Impact of Time of Day and Gender on Power Output in Division I Athletes

Power is increased in the afternoon compared to the morning. Whether this impact is similar for both sexes is not clear. PURPOSE: The purpose of this study is to determine if there is an interaction between sex and time of day on power. METHODS: 223 Men and 216 women division 1 athletes from soccer, volleyball, baseball, track and field, tennis, basketball, and cross country were tested. Athletes were asked to complete counter movement jumps, multiple times on a force plate (VALD) throughout the academic year. Dependent variables were jump height, relative peak power (RPP), absolute peak power (APP), and reactive strength index (RSI). Data was analyzed using two-way ANOVA using time and gender as main effects and then to determine if there was a time*gender interaction. RESULTS: For males, 5,191 jumps occurred before noon, while 1,563 were after noon. Jump ht. (39.8±6.3 vs. 44.4±7.3 cm, ƞ2=.079, p<.001), RPP (60.0±9.5 vs. 64.5 ±8.9 W/kg, ƞ2=.039, p<.001), APP (5073.4±1027.3 vs. 5174.3±883.3 W, ƞ2=.002, p<.001) and RSI were higher in the afternoon. There was no statistical difference for RSI (p=.306). For females, 3,621 jumps were before noon, 3,434 were after noon. Jump height (28.4±5.3 vs. 32.7±5.6 cm, ƞ2=.136, p<.001), RPP (45.5 ±6.3 vs. 50.1±6.6 W/kg, ƞ2=.111, p<.001), APP (3158.3±586.1 vs. 3379.5±450 W, ƞ2=.043, p<.001), and RSI (.668±.10 vs. .730±.12 m/s, ƞ2=.066 p<.001) were all increased in the afternoon hours. There was no significant interaction between gender and time of day for jump ht. (p=.346), RPP. There was an interaction for APP (p < .001) such that females increased more than males in the afternoon. CONCLUSION: Time of day should be considered when conducting performance testing to account for potential variations in results. Further research is needed to investigate why females demonstrated a larger increase in APP.