When time is in short supply, rest periods should be too (ideally kept to 30 seconds or less). Try this: Set a timer to reflect the length of the workout. Let’s pretend that’s 15 minutes. Now, create a circuit of three to five exercises. Then, start the clock and complete the circuit for as many rounds as possible in 15 minutes.

Of course, never compromise quality over quantity, but by the end of these workouts you should feel sufficiently exhausted.