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 3min 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±0.83W.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±0.14μmol.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. © Georg Thieme Verlag KG Stuttgart New York.