In reply to jayme:
> I have been running for a number of years without a problem however over the last couple of months my left glute starts to feel dead after about 10 km. I am fine at the start of the run however by the end i feel as if my left leg is just flopping in to place rather than actually running.
> Any ideas?
Possibly piriformis pressing on your sciatic in your left cheek. 'Flopping' sounds as if there is some neuro component. Massage left cheek by rolling it on a tennis ball, and do piriformis stretches?