It's easy to confuse muscle tone with muscle strength or muscle bulk, something you can improve with weight lifting, running, and regular workouts. Muscle tone refers to the level of tautness or looseness in a muscle and its ability to hold joints in place — something that is sorely lacking in many children with sensory integration disorder. This kind of muscle tone can't be improved by working out and bulking up. Sometimes it improves with time and therapy, but in the meantime, it makes kids extra floppy.