Above what current can a shock cause sustained muscular contraction, so that the victim cannot let go?

1. At 10 to 20 mA and above a current begins to drive muscles the way ordinary nerve impulses do. 2. The contraction is sustained for as long as the shock lasts. 3. Since the muscles that close the fingers are stronger than those that open them, the hand grips the conductor. 4. Contraction of the chest muscles may also stop breathing while the shock continues. 5. 100 to 300 mA is the fibrillation band, which is a heart effect rather than the grip effect asked about. _Source: OpenStax College Physics (CC BY 4.0), Ch 20 "Electric Current, Resistance, and Ohm's Law", section Shock Hazards_