Meanwhile, a research team led by A. R. Mark of the United States in 2008 claimed that muscle fatigue was caused by calcium ions (Ca2+) in muscle cells. Calcium ions stored in muscle cells control muscle contraction and relaxation. However, after severe exercise, calcium from muscle cells leaks out, weakening muscle contraction. However, the exact cause and mechanism of muscle fatigue are still being studied. 비앤비 여성전용아로마스웨디시 마사지