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Make Sure You’re Tired for Your Next Fitness Test

James Spragg is a young South African exercise physiologist who has carved out an interesting niche for his research. It is based on the idea that the fastest athlete on fresh legs is not necessarily the fastest athlete on fatigued legs, which is an important distinction, as in most endurance races, it is better to be the guy or gal who is fastest on fatigued legs. Yet conventional fitness testing protocols ignore this reality, which is a problem, because it has the potential to skew athletes’ training too far in the direction of improving fresh-legged performance.

In one of his early studies, Spragg teamed up with several other researchers, including Iñigo Mujika, whose name you might recognize from his work related to the 80/20 intensity balance, to compare power profiles in nine members of a U23 cycling team and five professional cyclists. Interestingly, they found that the U23 riders were able to generate as much power as the pros on fresh legs. Had this experiment been limited to non-fatigued performance testing, we would have been left to wonder why the U23 cyclists were not also on professional teams. But what Spragg and his collaborators also found was that, in U23 cyclists, achievable power outputs began to decline after 1,500 to 2,000 kilojoules (about 3,600 to 4,800 calories) of prior work was completed, whereas in professional cyclists, performance fell off only after 3,000 kJ of pedaling.

What’s more, a later study by Dutch and South African researchers found that, among top-tier professional cyclists, those able to do the most work before their power output capacity dropped off performed best in races. So, it appears that the ability to ride fast on tired legs is a key factor separating the best from the rest, both between and within echelons of cycling.

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Spragg’s recent study is also his most ambitious to date. It involved collecting power data from every training ride and race completed by 30 U23 professional cyclists over three years. The aim was to determine how individual cyclists’ fresh and fatigued power profiles changed over the course of a competitive season and how these changes related to their training. The main findings were as follows:

  • Fresh power profiles remained relatively stable throughout the season.
  • Fatigued power profiles changed over the course of the season.
  • The difference between fresh and fatigued power profiles also varied as the season unfolded, indicating that the two phenomena are independent.
  • More time spent at low intensity in training predicted better 2-minute power on both fresh and fatigued legs.
  • A shift away from moderate intensity toward high intensity was associated with a stronger fatigued power profile (i.e., a smaller delta between fresh and fatigued power)

An important implication of these findings is that, depending on the type of event an athlete is training for, performing fitness testing in a fresh state may be of limited value. If you specialize in the 400m freestyle event or the 1500m track event, then perhaps testing in a fresh state has greater relevance. But if you’re training for a marathon or an Ironman 70.3, I would imagine that fatigued fitness testing would tell you more. In a narrative review published in October 2021, Spragg, Mujika, and three other colleagues provide detailed recommendations for incorporating fitness testing into training for road cycling events, one of which is to “avoid single effort prediction trials, such as functional threshold power.” As a running and triathlon coach, I personally lean toward using regular workouts to assess fitness. For example, tacking a fast finish onto the end of a long run serves as a good measure of fatigued performance capacity in a marathoner while also functioning as a relevant fitness-builder for the marathon.

Another interesting finding from Spragg’s 2022 study is that cyclists who maintained their peak training load through the late season also maintained their fatigue resistance, whereas those who reduced their training load during this period lost fatigue resistance. This finding is consistent with other studies reporting a correlation between training volume and fatigue resistance/endurance. One example is a 2020 study byThorsten Emig of Paris-Saclay University and Jussi Peltonen of the Polar Corporation, who collected and analyzed training and racing data from devices worn by more than 14,000 runners for a combined 1.6 million exercise sessions. For the purposes of this experiment, endurance was defined as the percentage of VO2max running velocity that a runner could sustain for one hour, and the data showed a strong positive correlation between training volume and endurance thus defined.

I wish all of this science had been available when I wrote 80/20 Running back in 2014. It would have bolstered the argument I made therein about how the typical exercise science study design puts a thumb on the scale in favor of HIIT-focused training when compared against the type of training elite endurance athletes do. It’s less of a problem nowadays, but back then it was common to use fresh-legged VO2max tests as the basis for such comparisons. But we now know that a VO2max test performed after extensive prior exercise is likely to yield different results that are more relevant to real-world race performance, and that high-volume, mostly low-intensity yields better results in pre-fatigued fitness tests.

Oh, well. That’s what second editions are for, right? In the meantime, you can check out our cycling plans here – some are built to improve your FTP and can be used in your off season.

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