TERRI KRIVOSHA, a partner at a Minneapolis law firm, logs three miles each workday on a treadmill without leaving her desk. She finds it easier to exercise while she types than to attend aerobics classes at the crack of dawn.

Brad Rhoads, a computer programmer and missionary in Princeton, Ill., faces a computer monitor on a file cabinet and gets in about five miles a day on a treadmill while working in his home office.

“After a while, your legs do get kind of tired,” said Mr. Rhoads, 40, who started exercising in March, when doctors advised him to lose weight after open-heart surgery.

Ms. Krivosha and Mr. Rhoads are part of a small but growing group of desk jockeys who were inspired by Dr. James Levine, an endocrinologist at the Mayo Clinic. In 2005, Dr. Levine led a study showing that lean people burn about 350 more calories a day than those who are overweight, by doing ordinary things like fidgeting, pacing or walking to the copier.