The Effects of Heat Stress on Platelet Function and Coagulation

Abstract

The purpose of this study was to compare platelet function and coagulation following exercise-induced heat stress (EIHS) and passive heat stress (PHS) in young active males. During the EIHS protocol the men cycled in warm-up suits at 60rpm until core body temperature (Tco) reached 38.5°C or for 60 min; during PHS the subjects sat in a tank of warm water (38.9–40°C) until Tco reached 38.5°C or for 60 min. Blood was drawn before and immediately after EIHS and PHS, for analysis of prothrombin time (PT), partial thromboplastin time (PTT), collagen-EPI and collagen-ADP time to occlusion, and a complete blood count (CBC). Both conditions resulted in significantly elevated Tco (38.4°C and 38.5°C for EIHS and PHS respectively), and was achieved in a similar time period (51.1 and 46.7 min). There were significant increases in platelet number for both conditions (22% and 6% for EIHS and PHS, respectively). In both conditions, ADP-induced time to occlusion (17% and 8%) and PTT (6% and 4%) decreased significantly. Additionally, EPI-induced time to occlusion decreased significantly after EIHS. The findings of this study reveal that both EIHS and PHS activate coagulation and platelet function, and suggest that the combination of exercise and heat stress may cause greater activation than heat stress alone.