There are three types of muscle tissue: Visceral, cardiac, and skeletal.
Our understanding of aging muscle is limited in several respects. It is difficult to evaluate studies of a small number of subjects and changing patterns and designs of investigations.
Methods for quantifying longitudinal changes in gross lean muscle mass as well as subcellular adaptations continue to evolve, leading to variable results.
Mitchell et al 27 compared changes in muscle mass as a factor of global changes in body composition with age. Muscle mass decreases with advancing age, with men losing more absolute and relative muscle mass.
This seems to be most prevalent in the seventh decade and beyond. As a result, 70 years of age has been mentioned as the target age for clinical trials addressing sarcopenia. Frontera et al 16 presented one of the more thorough descriptions of aging skeletal muscle mass.
They measured the cross-sectional area of the thigh at 2 time points 12 years apart to help quantify muscle mass changes. These male patients started at The initial cross-sectional area of all thigh muscles measured at a specific portion of the thigh which was reproducible at the second time point was approximately cm2 at the onset of the study, and at completion, 12 years later, was cm2.
Knee extensors and flexors were both significantly smaller and weaker 12 years later. The change in muscle cross-sectional area was an independent predictor of strength at the later time point.
Metabolic Consequences of Aging Evans 11 described metabolic changes of aging as a significant contributor to sarcopenia. These changes include a decrease in muscle protein synthesis but little change in degradation.
This suggests that muscle turnover and repair capacity is likely decreased with age. This occurs in the setting of increasing insulin resistance and higher percentage body fat mass. In conjunction with a decreasing basal metabolic rate, it is clear that these factors all contribute to the decrease in lean body muscle mass.
These interact with decreased physical activity, lower hormone excretion, nutritional deficits, and possibly chronic inflammation, contributing to this complex change in body composition. Muscle, as a highly vascular and metabolically active tissue, is affected by oxygen delivery throughout the body.
Similarly, enzymatic changes in energy production occur with age; anaerobic enzymes seem to remain constant with age, while aerobic energy production is decreased with age. Type I fibers are small, slow-contracting, low-tension output fibers with many mitochondria and aerobic enzymes for energy production Krebs cycle and electron transport chain.
These fibers are highly resistant to fatigue and are capable of metabolizing fat for energy expenditure. Type II fibers are much larger and faster contracting fibers that produce large tension output but fatigue quickly.
While there is no consensus as to the exact numbers, it is clear that aging leads to an increasing percentage of type I fibers compared to type II.
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The changes seen in our muscles as we age are largely the result of loss of muscle cells, decreased size of muscle fibers, and increased muscle stiffn How do my muscles change as I age? Advertisement. Advertisement.
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