Why are my lats sore after push-ups?
Have you ever done a boxing or MMA class?
Your serratus muscles and back were probably sore the next day.
This is because explosively throwing your hands across your body recruits your back muscles in a significant way.
Ever looked at a boxer's "rib muscles?" those rib muscles are your serratus anterior muscles. The Serratus functions to pull your scapula forward. As in, your shoulder blades. Your back has a surprising amount of involvement in punching movements.