Some people will say in a disparaging way that this or that person is all THUMBS, suggesting an awkwardness in coordination, perhaps. And it seems that these digits can be a big, troublesome nemesis in navigating the keyboard smoothly if its SHORTcomings are FLESHED out. (falling down hard and interrupting scale passages and the like)
Here’s a thumbs ROLL into scale MOTION that avoids a CRASH….
By and large, I think of my thumbs in an Upbeat fashion. I love them for their capacity to lead and “measure” my family of fingers’ journey up and down the 88s. And I approach my thumb more LIGHT-heartedly than the rest of my God-given digits. (but it must give advanced notice of itself, an opinion challenged by some) There is a also a ROTATIONAL capacity of the thumb that is often overlooked. In slow motion when arpeggios are played, one can readily track this motion and avoid getting LOCKED in!
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Rather than write a THUMB TREATISE in the early 20th Century tradition, attaching fancy diagrams of this and that position as if I were publishing a Krafft-Ebing sex manual, I will refer to a few videos that might better amplify my POSITION about the THUMB. (Politically correct, or not)
An adult student practices the F# minor arpeggio experimenting with a smoother THUMB passage:
You will notice how her thumb was initially getting in the way:
Thumb to thumb “swings” are further referenced here: (Left Hand practice)
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In the context of this thumb ingratiating universe, I was asked the following question by a reader:
“On F# major arpeggio, what exactly is the thumb placement on the key?”
ME: Naturally each hand has variations in configuration, but I basically lay out my own thumb placement in this F# Major scale and Arpeggio video which obviously is not a stratified one as music in progress creates various angles and subtle angular thumb adjustments. But one’s own bio-feedback helps to clarify what is comfortable and allows fluidity from finger-to- finger, especially in the thumb shift cosmos.
In general, I regard, the thumb as my measuring rod, so to speak as it brings the five-fingers into a relaxed flowing form. Certainly jerky movements or TWISTS of the hand, wrists and elbows become thumb-traveling impediments, so I tend to avoid them.
In this video, that includes a blocking technique in playing the F# Major scale and arpeggio, I notice the relaxed comportment of my thumb and its position toward the edge of the F# KEY in the ARPEGGIO segment. (addressing the reader’s query)
Here’s a student with noticeably LARGE HANDS who navigates his thumbs quite well, though he has had to make some demonstrated adjustments.
Arioso7's Blog (Shirley Kirsten) 
Maybe not on topic, but as a beginner, I have had already tendon inflamation on both thumbs. After visiting a doctor and had an injection, it went away, but i feel that if i practise too much, it will come back. Are there any particular thing that i overlook to avoid these injuries?
Many thanks, Johan
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Thanks for sharing. Not being physician it’s hard to say what actually caused the inflammation in the first place. I would hope your doc can come up with a reason for your distress. If it were me, at the first sign of thumb pain, I would stop practicing. If you notice that you are tightening your thumb as you play, make note of it. Some of my students don’t notice the tension until I observe it and then they try to allow their whole hand/fingers to hang or relax. I often hang my arm/hands in the air as you can see in the pic as my model for what I imagine when I begin to play. When the thumb shifts under fingers I make a note not to strain or tighten it. A lot of mental imagery should help.
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