The effects of lengthened-partial range of motion resistance training of the limbs on arm and thigh muscle area: A multi-site randomised trial

This project represents a highly powered pre-registered comparison of full ROM (fROM) and 'lengthened partial' ROM (lpROM) resistance training [RT]. A randomized controlled cluster trial across 15 sites was employed. The outcomes were muscle cross sectional area (CSA) of the upper arm and thigh, and strength for chest press, leg press, and pulldown. Pre-testing preceded randomization to either the lpROM (n = 163) or fROM (n = 134) RT condition. Post-testing was completed following a 12-week intervention. Our primary estimand of interest was the condition by time interaction. The estimate for this effect for arm estimated muscle CSA was −0.032 and for thigh estimated muscle CSA was 0. The p-values for equivalence were p = 0.071 for the arm muscle, and p = 0.019 for the thigh muscle. Inference criteria with alpha were set at 0.01 and adjusted to 0.005 for multiple outcomes, as such, we were unable to reject the null hypothesis that the condition:time interaction effect was outside of the SESOI [−0.1, 0.1]. Exploratory analysis suggests that both the main effects of time, and any interaction effects for condition by time, are likely small. These findings support previous evidence comparing fROM and lpROM specifically and suggest that between condition effects are small and practically equivalent.