CrossFit makes use of three different standards or models for evaluating and guiding fitness. Collectively, these three standards define the CrossFit view of fitness.

The first is based on the ten general physical skills widely recognized by exercise physiologists.

The second standard, or model, is based on the performance of athletic tasks, while the third is based on the energy systems that drive all human action.

CrossFit’s First Fitness Standard - There are ten recognized general physical skills. They are cardiovascular/respiratory endurance, stamina, strength, speed, flexibility, power, coordination, agility, balance, and accuracy.

You are as fit as you are competent in each of these ten skills!

A regimen develops fitness to the extent that it improves each of these ten skills. Importantly, improvements in endurance, stamina, strength, and flexibility come about through training. Training raining refers to activity that improves performance through a measurable or organic change in the body.

By contrast improvements in coordination, agility, balance, and accuracy come about through practice.

Practice refers to activity that improves performance through changes in the nervous system. Power and speed are adaptations of both training and practice.

CrossFit’s Second Fitness Standard - The essence of this model is the view that fitness is about performing well at any and every task imaginable. Picture a hopper loaded with an infinite number of physical challenges where no selective mechanism is operative, and being asked to perform fetes randomly drawn from the hopper. This model suggests that your fitness can be measured by your capacity to perform well at these tasks in relation to other individuals.

The implication here is that fitness requires an ability to perform well at all tasks, even unfamiliar tasks, tasks combined in infinitely varying combinations.

In practice this encourages the athlete to disinvest in any set notions of sets, rest periods, reps, exercises, order of exercises, routines, periodization, etc. Nature frequently provides largely unforeseeable challenges; train for that by striving to keep the training stimulus broad and constantly varied.

CrossFit’s Third Fitness Standard - There are three metabolic pathways that provide the energy for all human action.

These “metabolic engines” are known as the phosphagen pathway, the glycolytic pathway, and the oxidative pathway.The first, the phosphagen, dominates the highest-powered activities, those that last less than about ten seconds. The second pathway, the glycolytic, dominates moderate-powered activities, those that last up to several minutes. The third pathway, the oxidative, dominates low-powered activities, those that last in excess of several minutes.

It is the development of all three of these “metabolic engines” that allows athletes to produce energy across broad base modal demands. Any athlete that trains and does not adequately develop all three of these systems, could surely not be classified as achieving true fitness.

This article is courtesy of CrossFit.com;
http://journal.crossfit.com/2002/10/what-is-fitness-by-greg-glassm.tpl