Effect of the Stretch-Shortening Cycle on the Relationship Between Maximum Number of Repetitions and Lifting Velocity During the Prone Bench Pull

Abstract

Background: The fastest mean (MV_fastest) and peak (PV_fastest) velocity in a set are used to predict the maximum number of repetitions (RTF), but stretch-shortening cycle (SSC) effects on these relationships are unknown.

Hypothesis: Velocity values associated with each RTF would show higher values for eccentric-concentric and multiple-point methods compared with concentric-only and 2-point methods.

Study design: Cross-sectional study.

Level of evidence: Level 3.

Methods: After determining the prone bench pull (PBP) 1-repetition maximum (1RM), 23 resistance-trained male participants randomly performed 2 sessions (1 for each PBP exercise), consisting of single sets of RTFs against 3 relative loads (60%-80%-70%1RM). Individualized RTF-velocity relationships were constructed using the multiple-point (60%-80%-70%1RM) and 2-point (60%-80%1RM) methods.

Results: Goodness-of-fit was very high and comparable for concentric-only (RTF-MV_fastest, r² = 0.97; RTF-PV_fastest, r² = 0.98) and eccentric-concentric (RTF-MV_fastest, r² = 0.98; RTF-PV_fastest, r² = 0.99) PBP exercises. Velocity values associated with different RTFs were generally higher for eccentric-concentric compared with concentric-only PBP exercise, but these differences showed heteroscedasticity (R² ≥ 0.143). However, velocity values associated with different RTFs were comparable for the multiple- and 2-point methods (F ≤ 2.4; P ≥ 0.13).

Conclusion: These results suggest that the inclusion of the SSC does not impair the goodness-of-fit of RTF-velocity relationships, but these relationships should be determined specifically for each PBP exercise (ie, concentric-only and eccentric-concentric). In addition, the 2-point method serves as a quick and less strenuous procedure to estimate RTF.

Clinical relevance: Practitioners only need to monitor the MV_fastest or PV_fastest and the RTF from 2 (2-point method) or 3 (multiple-point method) sets performed to failure to construct an RTF-velocity relationship. Once these relationships have been established, coaches need only monitor the MV_fastest or PV_fastest of the set to estimate RTF against a given absolute load.

Keywords: fatigue; level of effort; linear position transducer; strength training; velocity-based training.

Figure 1.

Generalized relationship between the maximum RTF and MV_fastest (upper panel) or PV_fastest (lower panel) of the set during the concentric-only (filled dots and straight lines) and eccentric-concentric (open dots and dashed lines) Smith machine PBP exercises. MV, mean velocity; N, numbers of trials included in the regression analysis; PBP, prone bench pull; PV, peak velocity; r², Pearson’s multivariate coefficient of determination; RTF, number of repetitions performed to momentary muscular failure; SEE, standard error of the estimate.

Figure 2.

Least-square linear regression analysis and Blad-Altman plots comparing the predicted MV_fastest or PV_fastest associated with the RTF between the concentric-only and eccentric-concentric PBP exercises constructed using the multiple-point or 2-point methods. The Blad-Altman plot depicts the systematic bias and 95% limits of agreement (±1.96; dashed lines), along with the regression line (solid line). MV, mean velocity; PBP, prone bench pull; PV, peak velocity; r, Pearson’s correlation coefficients; R², coefficient of determination from Bland-Altman plots; RTF, maximum number of repetitions to failure.

Figure 3.

Least-square linear regression analysis and Blad-Altman plots comparing the predicted MV_fastest or PV_fastest associated with RTF between the multiple-point and 2-point methods during the concentric-only or eccentric-concentric PBP exercises. The Blad-Altman plot depicts the systematic bias and 95% limits of agreement (±1.96; dashed lines), along with the regression line (solid line). MV, mean velocity; PBP, prone bench pull; PV, peak velocity; r, Pearson’s correlation coefficients; R², coefficient of determination from Bland-Altman plots; RTF, maximum number of repetitions to failure.