this might not be amazing for you but for me it is, even if it was a slow pace, i just ran today and if found out i could run like a mile nonstop and probably keep going for like 2 miles and i use to couldnt even keep going for like half a mile! crazy for me man!! but im happy about it
And thats just for army... I imagine Marine/Seal basic must be... a life altering experience...
When I used to run, I could run a mile in like 5m20s... but I've never run for enjoyment or for excercise, I bike... When I go on a serious biking trip I'll be out for 8+ hours.