Just reading the word 'exercise' can provoke a whole cascade of self-addressed questions: Am I doing too little? Am I doing too much? Am I healthy? What exercise is best for me? Physical exercise, to be specific, is any activity that requires physical effort, and so enhances or maintains physical fitness and health. From marathons to evening walks, exercise can be performed for various reasons. This can be both physical, e.g. increasing athletic strength or weight-loss, but also mental. This is as exercise triggers a release of chemicals in the brain, such as serotonin, endorphins and dopamine. This can dull pain, better your mood and remove stress.