Aging attenuates vascular and metabolic plasticity but does not limit improvement in muscle Vo2 max

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Abstract
The interactions between exercise, vascular and metabolic plasticity, and aging have provided insight into the prevention and restoration of declining whole body and small muscle mass exercise performance known to occur with age. Metabolic and vascular adaptations to normoxic knee-extensor exercise training (1 h 3 times a week for 8 wk) were compared between six sedentary young (20 ± 1 yr) and six sedentary old (67 ± 2 yr) subjects. Arterial and venous blood samples, in conjunction with a thermodilution technique facilitated the measurement of quadriceps muscle blood flow and hematologic variables during incremental knee-extensor exercise. Pretraining, young and old subjects attained a similar maximal work rate (WRmax) (young = 27 ± 3, old = 24 ± 4 W) and similar maximal quadriceps O2 consumption (muscle V̇o2 max) (young = 0.52 ± 0.03, old = 0.42 ± 0.05 l/min), which increased equally in both groups posttraining (WRmax, young = 38 ± 1, old = 36 ± 4 W, Muscle V̇o2 max, young = 0.71 ± 0.1, old = 0.63 ± 0.1 l/min). Before training, muscle blood flow was ∼500 ml lower in the old compared with the young throughout incremental knee-extensor exercise. After 8 wk of knee-extensor exercise training, the young reduced muscle blood flow ∼700 ml/min, elevated arteriovenous O2 difference ∼1.3 ml/dl, and increased leg vascular resistance ∼17 mmHg·ml–1·min–1, whereas the old subjects revealed no training-induced changes in these variables. Together, these findings indicate that after 8 wk of small muscle mass exercise training, young and old subjects of equal initial metabolic capacity have a similar ability to increase quadriceps muscle WRmax and muscle V̇o2 max, despite an attenuated vascular and/or metabolic adaptation to submaximal exercise in the old.