Exertion level and the intensity of associated movements.

Associated movements in the contralateral limbs were measured quantitatively for 42 seven- to eight-year-old children who wrote with the right hand. Associated movements of the contralateral homologous muscles systematically increased as a function of the intensity of contraction of the active hand. The associated movements were more intense when the left hand was active. The order of hand use markedly affected the lateral asymmetry, indicating that the right and left hands were affected differentially by previous activity. Associated movements of the contralateral antagonist muscles were also observed, and their frequency varied as a function of active hand and exertion level.