1. 2-3 mile runs in standard athletic gear 2-3 times a week.
2. Circuit courses consisting of bear crawls, low crawls, 21s, medicine ball/sandbag exercises, 30 pound ammo can lifts, sprints, sit ups, fireman carrys, and pull ups.
3. 3-12 mile forced marches through mountainous terrain with about a 60 pound load.
4. 3-5 mile runs in boots and utility trousers, and sometimes 30 pounds worth of body armor and a conservative combat load.
Run, run, run. But make it challenging to, whether it be tackling long distances, wearing a weighted vest, heavy duty pack with kettle bells, or going through difficult terrain (IE very softly packed beach sand, or up hills) Since in any sort of sports fight, you'll be fighting dry, having good cardio that's conditioned for the most difficult conditions will give you the edge in an indoors ring.
When we got into ground fighting, it was pretty easy to tell that those who put out to the point of almost being broken off during circuit courses had the edge in stamina.
"Violence, naked force, has settled more issues in history than has any other factor, and the contrary opinion is wishful thinking at its worst. Breeds that forget this basic truth have always paid for it with their lives and freedoms." -