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This Article Full Text Full Text (PDF) All Versions of this Article: 92/4/731    most recent expphysiol.2007.037721v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by McDonough, P. Articles by Poole, D. C. Search for Related Content PubMed PubMed Citation Articles by McDonough, P. Articles by Poole, D. C.

¹ Department of Kinesiology, University of Texas Arlington, Arlington, TX 76019-19259, USA ² Division of Exercise Physiology, West Virginia University School of Medicine, Morgantown, West Virginia, 26506-9227, USADepartments of ³ Anatomy & Physiology⁴ Kinesiology, Kansas State University, Manhattan, Kansas 66506-5802, USA

Whether the speed of recovery of microvascular O₂ pressures () differs within muscles composed primarily of type II fibres with contrasting oxidative capacity has not been determined. We tested the hypothesis that, following contractions, the recovery of would be slower in the white (WG; low oxidative capacity) versus the mixed gastrocnemius (MG; comparatively high oxidative capacity). Radiolabelled microsphere and phosphorescence quenching techniques were used to measure muscle blood flow (, hence O₂ delivery, ) and during contractions (1 Hz twitch) at low (LO, 2.5 V) and high intensities (HI, 4.5 V) in rat (n = 15) MG and WG muscle and during subsequent recovery. Following the LO protocol, end-contraction was lower in WG (11.6 ± 0.5 mmHg) than in MG (16.2 ± 0.6 mmHg; P < 0.05) while, contrary to our hypothesis, the initial rate of change in during recovery (/dt; MG 0.11 ± 0.01 mmHg s^–1 and WG 0.06 ± 0.03 mmHg s^–1) and mean response time (MRT; MG 110.3 ± 5.1 s and WG 113.5 ± 8.4 s, P > 0.05) were not different. In contrast, end-contraction baseline was not different following the HI protocol (MG 10.3 ± 0.6 mmHg and WG 9.2 ± 0.6 mmHg; P > 0.05) but, in agreement with our hypothesis, /dt was slower (MG 0.07 ± 0.01 mmHg s^–1 and WG 0.03 ± 0.003 mmHg s^–1; P < 0.05) and MRT longer (WG 180.8 ± 4.5 s and MG 115.4 ± 6.7 s; P < 0.05) in WG versus MG following the HI protocol. These data suggest that following high-intensity, though submaximal, muscle contractions, recovers much faster in the more oxidative mixed gastrocnemius than in the less oxidative white gastrocnemius.

(Received 8 March 2007; accepted after revision 16 April 2007; first published online 20 April 2007)
Corresponding author P. McDonough: Department of Kinesiology, University of Texas Arlington, 112 Physical Education Building, 801 Greek Row Drive, Arlington, TX 76019-19259, USA. Email: mcdonough{at}uta.edu