A Novel Method for Assessing Load-Velocity Profiles With a Motorized Resistance Device in the Sit-to-Stand Test in Older Adults.

Abstract: Jiménez-Lupión, D, Chirosa-Ríos, I, Lizama-Pérez, R, Chirosa-Ríos, L, and Jerez-Mayorga, D. A novel method for assessing load-velocity profiles with a motorized resistance device in the sit-to-stand test in older adults. J Strength Cond Res XX(X): 000-000, 2025-The load-velocity (L-V) relationship correlates external load and lifting velocity, and the 2-point method for determining this relationship has become a reliable way to assess muscle mechanical capacities. This assessment could prove highly valuable in geriatrics and aging research because it helps identify early declines in muscle strength and power. Functional Electromechanical Dynamometry (FEMD) enables load, velocity, and power measurements during multijoint tasks, like the sit-to-stand (STS) test, facilitating comprehensive muscle function assessment in older adults. This study aimed to evaluate the test-retest reliability and concurrent validity of the 2-point method for determining the L-V relationship using FEMD during loaded STS tasks. Thirty healthy subjects (23 women, 7 men; mean age 61 ± 9.33 years; mean body mass 70.5 ± 14.7 kg; mean height 1.59 ± 0.07 m) participated. They performed unloaded and loaded 5-STS tasks with FEMD. Mean velocities from all loads were used to calculate individual L-V relationships. The absolute reliability demonstrated acceptable repeatability for L0 (i.e., load at zero velocity) (coefficient of variation [CV]: 9.97%; intraclass correlation coefficient [ICC]: 0.94), V0 (i.e., velocity at zero load) (CV: 5.70%; ICC: 0.95), and Aline (i.e., the area under the L-V relationship line) (CV: 7.60%; ICC: 0.98) with a CV < 10% in all cases. Regarding the concurrent validity of Aline variable with respect to mean mechanical power, a high correlation was observed (r = 0.82; p = < 0.001). This study confirms the reliability and validity of the 2-point method using FEMD for assessing L-V relationships and muscle power during 5-STS in older adults.