High Intensity Exercise Affects Diurnal Variation of Some Biological Markers in Trained Subjects

The study investigated if markers of muscle injury and antioxidant status were affected by a Wingate test performed at 2 different times of day. 15 young male footballers performed 2 tests (randomized) at 07:00-h and 17:00-h. Fasting blood samples were collected before and 3 min after each test for assessment of markers of muscle injury and antioxidant status. Resting oral temperature was recorded during each session. Peak power (10.76 +/- 1.05 vs. 11.15 +/- 0.83 W.kg(-1)) and fatigue index (0.41 +/- 0.04 vs. 0.49 +/- 0.13%) during the Wingate test, and core temperature, were significantly higher (all p<0.05) in the evening. Markers of muscle injury were significantly higher in the evening before and after exercise (e.g., 148.7 +/- 67.05 vs. 195 +/- 74.6 and 191.6 +/- 79.52 vs. 263.6 +/- 96.06IU.L-1, respectively, for creatine kinase; both p<0.001). Antioxidant parameters increased after the Wingate test but only resting values were significantly higher in the morning (e.g., 1.33 +/- 0.19 vs. 1.19 +/- 0.14 mu mol.L-1 for total antioxidant status; p<0.05). The results indicate that muscle injury and antioxidant activity after the Wingate test were higher in the evening, suggesting a possible link between the biochemical measures and the diurnal fluctuation of anaerobic performance. However, repetition of this study after prescribed rather than self-selected exercise intensity is recommended.