So I'm in alright fitness but I've always been sprinter not long distance. Im currently 5ft11 I weigh 67kg I'm 17 turning 18 soon. I have been going to the gym for quite a long time but most of my training has all been for sprinting as that's what I was good at. Now I want to get my body into longer distance as I want to join the Royal Marines. If someone could give advice on where to start from short to longer distance and what training I should do. If it's just advice or a training plan it's appreciated.