The FITT Principle
Although slow and gentle activity can enhance basic health, you need to work harder that is, at a greater intensity-to improve fitness. Whatever exercise you do, there is a level, or threshold, at which fitness begins to improve; a target zone, where you can achieve maximum benefits; and an upper level, at which potential risks out- weigh any further benefits. The acromym FITT sums up the four dimensions of progressive overload frequency(how often you exercise) intensity(how hard), time(how long and vine specific activity).