SEATTLE – The exercise ball is gaining popularity in offices as a replacement for chairs because they strengthen abs and build posture. At Core Fitness Center, which recently took over space in the Washington Mutual Tower building in downtown Seattle, marketing director Krystal Posey has been using one for 18 months. According to Working On the Ball: A Simple Guide to Office Fitness, entire office buildings in Canada and Europe have replaced chairs with the brightly colored exercise balls. It’s all the rage at Google’s Mountain View headquarters.

At Microsoft Corp., business director Sheryl Tullis, who has been sitting on an exercise ball for five and a half years, says the trend is picking up there as well. “People used to steal my ball, go bowling with it in the hallway and call it my hippity-hop ball,” she says. Now, friends who are in the tri-athlete community, as she is, use them too.

Tullis started using the ball as a remedy for carpal-tunnel symptoms after Microsoft’s ergonomic assessment team recommended one.

“You naturally sit straight on it and it makes you more aware of your posture,” she adds. “Sometimes on boring conference calls, I’ll do some crunches.”