Low volume high intensity training improves insulin sensitivity but reduces aerobic power in trained middle‐aged runners

Objective To investigate if high intensity interval training (HIIT) improves performance and insulin sensitivity in trained middleaged runners. Methods Sixteen male runners (47±2 years and VO 2 max of 50±2 mlO 2 /kg/min) were randomly assigned to 6 weeks of HIIT (6–10 one minute intervals at 100% maximal running speed, 3 times per week) or habitual training (CON). HIIT replaced ~25–44% of the subjects’ aerobic based training, reducing running volume by 26.2% compared to before the experiment. Before and after the training period, performance was tested on the treadmill and insulin sensitivity was measured by oral glucose tolerance test using the Matsuda Index. Resting muscle biopsies were also obtained from the m. vastus lateralis. Results HIIT improved the lactate threshold ( P<0.001 ) and the velocity associated with VO 2 max ( P <0.01) whereas they were unchanged in CON. HIIT training increased CD31 content ( P<0.05 ), whereas VO 2 max ( P<0.001 ) and the content of oxidative enzymes was reduced ( P<0.05 ). The monocarboxylate transporter 4 and the Na + /H + exchanger 1 were unchanged. Insulin sensitivity increased by 23±11% in the HIIT group ( P<0.05 ), and was higher than the CON group after training ( P<0.05 ). Conclusion In middle‐aged runners, HIIT improves insulin sensitivity, but impairs aerobic power and oxidative enzyme content.