Long Versus Mixed Muscle Length Training On Changes In Arm Circumference

PURPOSE: This study investigated the effect of training with a long muscle length bias (LONG) versus training at both long and short muscle lengths (MIXED) on arm circumference using a replicated within-subjects design. METHODS: Seven males and females (age 23.00 ± 2.00 yrs; training experience 5.43 ± 2.14 yrs) trained twice per week for eight weeks, underwent a six week washout period, then had limbs re-randomized to conditions and repeated the protocol, effectively doubling the number of observations. In LONG, subjects performed six sets of incline cable curls; in MIXED, subjects performed three sets of incline cable curls and three sets of high cable curls. All sets consisted of 8-12 repetitions to momentary muscular failure. Arm circumference was assessed at 30%, 50%, and 70% of length for each limb separately. Arm length was defined as the distance between the acromion process of the scapula and the lateral epicondyle of the humerus, on the posterior side of the arm. To compare changes between LONG and MIXED conditions, a Bayesian linear mixed effects model was constructed with condition, phase, site, the interaction between condition and site, and the mean-centered pretest value of the dependent variable included as fixed effects, and nested random intercepts at the subject and limb levels to account for multiple observations. The model was fit with the maximal random effects structure. Probability density functions were compared to a region of practical equivalence (ROPE) based on measurement error to aid with interpretation. RESULTS: The modal values for the contrasts between conditions were -0.59 mm [95% HDI: -1.77, 0.66], -0.37 mm [95% HDI: -1.86, 1], and -0.12 mm [95% HDI: -1.93, 1.44] for the distal, middle, and proximal regions, respectively, with 83.96%, 73.94%, and 59.76% probabilities of LONG being superior to MIXED for the distal, middle, and proximal regions, respectively. The probability these differences between conditions exceeded the ROPE was 60.21%, 50.41%, and 37.46% for the distal, middle, and proximal regions, respectively. CONCLUSIONS: Greater changes in arm circumference were observed for LONG versus MIXED, especially at the distal site, with moderate probabilities that between-condition differences exceeded the ROPE. However, these differences were quite small.