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Perfusion heterogeneity does not explain excess muscle oxygen uptake during variable intensity exercise
Author(s) -
Laaksonen Marko S.,
Björklund Glenn,
Hein Ilkka,
Kemppainen Jukka,
Knuuti Juhani,
Kyröläinen Heikki,
Kalliokoski Kari K.
Publication year - 2010
Publication title -
clinical physiology and functional imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.608
H-Index - 67
eISSN - 1475-097X
pISSN - 1475-0961
DOI - 10.1111/j.1475-097x.2010.00934.x
Subject(s) - perfusion , isometric exercise , medicine , contraction (grammar) , cardiology , nuclear medicine
Summary 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.