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Spatial heterogeneity of quadriceps muscle deoxygenation kinetics during cycle exercise

¹Applied Physiology Laboratory, Kobe Design University, Kobe, Japan; ³University of Leeds, Leeds, United Kingdom; ⁴Kobe University, Kobe, Japan; ⁵Hamamatsu Photonics K. K., Hamakita, Japan; and ²Department of Kinesiology, Anatomy, and Physiology, Kansas State University, Manhattan, Kansas

Submitted 12 June 2007 ; accepted in final form 19 September 2007

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 O₂ uptake (pO₂) 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 [intersite coefficient of variation (CV), 356% for <GET, 221% for >GET]. The primary component kinetics (time constant) of muscle deoxy(Hb + Mb) reflecting increased O₂ extraction were also spatially inhomogeneous (intersite CV, 648% for <GET, 747% for >GET) and faster (P < 0.05) than those of phase 2 pO₂. However, the degree of dynamic intersite heterogeneity in muscle deoxygenation did not correlate significantly with phase 2 pO₂ kinetics. In conclusion, the dynamics of quadriceps microvascular oxygenation demonstrates substantial spatial heterogeneity that must arise from disparities in the relative kinetics of O₂ and O₂ delivery increase across the regions sampled.

near-infrared spectroscopy; oxygen uptake kinetics; muscle oxygen delivery; muscle oxygen utilization

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