Thought Bytes...
February/March 2005

Going to Extremes in Seating

I had a call recently from a client who needed advice about an unusual request for furniture. A worker in a control room, who had chronic back pain, was convinced that he should be using a "zero gravity" chair. When working in the control room currently, he raises his chair and tilts it all the way back. From this position, his feet are dangling and he has to twist his body to the side to access the controls.

The concept of the "zero gravity" position stems from photographs of astronauts asleep in space. In a zero gravity environment and in the relaxed position of sleep, the hips are flexed to approximately 75 degrees, the lower back loses it's lumbar curve, the shoulders elevate slightly, the arms reach forward, the hands pronate (thumbs rotate toward the midline of the body) and the head shifts forward. There is a very good description of what happens to the body in a zero G environment at http://mitglied.lycos.de/zero_g/bodyreactions.html. This web site states that this is considered "the most relaxed posture the human body can obtain" but makes a point that exposure to the zero gravity environment usually causes physical distress.

The problem is that the human body has evolved in a gravity environment.

When put into a weightless environment, there is no loading on the disks and they swell. This can cause significant back pain. This is why many people experience back pain if they spend too long in bed. In zero G there is also no loading on the bones and they become brittle. The muscles atrophy (become weaker) because they don't have to work against gravity.

For some people who have specific conditions where their spinal disks are compressed, temporary relief can sometimes be achieved by reducing the load on the disks. This is what traction does. To build strength to the back while reducing the load on the disks, exercising in water can partially create a weightless environment.

So, back to the "zero gravity chair". This is a piece of furniture that places the body in the "zero gravity" position. The entire posterior of the body, from feet to head, are supported. Once seated, the chair rocks back until the spine is almost parallel to the ground, and the feet are higher than the heart. While softer, this is no different than lying on the floor with your calves and feet on the couch or coffee table - a position often used by therapists to unload the disks.

In the home, it sounds like a comfortable recliner chair. But in the workplace, this piece of furniture presents some biomechanical as well as safety concerns.

In a control room where this chair was potentially destined, the reclined position would have to be placed parallel to the counter of the control panels due to the solid backing on the console. This would require the worker to reach to the side and twist the torso to access the keyboards, mouses and other tools used to control the processors. The worker would have to turn his head to the side to view the monitors. These unbalanced movements of the postural control muscles are known to contribute to muscle and joint pain.

If the chair were aligned perpendicular to the control panel so that the worker was facing the monitors, he would have to repeatedly lift and flex the neck to see the screens because the head and torso are lower than the feet. In order to respond to alarms or set the controls, he would have to pivot the chair forward and assume and upright and unsupported seated position. Abrupt movements from a fully relaxed position, plus sudden loading of the disks could create an injury situation. Because of the backing of the control panel leg space, the chair would have to be positioned back from the console, so the worker would likely have to stand to operate the controls and computers. Because the consoles are hard built, they are not able to adjust to a standing position. Then the worker would have to flex his back and lean forward to use the keyboard and mouse, a position known to contribute to back injuries.

One of the other safety issues relates to vigilance tasks. There is such a thing as being too comfortable. The human body and mind tend to assume that a reclined position is a resting position. A worker is far less likely to fall asleep on the job in a supported position in a proper chair - an important feature whether the worker is mixing fuel at a refinery or monitoring nuclear reactors.

Probably the first question that should be asked is "why does the worker think that he needs this chair anyway"? Has he been to a doctor/ physical therapist/ chiropractor/ massage therapist to seek treatment for his ailment? Does he participate in an exercise program to strengthen the back and torso to help his cope with his sedentary occupation (and likely sedentary lifestyle)?

I would rather see the employer spend the same amount of money on a treadmill so that the workers can do what the human body (in a gravity environment) was designed to do - walking.

Feedback

Sharon,
Sorry but I have to disagree with you final comment regarding the zero-gravity chair ... your article / comments were all excellent regarding the chair and whether it can / should be used in a control room setting ... but your final comment:

"I would rather see the employer spend the same amount of money on a treadmill so that the workers can do what the human body (in a gravity environment) was designed to do - walking."

misses what I think is a key issue with many control room work settings. The problem is that the work is organized so that people are expected / required to sit for 8 - 12 hours with little or no opportunity, or incentive, to get out of their chair. The workers are often not relieved for break ... i.e. they take 'breaks' at their work station - eating lunch and / or dinner and drinking their coffee in front of the monitors. Since they are not provided with relief workers to fill in for them they have to stay at their control panels to keep watch and respond to alarms. Not only does this result in boredom, monotony, and vigilance problems, especially when the system is 'working well', but the job is very sedentary and the worker spends long periods of time in a seated posture. In these instances most workers are likely to develop discomfort and pain, no matter now good the chair is, just because they are required maintain a seated posture for far too long (note: of course a good chair is very important ...)

The workplaces that have control room operators should be looking to change how the actual job is 'designed' so that the worker is not required to spend all shift doing the same task and sitting in front of the control panel. At the very least these workers should be provided with relief workers who take over the responsibility of the control room operator while he/she gets a coffee break and while he/she eats lunch / dinner. The control room worker, like all workers, need to get away from their task for brief periods during the shift to give their minds (and, hopefully, bodies) a rest. These workers should also be encouraged to take active breaks so they don't automatically go from sitting in front of the control panel to sitting in the coffee / lunch room.

But, it would be much more effective, if the workplace would redesign the job tasks so that the worker did a number of different tasks, during their shift ... tasks that would provide both physical and mental variety for the worker. Some workplaces try to do this by requiring the control room worker to conduct inspections of the equipment at regular intervals during the shift. Others look to actually rotate workers from 2-4 different tasks during the shift. Either way the key is to actually think about how the job is designed and then to redesign it so that the job is a healthier job, providing workers with a variety of physical and mental tasks during the shift.

This is the best way to overcome the problems of sitting / sedentary jobs. Your suggestion of paying for a treadmill is not likely to succeed ... past experience has shown that pieces of exercise equipment like this are rarely if ever used ... and if they are used they are used by workers who already take part in regular fitness activities and not those who 'really need it'.

Hope this isn't too harsh ...
J

(My colleague is absolutely right. By saying that humans were not designed to sit, I didn’t stress the point enough that we have to design variability into jobs. ST)

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