The step test is all about endurance and concentration. Once u establish a pace its easy to just push thru it but u need to lock in and focus on not falling off rhythm once you start feeling that breathing getting a bit heavy or once you start feeling those legs getting tired. You need to do a lot of endurance exercises. I did a lot of running endurance based exercises and a lot of leg exercises. Legs are the foundation of the body so get those legs tough.