So after much research and looking back, It appears Gavin's issues all stem from muscle atrophy on his affected leg that had radiation therapy on it 2 years ago. I noticed that Gavin's 'stamina' never quite came back aster. And that was based on walks and hikes, where he was much slower going uphill (there aren't many hills here, so not many other examples),and as soon as we went downhill he was happy as a clam. I also attributed it to heat. I did not know that uphill walking is what really builds muscle, or that struggling uphill was a sign that he needed more muscle building work. I guess I walked and hiked him enough in the past that he never developed signs other than that. But this past year he did start to show slightly different gait when tired (like after a long beach trip). I did mention it to his vet, and had him take a look, but he did not notice anything amiss. So it is quite possible he had a slight muscle loss/imbalance starting middle of last year that contributed to his slipping on stairs and ending up with a Groin Pull. That just led to more and more disuse atrophy over time. He still limps, poor guy, and I am doing as much PT exercises as I can with him at home. As well as lots of heat and massages. He has no problems getting up or laying down, and his x-rays came back OK. This is going to be a LONG project..anyone have experience with something like this? Would an at home TENS machine or LLLT (low level laser) be good?