Specific physiological testing during a Hyrox race

Specific Testing during a Hyrox race

Testing Hyrox athletes during Hyrox training for maximum improvements

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The human body is extremely specific and adaptable. One of the most important principles within sport and rehabilitation is the SAID principle, which is an abbreviation of "Specific Adaptations to Imposed Demands". The body becomes better at performing exactly the type of work it is exposed to. If the body is exposed to a lot of running, it becomes better at running, but not necessarily at cycling.

If you dive further into the exposure and look at what type of stimuli the body is exposed to, it is precisely the output of this, that is improved:
If you run short and fast, the physiological processes required for this are improved.
If you run long and slowly, the physiological processes required for this are improved.
…You get the point.

However, there is an overlap in these physiological adaptations. Some of the effects also benefit other than exactly what triggered the adaptation. For example, slow prolonged running (Zone 2) can also benefit top speed and short-term maximal performance. This is because some of the adaptations that occur with this type of stimulation enable the body to perform at a relatively higher intensity without burning out.

But why this long introduction about the SAID principle when the blog post is about specific physiological testing during performance in a Hyrox race?

When we know how specific the body is in the adaptations it makes based on the stimuli it receives, then it clearly makes the most sense to be specific in the tests that are carried out. 
With data that shows exactly what happens in the body during the exact work we want to improve, we can create a training plan with the most targeted effort.

We have therefore prepared a test protocol targeted at Hyrox athletes.

A Hyrox race requires many different skills, and to win the race you need to have a high performance at all the stations and runs.

In order to clarify where the individual athlete's strengths and weaknesses lie, we have structured our performance test so that we gain insight into all the physiological biomarkers during a Hyrox race, which clarifies the athlete's limitations as well as strengths.

With this insight, a concrete training plan can be drawn up to purposefully improve the physiological processes needed to perform even better.

Example of a physiological Hyrox performance test

So to best determine the physiological demands of a Hyrox race, we set out to perform the actual event with our VO2Max equipment, while simultaneously performing lactate tests after each run and station. By doing that, we have gathered a large amount of data, useful for determining how to best improve an athletes performance, and optimize their training. The following is a brief walkthrough of some of the data gathered during the Copenhagen Hyrox race 2024.

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Analysing the data

Hyrox nino - Lactate - HR - Time.pngOxygen levels (VO2), Carbondioxide excretion (VCO2), Lactate measurements, Heart rate, Time pr. station for all 8 runs and 8 stations

VO2 and VCO2

When looking at the VO2 intake and CO2 excretion during the race, we see there is a large increase in both right from the start. This is most likely due to "pre-race hype", which causes the athlete to start with too high of an intensity. Later in the test, a significant decrease in both VO2 and VCO2 is seen.  This is most likely due to a lack of carbohydrate (energy) availability, stemming from our test subject having had a less than optimal diet leading up to the race. A lack of carbohydrate availability can cause a decrease in performance intensity, due to the body not being able to produce the energy needed at higher intensities. A shift from carbohydrates as the sole provider of energy to the body, to a mix of carbohydrates and fats as energy providers, leads to the athlete having to decrease the pace, to make sure the body is getting the energy needed for the task at hand.

An example of the intensity decrease can clearly be seen during the runs, as the fastest run is at 4:48 min/km and the slowest run is at 6:27 min/km.

When working for a longer period of time, we optimally would like to see the athlete having an oxygen surplus for the main bulk of the race, as this allows the body to save carbohydrates, and utilize the fat oxidation to provide energy for as long as possible, as we then will be able to utilize our limited amount of stored carbohydrates for when the athlete needs to be able to produce energy at a rapid pace, i.e. when they reach a point where the race gets really tough. Unfortunately this is not the case during our test-race, as we can see our athlete becomes oxygen-deprived from the start, which undoubtedly has a negative impact on the performance later in the test. This most likely happens due to an non-optimal warmup where the body never had a chance to adapt to the upcoming work, and therefore had to use the first run as a place to get into a steady state.

Regardless of the start and the oxygen-deprivation seen here, we see that as the race moves along there is an upward development in the oxygen uptake relative to the CO2 excretion and the athlete gets an oxygen surplus again. This stage starts when the athlete performs the burpee broad jumps. This happens because the total work intensity is lowered, due to the athlete only having to move their bodyweight (not push or pull a sled), while simultaneously getting short breaks, when his partner was working. From this point onwards we see a negative trend in the athletes performance, with their paces dropping drastically during the runs, and in relation to that, lowering the body’s need for oxygen, making the overall oxygen consumption drop. 

When looking at the running vs. the stations we see that all runs raise the VO2 and VCO2, while all the stations lower them. This is because running generally has a quite high oxygen intake demand, due to the constant work and nature of running.
The stations, on the other hand, all have small breaks while the partner works, but also in the workload itself (i.e. sled pull, where there is a short break between each move).



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Blood lactate concenrations after each stations of the race.

At the stations, however, the power output/strength requirement is more prominent, which is clearly seen in the blood lactate, where it rises significantly (i.e. sled push and walking lunges).

This is because, for our athlete, it is all-out effort work, which results in a lot of anaerobic work and thereby a high lactate production.

After station 2 & 3 (sled push & sled pull), the blood lactate concentration drops within every run. This is due to the fact that the athlete is far more adapted to running than to the workload of the stations. Here the specificity of the SAID principle is clearly seen.

Overall, there is a tendency for the athlete to lower/clear the blood lactate during running, but increases it at the stations. This is consistent with the fact that this athlete is far more experienced with running than with the more strength-demanding stations, so for his upcoming training, a heap of strength training, and later on more Hyrox specific movements would be programmed for this particular athlete.

However, a large increase in lactate is seen during the first 1 km run. This is due to a combination of "pre-race hype" high adrenaline level and minimal warm-up, which causes energy turnover from the anaerobic processes and thus increase in lactate level. 

The reason for this is that there is not enough oxygen present to convert pyruvate (the end product of glycolysis) to Acetyl-CoA so it can enter into the Krebs cycle and further oxidize it’s molecules to enter the electron transport chain, where energy is formed. The body is simply put too slow to deliver oxygen to the muscles at the start of the race/test.

In addition, a large amount of energy is simultaneously generated via the anaerobic breakdown of ATP.

It takes several minutes of "steady" work (sub-max) before hydrogen production and the associated beta-oxidation and ATP production become proportional to the given work.


Heart rate


Looking at the heart rate a large increase is seen in the first run. As mentioned above, this is due to "pre-race hype", and the body needing to adapt to the working condition it is given.

After that, the heart rate is relatively constant for the rest of the race, with a few fluctuations, when there are longer breaks at the stations where the partner does the work, or our athlete simply is more efficient at the movement at hand.

Overall the heart rate is slightly above this particular athletes threshold, which agrees well with the athlete ending up having to decrease his pace, and being unable to keep his intensity.

For further information about our data, or any other interests regarding physiological testing, training or how we can use these data to improve your performance and training, don’t hesitate to reach out to us.

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