Are subjective reports of exercise intensity accurate in recreational athletes?

Background: 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.

Methods: 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 (RPE_Word) and numerical Borg scale (RPE_Borg) were obtained during and 30 min. post ride and were related to cardiac (HR) and metabolic (MET·min) exercise endpoints.

Results: 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 RPE_Borg vs. mean exercise HR and %HR_peak (both r_s=.29, p=0.07), with no agreement between either scale vs. other objective endpoints. Agreement between RPE_Borg and RPE_Word was good during exercise (r_s=0.86, 95% CI 0.75 to 0.92, P=0.001), but diminished post ride (r_s=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.

Conclusions: 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.