Take-Off Velocity and Trunk Inclination Enhance Countermovement Jump Assessment in Older Women

ABSTRACT: Papale, O, Di Rocco, F, Festino, E, Capranica, L, Picerno, P, Cortis, C, and Fusco, A. Take-off velocity and trunk inclination enhance countermovement jump assessment in older women. J Strength Cond Res XX(X): 000-000, 2026-The aims of the study were (1) to analyze different countermovement jump height (CMJ) performance equations to compare the agreement and reliability of these methods and (2) to investigate the influence of forward trunk inclination (Bend@Jump) on take-off velocity (TOV) during CMJ in older women. Twenty subjects (age: 70.6 ± 6.2 years; body mass: 59.1 ± 10.7 kg; height: 159 ± 6.1 cm) were assessed. During the jump trials, TOV, Bend@Jump, and flight time were measured using a wearable inertial measurement unit (IMU) and a photoelectric Optojump (Opto) system to derive 3 CMJ outcomes: jump height estimated from TOV (TOV-CMJ), IMU (IMU-CMJ), Opto (Opto-CMJ). Linear mixed models, intraclass correlation coefficients, Bland-Altman Plots, and Standard Error of Measurements (SEM) were used to assess agreement and reliability. Regression analysis was used to evaluate the influence of Bend@Jump on TOV. Significance level was set at p < 0.05. For each CMJ methodology, means and SDs were calculated (TOV = 1.1 ± 0.2 m·s-1; Bend@Jump = 10.1 ± 7.9°; TOV-CMJ = 8.4 ± 2.9 cm; IMU-CMJ = 10.6 ± 3.6 cm; Opto-CMJ = 7.1 ± 3.8 cm). High intraclass correlation coefficient values emerged (TOV-CMJ = 0.84; IMU-CMJ = 0.88; Opto-CMJ = 0.91). SEM resulted higher in IMU-CMJ (1.24 cm) than TOV-CMJ (1.18 cm) and Opto-CMJ (1.15 cm). A significant (p < 0.0001) relationship (R2 = 0.96) between Bend@Jump and TOV emerged. Jump height estimations based on flight time tend to overestimate performance compared with TOV. Given the high reliability observed across the measurement methods and the strong relationship between Bend@Jump and TOV, IMU-based assessment integrating TOV and Bend@Jump may represent a practical approach for evaluating CMJ in older women.