CrossFit defines fitness as increased work capacity across broad time and modal domains.
Basically, CrossFit uses three models for determining how to define fitness.
The first is via the 10 physical skills:
“They are cardiovascular/respiratory endurance, stamina, strength, flexibility, power, coordination, ability, power, 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.”
The second is general physical ability:
“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 third is via metabolic ability:
“There are three metabolic pathways that provide energy for all human action. Total fitness, the fitness that CrossFit promotes and develops, requires competency and training in each of these three pathways or engines. Balancing the effects of these three pathways largely determines the how and why of the metabolic conditioning that we do at CrossFit.”