Myoglobin desaturation with exercise intensity in human gastrocnemius muscle

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 1999-07, Vol.277 (1), p.R173
• Main Authors: Molé, Paul A, Chung, Youngran, Tran, Tuan Khanh, Sailasuta, Napapon, Hurd, Ralph, Jue, Thomas
• Format: Article
• Language: English
• ISSN: 1522-1490

The present study evaluated whether intracellular partial pressure of O ([Formula: see text]) modulates the muscle O uptake (V˙o ) as exercise intensity increased. Indirect calorimetry followedV˙o , whereas nuclear magnetic resonance (NMR) monitored the high-energy phosphate levels, intracellular pH, and intracellular[Formula: see text] in the gastrocnemius muscle of four untrained subjects at rest, during plantar flexion exercise with a constant load at a repetition rate of 0.75, 0.92, and 1.17 Hz, and during postexercise recovery.V˙o increased linearly with exercise intensity and peaked at 1.17 Hz (15.1 ± 0.37 watts), when the subjects could maintain the exercise for only 3 min.V˙o reached a peak value of 13.0 ± 1.59 ml O ⋅ min ⋅ 100 ml leg volume . The P spectra indicated that phosphocreatine decreased to 32% of its resting value, whereas intracellular pH decreased linearly with power output, reaching 6.86. Muscle ATP concentration, however, remained constant throughout the exercise protocol. The H NMR deoxymyoglobin signal, reflecting the cellular[Formula: see text], decreased in proportion to increments in power output andV˙o . At the highest exercise intensity and peakV˙o , myoglobin was ∼50% desaturated. These findings, taken together, suggest that the O gradient from hemoglobin to the mitochondria can modulate the O flux to meet the increasedV˙o in exercising muscle, but declining cellular [Formula: see text]during enhanced mitochondrial respiration suggests that O availability is not limitingV˙o during exercise.