Physiological Impact of Cyclocross Racing
With the cyclocross season in full swing, I thought it would be fun to dive into the physiological impact of cyclocross racing. Anyone who has raced or watched cyclocross, knows that it consists largely of anaerobic/explosive effort. Races start out at a full sprint, followed by a series of short hard efforts, as riders navigate the various aspects of the track (corners, hills, adverse cambers, etc).While power has become the mean measurement of a cyclist output (for good reason), when it comes to cyclocross heart rate is perhaps the most accurate method of measuring the physiological impact of the race.
If you watch any European cyclocross race, you will notice that as soon as the riders cross the line they click a button on their wrist watch.The watch is a heart rate monitor and the riders are clicking the button to mark the end of the race. Even though those riders train and sometimes race with power meters, it is clear that they value the heart rate data more than anything else. As we dive into the physiological impact of cyclocross racing, we will also take a look at the data from other disciplines in cycling i.e. road, mountain, criterium.
What does the Research Say?
I was only able to find one paper that specifically looked at the physiological impact of cyclocross racing*. A 2017 study entitled Physiological Response to Cyclocross Racing (Carmichael et. al.) took a look at the intensity profile of cyclocross racing. They used heart rate (HR) data from a lab session as a baseline for their riders.
If you’re interested in the nitty gritty, the paper is available online, but I just wanted to highlight a few points and observations they made that I think are applicable to this article. The one major caveat for this study is that the subjects were not elite racers. The subjects were cyclocross racers classified as category 2 or 3 according to USA Cycling. In European terms, these riders are just below Elites without contracts.
Methods
Each subject completed a laboratory and field testing session. During the laboratory testing session, peak oxygen consumption (V̇ O2peak) was determined and HR and [La- ] were measured during a graded cycling exercise test. Heart rate and [La- ] values from the laboratory test were then used to identify HR at the following exercise intensities:
- Low (HR below 2 mmol. L-1)
- Moderate (HR between 2 and 4 mmol. L-1)
- High (HR above 4 mmol. L-1)
During field testing, subjects participated in an actual cyclocross race. HR was monitored throughout the race, and time in LOW, MOD, and HIGH was based on laboratory data.
I like that this study used HR versus power. In terms of power, cyclocross is very punchy. However, HR can stay elevated throughout the entire race. If you watch (no pun intended) closely as riders cross the finish line at the end of the race, they’ll push a button on their watch that’s recording HR. On one episode of Curtis White’s In the Red podcast, he discusses this in detail. As you can see from the figure below, power is constantly up and down, but HR is relatively consistent (and elevated).
Race Data
The subjects raced a typical category 2/3 cyclocross race of roughly 45 minutes. As you can expect from the sample figure above, the subject’s HR went up very quickly and stayed elevated throughout the race. Here’s the breakdown of the time spent in the three HR “zones” (on average) for the subjects:
- Low: 9 seconds or 0.4% of the race
- Mod: 2:32 or 6.1% of the race
- High: 39:39 or 93.6% of the race
HR increased immediately at the start of the race and remained elevated for the duration of the effort. Subjects had an average HR of 176 beats per minute (bpm) and a HRmax of 186 bpm while participating in the race. In comparison, while participating in the laboratory, subjects recorded a HRmax of 183 bpm.
HR Comparison Across Disciplines
The V̇ O2peak of the male subjects (68.6 mL.kg-1.min-1) indicated a high level of fitness, but was lower than values reported for elite male road cyclists and mountain bikers. Again, it should be noted that the subjects were category 2 and 3 riders. While the study says they’re not elite riders, in the US the category 2 riders generally race in the Elite race. In fact, at the US National Championships, 34% of the field were category 2 riders.
In their review, Lucia et al reported values between 70 and 80 mL. kg-1.min-1 for professional road cyclists. Impellizzeri and Marcora reported values between 66.5 and 78 mL.kg-1.min-1 for elite cross-country mountain bikers. Lim et al evaluated the intensity of a criterium race. Not surprisingly, the exercise intensity of the criterium race was higher than the road race (Time in High = 63%), but the effort was still far lower than what we saw during cyclocross racing (Time in High = 93.6%)
Here’s a direct comparison of the subjects of this study, versus the male subjects of the other ones:
Road Race | Criterium | MTB | Cyclocross | |
LOW | 57% | 10% | 18% | 0.4% |
MOD | 10% | 27% | 51% | 6.1% |
HIGH | 33% | 63% | 31% | 93.6% |
Closing the Research Gaps
As previously mentioned, one of the issues with this study is that they did not test professional cyclocross racers. While I believe the results would be the same, we cannot directly compare the four studies in a scientific manner. Therefore, there is room to expand on this study by looking at athletes on a similar level across disciplines. Ideally, the study would use the same athletes across the four disciplines in the same year.
Unfortunately, I do not have that kind of data for myself. Having only done two XC MTB races in my life and most road races disappearing in PA, my data is not from the same year. However, I still decided to dissect it and see how it compares to the study referenced above.
A Quick Breakdown of the Races
Road Race
The road race was a relatively straightforward loop with two high speed turns and one 180 degree turn. There was a tricky chicane (hence the last lap crash I had to avoid) before a short, punchy, uphill drag to the line. Total race time was just over two-hours for 50 miles. It was the second day of a stage race, so I just chilled in the pack and waited for the finish.
Criterium
This criterium was typical for Eastern PA. It had one punchy climb and a few rollers, but was most flat and wide open. We completed the 30mi race in 1:10. This race is indicative of my racing style with lots of attacks, bridging, and general agressiveness. There was plenty of time spent in the pack as well.
MTB
For the mountain bike race, it was a typical East Coast style course, with punchy climbs and plenty of rocks and roots. The race was about two-hours long, but a mechanical forced me to take a break mid-race while I fixed it. This obviously caused a significant HR drop.
Cyclocross
The cyclocross course was very flat, high speed and wide open. It was a large field and I had a poor start position, so it was about constantly moving up and taking risks. The race was just under one-hour and I pushed it the entire time.
HR Comparison
Below is the heart rate comparison chart for the four different races I competed in. The percentage of the studies mentioned above are in parenthesis.
Road Race | Criterium | MTB | Cyclocross | |
LOW | 6% (57%) | 1% (10%) | 10% (18%) | 1% (0.4%) |
MOD | 53% (10%) | 17% (27%) | 23% (51%) | 1% (6.1%) |
HIGH | 42% (33%) | 82% (63%) | 67% (31%) | 98% (93.6%) |
As you can see, my numbers for the cyclocross race almost match up completely. The criterium and MTB races are similar in terms of relative time spent in the three zones. As I expected, the major outlier is the road race.
While this particular road race was flat and I spent time in the pack, it was the second day of a stage race. In addition, there was a yellow line rule in effect, so there was not a lot of room to maneuver when things got sketchy. I think both of those factors contributed to the significant amount of time in the moderate zone.
I rode the crit very hard, which explains why there was so much time in the high zone. It was a very aggressive race on my part so there were a lot of super hard efforts, keeping the heart rate high.
What Does This All Mean?
Based on the scientific and anecdotal data, it is clear that the physiological impact of cyclocross racing is largely anaerobic. A majority of riders spend around 90% of the race high zone ( (HR above 4 mmol. L-1). While we must not ignore the value and necessity of base training, we must also be aware that power numbers alone do not tell the whole story. Looking at power data, you will see short, high bursts of power, closely followed by periods low to no power. This will repeat for the duration of the race. However, in those periods of lower power, cyclocross riders will continue to have a significantly high heart rate. Therefore, the physical impact is significantly more than what the power numbers are telling us.
When looking at this compared to other types of racing, there are some similarities. However, as you can see from the tables above, there is significantly more time spent in the low and moderate zones for road, criterium and MTB races. Thus, the physiological impact tends to be significantly lower than cyclocross. From my personal data, you can see that mountain biking and criterium racing have a similar physiological impact when compared to cyclocross racing.
Tweak Training Based on Comparison Data
While each rider will differ, looking at the physiological impact of racing measured by heart rate, we can help better shape a rider’s training. For instance, in the six to eight weeks leading up to the cyclocross season, it would be a good idea for me to do a mix of criterium and MTB racing. While there is value in me doing some road races, as we approach the specificity of cyclocross preparation, criterium and MTB racing generate a similar impact.
In the end, it is clear that as coaches and riders we should look beyond power when training and preparing for cyclocross racing. While looking at power numbers in a race can be beneficial, the measurement of the physiological impact of cyclocross racing is better analyzed with heart rate data. With that said, either way you look at it, cyclocross racing gets the ride into their threshold/anaerobic zones and never backs down.
* A second study was recently released, but I have not read and disseminated it.
References
Ryanne D. Carmichael, David J. Heikkinen, Elizabeth M. Mullin, Nolan R. McCall (2017) Physiological Response to Cyclocross Racing
Lucia A, Hoyos J, Perez M, Chicharro JL (2000) Heart rate and performance parameters in elite cyclists: a longitudinal study.
Impellizzeri and Marcora MTB
Lim, A. C. , Peterman, J. E. , Turner. B. M. , Livingston, L. R. (20122)
Comparison of male and female road cyclists under identical stage race conditions