CrossFit is defined as constantly varied functional movement executed at high intensity. It is a fitness program that is broad, general and inclusive by design. The aim is to improve your fitness by increasing your work capacity across broad time and modal domains.
Basically, use movements that are safe, natural and essential to independent life to create a fitness program that will be executed at high intensity. Intensity is relative and everyone will find their own intensity level to see true results.
Here is the founder of CrossFit, Greg Glassman’s, definition of world-class fitness in 100 words…
Eat meat and vegetables, nuts and seeds, some fruit, little starch and no sugar. Keep intake to levels that will support exercise but not body fat. Practice and train major lifts: Deadlift, clean, squat, presses, C&J, and snatch. Similarly, master the basics of gymnastics: pull-ups, dips, rope climb, push-ups, sit-ups, presses to handstand, pirouettes, flips, splits, and holds. Bike, run, swim, row, etc, hard and fast. Five or six days per week mix these elements in as many combinations and patterns as creativity will allow. Routine is the enemy. Keep workouts short and intense. Regularly learn and play new sports.
~ Greg Glassman