Exercise is cathartic, meaning it can help relieve stress. Stress is a response from the body that enables us to be ready for any emergency situation. What stress does not do, however, is improve our performance at everyday jobs or other tasks. When an individual is stressed out about an upcoming test and then decides to exercise that day, the body responds by using energy other than the brain, depriving the brain and body of sufficient amounts of glucose to function optimally in stressful situations like test-taking.