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Vascular and metabolic response to isolated small muscle mass exercise: effect of age

Department of Medicine, University of California, San Diego, La Jolla, California 92093-0623

Submitted 19 February 2003 ; accepted in final form 28 April 2003

To determine the effect of age on quadriceps muscle blood flow (QMBF), leg vascular resistance (LVR), and maximum oxygen uptake (Q_{O2 max}), a thermal dilution technique was used in conjunction with arterial and venous femoral blood sampling in six sedentary young (19.8 ± 1.3 yr) and six sedentary old (66.5 ± 2.1 yr) males during incremental knee extensor exercise (KE). Young and old attained a similar maximal KE work rate (WR_max) (young: 25.2 ± 2.1 and old: 24.1 ± 4 W) and Q_{O2 max} (young: 0.52 ± 0.03 and old: 0.42 ± 0.05 l/min). QMBF during KE was lower in old subjects by 500 ml/min across all work rates, with old subjects demonstrating a significantly lower QMBF/W (old: 174 ± 20 and young: 239 ± 46 ml · min^–1 · W^–1). Although the vasodilatory response to incremental KE was 142% greater in the old (young: 0.0019 and old: 0.0046 mmHg · min · ml^–1 · W^–1), consistently elevated leg vascular resistance (LVR) in the old, 80% higher LVR in the old at 50% WR and 40% higher LVR in the old at WR_max (young: 44.1 ± 3.6 and old: 31.0 ± 1.7 mmHg · min · ml^–1)_, dictated that during incremental KE the LVR of the old subjects was never less than that of the young subjects. Pulse pressures, indicative of arterial vessel compliance, were 36% higher in the old subjects across all work rates. In conclusion, well-matched sedentary young and old subjects with similar quadriceps muscle mass achieved a similar WR_max and Q_{O2 max} during incremental KE. The old subjects, despite a reduced QMBF, had a greater vasodilatory response to incremental KE. Given that small muscle mass exercise, such as KE, utilizes only a fraction of maximal cardiac output, peripheral mechanisms such as consistently elevated leg vascular resistance and greater pulse pressures appear to be responsible for reduced blood flow persisting throughout graded KE in the old subjects.

vascular resistance; quadriceps; pulse pressures; O₂ conductance