A High-Fat Diet Aggravates the Age-Related Decline in Skeletal Muscle Structure and Function

Hans Degens; Anandini Swaminathan; Jason Tallis

Disclosures

Exerc Sport Sci Rev. 2021;49(4):253-259. 

In This Article

The Effects of Aging on Skeletal Muscle

In humans, aging is associated with a decrease in muscle mass (sarcopenia) that is attributable to fiber loss and atrophy of specifically type II fibers.[8] Particularly, postural and locomotor muscles suffer from sarcopenia, with the muscles of the upper body being less affected.[2] In mice, it has even been reported that the diaphragm may, at least transiently, show an age-related hypertrophy,[9] perhaps in response to the increased cost of breathing in old age. During aging, the loss of muscle mass is accompanied by an increase in fat mass and body mass index (BMI),[8] something also seen in rodents.[9,10]

Clearly, the age-related loss of muscle mass is a significant cause of muscle weakness in old age. It is, however, not the sole explanation as the loss of strength is more than proportional to the loss of mass and results in a lower specific tension (force per muscle cross-sectional area) in muscles from both old humans[8,11] and rodents.[12] Such reductions have also been reported at the single fiber level, although this is not unequivocal, suggesting problems at the myofibrillar level.[2] An age-related slowing of the muscle, due to a combination of an increased volume percentage of slow fibers (as there is selective atrophy of type II fibers) and slowing of, in particular, type I fibers, will aggravate the loss of power on top of that incurred by atrophy.[2]

The significance of a reduced muscle quality is reflected by the observation that it is not so much loss of muscle mass, but rather the age-related loss of power that is linked with reduced balance, mobility, and all-cause mortality.[13] One of the potential causes of a reduced specific tension in muscle fibers is the age-related reduction in myosin concentration,[2] perhaps accompanied by lipid accumulation. However, the lower specific tension in old mouse muscle[14] was not associated with IMCL accumulation in muscle fibers.[9] Perhaps other factors, such as oxidative modifications or glycation of the myosin head, underlie the reduced specific tension and shortening velocity in old age.[2]

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