It’s pretty easy to see how finger position makes a big difference in your guitar playing.
But what about your thumb?
The position of your thumb could actually be hampering your playing!
First, placing your thumb in the middle of your guitar neck serves two purposes:
Your thumb stops the fretboard from moving backward as you press your fingers to squeeze the strings.
Your thumb’s position is directly related to the shape your palm forms when holding the guitar neck. This affects both the dexterity of your fingers and how many frets you’re able to reach.
Let me explain this second point in more detail.
If you hold your guitar with your thumb high or over the back of the fretboard, your palm flattens and makes your fingers seem shorter. With flatter fingers, you increase the likelihood that your collapsing knuckles will accidentally touch the strings below the one you are trying to play.
As you move your thumb down the back of the neck toward the middle, your palm hollows out making it easier to bend your knuckles and your fingers seem “longer”. This will allow you to arch your fingers and press the strings down using your fingertips rather than the “fingerprint” area of your fingers.
When playing open chords this allows you to press your fingertips on specific frets without dampening other strings and allows you to play single strings with clarity and precision.
Voila! Focusing on your thumb placement will give you an instant improvement!
One more thing…
While it is commonly done and may look cool, guitarists who rest their guitar on the leg opposite of their fretting hand have a harder time getting their thumb in the correct position.
If this is you, try resting your guitar on the same leg as your fretting hand.
This is more of a classical guitar position. While it might feel awkward at first, this position frees up your fretting hand and makes it easier to rotate your thumb and wrist to support your fretting fingers.
Better yet, use a guitar strap and set it so that your guitar is close to the same height whether you are sitting or standing. Read more about that here. This will also free up your fretting hand and allow you to exercise proper thumb placement when playing the guitar!