Agreement and Reliability of Running Stride-Time Variability Analyses from Wearable Devices

Stride-time variability is typically quantified using measures including the coefficient of variation (CV) and detrended fluctuation analysis (DFA). Whilst several studies have reported guidelines for applying such measures, few have considered the sensitivity of these measures to the way stride times are obtained. This study investigated the agreement and between-day reliability of stride-time variability measures derived from wearable devices compared to measures derived from an instrumented treadmill. Thirty-one runners completed eight minutes of running on two days. Stride times were obtained concurrently using Loadsol^® insoles, Blue Trident inertial measurement units (IMUs) at four sampling rates, RunScribe™ IMUs and an AMTI instrumented treadmill. Stride-time CV and DFA-α were calculated on time-matched series. Agreement with the instrumented treadmill was quantified using Bland Altman plots and concordance correlation coefficients. Loadsol^® insoles and RunScribe™ IMUs displayed the highest and lowest agreement, respectively. For the Blue Trident IMU, sampling below 400 Hz reduced agreement relative to higher rates. Between-day reliability was moderate-to-good and poor-to-moderate for stride-time CV and DFA-α, respectively, although within narrower bands than reported across studies using different measurement devices. Hence, Loadsol^® insoles and Blue Trident IMUs, at sufficient sampling rates, can facilitate stride-time variability analyses, although changes over time should be interpreted cautiously.