Abstract
BACKGROUND: Resistance training is a well-established strategy to promote muscle hypertrophy and strength gains. Performing sets to concentric muscle failure (MF(CON)) is commonly used to maximize neuromuscular adaptations. However, after reaching MF(CON), there is a remaining capacity for eccentric contractions that could be used. Increasing eccentric contraction volume may represent a promising and practical alternative to enhance training volume load and optimize adaptations, although its effectiveness in this specific application has not yet been tested. OBJECTIVE: This study aims to investigate whether performing additional eccentric contractions to eccentric muscle failure (MF(EXC)), after the occurrence of MF(CON), enhances neuromuscular and morphological adaptations beyond those promoted by a traditional protocol to MF(CON). METHODS: In a randomized within-subject design, untrained young adult females will perform 2 upper-limb resistance training protocols over 10 weeks, including traditional (TRAD) training to MF(CON) and a training protocol (ECC+) consisting of sets to MF(CON) followed by eccentric-only contractions to MF(EXC). Each arm will be assigned to one of the protocols. Sessions (twice per week) will consist of 6 sets of unilateral elbow flexion with a load between 9 and 12 repetition maximum, with 2-minute rest intervals. Muscle function (isometric, concentric, and eccentric strength) and body composition (biceps brachii and brachialis muscle thickness and dual-energy x-ray absorptiometry [DXA]-based analysis) will be assessed pre and post intervention. Comparisons between limbs and across time will be analyzed using 2-way ANOVA. The level of significance will be set at P<.05. RESULTS: As of July 2024, a total of 7 participants have completed the intervention. Data collection was conducted between March and July 2024, with a new phase planned for the first half of 2025. Manuscript submission is expected in the second half of 2025. CONCLUSIONS: If the hypothesis is confirmed, the ECC+ protocol may represent a practical, simple, and low-cost strategy to increase training volume and optimize strength and hypertrophy outcomes. This study may contribute to evidence-based resistance training prescriptions, particularly for women, and support the use of additional eccentric contractions as an effective tool to enhance localized muscle adaptations. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/67537.