Sarcopenia may also cause reduced strength, functional decline and increased risk of falling. Sarcopenia may also have no symptoms until it is severe and is often unrecognized. Research has shown, however, that hypertrophy may occur in the upper parts of the body to compensate for this loss of lean muscle mass Therefore, one early indicator of the onset of sarcopenia can be significant loss of muscle mass in the anterior thigh and abdominal muscles. Causes
There are many proposed causes of sarcopenia and it is likely the result of multiple interacting factors. Understanding of the causes of sarcopenia is incomplete, however changes in hormones, immobility, age-related muscle changes, nutrition and neurodegenerative changes have all been recognized as potential causative factors.The degree of sarcopenia is determined by two factors: initial amount of muscle mass and rate at which muscle mass declines. Due to variations in these factors across the population, the rate of progression and the threshold at which muscle loss becomes apparent is variable. Immobility dramatically increases the rate of muscle loss, even in younger people. Other factors that can increase rate of progression of sarcopenia include decreased nutrient intake, low physical activity, or chronic disease. Additionally, epidemiological research has indicated that early environmental influences may have long-term effects on muscle health. For example, low birth weight, a marker of a poor early environment, is associated with reduced muscle mass and strength in adult life.
Supplements
A component of sarcopenia is the loss of ability for aging skeletal muscle to respond to anabolic stimuli such as amino acids, especially at lower concentrations. However, aging muscle retains the ability of an anabolic response to protein or amino acids at larger doses. Supplementation with larger doses of amino acids, particularly leucine has been reported to counteract muscle loss with aging. Exercise may work synergistically with amino acid supplementation.β-hydroxy β-methylbutyrate (HMB) is a metabolite of leucine that acts as a signalling molecule to stimulate protein synthesis. It is reported to have multiple targets, including stimulating mTOR and decreasing proteasome expression. Its use to prevent the loss of lean body mass in older adults is consistently supported in clinical trials. More research is needed to determine the precise effects of HMB on muscle strength and function in this age group. Epidemiology
The prevalence of sarcopenia depends on the definition used in each epidemiological study. Estimated prevalence in people between the ages of 60-70 is 5-13% and increases to 11-50% in people more than 80 years of age. This equates to >50 million people and is projected to affect >200 million in the next 40 years given the rising population of older adults. Public health impact
Sarcopenia is emerging as a major public health concern given the increased longevity of industrialized populations and growing geriatric population. Sarcopenia is a predictor of many adverse outcomes including increased disability, falls and mortality. Immobility or bed rest in populations predisposed to sarcopenia can cause dramatic impact on functional outcomes.