Changes in kinetics and kinematics of handwriting during a prolonged writing task in children with and without dysgraphia.

Handwriting difficulties or dysgraphia have a profound impact on children's psychosocial development, and yet, 10-30% of school-aged children are reported to experience difficulties mastering this skill. Several studies have examined the nature and biomechanical underpinnings of handwriting difficulties in children with and without dysgraphia. While the majority of these studies have considered short handwriting activities involving a sentence or a paragraph, handwriting quality and speed are reported to vary with the length of the writing task. Further, it is suggested that the biomechanics of handwriting also evolve over extended writing periods, and that these changes may be distinct between children with and without dysgraphia. The nature and specificity of these biomechanical alterations remain unknown. To address this knowledge gap, we examined changes in writing speed, grip forces on the pen barrel, and normal forces on the writing surface, over the course of a 10-min writing task, in a large cohort of 4th grade children with and without dysgraphia. Horizontal stroke speed, grip force and normal force increased over time while vertical stroke speed decreased in all children. These biomechanical changes may be attributable to physical and psychological fatigue and the corresponding compensatory processes invoked by the motor system.