Short-term muscle power and speed in preschoolers exhibit stronger tracking than physical activity

The purpose of this study was to examine the tracking of short-term muscle power, speed, and physical activity over a 15-month period in a sample of healthy Canadian preschool-aged children. Seventeen preschoolers (age, 4.4 +/- 0.8 years) completed exercise testing and physical activity monitoring at baseline and follow-up separated by 14.6 +/- 4.1 months. Short-term muscle power was measured using a modified 10-s Wingate test with peak power and mean power normalized to body mass. Speed was assessed with a 25-m dash. Physical activity was measured by accelerometry (Actigraph GT1M) using a 3-s epoch over 7 consecutive days. Total physical activity and moderate-to-vigorous physical activity, expressed as a percentage of accelerometer wear time, were examined. Tracking of the variables between year 1 and year 2 was analyzed using Spearman rank order correlations and Kappa statistics. Paired t-tests were used to assess differences in performance and physical activity between year 1 and year 2. Total physical activity was not significantly different at year 2 (p > 0.05) and showed fair tracking (r = 0.51, p = 0.05; kappa = 0.30). Moderate-to-vigorous physical activity was increased at year 2 (p = 0.03) and exhibited poor tracking (r = 0.29, p = 0.28; kappa = 0.00). Short-term muscle power and speed was increased at year 2 (p < 0.0001) and exhibited significant tracking: peak power (r = 0.72, p = 0.001; kappa = 0.46), mean power (r = 0.83, p = 0.00004; kappa = 0.82), and 25-m dash (r = 0.82, p = 0.0001; kappa = 0.47). Moderate-to-vigorous physical activity increased in this sample of boys and girls during the preschool years, and short-term muscle power and speed exhibited stronger tracking than physical activity.