Specialist Seating – The Q&A Series:

The Importance of Chair Set-Up

Every chair must be set up to fit its user – supporting posture appropriately and ensuring maximum contact with the support surface to distribute weight evenly, whilst maintaining comfort and independence.

It is critical that the seating prescription and subsequent set-up is based on the individual’s body shape and size determined during the seating assessment; if it is not then it can cause more harm than good. The way in which the chair is set-up influences positioning, which can consequently impact on the risk of secondary complications, including postural deterioration, pressure injury and reduced quality of life.

chair measurements


1. Why is seat depth important?

A chair with the right seat depth ensures pelvic stability by supporting the pelvis posteriorly. Without posterior support, the pelvis can tilt backwards and encourage sacral sitting with a posterior pelvic tilt.

If the seat depth is too long, the user won’t be able to bend their knees over the seat edge so they will slide forward in the chair to seek support through the feet. If the seat depth is too shallow the area over which body weight is distributed may be reduced, which increases the risk of pressure injury.

When set correctly, the individual’s pelvis should be positioned at the back of the chair, with an approximately two-finger gap between the back of the knee and the front edge of the seat cushion.


2. Why is seat width important?

Seat width adjustment helps to laterally stabilise the pelvis. Correct seat width can reduce the tendency for the user to lean or shuffle the pelvis. These undesirable movements can result in pelvic obliquity or pelvic rotation and the posture becoming increasingly unstable with unequal loading on tissues. Left unmanaged, this leaning posture could lead to the development of a scoliosis.

Chairs with adjustable armrests, such as the MultiAdjust, can be utilised to set different seat widths from front to back and left to right, which may be indicated for users with fixed lower limb postures such as windsweeping, or those with increased body mass in the gluteal and hip areas.

3. Why is seat height important?

Seat height is important for maintaining independence and function for individuals who are ambulant or able to rise to standing for transfers. If the chair’s seat height is too high, the user will be unstable when they rise to standing or it will encourage a posterior pelvic tilt as the user seeks foot support. If seat height is too low then they may not have adequate strength to complete a sit to stand.

If the individual is non-ambulant or hoist transferred then correct seat to footrest height is needed to achieve adequate foot support, which is critical for pelvic and upper trunk stability as the feet take 19% of the body’s weight in sitting1. A height adjustable footplate can be utilised to support the feet appropriately for comfort and pressure distribution depending on lower leg length.

4. Why is arm height important?

The height at which armrests are set is important for users who can rise to standing by pushing up and out of the chair. It also encourages repositioning and enables optimum upper limb position for activities.

Arm support can relieve tension in the neck muscles; it should not be used to achieve trunk alignment or control however. Transfer armrests can also be prescribed to aid user transfers and positioning, or for cleaning and servicing, as seen on the HydroFlex.

5. What seating considerations are needed for the plus-size population?

An individual with increased body weight and size may present with any of the following postural challenges:

When prescribing seating, the following considerations are recommended to ensure safe and appropriate chair set-up:

  • Careful attention to the equipment’s maximum user weight limit is needed to ensure safe and appropriate use. There is also the need to be mindful of the potential for weight fluctuation; therefore, an adjustable chair that can adapt to changing need is essential.
  • As aforementioned, the correct seat depth is essential to encourage pelvic stability and to ensure the maximum surface area is in contact with the chair to reduce interface pressures.
  • Ensuring lateral pelvic stability through correct seat width is also critical to reduce the tendency for the user to lean or shuffle the pelvis.
  • Improved pelvic positioning and the correct seat height can improve sit to stand transfers, reducing the need for hoisting. This can empower individuals to continue being mobile and thus physically active.
  • Extra support for the gluteal shelf may be indicated; without support, the increased gluteal shelf can push the person anteriorly increasing the risk of falling out of the chair and undesirable postural changes such as a posterior pelvic tilt.
  • Larger calves or oedematous lower legs can position the lower limbs too far forward restricting knee flexion and resulting in inadequate foot support. A negative angle legrest can help accommodate larger lower limbs whilst maintaining optimum knee flexion position; weight can then be evenly distributed through the feet. The negative angle can also allow a more stable placement of feet for sit to stand transfers.
  • Pressure care should also be addressed to reduce the risk of developing or worsening pressure injuries as a result of increased interface pressures and unequal loading of tissues.

To ensure a true holistic approach, the caregivers’ needs should also be considered. Seating individuals who are obese can pose risks to their family, friends and/or support staff, as their unique body shape and their increased weight and size can increase the risk of injury to caregivers. Powered functions and heavy duty castors can make chair use and manoeuvrability smoother and safer for the individual and their support network.

HydroTilt XL


6. What is the best chair to support the plus-size population?

The HydroTiltXL includes all the tried and trusted features of the much loved HydroTilt but has an increased 35stone/220kg maximum user weight. It is an ideal solution for plus-size individual prescriptions; its adjustability and choice of accessories make it configurable for a wide range of seating needs in domestic, health and social care settings. It is particularly suited for those who present with obesity, lymphoedema, osteoarthritis or those recovering from stroke.

The HydroTiltXL is a robust supportive chair that offers comfort with optimum posture and pressure management for individuals with increased body weight and size:

  • Adjustability can ensure safe and appropriate chair set-up individualised to the user based on their unique body shape to promote postural stability.
  • Powered tilt-in-space, if safe and appropriate, can further improve pelvic stability and positioning by encouraging the pelvis to remain at the back of the chair without affecting the critical angles for sitting.
  • Powered tilt-in-space can also promote energy management by allowing periods of rest, and encourage pressure redistribution away from the buttocks to reduce the risk of pressure injury.
  • Integrated WaterCell Technology can further encourage maximum support with the aim of managing pressure injury risk.
  • The reconfigured waterfall back can allow extra space to comfortably accommodate the gluteal shelf improving pelvic stability.
  • Where indicated, a back rest wedge can be utilised to adjust the user’s hip angle if pressure needs to be relieved off the abdomen.
  • The negative angle legrest can allow a more stable placement to assist with standing, empowering the individual.
  • Four braked heavy-duty castors with sealed bearing hubs offer enhanced durability and smoother manoeuvrability. With the brakes applied, the user can also confidently transfer from the chair without fear of the chair moving.
  • To help in hospital settings or multi-user environments, where attention to IPC is critical, specialist covers are available; Velcro is replaced in all exposed areas with plastic profile fittings, and exposed seams are minimised.


  1. Collins F (2001) An adequate service? Specialist seating provision in the UK Journal of Wound Care 10(8):333–7