I run 3-5mi. five days a week unless we are on an assignment. One thing that I have been doing for about the past three months that I have noticed is really adding some definition (definition is getting harder to keep @ 35yrs old) is as follows:
Pushups till I can't do them anymore, really max out, do them until you can't get your pelvis off the floor if your life depended on it. Depending on the day between 75-90.
Crunches, 10 straight, 10 alternating right elbow to left knee, left elbow to right knee, 10 bicycles, till I can't do anymore.
Back to push ups, then to crunches...
Repeat 8 times....with no rest in between.
You will be amazed how few pushups you can do on that 8th set.
What I like about this workout is that I can do it anywhere without any specialized equipment
I try to mix it up with some weight work, if they are available, or an impromptu obsticical(sp) course that we have out at the helibase.