Making Sense of Muscle Protein Synthesis: A Focus on Muscle Growth During Resistance Training.

Oliver C Witard,Laurent Bannock,Kevin D Tipton

doi:10.1123/ijsnem.2021-0139

Abstract

The acute response of muscle protein synthesis (MPS) to resistance exercise and nutrition is often used to inform recommendations for exercise programming and dietary interventions, particularly protein nutrition, to support and enhance muscle growth with training. Those recommendations are worthwhile only if there is a predictive relationship between the acute response of MPS and subsequent muscle hypertrophy during resistance exercise training. The metabolic basis for muscle hypertrophy is the dynamic balance between the synthesis and degradation of myofibrillar proteins in muscle. There is ample evidence that the process of MPS is much more responsive to exercise and nutrition interventions than muscle protein breakdown. Thus, it is intuitively satisfying to translate the acute changes in MPS to muscle hypertrophy with training over a longer time frame. Our aim is to examine and critically evaluate the strength and nature of this relationship. Moreover, we examine the methodological and physiological factors related to measurement of MPS and changes in muscle hypertrophy that contribute to uncertainty regarding this relationship. Finally, we attempt to offer recommendations for practical and contextually relevant application of the information available from studies of the acute response of MPS to optimize muscle hypertrophy with training.

Highlights

Muscle protein synthesis (MPS) is the metabolic process that describes the incorporation of amino acids into bound skeletal muscle proteins
The synthesis of myofibrillar proteins is primarily responsible for changes in skeletal muscle mass following resistance training, whereas mitochondrial proteins are primarily synthesized in response to endurance type training (Wilkinson et al, 2008)
It is crucial that the real-world significance of acute MPS measurements that are used to determine the superiority of nutritional interventions for muscle hypertrophy is understood within the context and limitations of these methods

Summary

Introduction

Muscle protein synthesis (MPS) is the metabolic process that describes the incorporation of amino acids into bound skeletal muscle proteins. The assessment of the acute response of MPS to combined exercise and nutrition interventions is commonly used as the scientific basis to inform sport and exercise nutrition, in particular protein nutrition, recommendations for the training and performance of athletes and other exercisers This longstanding assumption is Viewed through the lens of the applied sport and exercise nutrition practitioner, it is crucial to understand the real-world significance of the stated and/or perceived superiority of one nutritional strategy over another. It has been proposed that muscle hypertrophy following RET stems from a cumulative accretion of muscle proteins resulting from the repeated increase in response of myofibrillar–MPS to successive bouts of REx (Hawley et al, 2006) According to this traditional definition of muscle hypertrophy, it may seem intuitively satisfying that assessment of the acute response of MPS to REx provides an informative tool when devising RET and nutritional interventions to maximize muscle hypertrophy in athletes and other exercisers

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