Tibial Acceleration Measured from Wearable Sensors Is Associated with Loading Rates in Injured Runners

Background The loadrate of the vertical ground reaction force at impact has been associated with a variety of running injuries. Peak tibial shocks occur during the early stance phase and has been shown to be correlated to the loadrates in healthy runners using a rearfoot strike pattern. As a result, tibial accelerometry has been used as a surrogate for loadrates. However, these correlations have not been assessed in injured runners nor in runners with differing footstrike patterns. Objective To examine the relationship between tibial acceleration and loadrates in injured runners who are habitual rearfoot (RFS), midfoot (MFS), and forefoot (FFS) strikers. Tibial acceleration was expected to be positively associated with loadrates across all footstrike patterns. Design Cross-sectional cohort. Setting Academic medical center with biomechanics laboratory. Participants One hundred sixty-nine injured runners (age 38.7 +/- 13.1 years, 127 RFS, 17 MFS, 25 FFS). Methods Each participant completed a biomechanical assessment for injury including evaluation on a force treadmill with a triaxial accelerometer fastened by a Velcro strap to the distal medial tibia. Peak vertical and resultant tibial acceleration (VTA, RTA) were measured from the accelerometer. Vertical average and instantaneous loadrates (VALR, VILR) and the resultant instantaneous loadrate (RILR) were determined from the force data. Main Outcome Measurements The relationship between tibial acceleration and loadrates measured using Pearson's correlation coefficient (r). Results Loadrates were each associated with VTA (r = 0.66-0.82, P < .001) and RTA (r = 0.41-0.68, P < .05) across all footstrike groups with the exception of association of VILR to RTA in the FFS group. The strength in correlations was lowest between RTA and loadrates for the FFS runners (r = 0.41-0.47, P < .05). Conclusion Vertical tibial acceleration is the stronger surrogate for loadrates in injured runners across differing footstrike patterns.