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Technical Briefs

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

[+] Author and Article Information
Tiago H. Falk, Heidi Schwellnus

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

Tom Chau1

Bloorview Research Institute, Holland Bloorview Kids Rehabilitation Hospital, Institute of Biomaterials and Biomedical Engineering, University of Toronto, 150 Kilgour Road, Toronto, ON, M4G-1R8, Canadatchau@bloorview.ca

1

Corresponding author.

J Biomech Eng 132(11), 114504 (Oct 15, 2010) (5 pages) doi:10.1115/1.4002611 History: Received May 28, 2010; Revised September 13, 2010; Posted September 23, 2010; Published October 15, 2010; Online October 15, 2010

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, p<0.01) 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.

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Copyright © 2010 by American Society of Mechanical Engineers
Topics: Force
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Figures

Grahic Jump Location
Figure 1

Plots of Minnesota Handwriting Assessment scores for (a) legibility and (b) form versus ζrms for proficient and nonproficient writers. Dashed and solid curves represent linear fits for nonproficient and proficient writers, respectively. The R2 statistics and p-values are also reported for each regression line.

Grahic Jump Location
Figure 2

Plots of (a) average per-stroke duration (μS) and (b) standard deviation of all stroke durations (σS) versus grip force coefficient of variation (ζrms) for proficient and nonproficient writers. Dashed and solid curves represent linear fits for nonproficient and proficient writers, respectively. The R2 statistics and p-values are also reported for each regression line.

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