Lifting velocity predicts the maximum number of repetitions to failure with comparable accuracy during the Smith machine and free-weight prone bench pull exercises

Abstract

This study compared the accuracy of the fastest mean velocity from set (MV_fastest) to predict the maximum number of repetitions to failure (RTF) between 2 variants of prone bench pull (PBP) exercise (Smith machine and free-weight) and 3 methods (generalized, individualized multiple-point, and individualized 2-point). Twenty-three resistance-trained males randomly performed 2 sessions during Smith machine PBP and 2 sessions during free-weight PBP in different weeks. The first weekly session determined the RTF-MV_fastest relationships and subjects completed single sets of repetitions to failure against 60-70-80-90%1RM. The second weekly session explored the accuracy of RTFs prediction under fatigue conditions and subjects completed 2 sets of 65%1RM and 2 sets of 85%1RM with 2 min of rest. The MV_fastest associated with RTFs from 1 to 15 were greater for Smith machine compared to free-weight PBP (F ≥ 42.9; P < 0.001) and for multiple-point compared to 2-point method (F ≥ 4.6; P ≤ 0.043). The errors when predicting RTFs did not differ between methods and PBP variants, whereas all RTF-MV_fastest relationships overestimated the RTF under fatigue conditions. These results suggest that RTF-MV_fastest relationships present similar accuracy during Smith machine and free-weight PBP exercises and it should be constructed under similar training conditions.

Keywords: Fatigue; Level of effort; Linear position transducer; Strength training; Velocity-based training.

Fig. 1

Overview of the experimental design. 1RM, one-repetition maximum; RTF, maximum number of repetitions performed before achieving momentary muscular failure. Note that the order of the 65%1RM and 85%1RM loads in the third and fifth testing sessions was randomized.

Fig. 2

Upper panel represents the generalized relationship between the maximum number of repetitions performed before achieving momentary muscular failure (RTF) and the fastest mean velocity of the set (MV_fastest) during the Smith machine (filled dots and straight lines) and free-weight (open dots and dashed lines) prone bench pull (PBP) exercises. Lower panel represents the individualized RTF-MV_fastest relationship of a representative participant obtained using the multiple- and 2-point methods during the Smith machine and free-weight PBP exercises. r², Pearson's multivariate coefficient of determination; SEE, standard error of the estimate; N, numbers of trials included in the regression analysis.

Fig. 3

Comparisons and associations of the fastest mean velocity of the set associated with each maximum number of repetitions performed before reaching momentary muscular failure (RTF) between methods (multiple-point vs. 2-point; upper-panel) and prone bench pull (PBP) exercises (Smith machine vs. free-weight; lower-panel). ES, Cohen's d effect size; r, Pearson's product-moment correlation coefficient.

Fig. 4

Comparison of the raw and absolute errors when predicting the maximum number of repetitions performed before achieving momentary muscular failure (RTF) between different methods (generalized vs. multiple-point vs. 2-point), prone bench pull (PBP) exercises (Smith machine vs. free-weight) and sets (set 1 vs. set 2) during sets performed against the 65% and 85% of the one-repetition maximum (1RM). Data are presented as means ± standard deviations. *, significant greater errors during the RTF prediction in the set 2 compared to the set 1.