Abstract
We analyzed videos of boxing matches and mixed-martial-arts fights. We observed an immediate and severe loss of muscle tone following a knockout. This impact-induced loss of muscle tone was typically transient, lasting seconds or less. This phenomenon involved muscles in the upper and lower limbs, and possibly axial muscles as well as the facial musculature. The observation is best described as an active person instantaneously transformed into an inanimate object, followed by a free fall in gravity accompanied by flaccidity or paralysis. Analyzing double-knockouts, we concluded that the observed impact-induced loss of muscle tone occurred within tens of milliseconds of a head hit. The speed, scope, and severity of the muscle tone loss are not consistent with a local loss-of-function mechanism. Because such loss of muscle tone closely resembles sudden attacks in cataplexy patients, we hypothesized that severe head impacts may directly involve brain centers that regulate rapid eye movement sleep. These brain centers may be part of an active mechanism to shut down the muscle tone quickly and globally. When muscle tone is low or absent, athletes are at elevated risk for further injuries in combat or contact sports. Athletes, athletic trainers, and referees in combat as well as contact sports should be vigilant and recognize signs of impact-induced loss of muscle tone in order to improve player safety and better protect these athletes.