Mechanisms of human skeletal muscle remodeling in response to concentric and eccentric loading paradigms

Franchi, Martino V. (2014) Mechanisms of human skeletal muscle remodeling in response to concentric and eccentric loading paradigms. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

It is common knowledge that resistance exercise promotes muscle growth (hypertrophy) and increased strength and function: thus, regular exercise can help minimize the loss of muscle mass and function in healthy ageing. Skeletal muscle can contract by either shortening or lengthening (concentrically or eccentrically, respectively). A substantial number of studies focused on the effect of concentric versus eccentric training protocols on muscle morphological and functional changes: eccentric contractions are generally thought to result in more increased muscle hypertrophy and strength, because of the higher force produced by the muscle and the more severe exercise induced muscle damage, which may lead to a stronger adaptations in muscle remodeling and repair processes. Study 1 shows that ECC and CON exercise protocols lead instead to similar gains in muscle size, but through different architectural remodeling mechanisms: moreover, acute contraction-specific molecular responses have been characterised. Study 2 and Study 3 were then performed in order to gain novel insights into the relationship between these morphological adaptations and the metabolic responses (MPS, muscle protein synthesis) of human skeletal muscle in response to chronic ECC vs. CON loading paradigms. Study 2 was first carried out in order to validate the use of deuterium oxide isotope tracing technique for measuring changes in MPS in free-living subjects over longerterm periods (compared to normal AA infusion studies) of resistance exercise. After assessing the feasibility of deuterium oxide tracing technique in measuring MPS response during resitance-training protocols, study 3 investigated the chronic responses in MPS to ECC vs. CON loading in two 3 different sites of the human vastus lateralis, presenting novel insights into MPS and skeletal muscle homogeneity, attempting to link MPS changes to the different mechanisms of muscle morphological remodelling occurring after ECC vs. CON training.