Abstract Background Velocity monitoring has become a fundamental method for prescribing training volume in resistance exercise. This study examined how relative load, equipment type, and sex affect the relationship between velocity loss (%VL) and the percentage of completed repetitions (%Rep) during the bench press exercise. Methods 16 males and 12 females completed two sessions using the Smith machine and two sessions using the free weights. Each session consisted of three sets of repetitions performed to failure at 65–75–85% of the one-repetition maximum, with a 10-min rest interval between sets. Results Free weights resulted in higher %Rep estimates at 10%VL compared to the Smith machine in both sexes ( P = 0.039), while females exhibited higher %Rep estimates than males at 10%, 20%, and 30%VL ( P ≤ 0.018). However, %Rep estimates based on individualized %Rep–%VL relationships demonstrated poor between-session reliability (within-subjects coefficient of variation CV = 9.5–30.8%) and high inter-individual variability (between-subjects CV = 12.6–34.5%). Moreover, the predictive accuracy for estimating %Rep in a second testing session based on generalized and individualized %Rep–%VL equations from the first session was acceptable in only 5 out of 24 conditions, with average absolute errors > 10%. Finally, errors were generally higher for free weights compared to the Smith machine ( P ≤ 0.028). Conclusions These findings question the practical applicability of %Rep–%VL relationships for monitoring and prescribing resistance training volume in the bench press for both males and females. Practitioners should critically assess whether velocity-based methods provide meaningful advantages over simpler, non-technological approaches.
Pérez‐Castilla et al. (Tue,) studied this question.