FULL TEXT http://individual.utoronto.ca/falkt/...BE_Nov2010.pdf

Grip Force Variability and Its Effects on Children’s Handwriting Legibility, Form, and Strokes

Tiago H. Falk
Bloorview Research Institute,
Holland Bloorview Kids Rehabilitation Hospital,
Institute of Biomaterials and Biomedical Engineering,
University of Toronto,
150 Kilgour Road,
Toronto, ON, M4G-1R8, Canada

Cynthia Tam
Department of Occupational Science and Occupational
Therapy,
University of Toronto,
500 University Avenue,
Toronto, ON, M5G-1V7, Canada

Heidi Schwellnus
Tom Chau1
e-mail: tchau@bloorview.ca
Bloorview Research Institute,
Holland Bloorview Kids Rehabilitation Hospital,
Institute of Biomaterials and Biomedical Engineering,
University of Toronto,
150 Kilgour Road,
Toronto, ON, M4G-1R8, Canada

A comprehensive understanding of the underlying biomechanical
processes during handwriting is needed to accurately guide clinical
interventions. To date, quantitative measurement of such biomechanical
processes has largely excluded measurements of the
forces exerted radially on the barrel of the writing utensil (grip
forces) and how they vary over time during a handwriting task. An
instrumented writing utensil was deployed for a direct measurement
of kinematic and temporal information during a writing task,
as well as forces exerted on the writing surface and on the barrel
of the pen. The writing utensil was used by a cohort of 35 students
(19 males), 16 in first grade and 19 in second grade, as they
performed the Minnesota Handwriting Assessment (MHA) test.
Quantitative grip force variability measures were computed and
tested as correlates of handwriting legibility, form, and strokes.
Grip force variability was shown to correlate strongly with handwriting
quality, in particular for students classified by the MHA as
nonproficient writers. More specifically, static grip force patterns
were shown to result in poor handwriting quality and in greater
variation in handwriting stroke durations. Grip force variability
throughout the writing task was shown to be significantly lower
for nonproficient writers (t-test, p0.01) while the number of
strokes and per-stroke durations were shown to be higher p
0.03. The results suggest that grip force dynamics play a key
role in determining handwriting quality and stroke characteristics.
In particular, students with writing difficulties exhibited more
static grip force patterns, lower legibility and form scores, as well
as increased variation in stroke durations. These findings shed
light on the underlying processes of handwriting and grip force
modulation and may help to improve intervention planning.
DOI: 10.1115/1.4002611
Keywords: handwriting, dysgraphia, children, digitizing tablet,
grip force