The one-week and six-month reliability and variability of three-dimensional tibial acceleration in runners*

Abstract Tibial acceleration is a surrogate measure for impact loading and lower limb fatigue injury in runners. Triaxial accelerometers may offer reliable and practical measurement of resultant peak tibial acceleration (PTA). With such potential in mind, this study examined variability and measurement reliability of tibial acceleration in 14 runners at baseline at one week, and eight of the runners again at six months. Triaxial accelerometers were attached to the distal tibiae of runners before they ran on a treadmill for two minutes each, at speeds of 2.7, 3.0, 3.3 and 3.7 m/s in standardised shoes. Resultant PTAs were calculated for each speed and session. Reliability outcomes were presented as percentage change and effect sizes. Variability outcomes included intraclass correlation coefficients and the typical error of the measurement. Smallest worthwhile change and performance/noise ratio were also calculated. While runners demonstrated marginally lower reliability and higher variability over six months, compared to one week, in all cases the measures of reliability and variability were of ‘good’ to ‘moderate’ reliability, and ‘small’ to ‘moderate’ variability using magnitude-based inferences. We can be confident that resultant PTA can be used with runners to assess and monitor their impacts throughout a six-month intervention.