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This Article Full Text Free Full Text (PDF) Free All Versions of this Article: 97/3/867    most recent 00213.2004v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Mizuno, M. Articles by Muraoka, I. Search for Related Content PubMed PubMed Citation Articles by Mizuno, M. Articles by Muraoka, I.

Inflection points of cardiovascular responses and oxygenation are correlated in the distal but not the proximal portions of muscle during incremental exercise

¹Graduate School of Human Sciences and ²School of Sport Sciences, Waseda University, Tokorozawa, Saitama, 359-1192 Japan

Submitted 25 February 2004 ; accepted in final form 20 April 2004

To test whether there is a regional difference in the exercise pressor reflex within a given muscle, we investigated the relationship between the inflection points of cardiovascular responses and muscle oxygenation during exercise. Seven subjects performed incremental exercise, which consisted of incremental 30-s static knee extensions, each separated by 30 s of recovery. The workload started at 5% maximal voluntary contraction (MVC) and increased by 5% MVC for each increment until exhaustion. Changes () in the concentrations (denoted by brackets) of oxygenated Hb (O₂Hb) and deoxygenated Hb (HHb) were monitored in proximal and distal portions of the vastus lateralis by near-infrared spectroscopy. The inflection points of mean arterial pressure (MAP), calf vascular resistance (CVR), and muscle deoxygenation index ([O₂Hb – HHb]) were calculated as the intersection point of two regression equations obtained at lower and higher workloads. The inflection point of [O₂Hb – HHb] differed significantly between proximal and distal portions (28.5 ± 3.0 vs. 39.5 ± 3.0%MVC, P < 0.05). Linear regression analysis showed significant correlations between the inflection point of [O₂Hb – HHb] in the distal portion and MAP (r = 0.89; P < 0.01) and CVR (r = 0.89; P < 0.05), but no significant relationship between the inflection point in the proximal portion and MAP or CVR. These data show that the inflection point of muscle deoxygenation differs between proximal and distal portions within the vastus lateralis during incremental exercise and suggest that the distal portion of the vastus lateralis contributes more to the pressor response than does the proximal portion.

near-infrared spectroscopy; exercise pressor reflex; regional difference