Skeletal muscle adaptations to resistance training with ischemia
Elder, Christopher Paul
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Resistance training has been shown to produce increases in muscle size, strength, and whole body function in a wide array of patient populations. There is a need to develop new training approaches that either use lower training intensities or which maximize the adaptation to resistance training. Moderate resistance training with ischemia has been shown to enhance strength and size development relative to moderate resistance exercise without occlusion, and similar to an equal volume of heavy training without ischemia. The limitation of these studies has been an incomplete understanding of the mechanisms behind ischemic resistance training. The present experiment was designed to test the hypothesis that ischemia added to heavy resistance training results in enhanced strength and muscle size development relative to an equal volume of heavy resistance training without ischemia. Thirty (14 men, 16 women) untrained but recreationally active subjects volunteered to participate. Elbow flexor muscle volume was assessed via magnetic resonance imaging (MRI) and strength was assessed via one-repetition maximum before and after 12 weeks of resistance training 3 days per week. Increased muscle volume was observed only after heavy resistance training. There was no effect of ischemia in either moderate or heavy resistance conditions. Further studies were designed to determine if adaptations to training were related to muscle electrical activity measured with surface electromyography (EMG) during exercise, and to verify ischemic conditions during exercise via near infrared spectroscopy (NIRS). In 22 subjects, there was a significant effect of resistance, and a significant effect of ischemia (speed) on EMG. EMG during exercise was related to muscle hypertrophy following training and ischemia resulted in a decrease and not an increase in EMG activity. Oxygen saturation measured with NIRS was minimal during ischemic conditions and significantly higher during control conditions. It is concluded that ischemic resistance training did not have an independent effect on muscle size and strength, contrary to previous ischemic training studies. Slow continuous exercise appeared to be a valid method for producing ischemia, compared to rapid, discontinuous exercise. The absence of ischemic effects is important to understand how ischemia may enhance muscle hypertrophy in response to resistance training.