This study is the first, to our knowledge, to examine associations between quantitative measures of drawing quality (shape accuracy and errors) and upper arm kinematics during graphomotor tasks made by typically developing children and children with handwriting problems. The results revealed greater errors in copying tasks than in tracing tasks, and children with handwriting problems demonstrated less accuracy drawing shapes than typically developing children. For both groups, movement was larger in the distal joints than in the proximal joints, when tasks were performed on a horizontal plane than on a vertical plane and when tracing than when copying. Furthermore, children with handwriting problems demonstrated greater dissimilarity between shapes made distally than with the proximal joints compared to typically developing children. Finally, the drawing variables recorded on the tablet were significant predictors of legibility, speed of writing, visual motor integration and motor coordination; in contrast, the dissimilarity measure of joint movement was a significant predictor of speed of writing and motor coordination.
The current findings show that children with handwriting difficulties make less accurate shapes as assessed by both standardized paper-and-pencil tests and by more objective tablet data than typically developing children. These differences in drawing were evident not only in the shapes drawn on the tablet, but also in the scaled versions made by displacements of the upper arm joints. These findings suggest a relationship between proximal joint movements and handwriting quality; identifying the mechanisms behind this relationship requires further research.
As expected, the distal segments of the arm moved more than the proximal parts, as observed in other studies [29]. This suggests that there may be greater stability in the proximal joints and greater mobility in the distal joints during graphomotor tasks, as reduced displacement is generally associated with greater stability [38]. Furthermore, as the joints became more proximal, the dissimilarity between joint movement and drawn or copied shapes increased, perhaps demonstrating that “responsibility” for achieving the shape is due to decreasing contributions of movement of the fingers, then the wrist, then the elbow and least by the shoulder and trunk. On the other hand, it may be a matter of strategic choice by some children; those who are unable to accurately produce movements in their fingers may utilize compensations in their more proximal joints to produce the shape. This possibility requires further investigation, for example, by experimentally obliging children to use a specific strategy such as constraining shoulder movement, and examining which strategy is most efficient for writing. In keeping with this suggestion, performing a manual task seated as opposed to standing, for example, may provide a child with greater postural stability while completing a graphomotor task thereby reducing their tendency to use trunk compensations [38]. Reducing the degrees of freedom a child needs to perform a task may facilitate stability by limiting the need for greater manual control to achieve accuracy [39].
Miyahara et al. [27] found that inaccurate drawers demonstrate more coincidental proximal movements in their head and shoulders when making drawing errors, and concluded that inaccurate drawing was a result of proximal instability. In contrast, we did not find between-group differences in the magnitude of the shoulder and trunk joint displacements. It should be noted that Miyahara et al. [27] used a different measure for stability (significant extraneous abrupt movement) than the measures used in the current study. We found a difference in the dissimilarity of the joint movements for the shapes at the proximal joints and not in the magnitude of the movements; the children with handwriting difficulties had joint displacements that were more dissimilar to the drawn shape than in the control group. Previous studies of drawing shapes have demonstrated that the shoulder creates a foundation for movement of the entire arm [40]. It appears as though handwriting is also a “whole arm” task such that all of the joints, including the more proximal ones, contribute to the shape and size of the drawn figure. [30]. Sharing the task across multiple arm joints may also improve performance by taking advantage of the redundancy in the degrees of freedom when performing this task [41].
It may be that children who are less proficient writers utilize less control in the proximal joints when drawing a shape; we suggest that the observed movements in this group are more a result of joint reaction forces rather than active control, compared to the control group. It is therefore important for clinicians to consider training the whole arm including the shoulder and utilizing a sensory-motor approach when working on handwriting and other graphomotor tasks. Further studies should explore differences in adopting a more proximal, more distal or uniform strategy during treatment for handwriting.
In addition, there was more joint movement when performing the task on a horizontal surface than on a vertical surface, although there was no difference in accuracy between the two planes. This is similar to findings of other studies which found that although different movement strategies are utilized when drawing on different planes of movement, the accuracy of the product is similar [28].
Another noteworthy finding was that during a tracing task, joint movement is greater than during a copying task, while there were more drawing errors for copying than for tracing. This appears to strengthen the notion that the amount of joint movement does not impact the accuracy of the shape. It appears reasonable that there would be fewer drawing errors during tracing, as tracing is performed on the shape itself and involves primarily motor coordination. In contrast, copying requires higher level cognitive processes such as visual motor integration skills where children need to rely on vision and alternate their gaze between the form that is copied and the form that is produced [42].
It is interesting to note that drawing error was the best predictor of functional outcomes of both speed and legibility, followed by dissimilarity, and that the amount of movement or size of the shape did not predict any of the functional performance outcomes. It appears that children utilize different movement strategies in handwriting, and the amount of movement does not necessarily have an effect on a child’s writing proficiency.
Furthermore, it may be that children with handwriting difficulties have no innate difficulty in controlling joint dynamics, as the difference was found mainly in the copying task and not in the tracing task. Drawing is a complex task involving many skills, including both sensorimotor processes and higher-level cognitive process skills [8,9,10]. Thus, it may be that the differences that arose in the copying task are primarily related to a higher-level cognitive issue, such as difficulty with planning, imitation or visuomotor transformation, and less dependent on proximal or distal joint dynamics. A limitation of the present study was that movement patterns were examined during tasks that involved copying and tracing basic shapes rather than actual handwriting. This limitation was intentional in an effort to identify associations during such simple, more constrained graphomotor tasks. Further studies are necessary to examine more specific relationships between the different upper extremity joints during handwriting, and whether these relationships differ in children with and without handwriting problems. In addition, our technique of analyzing the shapes drawn by each joint may have been affected by the size of the shapes, as was found previously [30]. Larger shapes may trace 3D paths in space, rather than the largely two-dimensional shapes observed in this study, affecting the outcome variables. We expect that this effect was minor due to the relatively small shapes used; however, to better understand the role of the proximal joints in producing end effector motion, shapes of different sizes should be tested in future studies. This will support an investigation of whether handwriting difficulties are related to recruiting the appropriate arm dynamics for a given task, whether they are due to impairment of proximal muscle control, or whether they are related to higher level cognitive processes. Thus, it is not possible to determine conclusively that proximal joints are responsible for task performance rather than stabilization based on results of this study.