The post by deevius is good. One thing to add, the zeppelin round (Act 3, Chapter 7) is a good place to finish this off. Once you take out the boat and clear the enemies at the beginning of the level, there are 2 long walkways in front of you which are straight,
I found holding down the button for 3 seconds at a time kept him sprinting without needing a recharge, Just lift up from the button and go right back down,
Ths is if you were like me and walked through most of the game to that point.