What current threshold causes muscles to contract such that a hand grip on an energized object cannot be released?

The let-go threshold refers to the level of electrical current that causes involuntary muscle contractions, preventing a person from releasing their grip on an energized object. This phenomenon occurs because electrical current affects the neuromuscular system, leading to a loss of voluntary control over muscle movement.

When a person comes into contact with an energized object, and the current exceeds the let-go threshold, the muscles in the hand contract tightly, making it nearly impossible for the individual to let go of the object. This is particularly dangerous in electrical hazards, as the individual may remain in contact with the source of electricity for an extended period, increasing the risk of severe injury or fatality.

Understanding the let-go threshold is critical for safety in environments where electrical hazards are present, as it helps individuals recognize the point at which they may become incapacitated by electrical shock. The other options refer to different aspects of electrical safety but do not define this specific involuntary muscle response.