Sedentary behaviour and step count are related to skeletal muscle insulin sensitivity in young adult normal-weight women without regular exercise habits: an accelerometer and doubly labelled water method study.

PURPOSE: Lifestyle habits in young adult women and health maintenance are crucial for lifelong disease prevention in middle-aged and older adults. Evidence regarding associations between free-living physical activity (PA) and glucose tolerance in non-underweight, non-overweight young adult women remains limited. We examined associations between glucose tolerance-related blood markers and PA indices, including intensity-specific PA and energy expenditure variables, using validated objective measures in normal-weight young adult women without an exercise habit. METHODS: This exploratory cross-sectional study enrolled 28 healthy young adult women (22 ± 2 years; body mass index, 20.9 ± 2.3 kg/m2) without regular exercise habits. Under free-living conditions, daily energy expenditure and PA intensity distribution (percentage time in light, moderate, and vigorous activity), sedentary behaviour (SB) and daily step count were assessed using doubly labelled water and an accelerometer. The muscle insulin sensitivity index (MISI), hepatic insulin resistance index (HIRI), and whole-body insulin sensitivity were calculated from oral glucose tolerance test blood biochemistry data. RESULTS: The mean PA level was 1.58 ± 0.16, corresponding to a low-to-moderate range. Fasting blood test values did not indicate impaired glucose tolerance. In single correlation analyses, MISI demonstrated significant negative correlation with %SB (rs =  - 0.455, p = 0.015, 95% CI =  - 0.761 to - 0.042) and positive correlation with step counts (rs = 0.490, p = 0.008, 95% CI = 0.155 to 0.739). Conversely, HIRI showed no association with PA indices. CONCLUSION: Lower time spent in SB and a greater number of daily steps were associated with higher muscle insulin sensitivity, even in healthy normal-weight young adult women.