Biomechanical implications of skeletal muscle hypertrophy and atrophy: a musculoskeletal model.

Andrew D Vigotsky,Chris Beardsley,Bret Contreras

doi:10.7717/peerj.1462

Andrew D Vigotsky, Chris Beardsley + Show 1 more

Open Access

https://doi.org/10.7717/peerj.1462

Copy DOI

Abstract

Muscle hypertrophy and atrophy occur frequently as a result of mechanical loading or unloading, with implications for clinical, general, and athletic populations. The effects of muscle hypertrophy and atrophy on force production and joint moments have been previously described. However, there is a paucity of research showing how hypertrophy and atrophy may affect moment arm (MA) lengths. The purpose of this model was to describe the mathematical relationship between the anatomical cross-sectional area (ACSA) of a muscle and its MA length. In the model, the ACSAs of the biceps brachii and brachialis were altered to hypertrophy up to twice their original size and to atrophy to one-half of their original size. The change in MA length was found to be proportional to the arcsine of the square root of the change in ACSA. This change in MA length may be a small but important contributor to strength, especially in sports that require large joint moments at slow joint angular velocities, such as powerlifting. The paradoxical implications of the increase in MA are discussed, as physiological factors influencing muscle contraction velocity appear to favor a smaller MA length for high velocity movements but a larger muscle MA length for low velocity, high force movements.

Highlights

Muscle hypertrophy is a common adaptation to mechanical loading, typically delivered in the form of long-term programs of resistance training
Sugisaki et al (2010) and Akagi et al (2012) described a positive correlation between muscle size and muscle moment arm (MA) length. These findings suggest that larger muscles are likely to benefit from a longer MA and that hypertrophy may lead to increases in MA length and atrophy to decreases in MA length, which may have impacts on the joint moment that go above and beyond alterations in muscle force
Since the relationship between MA length and muscle size is not fully understood, the purpose of this paper is to develop a two-dimensional mathematical model to describe how changes in anatomical cross-sectional area (ACSA) of the proximal elbow flexors change MA length, θp, and joint moment contributions

Summary

Introduction

Muscle hypertrophy is a common adaptation to mechanical loading, typically delivered in the form of long-term programs of resistance training. Muscle atrophy is a response to disuse that occurs quickly following even short periods of mechanical unloading, which can be as little as one week of strict bed rest (Dirks et al, 2015). Both muscle hypertrophy and atrophy have important implications for clinical, general, elderly and athletic populations, because of the relationship between measures of muscle mass or size and a range of performance and health outcomes. Reports have been made of increasing mortality or re-hospitalization rates in individuals with lower levels of muscle mass (Greening et al, 2014; Streja et al, 2011; Weijs et al, 2014)

Objectives

Methods

Results

Discussion

Conclusion