This is an enhancement over the base ICD-10 classification, which only skeletal system pdf notes the 5th character position within Chapter XVII to identify the anatomical site of occurrence. Severe sarcopenia requires the presence of all three conditions.
Sarcopenia is determined by two factors: initial amount of muscle mass and rate at which aging decreases muscle mass. Due to the loss of independence associated with loss of muscle strength, the threshold at which muscle wasting becomes a disease is different pathologically from person to person. 2 fibers are often converted to type 1 fibers by reinnervation by slow type 1 fiber motor nerves. These cells then differentiate and fuse into the muscle fiber, helping to maintain its function. One theory is that sarcopenia is in part caused by a failure in satellite cell activation. These proteins compile in the skeletal muscle tissue, but are dysfunctional.
This leads to an accumulation of non-contractile material in the skeletal muscle. This helps explain why muscle strength decreases severely, as well as muscle mass, in sarcopenia. Epidemiological research into the developmental origins of health and disease has shown that early environmental influences on growth and development may have long-term consequences for human health. Low birth weight, a marker of a poor early environment, is associated with reduced muscle mass and strength in adult life. One study has shown that lower birth weight is associated with a significant decrease in muscle fibre score, suggesting that developmental influences on muscle morphology may explain the widely reported associations between lower birth weight and sarcopenia. Lack of exercise is thought to be a significant risk factor for sarcopenia.
Master-class athletes maintain a high level of fitness throughout their lifespan. However a gradual loss of muscle fibres begins only at approximately 50 years of age. 2015, HMB supplementation appears to be useful as a treatment for preserving lean muscle mass in older adults. More research is needed to determine the precise effects of HMB on muscle strength and function in this age group.