Author(s): KUMAHARA, H., AIKAWA, H., HATAMOTO, Y., YOSHIMURA, E., TOBINA, T., ICHIDA, Y., KATO, M., AYABE, M., Institution: NAKAMURA GAKUEN UNIVERSITY, Country: JAPAN, Abstract-ID: 1541

INTRODUCTION:
Healthy lifestyle habits and the maintenance of improved health status in young adult women are crucial for lifelong disease prevention in middle age and beyond. Issues regarding impaired glucose tolerance caused by physical inactivity and poor dietary intake in thin young adult women have recently been reported. However, research on the association between free-living physical activity (PA) and glucose tolerance in normal-weight young adult women remains scarce. This study aimed to elucidate the association between blood markers related to glucose tolerance and PA indices, including PA intensity and energy expenditure–related variables, using the doubly labelled water technique and a validated activity monitor in normal-weight young adult women without a regular exercise habit.
METHODS:
This study enrolled 28 healthy young adult women with a mean age of 22 ± 2 years and a mean body mass index of 20.9 ± 2.3 who did not regularly exercise. Daily energy expenditure and PA intensities, including the percentage of time spent engaging in light (%LPA), moderate and vigorous intensities, as well as sedentary behaviour (%SB), were measured using the doubly labelled water method and an accelerometer under free-living conditions. The muscle insulin sensitivity index (MISI), hepatic insulin resistance index (HIRI) and whole-body insulin sensitivity were calculated using blood biochemistry data obtained from a 75-g oral glucose tolerance test.
RESULTS:
The PA level of the participants was 1.6 ± 0.2, which falls within the low-to-moderate range. The fasting blood test results did not indicate impaired glucose tolerance. Partial correlation analyses revealed that the MISI exhibited significant positive correlations with %LPA (r = 0.43 to 0.44) and negative correlations with %SB (r = −0.50 to −0.49), even after adjustment for age and some types of body composition variables. Conversely, no associations between the HIRI and PA indices were observed.
CONCLUSION:
These findings suggest that less time spent in SB and higher time spent in LPA are associated with greater muscle insulin sensitivity, independent of muscle or fat mass volume, even in healthy, normal-weight young adult women. This is the first study to investigate the association between PA-related metrics under free-living conditions and glucose tolerance using validated objective methods in young adult women.