Three Minutes of All-Out Intermittent Exercise per Week Increases Skeletal Muscle Oxidative Capacity and Improves Cardiometabolic Health

We investigated whether a training protocol that involved 3 min of intense intermittent exercise per week - within a total training time commitment of 30 min including warm up and cool down - could increase skeletal muscle oxidative capacity and markers of health status. Overweight/obese but otherwise healthy men and women (n = 7 each; age = 29 +/- 9 y; BMI = 29.8 +/- 2.7 kg/m(2)) performed 18 training sessions over 6 wk on a cycle ergometer. Each session began with a 2 min warm-up at 50 W, followed by 3x20 s "all-out" sprints against 5.0% body mass (mean power output: similar to 450-500 W) interspersed with 2 min of recovery at 50 W, followed by a 3 min cool-down at 50 W. Peak oxygen uptake increased by 12% after training (32.6 +/- 4.5 vs. 29.1 +/- 4.2 ml/kg/min) and resting mean arterial pressure decreased by 7% (78610 vs. 83610 mmHg), with no difference between groups (both p < 0.01, main effects for time). Skeletal muscle biopsy samples obtained before and 72 h after training revealed increased maximal activity of citrate synthase and protein content of cytochrome oxidase 4 (p < 0.01, main effect), while the maximal activity of beta-hydroxy acyl CoA dehydrogenase increased in men only (p < 0.05). Continuous glucose monitoring measured under standard dietary conditions before and 48-72 h following training revealed lower 24 h average blood glucose concentration in men following training (5.4 +/- 0.6 vs. 5.9 +/- 0.5 mmol/L, p < 0.05), but not women (5.5 +/- 0.4 vs. 5.5 +/- 0.6 mmol/L). This was associated with a greater increase in GLUT4 protein content in men compared to women (138% vs. 23%, p < 0.05). Short-term interval training using a 10 min protocol that involved only 1 min of hard exercise, 3x/wk, stimulated physiological changes linked to improved health in overweight adults. Despite the small sample size, potential sex-specific adaptations were apparent that warrant further investigation.