Background Although the superior effectiveness of free-weight over machine-based training has been a traditionally widespread assumption, longitudinal studies comparing these training modalities were scarce and heterogeneous. Objective This research used the velocity-based method to compare the effects of free-weight and machine-based resistance training on athletic performance and muscle architecture. Methods Thirty-four resistance-trained men participated in an 8-week resistance training program allocated into free-weight (n = 17) or machine-based (n = 17) groups. Training variables (intensity, intraset fatigue, and recovery) were identical for both groups, so they only differed in the use of a barbell or specific machines to execute the full squat, bench press, prone bench pull, and shoulder press exercises. The velocity-based method was implemented to accurately adjust the planned intensity. Analysis of covariance and effect size (ES) statistics were used to compare both training modalities on a comprehensive set of athletic and muscle architecture parameters. Results No between-group differences were found for any athletic (p = 0.146) and muscle architecture (p = 0.184) variable. Both training modalities significantly and similarly improved vertical jump (Free-weight: ES = 0.45, p = 0.001; Machine-based: ES = 0.41, p = 0.001) and lower limb anaerobic capacity (Free-weight: ES = 0.39, p = 0.007; Machine-based: ES = 0.31, p = 0.003). Additionally, the machine-based group meaningfully enhanced upper limb anaerobic power (ES = 0.41, p = 0.021), whereas the free-weight group significantly improved the change of direction (ES = -0.54, p = 0.003) and 2/6 balance conditions analyzed (p = 0.012). Changes in sprint capacity (ES = -0.13, p = 0.274), fascicle length, and pennation angle (ES = 0.19, p = 0.129) were not significant for either training modality. Conclusion Adaptations in athletic performance and muscle architecture would not be meaningfully influenced by the resistance modality trained.
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