The Impact of Fatigue and What Determines This?
by Doug Stewart
I have written a number of times about the impact of fatigue on endurance performance, the most recently here, discussing its effects across the Moderate, Heavy and Severe exercise intensity domains.
A recently published paper took 12 male professional cyclists and explored the impact of fatigue on their 20-minute time trial performance. The average age of the cyclists was 26. They had an average VO2max of 83, and a 20-minute power output of 386w – so these are extremely talented riders!
The researchers had the athletes complete several 20-minute time trial tests. The initial test aimed to determine their average power outputs over the 20 minutes when the cyclists were fresh. As mentioned, across the 12 cyclists the average power output was 386w.
Then, to assess the impact of fatigue on this 20-minute power output, the cyclists were asked to ride for 4 hours at an endurance effort (so not hard) and then complete the same test. Their average power over this second 20-minute time trial was 375w. So, on average, they lost 11w, or 2.9%. However, at individual levels, there was a range from an 8.5% decrease to a 1.1% improvement.
In addition to the time trial tests, the cyclists were also assessed on a ramp test for their thresholds, peak power outputs and their VO2max. What was interesting in the findings was that these traditional style physiology tests were not indicators of how much power the cyclists lost when fatigued. Furthermore, their training data for the 4 weeks prior to the test period was assessed. Again, there was no correlation between this and the drop-off in power.
One reason for this may be that 4 weeks it too short a period of training to find any correlations.
However, the researchers conclude that there may need to be specifically designed tests to determine the durability of elite cyclists.
Other research has discovered that, with 10 younger cyclists (19 years old) with an average VO2max that was lower than that of the first group (74.4), physiological testing did have an impact in assessing their durability.
In this paper, the researchers explored the decrease in Critical Power when fatigued. This was linked to the cyclists’ peak power ouput, VO2max and power output at different thresholds. They used a different approach to fatigue the cyclists - a ride with five x 8 minute hard efforts.
Also, it is worth flagging that the Critical Power tests involved a 3-minute and 12-minute block at maximum effort (once when fresh, and once when fatigued), which is different from the 20-minute time trial completed in the first study.
For all endurance sports, durability is important, as often in longer events the winner is the one who slows down the least. Therefore, being able to determine indicators of what impacts this would be helpful for endurance athletes and coaches. It may be that the difference in the cyclists’ age and ability, or the testing protocols used (20 min time trial versus Critical Power), or the fatiguing approach adopted (5 x 8 minutes harder versus 4 hours endurance riding), or a combination of all of these factors led to differences in the findings in these two studies. However, for endurance athletes, it is great to see these areas being researched and creating debates amongst sport scientists. Hopefully, more interesting and consistent findings will emerge in the coming months.
From everyone at TMR Coaching, wishing you a wonderful Christmas.
References:
Spragg J, Leo P, Swart J. The Relationship between Physiological Characteristics and Durability in Male Professional Cyclists. Med Sci Sports Exerc. 2023 Jan 1;55(1):133-140. doi: 10.1249/MSS.0000000000003024. Epub 2022 Aug 12. PMID: 35977108.
Valenzuela, P. L., Alejo, L. B., Ozcoidi, L. M., Lucia, A., Santalla, A., & Barranco-Gil, D. (2022). Durability in Professional Cyclists: A Field Study. International Journal of Sports Physiology and Performance, 1(aop), 1-5.