Influence of sex and strength differences on the load–velocity relationship of the Smith-machine back squat

Abstract

PurposeWe aimed at determining whether the load–velocity relationship of the Smith machine concentric-back squat differs between sexes and persons with different levels of strength.MethodsThirty-two participants (16 males: 23.3 ± 3.8 years and 16 females: 26.1 ± 2.7 years) were included. Load and mean concentric velocity (MCV) were obtained individually during an incremental test (30–90% one-repetition maximum—1RM).ResultsWe obtained strong linear relationships between the individual MCV and relative load (R2>\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${R}^{2}>$$\\end{document} 0.95). Overall, relatively strong persons reached faster MCVs throughout the full range of relative loads (effect size [ES]: 0.48–0.93), except at 1RM. We also obtained steeper slopes and higher velocity intercepts (y intercepts) in relatively strong participants (ES: 0.05 and 0.83, respectively; p < 0.01). Finally, we found that males attained steeper load–velocity relationships (ES favoring relatively strong and weak males: 2.8 and 1.4, respectively) and higher velocity intercepts (ES favoring relatively strong and weak males: 2.0 and 1.0, respectively) than females (p < 0.0001).ConclusionMCV can be used to estimate relative load on the Smith machine concentric-back squat in males and females with different levels of muscle strength; however, the load–velocity relationship is affected by muscle strength and sex. Therefore, the extraction of individual load–velocity relationships is advisable instead of computing group estimations.