Physiology When a muscle is not contracting, actin and myosin are prevented from reacting by: A Troponin-tropomyosin B Phosphocreatine C Heavy meromyosin D Acetylcholinesterase 💡 Explanation When a muscle is not contracting, actin and myosin are prevented from reacting by: ✓ Correct Answer: A. Troponin-tropomyosin