" Physical fitness is not only one of the most important keys to a healthy body, it is the basis of dynamic and creative intellectual activity. Intelligence and skill can only function at the peak of their capacity when the body is healthy and strong"-JFK

i think this means that when you are in shape than your body functions better. like when you been healthy so then your brain works better and so you are more intelligent. when you are fit then you are capable of doing more than what you often do. you can do better and do more things with your body. people were choosing the wrong often so in the future they did something really bad like kill the president.