[音频]After a tough (1)__________ or a day full of physical activity, ifs common to find your muscles aching. But where do these pains come from? According to a German professor, the (2)__________ comes from straining your muscles in an uncommon way, for example, jumping on a bicycle for a ride, because you haven't ridden in a long time. Soreness (3)__________ since your leg muscles aren't used to that movement. When muscles (4)__________ an activity they aren't regularly (5)__________ to, the tiny fibres that are inside them are being tom apart. As muscle soreness develops, the body has to work to repair the muscle tears. But this doesn't happen immediately. First, the body must realise the muscles are (6)__________. When the body realises the muscles are hurt，the (7)__________ is to increase blood flow to the area and increase body heat. Damaged cells are then cleaned up and the body sends cells specially designed to break down the large muscle fibre (8)__________. Healing can take place after this. It takes about a day until these cells make it to your aching muscles. That's why there is most often a delay (9)__________ with muscle soreness. Repair of damaged cells takes about two days, and afterwards the soreness disappears. Unfortunately, there is little that can be done to relieve muscle soreness. Pain-relieving creams don't work, but a hot shower or warm bath can provide some (10)__________.