Our understanding of O₂ uptake (O₂) control mechanisms during exercise may be improved by the simultaneous determination of the kinetics of intramuscular high-energy phosphate turnover and pulmonary O₂. We therefore developed a technique for remote gas-exchange analysis while subjects exercised in a whole body 1.5-T NMR system. Knee-extension exercise was performed against restraining rubber bands in the prone position. Free induction decays were acquired every 1,875 ms by using a transmit-receive coil, which was placed under the quadriceps. This allowed ³¹P spectra of intramuscular ATP, P_i, and creatine phosphate dynamics to be determined every 15 s. Airflow was measured with a custom-designed turbine and a 45-ft.-long cable to reach the volume-measuring module. This was located in an adjacent radio-frequency-shielded room, as was the respiratory mass spectrometer, which also used a 45-ft.-long sampling line. The respired gas profiles were not discernibly different from those that used the standard inlet; the increase in the delay was readily incorporated into the breathby-breath algorithm, allowing the O₂ kinetics to be determined in concert with those of intramuscular phosphate metabolism.

phosphorus-31 nuclear magnetic resonance; remote sensing; quadriceps exercise

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