How accurate is RPE at measuring fatigue? This study examined the validity of using RPE to assess muscle fatigue. 15 healthy male adults were educated on the Borg CR-10 scale. They all completed an anchoring protocol to improve RPE accuracy, in which they performed sets of unilateral bicep curls and leg extensions to failure. Each participant then complete three exercise conditions consisting of 30% (Low, L), 60% (Medium, M), and 90% (High, H) volumes were performed in random order. The volume was based on the anchoring set. For example, if they maxed out at 20 reps, the high volume condition would be an 18-rep set.
After 5 minutes of rest, the participants were asked to complete a set of biceps curls or leg extensions (the opposite arm from the anchoring procedure). They were not told how many reps they would perform beforehand. Instead, the researchers told them to stop as soon as they reached the prescribed number of reps according to the volume condition they were assigned to. The participant then provided their RPE. The RPE score, sEMG signal, and velocity were recorded throughout the experimental conditions.
The researchers found significant differences in RPE and spectral fatigue index (using sEMG) but not velocity between the testing conditions. Velocity is an effective measure of fatigue for explosive events (powerlifting, Olympic style weight lifting, sports) but not for resistance training that targets hypertrophy as the goal is to increase time under tension. The study builds off previous research that shows a 1-10 scale of RPE (similar to RIR) can be an effective tool for measuring exercise intensity and fatigue.