Modern medicine is expensive, and pills usually have side effects. Many people also argue that they treat the symptoms, not the cause of the problem For all these reasons, some doctors believe taking more and more medication can't be a good solution to health problems. Some suggest exercise could be a more effective treatment for certain health conditions. However, this relationship between health and exercise isn't new. He lived around 2,500 years ago, when doctors in Greece believed that good health depended on the body being in balance. The theory, which some people still believe today, is that if you are ill your body must be out of balance. To keep the body in balance, you must have the right diet and do the right amount of exercise not too little and not too much. Doctors know that exercise reduces pain in people with illnesses such as arthritis, Exercise helps because strong muscles help support the bones and joints. Exercise might also lead to a reduction in painful inflammation, or swelling, in the body. Exercise can also help people with mental health problems, like depression. For example, some scientists think swimming in cold water in lakes and in the sea may be a better, and more effective, treatment than antidepressants. They are not sure yet why it works exactly, but they see it does. ​