The decline in muscle strength with aging may be attributed to the loss of muscle mass (decrease in skeletal muscle fiber number, decrease in muscle fiber size), to some alteration of the muscle's capacity to generate force (recruitment of skeletal muscle fibers, force/cross-bridge), or to a combination of these two mechanisms, thus making older muscle intrinsically weaker. Men, from 24-80 years, lose approximately 40% of total skeletal muscle mass. Total muscle cross-sectional area peaks at the age of 24 years. From 24-50 years of age, 10% of the total muscle cross-sectional area is lost. Thereafter, muscle atrophy is accelerated so that between 50 and 80 years of age, an additional 30% of total muscle cross-sectional area is lost. The decline in muscle mass may account, in part, for the decline in muscle strength seen with aging. Interestingly, postural muscles, such as the quadriceps and soleus, show age-related atrophy to a greater extent than non-postural muscles.
The age-related atrophy of the human vastus lateralis muscle is a function of equivalent losses in the numbers of both Type I and II muscle fibers, and a preferential greater loss of Type II fiber cross-section. No reduction in the mean cross-sectional area of Type I fibers has been observed. This may account, in part, for the slowing of contraction times with aging. Muscle fiber loss is non significant (about 5%) from the ages of 24-52 years. However, a dramatic 35% loss of muscle fibers has been observed in human subjects from ages 52-77 years. Thus, some aging-related atrophy seems to be due to loss of muscle fibers, as well as to the decreased fiber cross-sectional area.
Finally, the prevalence of common chronic diseases in the elderly population is high. Illnesses affecting the musculoskeletal system, the heart and circulation, and the kidneys may be associated with muscle atrophy and weakness. The loss of muscle strength may be a result of the pathological process itself or the accompanying reduction in physical activity. In conclusion, a gradual loss of strength can be attributed to alterations in skeletal muscle mechanical and morphological properties. Further understanding of age-related muscle changes could enable the development of interventions that will slow the decline of muscle function with aging. Older persons who remain physically active have only moderate losses in skeletal muscle mass, but exactly how much of the decrease in muscle is a consequence of aging or a reduction in physical activity or specific types of activity, or both, is currently unknown.
Training has effects on the physical capacity of older persons irrespective of whether they trained in youth. Older adults have much to gain by exercising. Taekwondo instructors can teach their older students how to safe and effective train.