The role of left thumb
Much of the hand frame, dexterity, and flexibility of your left hand is determined by how you are placing the thumb on the neck. It is extremely important that you understand how your thumb is behaving.
The thumb needs to be relaxed. We can vibrate better, shift more smoothly, and play faster notes with more ease when we can relax the thumb. In this article, we will explore ways to practice so our thumb stays relaxed.
Do not pull the thumb back too much
Open your left hand, and make a fist gently. Go back and forth several times. Now, pretend you are holding the neck of a violin as you make a fist. Your thumb should be across from the index or middle finger. That's how our hand feels most natural. To keep our body or any part thereof relaxed we need to situate them in a natural state as much as we can. When we do something that our body does not do naturally, that could become a source of creating tension.
Once you understand where your thumb naturally wants to be, pull the thumb back. You will feel that your hand becomes tight right away. Your hand feels pulled, and it is not as relaxed as when you had your thumb close to index and middle fingers.
To make this point even more clear, move your fingers with thumb pulled back. Then bring your thumb close to index and middle fingers, and move your fingers again. Which way do you feel your fingers move in a more relaxed manner? Most people would find it easier to move the fingers when the thumb is close to the index and middle fingers.
This is why it is not advised to pull the thumb back too far. You will feel the whole hand gets tight when the thumb is pulled back too much. Your hand is in a forced position, and that is something you would want to avoid as much as you can. Playing the violin is not easy, there is no reason to make it even harder by putting yourself in a forced position physically.
Do not bend the thumb too much
You can bend the thumb slightly on the neck if you'd like. There is no need to keep it completely straight. However, do not bend the thumb too much. When you keep bending the thumb more on the neck, you wil get to a point where you feel like the thumb is about to grip the neck. That would be too much bending of the thumb. When you start to grip the neck, your thumb tightens up. When your thumb gets tight, your whole hand gets tight immediately, and that is why you want to avoid bending the thumb too much.
You can keep your thumb straight or bent slightly, it is up to the individuals. What is important is that your thumb stays completely loose and relaxed.
Practice with the thumb up in the air
Pay a closer attention to the thumb, and you might notice that your thumb is a little tight. If that is happening to you, here is what I suggest trying.
Do not allow the thumb to touch the neck. Keep your thumb up in the air and start playing. It's awkward and difficult to play this way, but do it for a minute or two. Then keep doing the same, but this time wiggle the thumb as you play, while it is up in the air, to make sure your thumb is not tight.
Once you get good at it, place your thumb back on the neck very gently as you play. Keep your focus on the thumb. You should be able to feel that the thumb is more relaxed now, and you will notice right away when your thumb gets tight. When it gets tight, have your thumb leave the neck, wiggle a few times, and gently put it back on the neck again.
Repeat this process many times until you don't have to think about keeping your thumb relaxed any longer. Be patient and believe in yourself, you will get there eventually.