One of the greatest mistakes with muscle conditioning is to try to strengthen both muscle partners at the same time. This often entails utilizing speed and momentum rather than control. Using the agonist and antagonist muscles simultaneously does not specifically target either side of the muscle pair. Work and overload is created when a muscle is fatigued with sufficient repetitions using control to both start and stop the action. When an instructor incorporates momentum into strength training design they are often working more joint stress. As a result the desired muscle group will not reach overload to become stronger and the resulting joint stress may cause injury.