Proper placement of the left hand thumb on ukulele is essential to relaxing the hand and getting good sustain.
The Thumb Position
I like to keep the thumb around the center of the neck right in line with the 2nd finger. To set the hand up this way, make a “C” shape with your hand and touch the thumb and 2nd finger. Make sure the tip joint of the thumb is relaxed and not curved into the palm. Imagine you are giving the “thumbs up” sign then move the thumb from the back knuckle until it touches the 2nd finger.
First Position, First String
Now try this on the ukulele in first position with the 1st finger at the 1st fret of the 1st string. Place the other fingers inline on the same string on the 2nd, 3rd, and 4th frets. Make sure the forearm is rotated slightly forward to the right so that the 4th finger can stay curved in a “C” shape. Now keep an eye on your thumb position and make sure it is flat in the middle of the neck behind the 2nd finger. Imagine a magnet connecting it to the 2nd finger and thumb.
With this position you won’t need to apply much pressure with the thumb. It is just there to balance out the hand. Try playing the four notes now on the 1st string (Bb, B, C, and C#) from the 1st through 4th frets. The wrist should be parallel to the neck. I even rotate to the forearm slightly to the right to keep the 4th finger curved and relaxed. I like to do stretches when needed with the index finger before stretching with the 4th finger which is weaker.
When playing this set of 4 notes is comfortable, move to other strings and play the same set of frets. Continue to watch your thumb position and keep it lined up with the 2nd finger. The thumb can move up and you move to the 2nd, 3rd and 4th strings.
The next step is to change positions while making sure the thumb moves along with the hand. The goal is to keep the thumb/2nd finger setup consistent when moving up and down the neck.
Before playing any notes, set up your left hand with the “C” shape and gilde up the neck. There may be a tendency to leave the thumb behind as you move up the neck. This will make it harder to play and will require more tension in the hand to get notes to sound clearly. Make it a goal to keep the thumb and 2nd finger in perfect alignment as you move the hand to new positions.
When this feels good try playing the notes with the four fingers in each new position you move to. You can try a chromatic scale from the 1st through 12th fret. 1, 2, 3, 4 shift to 5th position. 5, 6, 7, 8 shift to 9th position then 9, 10, 11, 12.
If you can move up and down through this smoothly while keeping your thumb in line with the 2nd finger without applying much pressure with the thumb you will be well on your way to having a relaxed left hand.
At Ukulele Corner Academy we have a full structured curriculum on fingerstyle ukulele, including technical elements like the left-hand thumb. To start learning, join Ukulele Corner Academy today!