9 - Smart sitting and standing postures at the workplace

Upright sitting

Sitting upright refers to a posture in which the upper body is aligned in a vertical, straight line while the spine retains its natural S-shape. However, when sitting, the natural inward curvature of the five lumbar vertebrae (lordosis) must be actively induced by tensing (contracting) the hip and back muscles. This is due to the automatic tilting back of the pelvis when assuming a seated position (Eklund and Liew 1991; Harrison et al., 1999 ).

In order for the pelvis to remain in the tilted forward position when sitting upright, the muscles must be permanently tensed (static muscle work). According to a study by Björkstén and Jonsson (1977), however, this tension should not be too strong. If the muscles work for longer than an hour, the load should be no more than 5-6% of the maximum possible force. If the muscles tire and the lower back becomes rounded, the body relies more heavily on passive support tissue such as ligaments and intervertebral discs (Beach, Mooney & Callaghan, 2003).

If the upper back is also bent forward, this is known as a kyphotic posture (hunched posture). This posture is one of the most harmful and is often associated with lower back pain (Makhsous et al., 2003).

When adopting an upright sitting position, it is important to ensure that the pelvis is not tilted too far forward in order to avoid the formation of a hollow back (hyperlordosis). Ergonomic office chairs with lumbar support can help to maintain a natural posture (Makhsous et al., 2003).

Studies have shown that lumbar lordosis decreases by approximately 15 to 21 degrees during the transition from standing to sitting if it is not actively restored by sitting upright. This decrease is associated with increased intradiscal pressure, which can contribute to low back pain (Hey et al., 2017; Lord et al., 1997).

While the pressure on the intervertebral discs increases by 40% when sitting compared to standing (Wilke et al., 2001), the additional load is already 90% when the upper body is bent forward by 10°.

Regularly sitting upright for long periods with the pelvis tilted forward can reduce this increased strain, but can also lead to chronic pressure on the intervertebral discs. A lack of variation in pressure distribution due to a lack of movement reduces the microcirculation in the intervertebral discs, which is responsible for supplying them with nutrients. This in turn impedes the regeneration of the intervertebral discs (Schäfer et al., 2015).

In addition to the negative effects on the intervertebral discs, sitting upright for long periods also leads to a shortening of the hip flexor muscles and thus to muscular imbalances (Merritt & Merritt, 2017). Insufficient stretching of the hip flexor muscles is not only painful, but can also restrict the body's functionality in everyday life (Schmidt et al., 2014).

However, from a biomechanical perspective, sitting upright has the greatest potential for postural variation, which is crucial for a healthy spine (Alexander et al., 2007; Vergara & Page, 2002). The hip and knee joints are in the middle range of their mobility, which means that they can be flexed and extended without affecting the upper body (Harrison et al., 1999). This not only promotes blood circulation, but also a variety of movement options that help to prevent muscular imbalances.

When sitting, the body also carries less weight on the legs than when standing. The feet only take up around 25% of the body weight, so the ankles can be easily extended or contracted while the upper body remains stable (Harrison et al., 1999). The more stable body status in sitting leads to lower energy expenditure and enables improved attention for mental activities, as less energy has to be used to maintain posture.

However, the low metabolic rate and blood circulation are also negative aspects of sitting upright. Dynamic sitting concepts in particular aim to increase the metabolic rate and blood circulation. Several concepts have already been explored that maintain the 90-degree sitting position but incorporate multidirectional instability of the chair base to duplicate the experience of sitting on a stability ball (Barrett 2019; Ellegast et al., 2012; Grooten et al., 2013, 2017). Laboratory and field trials with these chairs show that the movement generated is not sufficient to influence posture, muscle activation or metabolic rate (Barrett 2019; Ellegast et al., 2012; Grooten et al., 2013, 2017).

The danger of prolonged sitting is therefore not sitting upright per se, but the adoption of prolonged postures in which the metabolic rate and blood circulation are low and the vertebral joints and intervertebral discs are exposed to increased or prolonged stress. Prolonged sitting is therefore defined as remaining in a static sitting position for more than 30 minutes without interruption and involves adopting poor postures (Strand, 2000; Triglav et al., 2019).

Thus, only regular changes in posture can help to promote back health and prevent complaints. The key also lies in finding the right balance between stability and movement, which can be achieved through small but regular changes in posture when sitting or standing.

Standing

To reduce sedentary inactivity, standing is promoted in many office environments as a healthier alternative to sitting (Commissaris et al., 2016). It leads to increased oxygen uptake and lower blood glucose levels compared to sitting (Reiff et al., 2012; Healy et al., 2017). In addition, standing is associated with the least strain on the spine, as it promotes natural lumbar lordosis and the force exerted is transferred to the leg muscles (Wallden 2009). Studies show that standing can lead to better posture (Halim & Rahman Omar, 2012; Reiff et al., 2012). However, prolonged standing for more than one hour is not recommended, as standing can lead to muscle fatigue and associated discomfort and pain in the back, legs and feet (Halim & Rahman Omar, 2012; Leroux et al., 2005). Prolonged standing (>50% of working time) even increases the risk of back pain, heart disease and circulatory disorders (Tomei et al., 1999; Callaghan & McGill, 2001; Messing et al., 2015).

Only standing for short periods during the working day reduces the risk of back pain (Robertson et al., 2013). If you want to stand for up to an hour, you should be active while standing and, for example, rotate your hips while standing or actively shift your weight between your legs.

In particular, alternating between standing and sitting at a ratio of 1:3, e.g. 5 minutes standing after 15 minutes sitting (Bridger, 2019), should alleviate back pain by increasing lumbar flexion and muscle activity (Fewster et al., 2019). However, a 1:1 ratio of sitting to standing without prolonged static phases is also recommended (Callaghan et al., 2015).

Half-sitting

Inclined sitting, also known as “half-sitting”, is a sitting position characterized by a slightly forward leaning seat surface. This posture is often used in combination with unstable surfaces to promote dynamism and support a dynamic sitting posture (Faulk et al., 2019). The chair is designed so that the seat is tilted forward by around 15°, which opens up the trunk-thigh angle. This can not only counteract a shortening of the hip flexor muscles, but should also actively support lumbar lordosis. This position also reduces the activity of the paraspinal muscles compared to sitting upright. This means that the back is relieved as there is less tension on the back muscles (O'Sullivan et al., 2012). Studies show that people who previously suffered from back pain experience less discomfort in this position (O'Keeffe et al., 2013).

In addition, light contractile activity in the lower limbs with a high frequency and duration (micromovements ), as recommended in dynamic sitting, can slightly increase energy expenditure due to the change in angle, which contributes to better blood circulation and keeps the body more active (Synnott et al., 2017). However, the “micro-movements” in inclined sitting are not sufficient to achieve significant cardiovascular effects, such as those observed in active sitting concepts with regular standing (Synnott et al., 2017). In addition, studies show that activation of the trunk muscles is not significantly increased in this position, which means that the benefit for back health in this respect remains limited (Noguchi et al., 2019).

However, this posture can also lead to increased knee and ankle extensor activity, which in some cases can put more strain on the muscles and lead to swelling in the legs (Antle et al., 2015). This increased muscle strain can therefore also have a negative impact on comfort. In some cases, reclined sitting can even lead to uncomfortable or harmful strain due to shear forces on the seat surface (Rasmussen et al., 2009).

Another disadvantage of this posture is that it can quickly lead to a static position, especially if there is no backrest to provide additional support. Such a position can lead to a 'slouched posture' in which the trunk muscles are less active and therefore the benefits of maintaining lumbar lordosis and reducing back strain are quickly lost (Grooten et al., 2013).

Reclined sitting

Reclined sitting is a variation of upright sitting in which the backrest of the chair is tilted backwards. Ideally, the angle of inclination of the backrest should be between 110° and 120° in order to achieve the greatest possible benefit.

Studies show that an inclination of around 20° from the vertical (i.e. 110°) reduces the intervertebral disc pressure the most and returns the lumbar lordosis almost to its natural curvature (Andersson, 1987; Link et al., 1990). A backrest angle of 120° is also considered advantageous, as it also reduces muscle activity (Harrison et al., 1999).

Leaning back helps to avoid the kyphotic posture caused by prolonged sitting, reduce pressure on the intervertebral discs, promote blood flow to the intervertebral discs and reduce muscle activity in the supporting muscles of the pelvis and lumbar spine (Nazari et al., 2012; Holm & Nachemson, 1983).

It has also been shown that this tilt angle is particularly beneficial for activities such as reading and arithmetic (Groenesteijn et al., 2009; Gscheidle & Reed, 2004b).

However, there are also disadvantages to this position. The head can tilt forward, particularly during longer periods of work in a reclined position, which leads to increased strain on the cervical and thoracic spine (Corlett, 2006; Horton et al., 2010). Leaning back can also affect working comfort, as the head, shoulders and arms are moved away from the desk, making it more difficult to work at the computer.

Another problem is that leaning back can be seen as a passive change of position that does not stimulate the activity of the trunk and leg muscles. In this position, energy expenditure is not significantly increased, which makes it less beneficial when it comes to actively stimulating the muscles (Bridger, 2019; Mansoubi et al., 2015).

Ideally, leaning back should be done in a way that ensures that the upper body, arms and head remain in ergonomic alignment with the desk and screen to ensure efficient and pain-free working.

What is the maximum time you should hold static postures?

As static postures cannot be prevented in the workplace, it is important to understand which postures are suitable for prolonged exposure. Assessing the degree of static loading, or the forces exerted that lead to fatigue and subsequent tissue damage, depends on the amount of time a person is exposed to the load. Grandjean (1988) divides static load into three categories:

- At a high force, static muscle actions should last less than 10 s.
- With a medium force, less than 1 min.
- less than 4 min. for a low force.

Since the force acting on the tissue depends on the posture and individual muscular fitness, this classification can initially only be applied to the relative change in spinal load due to the posture. For example, a reclined posture can be assumed for longer than an upright or bent forward posture.

Summary

In summary, it can be seen that a healthy sitting and standing posture at the workplace cannot be achieved through a single optimal position, but through regular changes in posture and dynamic movements. Sitting upright allows for the greatest postural variation, but without movement it can lead to muscular imbalances and strain on the intervertebral discs. A semi-sitting posture supports lumbar lordosis and prevents hip flexion shortening, but can lead to increased muscle strain and loss of comfort with prolonged use. Leaning back reduces the pressure on the intervertebral discs and relieves pressure on the back muscles, but makes it more difficult to concentrate at a desk for long periods of time. Standing as an alternative to sitting improves blood circulation and reduces metabolic risks, but should not be done for long periods without movement.

Overall, the best strategy is to combine sitting and standing times in a balanced ratio, ideally alternating 1:3 or 1:1, integrating short periods of activity such as weight shifting or micro-movements into the working day to promote blood circulation and avoid muscular fatigue. Only a combination of stability and movement can ensure a healthy working posture in the long term and minimize the risk of back problems.

How can ergofox help?

To find out whether and for how long you are adopting the postures presented in this article during your working day, you can carry out a posture analysis at your workplace. Ergoscreening from ergofox offers you an ideal opportunity to analyze your sitting posture and improve it with online coaching.

In addition to good posture, you should also integrate active breaks into your daily work routine. The Ergogames from ergofox are ideal for this. Not only is playing a lot of fun, but it also promotes movement of the upper limbs, unlike traditional walking.

Take a look around our website and get in touch if you have any questions.

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Posture Analysis

Smart sitting and standing postures at the workplace