Principles of training and FITT

A swimmer does most of her training in the pool rather than on a bike. Which principle of training is she applying?

A weightlifter adds 2.5 kg to the bar every two weeks. Which principle is this?

A footballer breaks his leg and cannot train for eight weeks. His fitness drops. Which principle explains this?

A runner changes her routes and adds swimming sessions to avoid getting bored. Which principle is she applying?

In FITT, which letter is changed when a cyclist rides at a higher heart rate?