I am a healthy 71 year old lady who is training to hike Mt. Kilimanjaro in July. Doing 153 flights of stairs at the gym most days which takes me an hour to accomplish (41 steps/min). Distance is 3.2 miles in that time frame. Experiencing low back pain off and on since training began in Jan. Have always been very active my entire life and exercise is a daily priority for me. No sciatica pain. I assume I am experiencing muscle strain. Any suggestions?