In Part 1, we explained the defining characteristic of functional movements is their ability to move large loads long distances, quickly. This definition represents three variables: force, distance and time. These variables are used to calculate power, where average power = force times distance/time. Force times distance is equal to work, so power is also equal to work/time.
For CrossFit, power is exactly equal to intensity. In a manner similar to the term “functional,” the term “intensity” historically has been nebulously defined, often based on perceived efforts or correlates rather than an objective and measurable assessment. Heart rate, VO2max, sweating, vomiting, etc. can all be related to intensity, but they are not necessarily a measure of it. For example, your heart rate could be very high pre-workout due to nervousness, but this does not mean you are getting fit! Similar problems emerge in the consideration of VO2 max (the maximum amount of oxygen a person can utilize during exercise), which is a measure of potential, not outcome or actual work accomplished.
CrossFit’s measure of intensity is power. This is important because now we can establish measurable, observable, and repeatable data from our workouts by calculating intensity.
Force is simply determined by weighing the load lifted (such as a barbell, sandbag, or medicine ball) or the body weight of the athlete during unloaded movements. Distance is measured by how far the load is displaced vertically (against gravity) during the movement. Every repetition completed adds to the total distance of the workout. The total work completed in the workout is a product of the force and distance. The duration of effort, or time, acts as the denominator in the equation. Therefore, the faster the work is completed, the more intense the effort.
Generally speaking, increasing the loads you lift will develop strength. Increase the repetitions you can complete to raise stamina and endurance. Strive to complete a predetermined amount of work faster than a previous effort to see a systemic increase across several capacities at once. By recording and improving these metrics, we begin to develop an objective measurement of fitness based on quantifiable data, not speculation.
This matters because intensity is the independent variable most commonly associated with maximizing the rate of return on favorable adaptation to exercise — i.e., training with high intensity will produce more of the results we seek more quickly. The larger systemic effect experienced with intensity transcends any muscle fatigue directly involved with the movement(s) at hand. If you want to increase muscle mass, decrease body fat, increase bone density, or insulin sensitivity — if you want to look better, feel better, work better, sleep better, play better — intensity will get you there.
As important as intensity is, it is even more important to understand the application of it. The level of intensity at which a person works needs to be appropriate relative to their physical and psychological tolerances. That is, the intensity at which someone should work is always and only relative to that individual. As long as someone is working near the limits of their capacity, they will find the same increased benefits from the program whether they are an elite athlete or simply trying to maintain functional capacity for independent living. The important metric to track is not the absolute output of the athlete but rather their output today relative to what they were capable of last week, last month, or last year. If the relative intensity is rising over time and across many different workouts, it follows that the athlete is becoming fitter.
Additional Reading
To learn more about human movement and the CrossFit methodology, visit CrossFit Training.
Defining CrossFit, Part 2: Intensity