I don't on the treadmill, sorry, Roger. But when I'm out running I do. So I've looked it up on google and its all to do with getting oxygen around your body and how there is an extra bit of oxygenated blood in your spleen. So if you can't pump it around quick enough your spleen kick is and to get the red stuff out out and circulating, your spleen contracts. This feels uncomfortable like a muscle cramp. Or a stitch in your side.
Bet you'll sleep better now knowing that!!
