Influence of Glenohumeral Joint Position on Estimated One-Repetition Maximum of the Triceps Brachii Muscle in Trained and Untrained Individuals

Background and Objective: Maximal strength is a critical indicator of neuromuscular function essential for assessing physical performance and prescribing resistance training. Nevertheless, indirect estimation of one-repetition maximum (1RM) depends on both the predictive model and joint positioning during task execution. The aim of this study was to evaluate the influence of different glenohumeral joint positions on the estimated 1RM of the triceps brachii muscle in trained and untrained individuals, using the Matveev, Adams, and Epley equations. Methods: Utilizing a descriptive, cross-sectional, and quantitative design, this study examined 20 men separated into trained (n = 10) and untrained (n = 10) groups. Unilateral elbow extension was executed at three glenohumeral positions: 10 degrees flexion, 45 degrees extension, and 130 degrees flexion. The 1RM was estimated via the Matveev, Adams, and Epley equations, with data assessed using analysis of variance and a subsequent Tukey test (p <0.01). Results: Trained individuals exhibited higher estimated 1RM values in all evaluated positions. Glenohumeral joint position influenced estimated 1RM, with higher values at 10° of flexion and lower values at 130° of flexion. No significant differences were observed between the Matveev, Adams, and Epley equations. Conclusion: Training level and glenohumeral joint positioning influence the estimated 1RM of the triceps brachii, whereas the three equations show similar performance when applied using a standardized protocol.