Nowadays, people are busy with their work and stay at home after work. There are fewer and fewer outdoor activities. In order to facilitate fitness, many people use treadmills instead of outdoor sports. In fact, this is also a good way to exercise, even if the work is busy, you can also see the stitches and needles to exercise, for more and more "house" urban white-collar workers, it is really helpful and worry-saving. But treadmills aren't for everyone. There are four types of people who can't use treadmills. 1. Patients with heart disease, because the treadmill speed is difficult to control, the heart load is relatively large, once an accident occurs, it is very dangerous. 2. For people with cervical spondylosis and lumbar spondylosis, running for a long time under the condition of high concentration of attention will cause tension of neck and back muscles, and treadmill has backlash on the spine, which may aggravate the original condition. 3. People with arthritis, meniscus or ligament injuries or who have undergone artificial replacement of joints will suffer from repeated wear and tear of hip, knee and ankle joints due to high-frequency running. People with joint problems will run more and more. 4. People with osteoporosis are prone to sprain and fall during high-intensity running because of their low bone density and loose ligaments, which lead to fracture.