It used to be that only occupations like playing football or construction work carried risks for on-the-job injuries. But in today's computer-centric world, people who spend many hours of their days using computers are also at risk for physical strain, tissue damage and even disabling conditions like carpal tunnel syndrome.

People with neuromuscular diseases need to be especially aware, because traditional computer equipment and work stations aren't usually designed with mobility limitations or muscle weakness in mind.

That's the bad news. But here's the good news: Much discomfort and injury from cumulative stress on your muscles can be prevented or lessened by some simple steps.

Experts in ergonomics (the applied science of designing and using equipment to reduce fatigue and discomfort) say, whether you use a computer for work or fun, the setup of your work station and your work habits can greatly affect your long-term health.

First, take a look at your work station.

The goal is to be comfortable, and not overexert your muscle tissues, said Gary Karp, ergonomics consultant in the San Francisco area.

"Ergonomic strain comes from continuously held, low-level muscle contractions — continuous exertions that don't feel like effort, but at the end of the day, add up to strain," said Karp, who became paralyzed from a spinal cord injury in 1973. He uses a manual wheelchair and is the author of Life on Wheels.

The Keyboard Is Key

Keyboard positioning is one of the biggest issues for frequent computer users, Karp said.

Keyboards generally need to be down low, just above lap level, so the user can sit upright, supported in the upper body, letting the arms tilt downward and keeping elbows at a comfortable angle. If a keyboard is too high, then people tend to push forward and lean forward on their arms.

"You shouldn't have to be carrying your body or supporting yourself while using the computer," said Karp, who has experienced severe tendonitis from frequent computer use, a condition that he said has been more disabling than his spinal cord injury.

Monitor position is also important, said Dan Eisman, co-founder of HealthyComputing.com, a San Diego company that works to provide the latest information about office ergonomics and safety.

"For most people, this means having your eyes roughly level with the top of the monitor, or having them a bit higher if you wear bifocals," Eisman said.

Karp said that placing the screen just below eye level prevents users from having to continuously lift their chins, which puts a lot of strain on the neck and shoulders.

An adjustable, office-type chair that can change height and adjusts to support your lower back is ideal for good positioning. But such chairs usually aren't an option for wheelchair users, so the experts recommend improvising with monitor placement, and making the best use of the overall arrangement of your workspace.

Be Smart About Your Stuff

Most wheelchairs don't spin or twist like office chairs. Turning requires some special strategies so computer users don't end up overcompensating by twisting their trunks.

Correct keyboard placement and height-adjustable tables such as this one from AD-AS make the work environment more comfortable.

The "stuff" on our desks that we use most often — telephones, papers, staplers, binders or reference books — should be within a comfortable radius of reach that doesn't make you have to twist your body, Karp said.

Wheelchair features like arm handles and joysticks should also be considered when looking at your work station.

A power wheelchair joystick should be able to pivot or swing out of the way if it's preventing you from getting close enough to the keyboard, Karp said. The same goes for long armrests.

Also, make sure trash cans, recycle bins, purses or other items of clutter aren't blocking leg room under the desk.

Take a Break,and Use the Technology

Equal in importance to body position are your work habits.

Karp and Eisman advocate breaks and varying your body position and motions to help reduce strain.

"Use a strategy called 'micro breaks,' which means at least a couple of times an hour, at least for a couple of minutes, stop," Karp said. "Move away from the computer, stand up if you can, rest your eyes, stop looking at the screen, breathe, take a moment to become aware if you are holding your shoulders up, massage your forearms or do stretches. All these things are very powerful, proactive strategies."

Breaks can be especially important for those who use wheelchairs with armrests and legrests, Eisman said. They might be "less likely to recline, fidget or make subtle changes in position throughout the day — all motions that would help someone in a traditional office setting vary their posture to avoid injury."

Since eyestrain can also be a problem for frequent computer users, Eisman recommends following the 20/20/20 rule: Every 20 minutes, look 20 feet away for 20 seconds to rest your eyes.

Technology that's built into your computer can also reduce the unnecessary typing and clicking that most people tend to do, leading to strain. Learn your software and you'll probably find some built-in strain savers.

Take advantage of macros, keyboard equivalents, shortcuts and style sheets in word processors and other programs. These can save time and increase productivity, said Karp, who also favors word-prediction and word-expansion software.

"It's about balancing the load. If you do a certain thing a couple of different ways, then different muscle tissues are going to be doing that work. That helps avoid strain. But if you always use the mouse for everything, you are putting your arm and elbow at risk," Karp said.

For example, "You should never reach for the mouse just to hit the 'cancel' button on a dialogue box. Just hit the 'escape' key."

I Have to Buy What?

In order to achieve the best position, you may need an adjustable keyboard tray or, ideally, an ergonomically sound desk or cart with adjustable levels. Fully adjustable desks and carts, costing $300 and up, can provide an optimal ergonomic environment. Printer carts, adjustable tables and other accessories cost less and can often enhance the safety of your workspace.

Ergonomic accessories are part of what Eisman calls a "burgeoning" market of items for safer computing. Such examples as articulating keyboards, document holders, footrests, trackball mice, glare screens and telephone headsets are less expensive alternatives that may work wonders in personal comfort.

While the cost of one more piece of furniture may be unappealing or even prohibitive, the long-term costs make having a healthy work station a worthwhile investment, the experts said.

"The most important goal is to learn what these adjustments are designed to accomplish. If you know the ergonomic theories behind these adjustments, then you can decide which products you need, and on which you can improvise," Eisman said. "You might find great results by rolling up a towel to provide lower back support, or using a seat cushion to help raise your seat height."

If you can't alter your equipment, then you must compensate with work habits, Karp said. He also reminds people not to panic if they feel symptoms of cumulative strain.

"It doesn't mean they've damaged themselves. But it means they've got an early warning system that's telling them that they are exceeding their limits," Karp said.

Awareness of ergonomics and a healthy work station is "a different way of thinking about the body," Karp said. "It's about not taking those small discomforts for granted and about thinking instead, 'Oh I'm feeling this thing, there's something that's causing that, and there's something I can do about it.' Not waiting for something to hurt enough that now you think it's a problem. That can be too late."

Some Ergonomically Sound Holiday Gifts

Adjustable computer tables — AD-AS offers a line of accessible computer work stations with height adjustment. Tables in the Equity series adjust with an easy-to-turn hand crank. Models include the Equity 4830, a single-surface table for $766. Accella 6030 is a sit-to-stand adjustable work station for $989. www.ad-as.com or (800) 208-2020.

LapGenie — This ergonomic aid for laptop users weighs less than 2 pounds and is adjustable for height and angle. It also folds for transport. $129. www.lapgenie.com or (877) 388-0072.

MouseMattress — This extra-thick pad rests on the computer user's thigh, allowing for less stretching and neck pain. It's available in a variety of colors with lycra surface for $18.99 or suede for $24.99. www.mousemattress.com or (858) 459-4755.

Magic Arm and Device Tray — Customize the position of your computer and accessories. The Magic Arm ($199) base clamp attaches securely to wheelchair tubing, table or just about anything, and one dial tightens all three joints. The arm pairs well with the Device Tray ($99), which is ideal for holding keyboards. www.rjcooper.com or (800) RJCooper (752-6673).