The aim of the present study was to examine the rate of central and peripheral contributions in circadian rhythms and gender differences after exhausted maximal exercise. From 36 volunteers, 12 healthy male and female subjects who had H‐reflex (It is elicited by electrical stimulation and it has been suggested to be one of mechanisms that could cause central fatigue) were selected (mean age of 23.5±1.37 years, height of 166.83±5.11cm, weight of 59.8±9.15 kg, VO2max of 33.14±4.71 ml. kg‐1. min‐1in male subjects and mean age of 23±6.32 years, height of 165.17±2.48 cm, weight of 56±2.09 kg and VO2max of 29.05±2.89 ml. kg‐1. min‐1 in female subjects) and took part in this investigation. Central (MVC, latency of H‐reflex, amplitude of H‐reflex and ratio of H‐reflex to M‐wave) and peripheral properties of fatigue (blood lactate and M‐wave) were recorded before and after an exhausted maximal exercise at two different times of day: 9 am and 6 pm which is separated by a week. Significant differences were found in HR, blood lactate and latency of H‐reflex before and after exercise. However differences between male and female in MVC, amplitude of H‐reflex, ratio of H‐reflex to M‐wave and M‐wave was significant. With induced –exercise, central and peripheral fatigue was higher in men in the morning and in women in the afternoon., thus our results recommended designing suitable exercise programs for men and women in the afternoon and morning, respectively. However, further studies are needed to confirm these results, especially in recommending using transcranial magnetic stimulation.

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