So why would we find a higher H plus concentration in exercising muscle cells? Well, when muscle cells are exercising, sometimes there is not enough oxygen to actually go around those cells. And so to basically continue producing those NAD plus molecules, our cells begin lactic acid fermentation. And when lactic acid fermentation takes place, we produce a lactic acid ionic acid molecule and that quickly dissociates into lactic acid and releasing that H plus ion. And so as the fermentation process takes place it increases the H plus concentration, that decreases the PH, increasing the acidity and that can cause damage to that exercising muscle tissue. And so what our cell does is to prevent damage due to that acidity our glycolysis process is shut down to prevent any further production of those H plus ions.