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

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.

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