I was asked what burpees are, and they're a very old-school fitness move. They're done in four counts, starting in a standing position.
Count 1: squat down and touch your hands to the floor
Count 2: jump your legs back into push-up position
Count 3: jump your legs forward into a squat again
Count 4: jump back to standing
I did 15, but it was with a couple of stops for heavy breathing with hands on knees. Hard, but effective.