Effect of High-Intensity Interval Exercise in the Morning and Evening on Platelet Indices and Exercise-Induced Thrombocytosis

Background: Platelets (plts) are involved in thrombosis. However, intense exercise can affect the number and activation of plts. Objectives: The purpose of this study was to compare the effects of acute high-intensity interval exercise performed in the morning and the evening on plt indices and exercise-induced thrombocytosis. Methods: Eleven healthy youngadult activemale(70.608.26 kg) subjects performed high-intensity interval exercise (40mshuttle sprints at maximum speed for 20 m in a track) on two distinct experimental days (at 8:00 - 9:00 and 15:00 - 16:00) separated by a three-day washout period. Blood samples were taken before and immediately after each exercise session from the antecubital vein by a repetitive venous puncture in a sitting position. Results: Data indicated that after high-intensity interval exercise, there were increases in the number of plts in the morning (P = 0.03) and the evening (P = 0.001). In addition, it was observed that mean plt volume and plt larger cell ratio was higher in the morning pre-test and post-test (P < 0.05), while plt distribution width was only higher in the morning pre-test (P = 0.03). Conclusions: It seems that it may be safer to perform high-intensity interval exercise in the evening due to lower mean plt volume, plt larger cell ratio, plt distribution width, and risk of thrombosis.