Abstract: A non-invasive, near-infrared tissue spectrophotometer has been previously described. The device utilizes the differential absorption characteristics of oxy-hemoglobin (HbO$-2$/) and deoxy-hemoglobin (Hb) at 760 and 850 nm to indicate localized changes in tissue oxygenation. The present study was undertaken to examine the relative magnitude of vastus lateralis deoxygenation in highly-trained cyclists at maximal effort. A ramp exercise to exhaustion was immediately followed by a cuff ischemia to elicit a maximal Hb signal. All of the subjects exhibited further deoxygenation upon cuff ischemia; determined to be 63%, 69%, 72%, and 56% of maximal Hb signal. This suggests that there was incomplete depletion of oxygen supply in the vastus lateralis muscles of these subjects at exhaustion. !7
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