1. Training causes microtrauma to muscle fibers which disrupts the bundles and triggers an inflammatory response and muscle swelling as the body works to repair the damaged fibers. 2. The inflammatory response brings chemicals and increased blood flow to break down and clear away damaged tissue, while also sensitizing nerve endings and causing pain. 3. Proper recovery is needed after training to allow the body to repair and rebuild the damaged muscle fibers through actions like cooling down, stretching, hydrating, foam rolling, massage, decreasing stress, and getting sufficient sleep and nutrition over subsequent days.