You can train with 4 major lifts "circuit style" where you are moving from one exercise to the next without much rest, but giving the target area 3-5 minutes for a full recovery. For example, if your four exercises were squat, bench press, bent-over row, RDL, you could do them all in sequence, and your quads will be fully recovered by the time you come back around to squats. Very efficient method of training. You can get in and out of a workout in 30 minutes that way. Or do some Crossfit style combos and finish yourself off soundly in 10 minutes!