Reliability and Accuracy of Stryd to Detect Changes in Vertical Displacement of the Center of Mass While Running.

Abstract: Somma, M and Lawrence, MA. Reliability and accuracy of Stryd to detect changes in vertical displacement of the center of mass while running. J Strength Cond Res XX(X): 000-000, 2024-The purpose of this study was to determine if Stryd can reliably and accurately detect changes in vertical displacement of the center of mass (VCoM) that are produced when cadence was increased by 5 and 10%. A secondary purpose of this investigation was to determine the interlimb reliability of Stryd for VCoM and cadence. Twenty healthy individuals (5 males, 15 females; age: 24.5 ± 1.5 years; mass: 67.1 ± 12.2 kg; height: 1.66 ± 0.01 m) were fitted for motion capture and 2 Stryd devices. After warm-up, subjects ran at a self-selected speed on the treadmill for each condition (self-selected, +5%, and +10% cadence) while VCoM and cadence were collected simultaneously from Stryd and motion capture. Reliability between the Stryd devices on different limbs was excellent for both cadence (intraclass correlation coefficient [ICC] = 0.999, p < 0.001) and VCoM (ICC = 0.993, p < 0.001). Cadence was not significantly different between the Stryd device and motion capture (p = 0.153). Stryd produced significantly (p < 0.001) smaller values for VCoM regardless of condition, with average differences ranging between 4.4 and 4.6 cm. A linear regression revealed that Stryd predicted 50.7% of variation in motion capture VCoM (p < 0.001). Stryd can reliably measure both cadence and VCoM regardless of which limb it is placed on, as indicated by the near-perfect agreement between Stryd devices, and the Stryd device can detect and predict changes in VCoM. However, Stryd consistently underestimates VCoM, which can be corrected by using a linear regression equation.