Low-Volume Interval Training Improves Muscle Oxidative Capacity in Sedentary Adults

HOOD, M. S., J. P. LITTLE, M. A. TARNOPOLSKY, F. MYSLIK, and M. J. GIBALA. Low-Volume Interval Training Improves Muscle Oxidative Capacity in Sedentary Adults. Med. Sci. Sports Exerc., Vol. 43, No. 10, pp. 1849-1856, 2011. Introduction: High-intensity interval training (HIT) increases skeletal muscle oxidative capacity similar to traditional endurance training, despite a low total exercise volume. Much of this work has focused on young active individuals, and it is unclear whether the results are applicable to older less active populations. In addition, many studies have used all-out variable-load exercise interventions (e.g., repeated Wingate tests) that may not be practical for all individuals. We therefore examined the effect of a more practical low-volume submaximal constant-load HIT protocol on skeletal muscle oxidative capacity and insulin sensitivity in middle-aged adults, who may be at a higher risk for inactivity-related disorders. Methods: Seven sedentary but otherwise healthy individuals (three women) with a mean +/- SD age, body mass index, and peak oxygen uptake ((V) over dotO(2peak)) of 45 perpendicular to 5 yr, 27 perpendicular to 5 kg.m(-2), and 30 perpendicular to 3 mL.kg(-1).min(-1) performed six training sessions during 2 wk. Each session involved 10 x 1-min cycling at similar to 60% of peak power achieved during a ramp (V) over dotO(2peak) test (eliciting similar to 80%-95% of HR reserve) with 1 min of recovery between intervals. Needle biopsy samples (vastus lateralis) were obtained before training and similar to 72 h after the final training session. Results: Muscle oxidative capacity, as reflected by the protein content of citrate synthase and cytochrome c oxidase subunit IV, increased by similar to 35% after training. The transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator 1 alpha was increased by similar to 56% after training, but the transcriptional corepressor receptor-interacting protein 140 remained unchanged. Glucose transporter protein content increased similar to 260%, and insulin sensitivity, on the basis of the insulin sensitivity index homeostasis model assessment, improved by similar to 35% after training. Conclusions: Constant-load low-volume HIT may be a practical time-efficient strategy to induce metabolic adaptations that reduce the risk for inactivity-related disorders in previously sedentary middle-aged adults.