Live strong and prosper: the importance of skeletal muscle strength for healthy ageing

Abstract

Due to improved health care, diet and infrastructure in developed countries, since 1840 life expectancy has increased by approximately 2 years per decade. Accordingly, by 2050, a quarter of Europe's population will be over 65 years, representing a 10 % rise in half a century. With this rapid rise comes an increased prevalence of diseases of ageing and associated healthcare expenditure. To address the health consequences of global ageing, research in model systems (worms, flies and mice) has indicated that reducing the rate of organ growth, via reductions in protein synthetic rates, has multi-organ health benefits that collectively lead to improvements in lifespan. In contrast, human pre-clinical, clinical and large cohort prospective studies demonstrate that ageing leads to anabolic (i.e. growth) impairments in skeletal muscle, which in turn leads to reductions in muscle mass and strength, factors directly associated with mortality rates in the elderly. As such, increasing muscle protein synthesis via exercise or protein-based nutrition maintains a strong, healthy muscle mass, which in turn leads to improved health, independence and functionality. The aim of this review is to critique current literature relating to the maintenance of muscle mass across lifespan and discuss whether maintaining or reducing protein synthesis is the most logical approach to support musculoskeletal function and by extension healthy human ageing.

Keywords: Health; Physiology; Protein metabolism; Protein synthesis; Skeletal muscle; Strength.

Fig. 1

Loss of skeletal muscle size and quality occurs during healthy ageing. Skeletal muscle cross sectional area (CSA) declines across lifespan (a) with a preferential decline observed in type 2 fibres (b). Representative MRI images depict skeletal muscle architecture in young (c), old-inactive (d) and old-active (e) males. a and b are adapted from (Lexell 1995). Text represents subject characteristics relating to the images in c–e

Fig. 2

Skeletal muscle strength and cardiorespiratory fitness is associated with healthy ageing. Over the age of 60 years, all cause (a) and cancer-associated (b) mortality is twice as likely in individuals with low compared to high skeletal muscle strength. In addition, irrespective of strength, low cardio-respiratory fitness is associated with ~ twice the incidence of all cause mortality (c). Adapted from (Ruiz et al. 2008)

Fig. 3

Ageing is associated with a blunted anabolic response to protein ingestion in humans. Comparative analysis indicates that the protein dose required to maximally stimulate myofibrillar fractional protein synthesis rates in young individuals (a) is 40 % lower than in old individuals (b). Data adapted from (Moore et al. 2015)

Fig. 4

Inhibition of mTORC1 activity using the compound Rapamycin causes anabolic resistance in young, healthy males. Increases in mixed-muscle synthesis rates are blocked following resistance exercise (a) and essential amino acid (EAA) ingestion (b) in young healthy males. a Adapted from (Drummond et al. 2009); b Adapted from (Dickinson et al. 2011)