Time-of-day effects in maximal anaerobic leg exercise in tropical environment: a first approach

The aim of this study was to establish the effect of time of day on maximal anaerobic leg power in a tropical environment (French West Indies). Twenty-three physical education students (15 males and 8 females) who trained 10.5 hours a week (SD 6) volunteered to participate in the study. Their mean age, height and body mass were 22.8 (SD 3) years, 172.6 (SD 8) cm, and 64.6 (SD 7) kg, respectively. The chronotype of all subjects was moderate or intermediate. Tests were scheduled at 08 : 00, 13 : 00 and 17 : 00 hours on separate days in random order and constant conditions (room temperature: 28.1 degrees C [SD 0.6], relative room humidity: 62.6 % [SD 3.4]). On test days, the subjects were first measured at rest for body mass, heart rate and rectal temperature and they then performed vertical jump tests and a force-velocity test. The results showed a time-of-day effect on rectal temperature, which was significantly (p < 0.005) higher by the afternoon (13 : 00 and 17 : 00) than the morning (08 : 00). However, our results failed to show any daytime variation in maximal anaerobic power under the influence of tropical climate, which suggests that a hot and humid environment may have blunted the time-of-day effect by a passive warm-up effect.