Exercise Intensity And The Perception Of Exertion Across 100 Hours Of Competitive Exercise

Abstract

The relationship between perceived and actual exertion and the magnitude and patterns of stress and strain throughout adventure races (typically 100+ hours of almost continuous exercise) are currently unknown. PURPOSE To examine actual and perceived exertion during ∼100 hours of sustained competitive exercise, and whether heart rate or perceived exertion uncouple from actual intensity. METHODS Cardiovascular strain and work rate were estimated from three teams (n=11) competing in the 2003 Southern Traverse (96–126 h duration) using heart rate and a Global Positioning System. Ratings of perceived exertion (RPE) were obtained periodically using a 5-point Likert scale, ranging from 'nothing at all' to 'extreme'. Heart rate (via 3-lead ECG) and RPE data (n=9) were also recorded during 8-min cycling bouts on an electromagnetically-braked ergometer at 25% and 50% aerobic peak power output (PPO) before and within 3 h of completing the race. RESULTS During the first 12 hours of racing, heart rates averaged 64% (95% CI: 60 to 68%) of heart rate range (HHR), but by 24 hours heart rate had dropped to 41% (38 to 44%), and remained at approximately this level thereafter. This pattern during the first day was homogenous across all participants despite one team leading and one trailing all 29 other teams. Participants' RPE varied between teams and within each team over the race. Relative to pre race, the end-race RPE was higher at both 25% PPO (+8%, p=0.07) and 50% PPO (+18%, p<0.01). In constrast, post-race heart rate was minimally affected at rest (68 vs 68 b·min−1, P=0.90) and at both 25% PPO (99 vs 106 b·min−1, P=0.20) and 50% PPO (138 vs 139 b·min−1, P=0.82). Individual differences were evident for heart rate, with one athlete showing a drop from 123 to 103 b·min−1 at 50% PPO, and two athletes showing increases. CONCLUSION Prolonged, sustained exercise is regulated to a low-to-moderate intensity (∼40% HHR continuously). Although the perception of effort during standardised work rates is higher following 96–126 hours of sustained exercise, the heart-rate to work-rate relationship is, on average, preserved.