title: Perfusion heterogeneity does not explain excess muscle oxygen uptake during variable intensity exercise.
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.
authors.affiliation: Swedish Winter Sports Research Centre, Department of Health Sciences, Mid Sweden University, Ostersund, Sweden. marko.laaksonen@miun.se
authors.forename: Marko S
authors.initials: MS
authors.lastname: Laaksonen
authors.forename: Glenn
authors.initials: G
authors.lastname: Björklund
authors.forename: Ilkka
authors.initials: I
authors.lastname: Heinonen
authors.forename: Jukka
authors.initials: J
authors.lastname: Kemppainen
authors.forename: Juhani
authors.initials: J
authors.lastname: Knuuti
authors.forename: Heikki
authors.initials: H
authors.lastname: Kyröläinen
authors.forename: Kari K
authors.initials: KK
authors.lastname: Kalliokoski
mesh_terms: D000328:Adult; D001794:Blood Pressure; D004576:Electromyography; D015444:Exercise; D006339:Heart Rate; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000000981:diagnostic imaging / Q000378:metabolism*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D055420:Perfusion Imaging / Q000379:methods; D049268:Positron-Emission Tomography; D012039:Regional Blood Flow; D055070:Resistance Training; D013997:Time Factors; D055815:Young Adult
chemical_list: D010100:Oxygen