted in statistically significant (p < .01) mean differences between observed and predicted VO2max for both predictions. The association between the Ebbeling prediction and observed VO2max was r = .90 (95% CI = 0.76, 0.96), R² = .81, and TE = 6.5 ml/kg/ min. The association between the Nemeth prediction and observed VO2max was r = .81 (95% CI = 0.57, 0.92), R² = .66, and TE = 5.6 ml/kg/min. CONCLUSION The Nemeth submaximal treadmill protocol provides a better estimate of fitness than the Ebbeling in adolescents with T1DM.