A progressive decline in maximal O2 consumption (V̇(O2 max)) expressed traditionally as per kilogram body weight generally occurs with advancing age. To investigate the extent to which this decline could be attributable to the age-associated loss of metabolically active tissue, i.e., muscle, we measured 24-h urinary creatinine excretion, an index of muscle mass, in 184 healthy nonobese volunteers, ages 22-87 yr, from the Baltimore Longitudinal Study of Aging who had achieved a true V̇(O2 max) during graded treadmill exercise. A positive correlation was found between V̇(O2 max) and creatinine excretion in both men (r = 0.64, P < 0.001) and women (r = 0.47, P < 0.001). As anticipated, V̇(O2 max) showed a strong negative linear relationship with age in both men and women. Creatinine excretion also declined with age in men and women. When V̇(O2 max) was normalized for creatinine excretion, the variance in the V̇(O2 max) decline attributable to age declined from 60 to 14% in men and from 50 to 8% in women. Thus comparing the standard age regression of V̇(O2 max) per kilogram body weight with that in which V̇(O2 max) is normalized per milligram creatinine excretion, the decline in V̇(O2 max) between a hypothetical 30 yr old and a 70 yr old was reduced from 39 to 18% in men and from 30 to 14% in women. We conclude that in both sexes, a large portion of the age-associated decline in V̇(O2 max) in non-endurance-trained individuals is explicable by the loss of muscle mass, which is observed with advancing age.
ASJC Scopus subject areas
- Physiology (medical)