OPTION 1: blitz your body

You can get a total-body workout with five basic exercises and no exercise equipment, says Kathy Kaehler, author of Kathy Kaehler's Celebrity Workouts. Do these five exercises for one minute each without stopping:

• chair squats (squat in front of a chair and sink down until your butt just touches the seat)
  lunges
  push-ups
  crunches
  jumping jacks.

Do the circuit four times; for more of a burn, pick up the pace. "It doesn't have to be fancy, but treat fitness like you're trying to catch the train," Barrett says. To add variety, mix in leg lifts, side ab curls and tricep dips, and do each as fast as possible for 30-second or one-minute intervals. Do a five-minute warm up (mix jumping jacks with some dynamic stretches) and a five-minute cool down (an easy walk and some static stretches), and go hard for 20 minutes in between.

OPTION 2: superset strength

If you normally work your upper body on one day and your lower body on another, maximise your time and kilojoule burn by doing both in the same workout. Simply superset your exercises by alternating moves in between sets - without taking more than 15 or 20 seconds of rest in between. If you do a set of squats, do a set of bench presses next. If you move on to lunges, superset with lat pulldowns or rows. "Even though your body is still being taxed and your heart rate is up, you're at least getting some moderate level of recovery," Mejia says.

OPTION 3: play, don't think

Add intensity by forgetting about how hard you're working - in the form of tennis, volleyball, or anything competitive. "You're exercising, you're sweating, and that's when you really change your body. But you're also getting out of your head," Joujon-Roche says, which is a good thing. No opponent? Hit the netball court. Every time you miss a goal, do sets of walking lunges, push-ups, crunches, or full-court sprints.