[Mary Wilkinson] is one of about 650,000 adults haunted by a disease they thought they had conquered. An estimated 125,000 polio survivors are suffering from post-polio syndrome.

Most who contracted the polio virus in the 1940s and 1950s, before a vaccine was developed, followed medical advice and exercised vigorously. Now, physical therapists say, the strain they put on their muscles back then may be the cause of post-polio syndrome.

Perhaps 60% of polio survivors can expect to get symptoms of post-polio syndrome, said Dr. Lauro S. Halstead, director of the Post-Polio Program at National Rehabilitation Hospital in Washington, D.C.