Skeletal muscle mitochondrial capacity (mito), tissue blood flow (BF) capacity, and oxygen exchange capacity (e.g., DO2) appear to be well matched. The different skeletal muscle fiber types and muscle remodeled, due to inactivity >(e.g., related to aging or disease) or exercise training, exhibit widely differing aerobics capacities (V̇O2max). Yet, there are remarkably coordinated alterations in these 3 parameters in each of these conditions. With such a balance, there is likely shared control among these parameters in limiting (V̇O2max) of muscle, although this is a matter of considerable debate. The reduction in aerobic capacity in elderly can be improved by submaximal aerobic exercise training; this is related to increases in muscle mitochondria concentration and capillarity, but probably not BF capacity, as this is limited by central cardiovascular function. Thus, exercise-induced biochemical adaptations and angiogenesis occur in the elderly. The increase in muscle capillarity likely contributes to the increased oxygen exchange capacity, typical of endurance type training. The increase in [mito] appears essential to realize the increased in muscle V̇O2max with training and amplifies the rate-limiting influence of the muscle’s oxygen exchange capacity. Further, vascular remodeling induced by exercise in the elderly could be effective at improving flow capacity, if limited by peripheral obstruction. Thus, the limits to aerobic function specific to aged muscle appear most influenced by inactivity, whereas central cardiovascular changes impact whole body performance. Some may consider the aged myocyte as a small, inactive, normal myocyte in need of activity!
R.L. Terjung is with the Department of Biomedical Sciences in the College of Veterinary Medicine, R. Zarzeczny at the time the research was conducted was with the Department of Physiology in the College of Medicine, and H.T. Yang is with the Dalton Cardiovascular Research Center, all at the University of Missouri, Columbia, MO 65211. Zarzeczny is presently with the University of Pedagogics, 4/8 Waszyngtona St., 42-201 Czestochowa, Poland.
Editor’s note: The following article, from the proceedings of the 11th International Conference on the Biochemistry of Exercise, was originally scheduled to appear in the Supplement to Volume 11 of IJSNEM. It appears now at the request of the Supplement’s guest editor, William J. Evans.