Michael Mosley teams up with Olympic athletes to test which types of exercise give you the strongest bones. Geneticist Dr Giles Yeo investigates how to stay healthy if your body clock is out of sync with your work day. GP Dr Zoe Williams looks into which health advice on the internet you can trust. And surgeon Gabriel Weston carries out an experiment to discover if cleaning our homes with antibacterial products could be responsible for the rise in allergies and asthma.