Superimposed direct and alternating current on maximum voluntary isometric torque production and electromyographic activity

Abstract

Neuromuscular electrical stimulation (NMES) is a widely accepted exercise technique used to supplement maximum voluntary contractions (MVC) and increase muscular torque production. Within the rehabilitative setting, NMES has been used to neuromuscularly re-educate, restore and optimize motor unit recruitment inhibited postsurgery or via pathology. Muscular inhibition normally exists within different muscle groups during MVC relative to age, individual motivation, and training level. Training asymptomatic individuals via superimposed NMESand voluntary contractions enhances torque production by increasing motor unit recruitment. Superimposed alternating current involving trained and untrained subjects coupled with concentric andlor eccentric exercise has been proven to increase muscular torque production more than exercise alone It, . However, a review often superimposed NMES training studies revealed inconclusive and controversial results and only one of the studies involved direct current NMES superimposed during isokinetic training and results indicated torque production was not different than voluntary contractions alone. Recommendations of these studies include electromyography (EMG) assessment to help determine the mechanisms ofsuperimposed muscular activity on increases in strength or power. Unfortunately, to our knowledge EMG has not been utilized to assess the effects of direct or alternating current NNIES with superimposed contractions. Additionally, no studies have utilized isometric exercise superimposed with direct current. Therefore, the purpose of this study was to investigate the effect of superimposed direct and alternating current on quadriceps femoris isometric torque production via EMG assessment following a six-week training period with healthy intermediately trained subjects. It was hypothesized that isometric torque training superimposed with direct or alternating current will elicit greater motor unit recruitment resulting in increased torque production when compared to controls.