Ergonomic Chair Structure, How to Choose?

During World War II, pilots were required to endure long hours in the cockpit during combat missions. To enhance their comfort while sitting for extended periods, engineers began researching chairs that adhered to ergonomic principles. Fast forward to 2024, and while we no longer engage in intense aerial dogfights, the amount of time we spend seated has dramatically increased, often exceeding that of wartime pilots.

Traditional chair backs fail to align with the natural curvature of our spines, leading to discomfort in the neck and lower back after prolonged sitting. Over time, this can result in more serious issues, such as hunchback or lumbar disc herniation. So, how can you choose a chair that suits you best? First, it’s essential to understand its structure.

The Components of an Ergonomic Chair

An ergonomic chair is specifically designed to provide optimal comfort and support during extended periods of sitting. It achieves this by incorporating various components that work together to adapt to the user's body and posture. Understanding these components and their functions is crucial when selecting a chair that aligns with your comfort and ergonomic requirements. Key elements of an ergonomic chair include the headrest, backrest, armrest, seat cushion, base, cylinder, support feet, and casters.

Caster part

Casters provide mobility to the chair, allowing us to easily adjust the position of the chair. Unlike traditional chairs, ergonomic chairs usually use quieter plastic wheels instead of metal wheels. Among plastic wheels, PU (polyurethane) wheels are the softest and quietest, and are ideal for hardwood floors. PA (nylon) wheels are more durable but harder, suitable for carpeted areas. PP wheels are the most cost-effective, but also the least durable.

Supporting foot part

The support feet are the key to the load-bearing and weight-distributing of the chair, and are also an important indicator of the quality of the chair. Support feet are usually made of nylon, steel, or aluminum alloy. Although aluminum alloy is not as strong as steel, it is more beautiful after processing and will not rust, but the cost is higher. Nylon support feet are the cheapest and have the lowest load-bearing capacity.

In addition to the material, the radius of the support feet is another key factor in determining quality. Most ergonomic chairs on the market have a radius of 320-330mm, but some can go up to 340-350mm. The larger the radius, the greater the weight capacity. Even the nylon feet can support up to 400 pounds, which is perfect for daily use, although the aluminum alloy feet provide a better tactile experience.

Gas cylinders

People of different heights require chairs of varying heights, and the component responsible for height adjustment is the gas cylinder. The gas cylinder's cross-section mainly comprises a gas rod and a sleeve. 

The gas chamber is filled with high-pressure nitrogen, which exerts pressure on the chamber walls due to the higher internal pressure compared to the outside. Forces acting in opposite directions cancel each other out. The key to the piston's upward and downward movement lies in the pressure on these two parts. 

When the adjustment lever is opened, the gas chamber is connected on both sides of the piston. Under the influence of pressure differences, the piston rod is pushed out, raising the seat. Once the seat height is adjusted, closing the lever prevents gas movement between the two chambers, and the piston remains stationary due to the gas pressure.

However, if a substandard gas cylinder is used, it may develop cracks during use, ultimately leading to an explosion. But there’s no need to worry too much—most certified chairs use gas cylinders that meet standard certifications, with EN 16955 being the most crucial. Testing agencies use metal fatigue testing instruments to clamp both sides of the outer cylinder and repeatedly try to bend it based on the alternating bending moments of the gas cylinder, classifying it into four levels from low to high.

Today’s manufacturing processes for gas cylinders are highly advanced, and cylinders rated at level 3 or above generally pose no safety concerns. For added peace of mind, you can consider ergonomic chairs with protective steel plates.

Chair Cushions

Human beings have evolved over thousands of years to develop an S-shaped spine, which effectively distributes weight when we stand upright. However, when we sit, both the spine and the ischial tuberosities, which connect to the lower limbs, bear significant pressure. A well-designed ergonomic chair alleviates this pressure through its seat cushion and backrest.

Traditional foam seat cushions conform well to the shape of the buttocks and provide reasonable support but can feel stuffy after prolonged sitting. 

Mesh seat cushions offer less conforming support but provide better breathability, elasticity, and support. 

Even within the same brand, mesh can vary, so it’s important to test the chair personally to find the best fit.

Chair Back

The backrest is where ergonomic chairs differ most from traditional chairs, typically offering either single-back or double-back designs. 

Double-back designs generally provide stronger lumbar support, while single-back designs are softer. People with different body types require different levels of lumbar support elasticity. 

Heavier individuals need stronger lumbar support, while lighter individuals might find it too firm. Some double-back ergonomic chairs offer an adjustment knob to fine-tune the lumbar support’s tension.

Certain ergonomic chairs, designed for long periods of sitting, also separate the upper part of the backrest into two sections, providing better shoulder support. However, those with narrow shoulders might find this uncomfortable.

Armrests and Seat Pans

A good ergonomic chair should have adjustable armrests, essential for tasks like typing or writing. Ideally, the armrest height should match the desk height, ensuring that the elbow joint and desktop are aligned, reducing shoulder strain.

Over time, we might unconsciously lean back or to the side. A flexible seat pan can accommodate these small movements. Most ergonomic chairs use spring-loaded seat pans, with torsion and compression springs being the most common. 

Torsion springs work like a hairpin, providing more comfort during reclining by increasing the backrest’s support. Compression springs, on the other hand, convert the clockwise force applied during reclining into lateral compression of the spring, helping the backrest stay close to the body.

Many ergonomic chairs use a standard single-spring seat pan, which may not provide sufficient support and require a lock for recline adjustment. Double-spring seat pans, however, allow for more natural reclining and sometimes include a knob for adjusting the spring tension, offering stronger support when needed.

Some high-end chairs use a wave spring seat pan that provides consistent recline resistance without becoming stiffer the further you lean back, though these are more expensive. Generally, a double-spring mechanism is sufficient for most needs.

Seat Height

Different body types require different seat heights and depths. According to ergonomic principles and guidelines from organizations like OSHA, the correct seat height should be the sum of lower leg length and foot height, plus about 2 cm of clearance. This allows the knees to bend naturally, with the angle between the lower and upper legs slightly greater than 90 degrees. The proper seat depth should be the distance from the back of the thigh to the knee, minus 5 cm. This leaves a gap of 5-10 cm between the edge of the seat and the back of the knee.

Tips for Choosing an Ergonomic Chair

When selecting a chair, comfort is determined not just by materials but also by whether it can be adjusted to fit your body. Most ergonomic chairs are designed to suit individuals around 175 cm tall with an average weight. However, if your weight exceeds 90 kg, you should pay attention to the chair’s size and weight capacity.

For those with particularly full hips, a seat width of at least 50 cm is recommended, and the support base should preferably be made of aluminum alloy. Additionally, you can inquire with the seller about the maximum weight capacity of the chair. As long as your weight is within the supported range, there should be no significant issues.

While ergonomic chairs can greatly improve comfort during long periods of sitting, it’s important to remember the advice from OSHA: regardless of how well you sit, remaining in the same posture for extended periods is unhealthy. Regularly standing up and moving around is far more important than the chair you choose.