Sedentary Behaviour and Free-Living Physical Activity Intensity as Determinants of Physical Activity Level in Young Adult Women without Regular Exercise Habits

There is a growing amount of research on the association of physical activity level (PAL) and physical activity-related energy expenditure (PAEE) with physical activity (PA) intensity or body composition variables; however, the age of the target population, especially young adults, is limited. In this study, we aimed to investigate the association between PA indices such as each PA intensity, including sedentary behaviour (SB), and free-living energy expenditure using the doubly labelled water (DLW) method. Using the DLW method under free-living conditions, total energy expenditure was evaluated in 32 healthy women without regular exercise habits in their 20 s. PA, including the percentage of time spent engaging in light, moderate, and vigorous physical intensities, was measured using a validated accelerometer. The %SB was also calculated. Partial correlation coefficients of the relationship between the PAL and PA variables, including sleeping time, age, and body composition indices, were calculated while controlling for the effect of multiple variables. PAEE normalised for body weight (PAEE/kg) and average PAL were 10.2±3.0 kcal/kg/d (42.7±12.7 kJ/kg/d) and 1.60±0.17, respectively. PAL and PAEE/kg had significant negative partial correlations with %SB (r=-0.428, p=0.033 and r=-0.484, p=0.014, respectively). The results indicate that reducing SB attributes to higher values of PAL and PAEE/kg. This is the first study to clarify the contribution of SB and other PA indices to the intensity of PAL and free-living energy expenditure using DLW in young adult women without regular exercise habits.