The New Science of “Fatigue Resistance”

When the lab data from the Nike Breaking2 marathon project was finally released last fall, the most interesting findings were the “dog that doesn’t bark at night” variety. Among a group of some of the greatest distance runners in history, none of the standard physiological measurements – VO2 max, lactate threshold, running economy – gave any serious abnormal values. To understand why these runners did so well, the researchers might need another variable: fatigue resistance, which they defined as the “degree of deterioration of the three.” [other variables] over time.”

Interestingly, the same new variable appears in a new analysis of professional cyclist performance data. An international research team led by Peter Leo, a doctoral student at the University of Innsbruck, and James Spragg, a British cycling trainer, have figured out the numbers of a group of elite and professional cyclists in a five-day race called Tour of the Alps. The best predictor of race performance, level of competition, and event specialty wasn’t the raw performance or heart rate data – it was fatigue resistance again.

The subjects of the new study, which was published in the International Journal of Sports Physiology and Performance, came from three European cycling teams: Tirol KTM, Bora Hansgrohe and Androni Giocattoli-Sidermec. The 14 participants from Tirol KTM were all U23 riders who took part in the development of the continental cycling competition. The ten participants in the other two teams were professionals. There are many ways to compare the two groups of riders, from simple observations (the pros were shorter and lighter than the U23 riders) to complex analyzes of their “performance profile” (the highest performance achieved for various periods of time from five seconds to five Seconds is maintained) 30 minutes over the course of the five-day race).

The performance profile can tell you a lot of useful things about your strengths and weaknesses as a driver. If you’re really good at sustaining a sky-high performance for five seconds, this is a good sign of your ability to win sprint finishes and cover sudden moves during the race. If your 30 minute performance is unusually good, it suggests that you may be a climber or a time trialist. Overall, the performance profiles turned out to be almost perfect, in which order the drivers finished and how far they lagged behind the leaders.

However, there was a surprise in the performance profile data that was somewhat reminiscent of Breaking2’s VO2 max data. When comparing the U23 drivers with professionals, there were no significant differences in the performance profiles of the two groups – with the minor exception of the five-second performance, which was actually higher in the U23. Similarly, when comparing different types of cyclists such as climbers and all-rounders, there were no significant differences in performance profiles.

The standard performance profile was created by searching each driver’s data for the entire five-day race to find, for example, the five-second window with the highest average performance. The same goes for ten seconds, 15 seconds, and so on up to 1,800 seconds (ie 30 minutes). However, you can do a similar analysis while narrowing your search to the five-second maximum power produced after, say, 1,000 kilojoules of cycling that day. According to Leo, a typical professional cyclist can collect 800 to 900 kilojoules of work during an hour of training and up to 1,500 kilojoules per hour during a race.

Therefore, the researchers repeated this process to create separate performance profiles for the drivers after 1,000, 1,500, 2,000, 2,500, and 3,000 kilojoules of work. This is what the resulting performance profiles looked like for the professionals compared to the U23 drivers:

(Images: International Journal of Exercise Physiology and Performance)

As would be expected, the maximum powers are highest for the short bursts (on the left side of each graph) and lowest for the longer periods of time (on the right side). For the professionals, the lines are usually bundled one above the other. This means that even if you’ve been riding pretty hard for a few hours, you can get up almost as quickly as possible for a minute or two if they’re fresh. Only when extremely tired after 3,000 kilojoules of work does the sprint performance decrease noticeably.

In contrast, the performance profiles for the U23 drivers are much more distributed. Even after only 1,500 kilojoules of work, your ability to sustain intense exertion is noticeably impaired. In other words, it’s fatigue resistance that sets professionals apart from U23s.

You will see something similar when you compare different driver styles. The way they split up drivers is a little tricky. First, they used size, weight, and body surface area to divide them into climbers (small, light cyclists who are ideal for pedaling in the Alps) and all-rounders (taller, more versatile cyclists who are good at sprinting and time trials in addition to climbing) . . Then they divided the climbers into GC (General Classification) drivers, who came in the top ten overall, and Domestiques, who placed outside the top ten. This is what their performance profiles looked like:

Fatigue Resistance-Diagrams-2.jpg(Images: International Journal of Exercise Physiology and Performance)

The difference is even bigger here. The GC drivers – those who hope to actually win multi-stage races – have practically no difference in their performance profile even after 3,000 kilojoules. The less accomplished domestics show a much greater fatigue effect. And the all-rounders have the greatest drop in performance, which is why they probably won’t be awarded the contract to win the overall race. You can only win a tiered tour if your fatigue resistance is exceptional.

There are a number of nuances to consider. For one, this data was collected during a race in the real world. This means that the performance data will reflect the tactics used by each team and the progression of each stage. During an early outlier period, no one really needed to exhaust their five-second strength. And the role of each driver has an impact on the resulting performance profiles: the differences between GC driver and all-rounder profiles can be partly due to the jobs assigned to them.

Quantifying fatigue based on the number of kilojoules consumed is also a very clear measure. If you drive at a constant 250 watts for an hour, you will use 900 kilojoules. But also cruises with 230 watts and a few one-minute voltage peaks with 600 watts. The latter is likely to ruin your legs far more than the former, and professional stage racing is full of sudden changes between low and high intensity.

This complexity makes it difficult to figure out why some drivers have better fatigue resistance than others. After all, fatigue has many different components: metabolic disorders in your muscles, altered signals from your brain and through your spinal cord, depleted motivation and cognitive resources. The exact mix of these components at any given point during a five-day race varies widely. Hence, it is not clear what superpower the GC drivers have that allows them to shake off a few hours of hard driving.

When I asked Leo how he could develop fatigue resistance, he still had some practical suggestions. One of these is that a lack of carbohydrates appears to decrease fatigue resistance – an observation that is in line with other data from the Breaking2 project, which found that consuming 60 grams of carbohydrates per hour improved fatigue resistance. In training, Leo and his colleagues hypothesize that the volume of training you do is more important than the intensity in developing resistance to fatigue. And you could try including intervals or sprints towards the end of a long ride, he suggested: four x 8:00 hard with 4:00 recovery after three to four hours of low-intensity driving, for example.

There are currently more questions than answers about fatigue resistance. But I suspect we’ll do a lot more research on this in the years to come. “Long-term endurance events,” Leo emphasizes, “are about how to perform in a tired state and not in a fresh state.”

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Main photo: Dylan M Howell Photography / Stock

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