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Determinants of Durability

Spragg, Leo & Swart (2022) The Relationship between Physiological Characteristics and Durability in Male Professional Cyclists. MSSE.

TLDR: Durability is emerging as a determinant of cycling performance. In U23 Continental riders, the decline in critical power after a fatiguing protocol was associated with classic markers of aerobic fitness, and higher carbohydrate oxidation rates were associated with greater decreases in W'. Training volume may be an important contributor to improving durability.


Previous research has shown that changes in physiological profiles (e.g., a reduced ability to produce power in the fatigued state) following prolonged riding impact on race results.

Successful climbers are better able to maintain their 5-20 minute power and top sprinters are better able to maintain their 20 second power at the end of races.

As more research highlights the importance of durability for endurance performance, little is known about what physiological characteristics underpin durability (e.g., metabolic, substrate depletion, neuromuscular, bio-mechanical etc.).

The aim of the study was to investigate if lab-based physiological measures could explain the differences in the power-duration relationship in the fatigued state.

What did they study?


10 U23 professional cyclists (UCI Continental Team)

VO2max = 74.4 mL/kg/min

Critical power = 5.6 W/kg (340-440W)

W' = 23.7 kJ


1 x lab-based graded exercise test

1 x fresh critical power test

1 x fatigued critical power test

They used the 3 and 12-minute critical power/W' testing protocol. In this test you complete a 3-minute max effort, recover for 40 minutes, and complete a 12-minute max effort. You can then use your 3 and 12-minute power values to estimate your critical power and W' using a calculator.

For the fatigued critical power test, they asked the riders to complete the following fatiguing protocol:

Warm up (20 minutes)

Complete 5 x 8 minutes @ 105-110% critical power (8 minute recovery)

Ride easy (40 minutes)

Complete the fatigued 3 and 12-minute critical power testing protocol

What did they find?

Critical power decreased by 11 W and W' decreased by 4.7 kJ in the fatigued state.

There was a positive relationship between changes in critical power and markers of aerobic fitness (VO2max, ventilatory thresholds, and efficiency). I.e. higher VO2max values were associated with smaller decreases in critical power in the fatigued state.

There was a negative relationship between changes in W' and carbohydrate oxidation at 300W. This means that riders with higher carbohydrate oxidation rates showed greater decreases in the W' under fatigue.

What can we learn from the study?

The associations between markers of aerobic fitness (VO2max, sub-maximal thresholds, and efficiency) and durability suggest that continued aerobic development may support improvements in durability. This lines up with personal observations from athletes I work with - those with better developed aerobic capacities tend to maintain their performance across prolonged durations.

You might say, well isn't continued aerobic development the goal of nearly every endurance training programme in the world? And you'd be right. So, the question is which elements of training programmes can we manipulate to specifically target improvements in durability?

The authors suggest that the findings of the study, along with a previous paper from the same group, suggest that training volume is an important contributor to improved durability - potentially via improvements in efficiency and fat oxidation.

The relationship between fat utilisation and durability suggests that improving fat oxidation helps to spare muscle glycogen, which may contribute to smaller decreases in critical power and W' after prolonged exercise.

When we compare the results of this study to previous studies looking at how prolonged exercise impacts on critical power and W', elite U23 cyclists display a smaller decrease in critical power following prolonged exercise compared to recreational cyclists (elite 3% vs. recreational 11%). So, we need to take the performance level into account when thinking about changes in performance under fatigue.

Testing your durability

To determine your own durability or fatigue resistance, you can implement the same (or similar testing protocol) used in this study:

1 x fresh critical power test

1 x fatigued critical power test

For the fatigued critical power test, you could use the 5 x 8 minutes @ 105-110% CP (8 minute recovery) used in the study, or you could design your own fatiguing protocol with intervals that are relevant to the events you are competing in.

The fatigued critical power test looks like:

Warm up (20 minutes)


Ride easy (40 minutes - this is important to replenish your W')

Complete the fatigued 3 and 12-minute critical power testing protocol

If your training/racing involves long climb of 15-20 minutes, then your fatiguing protocol could be: 2 x 15 minutes @ critical power (10 minute recovery).

If your training/racing has repeated short efforts, then your fatiguing protocol could be: 10 x 1 minute @ 150% critical power (5 minute recovery).

One key point here is to try and prescribe your fatiguing protocol as a % of critical power - this helps maintain a similar relative intensity and ensure you are in the same exercise intensity domain.

Thanks for reading and if you have implemented this fatiguing protocol, get in touch and let me know how you get on!


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