What is CrossFit?: Part Three

The definition of CrossFit is “constantly varied functional movements performed at high intensity.” This is the last of three blog posts dissecting and briefly overviewing this prescription for fitness. Today we will be talking about “high intensity”: What is it, why is it important, and how do we apply it to everyone from elite athletes to the average couch potato? 

Part three: High Intensity

One of the misgivings that I hear from non-CrossFitters is “CrossFit is too intense!” Well, any of us who have walked in the door know that each WOD is scalable to any fitness level, and these people are likely intimidated by watching elite athletes, such as those in the CrossFit Games, compete at the highest level of intensity. While it’s true that intensity is a crucial part of the CrossFit methodology, each person will have a different level of intensity based on their physical and psychological tolerances, and CrossFit can be catered to each and every person. But when we’re explaining this to our friends and coworkers, it’s important to understand what we actually mean by “intensity”. 

First of all, intensity is NOT yelling the loudest, sweating the most, or getting your heart rate the highest. It’s not a perceived feeling of how hard you are working. CrossFit is based on measurable, observable, and repeatable data, so you better believe that their definition of intensity is concrete too! So then, what IS intensity? 

Let’s break it down to a scientific level. The measure ofIntensity is exactly equal to Power. I will use both words interchangeably in this post. Going way back to high school physics, Power is Force times Distance (also known as Work), divided by Time—in essence, Power is calculated by how heavy, how far, and how fast. The faster we do Work, the more Power we are producing, thus the higher Intensity we have. We’ve already talked about Functional Movements, and how they are all about moving heavy loads long distances quickly, so they go hand-in-hand with intensity. The faster, farther, and heavier we perform functional movements, the higher our intensity. 


Ok, so we have intensity defined, but why does it matter? Well, the higher our intensity, the more adaptations and changes our bodies go through—in essence, we get RESULTS. These results include better body composition and fitness in the gym, as well as improved health markers like blood pressure, bone density, and resting heart rate. High intensity functional movements give us a neuroendocrine response in our bodies, actually changing our natural hormones and our neurology for the better! In sum, Intensity = Power = Results! By doing workouts at a higher level of intensity, we “increase our work capacity over broad time and modal domains.” This well-known CrossFit phrase basically means that we get fitter and more capable in every foreseeable area. Intensity is the shortcut, if you will, to fitness. 

But what about people who are more used to their couch than the gym? They can’t create the same level of intensity as an elite athlete! Well, this is where relative intensity comes into play. A 20-year-old collegiate athlete will have a different fitness level than his 90-year-old grandmother, but both of them can still find their own level of high intensity and perform their WODs to this standard. Relative intensity will be different for each person from day to day, based on physical and psychological factors (stress, soreness, fitness level, etc.) Finding your own high relative intensity is basically toeing the line between pushing yourself hard, and getting into “Pukie” territory. For new or deconditioned athletes, this line will be found more quickly, at a lower power output. As we get fitter, our “engines” become stronger, and our power output increases. If time permitted, we could each calculate our exact power output in every WOD, by plugging in the weight we moved, how far we moved it, and how fast we moved it. Instead, to save ourselves some time and math, we retest benchmark workouts periodically to see if we have increased our work capacity. We know that if we shave 30 seconds off our Fran time, we have generated more power, and thus are fitter athletes! 

Now, it’s important to note here that rest and recovery are incredibly important, especially when it comes to high intensity. CrossFit methodology encourages us to keep intensity super high in our workouts, but this simply isn’t sustainable without rest. Greg Glassman, the founder of CrossFit, advises a 3-days-on, 1-day-off, 2-days-on, 1-day-off approach to WODs, in order to be able to keep that intensity super high on our workout days. In addition to taking rest days, sometimes athletes are sick, stressed, dealing with adrenal fatigue or autoimmune illnesses, pregnant, recovering, and more. In these cases, it’s important to still show up to the box and move your body, but modify your intensity in order to keep your body recovering. 

I would be remiss not to mention Rhabdomyolysis, a rare condition where muscle tissues are damaged to the point that they begin breaking down and releasing their contents into the blood stream, potentially causing kidney damage or even kidney failure. Rhabdo can be caused by various things like a car crash, snake bite, or working out with too much intensity. Symptoms of rhabdo include muscle tenderness, localized heat and swelling, and dark-colored urine. (IF you ever have these symptoms, please see your doctor!) I’ve seen rhabdo happen most often with deconditioned athletes trying to work out beyond their current ability level (let’s keep that ego in check!), or while doing high reps of eccentric muscular training (lengthening the muscle under load). Rhabdo is quite rare, and in my nearly 7 years of doing CrossFit I have only seen a handful of cases, not all from CrossFit. However, if you feel nervous about rhabdo, don’t be afraid to ask one of your coaches for some more information. I don’t bring this up to scare anyone, but to educate you on just how much of an effect intensity can have on your body!

This is why it’s incredibly important to know yourself and your limits. If you’re simply too exhausted or overworking yourself, scale back that intensity. However, when you CAN, give each workout everything you’ve got. If a workout doesn’t leave you lying on the floor afterwards, you probably need to add weight, go faster, or go farther! The higher that intensity level is, no matter how long the workout is, the better you will adapt and the better results you will get. In summary, in the words of Pat Sherwood, “Do more work in less time (without overdoing it), and you’ll get fitter faster.”


A Note to Readers:This is a brief overview of the CrossFit methodology based on the empirical findings of Greg Glassman, the CrossFit community, and basic CrossFit methodology. That being said, blog posts are typically user-contributed pages where the information has not been peer-reviewed. I encourage you to use this blog post as a starting point for your own questions and research!  

-Coach Sonja Rootvik



K. Bowler, C. McDonald, and N. Shatila. CrossFit Level One Certification Course, presented at CrossFit Belltown, Seattle, WA. 20-21 August 2016. 

CrossFit Pierce County, “CrossFit Certification Seminar Notes.” 10-13 February 2006. Pages 2-5. (Online) Available from: https://www.crossfit.com/legacy-pdf/cf-info/FEB06CFNotesNoPics.pdf. (Accessed May 2019.) 

G. Glassman. “Foundations.” The CrossFit Journal, 1 April 2002. (Online) Available from: https://journal.crossfit.com/article/foundations-classics. (Accessed May 2019.)

G. Glassman. “Understanding CrossFit.” The CrossFit Journal, Issue 56, 1 April 2007. (Online) Available from: http://library.crossfit.com/free/pdf/CFJ_56-07_Understanding.pdf. (Accessed May 2019.)

G. Glassman. “What is Crossfit?” The CrossFit Journal,28 November 2009. (Online) Available from: http://journal.crossfit.com/2009/11/what-is-crossfit.tpl. (Accessed May 2019.)

M. Lloyd. “The Neuroendocrine Response.” Mountain Strong, 2 October 2017. (Online) Available from: https://www.mountainstrongtraining.com/the-neuroendocrine-response/. (Accessed May 2019.)

P. Sherwood. “Intensity (and its Role in Fitness).” The CrossFit Journal, 13 March 2009. (Online) Available from: http://journal.crossfit.com/2009/03/intensity-and-its-role-in-fitness.tpl. (Accessed May 2019.)

Photo Source: CrossFit Inc, “CrossFit – CrossFit Whiteboard: Intensity.” CrossFit YouTube Channel, 18 September 2012. (Online Video Screenshot). Available from: https://www.youtube.com/watch?time_continue=3&v=meH9roHylwE. (Accessed May 2019.)

WebMD. “Rhabdomyolysis.” WebMD Medical Reference, Reviewed by Jennifer Robinson, MD, 13 March 2019. (Online) Available from: https://www.webmd.com/a-to-z-guides/rhabdomyolysis-symptoms-causes-treatments#1. (Accessed May 2019.)