(2) Analysis of comfort and health in chair design based on ergonomics

Adjustment of sitting posture:

If your body remains in the same sitting position for a long time without moving, even if it is a comfortable sitting position, problems will occur over time. Long-term accumulation of pressure will not only cause local muscles to feel stiff, but it is also detrimental to the health of the spine and the human body will feel uncomfortable. Therefore, when sitting for long periods of time, you should often and consciously adjust and change your sitting posture, move your body (including walking regularly), and change your body position.

Humanized design of chair backrest - key points for chair health and comfort:

In the words of Danish design master Hans Wegner, the essence of a chair is four legs (or understood as a bracket), a seat, plus armrests and a backrest connected together, which is a chair.

Here, I will just focus on some thoughts on the design of the chair backrest. The reason is that the backrest is the fundamental factor that determines the health and comfort of chair furniture. It improves the lumbar spine condition of the sitting posture and maintains a better sitting posture. This is mainly due to the chair backrest. to achieve. Designing the backrest is not only much more important than designing the seat surface, but it is also much more complicated. It is the most difficult thing to satisfy the human body. When designing the backrest, you should pay attention to the following points:

Seat backrest inclination - assists the human body in forming a certain sitting posture:

Seat back inclination refers to the angle between the seat back and the seat surface. What is the basis for the size of the backrest inclination? The backrest inclination serves the sitting posture of the human body, and its main function is to assist the human body in forming a certain sitting posture. Therefore, the backrest inclination of the seat should be determined based on people's sitting needs.

Commonly used sitting postures include forward leaning posture, straight waist sitting posture, and backward sitting posture. The backrest inclination angle of the seat can be selected from three situations: less than 90°, equal to 90°, or greater than 90°. What is the relationship between the three common sitting postures of people and the three backrest inclination angles of the seat? People often mistakenly believe from superficial phenomena that there is a one-to-one correspondence (unique correspondence) between the three commonly used sitting postures and the seats with three backrest inclinations. That is, the forward-leaning sitting posture corresponds to the seat with a backrest inclination less than 90°. The lumbar sitting position corresponds to a seat with a backrest inclination equal to 90°, and the reclined sitting position corresponds to a seat with a backrest inclination greater than 90°. This is purely a misunderstanding. The actual situation is that there is no one-to-one correspondence (unique correspondence) between the three common sitting postures and the seats with three backrest angles.

For example, when sitting forward, you are not limited to seats with a backrest inclination less than 90°, but you can also choose seats with a backrest inclination equal to or greater than 90°. Because the forward leaning posture allows the person's back to exist independently from the back of the seat, that is to say, whether the inclination angle of the seat back is less than 90°, equal to 90°, or greater than 90°, the person sitting can choose independently. Sit forward. This shows that there is no one-to-one correspondence between forward-leaning sitting postures and seats with backrest inclinations less than 90°.

In the same way, sitting with a straight waist is not the only option to use a seat with a backrest inclination equal to 90°, but you can also choose to use a seat with a backrest inclination less than 90° or greater than 90°. Therefore, there is no one-to-one correspondence between a straight-back sitting posture and a seat with a backrest angle equal to 90°.

The situation of reclining sitting posture is more complicated. Under the two conditions of backrest inclination angle less than 90° and equal to 90°, people cannot form a suitable reclining sitting posture. They can only choose to use seats with backrest inclination angle greater than 90°. Only here. Only on the premise that this kind of backrest cooperates with the person's posture, and it is the only premise, can people form a suitable reclining posture. Without the conditions of this kind of backrest, the individual seated person cannot complete the reclining sitting posture alone. , therefore, the reclining posture must only use a seat with a backrest inclination greater than 90°; however, conversely, when the backrest inclination is greater than 90°, the person sitting is not limited to the reclining sitting position, he can also freely choose to sit forward. Reclined sitting posture or straight-back sitting posture, this means that there is no one-to-one correspondence between the reclined sitting posture and the seat with a backrest angle greater than 90°.

In the previous part of this article, "Research on Sitting Postures," we have reached the conclusion that, on the one hand, theoretically speaking, a healthy and comfortable reclined sitting posture should be promoted and recommended. To meet the needs of this sitting posture, a backrest inclination angle greater than 90 must be selected. ° seats; it was also mentioned in the "Sitting Posture Research" that on the other hand, from the actual situation, when working on the desktop, it is impossible to just sit back and have to sit forward or straight. Sitting posture, that is, the sitter must be able to choose all three commonly used sitting postures. To meet all these sitting posture requirements, you can only choose a seat with a backrest inclination greater than 90°, and not others. Only in this way can it meet the needs of modern people. living habits and sitting posture needs. This leads to the conclusion that when designing a seat, a backrest inclination angle greater than 90° must be used.

According to the different target positions of the seats in the design, such as work chairs, rest chairs, multi-function chairs, etc., backrest inclination angles that are all greater than 90° but of different sizes will be used.

For low-back chairs and mid-back chairs, the backrest inclination angle is greater than 90°, but generally does not exceed about 110°. The reason is that if the backrest inclination angle exceeds 110°, although the lumbar spine will feel more comfortable, the human body is a whole system and the balance of each part must be considered comprehensively. For low and medium-back chairs, because the backrest is relatively short, there is no The headrest on a high-back chair will cause new problems for people's cervical vertebrae. The inclination of the backrest is too large and the head is tilted back excessively, which will cause the center of gravity of the head to exceed the support surface of the neck. In order to maintain the balance and stability of the head , causing the cervical spine to be straight and the neck muscles to be in a state of continuous tension to support the backward posture of the head. Over time, fatigue and strain of the cervical spine will inevitably occur. Therefore, at this time, the backrest must be raised from the low and middle backrests to a high-back chair, and a headrest must be added to the upper part of the backrest to support the head (lower part of the back of the head) and cervical vertebrae. Therefore, the backrest inclination angle of low and medium-back chairs is greater than 90°, but generally does not exceed about 110°.

Three-dimensional shape of the backrest panel:

The shape of the backrest should be as close as possible to the shape of the human back when sitting, that is, the normal S-shaped physiological curvature of the human spine. The effect is that, on the one hand, when the body is in a reclined sitting position, if the shape of the backrest of the chair is closer to the person's back, fits better, and has a sense of wrapping, the mutual contact area will be larger and the pressure will be smaller. On the contrary, if the backrest shape is The backrest does not match, causing local pressure concentration and making the back feel uncomfortable; on the other hand, the closer the backrest is to the shape of the person's reclining spine, the support for the spine, especially the lumbar spine, is conducive to maintaining the spine close to the normal S Shape physiological curvature, reduce the pressure in the lumbar intervertebral disc, and make the lower back feel comfortable.

The shape of the backrest in the longitudinal section (midsagittal plane):

The tangent line of the backrest on the longitudinal section is close to the normal S-shaped physiological curvature of the spine, that is, the corresponding segments of the backrest with the cervical and lumbar vertebrae protrude forward, and the corresponding segments with the thoracic and sacral vertebrae protrude backward. To be more precise, the S shape here is not one S, but two S shapes stacked from top to bottom.

However, it should be noted here that the "physiological curvature" and "physiological curvature" of the spine are two different concepts. The normal S-shaped physiological curvature refers to the direction of lordosis or kyphosis of the four segments of the spine respectively. The physiological curvature refers to the amount of lordosis or kyphosis. In different postures, the physiological curvature of the spine is mostly similar in direction, but the physiological curvature changes. For example:

A. Standing upright, the S-shaped bend is about 4-6cm deep in the lumbar segment (H);

B. Lying on your back, the S-shaped bend is about 2-3cm deep in the lumbar segment (H/2);

C. Some kind of reclined sitting posture, the S-shaped bend is about 1-1.5cm (H/4) deep in the lumbar segment.

In the design of the backrest, the changes and differences in the S-shaped bending direction and curvature of the backrest should be taken into consideration.

The shape of the backrest in cross section (horizontal section):

The tangent line of the backrest on the horizontal section should be close to the left-right symmetrical concave arc, that is, the backrest is an arc backrest plate. Combining the longitudinal and transverse shapes, the backrest panel should be an annular complex space surface.

Main points of support on the backrest:

The main support point on the backrest is a small area of "point" that effectively supports several human bones on the back of the human body. It is the point where the pressure distribution on the entire backrest is maximum. Specifically, it refers to the lumbar support (at the lumbar vertebrae, one point in one place, protruding forward), shoulder support (at the left and right shoulder blades, located near the fifth and sixth thoracic vertebrae, two points in one place, one point on the left and right sides, Protruding backward), headrest (headrest, lower part of the back of the head and cervical spine, one point at a time, protruding forward).

At these three four-point support positions, the backrest is required to support the human body to a certain support strength (support hardness) to ensure the stability of the support. If there is a soft cushion at the support point, be careful that the material is not too soft, because if the cushion expands and contracts with the pressure of the back, it will give people a feeling of instability.

Let me emphasize again the design of the "lumbar support". The lumbar spine is the most unbalanced skeletal part of the human spine. It has to bear the weight of the entire upper body and maintain the balance and stability of the body. On this basis, it also needs to carry out large-scale activities of the waist. Therefore, the lumbar spine is the most important part of the human body. As for the connection part, the lumbar spine is the most tiring part in sitting position. The lumbar spine is the human organ most prone to pain and disease in sitting position. The first consideration for health and comfort in seat design is to support and protect the lumbar vertebrae, allowing the lumbar vertebrae to fully relax and rest. The curved shape of the seat back is to make the spine close to the S-shaped physiological curvature in the normal state when sitting, especially to maintain the physiological characteristics and good shape of the lumbar curve of slight convexity. Therefore, the backrest is convex forward. The lumbar support that supports the lumbar spine is the most important support point in the backrest design. The specific location of the lumbar support is near the fourth lumbar vertebra. Because everyone's height and shape are different, it is impossible for a fixed lumbar support to adapt to the lumbar vertebrae of many people in the design of the lumbar support. For this reason, you can design a small waist pad that can be adjusted up and down to meet personalized design needs.

The smoothness, feel and touch of the contact point between the backrest and the human body:

All parts of the seat back, especially those in contact with the human body, are not allowed to have sharp corners, sharp edges (sharp edges), or protrusions (small protrusions) that can easily hurt or hurt people. They must be round, smooth, and feel good. Nice touch.

Backrest and long-term sitting posture adjustment:

When sitting for a long time, the sitting posture should be adjusted frequently and actively. Therefore, some new requirements will be put forward for the seat and backrest. First, there is space for sitting posture adjustment, and it is convenient to change the sitting posture. It will be more comfortable if the backrest has a wrapping feeling, but it should be too tight to hinder the adjustment of the sitting posture. Second, when the body is properly rotated on the seat, the backrest needs to always support and lean on the sitter's waist to maintain comfort.

Human-chair coordination: Be able to sit and develop good sitting habits:

The seat occupies an extremely important position in the formation of sitting posture. Whether the sitting posture is good or not, the most direct material condition is the seat. However, even if you have a properly designed chair, can you ensure a good sitting posture? not necessarily! Seats only affect people's sitting posture to a great extent, but they may not completely determine people's sitting posture, because there is not only one fixed sitting posture on a chair, but the seater can choose N sitting postures independently. : For example, judging from the position of the buttocks on the seat surface, you can sit shallowly, deeply, or fully seated; judging from the angle changes of the upper body in the front-to-back direction, even if you sit on a seat with a backrest inclination greater than 90°, you can sit anywhere. Choose to sit forward, sit with your waist straight (sitting upright), sit relaxedly, or sit back; from the angle changes of the upper body in the left and right directions, you can tilt to the left, the upper body upright, or tilt to the right; from the posture of the calves , you can stretch your legs forward, stand upright, hook your back, and even cross your legs, or sit diagonally with your legs on the armrests; in addition, there are changes in sitting postures such as raising your chest and raising your head or holding your chest and hunching your back; and Ge You's lying down (Beijing paralysis) posture Bad sitting postures, etc. In short, people's sitting postures can be ever-changing, and there is no limit to one sitting posture on a chair.

Therefore, a good sitting posture depends on two factors. One factor is the "object" condition, which requires a chair with a reasonable design, especially a height suitable for you (tailor-made) and a suitable backrest; the other factor is from In terms of "people", there is a problem of coordination between people and chairs. People must "know how to sit" when sitting on a chair and develop a good sitting habit, rather than adopting a blind and casual (laissez-faire) sitting posture.

Good sitting habits should mainly meet the following requirements:

A. The buttocks sit firmly and fully cover (fully cover) the chair surface.

B. The buttocks and lower back are naturally placed against the back of the chair, allowing the back to function, and try to sit in a reclined posture.

C. In particular, keep the waist close to the waist support and do not let the waist hang in the air. For seats where the lumbar support is not suitable, add a lumbar cushion for adjustment.

D. After sitting, always consciously move your body, adjust and change your sitting posture, including standing up and walking around. It is not advisable to stay in one sitting posture for a long time.

Avoid bad sitting posture:

A. The upper body is hunched over (sitting forward): This is a sitting posture that leans too far forward, and the spine is deformed into an arch (C shape).

B. Sitting shallowly and leaning back, sitting crookedly: The shape is like Ge You lying down (Beijing paralysis), sitting shallowly, with the upper body leaning too far back, with only the shoulders leaning back on the back of the chair, a semi-lying position, with the waist hanging in the air and no waist support. , this is an "abnormal reclined sitting posture". Sitting for a long time can cause lumbar disc herniation and produce degenerative diseases.

C. Crossing the legs for a long time: The physiological lordosis of the lumbar spine is reduced, disappeared or even kyphosis, the normal physiological curve of the lumbar spine is destroyed, and the lumbar muscles are in a state of tension, leading to lumbar muscle strain.

Only by combining a well-designed seat with good sitting habits can a healthy and comfortable sitting posture be achieved.