The Science of Active Sitting: Why Your Next Posture Is Your Best Posture

Active sitting is an ergonomic approach that encourages continuous, low-level movement while seated, countering the effects of prolonged static sitting. By introducing gentle instability or allowing multi-directional movement, active sitting chairs keep muscles working at a low level, make posture changes easy, and let the pelvis move rather than locking it in place. Controlled studies have measured both effects: sitting on compliant surfaces raised energy expenditure by around 10% compared with a flat, firm chair [1], and active sitting on a dynamic office chair was found to be controlled by a distinctive pattern of lumbar trunk muscle activity [2]. This article sets out what that research actually found — including where it does not say what chair marketing often claims — and why the HÅG Capisco is the best-known chair built on the idea.

The scale of the problem is not in dispute. Up to 72% of the population in the western world works predominantly in a seated position [2], and standard office chairs are designed to support the body in a single position rather than to help it change. This article reviews the clinical evidence on static and dynamic sitting, and is the technical companion to our plain-English introduction, what is active sitting.

What static sitting does

For decades ergonomic design chased a single "correct" sitting posture, typically 90 degrees at the hips, knees and elbows. The research has moved on: holding any one posture for long periods is the problem, however well chosen the posture is.

The reverse sitting position on the HÅG Capisco, with the backrest used as a chest support — one of the positions the chair is designed to make easy.

Three measurable things happen when sitting is static.

• The lumbar curve flattens. A radiographic study of 30 healthy volunteers measured a mean lumbar lordosis of 47.1° standing, falling to 17.7° in a 90°-angled chair, 0.6° on a stool and −7.4° sitting cross-legged — that last figure being an actual reversal of the curve [3]. Flattening the lumbar spine shifts load onto the discs and the posterior ligaments.
• Trunk muscles switch off for long stretches. Lumbar trunk muscles have been found to be inactive for around 30% of sitting time [2]. Static sitting asks for continuous low-level isometric work and then, in practice, does not get it.
• Sedentary time carries measurable cardiovascular risk. An accelerometer-based study of sedentary behaviour published in the Journal of the American College of Cardiology in 2024 identified a threshold of about 10.6 hours of sedentary time per day, beyond which the risk of heart failure and cardiovascular mortality rose — including among people who met exercise guidelines [4]. Exercise does not fully offset a sedentary day.

The response to that is not only to stand more. It is to sit differently.

The biomechanics of active sitting

Active sitting, or dynamic seating, keeps the body in continuous small motion. Rather than fixing the pelvis and spine, an active chair lets the body tilt, sway and shift its centre of mass. Two studies are worth reading closely, partly because what they found is more specific than the marketing built on top of them.

1. Energy expenditure: about 10%, and it comes from the legs

A study in the Journal of Sport and Health Science compared sitting on compliant surfaces with sitting on a flat, firm chair, measuring indirect calorimetry and surface EMG [1]. Sitting on a stability ball raised energy expenditure by 10.4% and an air-filled cushion by 9.6% over the flat firm surface, with no significant difference between the two compliant surfaces.

The important detail is where that came from. The increase was associated with greater activation in the lower extremity muscles — tibialis anterior, soleus and adductor longus. No trunk muscle differences were found between the surfaces. If you have read that unstable seating gives you a core workout, this study does not say so. What it does say is that a compliant seat keeps the legs working, and that is where the extra energy goes.

2. Trunk control: a dynamic chair is a different thing from a wobbly surface

A 2020 study in PLOS ONE asked whether active sitting on a purpose-designed dynamic office chair is controlled by the trunk muscles [2]. It found that it is: active sitting was governed by a characteristic pattern of cyclic loading and unloading of the iliocostalis and multifidus, and to a lesser degree the longissimus, while neither thigh muscle activity nor lateral weight shift changed much. The authors suggested this could have a positive effect on back health over long periods of sitting, while noting the need for studies in real offices.

Read together, the two studies say something more useful than either alone. A compliant surface and a dynamic chair are not the same intervention. A ball or cushion works the legs; a properly designed dynamic chair engages the lumbar trunk musculature in a cyclic pattern. That is the argument for buying a chair rather than a ball.

3. Movement and the discs

Intervertebral discs have no direct blood supply in adulthood. They depend on fluid exchange driven by movement and changes in load to take up nutrients and clear waste — which is why sustained static loading is unhelpful to them, and why varied posture is not merely a comfort question. Active sitting has been shown to increase trunk motion during seated work [5]; the physiological benefit of that motion for disc nutrition is well established in the spine literature rather than demonstrated by any one seating study.

Lumbar lordosis by sitting position

The radiographic study cited above measured lumbar lordosis across standing and five sitting positions in 30 healthy volunteers [3]. These are its figures, unedited:

One honest caveat, because it matters. That study did not test a saddle chair, and we are not going to pretend it did. What it establishes is the size of the problem — a conventional 90° chair leaves you with roughly a third of your standing lumbar curve, and unsupported sitting leaves you with none of it — and that a back support which actually reaches the lumbar spine is worth having. The case for saddle sitting rests on the open trunk–thigh angle and on the ease of changing position, not on this study.

The HÅG Capisco: the chair built on the idea

Most active sitting solutions are accessories — balance cushions, exercise balls — which is exactly the intervention the first study measured, and they come with no back support and no height adjustment. The HÅG Capisco, designed in 1984 by the Norwegian industrial designer Peter Opsvik, was drawn from the other direction.

The saddle seat opens the trunk–thigh angle and lets the pelvis tip forward rather than roll back.

Opsvik’s design principle was one sentence:

The best sitting position is, after a while, always the next one.
— Peter Opsvik (1939–2024) [6]

Rather than designing a chair that holds the body in one correct position, Opsvik designed the Capisco to offer as many sitting positions as possible and to make moving between them effortless. He died on 30 September 2024, aged 85; we wrote about his work in remembering Peter Opsvik.

What the Capisco actually does

• The saddle seat. The saddle shape lets the thighs angle downwards, opening the trunk–thigh angle well beyond the 90 degrees of a conventional chair. The pelvis tips forward and the lumbar curve follows from the geometry rather than from a pad pressing on the lower back.
• The cut-out backrest. The backrest’s shape leaves room for your arms and torso, so you can sit sideways, sit backwards using the backrest as a chest support, or recline — each of them a supported position rather than a compromise.
• HÅG in Balance. A balanced tilt mechanism that follows your centre of gravity, so a shift of weight is enough to tilt forward or recline without unlocking anything.
• Gas lift range. Three cylinders cover very different heights. On the Capisco 8106, Flokk publishes seat heights of 400–540 mm (150 mm lift), 460–640 mm (200 mm lift) and 550–810 mm (265 mm lift), which is what lets one chair work at a conventional desk, a sit-stand desk or a raised bench. Full figures for every model are on our Capisco measurements page.

The Capisco 8106 is certified to EN 1335 (2020) Type A and Ax, ANSI/BIFMA, EN 16139 and GS. Flokk publishes no maximum user weight for it — the 110 kg figure often quoted is a condition of the ten-year warranty, not a load rating, and we do not publish it as one.

Who benefits most

• People with height-adjustable desks. The Capisco covers the middle of the sit-stand range, letting you perch at an intermediate height instead of choosing between sitting and standing.
• People who move between tasks. Sketching, collaborating, turning to a bench — the open frame makes getting on and off the chair, and sitting backwards to lean into the work, easy.
• People who stiffen up in one position. The argument here is variation rather than treatment. If you have a diagnosed back condition, ask your physiotherapist or doctor what seating they recommend before you buy — we can tell you what a chair does, not what will treat a condition.
• Students and older children at a home desk. The Capisco Puls suits a study desk well, with one practical check first: its published seat height starts at 390–400 mm depending on model and lift, so measure the child before assuming it will go low enough.

Setting up an active workstation

1. Pair it with a sit-stand desk. Check the desk raises high enough for a perch. Alternating between sitting, perching and standing across the day is the point; the exact interval matters less than actually changing.
2. Add a footring or StepUp if you sit high. At perching height your feet may not reach the floor. The HÅG Footring fits 200 mm and 265 mm lifts only and is colour-matched to the lift, so specify the two together; HÅG StepUp gives two foot levels instead of one.
3. Put the screen on an arm. Your eye height changes as you change position, so the screen has to follow. The CBS Flo Single or CBS Flo Dual will do it.

Frequently asked questions

Does active sitting feel tiring at first?

Mild muscle awareness in the first few days is common and normal. An active chair leaves muscles doing work that a conventional chair does for you, so build up gradually — an hour or two a day at first, increasing as it stops registering.

Can I use the HÅG Capisco for a full 8-hour workday?

Yes. It is a commercial-grade ergonomic chair with a height-adjustable backrest and a balanced tilt mechanism, not a perch. The way to be comfortable across a long day is to use the range of positions it offers rather than settling into one. Note the warranty condition for long days: Flokk's ten-year HÅG term applies to normal use of up to 9 hours per day, stepping down to 5 years beyond that.

Is a saddle chair suitable for people of all heights?

Largely, because the gas lift is the variable rather than the frame. On a Capisco 8106 the 150 mm lift gives 400–540 mm, the standard 200 mm lift gives 460–640 mm and the 265 mm lift gives 550–810 mm. Choose by your lower leg length and your desk height rather than by your overall height, and remember the lifts shift the range rather than extend it — the tall lift does not come down to where the standard one starts.

How does active sitting compare with using an exercise ball?

A ball does produce a measurable effect — the 10.4% increase in energy expenditure quoted above was measured on a stability ball [1] — but that effect came from the lower limbs, and the same study found no trunk muscle difference. A ball also has no backrest, no height adjustment and no castors. The dynamic-chair study [2] found trunk muscle control that the compliant-surface study did not, which is the substantive reason to prefer a chair.

Does the HÅG Capisco have a maximum user weight?

Flokk publishes none. The 110 kg figure in circulation is a condition of the ten-year warranty rather than a tested load rating, and we will not restate it as a capacity. If it is the deciding factor for you, call us and we will put the question to Flokk.

Try it

Active sitting is not a trend so much as a response to a measurable problem: most desk work is seated, most seated work is static, and static is what the evidence keeps pointing at.

Explore the HÅG Capisco and Capisco Puls saddle chairs or the full HÅG range. Chair Dinkum is the exclusive Australian distributor for the Flokk group, of which HÅG is one of eleven brands, and stock is held in Sydney. To sit in one before deciding, contact us and book a showroom visit in Pyrmont.

References

1. Dickin, D. C., Surowiec, R. K., & Wang, H. (2017). Energy expenditure and muscular activation patterns through active sitting on compliant surfaces. Journal of Sport and Health Science, 6(2), 207–212. https://pubmed.ncbi.nlm.nih.gov/30356581/
2. Kuster, R. P., Bauer, C. M., & Baumgartner, D. (2020). Is active sitting on a dynamic office chair controlled by the trunk muscles? PLOS ONE, 15(11), e0242854. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0242854
3. Cho, I. Y., Park, S. Y., Park, J. H., Kim, T. K., Jung, T. W., & Lee, H. M. (2015). The effect of standing and different sitting positions on lumbar lordosis: radiographic study of 30 healthy volunteers. Asian Spine Journal, 9(5), 762–769. https://www.asianspinejournal.org/journal/view.php?doi=10.4184/asj.2015.9.5.762
4. Khurshid, S., et al. (2024). Accelerometer-measured sedentary behavior and risk of future cardiovascular disease. Journal of the American College of Cardiology. https://pubmed.ncbi.nlm.nih.gov/39545903/
5. Wang, H., Weiss, K. J., Haggerty, M. C., & Heath, J. E. (2014). The effect of active sitting on trunk motion. Journal of Sport and Health Science, 3(4), 333–337. https://www.sciencedirect.com/science/article/pii/S2095254614000076
6. Flokk. Peter Opsvik (1939–2024) in memory. https://focus.flokk.com/peter-opsvik-1939-2024-in-memory