Are subjective reports of exercise intensity accurate in recreational athletes?

Abstract

Quantifying exercise intensity accurately is crucial for understanding links between cumulative exercise and cardiovascular outcomes. Exercise burden, the integral of intensity and duration is often estimated from subjective self-reports which have uncertain accuracy. We studied 40 endurance athletes (EA) 41 to 69 yrs. with >10 yrs. training history during a scripted outdoor 42 km cycling training session. Heart rate (HR) and power output (Watts) were continuously measured. Reports of perceived exertion (RPE) using a word (RPEWord) and numerical Borg scale (RPEBorg) were obtained during and 30 min. post ride and were related to cardiac (HR) and metabolic (MET·min) exercise endpoints. RPEs were highly variable, underestimating objective metrics of exercise intensity. Poor agreement was observed between either scale reported 30 minutes after exercise relative to heart rate: exercise RPEBorg vs. mean exercise HR and %HRpeak (both rs=.29, p=0.07), with no agreement between either scale vs. other objective endpoints. Agreement between RPEBorg and RPEWord was good during exercise (rs=0.86, 95% CI 0.75 to 0.92, P=0.001), but diminished post ride (rs=0.54, 95% CI 0.28 to 0.73, P=0.001). Different cardiac and metabolic profiles during exercise and a contrast between metabolic and cardiac burden was greater in less fit individuals as they accrued greater cardiac (14039±2649 vs. 11784±1132 HR·min, P<0.01) but lower metabolic (808±59 vs. 858±61 MET·min, P<0.05) burden vs. fitter EA. Caution is advised in interpreting MET·min and HR burden estimated from self-reports. Objective measurements of exercise intensity are required for detailed assessment of the risks and benefits of long-term exercise.