I have beefy thumb muscles from years in construction. The problem is there's not as much stamina as I would like in my throttle hand. What exercises can I do to fix it? I end up with my pinky and side of my hand on the bar weights. It reminds me to loosen my grip. I have had ex wives quit holding my hand while walking because I start squeezing without realizing I'm doing it. My hands still feel relaxed to me.