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 (EAs) 41 to 69 years of age with > 10 years of training history during a scripted outdoor 42-km cycling training session. Heart rate 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 minutes postride and were related to cardiac (heart rate) and metabolic (metabolic equivalent [MET] per minute) 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 heart rate and % heart rate_peak (both r_s = 0.29; 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% confidence interval (CI), 0.75- 0.92; P = 0.001), but diminished postride (r_s = 0.54; 95% CI, 0.28-0.73; 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 (14,039 ± 2649 vs 11,784 ± 1132 heart rate per minute; P < 0.01) but lower metabolic (808 ± 59 vs 858 ± 61 MET per minute; P < 0.05) burden vs fitter EA.

Conclusions: Caution is advised in interpreting MET per minute and heart rate burden estimated from self-reports. Objective measurements of exercise intensity are required for detailed assessment of the risks and benefits of long-term exercise.