Cold baths, cherry juice and sleep: the secret to staying fit in your 40s

Age really is just a number. Despite aching backs and stiff joints, a growing number of elite athletes, from Zlatan Ibrahimović to Serena Williams, are pushing the clock back. Is this something everyone can achieve? Simon Usborne asks experts to reveal what can be done to reduce dodgy joints, increase fitness and stay healthy during this pivotal decade.