Comparison of manual and automated measures of walking speed: Distance and pace matter

Background: Walking speed (WS) represents a global marker of individual health and provides a simple and objective measure of motor performances for use in clinical and research settings. WS is most often measured over relatively short distances at usual (UWS) or fast (FWS) pace, using manual (e.g., stopwatch) or automated methods (e.g., photoelectric cells). As the time needed to walk over these distances is very short, we hypothesized that measurement error related to manual compared to automated WS measures is more pronounced for shorter distances and FWS and investigated the reliability and agreement of WS in a subsample of the Constances cohort at two paces and over two distances. Methods: We recruited 100 community-dwelling participants (50 % women) aged 45-70y (mean = 56.1y). WS was measured manually (stopwatches) and using photoelectric cells, at two paces (UWS/FWS) and over two distances (3 m/5 m). Agreement was examined using Bland and Altman plots and intraclass correlation co-efficients (ICC). Results: Participants were on average 169.8 cm tall, and their mean body mass index was 25.4 kg/m2. Agreement between manual stopwatches and photoelectric cells was excellent (ICCs between 0.92 and 0.97), but it was lower for smaller distances, with significantly lower ICCs over 3 m compared to 5 m both for UWS (differenceICC =-0.04) and FWS (differenceICC =-0.05). Bias of manual measures was constant for UWS and increased with increasing FWS. There were inter-rater effects, with better agreement for UWS and 5 m compared to FWS and 3 m. Conclusions: Both distance and pace have an influence on the reliability of WS measures using manual timing methods. Our findings also suggest the presence of rater effects and better agreement for 5 m and UWS. These findings are helpful for the design of studies that include manual measures of WS, especially FWS, in order to reduce measurement error and suggest that longer distances are preferable.