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

To determine the effect of age on quadriceps muscle blood flow (QMBF), leg vascular resistance (LVR), and maximum oxygen uptake (Q(V)over dotO(2 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 (WRmax) ( young: 25.2 +/- 2.1 and old: 24.1 +/- 4 W) and Q(V)over dotO(2 max) ( young: 0.52 +/- 0.03 and old: 0.42 +/- 0.05 l/min). QMBF during KE was lower in old subjects by similar to500 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 similar to142% 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, similar to80% higher LVR in the old at 50% WR and similar to40% higher LVR in the old at WRmax ( 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 similar to36% 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 WRmax and Q(V)over dotO(2 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.