Experts in the area of repetitive work-related injuries do advise frequent breaks. Many doctors and therapists tell patients to take stretch breaks every 20 minutes. Others use the one-hour mark. The perfect number of breaks isn't really known.
Engineers at the Occupational Medicine Research Center in Louisiana report that the elasticity of soft tissues doesn't go back to normal even after seven hours of rest. They used cats in their research but the results were similar to other studies done in humans.
Studies are being done around the world to find out just how many repetitions of movement it takes to cause an injury. Number of hours of rest needed for tissue recovery is also under investigation. Finding a safe work-to-rest ratio would go a long way in preventing soft tissue trauma from repetitive activities.