Balloon exercise
Don’t worry about technique, or gaining strength for your left hand. Get 2 balloons, that is blown through your mouth. Bounce one balloon in the air, and then do the same for the other afterward. Keep the 2 balloon in the air for as long as you can, using only your left hand. If you master 2 balloons, then you can add more, to challenge yourself.
Keep doing this until you feel any tiredness in your left arm. The goal is to gain coordination for your left arm.
