Muscular strength can be measured by cable tensiometry, non-motorized dynamometry (e.g., handgrip dynamometer), motorized dynamometry, or with free weights or exercise machines. Advantages and disadvantages of each are discussed. Cross-sectional studies indicate that isometric and concentric strength levels peak between the second and third decade, remain unchanged until the fourth or fifth decade, and start to decline from about the fifth decade at a rate of 12% to 15% per decade until the eighth decade in men. Greater strength losses in both men and women have been suggested from the few longitudinal studies available on this topic. However, concentric strength levels in women tend to peak sooner, start to decline earlier, and decrease at a slightly slower rate than men. Age- and inactivity-induced sarcopenia explains some but not all of the losses in strength with age. There is a need to determine the separate roles of disease, inactivity, and normal aging on these losses. New findings from the Baltimore Longitudinal Study of Aging suggest a preservation of eccentric strength levels with age in women.