Why do three sets when you can accomplish what you need to in one set? There is significant research to prove that the results between one set and three sets is insignificant and some say, if it is done correctly, one set produces far greater results than multiple sets. When it comes to exercise, the body does not respond to how many, how long, or how often. It only responds to the demand you place on it. In order to increase muscle, you need to overload the muscle to exhaustion within a certain amount of time frame, with good form (to keep you safe from injury). If you do this effectively in one set, than doing 2 or more sets would be like paving the same road 3 times. Also, the more repetitions you do around the joint, the more wear and tear you create within that joint, thereby, increasing the risk of injury.