As parks and gyms fill with people hoping to make 2024 their year of fitness, Ian Sample speaks to Martin Gibala, professor of kinesiology at McMaster University in Canada, about how much exercise we should be doing, the benefits of interval training, and how to make a new regime stick. Help support our independent journalism at <a href="https://www.theguardian.com/sciencepod">theguardian.com/sciencepod</a>
