ORIGINAL RESEARCH article
Front. Physiol.
Sec. Exercise Physiology
Volume 16 - 2025 | doi: 10.3389/fphys.2025.1592477
This article is part of the Research TopicResponses and Adaptations to Novel Exercise ModalitiesView all 15 articles
Effects of Asymmetric Load Bench Press Offset Training on Muscle Activation Levels and Exercise-Induced Fatigue in Collegiate Bodybuilders
Provisionally accepted
- 1Henan Sport University, zhengzhou, China
- 2Wuhan Sports University, Wuhan, Hubei Province, China
- 3Nanjing Medical University, Nanjing, Jiangsu Province, China
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Objective This study systematically investigated the effects of graded asymmetric load bench press offset training on muscle activation patterns, exercise-induced fatigue, and movement performance in bodybuilders. Methods Ten male athletes (age: 24.20 ± 1.91 years; 1RM bench press: 120.00 ± 14.66 kg) underwent randomized crossover trials with 0% (symmetrical), 2%, 4%, and 6% asymmetric load interventions (70% 1RM total load). Surface electromyography (sEMG) quantified activation levels of pectoralis major (PM), anterior deltoid (AD), triceps brachii (TB), and external oblique (EO), while barbell kinematics, blood lactate, and heart rate were analyzed to assess fatigue. Result Key findings revealed significant interlimb asymmetry under symmetrical loading, with dominant-side PM (51 ± 6.82 vs. 35 ± 5.32 MVIC%, p = 0.009) and AD (48.2 ± 5.05 vs. 32.6 ± 9.21 MVIC%, p = 0.038) exhibiting higher activation than the non-dominant side. Asymmetric loading effectively mitigated this imbalance: 6% intervention increased non-dominant PM (54.4 ± 8.46 vs. 0%: 35 ± 5.32 MVIC%, p = 0.035) and AD activation (52.3 ± 12.7 vs. 0%: 32.6 ± 9.21 MVIC%, p = 0.022), but triggered compensatory EO recruitment (31.1 ± 12.3 vs. 0%: 12.8 ± 3.34 MVIC%, p < 0.001). Performance metrics declined progressively with higher asymmetry: 6% loading reduced barbell velocity (MV: 0.28 ± 0.03 vs. 0%: 0.38 ± 0.04 m/s, p < 0.001), repetitions (6.63 ± 2.40 vs. 0%: 13.90 ± 2.52, p < 0.001), and power (MP: 357 ± 43 vs. 0%: 437 ± 53.70 W, p = 0.009). Physiological fatigue markers intensified at 6% asymmetry, evidenced by elevated post-exercise blood lactate (7.42 ± 1.59 vs. 0%: 9.88 ± 0.75 mmol/L, p = 0.003) and prolonged heart rate recovery. Conclusion The study identifies 2-4% asymmetric loading as optimal for enhancing non-dominant muscle activation while minimizing fatigue, whereas 6% interventions induce core compensation and performance deterioration. These findings establish evidence-based thresholds for precision training protocols, addressing interlimb asymmetry while balancing neuromuscular efficacy and physiological strain. Methodological innovations include multidimensional analysis of biomechanical, electromyographic, and physiological responses, advancing the understanding of neuromuscular coordination in asymmetric resistance training.
Keywords: Interlimb asymmetry, Electromyography, Resistance Training, Neuromuscular adaptation, Fatigue threshold, core compensation
Received: 12 Mar 2025; Accepted: 14 Apr 2025.
Copyright: © 2025 Yan, Zhang, Li, Han and Hu. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Bin Yan, Henan Sport University, zhengzhou, China
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