Eight healthy and regularly physically active men, 44-69 years old, performed one- and two-legged dynamic knee extension exercise at increasing work intensities, including one leading to exhaustion. Leg blood Bow increased linearly in relation to work rate, reaching a peak value of 5.1 +/- 0.4 l min(-1). With a mean weight of quadriceps femoris of 2.2 +/- 0.1 kg, a peak perfusion of 2.3 +/- 0.1 l kg(-1) min(-1) was attained. The maximal leg oxygen uptake was 0.72 +/- 0.07 1 min(-1) (0.33 +/- 0.03 l kg(-1) min(-1)). At submaximal work the elevation in limb oxygen uptake accounted for between 70 and I00% of the rise in pulmonary oxygen uptake. Comparing two- with one-legged knee extension the cardiac output was 1.5 l min(-1) higher at each work level, reaching 13.7 +/- 0.7 and 12.3 +/- 1.0, respectively at exhaustion, leaving 3.5 and 7.2 l min(-1) of blood how to the remaining body (cardiac output-leg blood flow). The mean arterial pressure was 119 +/- 5 mmHg at rest and increased to 155 mmHg for both test modes at the maximal work rate. The femoral arterial and venous plasma concentrations of lactate, ammonia and noradrenaline were significantly higher for two-legged as compared with one-legged exercise at the maximal load performed. However, the rate of release per leg, for both lactate and ammonia, did not differ between the two test conditions. It is concluded that physically active middle-aged men, with a well-retained muscle mass, can maintain a high skeletal muscle perfusion, similar to that of young males. However, the blood flow is achieved with a higher mean arterial pressure and an elevated sympathetic activity, as reflected by noradrenaline in plasma and spillover from the exercising limb.
