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Perfusion heterogeneity does not explain excess muscle oxygen uptake during variable intensity exercise
Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
Turku PET Centre, University of Turku, Finland.
Turku PET Centre, University of Turku, Finland.
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2010 (English)In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 30, no 4, p. 241-249Article in journal (Refereed) Published
Abstract [en]

The association between muscle oxygen uptake (VO2) 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 O2 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 VO2 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). O2 extraction was higher during HI workloads (HI-1 62 ± 7 and HI-2 70 ± 7%) than LOW (45 ± 8%; P<0·01). O2 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 O2 delivery are unchanged between high-intensity workloads, whereas muscle VO2 is increased during the second high-intensity workload. Perfusion heterogeneity cannot explain this discrepancy between O2 delivery and uptake. We propose that the excess muscle VO2 during the second high-intensity workload is derived from working muscle cells.

Place, publisher, year, edition, pages
2010. Vol. 30, no 4, p. 241-249
Keywords [en]
blood flow, knee extension, oxygen delivery, positron emission tomography, skeletal muscle
National Category
Physiology
Identifiers
URN: urn:nbn:se:miun:diva-10421DOI: 10.1111/j.1475-097X.2010.00934.xISI: 000278564500004PubMedID: 20491840Scopus ID: 2-s2.0-77954093861OAI: oai:DiVA.org:miun-10421DiVA, id: diva2:278669
Available from: 2009-11-27 Created: 2009-11-27 Last updated: 2018-01-12Bibliographically approved
In thesis
1. Metabolic and Cardiovascular Responses During Variable Intensity Exercise
Open this publication in new window or tab >>Metabolic and Cardiovascular Responses During Variable Intensity Exercise
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Previous research investigating endurance sports from a physiological perspectivehas mainly used constant or graded exercise protocols, although the nature ofsports like cross-country skiing and road cycling leads to continuous variations inworkload. Current knowledge is thus limited as regards physiological responses tovariations in exercise intensity. Therefore, the overall objective of the present thesiswas to investigate cardiovascular and metabolic responses to fluctuations inexercise intensity during exercise. The thesis is based on four studies (Studies I-IV);the first two studies use a variable intensity protocol with cardiorespiratory andblood measurements during cycling (Study I) and diagonal skiing (Study II). InStudy III one-legged exercise was used to investigate muscle blood flow duringvariable intensity exercise using PET scanning, and Study IV was performed toinvestigate the transition from high to low exercise intensity in diagonal skiing,with both physiological and biomechanical measurements. The current thesisdemonstrates that the reduction in blood lactate concentration after high-intensityworkloads is an important performance characteristic of prolonged variableintensity exercise while cycling and diagonal skiing (Studies I-II). Furthermore,during diagonal skiing, superior blood lactate recovery was associated with a highaerobic power (VO2max) (Study II). Respiratory variables such as VE/VO2, VE/VCO2and RER recovered independently of VO2max and did not reflect the blood lactate oracid base levels during variable intensity exercise during either cycling or diagonalskiing (Studies I-II). There was an upward drift in HR over time, but not inpulmonary VO2, with variable intensity exercise during both prolonged cyclingand diagonal skiing. As a result, the linear HR-VO2 relationship that wasestablished with a graded protocol was not present during variable intensityexercise (Studies I-II). In Study III, blood flow heterogeneity during one-leggedexercise increased when the exercise intensity decreased, but remained unchangedbetween the high intensity workloads. Furthermore, there was an excessiveincrease in muscular VO2 in the consecutive high-intensity workloads, mainlyexplained by increased O2 extraction, as O2 delivery and blood flow remainedunchanged. In diagonal skiing (Study IV) the arms had a lower O2 extraction thanthe legs, which could partly be explained by their longer contact phase along withmuch higher muscle activation. Furthermore, in Study IV, the O2 extraction in botharms and legs was at the upper limit during the high intensity workload with nofurther margin for increase. This could explain why no excessive increase inpulmonary VO2 occurred during diagonal skiing (Study II), as increased O2extraction is suggested to be the main reason for this excessive increase in VO2(Study III).

Place, publisher, year, edition, pages
Sundsvall: Mittuniversitetet, 2010
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 86
Keywords
cross-country skiing, cycling, heart rate, lactate, O2 extraction, O2 uptake, performance, ventilation
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-11744 (URN)978-91-86073-76-3 (ISBN)
Public defence
2010-06-16, Q221, Östersund, 10:30 (English)
Available from: 2010-07-01 Created: 2010-06-21 Last updated: 2013-11-21Bibliographically approved

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Laaksonen, MarkoBjörklund, Glenn

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