Sport Specific Limitations In Crossfit
A Physiological Lens For Identifying & Training Sport Specific Limitations
“A high VO2max is necessary, but not sufficient for high level endurance performance”
-Dr. Andy Coogan
What I love above the Dr. Andy’s Coogan’s quote above is how broadly it applies across different disciplines. For example, a high VO2max is in fact necessary, but not sufficient for elite Crossfit performance. But, it goes further than that. If you replace ‘VO2max’ with other qualities and ‘endurance’ with Crossfit you get a sense of how far reaching this concept is. For example…
Being able to do 30 ring muscle-ups for time in under four minutes is necessary, but not sufficient to be an elite Crossfit athlete;
Being able to Snatch 125kg and Clean & Jerk 165kg is necessary, but not sufficient to be an elite Crossfit athlete;
Having a sub 6:30 2k Row is necessary, but not sufficient to be an elite Crossfit athlete.... the list is endless.
This whole concept reminds me of a quote by Marilyn Strathern that read "When a measure becomes a target, it ceases to be a good measure.” If sufficient rewards are attached to some measure, people will find ways to increase their scores on that measure one way or another, and in doing so will undercut the value of the measure in assessing what it was originally intended to assess.
If you want to be a competitive Crossfit athlete we know their are some minimum strength metrics you need to be able to hit, certain paces you need to be able to sustain for a given duration on the rower, air bike, etcetera, and some ballpark estimates you should be able to hit on workouts like 30 ring muscle ups for time, 100 strict handstand pushups for time, and so forth. However, hitting these metrics does not necessitate you'll be a great Crossfit athlete. It's a matter of necessity, versus sufficiency. Being able to hit these different metrics is equivalent to being accepted into a university. Just because you've been invited to step through the front door does not mean that you're eligible to graduate.
As a result, I'm always a little hesitant to throw athletes into these types of testing batteries. At best, I'll be able to check some boxes and see where an athlete stacks up relative to the field [and the elites]. This can help us determine what they need to prioritize, but it won't necessarily tell us how they translate their skills to the sport of fitness. Furthermore, it can create the illusion that improving on these tests is the goal in and of itself. Instead, I like to conceptualize Crossfit as a cyclical sport. The issue, for a given individual, arises when they cannot turn a metcon into cyclical work. So, rather than thinking in absolute terms or categorizing isolated components of the sport as 'beginner', 'intermediate', 'advanced', and 'elite' I'll think to myself, why can't this athlete make this movement cyclical? This is way more actionable at all levels of development. Let's take ring muscles ups for example. Instead of having an athlete do 30 ring muscles ups for time and seeing how they stack up against the competition I'll ask the simple question, "can you perform ring muscle ups in a cyclical fashion". If not, I'll then look to understand why. For a beginner athlete it may be a strength issue. For an intermediate athlete it may be a breathing or coordination issue, and for advanced or bubble level elite athletes it may simply be a maximal cardiac output issue. Now we know the problem - further down the page we'll begin to open up a dialogue as to how we fix them.
The Bioenergetics Of A Crossfit Metcon
Leading into the 2016 Crossfit Games regional qualifier an organization called Training Think Tank hosted an athlete camp where they brought in a number top competitors and had them throwdown on a series of workouts across a three day weekend. One of the workouts included a high volume of kettlebell Snatches and box jump overs and while watching this event the owner of the company, Max El-Hag, made an offhand comment to me that an athlete named Travis Mayer was able to take that metcon and turn it into a cyclical event. Max didn’t mean anything profound by this. He was making a simple statement that if you watch Travis do the event he doesn’t stop moving for more than a split second whereas a lot of the other competitors were breaking up their kettlebell snatches, taking longer transitions, and generally looked like they were approaching the metcon in more of a circuit style with defined work and rest periods.
Regardless, this statement really struck a chord. Particularly so because it matched my observations when I started doing physiological testing on Crossfit competitors. I found that the best Crossfit athletes can turn the majority of metcons into cyclical work whereas the rest of the pack cannot. What I mean by cyclical work is that there is steady blood flow to the working muscles, a near linear rate of oxygen desaturation from the start to finish, and more broadly that the physiological response to the metcon matches what you’d expect to see on a 2k row for example. To demonstrate this we’ll observe a NIRS trend from two Crossfit athletes going head to head in a metcon.
In the NIRS trend above we have two Crossfit Games competitors going head to head in a metcon that includes thrusters, burpees, and rowing. At the time of this workout the athlete on bottom was a top 10 individual games competitor and the athlete on top was a regional competitor who later qualified for the games as an individual. Note that the athlete on bottom has a near linear oxygen desaturation trend across the workout without any major dips or peaks. They were able to move through the workout nearly unbroken with minimal rests and transitions, which allowed for a very high rate of energy turnover. The athlete on top, on the other hand, had less steady blood flow to the working muscles (not featured in picture) and as a result they were forced to stop, rest, and complete the workout in a bout of work intervals interspersed with rests and long transitions. Interestingly, the total amount of work time for the athlete on top is actually slightly less than the athlete on bottom, indicating a faster rep speed, but it was so broken up that they ended up taking over two minutes more to finish the workout. This raises the question, Why can some athletes turn metcons into cyclical work but others cannot ? The rest of this article will be used to answer this question, as well as to provide some practical takeaways for how we can get an athlete to make metcons more cyclical in nature based on their individual sport specific limiters.
Understanding Local Muscle Fatigue
As a sports scientist, one of things I love getting to do is taking concepts from research and applying them in practice to see what the outcome is for an individual. If there is a specific problem I'm trying to solve I'll comb the research for some solutions, then put them to the test and observe the results. Sometimes clear trends emerge through this process and these protocols trickle down into my coaching practice, and other times the observed responses are so variable between individuals that it’s difficult to parse out why something did or didn’t get the desired effect.
Recently i’ve been interested in seeing why some athletes’ lower backs always ‘blow up’ during metcons (even metcons that don’t have a meaningful hinging component) while other athletes almost never experience this. I’ve observed a trend that the Crossfit athletes who have these lower back issues tend to be stronger and more heavily muscle individuals, and oftentimes they’re also the athletes with weak cardiac output who have to regulate their arterial blood pressure through extremity muscle vasoconstriction.
On a quick literature sweep I found a paper titled, “Assessment of lower-back muscle fatigue using electromyography, mechanomyography, and near-infrared spectroscopy”. According to this paper the restriction of blood flow due to high intramuscular mechanical pressure is one of the most important factors in lower back muscle fatigue and that the availability of oxygen in the lower back muscular is strongly linked to muscular endurance capabilities.
In the study they also saw that mechanical pressure drives blood out of the muscle and then blood volume remains low for the remainder of the contraction. This is a compression reaction and it’s something I can easily identify with NIRS.
A compression reaction is when muscle tension squeezes blood out of the muscle. This occurs within several seconds of the onset of tension and is diminished upon the release of tension. So, essentially what is occurring in individuals who suffer from low back ‘pumps’ during Crossfit metcons is that the mechanical pressure on their spinal erectors and stabilizing muscles is creating a scenario where blood is being squeezed out of the muscle at the onset of muscular contraction and steady flow to those tissues is not returning until tension is released. This means that those muscles will be prone to desaturating since oxygen utilization will supersede oxygen delivery. Because metcons typically entail a lot of volume done in a very short period of time this means that the stabilizing muscles in the lower back will not experience complete recovery and as a result fatigue will ensue.
I set out to test these theories and see what happens in the spinal erectors of athletes that do and do not experience issues with their lower backs ‘blowing up’ during metcons. The primary tool I used for this investigation was the Moxy muscle oxygenation monitor. Muscle oxygenation is a measurement of how much hemoglobin is carrying oxygen in the capillaries of the muscle and the subsequent transfer of oxygen to myoglobin, the oxygen carrying molecule located within the muscle. Muscle oxygenation is a localized measure that depends on level of blood flow, and changes in the hemoglobin dissociation curve. Muscle oxygenation is measured optically with NIRS, so it is completely non-invasive.
In the picture above you’ll find a sample NIRS trend from the spinal erectors of one of my athletes doing a 60 second long isometric back extension hold on a GHR. This serves as a nice baseline so you can see what a strong contraction in the spinal erectors followed by a relaxation looks like. Notice that upon the start of contraction muscle oxygen saturation (SmO2) drops rapidly then through the contractile period oxygen saturation stays depressed until the contraction ends and SmO2 rebounds. You’ll also notice that upon the start of contraction THb drops rapidly, plateaus at a low level, and then returns to baseline after the end of the contraction. This THb trend represents a compression reaction, which closely matches what was observed in the paper titled, “Assessment of lower-back muscle fatigue using electromyography, mechanomyography, and near-infrared spectroscopy” that I mentioned earlier. This athlete also reported that they felt a significant lower back pump after this set. Being that this matched the findings from the aforementioned paper I wasn’t too surprised, but this did get me excited to test this out in a metcon.
Below you’ll find a NIRS trend from the spinal erectors of an athlete who struggles with their back ‘blowing up’ during metcons. I had them do the following for time: 30 cal Echo Bike, 20 Deadlifts (225#), 25 Wall Ball (20#).
In the NIRS trend above you’ll see that it’s broken up as three distinct work bouts (the dead lifts and wall balls were completed unbroken) with a short rest in between. During the Echo bike you can see a compression reaction in conjunction with a steady drop in muscle oxygen saturation in the spinal erectors. This reaction shows that high intramuscular mechanical pressure in the spinal erectors is driving blood out of the muscle, and blood volume remains low for the remainder of the contraction. Between the echo bike and deadlift we see blood flow returning to the spinal erectors in conjunction with oxygen being resupplied. Then during the deadlifts we see an initial compression reaction followed by a venous occlusion, which indicates a stronger contraction force where venous outflow from the muscle is restricted. Because arterial blood is still entering the muscle this creates a ‘pooling’ effect in the muscle as well as the feeling of a muscle ‘pump’. At this point the athlete experienced their back ‘blowing up’. Finally, we see that during the wall balls this athlete gets another compression reaction. Note that muscle oxygen saturation stays depressed through both the dealifts and the wall balls, which is associated with muscle fatigue and reduced muscle endurance capabilities. This is a case where the observed response very closely matches what was reported in the literature.
Venous occlusion is when muscle tension restricts the outflow of blood from the muscle. This occurs over tens of seconds to minutes and upon the release of tension blood is able to leave the muscle. Now that we’ve identified a potential issue the next step will be to assess other athletes that struggle with this problem and then create an intervention to try and address it. While the obvious answer may seem like doing more back extensions, high rep hinging, and so forth that is seldom an effective long term solution for addressing this issue.
In order to determine what protocol is effective for solving a problem, it’s important to understand WHY the problem is occuring in the first place. Part of the way I make sense of coaching is through analogies. This problem reminds me of a lesson that I learned when reading a computer science textbook. In the section on algorithms there was a snippet that read “when we try to find an algorithm to solve our problem we should check that our problem meets the requirements of the algorithm, otherwise the algorithm won’t work.” Because computers can't talk they can’t tell us whether or not we’re selecting an appropriate algorithm. So, if we implement an algorithm it will still execute it’s steps even if it doesn’t make sense to do so and it will produce a nonsense answer. It’s up to the coder to make sure they’re using the right tool for the job. This isn’t dissimilar from coaching. We may be able to see that an athlete’s lower back blows up when they do high rep deadlifts, and as a result we might give them more high rep deadlifts in their training. The athletes are like a computer — they will carry out the ‘algorithm’ whether or not it makes sense to do so, and like the computer they may produce a nonsense answer — in this case, that means not improving what they wanted to improve.
As a coach it’s up to us to make sure they’re using the right tool for the job. One of the great things about technologies like NIRS is that it helps us parse out how tools work and if they’re getting us the desired result. After identifying athletes that struggle with their lower backs blowing up I tried out a handful of different methods, then I monitored week to week NIRS trends to see if they were acquiring the desired adaptations or if we missed the mark. Once I found some protocols that seemed to be working I tried them out on other clients who struggle with the same issues and I'll observe if I get the correct gross outcome. If the protocol then seems promising I'll start experimenting with different ways of tweaking it and modifying it with my coaching clients and eventually these protocols trickle down into my coaching practice as well as written content, like this article. Below I've posted a sample concept model to help you determine the causes of lower back muscle fatigue in an individual, followed by a practical step by step ‘algorithm’ you can work through to determine how you can solve this problem in a given individual. Despite the fact that the bottommost concept model is written with high rep hinging in mind, the same type of decision tree can be applied to any movement that a Crossfit athlete struggles to make ‘cyclical’.
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