I've found high intensity interval training works pretty well combines with weight lifting. By that I mean specifically sprints, I like to change it up from a 1 minute all out run, rest for a 1 minute, do this 3 times. Knock it down to 30 seconds and 30 seconds rest, do this 3 times. Then knock down to 20/20 for 3 times. I guarantee you're whooped by the end of it. It's great for conditioning work.