Calls for increasing daily physical activity in all segments of the population from early childhood through old age are common in discussions of public health policy Games, 1995; US Public Health Service, 1990). The increased energy expenditure that accompanies regular physical activity contributes to more efficient function ofvarious systems, weight maintenance, reduced risk of several degenerative diseases, reduced risk of mortality, and overall improvement of quality of life (Bouchard, Shepard, & Stephens, 1994). Habits of and attitudes towards physical activity developed during childhood are assumed to continue through adolescence into adulthood (Livingstone, 1994; Meredith & Dwyer, 1991; Simons-Morton, Parcel, O'Hara, Blair, & Pate, 1988). Physical fitness is a related construct, and it is also often assumed that the more habitually active are more fit and that the relationship is causal (Corbin & Pangrazi, 1993; Livingstone, 1994). The objective of this overview is to evaluate the tracking of physical activity and physical fitness from childhood through adulthood. This period encompasses a major portion of the lifespan. The lifespan features several transitions which are temporally arranged (eg, the biological and psychosocial transition of puberty, the transition into adulthood and the work force, marriage, child rearing, occurrence of disease, etc.). Earlier events in the lifespan may condition later events so that patterns of constancy and change, correlations, and risks can be identified. Physical activity and physical fitness occur within the context of lifespan transitions and cannot be viewed in isolation. Fetal and early childhood conditions should not be overlooked in the context oflater health and fitness status. There is an apparent link between low birth weight and adult hypertension, coronary heart disease, and syndrome-X: diabetes mellitus, hypertension and hyperlipidemia (Barker, 1992). The working hypothesis for syndrome-X is that the fetal environment impacts or" programs" the progression of circumstances related to increased insulin resistance, which includes a central or