Characteristics of very slow stepping in healthy adults and validity of the activPAL3™ activity monitor in detecting these steps

The use of activity monitors to objectively measure stepping activity allows the characterisation of free-living daily activity performance. However, they must be fully validated. The characteristics of very slow stepping were examined and the validity of an activity monitor, the activPAL3™ (PAL Technologies Ltd., Glasgow, UK) to detect these steps was assessed. 10M/10F healthy adults (36 ± 10y) performed a treadmill walking protocol from 1.0 m/s down to 0.1 m/s (0.1 m/s increments) whilst wearing the monitor under video observation (gold standard). Within the 800 stepping periods recorded the proportion of the steps correctly detected by the activPAL3™ was explored against speed and cadence. Below 0.4 m/s walking began to be intermittent, stepping interspersed with stationary postures. At 0.1 m/s almost 90% of walking periods were intermittent. The percentage of steps detected was over 90% for walking speed at or above 0.5 m/s and cadence at or above 69 steps/min. However, below these limits % steps detected reduced rapidly with zero steps detected at 0.1 m/s and at or below 24 steps/min. When examining the stepping activity of groups with limited stepping cadence the above thresholds of performance should be considered to ensure that outcomes are not misinterpreted and important very slow stepping activity missed.