There is a lack of universal acceptance as to what is fitness and who is fit. In order to better understand the CrossFit method it is important to formulate a working definition of fitness.
CrossFit evaluates fitness using three different standards or models. The first is to evaluate an individual's capacity in the ten different physical skills widely accepted by exercise physiologists. The second is based on an individual's ability in a variety of athletic tasks. The third model is based on the energy pathways used to drive all of human activity.
The Ten Physical Skills
The ten generally accepted physical skills are cardiovascular/respiratory endurance, stamina, strength, flexibility, power, speed, coordination, agility, balance, and accuracy. CrossFit develops fitness in each of these areas.
It is not uncommon to find an elite marathoner with a vertical jump
of only a few inches. This demonstrates a lack of power and an excess
of endurance training.
Out of the ten physical skills, four of them are improved by training alone: cardiovascular/respiratory endurance, stamina, strength, and flexibility. That is, there are measurable and observable organic changes that occur in body. Coordination, agility, balance, and accuracy are improved through practice. Practice refers to any activity that results in changes to the nervous system. Two of these skills, power and speed, are improved through a combination of both practice and training.
The Hopper
CrossFit's second fitness standard can be described using the idea
of a hopper. Imagine putting every imaginable physical task into a
hopper - run a 5k, 1RM deadlift, the Bridger Ridge Run, 100 pullups for
time, max push-ups, row 500 m, etc. At random, you
pull one physical task after another out of the hopper. Whoever performs best, on
average, at all the tasks is considered the most fit.
Life punishes the specialist. Few sports reward specialists, but few athletes are serious enough about their sport to train for such a specific fitness. Nor should they.
Metabolic Pathways
CrossFit's third standard for fitness can be described using the three metabolic pathways that drive all of human activity. Most people are familiar with the idea of aerobic or anaerobic activities. Anaerobic activity can be broken down into two different categories.
The first, the phosphagen pathway, fuels activities that last from 0-10 seconds. Examples of these activities include a max effort lift and the 50 meter dash. Most popular fitness programs completely ignore this pathway.
The second anaerobic pathway is the glycolytic pathway and it fuels activities that last between 10 seconds and 3 minutes. Examples of exercises that fall into this category are a 5RM lift, the 400m dash, and a max set of pullups.
The aerobic pathway is called the oxidative pathway and fuels exercises lasting longer than several minutes. Examples of activities that utilize the oxidative pathway include running 1 mile, walking down the street, and sitting on the couch.
Excessive training in any one pathway can be detrimental to the other pathways. Training in the aerobic pathway burns fat and increases aerobic capacity. However, it also decreases muscle mass. Anaerobic training burns fat and increases aerobic capacity. However, it also increases speed, power, and strength, increases muscle mass, and develops anaerobic capacity. Simply put, aerobic exercises burns muscle, anaerobic exercise builds muscle.