The impact of obesity on skeletal muscle strength and structure through adolescence to old age

Abstract

Obesity is associated with functional limitations in muscle performance and increased likelihood of developing a functional disability such as mobility, strength, postural and dynamic balance limitations. The consensus is that obese individuals, regardless of age, have a greater absolute maximum muscle strength compared to non-obese persons, suggesting that increased adiposity acts as a chronic overload stimulus on the antigravity muscles (e.g., quadriceps and calf), thus increasing muscle size and strength. However, when maximum muscular strength is normalised to body mass, obese individuals appear weaker. This relative weakness may be caused by reduced mobility, neural adaptations and changes in muscle morphology. Discrepancies in the literature remain for maximal strength normalised to muscle mass (muscle quality) and can potentially be explained through accounting for the measurement protocol contributing to muscle strength capacity that need to be explored in more depth such as antagonist muscle co-activation, muscle architecture, a criterion valid measurement of muscle size and an accurate measurement of physical activity levels. Current evidence demonstrating the effect of obesity on muscle quality is limited. These factors not being recorded in some of the existing literature suggest a potential underestimation of muscle force either in terms of absolute force production or relative to muscle mass; thus the true effect of obesity upon skeletal muscle size, structure and function, including any interactions with ageing effects, remains to be elucidated.

Keywords: Ageing; Functional limitations; Muscle strength; Obesity; Sarcopenic obesity.

Fig. 1

Representative DEXA scans taken from Tomlinson et al. (2014b) of a (i) young obese female versus young normal weight female and (ii) old obese female versus old normal weight female. Colour key: blue for bone, red for lean tissue, yellow for adipose tissue. (Color figure online)

Fig. 2

Interplay between obesity, inflammation and skeletal muscle. Solid arrows denote events with established evidence. CRP C-reactive protein, HGF hepatocyte growth factor, IL-1β interleukin-1β, IL-6 interleukin-6, IL-8 interleukin-8, IL-10 interleukin-10, IL-1Ra interleukin-1 receptor antagonist, MCP-1, monocyte chemoattractant protein 1, MIF macrophage migration inhibitory factor, NGF nerve growth factor, PGE2 prostaglandin E2, SAA 1 and 2 serum amyloid A proteins 1 and 2, SV stromovascular, TGF-β1 transforming growth factor-β1, TNF-α tumor necrosis factor-α, VEGF vascular endothelial growth factor, IGF-1 insulin-like growth factor-1