What is the '90' of the 90/60/20s of Office Injury Prevention (Ergonomics)?

Turns out that even though over 97% of the offices I visit are set up in a way that results in injuries over the long term, office ergonomic concepts are rather simple and easy to implement.

The things you need to know can be summarized in the numbers 90, 60 and 20.

The most complicated of the numbers is the '90' and it's only 'complicated' because there are a number of tips to keep in mind while trying to implement it. The 60 and 20 numbers will be covered in a later post.

90 is the number for posture. Aim for 90 degree angles for the knees, hips and elbows with everything else straight. For the record, a 90 degree angle is a bend at a joint that a cardboard box would fit snugly in. An example would be a 90 degree bend at the elbow with the elbows at the side of the body leaves a nice platform to put a cardboard box on the forearms, fitting snugly up against the upper arms too.

In terms of the office, this means that with the elbows at the side of the body, the elbows are resting lightly on the armrests and the bottom of the elbows are in line with the top of the desk and/or the keyboard.

For the knees this means that, with the feet flat on the floor or a foot rest, the thighs are resting evenly across the seat of the chair. We will talk about when to use the forward tilt mechanism of the chair and dynamic sitting in another blog.

The hip angle is just a bit more complicated as a 90 degree angle is just a little too tight for the chain of muscles starting at the lower leg and ending at your back. This tightness tilts the pelvis and makes your lower back round out. This position is related to most of the back pain people get when they sit too much as well as something called 'metabolic syndrome' (your hormones start changing in your body in a way that can't be reversed by exercise).

With this 90, the trick is to recline your seat back just a bit - 10 degrees will do - to take much of the pressure off of the lower back.

Some tips to make sure your chair is supporting your posture properly:

1. There should be 2 to 3 finger widths between the back of your knee and the seat edge to allow for movement of the legs without restricting blood flow.

2. Push your bottom all the way to the back of the seat. Slouching in the chair doesn't allow the lumbar support (lower back support) to do its job in combating the rounding of the lower back.

4. 'B' is for belly button. Line up the keyboard so that the letter 'B' is in front of the middle of your body and the center of the monitor. Having the keyboard too far to the left can cause wrist pain, particularly in the right wrist.

5. Don't reach for your mouse. Keep the mouse as close to the keyboard as possible or start mousing with your left hand. Reaching for the mouse can cause shoulder problems.

6. Eyes at the top of the monitor screen. The monitor height should be set so that the eye level is at the same height as the top of the monitor to avoid issues with neck strain (except when bifocals are involved - can be in another blog)

7. Arms supported lightly by the armrest. If the armrests are too high or too wide, they don't support the arms and tension in the neck and upper back can result. On the other hand, if the armrests are too high the result is called 'turtling' where the shoulders are raised up around the neck and it results in tension in the neck and upper back too. This is why much of the focus on a chair should be focused on the armrests to make sure they are properly supportive.

There you have it. Simple tips for good posture while sitting at the office and at home.

Let us know if there are any other topics you'd like to see covered in this blog.

Thanks!