Injury might not be the right word--it could be a stride problem. Since I began running three weeks ago, I've noticed that during and after my runs, my right leg (particularly the hamstring right above the knee and the upper part of the calf) are feeling the strain and a bit sore. Today, however, even though I felt much stronger in my lung capacity and heart rate and even though I actually wasn't feeling it too much in my leg during the run, after my workout, I started getting stiff in the hamstring and calf on the right leg, and now it's bed time (ran at 8.30 this morning, now it's a bit after 10 PM) and my leg is stiff and very sore. I'm limping. It does feel like muscle soreness as there are no sharp pains that might indicate something else. But it's curious to me that my left leg has felt perfectly fine after every run. It's just my right leg doing this. I'm thinking it must be the result of some sort of error in the way my right foot strikes the ground. Can someone help me? I don't want to do myself a mischief and end up unable to train at all, but if I can't figure out what's causing this, I may have to give up running. There's no way I'm going to pop a hamstring and end up having to give up the Firm or something horrible like that!!