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Aging attenuates vascular and metabolic plasticity but does not limit improvement in muscle VO_{2 max}

¹Department of Medicine, University of California, San Diego, La Jolla, California 92093-0623; and ²Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, Trondheim, Norway 7491

Submitted 10 November 2003 ; accepted in final form 16 December 2003

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 (WR_max) (young = 27 ± 3, old = 24 ± 4 W) and similar maximal quadriceps O₂ consumption (muscle O_{2 max}) (young = 0.52 ± 0.03, old = 0.42 ± 0.05 l/min), which increased equally in both groups posttraining (WR_max, young = 38 ± 1, old = 36 ± 4 W, Muscle O_{2 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 WR_max and muscle O_{2 max}, despite an attenuated vascular and/or metabolic adaptation to submaximal exercise in the old.

vascular resistance; quadriceps; pulse pressures; O₂ diffusional conductance; exercise training

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