The effect of a plant based protein source on the skeletal muscle metabolic and functional response to eccentric exercise

Abstract

Human skeletal muscle undergoes shortening and lengthening cycles of contractions as well as adaptive cycles of muscle protein turnover and remodelling. The role of dietary protein is to provide amino acids for the synthesis of new proteins, specifically skeletal muscle proteins, to ensure the health and functional ability of individuals across the lifespan. The principle aim of this thesis was to determine whether a plant-based protein supplement could accelerate recovery following a bout of damage inducing eccentric exercise and to determine if changes in muscle protein synthesis (MPS), over the initial 48 hours after exercise underpin any improvement observed. Contrary to the prevailing narrative that leucine dose and subsequent plasma leucinemia variables serve as an independent determinant of post-exercise MPS responses, Chapter 3 challenges this notion, highlighting the complexity of factors influencing protein synthetic responses and that post-exercise postprandial MPS response cannot be predicted from any single plasma leucine variable. Chapters 4-6 focused on the time course of recovery, encompassing both male and female participants, to assess the efficacy of a nutritional intervention providing ample protein and leucine following eccentric exercise. Chapter 4 demonstrates that a dose of ~20g of protein with ~2g of leucine, predominantly from animal derived protein isolates, supports recovery in recreationally active males. This accelerated recovery occurred by 24h and 48h post exercise suggesting that MPS responses earlier post eccentric exercise may have supported this accelerated rate of recovery. However, presented in chapter 5, a plant-based protein supplement (Pisum Sativum) with high leucine content and no apparent amino acid deficiencies failed to support post eccentric exercise recovery. Chapter 6, demonstrated that exogenous amino acid provision immediately following eccentric exercise tended to increase MPS and improve total isokinetic work 3h following exercise, suggesting a protective effect on subsequent damage inducing processes or that the exogenous provision provides sufficient substrate for muscle remodelling and the skeletal muscle adaptive response. However, this effect does not extend over 24 hours, as muscle functional recovery was not supported by the consumption of a plant based protein supplement and was not associated with elevated MPS rates over (Chapter 5). However, the rates of MPS over this time frame were notably high across both conditions, this was alluded to be due to an elevation in the endogenous provision of amino acids from muscle protein breakdown following damage inducing eccentric exercise. The sustained protein provision and exercise stimuli over 48 hours post-exercise led to elevated MPS rates and accelerated recovery, potentially when muscle protein breakdown had returned to basal levels. This thesis underscores the intricate interplay of dietary protein sources, muscle protein synthesis, and exercise stimuli in shaping post-exercise recovery processes. The findings contribute valuable insights for future interventions seeking to understand the nuanced influence of muscle protein synthesis on muscle function after eccentric exercise.