The mind-muscle connection, gripping the weight tightly, and contracting the muscle are key for improving strength in a weaker limb.

“I think the real key if you want a weaker arm or limb to get stronger is that mind muscle connection you know it means presumably unless there's some sort of under underlying neurologic thing and I don't want to scare you it's always possible it seems unlikely based on the way you worri the question is that you want to make sure you're gripping the handle the weight really tightly by the way that will increase your strength and performance on a set to grip tightly there's neural reasons for that and that you're really working hard to contract the muscle”