Key result
Continuous 24-hour cycling exercise accentuated the amplitude and mean of circadian rhythms for core temperature and heart rate with a phase lag (p<0.05) compared to continuous rest.
Why the study?
Does continuous physical exercise alter the circadian variations of core temperature and heart rate compared to continuous rest in ultra-distance cyclists?
Observational
No
Does continuous physical exercise alter the circadian variations of core temperature and heart rate compared to continuous rest in ultra-distance cyclists?
Circadian rhythms of core temperature and heart rate persist during continuous 24-hour physical exercise, though with increased amplitude and a phase lag compared to rest.
May warrant adjusted circadian monitoring during prolonged exercise; leaves open extension beyond ultra-endurance cycling.
Circadian rhythms have formed the subject of many researches in man during bed rest or usual routine, but have been little studied during continuous and sustained physical exercise. This study deals with the influence of time of day on biological markers in competitive cyclists during continuous physical exercise versus continuous rest. Ultra-distance cyclists were studied over a 24 h period (13:00 to 13:00 h the next day) in the laboratory. The subjects were requested to maintain a constant speed (set at 65% - 70% of their maximal aerobic speed obtained during a preliminary test) on their own bicycles which were equipped with home trainers. Workload, core temperature and heart rate were monitored continuously. The same measures were also recorded while the athletes were resting awake until 13:00 h the next day. Results show that in both situations, core temperature and heart rate exhibited significant circadian variations (p < 0.001). Furthermore, during exercise, an accentuation of amplitude and mean of every rhythm (p < 0.05) with a phase lag (p < 0.05) were observed. Despite a strenuous and continuous physical exercise requiring special physiological adaptations, the rhythmic variations observed at rest persisted, which highlighted the influence of biological clocks.
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Callard et al. (2001) conducted an observational in Healthy ultra-distance cyclists. Continuous cycling exercise vs. Continuous rest awake was evaluated on Circadian variations in core temperature and heart rate (p=<0.05). Continuous 24-hour cycling exercise accentuated the amplitude and mean of circadian rhythms for core temperature and heart rate with a phase lag (p<0.05) compared to continuous rest.
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