Circadian variation in swim performance

Abstract

Previous findings of time-of-day differences in athletic performance could be confounded by diurnal fluctuations in environmental and behavioral "masking" factors (e.g., sleep, ambient temperature, and energy intake). The purpose of this study was to examine whether there is a circadian rhythm in swim performance that is independent of these masking factors. Experienced swimmers (n = 25) were assessed for 50-55 consecutive hours in the laboratory. The swimmers followed a 3-h "ultra-short" sleep-wake cycle, involving 1 h of sleep in darkness and 2 h of wakefulness in dim light, that was repeated throughout the observation. The protocol distributes behavioral and environmental masking factors equally across the 24-h period. Each swimmer was scheduled to perform six maximal-effort 200-m swim trials that were distributed equally across eight times of day (n = 147 trials). Each trial was separated by 9 h. A cosine fit of intra-aural temperature data established the time of the lowest body temperature (Tmin). Swim performances were z-transformed and compared across the eight times of day and across twelve 2-h intervals relative to Tmin. Analysis of covariance, controlling for trial number, revealed a significant (P < 0.001) pattern in swim performance relative to environmental and circadian times of day. Performance peaked 5-7 h before Tmin (approximately 2300) and was worst from 1 h before to 1 h after Tmin (approximately 0500). Mean swim performance was 169.5 s; circadian variation from peak to worst performance was 5.8 s. These data suggest a circadian rhythm in athletic performance independent of environmental and behavioral masking effects.

Circadian Cycle and Its Influence on Parameters of Aerobic Training

“…The concept arose with Liglic inferences that proposed the identification of anaerobic threshold by comparing the behavior of blood glucose with the behavior of lactate minimum, where similarity was found between these two variables [20]. The GT is identified by the kinetics of glucose concentration [gluc], being found in exercise intensity corresponding to the lowest [gluc] during the test, representing the point in time when the activation hiperglicemic secretion of hormones such as cortisol and that glucagon will maintain the blood glucose concentration during the entire test [20,21].…”

“…The GT is identified by the kinetics of glucose concentration [gluc], being found in exercise intensity corresponding to the lowest [gluc] during the test, representing the point in time when the activation hiperglicemic secretion of hormones such as cortisol and that glucagon will maintain the blood glucose concentration during the entire test [20,21]. During exercise maintenance of plasma glucose levels are governed by the liver through feeedback signals, with increased glucose availability [21] these signals are inhibited, which could probably alter the kinetics of glucose at different times of day that could influence the performance of the workload achieved in Liglic.…”

The circadian clock and human athletic performance

“…But, when it comes to performance speeds, the best results were obtained between 08:30 h and 10:30h in the morning (Huguet et al, 1995). Reasons for the worse performance among athletes in the morning are associated with lower glycogen as a result of a night fasting, stiffness of joints after periods of rest and sleep, the less warming up the muscles in the morning compared to subsequent active period of the day and the fact that they are not yet sufficiently awake to keep their activity at a high level (Kline et al, 2007).…”

Phase-adjustment of human circadian rhythms by light and physical exercise

“…In addition, time awake influences mental fatigue and physical fatigue (due to muscle activity), these issues having been reviewed by 34) . Kline et al have investigated the circadian rhythm of swimming performance in subjects following a 3-h ultrashort sleep-wake cycle (120 min of waking and 60 min of sleep) under dim light 35) . Experienced swimmers lived on an ultra-short sleep-wake cycle for a period of 50-55h.…”