Effectiveness of Iso-Inertial Resistance Training on Muscle Power in Middle-Older Adults: Randomized Controlled Trial.

Background: Resistance training is commonly used to prevent the decline in muscle power associated with aging. Objective: This study aims to evaluate the effectiveness of iso-inertial (IN) training on power, physical performance, and variables associated with the risk of falls, compared to gravitational (GR) training, in physically active middle-older adults. Methods: A parallel-group, randomized controlled trial was conducted at Espai Esport Wellness Center (Granollers, Spain). In total, 44 physically active adults (age >57) were randomized 1:1 to either the IN (n=21) or GR (n=23) training groups (using R software; R Core Team). Participants completed a 6-week training program (2 sessions/week) consisting of 3 exercises (forward lunge, side lunge, and forward lunge with row). The primary outcome includes power in the eccentric phase of each exercise, evaluated using both IN and GR devices. Secondary outcomes include concentric power, physical performance, and variables associated with the risk of falls. Only outcome evaluators were blinded. We used multivariate linear regression models for the analysis. Results: In total, 27 participants completed the program (IN: n=15 IN; GR: n=12). IN training resulted in better eccentric power gains compared to GR training when assessed using the IN system, although the difference was only statistically significant for the side lunge. For forward lunge, between-group difference was 4.50 W (95% CI -2.94 to 11.94 W, P=.23); for side lunge, between-group difference was 9.24 W (95% CI 2.99-15.49 W; P<.01); and for forward lunge with row, between-group difference was 15.25 W (95% CI -0.63 to 31.13 W; P=.06). We observed no significant differences for the eccentric power using the GR system evaluation, concentric power, physical performance, and variables associated with the risk of falls. Both groups showed significant improvements from baseline across all outcomes. Conclusions: Although IN training appeared to result in greater power gains during the eccentric phase when assessed with the IN system, statistically significant differences were observed only for the side lunge exercise. Both training systems seemed equally effective in improving eccentric power as evaluated with the GR system, concentric power, physical performance, and reducing variables associated with the risk of falls.