Today Jimmy and John are joined by Darryl Edwards, creator of Primal Play from PrimalPlay.com to talk about the deep science that supports HIIT training. As you know, one of the hacks that Jimmy has added to his regimen is high-intensity interval training, mostly in the form of flipping his massive tractor tyre.

While Jimmy has commented numerous times about the immediate benefits he was getting from adding this to his weekly routine, Darryl breaks down exactly why he is responding so well to it, and why it might be just the thing for you too.