Seat height

Seat height is the foundational adjustment on any office chair. The correct seat height places the feet flat on the floor (or on a footrest) with the thighs roughly parallel to the floor and the knee joint at approximately 90°. This distributes body weight across the seat pan rather than loading the edge of the seat against the back of the thighs, which would restrict circulation.

For workers whose feet do not reach the floor at the correct desk-to-elbow height (typically shorter workers using a desk set for an average or taller user), a footrest is the appropriate solution. Footrests are referenced in Polish BHP regulation as mandatory provision when workstation geometry requires them. PIP inspections of workstations frequently cite absent footrests as a compliance issue in offices with fixed-height desks used by workers of varying statures.

Checking seat height

Sit in the chair with your back against the backrest. Feet should rest flat on the floor without the thighs being angled significantly downward (too high) or the knees sitting above hip level (too low). A 2–3 finger gap between the back of the knee and the front edge of the seat pan is a commonly used practical check. This gap allows blood to circulate in the lower leg without the seat edge pressing into the popliteal area.

Lumbar support

The lumbar region of the spine (lower back, L1–L5 vertebrae) maintains a natural inward curve (lordosis) when standing. When seated without support, this curve tends to flatten or reverse, particularly over longer periods, increasing load on the intervertebral discs and posterior ligaments. Lumbar support in a chair aims to maintain this curve in a seated position.

Most adjustable office chairs include a lumbar support mechanism — either a separate lumbar pad, a curved backrest that contacts the lumbar area, or an adjustable lumbar bulge. The support should contact the lower back at approximately the belt-line level (roughly L3–L4) and provide gentle forward pressure to maintain the curve without pushing the torso into a rigid posture.

Lumbar support positioned too high (pressing into the mid-back) or too low (below the lumbar curve entirely) does not reduce lumbar load. If the support is adjustable, position it where you can feel contact at your lower back when sitting upright with the backrest.

Backrest angle and recline

The traditional 90° sitting posture (thighs horizontal, torso vertical) has been challenged in occupational health research as potentially sub-optimal. A slight backward recline of the backrest — to approximately 100–110° from the seat — reduces compression on the lumbar discs relative to strict vertical sitting. This is because the hip-trunk angle opens slightly, reducing posterior pelvic tilt and maintaining lumbar lordosis with less muscular effort.

In practice, this means a chair backrest that leans slightly backward, not straight up. Recline tension should be adjusted so that leaning back briefly during pauses feels natural without requiring significant effort to return upright, and without the chair tipping back uncontrolled.

Armrests

Armrests reduce the load on the neck and shoulder muscles by supporting the weight of the arms. The trapezius and levator scapulae muscles sustain a continuous low-level contraction to hold unsupported arms, which contributes to upper shoulder and neck tension over working hours.

Armrests should be positioned so that the elbows rest naturally at approximately keyboard height — meaning the forearms are horizontal or slightly downward-angled when typing, with no upward shrug of the shoulders required to accommodate armrest height. Armrests set too high cause shoulder elevation; armrests set too low do not provide support during typing.

Armrests should not prevent the chair from being pulled close to the desk. If armrests force the worker to sit farther from the desk than correct monitor distance and elbow-to-keyboard position require, lowering or removing them is preferable to adopting a compensatory posture.

Seat pan depth and tilt

Seat pan depth should allow a fist-width gap (approximately 8–10 cm) between the front of the seat and the back of the knee. If the seat pan is too long for the worker's leg length, sitting against the backrest pushes the front edge into the back of the knees; workers often respond by sliding forward on the seat, losing contact with the lumbar support — which defeats the purpose of both adjustments.

Some chairs include a seat pan adjustment (forward-backward sliding or telescoping depth). Where available, this allows the seat depth to be matched to the worker's thigh length independently of backrest position.

Seat pan tilt (forward or backward) changes the angle of the hip joint and the inclination of the pelvis. A slight forward tilt of 5° opens the hip angle, facilitating pelvic tilt and lumbar lordosis in the same way that a slight backrest recline does. This can be useful when working tasks require forward-leaning (drafting, close reading of documents). Backward seat tilt increases lumbar load and encourages posterior pelvic tilt; it is generally not recommended for extended seated work.

Posture variation and movement

No single seated posture, however correctly adjusted, is appropriate for the full working day. Sustained static loading — maintaining any fixed position — creates progressive muscle fatigue and reduced circulation to discs and soft tissue. The occupational health consensus is that postural variation and movement interruptions are more effective than optimising a single static posture.

Polish BHP regulation requires a 5-minute break from screen work for every hour of continuous display screen use. This requirement exists partly for visual rest (eyes) and partly for postural relief. Standing up and walking briefly during these breaks — rather than remaining seated and looking away from the screen — provides more complete postural relief.

Practical movement patterns

Several structured approaches to workday movement have been described in occupational health literature:

  • Alternating between sitting and standing (for users with sit-stand desks) in intervals of 25–45 minutes
  • Standing briefly for phone calls or reading tasks that do not require keyboard input
  • Using a printer or document storage at a distance from the desk to create mandatory walking breaks
  • Setting a timer or using operating system reminders as a prompt to stand at regular intervals

Chair standards applicable in Poland

Office chairs sold in the EU — including Poland — are subject to EN 1335-1 (Office furniture — Office work chair, dimensions), which specifies minimum and maximum ranges for seat height, seat depth, backrest dimensions, and armrest geometry. When purchasing a chair for an office workstation, EN 1335 certification indicates that the chair meets the baseline dimensional requirements. Additional adjustability beyond the standard minimums significantly expands the range of users the chair can accommodate correctly.

Polish BHP regulation specifies that office chairs must be height-adjustable and must include a backrest. Armrests are not mandated by regulation but are recommended by CIOP-PIB for workers performing keyboard tasks for extended daily durations.

References