Biological Possible biological contributors to<unk>  include the nervous system’s deteriorating control of voluntary skeletal muscle activation and a decreased number of functioning motor units. The nervous system's lowered ability to stimulate a full muscle contraction subsequently leads to loss of muscle strength and power. A study by Harridge et al. also showed that all<unk>  subjects had incomplete voluntary activation during a maximum contraction (69-93%), suggesting that loss of voluntary muscle activation plays an important role in the loss of muscle strength. Studies involving the dissection of cadavers have uncovered a 43% decrease in the cell body size of neurons found in the premotor cortex compared to those of younger adults. New studies have recently verified this finding in living subjects using high resolution magnetic resonance imaging (MRI). Recent evidence suggests that aging is also related to the loss of myelinated nerve fiber length and the mass of white matter, with individuals losing approximately 45% of total nerve fiber length as they age. These changes that develop through the aging process affect the connectivity of the cortex within itself as well as its connectivity to the rest of the central nervous system. Another potential contributor to<unk>  is a disruption of the process that converts electrical signal given for muscular activation into an actual contraction. Particularly, impairments in the release of calcium (Ca2+) from the sarcoplasmic reticulum have been suggested to explain why decreased muscle quality is so prevalent in older adults. A systematic review on the literature regarding the relationship between type II muscle fiber loss and aging found that the total number of fibers in the vastus lateralis decreases tremendously with age. This decline is first observed around 25 years of age and proceeds at an even greater rate throughout the lifespan. The age-related Type II fiber loss highlights the negative effect of aging on muscle power. Nutritional It has also been suggested that nutritional factors may contribute to the onset of<unk> . It has been proposed that low levels of Vitamin E, carotenoids, and selenium are associated with lower levels of muscle strength. The activity of Vitamin D receptors on muscle has been found to decrease with aging. These receptors initiate the nuclear response leading to De novo synthesis of proteins. However, the results of multiple studies on the relation between Vitamin D and muscle strength have been highly controversial, making the effect of Vitamin D on muscle strength in need of further investigation. The Recommended Dietary Allowance (RDA) for protein is not very clear for older adults; it may underestimate the amount of protein needed to maintain optimal physical function with age. A study by Houston and colleagues showed how decreased protein intake may increase the risk of developing mobility limitations later on. The study revealed that 35.4% out of 43% of participants who consumed a significantly smaller amount of protein (mean: 0.38 g/kg body weight/d) than the RDA (0.8 g/kg body weight/d) developed mobility limitations over the 6 year follow-up. In contrast, participants who consumed more protein (mean: (≥1.0 g/kg body weight/d) than the RDA had a lower risk of developing mobility limitations over the 6 year follow-up.
Dynapenia
Neuroglycopenia
Neuromyotonia
Synkinesis
Paresis
Myotonia
Diplophonia
Cynanthropy