Stamina is fine, need to improve 'high intensity' fitness - how? Can keep running for the whole game, but I play in midfield and running from challenge to challenge, then breaking with the ball and chasing back really tires me out and I know I can be fitter in this area - any ideas on what I can do to increase this area of fitness? 

I'd like to be able to go from winning a challenge to setting up an attack then chasing down their defence after we've scored and still feel ready for more