Search

AB Introduction: At the present there are limited tools available to measure muscle function in young children. Ground reaction force plates measure lower-body function and postural control in older children and adults. The purpose of this study was threefold: 1) develop normative data for evaluating global muscle development; 2) determine the reproducibility of ground reaction force plates for assessing muscle function in preschool-age children; and 3) identify predictors of skeletal muscle function. Methods: Children's (n = 81, 1.8 to 6.0 yr; M = 52%) muscle function and postural control was measured for jump (JMP), sit-to-stand (STS), and both undistracted and distracted body sway tests using a ground reaction force plate (Kistler 9200A). Whole body composition used dual-energy x-ray absorptiometry (Hologic 4500A Discovery Series). Plasma 25-hydroxyvitamin D [25(OH)D] and parathyroid hormone concentrations were measured by chemiluminescence (Liaison, Diasorin, Mississauga, ON, Canada) as well as ionized calcium (ABL80 FLEX, Radiometer Medical A/S). Demographics, and anthropometry were collected. ANOVA and linear regression were used to identify predictors. Reproducibility was assessed by intersubject coefficient of variation. Results: Age was a consistent predictor in all models; body size or fat and lean mass were important predictors in 3 of the models - STS peak force, STS peak power, and JMP peak power. STS was the most reproducible maneuver (average coefficient of variation =15.7%). Distracted body sway testing was not appropriate in these youngsters. Conclusion: The novel data presented in this study demonstrate a clear age (developmental) effect without any effect of sex on muscle function and postural control in young children. Lean muscle mass was important in some models (STS peak force and JMP peak power). The STS test was the best of the 4 maneuvers.

Repeated maximal-intensity short-duration exercise (sprint interval training, SIT) can produce muscle adaptations similar to endurance training (ET) despite a much reduced training volume. However, most SIT data use cycling, and little is known about its effects on body composition or maximal cardiac output (Q?max). Purpose: The purpose of this study was to assess body composition, 2000-m run time trial, V?O2max, and Q?max effects of run SIT versus ET. Methods: Men and women (n = 10 per group; mean ± SD: age = 24 ± 3 yr) trained three times per week for 6 wk with SIT, 30-s all-out run sprints (manually driven treadmill), four to six bouts per session, 4-min recovery per bout, versus ET, 65% V?O2max for 30 to 60 min·d-1. Results: Training improved (P < 0.05) body composition, 2000-m run time trial performance, and V?O2max in both groups. Fat mass decreased 12.4% with SIT (mean ± SEM; 13.7 ± 1.6 to 12.0 ± 1.6 kg) and 5.8% with ET (13.9 ± 1.7 to 13.1 ± 1.6 kg). Lean mass increased 1% in both groups. Time trial performance improved 4.6% with SIT (-25.6 ± 8.1 s) and 5.9% with ET (-31.9 ± 6.3 s). V?O2max increased 11.5% with SIT (46.8 ± 1.6 to 52.2 ± 2.0 mL·kg·-1·min-1) and 12.5% with ET (44.0 ± 2.0 to 49.5 ± 2.6 mL·kg-1·min-1). None of these improvements differed between groups. In contrast, Q?max increased by 9.5% with ET only (22.2 ± 2.0 to 24.3 ± 1.6 L·min-1). Conclusions: Despite a fraction of the time commitment, run SIT induces similar body composition, V?O2max, and performance adaptations as ET, but with no effect on Q?max. These data suggest that adaptations with ET are of central origin primarily, whereas those with SIT are more peripheral