After years of sports and a few bike and car accidents, Blake Allison had such a stiff back that he could barely reach past his knees. Although his inflexibility was a joke in his family, it was also cause for concern. Says the 36-year-old District resident: “Being that stiff can really create problems,” including being more prone to injury.

A few unsuccessful physical-therapy sessions led him to try Pilates, a form of exercise designed to stretch, strengthen, and balance the body. After six sessions, Allison could easily touch his toes. He was hooked.

Like yoga and some other exercises that have become popular in recent years, Pilates isn’t new. It was developed in the early 20th century by Joseph Pilates, a German-born boxer and gymnast who was interned in England during World War I. While there, he helped rehabilitate the injured and created a series of movements to strengthen others at the camps.

Through small, controlled exercises, Pilates works the core postural muscles—abdominals, lower back, hips, and buttocks—which help keep the body balanced and support the spine.

Instructor Krisi Frazee of Alexandria’s Studio Body Logic says that by strengthening the core, everything else works more smoothly: “It’s about reintroducing the body to itself through breathing and simple exercise.” She says technique—which involves learning to engage the core muscles—is more important than lots of repetitions.

Pilates enthusiasts rave about increased flexibility, toned muscles, and greater core strength. Many claim to feel taller and more aware of their posture after one class.

There are two types of Pilates: work done on a mat that requires no equipment (mats usually provided) and apparatus exercises on special machines. Mat classes can be good for beginners because they’re cheaper and offered more frequently.

Many gyms offer Pilates-based classes that use some Pilates techniques but incorporate music, stretching, and yoga. If you want the authentic experience, look for certified studios and instructors. Classical Pilates (classicalpilates.net) , the New York Pilates Studio (pilates-studio.com) , and Power Pilates (powerpilates.com) offer certification or have searchable databases of instructors and studios on their Web sites.

—Mary Clare Fleury