Characterising human muscle protein synthetic responses across the physical activity spectrum

Shad, Brandon (2019). Characterising human muscle protein synthetic responses across the physical activity spectrum. University of Birmingham. Ph.D.

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Abstract

Maintenance of muscle mass, strength and quality across the lifespan is of vital importance. Whilst the impact of some forms of physical activity (i.e., resistance exercise) and inactivity (i.e., muscle disuse) on muscle mass regulation have been well-established, far less is known about the impact of other activities that span the physical activity spectrum. Similarly, strategies to optimise muscle mass regulation have begun to be developed but there is still scope for optimisation by considering different resistance exercise variables. Accordingly, the purpose of this thesis was to characterise the extent to which longer-term muscle protein synthesis rates are altered by differing activities across the physical activity spectrum. In the first experimental study of this thesis, a step reduction model was utilised to determine the impact of reduced physical activity and increased sedentary time on daily myofibrillar protein synthesis rates in healthy young men. This study provided novel data showing that one week of reduced physical activity and increased sedentary time led to a substantial (~27%) decline in daily myofibrillar protein synthesis rates. This was associated with increased skeletal muscle mRNA expression of myostatin and muscle atrophy F-box (MAFbx) and decreased mRNA expression of the mechanistic target of rapamycin (mTOR). Considering these findings, and the potency of resistance exercise to preserve muscle mass, the second experimental study of this thesis sought to compare daily myofibrillar protein synthesis rates over a seven-day period of volume-matched, low frequency and high frequency resistance exercise in young untrained men. The results demonstrated that resistance exercise frequency did not modulate daily myofibrillar protein synthesis rates or the phosphorylation status and total protein content of selected proteins implicated in skeletal muscle ribosomal biogenesis. These novel data showing that resistance exercise frequency did not modulate daily myofibrillar protein synthesis rates are in line with longer-term training studies. Collectively, the work contained within this thesis has successfully provided new knowledge and a clearer understanding of the extent to which longer-term muscle protein synthesis rates are altered by different activities that span the physical activity spectrum.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):