I do it to the top of my ears. Going too low in this motion can cause rotator cuff injuries. Especially in those of us who are older and or less flexible.
Most people have little problem with thyroid on hgh. I would suggest using T3 if you want to burn more fat. T4 is inactive unless converted so why bother with it.
Tren can increase strength very quickly. Perhaps the leg muscles increased in strength faster than the knee joint could become accustomed to the heavier weights.