I keep pulling the same muscle?!

First of all, if you're not doing a good 5-10 min stretch before hiking, then that's the source of the problem. If you already do that, then it must be the way you're hiking. Maybe you're taking bigger steps than you should that are over stretching your muscles. Hiking is good exercise only if your in shape for the specific route your taking. The current route you do may be a little too much for you're muscles to fully handle right now. I'd suggest always doing the 5-10 min stretch before hiking, trying to go a little slower and taking smaller steps and less adventurous routes. After that, if you still get the strain, consult your doctor for sure. It could be some underlying muscular problem that may be getting worse. Not trying to worry you, but you can never be to careful these days. Many deaths these days are a result of people having symptoms of something bad but ignoring it because they're not worried enough to consult a doctor. So you have do decide which is more important: you're well being, or not feeling awkward about going to the doctor about something trivial. Hope this helped! :)

Try stretching for at least 10 min before starting your hike, and post hike, if it feels pulled again, ice it dow, good luck

Stretch it before you hike.

stretch :)