I’m a violinist (amateur but play regularly). When I have an important note, which is held for a while and needs vibrato, I frequently decide to shift my left hand position so that my middle finger is responsible, rather than the index finger. It feels stronger, easier to nail the intonation (pitch) with precision, and freer to perform the desired type of vibrato. (String players do vibrato by wiggling the left hand finger, which affects the pitch and overtones / oscillation modes of the string.) In fact, I tend to avoid using the index finger on notes that require vibrato.

That preference might be explained here, by the precision/strength combination. I tried holding a hammer as described in the author’s hammer exercise, and there’s similarity, though it requires much more weight-holding. The left hand doesn’t hold the weight of the violin (consider a cello or a guitar with shoulder strap), but a little grip strength is required to securely hold down the string, especially with vibrato.

Overall, fascinating article. I feel quite motivated to read more on hand anatomy and biomechanics.