Five volunteers put their lives in Michael's hands to see if food, fitness and lifestyle changes can really transform their health and well-being within the span of just three weeks.

The group come together for a rooftop high-intensity training session and some 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.