CrossFit was and still is a fitness regimen whose origins date back to the Seventies, although it has started to draw the attention of the public only toward the second half of the Nineties when Greg Glassman founded in 1995 the first gym used to CrossFit in Santa Cruz in California. He was the first in history to define the Fitness so significant and measurable: "to increase the capacity of the work over time in an infinite series of activities and exercises." From the beginning, the aim was to create a fitness program broad, general and accomodating, trying to rebuild a methodology of training to prepare the subject to deal with every eventuality. This is not a Fitness program specialised, but a method that has been developed to increase individual competence in any physical activity, that it is known or unknown. This form is required for the soldiers of the army, the police, the fire brigade and for many sporting disciplines that require an excellent physique. The recipe to obtain this fitness is: "perform functional movements at high intensity always different". The movements say they are functional when reflect the gestures of daily life, natural movements made thanks to the synergistic contraction of more muscle groups and the involvement of more joints. This is the locomotives corponaturali, effective and efficient. But no aspect of the functional movements is more important than their ability to move large loads over long distances and to do it quickly. All Together these three attributes (load, distance and speed) qualify functional movements as ideal for the production of great power. The concept of power in CrossFit is defined exactly as intensity and expresses the degree of physical effort required in the execution of a particular activity or exercise. More work produce in less time, the more intense the effort. Then using an approach different constantly in the workout, in movements and in the intensity produces immediate results in physical form. This allows man to grow, maintain a good state of health and interact with the outside environment in the best way.