It is commonly believed that to achieve substantial muscle growth it is necessary to exhaust oneself in a gym and consume lots of protein supplements. No one can deny that training and nutrition are crucial for getting good results. Yet there is another factor, no less important—indeed, essential. It is the rest the body needs in order to repair and strengthen itself. Why is it necessary for the body to be fully restored before the next workout? Lack of proper rest can lead to cumulative exhaustion and the development of overtraining syndrome. When that happens, training progress slows down and results may start to diminish. You feel constant fatigue, yet there is no growth; you try training even more but there is no improvement. Instead the fatigue keeps growing and your motivation eventually starts to decline. If overtraining becomes chronic, it can even lead to health problems. The reason for that is the drop in anabolic hormone levels and the growth of catabolic hormones, especially cortisol. The immune system is weakened, muscle mass may be lost, and the body becomes more susceptible to infections and injuries of the muscles and tendons. Any physical effort puts stress on the body and provoke a state of emergency. The body reacts with something called supercompensation. It is important to understand that muscle growth happens not DURING training but AFTERWARDS—when you rest. The training itself produces micro-injuries—tiny tears in fibers and the connective tissues of muscles. This not dangerous; in fact, it is absolutely normal: the micro-injuries serve as a signal, telling your body that muscle mass needs to grow in order to cope with increased workload and to adapt to the new conditions. Time between workouts is when this adaptation (the increase in muscle mass) takes place. But that is not all. Rest is still needed to prepare the body for the next workout, to replenish its energy. The damaged muscles also have to be repaired. All that does not happen instantly: it takes time.