Stop! Freeze right there! Now, without moving a muscle, check out your posture. If you're like a lot of people at the computer, you are sitting sort of slumped over, leaning toward the computer with your shoulders rounded instead of sitting up straight.

Ergonomics refers to the study of the relationship between people and their surroundings. If you are slumping at the computer, you have poor ergonomics.

It might not seem like such a big deal, but think about how much time you spend sitting at the computer. And then you might go on to spend a little more time slouching in front of the TV playing video games. And then you get up to go to school the next morning and find yourself leaning forward to balance a very heavy backpack crammed with books.

Add all that up, and you get a lot of hours of sitting or standing with poor posture. When you don't practice good ergonomics, that's when the pain sets in.

James Melody of Houston, Texas, is the last person you might expect to be affected by a little thing like posture. James, 14, is an excellent athlete. He plays baseball and basketball and wrestles. But last spring when baseball training started up, he noticed pain in his back around his shoulder blades.

"At first I thought it was just sore, but the pain gradually built up into something more," he remembers. The pain got so bad that his mother took him to see a physical therapist, an expert who can help with pain in joints and muscles.

When ergonomics expert and physical therapist Bill Case saw James in his office, he realized that baseball training wasn't the cause of the discomfort. "He was in tip-top shape, but I saw his rounded shoulders right away, and asked his mom if he sat at the computer a lot." When James practiced pitching, the pain he felt came from muscles that were already strained by poor ergonomics.

Case wants kids to understand what he explained to James: You can end the pain or avoid it altogether with a few small changes. He even has a computer workstation set up in his office so he can show patients how to sit correctly.

"It is just great how these problems can be reversed," says Case. "I tell kids that when the way they sit feels good, it is probably wrong!" He means that sitting up straight will seem weird at first, but after a week or two you will feel the benefits.

James has a tip: Make sure the chair is close enough to the computer table, or else you won't be able to help leaning forward. "Sometimes it slips your mind, and you fall back into the old way for a while," he says. "But when I feel stiffness in my back, I correct for it now."

James also learned to wear his backpack correctly. He used to find himself leaning backward because his pack was too heavy and his straps were too loose.

Lots of kids think hanging a backpack off one shoulder or letting it dangle on long straps looks cool. But there's nothing cool about being sidelined by pain.

So besides being mindful of good posture when playing video games or surfing the Internet, James says, "Now I pack the heavier stuff closer to my body, and raise the pack on my back with the adjustable straps." And that's just what the physical therapist ordered.

James has been feeling great ever since he made a few changes, and you can too. Just follow these tips:

Good Ideas for Gaming and Computer Use

  • Sit up straight with your shoulders back.
  • Make sure your feet are on the ground.
  • Take frequent breaks; walk around and stretch.

Better Backpack Strategies

  • Carry less. Buying an extra set of books to keep at home is less expensive than doctor visits.
  • Tighten straps so the weight is close to your body, and don't let the backpack ride below the waist.
  • Put the heaviest items closest to your back and the pack will be less likely to pull you out of balance.
  • Kids should not carry backpacks that weigh more than 10 to 15 percent of their body weight. So students weighing 100 pounds (45 kilograms) should not carry more than 10 to 15 pounds (4.5 to 6.8 kilograms) in their packs.