Aetiology

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SarcopeniePublished by: SBGGLast published: 2021SarcopeniePublished by: BVGGLast published: 2021

Several risk factors have been found to predict the development of sarcopenia, including:

  • Advanced age - sarcopenia is typically a condition of older people. With ageing there are multiple biological changes, such as neuromuscular junction degeneration, hormonal changes, and a decreased metabolic and renewal capacity of the muscle, which puts people at a higher risk of developing the condition.

  • Sedentary lifestyle - insufficient physical activity is a risk factor for sarcopenia.[9] Physical activity is the primary effective strategy to increase muscle mass and strength and to improve gait speed.[5]

  • Low or high body mass index (BMI) - BMI is an anthropometric measurement based on weight (in kg) divided by height (in m) squared (kg/m²). It is used to diagnose sarcopenic obesity as it is an easy to perform estimation of adiposity as well as of cardiovascular risk. By the World Health Organization definition, any value ≥30 is diagnostic of obesity and a BMI of below 18.5 is considered underweight.[10] Both low and high BMI are associated with sarcopenia.

  • Low protein intake - insufficient protein intake can lead to loss of lean body mass, increasing the risk of sarcopenia.[11] Protein intake may need to be at levels higher than the current recommended dietary allowance of 0.8 g/kg/day to maintain muscle health in a person at risk of sarcopenia.[12]

  • A history of falls - falls can increase sedentary behaviour and fear of movement, increasing the loss of muscle mass and strength.[13]

  • Smoking - a meta-analysis of 12 studies (22,515 patients) found that cigarette smoking as an isolated factor may contribute to the development of sarcopenia.[14] However, the results of individual studies were largely inconsistent due to differing methods for measuring the main variables.

Many chronic diseases contribute to musculoskeletal weakness and deterioration of physical performance, such as chronic obstructive pulmonary disease, chronic heart failure, renal impairment, and cancer.[15] This is defined as secondary sarcopenia.[16]

Pathophysiology

The pathophysiology of sarcopenia is multifactorial and complex. Typically the amount of type II rather than type I muscle fibres is reduced in people with sarcopenia.[17] A combination of the following factors may contribute to sarcopenia:[18][19]

  • Unbalanced rates of muscle protein synthesis and breakdown

  • Anabolic resistance of dietary protein translating into lower rates of muscle protein synthesis

  • Reduced spinal motor neurons

  • Neuromuscular junction alterations with ageing

  • Anabolic hormonal decline

  • Mitochondrial dysfunction

  • Chronic inflammation

  • Oxidative stress

  • Increased myostatin signalling.

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