Question

Why do we get muscle cramps after heavy physical exercise?

Answer 1

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During very heavy physical exercise human muscles respire anaerobically and form lactic acid which accumulates in the muscles. Because of this, the muscles cannot continue working for long time. They get fatigue after some time causing muscle cramp.

Answer 2

During heavy exercise, the demand for energy is high but the supply of oxygen to produce energy is limited. Therefore, anaerobic respiration takes places in the muscles cells to fulfil the demand for energy. ... The accumulation of lactic acid in muscles leads to muscle cramps.