As part of the BBC’s mental well-being season, All in the Mind takes a deep dive into the evidence on the relationship between exercise and mental health. Not just whether getting moving can make a difference, but why. Claudia Hammond laces up her running shoes and goes for a jog on the seafront in Eastbourne with a group of people who are running for their mental health. Claudia meets the founder of 'Run Talk Run', Jess Robson, and talks to other members of the group about why they find exercise to be helpful.Back in the studio, Claudia speaks to Jonathan Roiser, Professor of Neuroscience and Mental Health at University College London. He’s about to embark on a major piece of research that should help us understand a lot more about what exercise does for people with depression. As well as explaining what they’re hoping to discover, he tells her about the latest research into exercise and mental health. Why does it work for some people and not others, and what’s the best exercise for your brain?Then there’s the commonly held belief that exercise is good for your mood because it ‘gets the endorphins going’, but we know that endorphins are not able to cross the blood-brain barrier. Claudia talks to Dr Hilary Marusak from Wayne State University School of Medicine in Detroit about one of the possible alternatives – the endocannabinoid system. Throughout the programme Claudia is joined by Dr Peter Olusoga, Senior Lecturer in Psychology at Sheffield Hallam University. Together they discuss the many barriers people face to improving their physical activity, including the fact that poor mental health itself can stop you wanting to exercise in the first place.And if getting more exercise really does sound like the worst idea you can think of, it turns out that watching sport on TV might also be good for you.Presenter: Claudia Hammond Producer: Ben Motley Content Editor: Holly Squire Production Coordinator: Siobhan Maguire