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1 Applied Physiology Laboratory, Kobe Design University, Kobe, Japan
2 Department of Kinesiology & Anatomy & Physiology, Kansas State University, Manhattan, Kansas, United States
3 Physiology, University of Kentucky, Lexington, Kentucky, United States
4 Institute of Membrane & Systems Biology, University of Leeds, Leeds, United Kingdom
5 Faculty of Human Development, Kobe University, Kobe University,Laboratory for Applied Human Physiology, Kobe, Japan
6 Hamamatsu Photonics K.K., Hamakita, Japan
7 Kinesiology, Kansas State University, Manhattan, Kansas, United States
* To whom correspondence should be addressed. E-mail: s-koga{at}kobe-du.ac.jp.
To test the hypothesis that, during exercise, substantial heterogeneity of muscle hemoglobin and myoglobin deoxygenation [deoxy(Hb + Mb)] dynamics exists and to determine whether such heterogeneity is associated with the speed of pulmonary O2uptake (pVo2) kinetics, we adapted multi-optical fibers near-infrared spectroscopy (NIRS) to characterize the spatial distribution of muscle deoxygenation kinetics at exercise onset. Seven subjects performed cycle exercise transitions from unloaded to moderate [<gas exchange threshold (GET)] and heavy (>GET) work rates and the relative changes in deoxy(Hb + Mb), at 10 sites in the quadriceps, were sampled by NIRS. At exercise onset, the time delays in muscle deoxy(Hb + Mb) were spatially inhomogeneous [inter-site coefficient of variation (CV), 3~56% for <GET, 2~21% for >GET]. The primary component kinetics (time constant) of muscle deoxy(Hb + Mb) reflecting increased O2 extraction were also spatially inhomogeneous (inter-site CV, 6~48% for <GET, 7~47% for >GET) and faster (P<0.05) than those of phase 2 pVo2. However, the degree of dynamic inter-site heterogeneity in muscle deoxygenation did not correlate significantly with phase 2 pVo2 kinetics. In conclusion, the dynamics of quadriceps microvascular oxygenation demonstrates substantial spatial heterogeneity that must arise from disparities in the relative kinetics of Vo2 and O2 delivery increase across the regions sampled.
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