Trying to do too much at once -- Enthusiasm can push you into doing too many sets, lifting too much or running too long. At best, your body's extra soreness hampers future workouts, but injury is the true risk. If you push your body too far, it breaks.{relatedarticles}You also want to get enough rest between workouts to let your body heal. Your body needs time to repair the damage a workout does. Alternate days of strength training -- do upper body one day, lower the next. This way, you'll be sure to minimize damage. A little soreness is OK, however. After all, the tiny tears in muscles that result from working out create mass as they're repaired.