Those of us who train regularly, and even those who train infrequently must be aware of how important it is to get enough rest after exercise. The body repairs itself in the time between workouts. If we look at athletes - continuous training can actually weaken their performances. Rest is physically needed so that muscles can repair, rebuild and strengthen. For those of us who are not professional athletes, it is still important to build in rest days as this can help maintain a better work/home/fitness balance. Too little rest and too few recovery days can actually lead to overtraining syndrome which is particularly hard to recover from. Recovery allows the body to adapt to stress of exercise, and therefore the actual training effect then takes place. Exercise causes fluid loss, muscle tissue breakdown and depletion of energy stores (muscle glycogen) Recovery allows the body to replenish energy stores and repair damaged tissues. If you do not allow the body time to repair and replenish the body will continue to breakdown.