Your potential "Why" to your left leg/hip/back pain: From information gathered thus far might conclude your pain is coming from the overuse of the left leg including the back and hip muscles. What can also be included with this idea is the the possible under-use of the core musculature, causing the deep muscles in the hip and back to compensate and be overly used.
The main plan has come in the form of getting your Right Leg to be used more as it is evident the R hip/leg is not being used adequately with the possible overuse of the Left Leg.
Upon assessment of the core, it appears it is weak, but also that the hip and back muscles might be compensating. When muscles compensate, they can cause pain, but due to the location of the deep muscle, the piriformis, pinching of the sciatic nerve can occur.
Treatment therefor is based on strengthening the Right let and getting your body to utilize all the time while walking (and playing golf). Treatment of the core and learning how to turn off the compensatory muscles also appear to be necessary as well.
Home Exercise Program
Here is a video on Low Back Pain tips. Near the end of the video, I discuss the basic core exercise I showed you the other day. This is just the basic exercise. The two knees up we did the other day was a progression. The thing to work on is to keep the back flat, turn the core on, and turn off the back and buttock muscles. Practice as able.
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