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

We examined the effects of dynamic one-legged knee extension exercise on me an blood velocity (MBV) and muscle interstitial metabolite concentrations i n healthy young subjects (n = 7). Femoral MBV (Doppler), mean arterial pres sure (MAP) and muscle interstitial metabolite (adenosine, lactate, phosphat e, 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 increas ed (P < 0.05) to a similar extent during the two exercise bouts, whereas th e 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 i nterstitial adenosine from rest to exercise was greater (P < 0.05) during t he 60% (0.80 +/- 0.10 <mu>M) compared with the 30% W-max bout (0.57 +/- 0.1 0 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+ de creased) at similar rates for the two exercise intensities. During exercise , interstitial lactate and phosphate increased (P < 0.05) with no differenc e observed between the two intensities. After 5 min of recovery, MBV decrea sed to baseline levels after exercise at 30% Wm,, (4.12 +/- 1.10 cm/s), whe reas 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 phos phate continued to increase during the recovery period. Thus an increase in exercise intensity resulted in concomitant changes in MBV and muscle inter stitial 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 m uscle blood flow during exercise.