Overload

The first principle of training is that you must overload a system to stimulate a training response. If one can do something without much effort, then the body does not need to adapt. As a task becomes more difficult, the body adapts according to the stress that is put on it. It takes little muscular effort for a person to lift a pen, so the muscles do not adapt physiologically. If one is not used to lifting heavy objects, however, it takes greater muscular effort to lift several books. This overload to the muscular system stimulates changes in strength as one repeats it. A person may be able to walk down the block and back without too much stress. If one increases the speed or length of the walk, the effort overloads the system slightly and, with repetition, strengthens the cardiovascular system. One can accomplish an overload through several means, the most common being to increase the intensity, duration, and frequency of the activity. As I discuss each type of exercise in the chapters that follow, I provide guidelines for progressing that type of exercise (although you must apply these guidelines cautiously and personalize them for your body).

Note that overload operates along a continuum. A certain amount produces a good training response, while too much overload increases the chance of injury. If you have not been active and have decided to start a cardiovascular exercise program, I recommend starting with walking. For an initial program walk several times a day at a comfortable pace, for only 5 to 10 minutes at a time. As this amount is more than you were doing previously, it overloads the system "but not so much that you develop an injury. One gentleman that I know decided to start walking after a layoff due to injury, only to have to take more time off because he started with an hour walk and had severe knee pain the next day. The idea that if a little is good for you, a lot is better does not necessarily hold true for exercise.