Abstract
Circadian rhythm affects maximal short-term performance, and it is an important determinant of the training component. This review aimed to summarise the influence of circadian rhythm on peak and mean power output of muscle, fatigue index, and blood lactate levels.
English language articles were searched through the following databases: PubMed, Web of Science, Science Direct, and Google Scholar, and pertinent randomized control trials were scrutinized.
The search revealed 17,481 articles, and 29 were included in this systematic review based on inclusion and exclusion criteria. Randomized control trials were selected, and the methodological validity of articles was evaluated using the 'Cochrane risk of bias tool'. Findings suggest that outcome variables muscle peak power output (p < 0.0001, Z = 7.22, I
= 57.42, SMD = - 0.91, 95% confidence interval CI = - 1.16, - 0.67), muscle mean power output (p < 0.0001, Z = 5.66, I
= 83.85, SMD = - 0.75, 95% CI = - 1.01, - 0.49), and fatigue index (p = 0.02, Z = 2.41, I
= 2.49, SMD = - 0.39, 95% CI = - 0.72, - 0.07) were higher in the evening while the level of blood lactate was higher in the morning (p = 0.79, Z = 0.27, I
= 0.73, SMD = - 0.05, 95% CI = - 0.46, - 0.35).
The results show that diurnal variation affects both peak and mean power output of muscle as well as fatigue index. However, there is no remarkable effect of circadian rhythm on blood lactate level. A major factor attributed to this finding was the variation in the training experience of participants. For an effective training prescription, it is very important to consider the effect of the biological clock on muscle power output since anaerobic exercise performance is discernibly influenced by the time of the day.