The relationship between perceived effort, muscle hypertrophy, and strength gains: a pilot study

The present study aimed to analyze the association between ratings of perceived exertion (RPE) and the responses of muscle hypertrophy and maximal dynamic strength after a period of resistance training. For this purpose, ten healthy, untrained adult women underwent 12 weeks of knee extension training, performing 3–6 sets of seven repetitions at 60% of one-repetition maximum (1 RM) with a three-minute rest between sets. At the end of the last set, the RPE (Borg scale: 6-20) was reported. Before and after the training period, the cross-sectional areas (CSA) of the vastus lateralis (VL), vastus intermedius (VI) and rectus femoris muscle (RF) were measured and summed, and maximal dynamic strength was assessed using the 1 RM test. Spearman’s correlation coefficient was used to verify the relationship between the percentage changes in individual and summed muscles CSA (CSA_summed), as well as 1 RM performance, and the median RPE reported by participants across the training sessions. The results indicated a weak and non-significant relationship between RPE and hypertrophy of VL (p = -0.050; p = 0.892), VI (p = 0.186; p = 0.607), and RF (p = 0.235; p = 0.513), as well as the CSA_summed (p = 0.242; p = 0.501). Likewise, no significant correlation was observed between RPE and maximal strength gains (p = 0.025; p = 0.946). Thus, under the present exploratory conditions, no clear association was detected between RPE and hypertrophy or strength outcomes, suggesting that RPE may not be a reliable predictor of chronic adaptations in untrained women.