I train at a pace of about 9:30/10:00 miles, I do about 25/30 miles a week. What my problem is that when I decide to do so speed sessions I get pain in both my hamstrings. I have trying interval training tempo fartlik etc but every time I try to go faster than what I plode along at I seem to get this pain for a few days after. Anybody got any ideas what I'm doing wrong. I warmup for 10/15 mins and warmdown fo rthe same?? Any ideas please????