Pressure distributions on the chair seat and backrest correlate with handwriting outcomes of school children

Abstract

BACKGROUND:

Postures while sitting are believed to have an important influence on the process of writing and quality of handwriting, but data in this field are sparse.

OBJECTIVES:

The current study was undertaken to investigate correlations between ‘ordinary’ children’s handwriting skills and their posture and stability while sitting.

METHODS:

Twenty-nine children with typical development (age 9.2±0.8 years) underwent the Hebrew Handwriting Evaluation, while the pressure distributions on their seats and backrests were recorded using a pressure mapping system.

RESULTS:

There was an increase in the odds of erasing and overwriting letters in dictation tasks when body displacements of the buttocks increased [Odds Ratio (OR) = 1.01, 95% CI 1.000–1.02, p = 0.050]. Children who did not lean on the backrest were more likely to have legible handwriting in copying tasks (OR = 0.136, 95% CI 0.026–0.723, p = 0.019).

CONCLUSIONS:

The awareness and involvement of health practitioners in sitting postures of children at school might promote activities such as writing. Further investigation of movement patterns while writing and of the correlations of these patterns with handwriting outcomes is recommended. More research regarding adjustments at the school environment for children with developmental disorders is also warranted.

Keywords

Pressure mapping sitting posture writing

1 Introduction

In elementary schools, writing is the main way for a child to express his/her acquired knowledge. Children use writing in almost all subjects learned at school and are graded according to their written outcomes [1, 2]. Writing is a complex activity requiring a multiplicity of physical, cognitive, perceptual and visual skills [1, 3–6 , 1, 3–6].

During children’s development, writing becomes possible at a maturation stage that occurs as a part of the proximal-distal development of their motor acquisition [7, 8]. Therefore, postural control of the trunk and center of the body is considered to be a prerequisite to fine motor function [9]. Even in adulthood, postural stability is correlated with the precision of manual control tasks [10].

Handwriting is a skill important to development at different ages even in the era where typing recording are as beneficial as they are today. Previous studies have found handwriting to be superior to typing in several terms, including the acquisition of a written language [11, 12], the speed of writing and the quality of the composition of a written text [13].

Poor handwriting has been shown to be associated with developmental disorders, such as Developmental Coordination Disorder, Attention Deficit Hyperactivity Disorder (ADHD), Autism Spectrum Disorder (ASD) and learning disorders [14]. Assessment of academic functioning is critically important when evaluating children for possible developmental disorders. Therapists should bear in mind that according to the International Classification of Functioning, Disability and Health (ICF), impairments can be either alleviated or aggravated by environmental factors [15].

Previous studies identified correlations between poor handwriting performance and impaired arrangement of the surroundings [16 –19]. Children with poor handwriting have been found to demonstrate postural instability, use incorrect paper and pencil positioning, and exhibit limited gripping ability compared with children with good handwriting [18]. Furthermore, using effective environmental factors (such as adjusted furniture) has been found to contribute to adequate body postures, eliminate musculoskeletal tensions and improve pupils’ well-being [17].

School environment tends to induce situations where children remain seated for extended periods of time in stooped, static postures. These are combined with prolonged sitting at computers and a sedentary lifestyle in general [20]. Breithecker [21] emphasized that the body, particularly a skeletally immature one, is not designed to sit still for long periods of time, and this may lead to the loss of important physical/sensory experiences. Nevertheless, others have claimed that movement while sitting results in decreased performance and poorer attention to classroom tasks [22]. According to both approaches, proper match between the human being and his/her environment can result in better academic performance [23, 24].

With the aim of shedding more light on the influence of the school environment on the outcomes of writing, the objective of this study was to investigate potential correlations between body movement and the use of the chair backrest while sitting and writing, and handwriting outcomes of ‘ordinary’ children (i.e. not diagnosed with any disabilities or other conditions that may affect their sitting habits) in elementary-school classrooms. Studying this correlation among ‘ordinary’ children may help therapists to better understand the possible effect of body movement and the use of the chair backrest during sitting, on writing of children with developmental disorders.

2 Methods

2.1 Participants

Twenty-nine apparently ordinary children [15 males and 14 females, aged 7.8–10.9 years, mean±standard deviation (SD) = 9.2±0.8] participated in this study after receiving their parents’ consent. Their mean body mass was estimated by their parents as being 29.8 kg. They were recruited by staff members (not the researchers) who sent e-mails to their colleagues and friends, asking them to recommend volunteers among parents of children who were studying in non-special-education schools and were free of neurological signs for any major disease, disability or disorder. In order to control for potential disorders in attention and hyperactive behavior, the parents were asked to fill in the Conners’ Parent Rating Scale (CPRS) [25].

2.2 Instruments

The Conners’ Parent Rating Scale (CPRS) [25] is a parent questionnaire that indicates hyperactivity symptoms and distinguishes between populations with and without ADHD. It is used as a screening tool among 6–14 year old children [25]. In this study we used the short version of the CPRS, with hyperactivity index scores ranging from 0 to 30 (higher score indicated more and/or stronger hyperactive symptoms). An exclusion criterion in our study was set at the score of 20 and above in order to control for potential extreme attention and hyperactive behavior. The CPRS had good inter-rater reliability (between both parents), which is within the range of 0.55–0.71. Construct validity, which was used to measure correlation with other tests, showed significant correlation between the short-version CPRS (hyperactivity index) and temperament-and-behavior questionnaire (r= 0.89), and behavior questionnaire (r= 0.76). The CPRS also has predictive validity. It distinguishes between population with ADHD and without ADHD, learning disorders and behavioral problems [25].

The Hebrew Handwriting Evaluation (HHE) [26] – developed to assess different aspects of Hebrew handwriting for second-to-fourth-grade children (aged 7–10 years) – was used in the study to evaluate the children’s written outcomes. The paragraph used for copying and dictating tasks contained all the letters in the Hebrew alphabet, and included 30 words and 107 letters in total. The test was used to collect data regarding handwriting outcome variables, which consisted of global legibility, letters erased and/or overwritten, unrecognized letters and spatial arrangement of the written text. High internal consistency (α = 0.81) and inter-rater reliability (ranging from r = 0.75 to r = 0.79) are reported. Construct validity of the HHE has been established by demonstrating significant differences between the performance of children with proficient handwriting and those with poor handwriting across several school grades (second and third). No significant differences have been found for gender [26].

A pressure mapping system (mFLEX, Vista Medical Ltd., Winnipeg, Canada), which has been previously employed in clinical and biomedical research for investigating the motions of healthy subjects during prolonged sitting [27], was used in this study. One pressure sensor unit (pad) was positioned on the child’s seat and another on the backrest of the chair in order to acquire pressure distributions which were subsequently used to quantify the child’s movement during various writing tasks. Time-dependent pressure distributions under the buttocks and on the backrest, with a time resolution of 3 Hz and a spatial resolution of 20.6 mm², were obtained. Pressure data were exported to MATLAB (version 7.1, MathWorks, MA, USA). The mean interface pressures (excluding values of zero) measured under the subject’s buttocks and behind his/her back were calculated at each time frame (units: kPa = kN/m²). The percentage of time of not using the chair backrest was also calculated for each part of the HHE (i.e., copying and writing from dictation; see below) for each subject. We further calculated the center of pressure (CoP) measured under the subject’s buttocks and behind his/her back at each time frame, and calculated its displacement (distance between positions) between each two subsequent time frames. In the next step, total distances (the sum of all displacements between subsequent time frames, units: mm) traveled by the CoPs during each part of the HHE were calculated for each subject; these were used as quantitative estimates of body movements. These were further divided by the duration of each part of the HHE (copying and writing from dictation) to yield values of mean CoP displacement velocity (units: mm/sec).

2.3 Procedure

This study was approved by the University Institutional Review Board. Informed consent was obtained from one parent and from the child prior to study entry.

Fig.1

The setup of the chair and desk.

Four undergraduate students were trained by a senior occupational therapist to administer and score the HHE and record pressure data. Two pairs of these students evaluated the children in a quiet area in their own homes. The setup of the chair (with no forearm support) and desk, as well as the manner in which the pressure-measurement units were used, were consistent across all children. The various desks at the children’s homes had different heights, but the child’s position was consistently adjusted as follows: the chair was adjusted to the desk in height, and a supportive stool was provided if the child did not reach the floor with his/her feet. All children were seated to allow them to lean comfortably against the backrest (Fig. 1). The pressure measurement units were consistently positioned on a hard surface placed on a chair. While the children were sitting on the pressure measurement units, they were given clear explanations of the procedures and had a few minutes to “warm up”. All children were writing in two situations: the first, while copying, and the second, while the text was dictated to them by the administrators. They used HB-2 pencils without erasers and a separated 14-line notebook page. The whole evaluation process lasted 15 min at the longest. In order to determine inter-reliability, the evaluation results of each participant were scored by one of the pairs of students. In the event of disagreement within a pair, the students consulted the senior therapist, whose scores were considered as the “gold standard”.

2.4 Data processing

At planning stage sample size was determined based on the assumption that 3 predictors would be included in a regression model (age, the total distance traveled by the CoP under the buttocks and percentage of time without leaning). Cohen’s statistical power analysis [28] was implemented to calculate the multiple regressions for the 3 independent variables with R² of 0.15–0.20, 80% of power and 0.05 significance. The determined sample size was 30 subjects (30 subjects were recruited, but one did not complete the procedure; n = 29).

Descriptive statistics was used to calculate the dependent variables and the independent variables. The Spearman and Pearson correlation coefficients were calculated in accordance with the scoring of variables to test correlations between the various handwriting outcomes in terms of the selected personal variables and sitting measurements and the percentage of time not using the chair backrest. Since the correlations between sitting measurements while copying and while dictating were very high (total distance traveled by the CoP under the buttocks, 0.938, total distance traveled by the CoP behind the back, 0.776, and percentage of time not leaning, 0.879), and given that the outcomes of the sitting measurements were virtually unchanged during the sessions of copying and writing from dictation, the sitting outcomes were calculated together as a function of time during both copying and writing from dictation (only for analysis purposes). Two multiple logistic regressions (for the two dependent variables that showed significant correlations with sitting measurements) were performed, controlling for age, in order to assess individualized contributions of the various sitting measurements to the children’s handwriting outcomes. The parameters of the model were estimated in the logistic regression using the maximum-likelihood forward stepwise method, and the criterion for entering into the model was a level of significance of 0.05. A Wald statistic of p = 0.10 was used to remove a variable from the model.

The dependent variable of letter(s) erased while writing dictated material was recorded as a dichotomist variable, with scores of≤2 taken as being “0” (no letter was erased and/or overwritten) and scores of >2 taken as being “1” (at least one letter was erased and/or overwritten). The dependent variable of global legibility in copying was also recorded as a dichotomist variable, with scores≤1 taken as “0” and scores >1 taken as “1”. Three parameters were used as predictors: the total displacement of the buttocks CoP, the percentage of time not leaning (which was the measure for the use of the backrest) and the child’s age. While the total distance traveled by the buttocks CoP and age were continuous variables, percentage of time not leaning was a dichotomist variable: children who had a percentage≤70% scored “0” and children who had percentage >70% scored “1”. The level of significance was set at 0.05 for all statistical tests.

3 Results

Statistic descriptions of handwriting outcomes and sitting measurement scores are presented in Table 1.

Table 1
Descriptive statistics of main dependent and independent variables (n = 29)

Variable Minimum Maximum Mean Standard deviation

Number of letters erased and/or overwritten in copying task 0 5 2.31 1.97

Number of letters erased and/or overwritten in dictation task 0 8 2.24 2.29

Global legibility in copying task (0–4 scale, lower scores indicate better performance) 0 4 1.66 0.9

Global legibility in dictation task 1 4 1.66 0.86

Conners’ Parent Rating Scale 0 19 6.2 4.99

Pressure under the buttocks (mmHg) 4.3 9.6 6.3 1.4

Pressure on the backrest (mmHg) 0 9.2 3.6 3.4

Total translation distance of traveled by the CoP¹ under the buttocks (mm) 397 7193 1666 1491

Total translation distance traveled by of the CoP¹ on the backrest (mm) 0 53 8 13

Percentage of time without leaning (%) 0 100 47 47

Variable	Minimum	Maximum	Mean	Standard deviation
Number of letters erased and/or overwritten in copying task	0	5	2.31	1.97
Number of letters erased and/or overwritten in dictation task	0	8	2.24	2.29
Global legibility in copying task (0–4 scale, lower scores indicate better performance)	0	4	1.66	0.9
Global legibility in dictation task	1	4	1.66	0.86
Conners’ Parent Rating Scale	0	19	6.2	4.99
Pressure under the buttocks (mmHg)	4.3	9.6	6.3	1.4
Pressure on the backrest (mmHg)	0	9.2	3.6	3.4
Total translation distance of traveled by the CoP¹ under the buttocks (mm)	397	7193	1666	1491
Total translation distance traveled by of the CoP¹ on the backrest (mm)	0	53	8	13
Percentage of time without leaning (%)	0	100	47	47

¹CoP –center of pressure.

Fig.2

Three-dimensional plots describing the location of the center of pressure (CoP) (horizontal plane) measured under the buttocks as a function of time (vertical axis) for two randomly chosen subjects representing a fidgety child (a) and a non-fidgety child (b). The horizontal x-axis is parallel to the coronal plane and perpendicular to the sagittal plane, while the horizontal y-axis is parallel to the sagittal plane and perpendicular to the coronal plane.

Three-dimensional plots describing the location of the CoP measured under the buttocks as a function of time for two randomly chosen subjects representing a fidgety child (a) and a non-fidgety child (b) are provided in Fig. 2. The range of total distance traveled by the buttocks CoP of the fidgety subject is clearly wider than that of the non-fidgety subject.

Table 2 lists the correlations between the various handwriting outcomes and sitting measurements. Moderately significant correlations were found between the variables that measured quality of handwriting (global legibility in copying tasks and number of letters erased and/or overwritten in dictation tasks), and sitting outcomes (total distance traveled by the buttocks CoP and percentage of time not leaning against the chair backrest) (highlighted in Table 2). Specifically, larger displacements of the CoP under the buttocks correlated with more letters erased and/or overwritten in dictation tasks, while a larger percentage of time not leaning correlated with more global legibility in copying tasks. No significant correlations were found between the other personal variables (e.g. age) and sitting measurements.

Twenty (69.0%) of the participants erased and/or overwritten more than two letters in the dictation tasks (score of 1). Our findings revealed that the likelihood of erasing and/or overwriting letters in dictation tasks increased with the total distance traveled by the buttocks CoP (Or= 1.01 95%, CI 1.00–1.02, p = 0.050). Age did not correlate with erasing and/or overwriting letters of dictated text. Fifteen (51%) of the participants had legibility scores of≤1 in copying tasks. The percentage of time sitting without leaning correlated with legibility in those tasks. Specifically, children with non-leaning scores >70% tended to demonstrate higher legibility in copying tasks compared with children with non-leaning scores≤70% (Or= 0.136, 95% CI 0.026–0.723, p = 0.019). Age did not correlate with legibility in copying tasks.

Table 2

Correlations between writing outcomes and sitting measurements

Sitting measurements	Letters erased and/or overwritten in copying tasks	In dictation tasks	Global legibility in copying tasks	Dictation tasks
Mean pressure under the buttocks	r= 0.024	r= –0.092	r= –0.249	r= –0.138
	p = 0.450	p = 0.317	p = 0.096	p = 0.238
Mean pressure on the backrest	r= –0.133	r= 0.107	r= 0.232	r= 0.047
	p = 0.246	p = 0.290	p = 0.113	p = 0.405
Total distance traveled by the CoP under the buttocks	r= 0.029	r = 0.314	r= 0.227	r= 0.119
	p = 0.44	p = 0.044	p = 0.11	p = 0.27
Total distance traveled by the CoP behind the back	r= 0.072	r= 0.150	r= 0.235	r= 0.054
	p = 0.356	p = 0.218	p = 0.109	p = 0.390
Percentage of time not leaning	r= 0.109	r= –0.173	r = –0.347	r= –0.149
	p = 0.286	p = 0.184	p = 0.033	p = 0.22

4 Discussion

The findings of this study revealed a low but significant increase in children’s tendency to have letters erased and/or overwritten with increased distance traveled by the buttocks CoP on the seats of their chairs, which reflects higher levels of body movements. These findings can be attributed to errors in writing being associated with the children’s movements that distracted them. The relationship between writing difficulties and high levels of movement has already been investigated in studies on children with attention disorders [29 –31]. The novelty of the current work is in demonstrating that the same trend can be observed among fidgety children, who are apparently ‘ordinary’ and have not been diagnosed with attention disorders, as well as in the method of using a pressure-mapping system to study the movements of school children in relation to their academic performance.

Although all of the participants were evaluated while sitting on chairs with backrests, most of them leaned back for only short periods of time while writing. These findings are comparable to those of an earlier study analyzing sitting positions of children at school during different tasks, which concluded that children spend up to 80% of their time without leaning on the backrest [32]. We found that when the child avoided leaning on the chair backrest the probability of achieving legibility of writing was higher. There are two possible explanations for the correlation between refraining from leaning on the backrest and higher legibility. One is that children who used their backrests sporadically tended to lean on their desks [33]. Another explanation can be rooted in the fact that children who have stronger postural muscles, which provide them with higher stability, are likely to use backrests less; these are the children who are more likely to demonstrate higher legibility owing to their strong muscles, which can assist them in various motoric skills. This seems to concur with the findings of previous research suggesting that it might be more ergonomically appropriate not to use a backrest, considering that children who did not use one had improved trunk muscle strength, better sitting and standing postures, and less musculoskeletal discomfort [34 –36].

It should be noted that we expected to find stronger correlations between writing outcomes and body movements and posture. The relatively week correlations could be attributed to the study participants, who were ‘typical’ children, which resulted in a low variance factor of movement and fewer difficulties in writing compared with children with developmental disabilities [37 –39].

This study has a number of limitations. First, it has a cross-sectional design and a relatively small sample size. Due to the limited sample size, the study results need to be interpreted with caution, and further research is needed to establish them. Second, the chairs and desks used during data collection were not standard, but each subject used the chair and desk he/she normally uses and feels comfortable with, which we found essential for a reliable investigation of the child’s typical performance.

With the advent of tablets and voice recognition, difficulties in handwriting seem to have less consequences; nevertheless, research demonstrates advantages of handwriting over laptop note-taking [11 –13]. Mueller and Oppenheimer [40] found that adult students who took notes longhand during a lecture processed the information better than students who took notes on laptops, which the researchers attributed to the act of actual writing allegedly encouraging the writer to be engaged in better processing of the information compared with laptop note taking. Such processing enhances encoding of the material learned and improves retention [40]. This observation is congruent with existing literature regarding child development, reporting link between fine motor skills (including writing and copying designs) and cognitive abilities along developmental milestones [41, 42].

The writing performance of children constitutes a major domain of concern which requires special attention to ergonomic aspects. While sitting posture and pencil grip, for example, are generally considered as important factors affecting the efficiency of handwriting, the displacement of the buttocks on the chair and the use of the chair backrest are seldom considered. In order to improve the legibility of handwritten text among ‘ordinary children’, it is recommended that the movement patterns of the buttocks on the seats and fractions of time without leaning while writing, are included in the ergonomic evaluation toolbox.

5 Conclusion

This study demonstrated a partial correlation between body movements, percentages of time without leaning while sitting and handwriting outcomes of typical children. The use of advanced and sensitive technology to measure even the slightest body movements might be helpful to ergonomists, occupational therapists, teachers and others who aim to achieve better writing skills among children. The awareness and involvement of health professions in sitting and stability postures of children in school might promote activities such as writing and may give a better perspective on writing outcomes. Deeper investigation of patterns of such movements and correlations of these patterns with handwriting outcomes is recommended and further research on the adaptation of school environment to children with developmental disorders is warranted.

Conflict of interest

All authors report no financial interests or potential conflicts of interest.

Footnotes

Acknowledgments

We gratefully acknowledge the students who supported data collection: Meital Harpaz, Shlomit Kopilov, Fanny Mishan-Swisa, and Tal Rasis.

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