Heat stress impairs proprioception but not running mechanics

Abstract

ObjectivesTo determine the effects of heat stress on ankle proprioception and running gait pattern. DesignCounterbalanced repeated measures. Methods12 trained runners performed a proprioception test (active movement discrimination) before and immediately after a 30min, self-paced treadmill run in HOT (39°C) and COOL (22°C) ambient conditions. Velocity was imposed during the first and last minute (70% of maximal aerobic velocity, 13.3±0.8kmh−1) for determination of running mechanics and spring–mass characteristics. ResultsRectal (39.7±0.4 vs. 39.4±0.4°C), skin (36.3±1.1 vs. 31.8±1.1°C) and average body (38.3±0.2 vs. 36.4±0.4°C) temperatures together with heart rate (178±8 vs. 174±6bpm) and thermal discomfort (6.5±0.5 vs. 4.3±1.3) were all higher at the end of the HOT compared to COOL run (all p<0.05). Distance covered was lower in HOT than COOL (−5.1±3.6%, p<0.001). Average error during the proprioception test increased after running in HOT (+11%, p<0.05) but not in COOL (−2%). There was no significant difference for most segmental and joint angles at heel contact, except for a global increase in pelvis retroversion and decrease in ankle dorsi-flexion angles with time (p<0.05). Step frequency decreased (−2.5±3.6%) and step length increased (+2.6±3.8%) over time (p<0.05), independently of condition. Spring–mass characteristics remained unchanged (all p>0.05). ConclusionsHeat stress exacerbates thermal, cardiovascular and perceptual responses, while running velocity was slower during a 30min self-paced treadmill run. Heat stress also impairs ankle proprioception during an active movement discrimination task, but it has no influence on gait pattern assessed at a constant, sub-maximal velocity.