It is well known that moderate intensity (lactate threshold level) exercise increases insulin sensitivity of glucose uptake in skeletal muscles. However, the effects of highintensity short duration exercise (e.g. sprint interval exercise), which intensity is far above lactate threshold, on muscle insulin sensitivity is not clear. In the present study, fasted rats underwent high-intensity intermittent swimming (HIS; ten 20-s swimming with a weight equal to 18% of body mass), which intensity is estimated at 140% VO₂max, or low-intensity prolonged swimming (LIS; 180 min swimming without weight), which intensity is estimated at 40% VO₂max. HIS induced 15 fold increase in AMP dependent protein kinase (AMPK) phosphorylation in epitrochlearis (EPI) muscles of fasted rats immediately after exercise. Previous study showed that AMPK activation increases muscle insulin sensitivity (Fisher et al. 2002), so that we hypothesized that HIS increases muscle insulin sensitivity. However, submaximal insulin (7.5μU/ml) stimulated increase in glucose uptake above basal uptake (insulin sensitivity) was not increased 4 hrs after HIS in EPI muscles. On the other hand, although LIS did not increase AMPK phosphorylation in EPI muscles immediately after exercise, insulin sensitivity was increased 4 hrs after LIS. These results suggest the possibility that 1) low intensity prolonged exercise is more effective for increasing muscle insulin sensitivity than high intensity short duration exercise in fasted rats, 2) some factor (s) other than activation of AMPK is necessary for exercise induced increase in muscle insulin sensitivity.

DESCENTE SPORTS SCIENCE Vol.27/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE