Stretching is a form of physical exercise in which a specific muscle, a tendon or muscle group is deliberately flexed or stretched in order to improve the muscle's felt elasticity and achieve comfortable muscle tone. This book is the 3rd volume of the series "The Art of Happiness" after Volume 1 "Happiness Guide - How to boost your Serotonin level-" and Volume 2 "Chromotherapy - colours and well-being." The target of this book is to make everyone understand why stretching is so important in all physical activities and why we need to achieve a comfortable muscle tone.