The left hand is a busy guy. And a bit conflicted.
While you’re exerting pressure downward into the string, you are also doing a variety of other actions. Shifting, vibrating, bridging between strings, playing chords or double stops, and God knows what else that I can’t think of off hand.
How is all of this possible? By not doing any one of those things to the point where it overtakes the others. Hold on loosely, but don’t let go, as the rock song advises. That should be my cellist’s motto.
Of particularly frequent concern is combining pushing down notes and vibrating. Those actions are extremely contradictory. My friend tried to show me how they work together. You actually use the pressing down as an anchoring device, around which you can vacillate for vibrato. That has always been a problem for me. Maybe it’s too complex and my brain isn’t able to send the correct information to my hand. It gets shorted.
Recently I’ve been enjoying great benefits from practicing basic scale exercises. My guess is that it takes all of the musical layers and emotions out of the equation, so that my body functions in its simplest and most efficient manner. That’s my guess. There I am playing my Klengel — it’s interesting to think of how many cellists over the decades have played the exact same thing, including Klengel himself. I guess if it worked for them, who am I to question it.