Hello, I have had low back issues this past year and worked with a PT to fix it. We deduced that the root cause of my problem was that my hips were too weak so we focused on doing lots of strength for glutes and hips. Today I did strides after my run and even though I didn't go fast at all (relatively) I feel slight irritation in my left hip flexor and slight low back tightness. I wanted to ask your opinions because this tightness I am feeling now feels incredibly mild compared to the tightness I dealt with in the past. I will be able to get my run in tomorrow and feel good, without a doubt. But why is it that as soon as I start doing strides (or anything faster for that matter) my low back gets tight?