Mixing Up Muscle Lengths: The Effects of Training at Different Muscle Lengths in the Elbow Flexors

Abstract

PURPOSE: This study investigated the effects of resistance training at only longer muscle lengths (LONG) compared to training with a combination of long and short muscle lengths (MIXED). METHODS: 7 recreationally trained males (n=5) and females (n=2) completed an eight-week replicated crossover within-participant design, with participants’ upper limbs randomized to LONG or MIXED conditions. LONG training involved only seated lengthened cable curls, while MIXED training involved half seated lengthened cable curls and half standing shortened cable curls. Elbow flexor cross-sectional area (CSA), regional muscle thickness (MT), dynamic strength, isometric strength, and arm circumference were assessed at pre- and post- testing. Session rating of perceived exertion (sRPE) and perceived soreness were assessed before and after every session. RESULTS: Changes in total CSA for LONG (6.01 cm2 [95% HDI: - 1.64, 14.66], 80.12% probability > ROPE) and MIXED (3.18 cm2 [95% HDI: -5.66, 12.69], 55.51% probability > ROPE) were considered meaningful, but the contrast between conditions was not meaningful. Changes in dynamic strength for the shortened cable curl and lengthened cable curl in both conditions were considered meaningful, but the contrast between conditions was not meaningful. Contrast estimates in arm circumference were meaningfully greater for LONG at the proximal, middle, and distal regions of the upper arm but had questionable relevance. Changes in regional MT, regional isometric force, total isometric strength, sRPE, and perceived soreness were not considered meaningful for either condition. CONCLUSIONS: Overall, it seems that neither training condition provides clearly superior outcomes for hypertrophy, strength, or perceptual fatigue.