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

Platelets (plts) are involved in thrombosis. However, intense exercise can affect the number and activation of plts.

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.

Eleven healthy young adult active male (70.60 ± 8.26 kg) subjects performed high-intensity interval exercise (40 m shuttle 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.

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).

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.