What makes lactic acid in an athletes muscle?

Lactic acid is the byproduct of anaerobic respiration, the body’s way of generating energy in low-oxygen conditions.

Cells get their energy from breaking down glucose. When we exercise, there often isn’t enough oxygen to meet our body’s energy demands which is why anaerobic respiration takes places to quickly provide a necessary burst of energy. Anaerobic respiration takes a molecule of glucose (sugar) and converts it directly into lactic acid. This is why you often get painful cramps after strenuous exercise.

Lactic acid is a product of anaerobic respiration. When exercising, the respiratory rate of muscles increases due to the increased energy need to fuel the more frequent and more powerful contractions. In turn, this leads to higher oxygen demands. When oxygen requirements exceed oxygen supply, the body is able to respire anaerobically - this means that lower levels of energy can continue to be produced despite the lack of oxygen. A by product of anaerobic respiration is lactic acid, which builds up and can lead to cramping but can be oxidised into carbon dioxide and water.