How can the f.i.t.t principle be used to create overload in a training programme?"

This is called the Principle of Overload.

The principle of overload is to train your muscles beyond what they usually do in order to create micro-tears which will later be repaired by protein. This makes the muscle grow back bigger and stronger.

The Overload Principle

Overload in PE is the principle of training that states we must work our body systems harder than usual in order for them to be improved.