Effectiveness of iso-inertial resistance training on muscle power in middle-older adults: a randomised controlled trial (Preprint)

BACKGROUND Resistance training is used to prevent the decrease in muscle strength associated with age. OBJECTIVE This study evaluates the effectiveness of iso-inertial training on power, physical performance, and risk of falls compared to gravitational training in physically active middle-older adults. METHODS Parallel-group, randomised controlled trial at Espai Esport Wellness Center (Granollers, Spain). Forty-four physically active adults (age >57) were randomised to iso-inertial (n=21) or gravitational (n=23) training groups (R software; 1:1 ratio). Participants had to complete a 6-week training program (2 sessions/week) consisting of three exercises (forward and side lunge, forward lunge with row). Primary outcome: power in the eccentric phase of each exercise evaluated with both iso-inertial and gravitational devices. Secondary outcomes: concentric power, physical performance, risk of falls. Only outcome evaluators were blinded. We used multivariate linear regression models for the analysis. RESULTS 27 participants completed the program (n=15 iso-inertial, n=12 gravitational). Iso-inertial training showed better eccentric power gains than gravitational training for the iso-inertial system evaluation, although the difference was only statistically significant for the side lunge. Forward lunge: between-group difference 4.50 W (95% CI: -2.94 to 11.94, p=0.23); side lunge: difference 9.24 W (95% CI: 2.99 to 15.49; p=0.00); forward lunge with row: difference 15.25 W (95% CI: -0.63 -to 31.13, p=0.06). We observed no differences for the gravitational system evaluation nor for concentric power, physical performance, and risk of falls. The two groups improved remarkably from baseline for all outcomes. CONCLUSIONS Iso-inertial training leads to better eccentric power gains than gravitational training and therefore could be considered by clinicians when prescribing resistance training to middle-older adults. Both training systems were equally effective in improving concentric power and physical performance, and reducing risk of falls. CLINICALTRIAL This study was registered at Clinicaltrials.gov (NCT06160089).