Sampling frequency impacts measurement of walking activity after stroke

The purpose of this study was to examine the effect of sampling epoch on total time spent walking and number of walking bouts per day in persons with stroke. Ninety-eight persons with average age of 63.8 yr and average time poststroke of 43.6 mo participated. Participants wore a StepWatch Activity Monitor for 3 to 5 consecutive days. The number of strides taken was collected in consecutive 5 s epochs and down sampled into 10, 20, 30, and 60 s epochs. Total time walking and total number of walking bouts were determined for each day. Low activity days were defined as days below the 25th percentile of total steps per day and high activity days as days above the 75th percentile of total steps per day. Total time walking and total number of bouts were different for each sampling epoch (p < 0.001 for all). The 5 s sampling epoch resulted in calculation of ~40% of the walking time and ~6 times as many bouts as a 60 s sampling epoch. Differences were greater for low activity days (p < 0.001 for all). Sampling epoch affects daily step activity variables whose calculation depends on time, especially during low activity days. Sampling epoch must be carefully considered when designing studies aimed at understanding patterns of daily walking activity.