The Importance of Knowing a Workout’s Intended Stimulus

Is there a ‘right’ way to complete a workout? How do you know? Is it measured by time? Reps? Exhaustion? Most, if not all, CrossFit workouts are written with an intended stimulus in mind – the level of intensity athletes should reach in order to get the most benefit from the programmed workout. There are several different ways this stimulus can be measured with the most common method being time. Knowing the appropriate time domain for a workout is important because not only does it give the athlete a goal for the workout, but it also ensures that different energy systems (or metabolic pathways) are being utilized for different workouts. 

The Crossfit Level 1 Training Guide uses four different models of fitness to answer the question: ‘What is fitness?’ One of these models of fitness is the metabolic pathways, or energy systems that are used for all human action. CrossFit argues that total fitness requires training and competency in all three of these pathways and balancing the effects of these three pathways helps determine the how and why of the cardio that is practiced in many CrossFit gyms. However, it can become quite common for athletes to favor one or two of the pathways over the other[s], which is a common fault in CrossFit training. Therefore, it is important that athletes understand the differences between these three pathways and which one is required for a specific workout. 

The first metabolic pathway is called the phosphagen pathway and it is responsible for the highest-powered activities, such as those that last less than ten seconds. Example activities in the phosphagen pathway are a 100-meter sprint or a 1-rep max deadlift. Each of these activities last only a matter of seconds but require a high level of power output. The glycolytic pathway fuels moderate-powered activities, or those that last up to several minutes. For example, a 400-meter sprint or an elite level ‘Fran’ time would fall under this energy system. Finally, the oxidative pathway dominates low-powered activities, such as a 1 mile run or longer metcon. When the intent of the workout is lost, athletes often end up training the same energy system over and over again and they develop a deficiency in one or two of the other metabolic pathways. This results in a loss of fitness. 

Consider the workout ‘Fran’: 21-15-9 barbell thrusters (95/65) and chin-over-the-bar pull-ups. When performed at an elite level, or with the appropriately scaled movements, an athlete should complete the workout around three minutes and will therefore use the glycolytic pathway to fuel this workout. However, for individuals who are newer to CrossFit and have not fully developed their skills or strength, this workout may prove to be more of a challenge because of the weight of the thrusters and volume of pull-ups. Therefore, in order to achieve the intended stimulus, it will be necessary for newer and less advanced athletes to modify the workout to something that is more manageable, such as performing ring rows instead of pull-ups and doing thrusters with an empty barbell. With these modifications, the athlete should be able to stay within the desired pathway and train the correct energy system. 

It is important to keep in mind that some workouts may target more than one metabolic pathway throughout different portions of the workout. For example, take a look at the following workout: 21-15-9 reps of deadlifts (355/235) and rowing for calories. While the rep scheme is the same as ‘Fran’ (listed above), the stimulus is very different. The shorter-duration row (where each row will probably take less than a minute) will push most athletes to work in the glycolytic pathway. However, the heavier deadlifts will shift the athlete to the aerobic pathway because their output will slow due to the increased load. In order to preserve the intended stimulus, it’s important to note that the loading on the deadlifts is supposed to be heavy. Therefore, for athletes who cannot perform the deadlifts as prescribed, they should still choose a weight that is moderately heavy (approximately 80-85% of their 1-rep max). If an athlete can perform all of their deadlift sets touch-and-go, then that is an indication that they didn’t go heavy enough. Therefore, as a coach and as an athlete, knowing the workout’s intended stimulus is extremely important because it helps ensure that each pathway is trained equally, which will then lead to better all-around fitness.