hi, i have been running for 10 years,and have acheived 59min for 10 miles,76 mins for 1/2 marathon. i have tried running at race pace all my runs. this left me shattered and tired all the time.overtraining, which is what u do when running at fast pace all the time.impacts on your times, making them slower and slower.i have bought a heart rate monitor which when set correctly makes you run slower than you think u should, but it enables your body to recover in time for your fast paced training.my times have got faster and i dont suffer the heartache of underacheiving in my races. hope this is of some use to u. good luck with your training.