Central and Peripheral Fatigue Following Free-Weight and Smith Machine Squat Training: Neuromuscular Efficiency in Knee Extensors

Free-weight (FW) and machine-guided exercises have been shown to promote similar strength and hypertrophy adaptations. Under such conditions, the exercise modality that induces less fatigue may be considered more efficient and advantageous for training prescription.

To compare the mechanical, perceptual, and neuromuscular fatigue induced by a squat strength training session performed with FW or a Smith machine (SM).

Nineteen young strength-trained men (age = 23.5 [3.8] y; strength training experience = 4.7 [2.4] y) completed 2 sessions in a randomized order, each involving 4 sets of 9 repetitions at 70% 1-repetition maximum and differing only in the squat modality (FW or SM). Mechanical fatigue was assessed by velocity loss during training and by pre-post changes in isometric force; perceptual fatigue was assessed by subjectively estimated repetitions in reserve and neuromuscular fatigue (ie, peripheral and central fatigue components) via the twitch interpolation technique during isometric unilateral knee extension.

No fatigue differences were observed for velocity loss or perceptual fatigue variables (P = .136-.313). In contrast, most peripheral and central fatigue variables showed significant posttraining differences (P < .001-.021), with FW squats promoting greater posttraining peripheral and central fatigue.

Given the comparable adaptations typically reported for FW and SM exercises, the SM squat may represent a more efficient option for promoting strength adaptations while minimizing neuromuscular fatigue in knee extensors.