Robust homeostatic control of quadriceps pH during natural locomotor activity in man

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Abstract
SPECIFIC AIMSIt is generally thought that intracellular pH (pHi) of skeletal muscle falls at least 0.5 units during intense activity, but all evidence on natural [i.e., voluntary, two-legged (2L)] locomotor exercise in humans has come from invasive biopsy studies. To provide the missing in vivo data, we collected 31P NMR spectroscopic data on the energetics and homeostatic pHi control of human quadriceps muscle during and after incremental bicycling exercise to exhaustion.PRINCIPAL FINDINGS1. Intracellular pH of human quadriceps muscle falls linearly and no more than 0.2 units during incremental bicycling exercise to exhaustionWe measured 31P nuclear magnetic resonance amplitudes and frequencies at 1.5 Tesla of phosphocreatine (PCr), inorganic phosphate (Pi), and ATP in the medial head of the right quadriceps muscle of six normally active human subjects during incremental supine bicycling exercise to exhaustion. The average pHi of quadriceps muscle cells at steady-states of ATP metabolism was determined f...