The physiological and biomechanical bases of muscular hypertrophy/ atrophy

McMahon, Gerard (2013) The physiological and biomechanical bases of muscular hypertrophy/ atrophy. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Introduction: The aims of the current investigations were to modulate muscle-tendon complex (MTC - vastus lateralis [VL] & patella tendon [PT]) adaptations through mechanical stress and strain. Groups performed resistance training (8 weeks) with the MTC placed in a shortened (SL) or a lengthened position (LL) with internal loading standardised. A third group trained over an entire ROM (LX) with the external loading matched to that in SL. MTC response to detraining (4 weeks) was also measured. A control, untrained group was measured during this 12-week period. Methods: Measurements using ultrasonography, dynamometry, electromyography and dual energy absorptiometry were made at baseline (week 0), post-training (week 8), detraining 1 (week 10) and detaining 2 (week 12). VL measurements included volume, cross-sectional area (CSA), and architecture. PT properties included stiffness and Young’s Modulus. Quadriceps MTC function was measured by isometric maximal voluntary contractions (MVC) over a range of joint –angles. Circulating levels of a growth factor (IGF-I) and cytokines (TGF-β1, TNF-α) were measured using enzyme-linked immuno-sorbant assay. Main Results: VL volume, CSA, fascicle length, PT stiffness, modulus, quadriceps MVCs and IGF-I (LL only) were significantly greater (p<0.05) in both LL and LX groups compared to SL post-training. During detraining, CSA, fascicle length, stiffness, modulus, IGF-I (LL only) remained significantly elevated in the LL and LX groups compared to SL. There was no significant change in the control group in any measurement during the study period (p>0.05). Conclusion: Training with the MTC in a lengthened position is more effective for inducing (and retaining) enhanced training MTC adaptations, owing to internal mechanical and physiological stress in this position. This loading method should therefore be incorporated into a structured resistance training program for a range of populations such as athletic, recreationally active, clinical or elderly individuals.