"Squeeze your buttocks. Good. Now relax to 50%. Good. 75%. Good. 25%. Excellent." In an attempt to correct knee pain picked up during an arduous summer of half-marathons, 100km walks and Alpine mountaineering, I have engaged a physio to prod and embarrass me on a weekly basis. Alison is making me work on my core muscles to provide better support for my knock-kneed pipe-cleaner legs with their tendency to let my feet over-pronate, my knees roll inwards and me generally run like a girl. "OK, now just tense your left buttock. No, not both, just the one." I can't, it's either all buttocks or none, not some mix of the two. How can this be? I'm a master at graceful movement through the virtual domains of my work and leisure hours, as at ease piloting the Master Chief around the battlefields of Halo 2 as I am at vaulting along the main highways and quieter backwaters of the internet. I can make my PC sing and could tell within a moment if it had sp...