When you run, you put force that is equal to three times your body weight on your feet. The human foot contains twenty muscles. This means that there is a lot that can go wrong when you run. Most sports have some kind of running or jumping So experts at many shoe companies work hard to design good sport shoes. First, a designer enters a plan for a shoe into a computer .Engineers then improve the design. A second computer designs a model for the shoe. Then a few pairs are made. Next, the shoe is tested. Different kinds of sports shoes are made for different uses. Some are made to help marathon  runners save energy during a race. Some are made for the stop-and-go kind of running tennis players. But all sport shoes have one thing in common: they are designed to help people's feet comfortable during sports. Today, nearly every sport has its own special shoe designed for just the kind of running that sport needs. What is not talked about in the passage?
The number of the bones of human muscles. The design for a shoe model. The materials of sport shoes. The effect of shoes upon sports.