Physical activity scaled to preferred walking speed as a predictor of walking difficulty in older adults: a 2-year follow-up

Background The usual accelerometry-based measures of physical activity (PA) are dependent on physical performance. We investigated the associations between PA relative to walking performance and the prevalence and incidence of early and advanced walking difficulties compared to generally used measures of PA. Methods Perceived walking difficulty was evaluated in 994 community-dwelling participants at baseline (age 75, 80 or 85 years) and two years later over two kilometers (early difficulty) and 500 meters (advanced difficulty). We used a thigh-mounted accelerometer to assess moderate-to-vigorous PA, daily mean acceleration and relative PA as movement beyond the intensity of preferred walking speed in a 6-minute walking test (PArel). Self-reported PA was assessed using questionnaires. Results The prevalence and incidence were 36.2 % and 18.9 % for early, and 22.4 % and 14.9 % for advanced walking difficulty, respectively. PArel was lower in participants with prevalent (mean 42 (SD 45) vs. 69 (91) mins/week, p<0.001) but not incident early walking difficulty (53 (75) vs. 72 (96) mins/week, p=0.15) compared to those without difficulty. The associations between absolute measures of PA and incident walking difficulty were attenuated when adjusted for preferred walking speed. Conclusions The variation in habitual PA may not explain the differences in the development of new walking difficulty. Differences in physical performance explain a meaningful part of the association of PA with incident walking difficulty. Scaling of accelerometry to preferred walking speed demonstrated independence on physical performance and warrants future study as a promising indicator of PA in observational studies among older adults.