No abstract

Muscular strength has been identified for the first time as an independent and powerful predictor of better insulin sensitivity in children. Lower strength, CRF and higher central adiposity are highly predictive of higher levels of insulin resistance in this cohort, and should be considered potential targets for interventions designed to enhance metabolic fitness in children and adolescents.

Background: High-intensity progressive resistance training (PRT) improves adiposity and metabolic risk in adults, but has not been investigated in children within a randomized controlled trial (RCT). Objective: We hypothesized that high-intensity PRT (8 weeks, twice a week) would decrease central adiposity in children, as assessed via waist circumference. Methods Design/Setting/Participants: Concealed randomization stratified by age and gender was used to allocate rural New Zealand school students to the wait-list control or PRT group. Intervention: Participants were prescribed two sets (eight repetitions per set) of 11 exercises targeting all the major muscle groups at high intensity. Primary Outcome: Waist circumference; secondary outcomes included whole body fat, muscular fitness (one repetition maximum), cardiorespiratory fitness (peak oxygen consumption during a treadmill test), lipids, insulin sensitivity and fasting glucose. Results: Of the 78 children (32 girls and 46 boys; mean age 12.2(1.3) years), 51% were either overweight (33%) or obese (18%). High-intensity PRT significantly improved waist circumference (mean change PRT À0.8 (2.2) cm vs þ 0.5 (1.7) cm control; F ¼ 7.59, P ¼ 0.008), fat mass (mean change PRT þ 0.2 (1.4) kg vs þ 1.0 (1.2) kg control; F ¼ 6.00, P ¼ 0.017), percent body fat (mean change PRT -0.3 (1.8)% vs þ 1.2 (2.1)% control; F ¼ 9.04, P ¼ 0.004), body mass index (mean change PRT À0.01 (0.8) kg m À2 vs þ 0.4 (0.7) kg m À2 control; F ¼ 6.02, P ¼ 0.017), upper body strength (mean change PRT þ 11.6(6.1) kg vs þ 2.9(3.7) kg control; F ¼ 48.6, Po0.001) and lower body strength (mean change PRT þ 42.9(26.6) kg vs þ 28.5(26.6) kg control; F ¼ 4.72, P ¼ 0.034) compared to the control group. Waist circumference decreased the most in those with the greatest baseline relative strength (r ¼ À0.257, P ¼ 0.036), and greatest relative (r ¼ À0.400, P ¼ 0.001) and absolute (r ¼ 0.340, P ¼ 0.006) strength gains during the intervention. Conclusion: Isolated high-intensity PRT significantly improves central and whole body adiposity in association with muscle strength in normal-weight and overweight children. The clinical relevance and sustainability of these changes in adiposity should be addressed in future long-term studies.

SummaryThe majority of resistance training (RT) research with children to date has focused on pre-adolescents and the safety and efficacy of this type of training rather than the potential metabolic health benefits. Our objectives, using computerized databases, were (i) to systematically review studies utilizing RT interventions with children and adolescents < 18 years; (ii) to investigate the metabolic health outcomes (adiposity, lipids, insulin, glucose) associated with RT; (iii) to provide recommendations for future investigations. A total of 12 studies met the review criteria. There is only a small amount of evidence that children and adolescents may derive metabolic health-related adaptations from supervised RT. However, methodological limitations within the body of this literature make it difficult to determine the optimal RT prescription for metabolic fitness in children and adolescents, and the extent and duration of such benefits. More robustly designed single modality randomized controlled trials utilizing standardized reporting and precise outcome assessments are required to determine the extent of health outcomes attributable solely to RT and to enable the development of evidence-based obesity prevention and treatment strategies in this cohort.

Purpose. To examine the effects of two doses of low-frequency (12 Hz), low-magnitude (0.3 g), whole body vibration on markers of bone formation and resorption in postmenopausal women. Methods. Women were recruited and randomized into a sham vibration control group, one time per week vibration group (1×/week), or three times per week vibration group (3×/week). Vibration exposure consisted of 20 minutes of intermittent vibration for the 1×/week and 3×/week groups, and sham vibration (<0.1 g) for the control group for eight weeks. Double-blinded primary outcome measures were urine markers of bone resorption: N-telopeptide X normalised to creatinine (NTx/Cr) and bone formation: bone-specific alkaline phosphatase (ALP). Results. Forty-six women (59.8 ± 6.2 years, median 7.3 years since menopause) were enrolled. NTx/Cr was significantly reduced (34.6%) in the 3×/wk vibration group but not in the 1×/wk vibration group compared with sham control (P < .01) group. No effect of time or group allocation was observed on the bone formation marker ALP (P = .27). Conclusion. We have shown for the first time that low-frequency, low-magnitude vibration 3×/week for eight weeks in postmenopausal women results in a significant reduction in NTx/Cr, a marker of bone resorption, when compared with sham vibration exposure.