LAUSR

Accumulation of intramyocellular lipid (IMCL) is observed in individuals with insulin resistance as well as insulin-sensitive endurance athletes with high peak oxygen consumption (VO 2 peak), which is called the athlete’s paradox. It remains unclear whether non-athletes with higher fitness levels have IMCL accumulation and higher insulin sensitivity in general. In this study, we investigated the association between IMCL accumulation and muscle insulin sensitivity (M-IS) in subjects with high or low VO 2 peak. We studied 61 nonobese (BMI, 23 to 25 kg/m 2 ), non-athlete Japanese men. We divided the subjects into four groups based on the median value of VO 2 peak and IMCL in the soleus muscle. We evaluated M-IS using a two-step hyperinsulinemic-euglycemic clamp. Among subjects with higher VO 2 peak (n = 32), half of those (n = 16) had lower IMCL levels. Both High-VO 2 peak groups had higher M-IS than the Low-VO 2 peak groups. On the other hand, M-IS was comparable between the High-VO 2 peak/High-IMCL and High-VO 2 peak/Low-IMCL groups, whereas the High-VO 2 peak/High-IMCL group had IMCL levels that were twice as high as those in the High-VO 2 peak/Low-IMCL group. On the other hand, the High-VO 2 peak/High-IMCL group had significantly higher physical activity levels (approximately 1.8-fold) than the other three groups. In conclusion, in nonobese, non-athlete Japanese men, subjects with higher VO 2 peak and higher IMCL had higher physical activity levels. IMCL accumulation is not associated with insulin resistance in individuals with higher or lower fitness levels.