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.
Pathophysiology
There are multiple theories proposed to explain the mechanisms of muscle changes of sarcopenia including changes in satellite cell recruitment, changes in anabolic signalling, protein oxidation, inflammation, and developmental factors. The pathologic changes of sarcopenia include a reduction in muscle tissue quality as reflected in the replacement of muscle fibers with fat, an increase in fibrosis, changes in muscle metabolism, oxidative stress, and degeneration of the neuromuscular junction.The distribution of muscle fibers types also changes in sarcopenic muscle causing a decrease in type II muscle fibers, or "fast twitch," with little to no decrease in type I muscle fibers, or "slow-twitch" muscle fibers. Deinervated type II fibers are often converted to type I fibers by reinnervation by slow type I fiber motor nerves.The failure to activate satellite cells upon injury or exercise is also thought to contribute to the pathophysiology of sarcopenia. Additionally, oxidized proteins can lead to a buildup of lipofuscin and cross-linked proteins causing an accumulation of non-contractile material in the skeletal muscle and contribute to sarcopenic muscle.An apparent protective factor is sufficient levels of the protein BNIP3, which prevents cells buildup of damaged mitochondria. Deficiency of BNIP3 leads to muscle inflammation and atrophy. Diagnosis
Multiple diagnostic criteria have been proposed by various expert groups and continues to be an area of research and debate.