Abstract:

Maximal voluntary isometric muscle contraction force-time curves for 32 normal, healthy children, age 8-11 years, 15 girls and 17 boys, performing three tasks representing separate muscle groups - finger flexors, forearm flexors, and forearm extensors - were recorded over trials and over days. Children's pattern of force production and degree of consistency over trials and days has not been reported in the literature. The primary objective was to identify curve components reproduced with sufficient consistency over trials and days to suggest possible value for providing new and unique information regarding muscle function. Each task was recorded three consecutive trials per day over two days separated by one week. Analog tracings of instantaneous and integrated force were obtained using a Daytronic Linear Voltage Transformer in series with a Brush Mark 280 recorder. Trial to trial and day to day consistency in force production by each muscle group represented by 14 curve variables was assessed using intraclass correlation based on a days x trials x subjects ANOVA for each variable. Force and maximal rate of force increase were quite reproducible; but time to selected force levels reflected considerable variation. The force variables - maximal force, force at which the curve plateaued, and force at the point of curve inflection - intercorrelated well, but correlated only moderately with maximum rate of force increase, and poorly with the time variables. Maximal rate of force increase gave the most promise of providing new information regarding muscle function in children.

High obesity rates in American Indian children led to Pathways, a randomized school- and community-based childhood prevention study. Seven tribes, 5 universities, the National Institutes of Health/National Heart, Lung, and Blood Institute, and 4 elementary schools partnered in the study. Increasing physical activity (PA) was an important intervention target. The PA assessment was based on study objectives, feasibility, and tribal acceptance. A time-segmented analysis was also desired. Two methods, a new PA questionnaire and accelerometry, were developed during pilot testing. Together, the methods provided qualitative and quantitative information and showed that 3 of 4 sites were able to increase average daily PA, although overall the control versus intervention difference was not significant. The main limitation was inability to distinguish PA among individuals. Accelerometer size and some community concerns led to a protocol based on a single day of wearing time. Newer model triaxial accelerometers that are much smaller and allow sampling of multiple days of activity are recommended for future studies.