Sitting is an activity that we tend to spend arduous amounts of time doing. Unfortunately, many people are unaware that sitting effects performance, posture, physiological health, metabolic health, work productivity and cognitive acuity. |
Sitting, as previously discussed in the past two newsletters, can have dire effects on one’s postural alignment through the simple law of “SAID” (selective adaptation to imposed demands). How you choose to use your body, will ultimately effect and affect your postural alignment. Our postural alignment is crucial to a well performing body.
The key principals in position to sitting ergonomics
Joint comfort zone
“The position of a joint where it works at optimum efficiency with minimum amount of strain”.
The middle one-third of a joints full range of motion is optimal for joint comfort.
Muscles attached to joints by tendons and the extracellular matrix (fasciae). If we place a joint in a position to which the soft tissue surrounding that joint is in an optimal position with minimal force production, then we impose less strain and will encourage the development of less postural related issues.
As discussed in the previous newsletter, it’s important not to place a muscle in a position which it is required to produce more than 4% total force production in a prolonged seated position. If you do, you run the risk of fatiguing these muscles, which if prolonged, could result in poor musculoskeletal balance, pain, discomfort and degenerative postural changes.
A good sitting posture is dependent on the following principals
The task The arrangement of equipment to perform a task Individual preference The seat Postion variability
A person’s task-at-hand will dictate the length and type of sitting required for optimal posture.
If you’re writing and reading, then you should require a desk that’s slightly higher than normal with an increase backward angle. This allows far better positioning of your upper back, neck, shoulder and visional angle.
It is your chair that dictates your pelvis and lumbar spine position and it is your desk that dictates your upper back, neck, head and visual positions.
Individual preference should come into account largely as a subsidiary position in respect to the ergonomic requirements for you bodies optimal postural health. You should first prioritise and organise your sitting posture based on the suggested principals, then preference second, how you would LIKE to sit within the suggested confines offered in this article.
What are our optimal joints angles when sitting?
Lower back (lumbar spine) and pelvis
A good lumbar spine and pelvic position, depend on where your hips and thighs are positioned. This angle is best kept between 110 – 130 degrees or 50 – 70 degrees – optimal in my personal experience being 120 or 60 degrees. If you have a forward tilting seat, then the top of your knee should align to the lowest part of the chair to meet this basic variable requirement
Head and neck
It’s important to ensure an erect upper back position that allows optimal balance between your deep cervical flexors and supraomohyoidmuscles.
These opposing muscle groups help keep your head and neck in a healthy aligned position. For every inch your head protrudes forward from your midline, you increase the stress on your upper cervical spine. It’s important that you keep from poking your chin forward as if trying to look at a screen with small writing on it, or rounding your shoulders forward to rest in a position of poor posture. Getting the correct hight of your desk and having the appropriate visual angle is very important.
Visual angle & eyesight distance
The optimal visual level should be at 10 – 20 degrees BELOW horizontal. This means if you were to look straight ahead with a correctly positioned spine and head, your field of vision will be slightly lower. The range of vision for optimal head and neck alignment is 15 degrees above or 15 degrees below – that is 15 degrees below the necessary 15 degrees below horizontal. You should place your work situated 30-60 cm away from your face. It’s important to have all your work as close to your midline field of vision as possible. Rotating the neck and torso constantly is not advisable in a sitting posture.
Your elbows must be supported by the desk at a 90 – 100 degree angle. Your elbows should remain close to your torso and not winged out. Your elbow joint should remain close to your midline, opposed to stretched out towards the desk.
You should keep your wrists supported in a neutral or slightly backward tilted position of up to 20 degrees, but no more. No Lateral deviation (side bending) is advisable. A good keyboard support mechanism can be beneficial. The height of your desk, relative to your chair is key in finding the correct elbow / wrist position.
Your knees should remain at a 60 – 120 degrees bend. Your knees should be supported with a good resting pad if you choose to adopt a kneeler chair. You should not straighten your legs out completely for prolonged periods of time. If you do, you may cause your lumbar spine to passively pull into a rounded posture, placing large amounts of stress on your intervertebral discs.
Your feet should be either flat on the floor or supported on a foot rest using a decline angle. Your feet should be able to firmly touch the ground. This will ensure you place bodyweight through your feet and prevent pressure points from accumulating as a result of resting your bodyweight on your butt or hamstrings.
The table should be height adjustable. The height of the desk depends upon three elements.
Your type of work (reading/writing or computer work) The height necessary to support a good postured based on joint angles The necessary visual angle being met
Anything that you must look at while working in a sitting posture, should not be below 30 degrees from a horizontal eye level. Your eyes optimal viewing angle is 10 – 15 degrees below horizontal. The eyes can cater for 15 degrees either side of this angle.
When you’re reading and writing like a student would studying, it’s important to have a slightly higher desk, with a downward slope of 10 – 40 degrees, the higher degree being suited more so for reading and the lower degree suited for writing tasks.
When you’re using a computer, it’s important to have the monitor set up at 10 – 15 degrees below horizontal. If you’re reading while using a computer, it’s suggested that you use a reading stand, placed close to your midline field of vision.
Without the correct seat, or the intelligent modification of your current seat, it can almost feel impossible to sit correctly, especially for prolonged periods of time.
The common sitting set up, that has people sitting with their ankle joint, knee joint and hip joint all situated at 90 degrees range of motion, isn’tnecessarily the correct posture based on the joint comfort zone principal. While this widely adopted, 90 degree angle position works in theory, practically, research has demonstrated that people generally generate 60 degrees range of motion from the hip joint and the remaining further 30 degrees from the lumbar spine, which can causes the lumbar spine (lower back) to round out, increasing the intervertebral disc pressure at your lower lumbar vertebra, primarily at levels L4, L5, S1 – the most commonly injured junctions.
Overtime, poor sitting posture can facilitate the weakening of a persons gluteal muscles, the tightening of a persons hamstrings, the tightening of a persons upper abdominal musculature, rounded shoulders, weak middle back extensors, forward head posture and poor breathing mechanics – all in all, resembling nothing less than a mechanical / biological mess.
Getting the seat set up right is pivotal for postural, physiological, metabolic and cognitive health. a good seat isn’t only important for longevity, overall health and performance – but it’s also important for good mental acuity and work performance. Tell that to your boss when requesting better seats and desks!
Different sitting positions and chair set up’s
The forward tilt chair
Largely developed by DR.A.C. Mandal. This posture requires a person to sit up with an erect spine. Your seat should maintain your thighs at 110-130’ (thigh to torso) or 50-70’ degrees from the lower limb. This requires the knees to be below hip level. Thisay mean a change in your seat hight and desk height. The chair should have a slight 5-10’ degree forward tilt of the bottom seat. This allows for the pelvis and lumbar spine to remain in an anatomically optimal position based on pelvic tilt and lumbar positioning.
If you can’t afford a new chair, at least look at other alternatives;
Angulated memory foam, made as a seat wedge. A towel rolled up behind your lumbar spine and a second one creating a slight forward tilt.
The kneeler chair’s widespread popularity has manifest itself from the need for better sitting posture and the call for pain free sitting by people with back injures. The kneeler chair posture is fantastic for allowing the pelvis, lumbar spine (lower spine) and shoulders to maintain optimal positions – with little muscular stress. The kneeler chair also assists in facilitating better breathing patterns by allowing a person to keep their chest proud.
The kneeler chair is a great option, however it does have a few minor set backs. For instances, generally for most people the ankles and knees are not in an optimal joint comfort position. Additionally, the forward tilt on the kneeler chair can also range anywhere from 10-30 degrees (too much). Keeping this in mind, a kneeler chair is still a fantastic sitting option. It’s important to purchase a kneeler chair that allows you to stabilise easily, without having to constantly prevent yourself from sliding forward.This may require the appropriate materiel on the seat and knee pads, which will have you stick to the seat better.
Swiss ball Using a Swiss ball, large enough to cater for the necessary angles of your hips, is a fantastic idea for those who are willing. I often recommend that people have a Swiss ball in their office, if not to sit on all day, at least to make use of for some of the day. A Swiss ball will have a person stabilise through activating their “titling responses”, the same mechanism needed to stabilise on a skate board or bicycle. The one consideration for using a Swiss ball, is ensuring you maintain the normal lordotic curve in your lower back andn upright upper back and neck positioning. This requires a little more meticulous effort of organising your desk height.
The lazy boy recliner chair & CEO seat
It’s important to realise sitting for relaxation requires a different posture than working. Sitting for relaxation generally has someone in a reclined position. Recliner chairs have a backward tilted seat, apposed to a forward tilt chair that caters for the person leaning forward This form of sitting is optimal for relaxing the hip joint. The more reclined, the better.
Most executives have large office chairs with reclining or backward tilting seats. If this executive is required to lean forward as they often are, then this type of chair is not suitable due to the backward tilt. If the seat reclines backwards and the person leans forward, this forward lean will round out the lower lumbar spine, increasing the pressure on the lower lumbar discs. I do not recommend this position, unless you’re going to make use of the reclined back rest, without leaning forward.
Paradoxically and oxymoronically there is actually no such thing as a perfect sitting posture. It’s important to understand the human body is designed to move for a multitude of reasons. Some such reasons include; Our intervertebral disc depend on movement for their nourishment, the circulatory pumping system is benefitted by movement, our digestion (peristalsis) relies on it and our health in general requires it.
When we sit for prolonged periods of time, we risk our postural stabilising muscles or phasic muscles becoming fatigued. This fatigue can result in all the associate problems we’ve already covered from a postural point of view. Even when a perfect posture is found, it’s still wise to change positions intermittently.
Changing positions can merely mean a change in seat (Swiss Ball to a forward tilt chair) or it can be as simple as getting up from your seat, moving around and even doing a little light stretching.
I suggest that a person goes no longer than 40-50 minutes sitting without moving, changing seated positions or stretching.
As a person who’s experienced severe spinal related injuries, I can tell you that moving often and changing my sitting posture, is utterly important for productive, pain free work (such as writing this article).
Additionally, it’s important to realise that our intervertebral discs rely on a different system from that of our circulatory pumping system for their nourishment. Hydration and movement is the key to nourishing and maintaining a healthy spine. A healthy spine is a healthy life – trust me!
For any more information on sitting ergonomics, please don’t hesitate to get in contact with me personally at JP@Jpsfitnesstoofittoquit.com
Love & Peace,
Holistic lifestyle coach Level 3 expert trainer C.H.E.K Exercise coach
For more natural health tips visit our blog at: http://www.alkalife.com.au/blog
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