Losey, C., Thrush, D., Malinowski, A., Piacentini, M., Gearhart, S., Norton, J., Schick, J., Salley, E., & Hayes, E. (2013). High-intensity aerobic interval training stimulates muscle hypertrophy in young untrained subjects. Medicine & Science in Sports & Exercise, 45(5), Supplement abstract number 749.

This study examined the impact of 10 weeks of high-intensity interval training on skeletal muscle cross-sectional area and function in a young adult population (college students; N = 12). Muscle cross-sectional area of the right vastus lateralis and leg extension speed were assessed before and after 10 weeks of three times per week of high-intensity interval training. The high-intensity interval training protocol consisted of four intervals of four minutes running at 95% maximum heart rate followed by four minutes of recovery at 70% maximum heart rate. Vastus lateralis cross-sectional area was determined by manual planimetry from panoramic ultrasound imaging and compared to a control group (N = 5). Leg extension speed at 40% one repetition maximum was measured with a custom made electronic timing system that used an infrared photogate to start and stop the timer as the weight stack ascended 20 cm on the leg extension machine.

Vastus lateralis cross-sectional area significantly increased by an average of 9%, while the control group cross-sectional area remained unchanged. Leg-extension time increased by an average of 0.09 seconds in the high-intensity interval training group.

Implication. Improvement in whole muscle size was shown in young people with high-intensity aerobic type training. The increase in leg extension time is consistent with decreases in single muscle fiber power in response to run training previously noted in the literature. Together, these results suggest that high-intensity aerobic exercise may alter skeletal muscle size and/or function in untrained young adults more than previously believed.

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