Plasma IL-6, BDNF and osteocalcin responses to single vs repeated bouts of acute HİGH-intensity interval exercise

Compared to a single session training twice exercise sessions performed a day results in greater metabolic adaptations that improve performance and health. Although it is known that interleukin-6 (IL-6), brain-derived neurotrophic factor (BDNF) and osteocalcin (OC), which play an important role in the regulation of energy, carbohydrate and fat metabolism as well as increase with acute exercise, their response to double-session high intensity interval exercise per day is not yet known. This study set out to assess the effects of acute high intensity interval exercise (HIIE) administered once or twice a day on plasma IL-6, BDNF and osteocalcin responses. Twenty male endurance (running, cycling and triathlon) athletes who regularly train at recreational level participated in this study. Volunteers participated in a single (HIIE-S) or double HIIE (HIIE-D) in a randomized crossover design. HIIE-D performed HIIE twice a day with an interval of 3 hours, and HIIE-S once a day. HIIE consisted of 10x1 min cycling at 100% maximal oxygen uptake, interspersed with 75 s of low-intensity cycling at 60 W. Ten ml of venous blood was drawn at rest and immediately following HIIE on day HIIE-s and the second HIIE on HIIE-D day. Plasma IL-6, BDNF and uncarboxylated osteocalcin (ucOC) levels were determined by immunosorbent test (ELISA) method. Two-way repeated measures ANOVA were used to analyse the data. Performing acute HIIE both once or twice a day resulted in significant increases in IL-6, BDNF and osteocalcin levels (p<0.001). However, no significant difference was found between the effects of acute HIIEs performed once and twice a day; IL-6 (HIIE-S: 31.04% HIIE-D: 33.90%; p=0.642) BDNF (HIIE-S: 236.01, % HIIE-D: 216.68; p=0.384) and ucOC (HIIE-S: 51.02% HIIE-D: 37.18%; p=0.439). As a result, performing twice a day HIIE provides similar effects on IL-6, BDNF and ucOC responses when compared to a single session HIIE. Thus, by repeating the effects of a single HIIE on IL-6, BDNF and ucOC levels twice a day HIIE provides the opportunity to benefit from the metabolic benefits of the acute increases in these molecules repeatedly in a day.