When muscle pH drops below 6.5, the acidity disrupts all sorts of links in the energy chain. For example, the enzyme phosphofructokinase is the rate limiting step in muscle use of glycogen. Below pH 6.5, it stops working altogether. And, he says, acidity also reduces muscle power directly by inhibiting the contractile action of muscle fibers. You can put all sorts of other chemicals into the bloodstream, but, unless you reduce acidity during exercise, your muscles will tie up.
Ammonia is toxic to cells, it reduces the formation of glycogen, and it inhibits the energy cycle.
He adds that, although we still do not know how much ammonia contributes to fatigue, we do know that the higher your blood ammonia, the poorer your performance. Immediately after marathon races, triathlons or other endurance events, some athletes have very low blood phosphate levels, Colgan said. Even athletes with high resting phosphate levels show marked reductions after endurance exercise. First, there is a loss of acid buffering. Phosphate is a major alkaline buffer of muscle.