Intra-Day Physical Activity Patterns in Young and Older Adults

Introduction While many studies report lower daily physical activity (PA) in older compared with young adults, few have focused on how PA patterns may vary over the course of a day. Our working hypothesis is that older adults who report fatigue may adjust their behavior such that they accumulate relatively more of their PA early in the day.

Purpose Our purpose was to develop and test a method to quantify intra-day PA behavior, based on accelerometer data, in young and older adults. We also explored the association between PA and symptomatic fatigue.

Methods Accelerometer data were collected from 22 Young (22.9 ± 0.5 yr, mean ± SE; 12 Male, 10 Female) and 21 healthy Older (73.0 ± 1.3; 9M, 12F) adults. Young and older groups were matched for total daily PA. An accelerometer (Actigraph GT1M, Pensacola, FL) was worn at the hip during waking hours for 10 days; activity was recorded in 60s epochs. A survival curve analysis (Mathworks, Natick, MA) was used to quantify the timing (relative to wear time) of PA use (relative to total daily counts) over the course of each day. The relative time remaining in the day when PA had accumulated to 25%, 50%, and 75% of daily total (TimePA25, TimePA50, and TimePA75, respectively) was calculated. In a subset of 12 Older adults, symptomatic fatigue was evaluated using the Multidimensional Fatigue Inventory (MFI; Smets et al, 1995).

Results Total PA did not differ between groups, nor did TimePA25. However, TimePA50 and TimePA75 were higher in Older, indicating that they completed a greater percentage of their daily PA earlier in the day than Young. In the older subset, MFI was correlated with PA50 and PA75 (r≥0.78, p<0.01), such that those with greater fatigue completed a higher percentage of their PA earlier in the day.

Conclusions These results illustrate the utility of this new approach, and suggest that older adults of comparable total PA accumulate their PA earlier in the day than do young adults. We also provide preliminary evidence that this shift may be associated with fatigue in older adults, supporting the possibility that these individuals may tire early and become sedentary during the latter part of their day. Support: NIH R01 AG21094