About a month ago I was very busy carrying and pulling things and developed a twitch in my right thumb. The twitch went away after a few weeks but since then I have felt that my grip, especially my thumb, has gotten weaker. Holding things feels a bit strange, especially if I try to tense up my thumb, and my fingers don't feel like they want to move. Could this be a muscle or nerve problem? And how should I go about taking care of this?

Thanks people

Hand problems can be tricky. Yes you might have tweaked a nerve, muscle or tendon. Don't know what's available in Japan but if you can make your way to a hand specialist. There are docs and also some PTs and OTs (physical and occupational therapists) who can help evaluate this. Good Luck....