For fitness you have to attend a PRMC at the commando training centre royal marines down at lympstone, devon.
It is 3 days and will test your fitness and DETERMINATION(One of the commando qualities) You will do a 3 mile run 1.5 miles of it will be done as a troop of 50 then the rest of the run which is 1.5 miles you have to do best effort under 10 minutes.
You will do a bleep test and have to achieve level 11 minimum( depends on how you scored on your phycometrics test eearlier on in the app process) You will do a gym test where they test your pull ups press ups and sit ups. you will do a determination test where u bassicaley run around doing pres ups and all sorts to see who keeps on going to see who is determined enough to pass, you will also do part of the tarzan assault course.