By BBC Radio 5 Live
Revealing how much exercise our bodies and minds actually want - the very latest research.
Should we essentially be aping how our caveman ancestors moved? And how burning 1600 calories can be as potent as Prozac.
Tim Samuels speaks to experts like Professors Daniel Lieberman and John Ratey - and fitness fanatic Paul Olima, who has been a body double for sports stars Usain Bolt, Anthony Joshua and Mario Balotelli.
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