Intended Stimulus

This article originally appeared on Tabata Times. 

By Rachel Binette

CrossFit works. All around the world, people are losing weight, getting stronger, and living better lives because of CrossFit.

But how does CrossFit work? What makes it special compared to other fitness regimens?

Here’s CrossFit’s definition of fitness, which may sound like nonsense to the layman: “Increased work capacity across broad time and modal domains.”

To put it another way, a person is becoming fitter when they can perform more work in weightlifting, gymnastics, and monostructural tasks (i.e.: running, swimming, biking, rowing) over varied periods of time. Note the “varied periods of time.” That’s going to be important later.

Still confused? Try this picture:


In CrossFit, the bottom picture is the ideal–more stimuli leads to more adaptation, and the result of adaptation is fitness. Variety is our friend, and “routine is the enemy.”


So how does this translate to our training? Programming! CrossFit programming is designed to maintain a variety of stimuli for increased adaptation. What are the different types of stimuli and how can we, as athletes, ensure that we’re getting the intended stimulus from each workout?


The Metabolic Pathways


Remember early on when I asked you to remember “varied periods of time?”


Our bodies are capable of exerting maximum effort over many different time domains. We can perform a 1RM back squat. We can do “Grace.” We can run a marathon. These tasks use different metabolic pathways to exert effort, by which I mean that they use different sources of energy.


We’ve all heard of aerobic and anaerobic training: aerobic training uses oxygen for energy, and anaerobic training doesn’t use oxygen. Here is a slightly more detailed breakdown:



Anaerobic sources of energy are ATP for the Creatine-Phosphate System, and stored carbohydrates, or muscle glycogen, for Glycolysis. The Creatine-Phosphate System is our top speed–it’s what we use when we are sprinting away from a bear, running for our lives. As we work at max effort, our ATP runs out after about 10-12 seconds. Then our body begins using muscle glycogen for energy, running out after 90 seconds to 2 minutes of work. Glycolysis is another energy system for high speed, but is not as explosive as the Creatine-Phosphate System. After we’ve run out of muscle glycogen, our body can only use the oxygen we are breathing in to continue to fuel our effort. Once we’ve started to use oxygen to fuel our effort, we are moving pretty slowly.


CrossFit workouts are designed to train all 3 of the metabolic pathways through a variety of programming.


Oftentimes, programmed rest is critical for allowing an amount of recovery to occur before exerting effort again. During rest, our ATP and muscle glycogen stores are replenished. Continuously working without rest keeps our training in the aerobic system, where resting allows us to start training over again in the Creatine-Phosphate and Glycolytic Systems. Training these systems allows us to kick into another gear at the end of a workout.


Monostructural, Gymnastics, and Weightlifting


The movements we perform are probably the easiest form of variety to spot in programming. Here are some quick examples of each of these “modalities” for your reference:


Monostructural (M): running, biking, swimming, rowing, jump roping. Think classic cardio.


Gymnastics (G): pull-ups, push ups, dips, handstands, toes-to-bar. Bodyweight movements.


Weightlifting (W): deadlifts, snatches, back squats, kettlebell swings. Movements with weight.


We may think that the only WODs we need to perform are the ones that combine all three of these modalities (known as MGW to programmers) for the greatest adaptation. That would sort of make sense, right? More variety in every WOD means more adaptation. But, we adapt to MGW WODs, just as we adapt to only performing monostructural work or only weightlifting. An MGW WOD is still only one type of stimulus.


As athletes, we gain the most adaptation by varying the WODs we choose to come to. Skipping heavy days or monostructural workouts keeps our adaptation lower.


Loads, Holds, Carries


In weightlifting and gymnastics, there are 3 more modalities to consider in training: loads, holds, and carries.


Load: a moving weight, whether it’s bodyweight, a barbell, or a kettlebell. Most CrossFit training incorporates loads through prescribed weights and bodyweight movements.


Hold: a static, or unmoving, position under tension. Examples include a handstand hold, the pause in a pause squat, and hangs from a pull-up bar. There are many articles on the benefits of training holds, but this is my favorite, because it explains the recruitment of different muscle fibers as a hold is performed.


Carry: you can guess this one. A weight that is carried; yoke carries, sandbag runs, and farmer’s walks are some examples.


Holds and carries are not trained nearly as frequently as loads in CrossFit, so they are beneficial as accessory training–adding more types of stimuli for greater adaptation.


Your Coach


Chances are good that your CrossFit coach talks about how the workout is supposed to be performed. All out sprint? Paced to speed up at the end? Heavy?


Knowing the intended stimulus of a workout allows your coach to help you choose appropriate loads and scaling modifications. If toes to bar are programmed and I can only perform singles, should I go Rx, or should I modify to a movement that I can string together quickly? It depends on the intended stimulus of the workout.


A coach’s job is to help us translate the workout into an event that allows us to gain the greatest adaptation. Sometimes athletes will benefit more from going faster with a lower skill over performing a high skill movement, and sometimes will benefit more from practicing movement over fewer reps than what is prescribed. A good coach will know how to vary skills and modifications to benefit individual athletes.


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