Human skeletal muscle-specific atrophy with aging: a comprehensive review

Abstract

Age-related skeletal muscle atrophy appears to be a muscle group-specific process, yet only a few specific muscles have been investigated and our understanding in this area is limited. This review provides a comprehensive summary of the available information on age-related skeletal muscle atrophy in a muscle-specific manner, nearly half of which comes from the quadriceps. Decline in muscle-specific size over ~50yr of aging was determined from 47 cross-sectional studies of 982 young (~25yr) and 1,003 old (~75yr) individuals and nine muscle groups: elbow extensors (-20%, -0.39%/yr), elbow flexors (-19%, -0.38%/yr), paraspinals (-24%, -0.47%/yr), psoas (-29%, -0.58%/yr), hip adductors (-13%, -0.27%/yr), hamstrings (-19%, -0.39%/yr), quadriceps (-27%, -0.53%/yr), dorsiflexors (-9%, -0.19%/yr), and triceps surae (-14%, -0.28%/yr). Muscle-specific atrophy rate was also determined for each of the subcomponent muscles in the hamstrings, quadriceps, and triceps surae. Of all the muscles included in this review, there was more than a 5-fold difference between the least (-6%, -0.13%/yr, soleus) to the most (-33%, -0.66%/yr, rectus femoris) atrophying muscles. Muscle activity level, muscle fiber type, sex, and timeline of the aging process all appeared to have some influence on muscle-specific atrophy. Given the large range of muscle-specific atrophy and the large number of muscles that have not been investigated, more muscle-specific information could expand our understanding of functional deficits that develop with aging and help guide muscle-specific interventions to improve the quality of life of aging women and men.

Slow or fast: Implications of myofibre type and associated differences for manifestation of neuromuscular disorders

“…These changes can influence the manifestation and progression of various neuromuscular disorders across the lifespan. 6.1.1 | Growth, energy metabolism, and onset of different neuromuscular diseases Many studies of skeletal muscles in humans and animal models use young adults. However, to accurately interpret the involvement of slow and fast myofibres in normal and diseased situations at different ages, it is important to consider the intrinsic age-related changes that occur in muscles.…”

“…The extent of sarcopenia varies between the different muscles throughout the human body. 6 Many of these changes (e.g., hormonal) fall outside the scope of this review but will clearly influence the onset and progression of many neuromuscular disorders. The important impact on slow and fast myofibres of age-related changes in the extrinsic components of muscle tissue, including neurons, ECM, and vasculature, has already been broadly discussed (see Section 5).…”

“…Pathological features often include variations in muscle fibre (myofibre) size, sometimes with preferential atrophy or loss of one (slow or fast) myofibre type, loss of myofibres due to some form of death (e.g., myonecrosis) or denervation, infiltration of inflammatory cells, and replacement of myofibres by fat and connective tissue. 2,3 With about 640 different skeletal muscles (usually paired bilaterally) in the human body, there are striking differences in the size, shape, loading, function, and composition: all muscles are clearly not the same (discussed in Grounds and Shavlakadze, 4 Randolph and Pavlath, 5 and Naruse et al 6 ). A notable feature of many neuromuscular disorders is that not all muscles are affected equally.…”

“…In the context of differential impact on major muscle groups, in normal ageing, the loss of muscle mass and function (sarcopenia) is pronounced initially in lower limb muscles, compared with upper limbs and other muscles. 6,7 For various inherited diseases, while a particular gene defect is present in all muscle nuclei (myonuclei), the pathology may manifest mainly in specific muscles. This is demonstrated by a diversity of muscle diseases (myopathies) that feature progressive loss of muscle mass and function, broadly termed muscular dystrophies.…”

“…With about 640 different skeletal muscles (usually paired bilaterally) in the human body, there are striking differences in the size, shape, loading, function, and composition: all muscles are clearly not the same (discussed in Grounds and Shavlakadze, 4 Randolph and Pavlath, 5 and Naruse et al 6 ). A notable feature of many neuromuscular disorders is that not all muscles are affected equally.…”