Combat Fit - Sprints
Running all out for short stretch. This chest bursting air-deficit stuff not just fast jogging. Look up a youtube of the Olympic 100 m and you will get an idea.
Tactical benefits - If you can outrun, speedwise, that which you wish to kill, or that which wishes to kill you, it is a good thing. Consider that the old lions that can't catch the gazelles tend to die.
Physical benefits - If there was ever a paleo exercise, this is it. It will produce the anaerobic capability of a monster while not giving up any amount of muscles. Look at a marathon runner and then at a sprinter. They both run. Who looks like they could kick ass better?
I sprint 100 yard increments about three times per week. There is a nice hill near the hacienda that is about a 10 degree angle. I get to the bottom and make sure I am warmed up. Then I sprint up as fast as I can. I wear toe shoes.
At the top I swear, turn around and walk back to the starting point. I repeat for ten sprints.
If you are more an image of a sumo wrestler than a runner, be careful not to hurt yourself. If you have not sprinted in a while do a few sessions at 75%. But once you have it down, step on the gas and haul ass.
Try that and see what it does for you