Smith attempts a biceps curl with way too much weight on the bar. He strains and struggles, but manages to bend his elbows to 90 degrees.

Mr. Smith attempts a biceps curl with way too much weight on the bar. He strains and struggles, but manages to bend his elbows to 90 degrees. Suddenly, his arms straighten and he slams the weight to the floor. What reflex was activated to protect Mr. Smith from destroying his biceps? Explain what happened to cause him to drop the weight.