Strengthening of Quadriceps by Neuromuscular Magnetic Stimulation in Healthy Subjects

Background: Quadriceps muscle strengthening is one of the rehabilitation strategies for improving walking in some people with gait impairments, and neuromuscular electrical stimulation (NMES) has been used for that reason. The strengthening effect of neuromuscular magnetic stimulation (NMMS) on the quadriceps has been demonstrated in various conditions, but not specifically for gait training. The purpose of this study was to determine whether the effect of NMMS is clinically applicable. Objective: To determine the effect of NMMS on quadriceps muscle strength, cross-sectional area (CSA) and thickness in healthy subjects. Design: Single-blind, prospective, case-control study. Setting: Tertiary academic hospital setting. Participants: A total of 40 healthy volunteers were randomly assigned to an NMMS (n = 20) or control group (n = 20). Interventions: Fifteen minutes of quadriceps NMMS of at maximum tolerable intensity, 3 times per week for 5 weeks. Main Outcome Measurements: At baseline and after the intervention, the CSA and thicknesses of the rectus femoris and vastus intermedius were measured by ultrasound. Isometric and isokinetic maximal and average peak torques of the dominant side knee extensors were also measured at pre- and postintervention. Results: There were no between-group differences in strength, CSA, or muscle thickness at baseline. Isometric maximum and average peak torque of NMMS group were increased significantly after 5 weeks of intervention (P < .001). The isokinetic maximum and average peak torque of NMMS group were increased significantly at both angle velocities of 60 degrees/sec and 120 degrees/sec after 5 weeks of intervention (P < .001). However, neither group showed a significant difference in cross-sectional area or thickness after training. Conclusion: NMMS can be a useful strengthening method for large skeletal muscles such as the quadriceps.