What blocks a bonding site in muscle?

Several things do. Neuromuscular-blocking drugs block neuromuscular transmission at the neuromuscular junction causing paralysis. Quaternary ammonium muscle relaxants are quaternary ammonium salts used as drugs for muscle relaxation, most commonly in anesthesia.
When a muscle is in a resting state, actin and myosin are separated. To keep actin from binding to the active site on myosin, regulatory proteins block the molecular binding sites. Tropomyosin blocks myosin binding sites on actin molecules, preventing cross-bridge formation, which prevents contraction in a muscle without nervous input.

Several things do. Neuromuscular-blocking drugs block neuromuscular transmission at the neuromuscular junction causing paralysis.

Quaternary ammonium muscle relaxants are quaternary ammonium salts used as drugs for muscle relaxation, most commonly in anesthesia.

Tropomyosin blocks myosin binding sites on actin molecules, preventing cross-bridge formation, which prevents contraction in a muscle without nervous input.