The Effect of High-Intensity Interval Training on Skeletal Muscle Oxidative Capacity in Middle-Aged Sedentary Adults

Abstract

There is growing appreciation of the potential for high intensity interval training (HIT) to rapidly stimulate metabolic adaptations that resemble traditional endurance training, despite a low total exercise volume. However, much of the work has been conducted on young active individuals and the results may not be applicable to older, less active populations. In addition, many studies have employed "all out", variable-load exercise interventions (e.g., repeated Wingate Tests) that may not be safe, practical or well tolerated by certain individuals. We determined the effect of a short program of low-volume, submaximal, constant-load HIT on skeletal muscle oxidative capacity and insulin sensitivity in sedentary middle-aged individuals who may be at higher risk for inactivity-related chronic diseases. Sedentary but otherwise healthy men (n=3) and women (n=4) with a mean (±SE) age, body mass index and peak oxygen uptake (VO_2peak) of 45±2 yr, 27±2 kg-m^2 and 30±1 ml·kg^-1·min^-1 were recruited. Subjects performed 6 training sessions over 2 wk, each consisting of 10 x 1 min cycling at 60% of peak power elicited during a ramp VO_2peak test (<90% of heart rate reserve) with 1 min recovery between intervals. Needle biopsy samples (v. lateralis) were obtained before training and <72 h after the final training session. Muscle oxidative capacity, as reflected by the maximal activity and protein content of citrate synthase, increased by ~20% after training, which is similar to changes previously reported after 2 wk of Wingate-based HIT in young active subjects. Insulin sensitivity, based on fasting glucose and insulin, improved by ~35% after training. These data support the notion that 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 adults.