Dynamics of self-injurious behaviors.

Self-injurious behavior was examined in a case study of head-banging by an 8-year-old girl with profound mental retardation and an autistic disorder. Trajectories of the arm movements and impact forces of the head blows were determined from a dynamic analysis of videotapes. Results revealed a high degree of cycle-to-cycle consistency in the qualitative dynamics of the limb motions, with one hand motions being faster than those with two hands (inphase and antiphase) and the motions with the helmet about 25% faster than those without the helmet. The impact force of SIBs as a percentage of body weights are near the low end of forces generated in boxing blows and karate hits.