Gabe Mirkin, M.D.
Most competitive athletes go crazy when they're injured because their competitors continue to train. They can maintain fitness by using a training technique called cross transference, and so can you.
When you exercise one leg or arm, you maintain strength, endurance and power in the other limb. The muscles in the injured limb are not strengthened directly (2). Each muscle is made of millions of fibers. Each fiber is stimulated by a single nerve. When you exercise, your brain sends messages along these nerves, telling only about one to two percent of the nerves to contract at the same time. With training, your brain learns to contract a greater percentage of muscle fibers simultaneously. So exercising one arm teaches your brain to contract more fibers in the other arm. Exercising your arms does not strengthen your legs. Baseball pitchers can maintain strength in their injured arm by using their other arm to throw and do resistance exercises.