Left Hand Violin Technique

Keeping a Relaxed Left Hand Important for Playing Fast and having a relaxed vibrato:

Violinist Nathan Cole, First Associate Concertmaster of the Los Angeles Philharmonic explains how to find the minimum finger weight necessary to keep the left hand relaxed while producing a clear tone. Start playing where the fingers touch the surface of the string. You can expect to hear a squeaky tone.  This is what you want to hear as your finger weight is minimal. Gradually use more finger weight until your tone is clear while maintaining a relaxed hand.  Explanation starts at 6:50: https://www.youtube.com/watch?v=SC4oO9l8P-8&t=655s