Original image source here. Used for non-commercial, educational purposes only.
1. Oistrakh (red): For violin playing, the use of the index finger on the bow and the use of the weight of the arm are not mutually exclusive – even in the classic Russian method, Oistrakh commented on the use of the weight of the upper arm in producing great projection. For viola playing, the use of the index finger is less or done away entirely, perhaps leaning to the middle finger use of the cello.
2. Primrose (yellow): William Primrose, the most famous violist in modern times, and known for his immense sound, told David Dalton that to him the distinction between arm weight and back muscle use was too difficult to pin-point, and that his pedagogical approach was to suggest that there was a hole in the floor, through which a rope was tied to your elbow, and while you played, a small man was pulling on the rope as would be a bell ringer.
3. Vangerov (dark blue): If photos and comments are any indication Vangerov leans far back when playing, likely so that the internal center of gravity allows easier arm weight. It is a good thing to try – I have found it useful, but I can’t sustain such a position without hurting my back.
4. Pedagogues I have met: Lim Soon Lee (light blue) suggests thinking of an outer ring encircling the arm – from the back muscles to the little finger, keeping playing as open as possible. Also, to have an imaginary wall, in which to push your upper arm against, and a complex balance of “float” and “lean” of the arm (see the next item). Ajarn Choochart Pitaksakorn suggests exercises in raising the arms and totally releasing them to feel natural arm weight – not a planned drop of the arms, but a real relaxed release. This is not shown in the picture because it is done without the instrument or bow.
5. Just me: I think that arm weight is the most accessible method in tone production and to understand the “float-lean” concept, one can go to a pool and feel the natural float of the arm because of water tension, even while leaning against the water. While you’re there, try out freestyle or backstroke, and try it once concentrating on NOT using your back muscles, and then stop, and try it again, more naturally. The same concept applies to using back muscles in violin playing.