Although training programs are usually tailored to suit individuals, some principles apply to all groups. To improve aerobic fitness, a regular program of aerobic exercise should be carried out. The F.I.T.T. principle can be used for all levels of exercise whether you are an absolute beginner or an athlete taking part in regular competitive sports. The F.I.T.T. principle is also an excellent way of maintaining your fitness levels or charting your progress if you have a specific goal.