Intramyocellular oxygenation during ischemic muscle contractions in vivo.

There is some evidence that the fall in intramyocellular oxygen content during ischemic contractions is less than during ischemia alone. We used proton magnetic resonance spectroscopy to determine whether peak deoxy-myoglobin (dMb) obtained during ischemic ankle dorsiflexion contractions attained the maximal dMb level observed during a separate trial of ischemia alone (resting max). In six healthy young men, the rate of myoglobin desaturation was rapid at the onset of ischemic contractions and then slowed as contractions continued, attaining only 75 +/- 3.3% (mean +/- SE) of resting max dMb by the end of contractions (p = 0.03). Myoglobin continued to desaturate while ischemia was maintained following contractions, reaching 98 +/- 1.8% of resting max within 10 min (p = 0.03 vs. end of contractions). Notably, contractions performed after 10 min of ischemia did not affect dMb (dMb = 100 +/- 1.5% of resting max, p > 0.99), suggesting that full desaturation had already been achieved. The blunting of desaturation during ischemic contractions is likely a result of slowed mitochondrial oxygen consumption due to limited oxygen availability.