Background
Fatigability, defined as fatigue in relation to a standardized task, predicts functional decline in older adults independent of reported tiredness or energy level. Although the sensation of fatigue, tiredness, and energy level adversely affect physical activity (PA), the association between fatigability and objectively measured PA is unknown.

Methods
Participants in the Baltimore Longitudinal Study of Aging (n = 557, 50% women, aged 50–97 years) were instructed to wear an Actiheart accelerometer for 7 consecutive days in the free-living environment. Perceived fatigability was assessed using the Borg rating of perceived exertion (RPE) after 5 minutes of treadmill walking at 1.5 mph (0.67 m/s) and categorized as low (6–7 RPE), intermediate (8–9 RPE), and high (10+ RPE) fatigability. Time-of-day PA differences between fatigability groups were assessed using mixed-effects modeling.

Results
Total daily PA was 1.3% lower for every unit increment in perceived fatigability after adjusting for demographic, behavioral, and medical factors (p = .01). In time-of-day analyses, the high fatigability group was less active compared to the low fatigability group throughout the day (8:00 am to 8:00 pm) and the intermediate fatigability group in the morning (8:00 am to 12:00 pm). Patterns of PA within the high fatigability group differed from both the intermediate and low groups in the morning but mirrored the intermediate group in the afternoon and evening.

Discussion
These results suggest that RPE is a bio-marker of fatigability associated with progressively lower PA with aging. Whether the effects of fatigability occurring at the end of the day reflect waning energy levels or a voluntary choice that could be modified remains to be evaluated.

Direct Link: https://doi.org/10.1093/gerona/glx181

Journal: The Journals of Gerontology: Series A. 2018 Apr 17;73(5):630-5.

Keywords: Aging, circadian rhythms, diurnal patterns, fatigue, older adults, Physical Activity,

Applications: Physical Activity,

CamNtech Reference: AH17063

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