Try HIIT (high intensity interval training) where you alternate flat-out sprints with slower recovery periods.

Typical ways of doing this is to sprint the straights on a running track, and walk or jog the bends, or to do one minute one flat out, one minute recovery on a cardio machine. I wouldn't recommend doing sprints on a treadmill, I don't think that's safe.

I personally like doing them when I'm cycling. I'll find a long straight section and go flat out, to the point where I am breathing at around one breath a second and couldn't get a word out if you paid me. Then I cycle at normal speed until I hit the next straight section.