Effects of dynamic exercise on mean blood velocity and muscle interstitial metabolite responses in humans

We examined the effects of dynamic one-legged knee extension exercise on mean blood velocity (MBV) and muscle interstitial metabolite concentrations in healthy young subjects (n = 7). Femoral MBV (Doppler), mean arterial pressure (MAP) and muscle interstitial metabolite (adenosine, lactate, phosphate, K+, pH, and H+; by microdialysis) concentrations were measured during 5 min of exercise at 30 and 60% of maximal work capacity (W-max). MAP increased (P < 0.05) to a similar extent during the two exercise bouts, whereas the increase in MBV was greater (P < 0.05) during exercise at 60% (77.00 +/- 6.77 cm/s) compared with 30% W-max (43.71 +/- 3.71 cm/s). The increase in interstitial adenosine from rest to exercise was greater (P < 0.05) during the 60% (0.80 +/- 0.10 <mu>M) compared with the 30% W-max bout (0.57 +/- 0.10 muM). During exercise at 60% W-max interstitial K+ rose at a greater rate than during exercise at 30% W-max (P < 0.05). However, pH increased (H+ decreased) at similar rates for the two exercise intensities. During exercise, interstitial lactate and phosphate increased (P < 0.05) with no difference observed between the two intensities. After 5 min of recovery, MBV decreased to baseline levels after exercise at 30% Wm,, (4.12 +/- 1.10 cm/s), whereas MBV remained above baseline levels after exercise at 60% W-max (Delta 19.46 +/- 2.61 cm/s; P < 0.05). MAP and interstitial adenosine, K+, pH, and H+ returned toward baseline levels. However, interstitial lactate and phosphate continued to increase during the recovery period. Thus an increase in exercise intensity resulted in concomitant changes in MBV and muscle interstitial adenosine and K+, whereas similar changes were not observed for MAP or muscle interstitial pH, lactate, or phosphate. These data suggest that K+ and/or adenosine may play an active role in the regulation of skeletal muscle blood flow during exercise.