The topic of Myoglobin often comes up in discussions about Near Infrared Spectroscopy (NIRS), especially in fitness applications when it’s desirable to measure muscle oxygenation, and when the oxygen consumption rates can be high and change rapidly. NIRS measures optical absorbance of tissues. Hemoglobin and Myoglobin absorb light nearly identically in the near-infrared region, so NIRS cannot measure their oxygen saturations separately.
The final leg of the path oxygen takes on its way to the mitochondria is diffusion through the interstitial fluids and cell walls. Oxygen diffuses from areas with high levels of dissolved oxygen to areas with lower levels. When interpreting the Hemoglobin and Myoglobin Dissociation Curves discussed in a previous blog, one might be tempted to conclude that hemoglobin always deoxygenates before myoglobin because the hemoglobin curve is to the right of the myoglobin curve. However, the location of the molecules along the diffusion path must also be considered.
Myoglobin is generally much closer to the mitochondria than the hemoglobin is, as it is found inside the muscle cell, whereas hemoglobin is found inside the red blood cell (See the sketch below. The O2 symbols represent the level of dissolved oxygen).
Oxygen from the hemoglobin has to diffuse out of the red blood cell, through the plasma, capillary wall, interstitial fluid, and into the muscle cell. When there is a high rate of oxygen diffusion, the level of dissolved oxygen could be much lower around the myoglobin. This means that it is uncertain whether the hemoglobin or myoglobin is deoxygenating first. It might be helpful to know the hemoglobin and myoglobin oxygenation states separately, but the current state of the technology doesn’t allow that.
Moxy Muscle Oxygen Monitor uses NIRS to provide valuable information on muscle oxygenation. It’s important to understand what the device can and can’t do in order to best be able to Train with Moxy.