Diurnal Variation: Does it Affect Short-term Maximal Performance and Biological Parameters in Police Officers?

Objectives: This study aimed to assess the diurnal variation of short term maximal performance and biological markers of hormonal [cortisol (CRT), testosterone (TST), melatonin (MLT)], biochemical [creatine phosphokinase (CPK), blood glucose (GLC), uric acid (UA)] and hematological [white blood cells (WBC), monocytes (MO), neutrophils (NE), lymphocytes (LY), red blood cells (RBC), hemoglobin (HB), hematocrit (HMT)] parameters in male police officers. Methods: Twenty male police officers performed a running-based anaerobic sprint test (RAST) at two different times of the day (TOD), in the morning (6:00 h - 7:00 h) and evening (19:00 - 20:00) where blood samples were collected from the participants on these two occasions before each exercise session. Results: Short term maximal performance [Peak power (PP), average power (AP) and minimal power (MP)] was higher in the evening as compared to the morning. It was noted that biological markers of hormonal, biochemical and hematological parameters exhibit diurnal fluctuation. Some of them peak in the morning (MLT, CRT, TST, UA, RBC, HB, and HMT) and others peak in the evening (GLC, CPK, WBC, NE, LY, and MO). Conclusions: Short term maximal performance, hormonal, biochemical and hematological parameters were strongly affected by the TOD in police officers. Thus, understanding changes in short term maximal exercice and these circulating mediators during different TOD provide a better understanding of the anaerobic metabolism and could help modulate and quantify training load.