听一分钟英文：Muscles-肌肉（在线收听）

Where would we be without muscles? Probably a mess on the floor. Muscles are pretty interesting things. Everybody has lots of them. Some people look after them better than others. Bodybuilders want to have really big muscles. The bigger the better. They spend hours in the gym lifting weights to make their muscles as big as they can. Athletes work on the specific muscles they need for their sport. If you look at a hundred-metre runner, you’ll notice they have large shoulder and arm muscles. This is so they can power ahead when they run. An interesting thing about muscles is that it takes more face muscles to frown than it does to smile. This means smiling uses less energy, so we should do it more.