Muscle mass and strength are critical components for maintaining physical function, here Dr Vera C Mazurak from the University of Alberta explains why.
Muscle mass and strength are critical for maintaining physical function, mobility and vitality. Sarcopenia was first coined to represent the loss of muscle that normally occurs during the aging process. Loss of muscle as a result of disease can be referred to as myopenia, keeping in mind that many older individuals may have lost muscle due to co-morbidities (chronic disease), recent hospitalisation, or medications. Regardless of the cause, or how it is defined, individuals with severe muscle wasting have difficulty performing daily tasks.
Disability, poor functional capacity and shorter survival contribute to high costs as a result of reduced quality of life, increased caregiver burden and health service utilisation. It has been revealed that low muscle mass is prevalent in every body size. Function of muscle is dependent in part on muscle quality. Muscle tissue normally contains only small amounts of fat not intended for long-term lipid storage, but rather as a short term energy source for skeletal muscle contraction. Myosteatosis, characterised by excess deposition of fat into muscle, is considered to be a pathological phenomenon. The more fat a muscle contains, the less dense it becomes, and low density muscle is poor quality muscle. Low muscle density has been described in conditions of aging, detraining, various types of muscle atrophy, insulin resistance, Type 2 diabetes and most recently, cancer. Both low muscle mass and myosteatosis have been identified to increase the risk of poor function and death in a variety of patient populations.
The causes of myopenia and myosteatosis are multifactorial and may share common pathways for development. The complexity of relationships between various tissues is emerging. There is communication (cross-talk) between tissues through the release of mediators from one organ system to another in response to physiological stimuli. Involvement of other tissues to alter amount and quality of muscle adds several orders of complexity to the problems of myosteatosis and myopenia. Many underlying factors contribute to a decline in muscle health, including catabolic humoral mediators (i.e. pro-inflammatory cytokines), anabolic failure (i.e. insulin insensitivity) and activation of proteolytic systems.
Finding a treatment for low muscle mass is on the agenda of many pharmaceutical companies. To date, there are no approved drugs to reverse muscle loss, however several phase 2 and 3 trials are in progress investigating promising potential treatments for muscle loss that occurs during aging and disease.
The ability to modify muscle wasting and intramuscular fat accumulation has a broad scope of application to aging, diabetes, obesity and various forms of muscle atrophy, which share these common features. While treatment for these conditions remains limited, a number of mechanisms may contribute to the ability various drugs and nutrients to alter body composition, however, a more complete understanding of the features of the muscle characterised by wasting and fat infiltration is required.
Dr Vera C Mazurak
Phd Nutrition and Metabolism
University of Alberta
Tel: +1 78 04 92 80 48