Growth rates in running speed and vertical jumping by boys and girls ages 11-13.

This study examined growth rates in running speed and vertical jump among middle school children. 45 boys and 31 girls ages 11-13 years were tested on running speed and vertical jump three times (September, February, and May) during the school year. Hierarchical linear modeling was used to estimate initial status and growth rates for the entire sample (base model) and the association of running and vertical jump with height, weight, and sex (conditional model). Positive overall growth rates were found for both running speed and vertical jump. Increased heightand weight at the time of measurement were not significantly associated with growth rate for running. The growth rate for vertical jump was positively associated with height but unrelated to increased weight. Boys showed steeper growth rates than girls in jumping. No sex differences were found in running speed for either initial status or in growth rate. Furthermore, these results suggest highly variable rates of physical maturation but no general period of 'adolescent awkwardness'.