The Physiology and Biochemistry of Skeletal Muscle Atrophy as a Function of Age

Abstract

The skeletal muscles are an important entity in the proper function of aging animals and humans. Studies have shown that until humans are 60-70 years old, age-related changes in muscle function and structure are relatively small, while after 70 years, these alterations are accelerated considerably. Factors responsible for the "aging" of skeletal muscles are complex and include intrinsic biochemical changes in muscle metabolism, changes in the distribution and size of muscle fibers, and a general loss of muscle mass. In addition, other factors like the control of muscle contraction by the motor neural system and the influence of external conditions such as exercise, immobility, nutrition and others may also contribute to the age-related decrease in muscle functions. Studies have shown that with age there is some loss of peripheral motor neurons, reduction in the number of motor units, alterations in the neuromuscular junctions, and selective denervation of Type II muscle fibers. These findings led to the concept of denervation atrophy of skeletal muscles as one of the major mechanisms for muscle degeneration in old age. However, it should be emphasized that the extent of age-related changes varies from muscle to muscle, and some do not seem to be affected by age. For example, it has been shown recently, in animal studies, that weight-bearing muscles are much more susceptible to senescent processes than non-weight-bearing muscles. More work is needed to clarify the contributions of the various factors, especially the role of muscle training in alleviating the symptoms of age-related muscle atrophy.

Sarcopenia, obesity, and inflammation—results from the Trial of Angiotensin Converting Enzyme Inhibition and Novel Cardiovascular Risk Factors study

“…Our findings also showed that the association of higher concentrations of inflammatory markers with sarcopenia was mostly explained by the concurrent presence of adipose tissue. Sarcopenia, which is the involuntary loss of skeletal muscle that occurs with advancing age (1), is characterized by a decrease of muscular strength and endurance and is significantly associated with a loss of autonomy in older persons (1,27). In a review, Roubenoff (10) suggested the presence of a vicious cycle between fat gain and loss of muscle, which act synergistically to lead to physical disability (2).…”

Development-related expression patterns of protein-coding and miRNA genes involved in porcine muscle growth

“…Moreover, FOXO1 can reduce muscle mass and fiber atrophy (Xu et al, 2012), and MURF ubiquitinates and degrades myosin heavy chains (Clarke et al, 2007); all of these changes negatively regulate muscle mass. Skeletal muscle shows remarkable changes in metabolism with increasing age, which is reflected by the distribution and size of the muscle fibers and a general deceleration in muscle mass gain (Carmeli and Reznick, 1994). We found that the expression patterns of MURF and FOXO1 were upregulated with age, suggesting a decrease in the deposition of protein with increasing age.…”

The Influence of Aging on Balance Function in Terms of the Foot Electromyographic Reaction Time

“…Among several types of muscle, the activity of type II fibers, fast muscles, becomes dominant when a fast contraction is required 13,20) , such as that required for the measurement in this study. Age-related muscle atrophy involving a decrease in the diameter of type II muscle fibers (atrophy) has been reported to markedly develop in the elderly aged over 85 4,24) . Based on these findings, it may be appropriate to explain the delay in MT in this study as a decreased muscle contraction velocity as a result of age-related atrophy chiefly of type II muscle fibers and a decline in muscle strength.…”