PHYSIOLOGY OF AGING

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Studies of age changes in physiologic systems have included renal, cardiovascular, and metabolic areas. Renal glomerular filtration rate as estimated by 24 hr creatinine clearance was not related to cardiac performance as estimated by resting or exercise cardiac output. Thus the age differences in renal function cannot be considered either as a marker for age changes in other systems nor as a result of primary changes in the cardiovascular system. Glucose metabolism as assessed by performance on a glucose tolerance test was not related to cognitive performance as assessed either by tests of memory or problem solving when age, education, obesity or disease were taken into account. Cross-sectional and longitudinal analyses agree that grip strength declines at an accelerating rate after age 40. However, the grip strength of a sizable proportion of individuals does not decrease, and this is true even in aged subjects. With advancing age, grip strength deteriorates more than is predicted by the age-related decline in muscle mass.