Frequently Asked Questions - Defense Centers for Public Health

Frequently asked questions

Are four-legged chairs considered to be ergonomically designed?

The number of legs on a chair is not an ergonomics issue but a safety issue. According to Department of Defense Design Criteria Standard Human Engineering, (Military Standard 1472-F paragraph 5.7.3.4.6 Seat base), "Chairs shall have at least four supporting legs. Swivel chairs should have five supporting legs". The greater the number of legs the more durable the chair and the less likely it will tip if body weight is shifted. Virtually all swivel chairs manufactured today meet the five-legged criteria and therefore should be provided to all employees who need one.

Are there any easy tips I can use to set up my computer workstation?

Setting up a computer workstation that is comfortable to work at is easy to accomplish. Here are some helpful hints. The more adjustable the workstation the better. Get a chair that is height adjustable, has an adjustable lumbar support, and has adjustable armrests. Get a desk that is adjustable. If this is not possible you can raise the desk height by placing blocks under the desk. The monitor should be placed in front of you so your neck does not twist, also the top of the monitor (not the top of the screen) should be positioned at eye level. The keyboard should be placed directly in front of the monitor and your bellybutton should be positioned in front of the "b" key on your keyboard. Your elbows should be bent 90 degrees and be close to your sides whenever you type or mouse, plus the arms, wrist, and hands should be in line with no twisting or bending. Lastly, your knees should be positioned about an inch higher than your hips and your feet should rest firmly on the ground. If you are a shorter person the use of a footrest may be needed.

Does using an exercise ball as a chair relieve back pain?

From an ergonomics perspective, stability balls are not an effective solution for reducing low back pain in the workplace because: • Active sitting increases the rate of fatigue due to constantly challenging your balance. In addition to fatigue, continuously maintaining your balance throughout the day may be an issue for some individuals and people with previous back injuries who have decreased postural control. • Balls do not have armrests or back supports, key features in supporting the body. • A reclined sitting position produces the least amount of disc pressure and muscle activity; this cannot be achieved with an exercise ball.

Q:	How much weight should a soldier carry in his backpack?
A:	The answer depends on the soldier's body weight and the activity being performed. Go to MIL STD 1472F Human Engineering paragraph 5.11.1.2.2 for more guidance.

I was told that it can be easier to lift 20 pounds of bricks than 20 pounds of feathers. I thought 20 pounds was 20 pounds.

You are right - 20 pounds is 20 pounds; they both weigh the same. However, weight alone does not influence how easy it is to lift something or the stress it puts on your back. Stress on the back is dictated by both the weight being lifted and the distance the weight's center of gravity is from the back. Since the feathers are bulkier than the bricks, their center of gravity is further away from the back. This is why 20 pounds of bricks is easier to lift than 20 pounds of feathers.

My wrists hurt when I type and mouse, will an alternately designed keyboard and mouse help?

It could, the deciding factor is what is causing the wrists to be in pain when you type. An alternatively designed keyboard or mouse will improve your wrist posture. If this is the primary risk factor causing you pain then the keyboard will reduce or eliminate the pain you are experiencing. However, there are other risk factors associated with typing. They are: repetition (strokes per minute), duration (how long do you type during the day), work rest scheduling (do you take small frequent breaks 1-5 minutes during the day), force used to strike the keys, and contact stress (are the wrists resting on a hard or sharp surface when typing or are you wearing tight fitting jewelry such as a watch or bracelet on the wrist?) A new keyboard or mouse may help but it is important to examine the other risk factors you are exposed to.