Muscle adaptation to 21 Straight Days of Elbow Flexor Exercise in Trained Individuals

Abstract

It is recommended for individuals engaging in resistance training to allow at least 48 h of recovery before repeating exercise which stresses the same muscle group. Despite this, studies have shown that training frequencies as high as four, five, or even six days per week have yielded robust increases in muscle size and strength; however, protocols implementing greater frequencies remain untested. PURPOSE: To determine the muscle size and strength adaptations following 21 straight days of elbow flexion exercise in well trained individuals. METHODS: Using a within subject design, five trained individuals were assigned both a control and experimental arm in a randomized fashion. The control arm performed a one repetition maximum (1RM) and maximal voluntary isometric contraction (MVC) every day for 21 straight days, while the experimental arm performed the same 1RM and MVC test in addition to three sets of elbow flexion exercises at 70% 1RM. Pre to post muscle thickness and strength differences within each condition and median differences between conditions were determined using non-parametric Wilcoxin tests. All significance was set at p≤ .05. Data are presented as median (25th, 75th percentile). RESULTS: 1RM strength increased from Pre to Post in both the experimental [Pre: 25.2 (22.6, 33.1), Post: 27.7 (25.1, 34.9) kg] and control [Pre: 22.5 (21.8, 32.6), Post: 25.0 (23.7, 34.2) kg] (p=0.043) arm, with no difference between arms (p=0.345). Individual data plots indicated that muscle growth occurred in the experimental arm for all individuals, however no changes in muscle size were observed at any location in the control arm. Median muscle size differences within the experimental condition were as follows: 50% (Pre: 3.8, Post: 4.2 cm; p=0.066), 60% (Pre: 4.4, Post: 4.7 cm; p=0.034) and 70% (Pre: 4.9, Post: 5.0 cm; p=0.066). Median differences in muscle size between the experimental and control arms found significant differences at the 50% site (p=0.041) with a trend at the 60% (p=0.068) and 70% (p=0.059) sites. CONCLUSIONS: Everyday training of the same muscle group appears to be effective for increasing muscle size over a relatively short duration, in trained individuals. Additionally, performing only 1RM testing every day may increase 1RM strength, which does not appear to be augmented by greater exercise volume.