Objectives: To compare the effect of electric stimulation (ES)-induced twitch with tetanic leg muscle contractions on blood flow responses and to assess blood flow responses in the contralateral inactive leg. Design: Intervention with within-subject comparisons. Setting: University research laboratory. Participants: A volunteer sample of 12 healthy men (mean age, 25.1±3.0y). Intervention: ES was applied at 1 and 3Hz to induce twitch contractions and at 35Hz to induce tetanic contractions of the lower- and upper-leg muscles. Exercise periods consisted of ES/rest cycles (6s/20s) for 5 minutes. Main Outcome Measures: Blood flow velocity changes measured by echo Doppler ultrasonography at rest and during the first 2 subsequent ES cycles. Results: Blood flow significantly increased from resting values for the tetanic 2-leg, tetanic 1-leg, and 3-Hz conditions, but not for the 1-Hz twitch condition or in the inactive leg. Conclusions: Both tetanic and 3-Hz twitch contractions, but not 1-Hz twitch contractions, increased leg blood flow in humans. Because blood flow elevations induced by the 3-Hz contractions did not differ statistically from those induced by the tetanic contractions but were realized with less discomfort, this mode is preferable for therapeutic interventions. Because stimulation of the ipsilateral leg muscles did not change blood flow in the contralateral inactive leg, the muscles in the area of desired effect must be stimulated. © 2003 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.