Acidosis occurs when exercise intensity is very high, and H+ ions begin to accumulate because ATP hydrolysis outpaces synthesis. The body has multiple avenues to cope with H+, but when exercise intensity is very high these become overwhelmed with the amount of H+. When this occurs, intramuscular pH decreases and muscle contraction is compromised. Table II from Cairns (2006) summarizes some of the possible mechanisms behind impaired muscle contraction during acidosis.