"Start with a longer aerobic cardio to warm up, such as 10-minute bike, then 10-minute cross trainer and then 10-minute treadmill at an easy to medium intensity – or just 30 minutes of one of these without rest periods – followed by a high intensity interval circuit," says personal trainer and traithlete Sarah Menlove.

Complete the following as fast as you can:

20 x push-ups20 x burpees20 x TRX rows (pull-ups)20 x squat press20 x box or squat jumps20 x mountain climbers (pictured)20 x medicine ball sit-ups20 x medicine ball slams

"Depending on level of fitness, this might be enough. However, if you're at a high level of fitness, include a rest after the first set then do it again – dropping the reps to 15 then taking a shorter rest and dropping the reps to 10 for a third set," she says.

Got more time?
Completing these kinds of circuits ever day (refresher: it takes 48 hours for your body to recover from HIIT training) isn't possible. So for a five-session-a-week program, you're going to have to change it up.

"You would have to alternate between cardio and weights training sessions. I would still include some of the high-intensity intervals and circuit sessions along with two or three weights or strength-based sessions a week," says Menlove.