I'm training for my first half marathon which is at the end of March. As part of my training plan I run 3 - 5 miles on Tuesday and Thursday, cross train on Wednesday for 30 - 40 minutes, long run on Saturday and 3 miles recovery run on Sunday. I ran 7 miles on Saturday (yesterday) which is the longest I've ran so far with this plan. The run went well. I've noticed for a day or two that I have some pain in my lower back and my legs are a bit stiff. When I went out to run today I could ony run for a few hundred yards as my back was painful. I plan to rest and just try and run as normal on Tuesday. Has anyone got any suggestions of what exercises I can do to strengthen my back and what it may be?