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Anatomy of a Chair

Anatomy of a Chair

All too often during an ergonomics assessment we see individuals sitting in expensive office chairs that are not set up to provide good support. Most office chairs are highly adjustable, in order to suit a large variety of individuals; but all these adjustable features means a lot of complicated knobs and levers. In this article we have laid out some of the features typically found in an office chair and have provided the common placement of the levers/knobs. We encourage you to test out all the features of your chair to ensure you have it set up to suit you best.

Chair Image Source: Global Furniture Group

NOTE: This image shows a wide range of potential chair adjustments. Your chair may not have all the features shown above or adjust in exactly the same way.

Anatomy of a Chair

Seat Depth: This feature allows you to lengthen or shorten the chair seat pan. When sitting with your hips all the way back in the chair, you should have at least a two finger width gap behind your knees and the front edge of the seat. To change the length of the seat pan you will need to hold the lever/bar and slide the seat forward or back on the base.

Armrests: Armrests may adjust up and down or in and out. There is typically a button on the side or bottom of the armrest that allows you to move it up or down. There may also be a knob or latch on the underside of the armrest where it meets the chair base that allows you to move the armrest in or out. The arm caps may slide forward and back, side to side or even pivot. While not imperative, armrests provide support for the upper body while working. Adjust armrests to support the forearms with relaxed shoulders and elbows bent.

Seat Height: Seat height allows you to raise and lower the chair. The adjustment lever for seat height is typically found on the right side directly below the armrest. Set the height so that your elbows are at, or slightly below, keyboard and mouse height. You may need a footrest to establish a stable base if your feet are not firmly supported on the floor when your chair is at an appropriate height.

Back Angle: Many chairs have the ability to change the angle of the backrest to suit the user. The lever for the backrest angle is typically located towards the rear of the seat pan on either the right or left side. Ideally you should sit with the backrest slightly reclined to facilitate good Shoulders Anchored posture.

Lumbar Support: Some chairs have lumbar support that may be height or depth adjustable. Depending on the type of chair, the lumbar support may be adjusted by raising or lowering a lumbar bolster, or sometimes the entire chair back moves up and down on a ratchet mechanism or post. Position the lumbar portion of the chair so that it is comfortable for you and fills the hollow in the small of your lower back.

Tilt Mechanisms

Over the years of teaching people how to set up office chairs, we have found that the feature set which causes the most confusion is the chair rock and tilt mechanisms. Users will often pull the tilt lever on their chair once, experience the fright of nearly being ejected out of their seat or falling back suddenly, then never touch the lever again! But ignoring this feature set means you don’t experience the benefit of rocking back in your chair to reset static posture and unwind some of those hunched postures we can sometimes get ourselves into throughout the workday.

Chair Tilt Rock/Lock: When locked, this lever prevents the chair from rocking back. When unlocked, the chair is able to rock back and forth like a rocking chair. The adjustment is typically found on the right side of the seat pan, and may be a lever you pull up or push down, or could be a knob you pull out or push in.

Seat Tilt: Seat tilt works in conjunction with the chair rock feature described above. The seat tilt lever/knob is typically located closest to the front edge of the seat and allows the seat pan to tip forward when unlocked and with the chair in rock mode. Some chairs will allow a gradient of seat tilts (typically those with a knob adjustment) while others only allow for a flat or forward tilt position (usually a sliding lever). For most users, having the seat pan tilt forward when rocking is not comfortable, so it is most common to lock the seat pan into a horizontal position. On many chairs, to lock or unlock the seat tilt, you must first unlock the tilt rock and physically rock back in the chair. In this rearward leaning position, you then unlock the seat pan tilt by adjusting the knob or lever. To lock the seat tilt back into a flat position, rock back in your chair again and move the seat pan knob back to its starting position.

Tilt Tension: This knob controls the amount of resistance required to move the chair when in the rock mode. The tension knob is typically located under the seat pan, or on the right side of the chair. Tension should be stiff enough to support you when sitting relaxed, but should not require excessive effort to push the chair back into a ‘Why Me’ stretch.

Summary

Different chair manufacturers have different lever placement and your chair may not contain all of these features. If you know the make and model of your chair you may be able to find an instructional video online. Here are the video links to some common chairs we recommend:

Global Tritek    Steelcase Leap    Herman Miller Aeron    Performance CoolMesh Pro

Now that you have your chair set-up for best fit, you can follow our workstation set-up guide to create an ergonomically sound workstation. If you are unsure if your set-up or equipment is working for you, contact us for a virtual ergonomics assessment of your workstation.

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