1. How can I use the Overload Principle (FITT) to improve aerobic fitness?

Explanation:

The overload principle is one of the seven big laws of fitness and training. Simply put, it says that you have to increase the intensity, duration, type, or time of a workout progressively in order to see adaptations. The adaptations are improvements in endurance, strength, or muscle size.

In other words, when a client first starts working out, from having been previously mostly sedentary, they will see some quick gains. But, as they get fitter, you will need to increase the intensity of their training to continue to see those gains. If they continue lifting the same weights for the same number of sets and reps, week after week, the body will have adjusted to the stress, there will be no more adaptations and they will plateau.