Force Production and Muscular Activation Patterns in Variable-Cam Resistance Training Machines: A Narrative Review

This review synthesizes the existing literature comparing force production and muscle activation patterns in variable-cam machines versus other resistances, such as isokinetic devices. A systematic search was conducted using PubMed, Web of Science, and Scopus with the Boolean strategy [(“resistive torque” OR “resistance torque” OR “variable resistance”) AND (machine*)], yielding 12 relevant studies. These studies analyzed the force production patterns and muscle activation provided by variable resistance machines, specifically evaluating their strength curves and alignment with human torque curves (HTC). Findings indicated a discrepancy between machine resistance torque (MRT) and HTC, suggesting that current variable resistance machines do not optimally accommodate natural strength profiles and therefore fail to optimize the muscle activation during the exercise. Given this misalignment, future research should focus on developing and validating new resistance machines that can be more near to the results presented in HTC, thereby maximizing neuromuscular efficiency and training efficacy. Expanding research into multi-joint exercises and experimental studies will provide deeper insights into the effectiveness of variable resistance machines relative to other training methods, such as free weights and pulley systems. Improved variable-cam designs could enhance resistance training and rehabilitation outcomes by optimizing muscle activation and reducing mechanical stress.