Eggers, TM, Massard, TI, Clothier, PJ, and Lovell, R. Measuring vertical stiffness in sport with accelerometers: Exercise caution! J Strength Cond Res 32(7): 1919–1922, 2018—This study aimed to determine the measurement accuracy of triaxial accelerometers, to determine vertical stiffness (Kvert) during overground running, and to examine the influence of device location. Seventeen healthy adults wore 2 triaxial accelerometers (positioned between scapulae and at lumbar spine) during a 2-minute continuous 20-m shuttle run (12 km·h−1), which was repeated 7 days later. Accelerometer-derived Kvert data were compared with that calculated from corresponding force-plate ground contacts (criterion measure). Moderate correlations (r = 0.65–0.66) between the accelerometer and criterion measure were identified, irrespective of unit location. However, accelerometer-determined Kvert had questionable reliability in both positions (intraclass correlation coefficient = 0.70–0.71). These results suggest caution be taken when using accelerometer-derived Kvert during overground running.