LAUSR

The authors examined whether the associations between physical activity (PA) levels and fatigue vary by body mass index and physical performance, and whether substituting sedentary time (ST) with low light PA, high light PA, and moderate to vigorous PA (MVPA) was associated with better mean fatigue scores. In total, 6,111 participants (aged 65 years and older) were from the Women's Health Initiative Objective Physical Activity and Cardiovascular Health Study. PA levels were from a hip-worn GT3X accelerometer. Overall fatigue, energy, and weariness subdomains were from the RAND-36 Vitality subscale. Isotemporal substitution models examined the time-substitution effects. Interactions were observed between MVPA and short physical performance battery performance measure (p < .05). Substituting ST with 34.3 min of MVPA was associated on average with a 1.63-point improvement in fatigue score. Substituting ST with 50.2 min of low light PA and 34.3 min of MVPA was associated on average with an energy score improvement of 1.18 and 2.06 points respectively. Substituting ST with 34.3 min of MVPA was associated on average with a 1.08-point improvement in weariness score (p < .05 for all).