Physical fitness and blood pressure: the role of age.

Most epidemiologic studies have shown an inverse relationship between resting blood pressure and usual levels of physical fitness or activity. The inference is that fitness lowers blood pressure. However, maximum oxygen uptake (VO2max--a widely accepted measure of fitness) and blood pressure are both correlated with age; young people usually have lower pressures and higher VO2max (ml X kg-1 X min-1). Systolic and diastolic pressures were measured and maximal oxygen uptake was estimated in 184 men and 227 women aged 18-65 years who were randomly selected as part of a cardiovascular risk factor survey conducted in two New England cities between April 1981 and March 1982. Initially, both measures of blood pressure were strongly and inversely correlated with estimated maximal oxygen uptake. However, when the effects of age were partialed out, the strength of the correlations decreased sharply for both males and females. The proportion of the variance in systolic pressure explained by maximal oxygen uptake decreased from 9.6 to 0.8% for males and 21.2 to 2.3% for females. Similar decreases were demonstrated for diastolic pressure in males (14.4 to 2.9%) and females (20.3 to 2.3%). These data indicate that the frequently observed relationship between fitness and blood pressure is strongly influenced by age. Future research to specifically examine the effects of physical activity and of physical fitness on blood pressure is needed.