The Impact of School Classroom Chair Depth and Height on Learning Tasks

Abstract

The purpose of this study is to investigate the effect of the seating condition on learning tasks. This physical setting and these cognitive activities (that participants then test) are not the totality of education practice and context, but desks and chairs are important physical elements for students to learn, because students always spend so much time learning at their seats. At present, the chairs purchased by the school have uniform specifications, so they cannot be customized. To provide students with more comfort, their sitting condition and backrest are commonly adjusted. This study investigated the effects of the sitting condition on the performance of short learning tasks that require high concentration, namely short-term number memorization, mathematical calculations, and logical judgment, through a two-way within-subjects design (seat depth and backrest height). Thirty adults over 20 years old, with visual acuity (including corrected visual acuity) greater than 0.7 and no history of musculoskeletal disease, participated in this experiment. The results indicated that seat depth and backrest height had an interaction effect on task performance. Sitting on the front third of a chair with a lower backrest produced excellent learning tasks outcomes; seat configuration may affect student performance on learning tasks. Thus, schools and educational institutions can try to require students to temporarily sit in this sitting condition to perform such tasks. In addition, schools can purchase chairs with a lower backrest and require that students use lumbar pads to adjust the seat depth to achieve superior learning task outcomes in classrooms.

1. Introduction

A classroom is a learning environment in which desks and chairs serve as crucial physical elements facilitating learning and creating a comfortable, stress-free environment. During class, information enters the short-term memory, and students perform mathematical calculations and logical judgements. Students’ concentration often weakens, and they gradually become distracted as teachers provide materials, distribute handouts, and write on the blackboard. Working while seated causes discomfort in the musculoskeletal system [1] from sitting too long and poor health among people of all ages [2]. Because students mostly remain seated during school, they may develop poor posture in the long run if the classroom desks and chairs are poorly designed, as stated by Dianat et al. [3]. During an interview with the website STAND, Professor Ikegaya Yuiji of the University of Tokyo indicated that posture is key to concentration [4]. Remaining seated with poor posture for extended periods can prevent students’ lungs from expanding, which causes poor blood circulation and accelerates oxygen consumption in the brain. HSUEH Kuang-Chieh, the attending physician of the Department of Family Medicine, Kaohsiung Veterans General Hospital, emphasized that brain hypoxia will cause unclear thinking; reduce learning ability; and greatly affect the ability to analyze, judge, and think clearly. Consequently, this prevents students from concentrating, which negatively affects their ability to learn [5].

Chair design is crucial for prolonged users. However, adjustable chairs are expensive and involve high maintenance costs. Therefore, schools often use unadjustable desks and chairs, which is unsuitable for most students. As discussed by Panagiotopoulou et al. [6], height and weight vary among students because of age, sex, and country. Most teachers agree that reducing sitting time is a crucial goal that benefits students [7]. However, accomplishing this goal is difficult. The height, size, and structure of desks and chairs in schools affect students’ learning efficiency [8]. Because desks and chairs often cannot be customized and students must remain seated during class, methods of maintaining excellent posture while seated have become a crucial research topic [9].

The backrest is essential to protecting the head and spine and can help the waist and the shoulders rest. Furthermore, one study pointed to rest–stimulus as being crucial to the elucidation of the brain’s contribution to mental states [10]. Resting has an interaction effect on self-feedback, which can give feedback a better state of the human body and brain. The effects of self-feedback only emerge at rest, indicating that the cognitive load of self-feedback is ameliorated through resting. Also, better learning results are achieved after a break [11]. As discussed by Carcone and Keir [12], backrests should have a 3-cm lumbar pad. Backrests should be 420 mm tall, and the width of the upper and lower parts of the backrest should be 360 and 400 mm, respectively. Chairs should be designed to accommodate the bodies of their users and to minimize their physical burden [13]. Similarly, Mehta et al. [14] reported that employees’ performance improved when their backrest was 350 mm tall and used ergonomics to identify design principles for comfortable static chairs. Therefore, the optimal backrest height should be between that of the upper and lower back. The first objective of this study was to investigate the effects of backrest height on learning tasks.

Seat depth strongly affects sitting comfort. A seat deeper than the horizontal length of the thigh creates a large incline with the backrest. A person slouching in a seat moves the pelvis forward so that the knees go over the edge of the seat while leaning against the backrest at an unsupported angle. In addition, the lower back lacks a supporting point and remains raised, thereby increasing the muscular activity of the lower back and causing fatigue. A deeper seat also causes the knee socket to feel numb, which is not ideal for standing up from the chair. The optimal seat depth is 410 mm [13]. As argued by Ravindra et al. [15], a seat depth of approximately 304 mm is preferable, but the ideal seat depth differs (ranging from 7.6 to 38 cm) depending on the user and type of work. However, in the long run, a large space between the back and backrest causes harm to the spine. Therefore, the optimal seat depth must be used to increase learning efficiency, ensure users’ health, and help learners concentrate on various tasks. The second objective of this study was to identify the optimal seat depth for each learning task.

Chair design should account for both the backrest height and seat depth and ensure that the burden on the buttocks, thighs, and back is lower than the threshold for discomfort [16]. Chairs should be suitable for users of various heights and weights to ensure maximum usability. This is particularly crucial for students, who spend most of their time seated [17]. Remaining stationary for a long time is a major cause of discomfort. When seated, individuals do not remain stationary but constantly make small adjustments to reduce pressure on the spine [18]. Seat depth and backrest height determine students’ posture while seated and therefore affect cognitive learning. The third objective of this study was to identify the optimal combination of seat depth and backrest height for each learning task.

Most studies have investigated the effects of sitting posture on comfort and health [19,20,21,22,23,24], and few have investigated their effects on learning outcomes [25]. Therefore, this study investigated university students’ in-class learning task outcomes in memory, calculation, and logical judgment abilities while seated to identify the posture that results in optimal cognitive learning. The results can help students perform various learning tasks while seated, improve learning outcomes, and avoid injury from remaining seated for long periods in the classroom.

2. Materials and Methods

This study used a two-way within-subjects design. The independent variables were seat depth (front third, front two thirds, and entire chair) and backrest height (no backrest, lower backrest, and upper backrest) (Figure 1). Depth was measured from the buttock to the knee socket, and backrest height was measured from the shoulders to the seat. The sitting condition was divided into sitting on the entire chair, sitting on the front two-thirds of the chair, and sitting on the front third of the chair. Three backrest conditions were used: no backrest, lower backrest (from the elbows to the seat), and upper backrest (from the elbows to the shoulders). Therefore, the three dependent variables for learning tasks outcomes were memory, calculations, and logical judgment.

2.1. Participants and Location

The participants comprised 30 adults aged older than 20 years (M = 20.9, S.D. = 0.73); 15 were men, and 15 were women. The demographic information of the experimental participants is shown in

Table 1. The demographic information of the experimental participants.

Participant	Gender	Age	Vision (Corrected)	Signed Consent Form
S1	Male	21	Normal	v
S2	Male	22	Normal	v
S3	Female	20	Normal	v
S4	Female	20	Normal	v
S5	Female	21	Normal	v
S6	Female	20	Normal	v
S7	Male	20	Normal	v
S8	Male	21	Normal	v
S9	Female	20	Normal	v
S10	Male	20	Normal	v
S11	Female	22	Normal	v
S12	Female	21	Normal	v
S13	Male	21	Normal	v
S14	Male	21	Normal	v
S15	Male	21	Normal	v
S16	Male	22	Normal	v
S17	Female	22	Normal	v
S18	Female	21	Normal	v
S19	Male	21	Normal	v
S20	Male	21	Normal	v
S21	Female	21	Normal	v
S22	Female	22	Normal	v
S23	Male	22	Normal	v
S24	Female	21	Normal	v
S25	Female	20	Normal	v
S26	Male	20	Normal	v
S27	Male	20	Normal	v
S28	Female	22	Normal	v
S29	Male	21	Normal	v
S30	Female	21	Normal	v

. The participants were required to satisfy criteria related to these seating condition, namely seat depth and backrest height. In addition, they were required to have a visual acuity (including corrected visual acuity) of higher than 0.7 and no history of musculoskeletal diseases. Before the experiment began, participants were fully informed about the purpose, procedures, and process through a detailed explanation. They then signed a consent form. The experiment was designed to prioritize participant well-being. If any subject experienced discomfort, the experiment was stopped immediately. Subjects were verbally thanked and received a compensation of 1000 CNY after completing the experiment. The entire experiment was approved by an expert review meeting. Interference must be reduced during experiments to obtain objective data and physiological signals. To create such an environment, the laboratory was airtight, soundproof, equipped with excellent lighting equipment, and locked during the experiment.

2.2. Equipment

2.2.1. Chairs

Most of the chairs in schools are made of wood or plastic. In addition, chairs on the market today can adjust the depth of the seat and the height of the backrest at the same time. This study stacked wooden boxes and used floor mats to adjust the height and angle between the soles of the feet and the floor for each participant (Figure 2).

2.2.2. Materials

In the short-term number memory test, numbers from 0 to 9 were randomly generated. Because most people can remember 7 ± 2 numbers at a time on average, the test began with five-digit numbers and gradually increased the length of the numbers to nine digits (Miller 1956). The test had two questions for each length, for a total of 10 questions. During the test, the symbol “+” would appear in the center of the computer screen for 0.5 s. Then, numbers would appear in the center of the screen for 0.5 s. Next, the symbol “?” would appear on the screen. The participants verbally answered without changing their posture, and the researchers recorded their answers.

The mathematical calculation test comprised questions involving two-digit numbers (13–99) multiplied by one-digit numbers (3–9). The numbers were all odd and randomly generated by computer. The participants verbally answered without changing their posture. Their scores were the number of correct responses within 5 min.

The logical judgment test consisted of number-based, word-based, and figure-based questions (

Table 2. Logic questions.

Type of Question	Question	Answer
Number-based question	2, 8, 18, 32, 50, ___	(A) 76, (B) 70, (C) 72, (D) 64
Word-based question	The pencil is related to the ___ as the ___ is related to the chalkboard eraser.	(A) chalkboard…teacher (B) worker…principal (C) eraser…chalk (D) tree…river
Figure-based question

). To eliminate the effects of the order of the questions, the three types of questions were presented randomly. During the test, the symbol “+” would appear in the center of the screen for 0.5 s. Then, a question would appear in the center of the screen, and the participants verbally answered without changing their posture; the researchers recorded their answers. The scores were the number of correct responses within 10 min.

2.3. Procedure

2.3.1. Preparation for Experiment

The researchers asked the participants about their visual acuity and health before the experiment. The participants were informed of the procedure and equipment and emptied their pockets before entering the laboratory. The participants were reminded to immediately notify the researchers if they felt unwell during the experiment; in which case, the researchers would immediately halt the experiment. The researchers explained to the participants how to adjust their sitting posture (Figure 3). First, the wooden boxes were adjusted to suit the height of each participant so that their elbows were parallel to the desk. Next, footstools were placed under the participants’ feet and adjusted so that the angle between the hip joint and knee joint was 90°. The participants’ feet were flat on the floor, and their upper body and the ischia formed a straight line to prevent bending of the spine. The headrest was adjusted so that the upper edge of the computer screen was parallel to the participants’ eyes and the distance from the screen was 60 cm (Figure 3, left). The participants were asked to sit in a comfortable posture. After the participants were seated, the height of the feet from the floor was adjusted so that the participants’ knees were parallel to their buttocks. A small gap was left between the knee socket and the front of the chair’s cushion. The backrest height was adjusted to no backrest, lower backrest, and upper backrest. The participants were asked to relax their shoulders, place their arms on the desk parallel to the floor, and keep their body upright (Figure 3, right).

2.3.2. Experiment

This study adopted a completely within-subject experimental design. Each participant underwent nine experiments (three seat depths and three backrest heights). Considering that the fatigue (mental and physical) of the participants affects the experimental results, the 30 subjects were tested according to the experimental schedule, and each test time was 30 min. The ABBA method was used during the experiment to adjust the sitting posture. The ABBA design is suitable for situations with only two independent variables (A and B) where subjects receive four experimental treatments in the ABBA order: two A conditions followed by two B conditions. This ensures that A comes before and after B and vice versa. Since the order effect in within-subjects designs can be systematic, the ABBA method effectively balances these time-based errors by counterbalancing the order of treatments. This design theoretically neutralizes the impact of order on the results, transforming it into a linear system.

Table 3. ABBA Model of Experimental Research.

		B	Short-Term Number Memory	Total Mathematical Calculations	Logical Judgements
	A	C
(A1) 1/3 depth × No backrest			A1 B1 C	A1 B2 C	A1 B3 C
(A2) 1/3 depth × Lower backrest			A2 B1 C	A2 B2 C	A2 B3 C
(A3) 1/3 depth × Upper backrest			A3 B1 C	A3 B2 C	A3 B3 C
(A4) 2/3 depth × No backrest			A4 B1 C	A4 B2 C	A4 B3 C
(A5) 2/3 depth × Lower backrest			A5 B1 C	A5 B2 C	A5 B3 C
(A6) 2/3 depth × Upper backrest			A6 B1 C	A6 B2 C	A6 B3 C
(A7) 3/3 depth × No backrest			A7 B1 C	A7 B2 C	A7 B3 C
(A8) 3/3 depth × Lower backrest			A8 B1 C	A8 B2 C	A8 B3 C
(A9) 3/3 depth × Upper backrest			A9 B1 C	A9 B2 C	A9 B3 C

presents the ABBA Model of Experimental Research.

ABBA helps researchers interpret the results of binomial experiments. In this kind of experiment, researchers run a number of trials, each of which ends in either a “successful” outcome or a “failure” outcome. Trials are divided into two or more groups, and the goal of the experiment is to draw conclusions about how the chance of success differs between those groups. This usually boils down to determining if the success rate is higher for one group than for another. The short-term number memory test was conducted first, followed by the mathematical calculation and logical judgment tests. The experiment lasted approximately 30 min.

2.3.3. After the Experiment

The total experimental time per participant was approximately 270 min. The participants received 1000 CNY as compensation. The data were analyzed using descriptive statistics and a two-way paired-sample analysis of variance (ANOVA) to explain the effect of the combination of seat depth and backrest condition on cognitive learning tasks.

2.4. Data Analysis

After the experiment, SPSS 20 was used to perform the two-way ANOVA and determine whether the differences in classroom chair design significantly affected memory, calculation, and logical judgment. If the two-factor interaction was significant, then the simple main effect was tested. In each statistical test, 0.05 was used as the threshold for significance.

3. Results

Table 4. Statistical data on the depth and backrest condition in the cognitive learning experiment.

Depth	Backrest Condition	Short-Term Number Memory		Total Mathematical Calculations		Correct Mathematical Calculations		Total Logical Judgements		Correct Logical Judgements
		M	Std.	M	Std.	M	Std.	M	Std.	M	Std.
1/3	No backrest	8.00	1.46	61.50	12.82	56.40	14.14	35.83	6.76	33.80	6.02
	Lower backrest	7.73	1.68	61.63	11.35	56.63	12.40	37.97	5.87	35.23	5.77
	Upper backrest	7.73	1.70	54.27	7.73	48.43	8.46	30.83	7.64	27.67	8.39
2/3	No backrest	7.63	1.67	56.27	10.62	50.57	11.80	30.37	7.86	28.27	7.14
	Lower backrest	7.40	1.61	61.10	10.19	56.00	11.26	31.20	7.14	28.13	7.10
	Upper backrest	8.17	1.46	58.13	11.46	52.73	12.67	37.30	5.31	35.17	4.85
3/3	No backrest	7.40	1.40	54.90	8.87	49.10	9.86	30.63	6.76	28.03	7.16
	Lower backrest	8.20	1.35	67.37	12.87	62.87	14.10	34.43	7.27	32.50	7.49
	Upper backrest	7.20	1.81	58.50	7.86	53.13	8.67	24.77	7.79	21.77	7.85

presents the descriptive statistics, and

Table 5. Two-way paired-sample ANOVA.

	Source of Variation	SS	df	MS	F	p-Value
Short-term number memory	Depth	2.252	2	1.126	0.977	0.383
	Backrest	0.496	2	0.248	0.216	0.806
	Depth × Backrest	26.993	4	6.748	6.754	0.000 **
Total mathematical calculations	Depth	142.274	2	71.137	1.572	0.216
	Backrest	2252.274	2	1126.137	17.076	0.000 **
	Depth × Backrest	1640.215	4	410.054	5.755	0.000 **
Correct mathematical calculations	Depth	171.785	2	85.893	1.564	0.218
	Backrest	2767.385	2	1383.693	17.565	0.000 **
	Depth × Backrest	1994.370	4	498.593	5.691	0.000 **
Total logical judgements	Depth	1112.985	2	556.493	30.168	0.000 **
	Backrest	585.830	2	292.915	14.474	0.000 **
	Depth × Backrest	2501.304	4	625.326	26.914	0.000 **
Correct logical judgements	Depth	1065.274	2	532.637	22.139	0.000 **
	Backrest	634.807	2	317.404	13.685	0.000 **
	Depth × Backrest	3049.681	4	762.420	32.964	0.000 **

** p < 0.01.

presents the results of the two-way ANOVA for the effect of sitting posture on memory, calculations, and logical judgment.

3.1. Short-Term Number Memory

The optimal performance was observed when the participants were seated entirely on the chair and had a lower backrest (mean (M) = 8.2 ± 1.35). The worst performance was observed when the participants were seated entirely on the chair and had an upper backrest (M = 7.2 ± 1.81). The Mauchly’s sphericity test revealed a significance of higher than 0.05, indicating that the data satisfied the requirements for the two-way ANOVA. The depth and backrest condition had an interaction effect on short-term number memory (F = 5.755, p = 0.00 < 0.05) (Table 5).

The simple main effect was analyzed, and post hoc comparisons were performed (

Table 6. Simple main effect test.

Source of Variation		SS	df	MS	F	p-Value	Post Hoc Comparisons
Short-term number memory	Fixed, no backrest	5.489	2	2.745	1.101	0.334
	Fixed, lower backrest	9.689	2	4.845	1.943	0.145
	Fixed, upper backrest	14.067	2	7.034	2.820	0.061
	Fixed, front one-third	1.422	2	0.711	0.285	0.752
	Fixed, front two-thirds	9.267	2	4.634	1.858	0.158
	Fixed, entire chair	16.800	2	8.400	2.820	0.036 *	Lower backrest > no backrest; lower backrest > upper backrest
Total mathematical calculations	Fixed no backrest	728.156	2	364.078	3.253	0.040 *	front one-third > front two-thirds front one-third > entire chair
	Fixed, lower backrest	724.267	2	362.133	3.236	0.041 *	entire chair > front one-third entire chair > front two-thirds
	Fixed, upper backrest	330.067	2	165.033	1.475	0.231
	Fixed, front one-third	1066.067	2	533.033	4.763	0.009 **	No backrest > upper backrest; lower backrest > upper backrest
	Fixed, front two-thirds	356.467	2	178.233	1.593	0.205
	Fixed, entire chair	2469.956	2	1234.978	11.036	0.000 **	Lower backrest > upper backrest > no backrest
Correct mathematical calculations	Fixed, no backrest	894.689	2	447.344	3.292	0.039 *	front one-third > front two-thirds front one-third > entire chair
	Fixed, lower backrest	864.067	2	432.033	3.179	0.043 *	entire chair > front one-third entire chair > front two-thirds
	Fixed, upper backrest	407.400	2	203.700	1.499	0.225
	Fixed, front one-third	1307.622	2	653.811	4.811	0.009 **	No backrest > upper backrest; lower backrest > upper backrest
	Fixed, front two-thirds	448.867	2	224.433	1.652	0.194
	Fixed, entire chair	3005.267	2	1502.633	11.057	0.000 *	Lower backrest > upper backrest > no backrest
Total logical judgements	Fixed, no backrest	569.956	2	284.978	5.845	0.003 **	front one-third > front two-thirds front one-third > entire chair
	Fixed, lower backrest	687.267	2	343.633	7.048	0.001 **	front one-third > entire chair > front two-thirds
	Fixed, upper backrest	2357.067	2	1178.533	24.173	0.000 **	front two-thirds > front one-third > entire chair
	Fixed, front one-third	804.356	2	402.178	8.249	0.000 **	Lower backrest > no backrest > upper backrest
	Fixed, front two-thirds	859.756	2	429.878	8.817	0.000 **	Upper backrest > no backrest Upper backrest > lower backrest
	Fixed, entire chair	1423.022	2	711.511	14.594	0.000 **	Lower backrest > no backrest > upper backrest
Correct logical judgements	Fixed, no backrest	639.267	2	319.633	6.631	0.002 **	front one-third > front two-thirds front one-third > entire chair
	Fixed, lower backrest	769.489	2	384.744	7.982	0.000 **	front one-third > entire chair > front two-thirds
	Fixed, upper backrest	2706.200	2	1353.100	28.073	0.000 **	front two-thirds > front one-third > entire chair
	Fixed, front one-third	969.267	2	484.633	10.055	0.000 **	Lower backrest > no backrest > upper backrest
	Fixed, front two-thirds	970.956	2	485.478	10.072	0.000 **	Upper backrest > no backrest Upper backrest > lower backrest
	Fixed, entire chair	1744.267	2	872.133	18.094	0.000 **	Lower backrest > no backrest > upper backrest

* p < 0.05 and ** p < 0.01.

). The results indicate that the simple main effect of short-term number memory was significant when the participants were seated entirely on the chair (p = 0.036 < 0.05). Therefore, the three backrest conditions had different effects on short-term number memory. The post hoc comparisons revealed that the participants’ performance with a lower backrest was superior to that without a backrest or with an upper backrest.

3.2. Mathematical Calculations

3.2.1. Total Mathematical Calculations

The optimal performance was observed when the participants were seated entirely on the chair (M = 67.37 ± 12.87). The worst performance was observed when the participants were seated on the front third of the chair and had an upper backrest (M = 54.27 ± 7.73). The Mauchly’s sphericity test showed a significance of higher than 0.05, indicating that the data satisfied the requirements for the two-way ANOVA. The depth of the sitting posture and backrest condition had an interaction effect on the total mathematical calculations (F = 6.754, p = 0.00 < 0.05) (Table 5).

The simple main effect was analyzed, and post hoc comparisons were performed (Table 6). The simple main effect of the total mathematical calculations was significant when the participants had no backrest, had a lower backrest, sat on the front third of the chair, and sat entirely on the chair. Without a backrest, the three depths had different effects on the total mathematical calculations. The post hoc comparisons revealed that sitting on the front third was superior to sitting on the front two-thirds or entirely on the chair. With a lower backrest, the three depths had different effects on the total mathematical calculations. The post hoc comparisons indicated that sitting entirely on the chair was superior to sitting on the front third or two-thirds of the chair.

When the participants were seated on the front third, the three backrest conditions had different effects on the total mathematical calculations. The post hoc comparisons revealed that the absence of a backrest yielded the optimal results, followed by the lower backrest and upper backrest conditions. When the participants were seated entirely on the chair, each condition had a different effect on the total mathematical calculations. The post hoc comparisons showed that the lower backrest condition yielded the optimal results, followed by the condition with an upper backrest and without a backrest.

3.2.2. Correct Mathematical Calculations

The optimal performance was observed when the participants were seated entirely on the chair with a lower backrest (M = 62.87 ± 14.10). The worst performance was observed when the participants were seated on the front third of the chair with an upper backrest (M = 48.43 ± 8.46). The Mauchly’s sphericity test showed a significance of higher than 0.05, indicating that the data satisfied the requirements for the two-way ANOVA. The depth and backrest conditions had an interaction effect on the correct mathematical calculations (F = 5.691, p = 0.00 < 0.05) (Table 5).

The simple main effect was analyzed, and post hoc comparisons were performed (Table 5). The simple main effect of the correct mathematical calculations was significant when the participants had no backrest and a lower backrest and sat on the front one- or two-thirds of the chair. Without a backrest, the three depths had different effects on the correct mathematical calculations. The post hoc comparisons indicated sitting on the front third was superior to sitting on the front two-thirds or entirely on the seat. With a lower backrest, the three depths had different effects on the correct mathematical calculations. The post hoc comparisons revealed sitting entirely on the chair was superior to sitting on the front one- or two-thirds of the chair.

When the participants sat on the front third of the chair, the backrest condition had different effects on the correct mathematical calculations The post hoc comparisons showed that the absence of a backrest led to the optimal results, followed by the lower and upper backrest conditions. When the participants sat entirely on the chair, the conditions had different effects on the correct mathematical calculations. The post hoc comparisons demonstrated that the lower backrest yielded the optimal results, followed by the upper backrest condition and absence of a backrest.

3.3. Logical Judgment

Total Logical Judgements

Sitting entirely on the chair with a lower backrest produced the optimal performance (M = 37.97 ± 5.87), and sitting entirely on the chair with an upper backrest yielded the worst performance (M = 24.77 ± 7.79). The Mauchly’s sphericity test revealed a significance of higher than 0.05, indicating that the data satisfied the requirements for the two-way ANOVA. The depth and backrest conditions had an interaction effect on the total logical judgements (F = 26.914, p = 0.00 < 0.05) (Table 5).

The simple main effect was analyzed, and post hoc comparisons were performed (Table 5). The simple main effect of the total logical judgements was significant under all conditions. Without a backrest, the three depths had different effects on the total logical judgements. The post hoc comparisons indicated that sitting on the front third was superior to sitting on the front two-thirds or entirely on the chair. With a lower backrest, the three depths had different effects on the total logical judgements. The post hoc comparisons revealed that sitting on the front third yielded the optimal results, followed by sitting entirely on the chair and on the front two-thirds. With an upper backrest, the three depths had different effects on the total logical judgements. The post hoc comparisons revealed sitting on the front two-thirds of the chair yielded the optimal results, followed by sitting on the front third and entirely on the chair.

When the participants sat on the front third, the three backrest conditions had different effects on the total logical judgements. The post hoc comparisons showed that the lower backrest yielded the optimal results, followed by the absence of the backrest and the upper backrest. When the participants sat on the front two-thirds, the three conditions had different effects on the total logical judgements. The post hoc comparisons revealed that the upper backrest was superior to the absence of the backrest and the lower backrest. When the participants sat entirely on the chair, the three conditions had different effects on the total logical judgements. The post hoc comparisons indicated that the lower backrest had the optimal results, followed by the absence of the backrest and the upper backrest.

3.4. Correct Logical Judgements

Sitting on the front third of the chair with a lower backrest yielded the optimal performance (M = 35.23 ± 5.77), whereas sitting entirely on the chair with an upper backrest yielded the worst performance (M = 21.77 ± 7.85). The Mauchly’s sphericity test revealed a significance of higher than 0.05, indicating that the data satisfied the requirements for the two-way ANOVA. The depth and backrest conditions had an interaction effect on correct logical judgements (F = 32.964, p = 0.00 < 0.05) (Table 5).

The simple main effect was analyzed, and post hoc comparisons were performed (Table 6). The simple main effect of correct logical judgements was significant under all conditions. Without a backrest, the three depths had different effects on correct logical judgements. The post hoc comparisons revealed that sitting on the front third was superior to sitting on the front two-thirds and entirely on the chair. With a lower backrest, the three depths had different effects on correct logical judgements. The post hoc comparisons showed sitting on the front third yielded the optimal results, followed by sitting entirely on the chair and on the front two-thirds. With the upper backrest, the three depths had different effects on correct logical judgements. The post hoc comparisons highlighted that sitting on the front two-thirds yielded the optimal results, followed by sitting on the front third and entirely on the chair.

When the participants sat on the front third, the three conditions had different effects on correct logical judgements. The post hoc comparisons revealed that the lower backrest yielded the optimal results, followed by the absence of the backrest and the upper backrest. When the participants sat on the front two-thirds, the three conditions had different effects on correct logical judgements. The post hoc comparisons showed that the upper backrest was superior to the absence of the backrest and the lower backrest. When the participants sat entirely on the chair, the three conditions had different effects on correct logical judgements. The post hoc comparisons demonstrated that the lower backrest yielded the optimal results, followed by the absence of the backrest and the upper backrest.

3.5. Difference in Cognitive Learning Task by Sex

A three-way ANOVA was performed to determine the effect of sex on the depth and backrest condition. The results for short-term number memory were F = 0.1, p = 0.982 > 0.05. The results for total mathematical calculations were F = 0.092, p = 0.985 > 0.05. The results for correct mathematical calculations were F = 0.08, p = 0.988 > 0.05. The results for total logical judgements were F = 0.863, p = 0.487 > 0.05. The results for correct logical judgements were F = 0.329, p = 0.858 > 0.05; short-term number memory, correct mathematical calculations, and correct logical judgements did not differ significantly (

Table 7. ANOVA on sex, depth, and backrest conditions.

Source of Variation	SS	df	MS	F	p-Value
Short-term number memory Total mathematical calculations Correct mathematical calculations Total logical judgements Correct logical judgements	0.993	4	0.248	0.100	0.982
	41.770	4	10.443	0.092	0.985
	44.356	4	11.089	0.080	0.988
	166.444	4	41.611	0.863	0.487
	64.289	4	16.072	0.329	0.858

).

In summary, the key finding of interactions between seat depth and backrest height on learning tasks is shown as Figure 4; on the other hand, this study analyzes the results of simple main effects and conducts post hoc comparisons. The results are shown in Figure 5. Figure 4 and Figure 5 can illustrate that seat depth and chair backrest height have an impact on learning tasks, but when performing different learning tasks, different sitting conditions may be required to improve the learning effect.

4. Discussion

This study explored the effects of seat depth and backrest height on cognitive learning tasks, with a focus on short, high-concentration learning tasks, namely short-term number memory, mathematical calculation, and logical judgement. The results indicated that the combination of seat depth and backrest height affected learning outcomes. Students should perform short learning tasks requiring high concentration while sitting on the front third of a chair with a lower backrest for the optimal results. This result is similar to those of other studies [14,15,19] and indicates that tensing the lower half of the body improves concentration. The lower backrest provided more comfort and helped the waist rest, which caused the cognitive load to provide feedback. However, schools often use unadjustable desks and chairs because of the cost. This restricts students’ sitting conditions and can cause muscle stiffness. Remaining seated or stationary for a long time can cause fatigue and lower back pain, which prevent students from concentrating on learning. Sitting should be a dynamic process of adjusting the pelvic muscles and other parts of the body to prevent functional problems and pain [26].

To our knowledge, many studies have shown a correlation between sitting posture and physical health. Incorrect sitting posture, characterized by asymmetrical or uneven positioning of the body, often leads to spinal misalignment and muscle tone imbalance. The prolonged maintenance of such postures can adversely impact well-being and contribute to the development of spinal deformities and musculoskeletal disorders [27]. Rodden, J. et al. [28] claimed that minimizing daily sitting time may expedite and potentially aid muscle recovery after an intense exercise bout. Few studies have examined the correlation between sitting and learning. The seating factor predicted student situational engagement in a smart classroom [29]. The findings of this study are that each combination of depth and backrest height had different effects during each task, and sitting on the front one third of a chair with a lower backrest positively affected the performance of short, high-concentration learning tasks; the results suggest that schools and educational institutions should require students to temporarily maintain this seating condition and a lower backrest for short, high-concentration learning tasks. In addition, the chairs of a school should use a lower backrest and require students to bring lumbar pads to adjust the seat depth.

The incline of the chair cushion is related to the incline of the pelvis, which is related to comfort. Therefore, studies on the incline of the cushion should consider the seat depth and compare their results with those of this study. Prolonged sitting is bad for health. Poor sitting condition can lead to scoliosis, disc herniation, uneven shoulders, long and short legs, and other diseases. Whether you are an office worker or a student, you often spend several hours sitting for work and study every day. Sitting for long periods of time is detrimental to human health, and a lot of the literature has also found that the sitting condition affects concentration, which shows the importance of high-quality seats for everyone. This study found that the seat type has a significant impact on learning effectiveness, and this impact will increase with the difficulty and time of the work. Based on this, this study proposes the practical value of the sitting condition and future research direction.

• Practical value:

First of all, to have the correct sitting condition, you need to choose the right chair and make the best choice for different users and different seat functions. However, people cannot choose the most suitable seat anytime and anywhere, so we should promote the correct sitting condition to help people reduce possible injuries caused by poor sitting conditions. Ways to promote the correct sitting condition:

(1) Relevant government departments collect a large amount of information on the correct sitting condition and post it on bulletin boards in public and private office buildings, schools, and communities. They regularly publicize the correlation between sitting condition and health and conduct publicity activities related to the correct sitting condition in schools.

(2) Relevant government departments urge seat manufacturers to design and produce high-quality seats based on the real needs of users and consider seats that can send out warning signals when users adopt a poor sitting condition.

(3) Relevant government departments provide places where seats are sold to post correct sitting condition propaganda and hold relevant seat exhibitions or sitting condition study activities for seat sales personnel and the general public to participate, so as to improve the industry and the public’s awareness that caring about sitting at work or studying also require physical health.

Secondly, according to the findings of this study, seat type has an impact on learning effectiveness. According to the sitting condition theory and the concept of human factors engineering seat design, the focus of seat design is to keep the individual in the most comfortable and effective sitting condition, avoid unnecessary loads, reduce the restrictions of the seat on the individual, and enable them to feel comfortable and move freely. Since students spend a long time studying on chairs every day, it is extremely important for learners to promote effective sitting conditions for learning. Therefore, how should we promote effective learning sitting conditions to help learners study well in a comfortable and healthy condition? Based on the experimental results of this study, the following explanations are proposed:

(1) Incorporate “correct sitting condition” into the school’s compulsory curriculum and adopt a practical assessment to establish a model for students to learn sitting conditions on a daily basis.

(2) Post pictures of the “correct sitting condition” in the corridors and bulletin boards of the campus and use electronic billboards to broadcast effective learning conditions every day to remind students to pay attention.

(3) Print the picture of the “correct sitting condition” on students’ contact books or textbook covers to increase students’ attention to an effective learning sitting condition.

(4) Seminars on the “correct sitting condition” are held from time to time, and on-site teachers and parents are encouraged to participate. It is hoped that, through the power of teachers, students can be guided to pay more attention to effective sitting conditions.

2.

Future research directions

The researchers used changes in the chair backrest height and seat depth to design nine different seat types to determine the differences in students’ learning outcomes. They found that the learning outcomes derived from seat types did not have a significant impact on short-term memory. The mathematical calculations and logical judgements showed significant effects. Therefore, seat types can indeed improve students’ attention and response goals in specific areas. According to the results of this study, changing the chair back height and seat depth can make learning more effective. Therefore, the researchers believe that if the interaction between backrest height and seat depth can match the student’s learning area, it can help students achieve more effective learning. Overall, the concepts developed in this study have achieved the planning objectives. Based on the experimental and testing experience of this study, it is recommended that future research directions are as follows:

(1) Follow-up research of this study

Past researchers mainly explored seat design and health, safety, and comfort. They all explored whether the characteristics of chairs can really have a healthy effect on people. Therefore, regardless of the style or material selection of the seat, most of them focused on measuring the user’s physiological feedback. This study refers to the sitting condition theory and the model of human factors engineering chair designs, indicating that the seat type will affect the comfort and concentration of learners and thus affect the learning effectiveness. Therefore, this study will be extended to explore whether sitting conditions and individual emotions are relevant. If the expression of individual emotions while sitting on a chair can be quantified and further become the content of analysis and discussion, there will be more quantitative evidence for describing the characteristics of people’s preferred living equipment. Therefore, follow-up research proceeding in this direction will be a great benefit to the public.

(2) Assessment of students of different age groups and other learning areas

The research subjects of this study are mainly college students over 20 years old, because the subjects are learners who have entered municipal universities through academic tests or guided examinations, and their vocabulary and computing skills are at a certain level. Therefore, it may not be possible to clearly measure the impact of sitting condition on learning performance in short-term memory. In the future, attempts should be made to actually apply this to students of other age groups to evaluate the impact of sitting condition on those students. In long-term research and discussion, it is still necessary to cooperate with the influence of different variables, such as experimental methods, test content, number of questions, etc., and through more detailed practical discussions, it is necessary to summarize in which areas the impact of the sitting condition is more significant, so as to improve learning effectiveness.

5. Conclusions

Since school seats cannot be designed to suit individual students and ergonomics, this study will explore how learning outcomes can be optimized in different sitting conditions. The three objectives of this study were to investigate the effects of backrest height on learning tasks, to identify the optimal seat depth for each learning task, and to identify the optimal combination of seat depth and backrest height for each learning task.

This study adopted a completely within-subject experimental design, with two independent variables: seat backrest height (no backrest, lower backrest, and upper backrest) and seat depth (front one-third, front two-thirds, and entire chair). According to the two factors of seat backrest height and seat depth controlled in the experiment, it is divided into nine experimental situations. The dependent variables are the performances of students’ short-term memory, mathematical calculations, and logical judgment in different sitting conditions. A three-way ANOVA was performed to determine the effect of sex on the depth and backrest condition. The results for short-term number memory, correct mathematical calculations, and correct logical judgements did not differ significantly.

The results from this study demonstrate that seat depth and backrest height had an interaction effect on learning tasks. However, different learning tasks had different performances in the nine sitting postures designed in the experiment. Take short-term number memory, when the participants were seated entirely on the chair with a lower backrest, they could perform better. In addition, in terms of mathematical calculations, no backrest and sitting on the front third of a chair produced excellent learning task outcomes; a lower backrest and sitting entirely on the chair also produced good results. In terms of logical judgements, when participants sat in the front third of the chair, with no backrest or lower backrest, it produced excellent learning task results; an upper backrest was paired with sitting in the front two-thirds of the chair to produce good results.

In summary, the sitting condition may have an impact on students’ cognitive learning; although the sitting posture is not the only factor that affects learning, based on past researchers and the results of this study, teachers can provide guidance when teaching cognitive learning by trying to require students to temporarily adopt distinct sitting conditions for different learning tasks. In addition, the school cannot purchase chairs with adjustable backrests, so students can use lumbar cushions to adjust the seat depth to achieve better learning outcomes. However, not only are chairs related to comfort and learning task outcomes, desks or other furniture can also affect sitting posture, and future research could explore desk design elements. In the future, we hope that more researchers will study the impact of classroom furniture on learning outcomes.