Glycolysis involved in glycolysis. The burning sensation in muscles during hard exercise can be attributed to the release of hydrogen ions during the shift to glucose fermentation from glucose oxidation to carbon dioxide and water, when aerobic metabolism can no longer keep pace with the energy demands of the muscles. These hydrogen ions form a part of lactic acid. The body falls back on this less efficient but faster method of producing ATP under low oxygen conditions. This is thought to have been the primary means of energy production in earlier organisms before oxygen reached high concentrations in the atmosphere between
Equine exertional rhabdomyolysis release of cell contents. Muscle spasms, caused by the lack of blood to the muscle tissue, are also painful. A horse developing ER will usually begin showing signs right after the beginning of exercise, although for mild cases, signs may not be seen until after the horse is cooled out. Signs include reluctance to move, stiffness or shortened gait when the animal is forced to move, and muscle spasms or cramps, with hard, painful muscles (especially the hindquarters) when palpated. If an observer is unfamiliar with ER, initial symptoms may appear to be tiredness or perhaps lameness but the condition