Whole Body Oxygen Uptake and Evoked Torque During Subtetanic Isometric Electrical Stimulation of the Quadriceps Muscles in a Single 30-Minute Session

ObjectiveTo evaluate the time course of fatigue in torque output and oxygen uptake during isometric subtetanic neuromuscular electrical stimulation (NMES) to facilitate the design of NMES-based rehabilitation protocols that can accumulate a defined aerobic exercise volume within a given time period.DesignSingle-arm intervention study with within-subject comparisons.SettingUniversity research laboratory.ParticipantsVolunteer sample of healthy men (N=11; mean age, 34.2±11.5y; range, 19–53y; body mass, 79.1±11.7kg; range, 58–100kg).InterventionA single 30-minute session of continuous bilateral isometric quadriceps NMES at 4Hz evoking a mean twitch amplitude of 12% of the maximum voluntary contraction.Main Outcome MeasuresWhole body oxygen consumption rate (V˙o2), and evoked torque were measured simultaneously throughout.ResultsMean increment in V˙o2 was 596±238mL/min, and average exercise intensity during the session was 3±.47 metabolic equivalents. The V˙o2 and torque declined slowly at a rate of −.54%±.31% and −.47%±.57% per minute, respectively.ConclusionsDespite having a higher incremental V˙o2, the observed fatigue rate was considerably less than that previously reported during intermittent isometric tetanic stimulation, suggesting that subtetanic isometric NMES is more sustainable for exercise interventions aimed at accumulating a therapeutic aerobic exercise volume.