In the late 19th century, fermentation chemists realized that juice left to ferment without adequate oxygen resulted in acid products. Then, in the early 20th century, when physiologists stimulated isolated frog muscles to contract until exhaustion, they found that the tissues had accumulated high amounts of lactic acid.

Lactic acid is the result of the glycolytic energy production system. It is an energy source to be used in muscle cells of origin, or adjacent fibres (cells), or fibres in the heart and cells in the brain. Lactic acid is also the material that the liver prefers to make glucose (sugar) for the blood when exercise is prolonged. Lactic acid production in muscle is stimulated in part by circulating adrenalin. Now, from de Paoli and colleagues we learn that adrenalin and lactic acid also help protect against the electrolyte imbalance across muscle membranes brought on by the loss of potassium.