The validity of submaximal ratings of perceived exertion to predict one repetition maximum

The One Repetition Maximum (1-RM) test is commonly used to assess strength. However, direct assessments of 1-RM are time consuming and unsafe for novice lifters. Whilst various equations exist to predict 1-RM, there is limited research on the validity of these equations. The purpose of this study was to assess the validity of using sub-maximal ratings of perceived exertion (RPE) to predict 1-RM in young adults, using the Borg 6-20 RPE Scale. Twenty healthy participants (ten male (Mean ± SD, 20.8 ± 0.6 y, 75.7 ± 9.3 kg, 1.8 ± 0.07 m) and ten female (20.3 ± 0.7 y, 68.4 ± 10.0 kg, 1.68 ± 0.03 m)) completed two trials involving resistance exercises for both the upper and lower body. In the first trial the 1-RM for the bilateral biceps curl (BC) and the bilateral knee extension (KE) were determined for each participant. In the second trial, participants performed blinded repetitions which were equivalent to 20, 40 and 60 % of 1-RM for both exercises. The RPE was recorded immediately after two repetitions had been completed at each intensity. The order of intensity of the repetitions was randomly assigned with participants wearing blindfolds to exclude the possibility of pre-determined judgments about load and RPE. Individual RPE recorded at each intensity was subjected to linear regression analysis and the line of best fit was extrapolated to RPE 20 to predict 1-RM in both exercises. There was no significant difference (p > 0.05) between the 1-RM predicted from RPE 20 and measured 1-RM for both exercises for the men and women. Measured and predicted values for men were 46.0 ± 4.6 and 45.2 ± 6. 1 kg for biceps curl, and 46.3 ± 3.8 and 43.0 ± 7.1 kg for knee extension, respectively. Measured and predicted values for women were 18.6 ± 5.7 and 19.3 ± 5.6 kg for biceps curl, and 25.5 ± 9.6 and 27.2 ± 12.6 kg for knee extension, respectively. Pearson product-moment correlation coefficients between actual and predicted 1-RM for the BC and KE were 0.97 and 0.92, respectively. These results provide evidence that submaximal ratings of perceived exertion can be used to provide reasonably accurate estimates of 1-RM in young and active men and women. Key pointsThe direct measurement of 1-RM is time consuming and impractical for large groups. This has led to the development of prediction models which employ sub-maximal loads in order to minimise the limitations and risks of maximal strength assessment.The principle of using the ratings of perceived exertion from sub-maximal work rates to predict maximal work rate has been established.With the exception of the present study, there are no published studies on the efficacy of using the Borg 6-20 RPE scale for predicting maximal strength.Perceived exertion ratings from the Borg 6-20 Scale may be used to provide reasonably accurate estimates of 1-RM.Sub-maximal exercise intensities in the range of 20 - 60% of the 1-RM can be used estimate the 1-Repetition Maximum for upper and lower body exercise.