Asymmetry in the Alignment of School Furniture and Anthropometric Measures: A Comparative Study Between Two Schools in Spain and Portugal

Abstract

Background: School ergonomics is a subject of growing interest for the scientific community due to the health problems that it is associated with in students, mainly asymmetries in the spine due to the use of chairs and desks that are inadequate for their anthropometry. This study aimed to analyze the anthropometric characteristics and asymmetries among fifth- to ninth-grade students in Spain and Portugal, with the goal of obtaining data on the ideal height of seats and desks. Additionally, it evaluated the correspondence in the recommended sizes of chairs and desks according to the parameters of the European Union catalog and examined the suitability of the height as a criterion for the allocation of school furniture. Methods: Different anthropometric variables, including the height, popliteal height, shoulder-to-seat height, and elbow-to-seat height, were measured in a stratified sample of 500 students (mean age = 12.7 years, SD = 1.2) across different grades (fifth grade = 86, sixth grade = 106, seventh grade = 95, eighth grade = 89, ninth grade = 124), genders (males = 256, females = 244), and countries (Spain = 191, Portugal = 309). These measurements were used to calculate the average ideal seat and desk heights based on anthropometric formulas, which were then compared to the current furniture allocation practices. The statistical analyses included t-tests, chi-squared tests, and effect sizes, with adjustments for multiple comparisons. Results: The results revealed significant asymmetries and low correspondence in the allocation of chairs and desks of the same sizes to students, with a match rate ranging between 40% and 70%. Moreover, the correspondence was even lower when using a formula based solely on height, compared to formulas validated with specific anthropometric measures, particularly for desks, where the asymmetries reached 100% in some grades. Conclusion: These findings highlight the need to improve the adaptation of school furniture to optimize student ergonomics and comfort, and they suggest disregarding the height as the primary criterion for furniture allocation. Additionally, assigning a desk size based on the recommended chair size is discouraged.

1. Introduction

Posture and spinal symmetry are essential for physical development, especially during childhood and adolescence, when the body grows rapidly [1]. The spine, which serves as the central axis of the musculoskeletal system, plays a crucial role in the body’s stability and mobility. Maintaining proper symmetry and posture is vital not only for musculoskeletal health but also for overall well-being [2]. During the early stages of life, postural habits are established that can prevent long-term back problems [3].

One of the most critical moments at which to focus on posture is in school. Students spend a significant amount of time sitting—approximately 6.5 h per day in school settings [4,5]. This prolonged sitting time, which can constitute between 70 and 90% of the school day [6,7], can lead to spinal asymmetries if proper posture is not maintained. In the short term, this may cause minor discomfort, but, over time, it can develop into more serious issues, such as scoliosis. In Spain, it has been found that 51% of boys and more than 69% of girls have experienced low back pain before the age of 15 [1,8]. Preventive intervention is crucial to prevent these problems from becoming chronic conditions in adulthood.

School furniture plays an essential role in the prevention of postural problems. A mismatch between the furniture dimensions and students’ anthropometric characteristics can negatively impact their posture and long-term health [9,10,11].

Historically, the allocation of school furniture has been based on general criteria such as the chronological age or the average height of students. However, this approach does not take into account individual variations in body proportions or the differences in physical development among students of the same age. Therefore, it is essential to determine whether this method is suitable for the anthropometric characteristics of the student population.

The European Standard 1729:1-2015 provides guidelines on school furniture dimensions, defining criteria for the design of chairs and desks based on students’ anthropometric characteristics [12]. This standard proposes eight different sizes to accommodate the variability in student dimensions throughout their education. To simplify allocation, it introduces a color-coding system that symmetrically associates each chair and desk size with a color. However, it is important to evaluate whether this symmetrical allocation truly matches the students’ anthropometric characteristics. Previous research has shown that, in some educational centers, the implementation of this standard is insufficient, with the continued use of proprietary size guides rather than adhering to the European recommendations [13,14].

Early intervention is key to correcting postural misalignments before they become chronic problems. Postural education programs in schools, which teach students the importance of correct posture when sitting, walking, and engaging in daily activities, are essential [15]. In the classroom, the sitting posture is particularly relevant. Many students adopt incorrect postures, negatively affecting their spinal alignment. Proper posture involves keeping the back straight, shoulders relaxed, feet flat on the floor, and knees at a 90-degree angle, which evenly distributes the weight and reduces the spinal pressure [16], seeking adequate symmetry in the spine. School furniture should be adapted to the physical characteristics of students to avoid forced postures and promote a healthy learning environment [9,17]. Thus, the combination of ergonomic furniture design with proper postural education can reduce the incidence of musculoskeletal problems [18].

Early intervention with the effective implementation of ergonomic standards in school furniture and the correct adaptation of school furniture is crucial in preventing future musculoskeletal problems. Therefore, the objective of this study was to analyze the morphological asymmetries between two populations (Spain and Portugal) differentiated by sex, assess whether students in the same grade use the same size of school furniture, and verify whether the height is an adequate criterion for its allocation. Additionally, the correspondence between the chair and desk sizes of the European catalog based on color coding was examined.

To address the objectives of this study, the following research questions were formulated.

Are there significant differences in the anthropometric characteristics and furniture needs of students based on their grade, gender, and country of origin (Spain and Portugal)?

Does the alignment between school furniture sizes and students’ anthropometric characteristics differ when using height-based criteria versus validated anthropometric formulas?

To what extent does the correspondence between chair and desk sizes meet the ergonomic needs of students as defined by the European school furniture catalog?

These questions aimed to explore the anthropometric disparities between the two populations and assess the adequacy of the current school furniture allocation practices.

2. Materials and Methods

2.1. Sample

The participants in this study were students from two public primary and secondary education schools located in a city in Southern Galicia and another in Northern Portugal. A total of 500 students (256 boys and 244 girls), with a mean age of 12.7 years (SD = 1.2), including boys (mean age = 12.10 years, SD = 1.44) and girls (mean age = 12.15 years, SD = 1.44), from grades 5 to 9 in Portugal and from the 5th and 6th grades of primary education and 1st to 3rd years of ESO (the equivalent of grades 7 to 9 in Portugal) in Spain, were invited to participate (see

Table 1. Description of the study sample.

Grade	Spain (n = 191)		Portugal (n = 309)
	Males (n = 91)	Females (n = 100)	Males (n = 165)	Females (n = 144)
5th grade	19	18	29	20
6th grade	25	23	25	33
7th grade	15	17	34	29
8th grade	13	19	36	21
9th grade	19	23	41	41
Total	91	100	165	144

Note: “Grade” refers to the academic year level of the students. For Spain, grades 5 and 6 correspond to primary education, while grades 7, 8, and 9 correspond to the 1st, 2nd, and 3rd years of ESO (secondary education). In Portugal, grades 5 to 9 represent consecutive years of basic education.

). A convenience sampling technique was used to facilitate the recruitment of the students. All students who provided signed informed consent from their parents or guardians, as well as their own assent, were included in the study. Repeating students were assigned to the grade corresponding to their biological age.

Students with diagnosed physical conditions or health issues that could affect their posture or anthropometric measurements (e.g., scoliosis, physical disabilities, or musculoskeletal disorders) were excluded from the study. This criterion ensured that the results reflected the typical anthropometric characteristics of the general student population.

To carry out this study, the necessary permissions were obtained from the school administration. All families and students were informed in advance about the research objectives, the procedures to be followed, the confidentiality statement, and the contact details of the researcher. The ethical principles of medical research involving human subjects, as outlined in the Declaration of Helsinki [19], were respected at all times.

The study received approval from the Ethics Committee of the Faculty of Education and Sport Sciences at the University of Vigo, under code 04/1019.

2.2. Measurements

The height, popliteal height, elbow height, and shoulder height were measured for this study. Anthropometric measurements followed the procedures established in previous, similar studies [9]. Students were assessed on the right side (except for height) while seated in an adjustable chair with a horizontal seat surface. The legs were kept at a 90º angle, with the feet fully resting on an adjustable footrest. During the measurement process, the students were barefoot and wore shorts and a short-sleeved shirt. A 60 cm Cescorf anthropometer, certified by the International Society for the Advancement of Kinanthropometry (ISAK), was used for all measurements, with the exception of the height, which was recorded with a portable Seca stadiometer (range 20–205 cm). Measurements were conducted over ten sessions, one for each grade level evaluated, and recorded in centimeters by an assistant; all were carried out by the same anthropometrist. This approach minimized the errors that can occur when multiple anthropometrists are involved [20]. The precision and repeatability of the measurements were ensured by the anthropometrist’s training, certified at ISAK Level 3, and their prior experience in such evaluations. At least two measurements were taken for each parameter, and, if the difference exceeded 0.5 cm, a third measurement was taken. The following anthropometric measures were included to calculate the ideal furniture dimensions [21] (see Figure 1).

• Stature (S): Defined as the vertical distance between the floor and the top of the head, measured with the subject standing upright and looking forward (Frankfurt plane).
• Seated shoulder height (SHS): The vertical distance from the sitting surface to the acromion.
• Seated elbow height (EHS): Measured with the elbow flexed at 90º. The vertical distance from the bottom of the elbow (olecranon) to the sitting surface.
• Popliteal height (PH): The knee should be bent at 90º. The vertical distance from the floor to the back of the knee (popliteal area).

The equations used to calculate the ideal heights of chairs and desks were as follows [22].

• Seat height (SH): (PH+2.5) cos30° ≤ SH ≤ (PH+2.5) cos5°;
• Desk height (DH): (SH+EHS ≤ DH ≤ (SH + EHS*0.7396 + SHS*0.2604).

2.3. Procedure

The anthropometric measurements were carried out over five consecutive days, from Monday to Friday, in both countries. The assessments were conducted during school hours, between 9:00 a.m. and 2:00 p.m. Each day, one grade level was evaluated, starting with the 5th grade and ending with the 9th grade. In Spain, the measurements were taken during the second week of March 2023, while, in Portugal, they were conducted during the third week of the same month.

The data were recorded in an SPSS spreadsheet, where the ideal seat and desk heights for each subject were determined using the previously mentioned formulas. Additionally, the corresponding seat and desk size for each student was estimated based on their stature. Subsequently, a correspondence analysis was performed between the size/color calculated from the anthropometric formulas, which included the popliteal height, elbow height, and shoulder height, and the estimation based solely on the stature. A discrepancy was considered when both calculations suggested a different size/color.

Furthermore, the degree of mismatch between the seat and desk size/color assigned to the students (see Figure 2) was evaluated using the formula based on multiple anthropometric measurements. A mismatch was considered when the size/color of one piece of furniture did not match the other, according to the parameters established in the reference furniture catalog of the European Union (e.g., yellow seat/size 3 and red desk/size 4).

2.4. Data Analysis

All statistical analyses were performed using the IBM Statistical Package for the Social Sciences, version 25.0 (IBM SPSS Inc., Chicago, IL, USA). A descriptive analysis, stratified by grade level, was conducted for each of the study variables through measures of the central tendency (mean and standard deviation). The normality of the sample was checked using the Kolmogorov–Smirnov test (with Lilliefors correction) for variables with more than 50 cases and the Shapiro–Wilk test for variables with 50 or fewer cases. The mean values of the quantitative variables studied were compared between males and females and between Spain and Portugal, using a t-test for independent samples when the sample was normal and the Mann–Whitney U test when the sample was not normal. Qualitative variables, such as the grade, sex (male/female), country of origin (Spain/Portugal), and types of seat and desk sizes according to the EU catalog, were compared using crosstabs to calculate the chi-squared statistic (χ² test of independence) and evaluate associations between categorical data.

To control for the risk of committing a type I error due to multiple comparisons, the Holm–Bonferroni correction was applied within each set of comparisons, ensuring the rigorous adjustment of the significance levels. For comparisons that remained significant after applying the Holm–Bonferroni correction, effect sizes (Cohen’s d) were calculated to assess the magnitude of the observed differences. The Cohen’s d values were interpreted as small (d = 0.2), medium (d = 0.5), and large (d = 0.8).

In all statistical tests, a significance level of p < 0.05 was considered, except for those adjusted using the Holm–Bonferroni correction.

3. Results

Descriptive Analysis

Table 2. Descriptive analysis of the study.

Grade	Spain
	Stature								Popliteal Height								Elbow Height								Shoulder Height
	Males			Females			t	p	Males			Females			t	p	Males			Females			t	p	Males			Females			t	p
	N	$\overline{\mathbf{X}}$	SD	N	$\overline{\mathbf{X}}$	SD			N	$\overline{\mathbf{X}}$	SD	N	$\overline{\mathbf{X}}$	SD			N	$\overline{\mathbf{X}}$	SD	N	$\overline{\mathbf{X}}$	SD			N	$\overline{\mathbf{X}}$	SD	N	$\overline{\mathbf{X}}$	SD
5th grade	19	142.3	9.2	18	145.2	7.1	−1.061	0.296	19	38.6	2.8	18	39.9	2.1	−1.657	0.106	19	18.5	2.2	18	19.0	1.8	−0.897	0.376	19	47.3	3.9	18	49.3	2.4	−1.976	0.056
6th grade	25	148.3	8.4	23	149.6	5.7	−0.650	0.519	25	40.6	2.6	23	40.4	2.3	0.296	0.769	25	19.6	2.4	23	19.9	2.1	−0.520	0.605	25	49.6	3.4	23	50.7	2.6	−1.184	0.243
7th grade	15	151.7	7.4	17	151.2	6.1	0.233	0.817	15	39.8	2.2	17	38.6	1.5	1.761	0.091	15	17.8	2.1	17	20.0	2.5	−2.696	0.011	15	49.5	2.7	17	51.2	3.2	−1.653	0.109
8th grade	13	163.4	6.2	19	157.9	5.6	2.583	0.015	13	42.2	1.9	19	40.3	1.9	2.817	0.008 *2	13	19.0	2.0	19	20.0	1.7	−1.612	0.117	13	53.8	2.9	19	52.5	2.4	1.310	0.200
9th grade	19	169.9	7.4	23	157.7	6.5	5.697	0.000 *1	19	43.6	1.8	23	39.1	2.3	6.740	0.000 *3	19	19.5	2.3	23	20.6	2.8	−1.418	0.164	19	55.5	3.0	23	53.1	3.0	2.622	0.012
t/sex	1.119								3.203								−3.092								−0.920
p	0.265								0.002 *4								0.002 *5								0.359
Grade	Portugal
	Stature								Popliteal Height								Elbow Height								Shoulder Height
	Males			Females			t	p	Males			Females			t	p	Males			Females			t	p	Males			Females			t	p
	N	$\overline{\mathbf{X}}$	SD	N	$\overline{\mathbf{X}}$	SD			N	$\overline{\mathbf{X}}$	SD	N	$\overline{\mathbf{X}}$	SD			N	$\overline{\mathbf{X}}$	SD	N	$\overline{\mathbf{X}}$	SD			N	$\overline{\mathbf{X}}$	SD	N	$\overline{\mathbf{X}}$	SD
5th grade	29	143.8	5.8	20	143.6	7.1	0.101	0.920	29	37.8	2.5	20	38.1	2.3	−0.404	0.688	29	19.9	2.9	20	21.9	3.8	−1.954	0.059	29	50.1	4.3	20	51.6	4.6	−1.125	0.266
6th grade	25	146.1	4.9	33	148.1	7.1	−1.275	0.207	25	38.2	2.8	33	39.1	2.6	−1.216	0.229	25	20.3	2.5	33	20.1	2.2	0.224	0.824	25	50.0	3.6	33	51.3	3.8	−1.286	0.204
7th grade	34	156.3	9.4	29	156.4	8.4	−0.047	0.991	34	39.9	2.9	29	39.2	2.4	0.991	0.326	34	22.5	3.7	29	24.4	3.9	−1.913	0.060	34	55.4	5.3	29	56.4	5.3	−0.816	0.417
8th grade	36	161.4	7.2	21	159.4	6.3	1.049	0.299	36	40.7	2.8	21	40.1	2.8	0.804	0.425	36	22.8	3.7	21	24.7	4.2	−1.806	0.076	36	56.5	3.6	21	56.7	3.9	−0.177	0.860
9th grade	41	166.2	8.7	41	159.1	8.4	3.740	0.000	41	43.1	3.4	41	40.9	2.2	3.405	0.001	41	23.6	3.7	41	25.5	3.6	−2.347	0.021	41	58.4	4.8	41	58.7	4.3	−0.281	0.779
U o t/sex	10,639.500								1.729								9572.000								−1.015
p	0.113								0.085								0.003								0.311
U o t/Country	6899.5			−1.251					1.516			0.206					3760.5			3471.0					−5.886			3907.0
p	0.284			0.212					0.131			0.837					0.000 *6			0.000 *7					0.000 *8			0.000 *9

Note: N = number of participants; $\overline{\mathrm{X}}$ = mean; SD = standard deviation; t = t-statistic (result of t-test); U = Mann–Whitney U-statistic; p = level of significance. p-values were adjusted using the Holm–Bonferroni correction to control for multiple comparisons. Only values marked with an asterisk (*) remained significant after adjustment. Cohen’s d values are provided for significant differences (Holm–Bonferroni corrected): ¹ d = 1.763; ² d = 1.000; ³ d = 2.153; ⁴ d = 0.474; ⁵ d = −0.452; ⁶ d = −0.962; ⁷ d = −1.004; ⁸ d = −0.722; ⁹ d = −0.849.

presents the descriptive analysis of the study, recording the measurements of the height, popliteal height, shoulder height while seated, and elbow height while seated with the elbow flexed at 90° to the seat. The analysis was performed by stratifying the data by country and by the students’ academic grade.

In the sample analyzed in Spain, statistically significant differences between males and females were observed in terms of the height and popliteal height in the eighth and ninth grades, as well as in the elbow-to-seat height in the seventh grade and the shoulder-to-seat height in the ninth grade. In all cases, males presented larger dimensions.

For the students in Portugal, significant differences between males and females were only found in the ninth grade for the variables of the height, popliteal height, and elbow-to-seat height. In all cases, except for the latter variable, males also showed larger dimensions.

No significant differences were found when comparing the results between Spain and Portugal in the variables of the height and elbow height. However, significant differences were observed in the elbow-to-seat height and shoulder-to-seat height, with larger dimensions in the Portuguese students in both cases.

Table 3. Descriptive analysis of ideal seat height and ideal desk height by grade and country.

Males	ISH Spain		ISH Portugal		t	p	IDH Spain		IDH Portugal		t	p
	$\overline{\mathbf{X}}$	SD	$\overline{\mathbf{X}}$	SD			$\overline{\mathbf{X}}$	SD	$\overline{\mathbf{X}}$	SD
5th grade	38.2	2.6	37.5	2.3	0.997	0.324	60.4	4.2	61.3	3.0	−0.853	0.398
6th grade	40.1	2.4	37.9	2.6	3.205	0.002 *1	63.7	4.2	62.0	3.1	1.545	0.129
7th grade	39.4	2.1	39.5	2.7	−0.112	0.911	61.3	3.3	66.3	4.1	−4.151	0.000 *2
8th grade	41.7	1.7	40.3	2.6	1.789	0.080	65.2	2.6	67.4	3.4	−2.208	0.032 *3
9th grade	42.9	1.7	42.5	3.2	0.668	0.507	67.0	3.2	70.6	4.8	−2.917	0.005 *4
Females	ISH Spain		ISH Portugal		t	p	IDH Spain		IDH Portugal		t	p
	$\overline{\mathbf{X}}$	SD	$\overline{\mathbf{X}}$	SD			$\overline{\mathbf{X}}$	SD	$\overline{\mathbf{X}}$	SD
5th grade	39.5	1.9	37.8	2.1	2.649	0.012 *5	62.5	2.7	63.5	4.8	−0.797	0.431
6th grade	39.9	2.1	38.7	2.4	2.004	0.050	63.9	3.9	62.9	3.5	1.013	0.315
7th grade	38.3	1.4	38.9	2.2	−1.055	0.297	62.3	3.3	67.4	4.2	−4.319	0.000 *7
8th grade	39.9	1.8	39.7	2.6	0.332	0.742	64.2	2.6	68.6	3.9	−4.117	0.000 *8
9th grade	38.8	2.2	40.5	2.0	−3.167	0.002 *6	63.6	2.9	70.3	4.1	−6.860	0.000 *9

Note: ISH = ideal seat height; IDH = ideal desk height; $\overline{\mathrm{X}}$ = mean; SD = standard deviation; t = t-statistic (result of t-test); p = level of significance. p-values were adjusted using the Holm–Bonferroni correction to control for multiple comparisons; only values marked with an asterisk (*) remained significant after adjustment. Cohen’s d values are provided for significant differences (Holm–Bonferroni corrected): ¹ d = 0.881; ² d = −1.289; ³ d = −0.684; ⁴ d = −0.820; ⁵ d = −0.847; ⁶ d = −0.820; ⁷ d = −1.309; ⁸ d = −1.314; ⁹ d = −1.802.

shows the mean ideal seat and desk height by age group for students from Spain and Portugal, together with a statistical comparison between the two countries.

Significant differences were found in the ideal seat height for males in the fifth grade, as well as in the desk height in the seventh, eighth, and ninth grades, when comparing students from Spain and Portugal. For females, significant differences were also observed between students from both countries in the ideal seat height in the fifth, sixth, and ninth grades and in the desk height for the seventh to the ninth grades. In all cases, Portuguese students required higher furniture than Spanish students.

Table 4. Types of seat sizes according to EU catalog by grade and country.

Grade		Males						Females
		Spain		Portugal		χ2	p	Spain		Portugal		χ2	p
		n	%	n	%				%	n	%
5th grade	S26	0	0.0%	0	0.0%	3.586	0.310	0	0.0%	0	0.0%	3.022	0.388
	S31	1	5.3%	1	3.4%			0	0.0%	1	5.0%
	S35	2	10.5%	10	34.5%			2	11.1%	4	20.0%
	S38	13	68.4%	14	48.3%			11	61.1%	13	65.0%
	S43	3	15.8%	4	13.8%			5	27.8%	2	10.0%
	S46	0	0.0%	0	0.0%			0	0.0%	0	0.0%
6th grade	S26	0	0.0%	0	0.0%	11.019	0.012		0.0%	0	0.0%	3.067	0.216
	S31	0	0.0%	4	16.0%			0	0.0%	0	0.0%
	S35	2	8.0%	1	4.0%			1	4.3%	6	18.2%
	S38	11	44.0%	17	68.0%			13	56.5%	19	57.6%
	S43	12	48.0%	3	12.0%			9	39.1%	8	24.2%
	S46	0	0.0%	0	0.0%			0	0.0%	0	0.0%
7th grade	S26	0	0.0%	0	0.0%	1.37	0.713		0.0%	0	0.0%	5.336	0.069
	S31	0	0.0%	0	0.0%			0	0.0%	0	0.0%
	S35	1	6.7%	5	14.7%			1	5.9%	7	24.1%
	S38	9	60.0%	20	58.8%			15	88.2%	16	55.2%
	S43	5	33.3%	8	23.5%			1	5.9%	6	20.7%
	S46	0	0.0%	1	2.9%			0	0.0%	0	0.0%
8th grade	S26	0	0.0%	0	0.0%	2.123	0.547		0.0%	0	0.0%	1.905	0.592
	S31	0	0.0%	0	0.0%			0	0.0%	0	0.0%
	S35	0	0.0%	2	5.6%			0	0.0%	1	4.8%
	S38	3	23.1%	14	38.9%			12	63.2%	12	57.1%
	S43	9	69.2%	18	50.0%			7	36.8%	7	33.3%
	S46	1	7.7%	2	5.6%			0	0.0%	1	4.8%
9th grade	S26	0	0.0%	0	0.0%	6.868	0.076		0.0%	0	0.0%	10.688	0.005
	S31	0	0.0%	0	0.0%			0	0.0%	0	0.0%
	S35	0	0.0%	1	2.4%			4	17.4%	0	0.0%
	S38	2	10.5%	13	31.7%			14	60.9%	20	48.8%
	S43	16	84.2%	20	48.8%			5	21.7%	21	51.2%
	S46	1	5.3%	7	17.1%			0	0.0%	0	0.0%

Note: n = number of participants; % = percentage; χ² = chi-squared statistic; p = level of significance; S26 = seat size 26; S31 = seat size 31; S35 = seat size 35; S38 = seat size 38; S43 = seat size 43; S46 = seat size 46.

provides a descriptive analysis of the seat sizes, according to the EU catalog, needed in classrooms from fifth to ninth grade, stratified by sex and country. Additionally, the analysis includes a comparison between students from Spain and Portugal.

The data showed that, considering the sex and country of origin, in the fifth grade, sizes 35 and 38 were predominant, with more than 72% of the students having anthropometric characteristics suitable for these two chair models. In the sixth grade, sizes 38 and 43 were the most common, with up to 68% of boys in Portugal requiring size 38. In the seventh grade, size 43 was the most frequent, with at least 55.2% of the students, regardless of sex and country, showing anthropometric dimensions compatible with this seat model. In the eighth and ninth grades, sizes 38 and 43 better suited the students’ morphological characteristics compared to other sizes. It is worth noting that up to 84.2% of Spanish boys needed size 43, while up to 60.9% of Spanish girls required size 38. It was found that using two sizes per grade, based on the needs, allowed the coverage of over 70% of the students, regardless of their sex and country of origin.

The analysis indicated that, except for sixth-grade boys and ninth-grade girls, there were no significant differences in the required chair sizes for classroom furniture from the fifth to ninth grade between students from Spain and Portugal.

The significant differences mentioned earlier indicated that, in the sixth grade in Spain, more boys required taller seats compared to Portugal. Specifically, more boys in Spain needed size 43 (48%) than in Portugal (12%). In the ninth grade, the opposite occurred: in Portugal, more girls needed size 44 compared to Spain (51.2% versus 21.7%).

In

Table 5. Types of desk sizes according to EU catalog by grade and country.

Grade		Males						Females
		Spain		Portugal		χ2	p	Spain		Portugal		χ2	p
		n	%	n	%			n	%	n	%
5th grade	D46	0	0.0%	0	0.0%	4.431	0.219		0.0%	0	0.0%	6.436	0.092
	D53	3	15.8%	1	3.4%			0	0.0%	1	5.0%
	D59	8	42.1%	12	41.4%			5	27.8%	7	35.0%
	D64	7	36.8%	16	55.2%			13	72.2%	8	40.0%
	D71	1	5.3%	0	0.0%			0	0.0%	4	20.0%
	D76	0	0.0%	0	0.0%			0	0.0%	0	0.0%
6th grade	D46	0	0.0%	0	0.0%	4.366	0.359		0.0%	0	0.0%	5.058	0.168
	D53	2	8.0%	2	8.0%			0	0.0%	1	3.0%
	D59	4	16.0%	8	32.0%			7	30.4%	11	33.3%
	D64	16	64.0%	15	60.0%			10	43.5%	19	57.6%
	D71	2	8.0%	0	0.0%			6	26.1%	2	6.1%
	D76	1	4.0%	0	0.0%			0	0.0%	0	0.0%
7th grade	D46	0	0.0%	0	0.0%	6.968	0.073		0.0%	0	0.0%	14.969	0.002
	D53	0	0.0%	0	0.0%			0	0.0%	0	0.0%
	D59	8	53.3%	7	20.6%			7	41.2%	2	6.9%
	D64	6	40.0%	15	44.1%			9	52.9%	10	34.5%
	D71	1	6.7%	10	29.4%			1	5.9%	15	51.7%
	D76	0	0.0%	2	5.9%			0	0.0%	2	6.9%
8th grade	D46	0	0.0%	0	0.0%	3.702	0.157		0.0%	0	0.0%	8.778	0.032
	D53	0	0.0%	0	0.0%			0	0.0%	0	0.0%
	D59	1	7.7%	1	2.8%			2	10.5%	0	0.0%
	D64	10	76.9%	19	52.8%			14	73.7%	9	42.9%
	D71	2	15.4%	16	44.4%			3	15.8%	10	47.6%
	D76	0	0.0%	0	0.0%			0	0.0%	2	9.5%
9th grade	D46	0	0.0%	0	0.0%	11.154	0.011		0.0%	0	0.0%	26.471	0.000
	D53	0	0.0%	0	0.0%			0	0.0%	0	0.0%
	D59	0	0.0%	2	4.9%			5	21.7%	0	0.0%
	D64	9	47.4%	6	14.6%			15	65.2%	10	24.4%
	D71	10	52.6%	23	56.1%			3	13.0%	22	53.7%
	D76	0	0.0%	10	24.4%			0	0.0%	9	22.0%

Note: n = number of participants; % = percentage; χ² = chi-squared statistic; p = level of significance; D46 = desk size 46; D53 = desk size 53; D59 = desk size 59; D64 = desk size 64; D71 = desk size 71; D76 = desk size 76.

, the same results are presented as in the previous table but regarding desks.

The analysis showed a predominance of sizes 59 and 64 for both sexes and countries in fifth grade. It is important to note that 55.2% of Portuguese boys and 72.2% of Spanish girls required size 64. In sixth grade, most students also needed size 64 (ranging from 43.5% to 64%), although a considerable percentage of boys and girls required size 59 (ranging between 16% and 33.3%, depending on sex and country). In seventh grade, the predominant sizes were 64 and 71, with a minimum of 34.5% of Portuguese girls and a maximum of 52.9% of Spanish girls needing size 64. Notably, 51.7% of Portuguese girls required size 71. In eighth grade, size 64 was clearly dominant, being needed by up to 76.9% of Spanish boys, 52.8% of Portuguese boys, 73.7% of Spanish girls, and 42.9% of Portuguese girls. Finally, in ninth grade, sizes 64 and 71 accommodated the majority of students, with more than half of Spanish boys and 53.7% of Portuguese girls requiring size 71, although only 13% of Spanish girls needed this size. It is worth noting that, in Portugal, a large proportion of students also needed size 76 (22.4% of boys and 22.0% of girls). Again, as with the chairs, it was found that using only two sizes could accommodate, in the worst-case scenario, up to 70% of students.

For boys, no statistically significant differences were found when comparing students from both countries in terms of the size required in class, except in ninth grade. At this level, a large percentage of Portuguese boys required size 76 (56.1%), which did not occur among Spanish students (0%).

Regarding girls, there were no differences in the fifth and sixth grades, but there were differences in the seventh to ninth grades. In these cases, Portuguese girls generally required larger sizes in a greater percentage than Spanish students.

The following presents an analysis of the asymmetry in the matching of school furniture to students. First, as shown in Figure 3, a general evaluation was conducted, without stratification by sex, grade, or country, to determine whether the chair size, as indicated by the color in the European Union catalog, matched the desk size of the corresponding color (e.g., chair size 26 cm —red— with desk size 43 cm —red—). Additionally, the agreement was compared between the recommended size for a student, obtained through formulas based on specific anthropometric measurements (popliteal height, elbow-to-seat distance, and shoulder-to-seat distance), and the size determined solely based on the student’s height.

The results showed a mismatch of over 50% when comparing the alignment between seat and desk sizes of the same color according to the European Union catalog. This percentage increased to more than 70% when the student’s height was used as the sole criterion to assign furniture.

Table 6. Degree of concordance of seat and desk size according to the European Union catalog (based on pre-set color) and degree of agreement in the calculation of the ideal seat and desk height according to the height formula or the validated anthropometric measures formula.

Grade			Males						Females
			Spain		Portugal		χ2	p	Spain		Portugal		χ2	p
			n	%	n	%			n	%	n	%
5th grade	Color Matching ISH–IDH	No	13	68.4%	14	48.3%	1.893	0.169	11	61.1%	13	65.0%	0.062	0.804
		Yes	6	31.6%	15	51.7%			7	38.9%	7	35.0%
	Matching Stature–ISH	No	9	47.4%	15	51.7%	0.087	0.768	8	44.4%	11	55.0%	0.422	0.516
		Yes	10	52.6%	14	48.3%			10	55.6%	9	45.0%
	Matching Stature–IDH	No	14	73.7%	23	79.3%	0.206	0.650	11	61.1%	16	80.0%	1.643	0.200
		Yes	5	26.3%	6	20.7%			7	38.9%	4	20.0%
6th grade	Color Matching ISH–IDH	No	15	60.0%	12	48.0%	0.725	0.395	12	52.2%	13	39.4%	0.896	0.344
		Yes	10	40.0%	13	52.0%			11	47.8%	20	60.6%
	Matching Stature–ISH	No	12	48.0%	16	64.0%	1.299	0.254	11	47.8%	21	63.6%	1.383	0.240
		Yes	13	52.0%	9	36.0%			12	52.2%	12	36.4%
	Matching Stature–IDH	No	19	76.0%	22	88.0%	1.22	0.269	16	69.6%	31	93.9%	5.97	0.015
		Yes	6	24.0%	3	12.0%			7	30.4%	2	6.1%
7th grade	Color Matching ISH–IDH	No	11	73.3%	18	52.9%	1.792	0.181	6	35.3%	19	65.5%	3.946	0.047
		Yes	4	26.7%	16	47.1%			11	64.7%	10	34.5%
	Matching Stature–ISH	No	9	60.0%	26	76.5%	1.384	0.240	15	88.2%	24	82.8%	0.249	0.618
		Yes	6	40.0%	8	23.5%			2	11.8%	5	17.2%
	Matching Stature–IDH	No	15	100.0%	28	82.4%	3.016	0.082	17	100.0%	19	65.5%	7.49	0.006
		Yes	0	0.0%	6	17.6%			0	0.0%	10	34.5%
8th grade	Color Matching ISH–IDH	No	10	76.9%	17	47.2%	3.406	0.065	6	31.6%	14	66.7%	4.912	0.027
		Yes	3	23.1%	19	52.8%			13	68.4%	7	33.3%
	Matching Stature–ISH	No	12	92.3%	29	80.6%	0.966	0.326	18	94.7%	16	76.2%	2.691	0.101
		Yes	1	7.7%	7	19.4%			1	5.3%	5	23.8%
	Matching Stature–IDH	No	13	100.0%	36	100.0%			19	100.0%	16	76.2%	5.17	0.023
		Yes	0	0.0%	0	0.0%			0	0.0%	5	23.8%
9th grade	Color Matching ISH–IDH	No	8	42.1%	18	43.9%	0.017	0.896	9	39.1%	21	51.2%	0.865	0.352
		Yes	11	57.9%	23	56.1%			14	60.9%	20	48.8%
	Matching Stature–ISH	No	18	94.7%	33	80.5%	2.068	0.150	22	95.7%	34	82.9%	2.181	0.140
		Yes	1	5.3%	8	19.5%			1	4.3%	7	17.1%
	Matching Stature–IDH	No	19	100.0%	29	70.7%	6.951	0.008	23	100.0%	26	63.4%	10.991	0.001
		Yes	0	0.0%	12	29.3%			0	0.0%	15	36.6%

Note: n = number of participants; % = percentage; χ² = chi-squared statistic; p = level of significance; ISH = ideal seat height; IDH = ideal desk height.

presents the previously described asymmetry analysis, but taking into account the students’ sex, grade level, and country.

The highest alignment was found in Spanish girls in the eighth grade, with 68.4%. In contrast, the greatest asymmetry was also found in the eighth grade but among Spanish boys, with 76.9%. Generally, the asymmetry ranged between 40% and 70%.

When the alignment was evaluated by determining the chair size using only the height, compared to the validated formula that incorporated several anthropometric measurements, a high degree of discordance was found. The best alignment was recorded in the fifth grade, with 52.6% for Spanish boys, but many alignments fell below 20%, especially in higher grades. In the fifth and sixth grades, the alignment ranged from 40% to 60% but then decreased significantly.

For the desks, the asymmetry was even greater, with very low alignment percentages from the fifth to the ninth grades. The best alignment, considering the grade, sex, and country, was 38.9% in Spanish girls in the fifth grade. In several grades in both countries, there was 100% discordance.

4. Discussion

The aim of this study was to analyze the morphological asymmetries between two populations differentiated by grade, gender, and nationality (Spain and Portugal). Additionally, it evaluated whether students in the same grade used a uniform size of school furniture. Furthermore, the study aimed to verify the degree of correspondence between the assignment of a specific size and color of chair and the corresponding type of desk, according to the European Union’s school furniture catalog. Finally, it examined whether the height was an appropriate criterion for the assignment of school furniture

This approach is highly relevant since inadequate school furniture is associated with a higher prevalence of musculoskeletal problems, especially at early ages, representing critical stages for posture and growth [23]. Moreover, morphological asymmetries and their relationships with furniture not only affect students’ comfort and efficiency but also directly influence their long-term health [24]. In this regard, this study provides key data to better understand the need for a more precise and personalized approach to school furniture design.

This study’s results confirm the trends observed in previous research [17,25]. In the fifth and sixth grades, girls tend to be taller than boys. However, in the seventh grade, the height differences between the sexes almost disappear. From the eighth grade onwards, a notable difference reappears, but in favor of boys, who show a tendency to be taller than their female classmates.

This growth pattern is related to the phases of pubertal development, which tend to occur earlier in girls. Anthropometric studies indicate that girls usually reach their growth peak before boys, explaining the difference observed in the early years of secondary education. However, once they reach puberty, boys experience a more prolonged and accelerated period of growth, eventually surpassing girls in height by the end of adolescence [26,27]. This phenomenon highlights the importance of considering not only sex but also the stage of biological development when designing and assigning school furniture [14,28].

National differences can also be related to genetic, nutritional, and socioeconomic factors, although these are not extremely significant between Spain and Portugal. Despite the cultural and geographical similarities between both countries, some studies have suggested that small variations in diet, physical activity, and access to healthcare may influence students’ growth characteristics [29]. However, the differences observed in this study are not pronounced enough to justify country-specific school furniture designs, reaffirming the viability of a common approach in Europe [12], as long as the diversity within each school population is considered.

The data on ideal chair and desk heights clearly show that it is not easy to standardize school furniture sizes by academic grade. There is no grade, not even when separating students by sex in Spain and Portugal, in which a single size of chair or desk can be suitable for all students.

This finding confirms what previous studies have indicated [14,28,30]: the variability in anthropometric dimensions within each school group is too large for a uniform approach to work effectively. Standardization based on the academic grade ignores the diversity in students’ growth and morphologies, potentially leading to a significant mismatch between ergonomic needs and the available furniture. Therefore, it is essential that school furniture design and assignment consider greater adaptability, allowing for personalized adjustments that accommodate individual variations.

Even when separating students by sex, the results indicate that at least two different sizes of chairs and desks are needed per grade. In the most complex scenarios, up to four different sizes of chairs and desks were required within the same grade and sex [25], highlighting the need for more adaptable and personalized furniture.

The wide variability in furniture sizes within the same grade emphasizes the importance of offering a broader range of furniture options, possibly through adjustable solutions [14,31,32,33]. The use of height-adjustable chairs and desks would allow for more precise adaptation to each student’s needs, promoting proper posture and reducing the risk of long-term musculoskeletal problems. This finding supports the need for educational policies that promote investment in flexible and ergonomically efficient furniture.

On the other hand, as previous research has shown [25,34], this study confirms that the strategy of assigning school furniture based solely on height is inadequate. There is considerable disagreement between the estimated chair and desk heights when using this technique and the students’ actual needs when validated formulas considering multiple anthropometric measurements are used.

This discrepancy highlights that the height is not a sufficient measure to determine a student’s ergonomic needs. Body proportions, such as the torso length, the arm length, and the distance from the floor to the thighs, are equally important in ensuring proper posture while seated [34]. Validated anthropometric formulas, which include these additional measurements, offer a more precise approach, but their widespread application in the school setting requires training and tools that are not currently available in all educational institutions [35].

Although not all teachers have the necessary training to use an anthropometer correctly, which could lead to inaccurate measurements, recent proposals have emerged that allow furniture size estimation without relying exclusively on students’ height.

These proposals include the use of digital applications and automated measurement tools, which could facilitate more accurate and efficient furniture assignment [17]. Some of these technologies can be easily integrated into the school environment, reducing the burden on teachers and improving the measurement accuracy, allowing for the greater individualization of the assigned furniture.

Moreover, this study also demonstrates that assigning desks based on the chair size, solely determined by popliteal height measurements, is not an effective strategy. The data revealed that the number of students whose chair size matched the corresponding desk size was alarmingly low. The popliteal height, while useful in determining the chair size, does not adequately consider the relationship between the leg and torso lengths, which is essential in determining the optimal desk height. This finding is consistent with previous research [32] that suggests that basing both decisions on a single anthropometric measurement is insufficient and potentially harmful to students’ posture. The European UNE-EN 1729 standard for school furniture, which associates chairs and desks by size and color, suggests a direct relationship between the two, but this study’s results indicate that this correlation is deficient.

This study questions the viability of the current European standard for school furniture, which rigidly associates chairs and desks. The findings suggest that a review of these standards is necessary to incorporate greater flexibility in furniture assignment, possibly adopting adjustable systems that can be modified according to individual students’ needs.

4.1. Practical Implications

The results of this study have relevant implications for the design and allocation of school furniture in the European context. Firstly, it is clear that the variability in anthropometric dimensions within the same school grade, both in Spain and Portugal, requires a more personalized approach in the selection of furniture. Adaptable furniture with various size options for chairs and desks is necessary to allow students to maintain an ergonomically correct posture, thus reducing the risk of postural and musculoskeletal problems.

Additionally, educational institutions and school furniture manufacturers should reconsider the strategy of assigning furniture based solely on the height or chair size, as these methods do not ensure precise correspondence between chair and desk sizes. Implementing more comprehensive ergonomic assessment tools, which include various anthropometric measurements, could significantly improve the suitability of the furniture and its impact on students’ postural health. It would also be beneficial to introduce training programs for teachers and administrative staff on ergonomic evaluation and the proper use of anthropometric measurement instruments.

4.2. Limitations and Future Perspectives

This study, while rigorous, presents some limitations that must be considered when interpreting the results. Firstly, the analysis focused on a sample of students from two specific schools, one in Southern Galicia (Spain) and another in Northern Portugal. While the findings provide valuable insights into the anthropometric characteristics and furniture alignment of students in these locations, they may not be generalizable to the entire populations of Spain and Portugal or to other European populations. Cultural, socioeconomic, and genetic differences, as well as variability in school furniture standards in other regions, could influence the results. It would be advisable to replicate the study in a broader and more diverse sample, including a multicenter approach to validate and expand upon these findings.

Another limitation is the reliance on anthropometric measurements obtained at a single point in time, which may not reflect changes in body dimensions throughout the school year. Growth patterns, especially during adolescence, can vary over short periods, affecting the validity of furniture recommendations based on these specific measurements. Furthermore, other factors, such as the posture adopted by students while using the furniture, were not analyzed, but these could impact their comfort and long-term health.

This study opens the door for several future research lines. Firstly, it would be interesting to expand the analysis at the European level, comparing the morphological asymmetries and the adequacy of school furniture in a broader context that includes countries with different socioeconomic and cultural backgrounds. This would allow for the evaluation of the effectiveness of the European school furniture catalog in different scenarios and establish recommendations that are more tailored to the reality of each country.

Additionally, longitudinal studies could be conducted to follow students over several years to observe how their body dimensions and furniture needs vary during their development. It would also be useful to investigate the relationship between the adequacy of school furniture and academic outcomes, as well as its impact on the prevention of health issues, such as back pain or postural asymmetries.

Finally, future research could focus on developing new tools and methodologies for the ergonomic evaluation of school furniture that are accessible to both educational staff and manufacturers, aiming to improve the accuracy in furniture allocation and optimize the educational experience for students.

5. Conclusions

This study demonstrates that, due to the significant variability in the anthropometric dimensions of students, it is not possible to standardize school furniture by grade level in Spain and Portugal. Even separating students by sex does not make it feasible to apply a single size for chairs or desks, highlighting the need for more adaptable and personalized furniture for each grade.

Furthermore, the system that assigns furniture solely based on height, or that links the size of the desk to that of the chair, proves ineffective. The mismatch between these two pieces of furniture indicates that the European catalog of chairs and desks by size does not meet the real needs of students.

Therefore, it is essential to adopt a more comprehensive approach that considers various anthropometric measurements to ensure an appropriate ergonomic posture. This will not only enhance the educational experience but also help to prevent long-term postural and health problems.

Finally, this study emphasizes the importance of continuing such research in other European populations and developing more accessible tools that allow for the estimation of suitable furniture without relying exclusively on the student’s height.