Comparative Effects of the Free Weights and Smith Machine Squat and Bench Press: The Important Role of Specificity for Strength Adaptations

Abstract

Purpose: Although previous studies have compared strength-training adaptations between free weights (FW) and machine-guided exercises, those studies did not use a Smith machine (SM), which most closely replicates the exercises performed with FW. Thus, the aim of the present study was to investigate the chronic effects of strength-focused, velocity-based training regimens using FW versus SM.

Methods: Thirty-seven sport-science students (14 female) were assigned, balanced by sex and relative strength, to either an FW or SM training group. The training program lasted 8 weeks (2 sessions/wk), and participants performed 4 sets per exercise (back squat and bench press) at 70% of their 1-repetition maximum with moderate effort levels (20%-25% velocity loss). Load-velocity profile parameters (load-axis intercept, velocity-axis intercept, and area under the load-velocity relationship line), cross-sectional areas of the vastus lateralis and pectoralis major muscles, and the number of repetitions to failure in the bench-press exercise were assessed before and after the training program. Mechanical variables were assessed using both FW and SM.

Results: All variables, with the exception of back-squat velocity-axis intercept (P = .124), improved in both training groups. The changes in load-axis intercept and area under the load-velocity relationship line were more pronounced when the training and testing conditions matched. Failure in the bench-press exercise and cross-sectional areas of the vastus lateralis and pectoralis major showed comparable improvements for both training groups, while velocity-axis intercept tended to improve more in the SM group.

Conclusions: The general population, unconcerned with the specificity of strength adaptations, can choose a training modality (FW or SM) based on personal preferences.

Keywords: functional training; machine-guided exercises; muscle cross-sectional area; strength training; velocity-based training.