The Impact of Fatigue on Performance
by Doug Stewart
A recently published paper provided an updated framework for fatigue and performance. Within this framework, the authors discuss how fatigue is psychophysiological – meaning that there is a performance decline from elements linked to physical factors, and then also an element linked to one’s own perception of fatigue.
Performance fatigue and perception of fatigue are interdependent and influence one another. This therefore makes fatigue both physical and psychological, with a number of dimensions that can impact performance.
Another recently published paper set out to explore the physical element of fatigue in relation to exercise intensity. They used the gas exchange threshold, so between the moderate and heavy intensity exercise domains.
This graphic from Poole et al., 2021 helps illustrate the varying definitions and thresholds:
Common thresholds that have been considered, though not unequivocally, to partition the primary exercise intensity domains: moderate, heavy and very heavy/severe
Source: Poole et al., 2021
As you can see on the graphic above, the gas exchange threshold (GET) is when the lactate begins to rise and represents the boundary between moderate and heavy domains.
In the fatigue research, 17 male athletes participated in a series of cycling tests at 110% of GET (in the heavy domain) and at 90% and 70% (moderate domain) for 90, 110 and 140 minutes respectively (so the total work matched across the various tests).
A number of tests, including maximal strength for a leg muscle, were completed prior to the cycling and then throughout, and upon completion of the cycling tests. The design of the research was in part assessing how the participants’ maximum strength test was impacted during the cycling at the various intensities.
When cycling in the moderate domain (70% and 90% of GET) there were similar reductions over the course of the test in maximum strength (-14% on average for both conditions). However, during the 110% of GET (heavy domain above the threshold) the loss in maximum power was 25%.
It is important to remember that, in the 110% test, the participants cycled for less time but lost more strength.
Therefore, it appears that the lack of difference in performance between the two tests completed in the moderate domain (70% and 90% of GET), paired with the large difference between the 90% and 110% (heavy), is of relevance to endurance athletes.
Whilst this research was completed by male participants whilst cycling, it is certainly worth considering for other endurance athletes when looking at training intensity and race pacing, as it has been shown that crossing the threshold has a significant impact on fatigue.
References:
Behrens, M., Gube, M., Chaabene, H. et al. Fatigue and Human Performance: An Updated Framework. Sports Med (2022). https://doi.org/10.1007/s40279-022-01748-2
BROWNSTEIN, CALLUM G.1; PASTOR, FREDERIC SABATER1; MIRA, JOSÉ1; MURIAS, JUAN M.2; MILLET, GUILLAUME Y.1,3. Power Output Manipulation from Below to Above the Gas Exchange Threshold Results in Exacerbated Performance Fatigability. Medicine & Science in Sports & Exercise: November 2022 - Volume 54 - Issue 11 - p 1947-1960
doi: 10.1249/MSS.0000000000002976
Poole, D. C., Rossiter, H. B., Brooks, G. A., & Gladden, L. B. (2021). The anaerobic threshold: 50+ years of controversy. The journal of physiology, 599(3), 737-767.
https://doi.org/10.1113/JP279963