Free-Weight and Smith-Machine Squats: Do They Produce Selective Chronic Adaptations in the Effectiveness of Force Application?

Abstract

Background: Force is applied more in the backward direction during Smith-machine (SM) squats than in free-weight (FW) squats, although it is still uncertain whether this discrepancy will result in chronic adaptations in that direction.

Purpose: We aimed to assess the effects of an 8-week squat training with FW or SM on longitudinal ground-reaction forces recorded during both FW and SM squats.

Methods: Twenty sport-science students (9 female) were assigned to either an FW or SM training group, balanced by sex and relative strength. The 8-week training (2 sessions/wk) consisted of 4 sets of back squats at 70% of 1-repetition maximum (1-RM) with 20% velocity loss. Pretesting and posttesting assessed ground-reaction forces during a single set of 10 repetitions at ~45% and ~70% 1-RM, performed with FW in one session and SM in another session.

Results: Squat type (FW or SM) had minimal influence on longitudinal impulse, its components (mean force and time), or the angle of the resultant ground-reaction force. The only significant difference was observed in longitudinal impulse during the propulsive phase at ~70% 1-RM in the SM squat (P = .037), where the FW training group exhibited a reduction in longitudinal impulse posttraining, while the SM training group showed an increase.

Conclusions: An 8-week squat training does not modify the effectiveness of force application, regardless of training or testing squat type. Therefore, both squat variations can be used interchangeably without systematically influencing the direction of force production, allowing athletes to select based on preference, equipment availability, or sport-specific demands.

Keywords: biomechanics; ground-reaction forces; guided exercises; strength training; velocity-based training.