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ABSTRACT: The association between muscle oxygen uptake (VO(2)) and perfusion or perfusion heterogeneity (relative dispersion, RD) was studied in eight healthy male subjects during intermittent isometric (1 s on, 2 s off) one-legged knee-extension exercise at variable intensities using positron emission tomography and a-v blood sampling. Resistance during the first 6 min of exercise was 50% of maximal isometric voluntary contraction force (MVC) (HI-1), followed by 6 min at 10% MVC (LOW) and finishing with 6 min at 50% MVC (HI-2). Muscle perfusion and O(2) delivery during HI-1 (26 +/- 5 and 5.4 +/- 1.0 ml 100 g(-1) min(-1)) and HI-2 (28 +/- 4 and 5.8 +/- 0.7 ml 100 g(-1) min(-1)) were similar, but both were higher (P<0.01) than during LOW (15 +/- 3 and 3.0 +/- 0.6 ml 100 g(-1) min(-1)). Muscle VO(2) was also higher during both HI workloads (HI-1 3.3 +/- 0.4 and HI-2 4.1 +/- 0.6 ml 100 g(-1) min(-1)) than LOW (1.4 +/- 0.4 ml 100 g(-1) min(-1); P<0.01) and 25% higher during HI-2 than HI-1 (P<0.05). O(2) extraction was higher during HI workloads (HI-1 62 +/- 7 and HI-2 70 +/- 7%) than LOW (45 +/- 8%; P<0.01). O(2) extraction tended to be higher (P = 0.08) during HI-2 when compared to HI-1. Perfusion was less heterogeneous (P<0.05) during HI workloads when compared to LOW with no difference between HI workloads. Thus, during one-legged knee-extension exercise at variable intensities, skeletal muscle perfusion and O(2) delivery are unchanged between high-intensity workloads, whereas muscle VO(2) is increased during the second high-intensity workload. Perfusion heterogeneity cannot explain this discrepancy between O(2) delivery and uptake. We propose that the excess muscle VO(2) during the second high-intensity workload is derived from working muscle cells.
Clinical Physiology and Functional Imaging 07/2010; 30(4):241-9. · 1.33 Impact Factor
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ABSTRACT: Because of technical challenges very little is known about absolute myocardial perfusion in humans in vivo during physical exercise. In the present study we applied positron emission tomography (PET) in order to 1) investigate the effects of dynamic bicycle exercise on myocardial perfusion and 2) clarify the possible effects of endurance training on myocardial perfusion during exercise. Myocardial perfusion was measured in endurance-trained and healthy untrained subjects at rest and during absolutely the same (150 W) and relatively similar [70% maximal power output (W(max))] bicycle exercise intensities. On average, the absolute myocardial perfusion was 3.4-fold higher during 150 W (P < 0.001) and 4.9-fold higher during 70% W(max) (P < 0.001) than at rest. At 150 W myocardial perfusion was 46% lower in endurance-trained than in untrained subjects (1.67 +/- 0.45 vs. 3.00 +/- 0.75 ml x g(-1) x min(-1); P < 0.05), whereas during 70% W(max) perfusion was not significantly different between groups (P = not significant). When myocardial perfusion was normalized with rate-pressure product, the results were similar. Thus, according to the present results, myocardial perfusion increases in parallel with the increase in working intensity and in myocardial work rate. Endurance training seems to affect myocardial blood flow pattern during submaximal exercise and leads to more efficient myocardial pump function.
AJP Regulatory Integrative and Comparative Physiology 09/2007; 293(2):R837-43. · 3.34 Impact Factor
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ABSTRACT: The relationships between electromyographic (EMG) activity and force as well as muscle blood flow and work have been well established. However, the association between muscle blood flow and EMG activity remains unsolved. Thus, to test the hypothesis that muscle EMG activity relates to muscle perfusion in different compartments of the quadriceps femoris (QF) muscle, 12 healthy male subjects were studied. During two very submaximal exercise bouts, at different exercise intensities, oxygen labelled radiowater and positron emission tomography were used to measure muscle perfusion. In addition, produced force of knee extensors and muscle EMG activity in the vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) muscles were recorded during both exercise bouts. Although the exercise intensity and average force production was higher during the second exercise bout (38 +/- 15 versus 51 +/- 17 N; P = 0.007), the mean EMG activity was lower (RF; P<0.001) or unchanged (VL; P = 0.722 and VM; P = 0.640). During the second exercise period, perfusion also remained unchanged in the entire QF muscle (P = 0.223) and in its separate muscles (VL, P = 0.703; VM, P = 0.141; RF, P = 0.113) in a group level. However, the individual changes in muscle perfusion were tightly related to changes in muscle EMG activity in VL (r = 0.84; P = 0.002) and VM (r = 0.68; P = 0.015) but poorly in the RF muscle (r = 0.40; P = 0.257). In conclusion, the different associations between muscle perfusion and EMG activity in different QF muscles suggests specific functional role of the vasti muscles and the RF muscle.
Clinical physiology and functional imaging 04/2006; 26(2):99-105. · 1.21 Impact Factor
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ABSTRACT: The effects of dynamic and intermittent isometric knee extension exercises on skeletal muscle blood flow and flow heterogeneity were studied in seven healthy endurance-trained men. Regional muscle blood flow was measured using positron emission tomography (PET) and an [(15)O]H(2)O tracer, and electromyographic (EMG) activity was recorded in the quadriceps femoris (QF) muscle during submaximal intermittent isometric and dynamic exercises. QF blood flow was 61% (P = 0.002) higher during dynamic exercise. Interestingly, flow heterogeneity was 13% (P = 0.024) lower during dynamic compared with intermittent isometric exercise. EMG activity was significantly higher (P < 0.001) during dynamic exercise, and the change in EMG activity from isometric to dynamic exercise was tightly related to the change in blood flow in the vastus lateralis muscle (r = 0.98, P < 0.001) but not in the rectus femoris muscle (r = -0.09, P = 0.942). In conclusion, dynamic exercise causes higher and less heterogeneous blood flow than intermittent isometric exercise at the same exercise intensity. These responses are, at least partly, related to the increased EMG activity.
AJP Heart and Circulatory Physiology 03/2003; 284(3):H979-86. · 3.71 Impact Factor
