Thoracic-Worn Accelerometers Detect Fatigue-Related Changes in Vertical Stiffness During Sprinting.

Horsley, BJ, Tofari, PJ, Halson, SL, Kemp, JG, Johnston, RD, and Cormack, SJ. Thoracic-worn accelerometers detect fatigue-related changes in vertical stiffness during sprinting. J Strength Cond Res XX(X): 000-000, 2023-Thoracic-mounted accelerometers are valid and reliable for analyzing gait characteristics and may provide the opportunity to assess running-related neuromuscular fatigue (NMF) during training and competition without the need for additional tests, such as a countermovement jump (CMJ). However, their sensitivity for detecting fatigue-related changes in gait across different speeds is unclear. We, therefore, assessed the changes in accelerometer-derived gait characteristics, including vertical stiffness (K vert ), following a repeated sprint protocol (RSP). Sixteen recreationally active subjects performed single and repeated CMJs on a force plate and 40 m run throughs overground at 3-4, 5-6, and 7-8 m·s -1 pre-post a 12 × 40 m RSP. Gait characteristics (contact time, step frequency, step length, K vert , etc.) were derived from an accelerometer contained within a global navigation satellite system unit on the thoracic spine using a validated algorithm. Changes in running gait and CMJ performance were assessed using a linear mixed-effects model (95% confidence interval [95% CI]; effect size [ES]). Significance was set at p < 0.05. A significant reduction in K vert occurred at 7-8 m·s -1 following the RSP (-8.51 kN·m -1 [-13.9, -3.11]; p = 0.007; ES [95% CI] = -0.39 [-0.62, -0.15]) which coincided with a decreased jump height (-0.03 m [-0.04, -0.01]; p = 0.002; ES [95% CI] = -0.87 [-1.41, -0.30]). However, all other gait characteristics were not significantly different irrespective of speed. Thoracic-worn accelerometers can detect changes in K vert at 7-8 m·s -1 which may be useful for monitoring NMF during sprinting. However, a RSP does not result in altered gait mechanics in subsequent running at lower speeds.