One of the most persistent myths in strength training is that muscle soreness represents progress and that if you are not sore the next day you did not work hard enough. This is based on the notion that breaking down the muscle causes them to increase in size and strength. This is an overly simplistic approach to a series of very complex physiological changes at the cellular level involving many hormones, growth factors, and nutrients. There is little scientific evidence that breaking down the muscle is the best stimulus for adaptation. While it is common to be sore for a few days when you take up a training program for the first time; attempting to be sore after every training session will quickly lead to overtraining and a variety of injuries, particularly tendonitis as the tendons do not recover as quickly from the stress of training as the muscles.