Effects of weight-bearing exercise on bone health in girls: a meta-analysis.

BACKGROUND: Because growing bone possesses a greater capacity to adapt to mechanical loading than does mature bone, it is important for girls to engage in weight-bearing activities, especially since the prevalence of osteoporosis among older women is considerably higher than that of older men. In recent years, the osteogenic potential of weight-bearing activities performed by children and adolescents has received increasing attention and accumulating evidence suggests that this type of activity may improve bone health prior to adulthood and help prevent osteoporosis later in life. OBJECTIVE: Because previous interventions have varied with respect to the exercise parameters studied and sometimes produced conflicting findings, this meta-analysis was undertaken to evaluate the impact of weight-bearing exercise on the bone health of female children and adolescents and quantify the influence of key moderating variables (e.g. pubertal stage, exercise mode, intervention strategy, exercise duration, frequency of exercise, programme length and study design) on skeletal development in this cohort. METHODS: A comprehensive literature search was conducted using databases such as PubMed, MEDLINE, CINAHL, Web of Science, Physical Education Index, Science Direct and ProQuest. Search terms included 'bone mass', 'bone mineral', 'bone health', 'exercise' and 'physical activity'. Randomized- and non-randomized controlled trials featuring healthy prepubertal, early-pubertal and pubertal girls and measurement of areal bone mineral density (aBMD) or bone mineral content (BMC) using dual energy x-ray absorptiometry were examined. Comprehensive Meta-Analysis software was used to determine weighted mean effect sizes (ES) and conduct moderator analyses for three different regions of interest [i.e. total body, lumbar spine (LS), and femoral neck]. RESULTS: From 17 included studies, 72 ES values were retrieved. Our findings revealed a small, but significant influence of weight-bearing exercise on BMC and aBMD of the LS (overall ES 0.19; 95% confidence interval (CI) 0.05, 0.33 and overall ES 0.26, 95% CI 0.09, 0.43, respectively) and BMC of the femoral neck (ES 0.23; 95% CI 0.10, 0.36). For both aBMD and BMC, overall ES was not affected by any moderator variables except frequency of exercise, such that weight-bearing activity performed for more than 3 days per week resulted in a significantly greater ES value for LS aBMD compared with programmes lasting 3 or fewer days per week [Cochran's Q statistic (Qbetween) = 4.09; p < 0.05]. CONCLUSION: The impact of weight-bearing activities seems to be site specific, and a greater frequency of weight-bearing activities is related to greater aBMD of LS in growing girls. Future investigations are warranted to better understand the dose-response relationship between weight-bearing activity and bone health in girls and explore the mediating role of pubertal status in promoting skeletal development among female youth.

Reliably measuring ambulatory activity levels of children and adolescents with cerebral palsy.

OBJECTIVE: To identify sources of variance in step counts and to examine the minimum number of days required to obtain a stable measure of habitual ambulatory activity in the cerebral palsy (CP) population. DESIGN: Cross-sectional. SETTING: Free-living environments. PARTICIPANTS: Children and adolescents with CP (N=209; mean age ± SD, 8y, 4mo ± 3y, 4mo; n=118 boys; Gross Motor Function Classification System [GMFCS] levels I-III) were recruited through 3 regional pediatric specialty care hospitals. INTERVENTIONS: Daily walking activity was measured with a 2-dimensional accelerometer over 7 consecutive days. An individual information-centered approach was applied to days with <100 steps, and participants with ≥3 days of missing values were excluded from the study. Participants were categorized into 6 groups according to age and functional level. Generalizability theory was used to analyze the data. MAIN OUTCOME MEASURES: Mean step counts, relative magnitude of variance components in total step activity, and generalizability coefficients (G coefficients) of various combinations of days of the week. RESULTS: Variance in step counts attributable to participants ranged from 33.6% to 65.4%. For youth ages 2 to 5 years, a minimum of 8, 6, and 2 days were required to reach acceptable G coefficient (reliability) of ≥.80 for GMFCS levels I, II, and III, respectively. For those ages 6 to 14 years, a minimum of 6, 5, and 4 days were required to reach stable measures of step activity for GMFCS levels I, II, and III, respectively. CONCLUSIONS: The findings of the study suggest that an activity-monitoring period should be determined based on the GMFCS levels to reliably measure ambulatory activity levels in youth with CP.

Reliability of daily step activity monitoring in adults with incomplete spinal cord injury.

We determined the number of days of step activity monitoring required to establish stable measures of walking activity in adults with incomplete spinal cord injury (iSCI). Eleven individuals with iSCI (mean age 49 +/- 14 years) wore a StepWatch Activity Monitor during waking hours for 7 consecutive days. We used generalizability theory to identify sources of variance in daily step counts and determine the minimum number of days necessary to obtain a reliability coefficient (G-coefficient) greater than or equal to 0.80. Average daily step activity (DSA) was 1,281 +/- 1,594 steps. Participants and days accounted for 70.9% and 1.3% of total variance in DSA, respectively, while unidentifiable error accounted for 27.8% of the total variance in DSA. A minimum of 2 days was required to achieve a G-coefficient greater than or equal to 0.80. An acceptably stable measure of walking activity in adults with iSCI can be obtained by averaging step count values from any 2-day period in a week. Results from this investigation should be useful in evaluating the effect of activity-based programs designed to enhance locomotor function in persons with iSCI.