This matters more than anything. The ideal stance, Wehner says, is "shoulders relaxed, back, and down, and no leaning to one side." To see how far off you are, Elattrache suggests sitting in a chair and looking straight at the wall. Do you have to cock your head back? If so, it means your chest is sunken in and your shoulders rolled forward. "Sit up straight and put a little arch in your back, and your neck doesn't have to bend like that," he says. One way to remind your body of proper alignment is to place a round pillow against the small of your back when you sit. "Just the trigger of the lump in your back subconsciously tells your muscles to get you some support," Elattrache says.

Make sure your workouts include not only the core muscles of the lower back and abdomen but also the shoulder blades. One of Elattrache's favorite preventive exercises—and, since my episode, my favorite—is what my daughter laughingly calls "the penguin," which works either on dry land, if you use an exercise band, or neck-deep in a swimming pool: Keeping upper arms at sides, elbows bent 90 degrees, start with palms facing each other, almost touching. Slowly bring both hands out to the side, pinching your shoulder blades as you press them together against resistance; then return to the starting position. Two sets of 10 repetitions every day, or every two days, will start to make a difference, Elattrache says.

It can be as simple as slowly shrugging your shoulders while sitting at your desk or watching TV, doing up to 10 repetitions at a time.

If your bag has a strap that rides diagonally across your body, use it. "That should distribute the weight better," says Wehner, "and you don't have the feeling it will slip off, so you're less likely to hike your shoulder." Also, swap sides so you're not always using the same shoulder.

Switch It Up
Carry the big bag some of the time, but either pack less into it or alternate with a smaller bag. And try to vary styles. "There are issues with any kind of bag," Elattrache says. "What you really don't want to do is overuse a single position."

Forget the Saying "Beauty Hurts"
Warning signs that you may be on your way to a big-bag injury include an ache in the shoulder blade area and frequent neck stiffness. Headaches—after sitting for long periods of time or at the end of the day—and pain radiating down the arm are also symptoms. If you're noticing these signs, and if ice and rest don't make them better after a week or so, grab a very small wallet, your cell phone, and car keys; pat your purse goodbye; and head for the orthopedist's office.