Michael runs tests on the five volunteers to assess their health, and examines what they eat. And then they begin a new training plan.

The group come together for a rooftop high-intensity training session. They also go cold-water swimming. And a self-confessed 'junk food vegan' makes some changes.

As the group tackle the final fitness challenge, Michael explores stress, exercise and inner motivation. He also reveals how far they've come in 21 days - with some astonishing results