Wired for Growth: Muscle Excitation as a Predictor of Long-Term Hypertrophy and Strength Adaptations. A Study Protocol of a PhD project

Abstract

Resistance training is crucial for athletic performance and clinical rehabilitation (El-Kotob et al., 2020). Practitioners frequently use acute surface electromyography (sEMG) to select exercise variations (AdavamPurath et al., 2020), assuming greater acute muscle excitation equates to superior long-term adaptations. However, sEMG amplitude does not directly reflect neural drive, and this paradigm lacks robust empirical validation (Vigotsky et al., 2022). Furthermore, stretch-mediated hypertrophy evidence suggests that training in lengthened partial ranges of motion (ROM) drives growth via passive mechanical tension, with almost no active sEMG excitation (Warneke et al., 2023). This PhD project therefore tests whether acute sEMG amplitude predicts 12-week changes in regional muscle hypertrophy and strength, regardless of whether the relationship proves strong or absent. Secondarily, the study contrasts full ROM (FROM) with lengthened partial ROM (LROM) to test the predictive utility of sEMG across mechanical stimuli (Plotkin et al., 2023). Methods: The project implements a three-stage framework: Phase 1: Evidence Synthesis (Completed): A scoping review mapped how training intensity, ROM, and repetition duration influence acute sEMG amplitude. Phase 2: Acute Biomechanical Investigations (Completed): Two laboratory studies (10RM bench press and prone barbell row) quantified neuromuscular responses across full, upper-half, and lower-half ROM conditions. Phase 3: Longitudinal Trial: A 12-week unilateral, intra-individual intervention in untrained adults (target n = 20, a priori sample size estimation based on Pallarés et al., 2021). In bi-weekly leg extension and leg curl sessions (8-10RM), the right leg trains with FROM (2s/2s), while the left leg trains with LROM (fully stretched position, 1s/1s). Regional muscle thickness (ultrasound) and MVIC torque will be correlated with standardized baseline 10RM sEMG recordings normalized to MVIC. Results: Phases 1 and 2 have been published, demonstrating that exercise execution parameters modulate acute sEMG amplitude significantly and muscle-specifically. The Phase 3 trial is currently underway with high participant compliance (>95%). Post-intervention data collection will conclude in August 2026. Conclusion: This project directly tests a widely applied but under-validated assumption. If predictive validity is confirmed, sEMG will be justified as a resource-efficient tool for evaluating training protocols. Conversely, if the relationship proves weak, or if LROM yields differential adaptations independent of baseline sEMG, this will caution against relying on acute sEMG and underscore passive mechanical tension as a driver of hypertrophy. Either way, and accounting for the likely muscle-specificity of the relationship, this work advances evidence-based exercise prescription from athletic performance to sarcopenia counter-measures.

References

AdavamPurath, F., et al. (2020). Activity of shoulder girdle muscles during the perfect push-up and push-up bar exercises using different hand positions in young overhead athletes. Sport Sciences for Health.

El-Kotob, R., et al. (2020). Resistance training and health in adults: An overview of systematic reviews. Applied Physiology, Nutrition, and Metabolism.

Pallarés, J. G., et al. (2021). Effects of range of motion on resistance training adaptations: A systematic review and meta-analysis. Scandinavian Journal of Medicine and Science in Sports.

Plotkin, D. L., et al. (2023). Hip thrust and back squat training elicit similar gluteus muscle hypertrophy and transfer similarly to the deadlift. Frontiers in Physiology.

Vigotsky, A. D., et al. (2022). Longing for a Longitudinal Proxy: Acutely Measured Surface EMG Amplitude is not a Validated Predictor of Muscle Hypertrophy. Sports Medicine.

Warneke, K., et al. (2023). Physiology of Stretch-Mediated Hypertrophy and Strength Increases: A Narrative Review. Sports Medicine.