Are Subjective Reports of Exercise Intensity Accurate in Recreational Athletes?

Abstract

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.