Understanding Fat Oxidation II: Practical Insights and Recent Studies
Introduction
The last blog post (see here: https://www.thethreshold.coach/single-post/optimizing-fat-oxidation-for-peak-cycling-performance-a-comprehensive-guide) explained the basics to understand about fat oxidation. This blog will provide some studies and practical viewpoints that can be used and applied to the training and performance of an athlete for improved performance. At the very least, a better understanding of the latest research in this quite controversial space within exercise metabolism.
Questions that we will examine:
What is the importance of preserving muscle glycogen?
What is durability/fatigue resistance/stamina?
What is the correlation between VO2 max, FTP, and Fatigue Resistance/Durability (Training Component)?
What is the correlation between glycogen stores and Fatigue Resistance/Durability (Nutrition Component)?
Summary
1. Importance of Preservation of Muscle Glycogen.
Maintaining muscle glycogen is important as depletion is linked to fatigue and performance decrement. Athletes need to enhance their fat oxidation, allowing more preservation of this limited fuel source where muscle stores approximately 2400kcal and the liver holds around 375kcal only. By preserving glycogen, athletes can ensure they have an ample supply of this vital fuel available for key race moments. Moreover, improving fat oxidation enables athletes to decrease the quantity of glucose they must carry, as well as potentially preventing gastrointestinal problems.
The Crossover point, as discussed in the previous blog post and illustrated in Fig 1 below, represents the concept of increased fat oxidation. This is the point at which carbohydrate utilization surpasses fat oxidation at higher exercise intensities. This phenomenon helps conserve muscle glycogen and improves fatigue resistance (referred to as durability in scientific literature), enabling athletes to exercise for longer durations or sustain high-intensity performance levels.
Let's further explore the idea of fatigue Fatigue Resistance/Durability below:
2. The Idea of Fatigue Resistance/Durability.
Being able to sustain muscle glycogen and perform well in the final stages of an endurance event is referred to as durability, fatigue resistance, or stamina. It involves maintaining performance levels throughout a given period of time. In Figure 2, it can be observed that the mean maximal power at 5 minutes is 444w, remains at 443w after 500kj, and even after expending 2000kj, there is no decline in power output. This cyclist demonstrates exceptional durability up to 2000kj, but beyond 3000kj, there is an 80w decrease in performance that requires attention. This situation suggests the need to consider both physiological (VO2 max, FTP etc) and nutritional factors to address the decline in performance.
3. The correlation between VO2 max, FTP, and Fatigue Resistance/Durability (Training Component).
As mentioned earlier, improving durability or resistance to fatigue by boosting fat oxidation to conserve muscle glycogen during more intense workouts is a potential performance advantage. Given this, what are the factors that contribute to this improved resistance to fatigue? Should the focus of training be on performance metrics or nutritional aspects? Lets consider previous research on this topic.
Valenzuela et al. 2022 recently published work that took 12 professional male road cyclists and tested their VO2 max and Threshold power in a few different conditions:
Initial Testing:
VO2 max and Threshold tested.
Follow-up testing 48 hours later:
After a 45min warm-up then a 20min time trial
Follow-up testing 48 hours later:
After accumulating around 2800kj of energy use (40kj per kilogram of body weight and 60g/h of carbohydrate intake)
Findings:
20min TT results
With only 45 min warm up average power of the 12 riders | After 2800 KJ energy burn average power of the 12 riders | |
386w | 375w | Loss of 2.9% |
Level of improvement or decrement in performance
More fatigue-resistant cyclists improvement in power from resting to 2800kj testing protocol | Less fatigue-resistant cyclists average decrease in power from resting to 2800kj testing protocol |
+1.1% | -8.5% |
The authors concluded that there was no correlation between fatigue resistance/durability and VO2 max/Threshold physiological parameters
There is no relationship between a high VO2max/Threshold and being a more fatigue-resistant and durable athlete.
However, testing these parameters does reveal the less fatigue-resistant athletes which presents an opportunity for intervention. Having an exceptionally high VO2 max or FTP does not guarantee an athlete will have superior fatigue resistance. Testing is training and training is testing!
4. The correlation between glycogen stores and Fatigue Resistance/Durability (Nutrition Component).
To delve deeper into the idea of fatigue resistance and durability, let's consider the nutritional dimension. In what way does the intake of carbohydrates impact performance and fatigue resistance? Just as we emphasized the training aspect previously, should we also give priority to nutrition?
Cark et al. 2019 published work with 16 competitive athletes and had them perform 3 min all-out cycle test under the following protocols:
(Read about Critical Power (CP) and W'prime test here:https://www.thethreshold.coach/single-post/unlocking-cycling-performance-understanding-critical-power-and-wprime-for-optimal-training)
Only warm-up
2 hours of riding with NO carbs
2 hours of riding with carbs (60g/h)
Before and after the muscle biopsy was used to measure muscle glycogen depletion
Results from the testing (taking into account the muscle biopsy)
2-hour ride with NO carbs | 2-hour ride Carbs | Just warm-up | |
W Prime | 13.8KJ (significant decrease) | 13.5KJ (significant decrease) | 17.9KJ |
Critical Power (CP) | 236w (significant decrease) | 254w | 260w |
According to the results presented and the authors' findings, there is no relationship between the decrease in glycogen and the reduction in Critical Power (CP).
However, the more glycogen decreased, the greater the W Prime decreased
Muscle glycogen is a key determining factor in fatigue resistance/durability for maintaining W Prime (FRC or anaerobic power) which is above threshold power and key to race winning moves
5. Summary
Increasing fat oxidation helps to preserve glycogen stores as exercise intensity and/or duration increases
Increased glycogen stores help to preserve the performance of an athlete as intensity and/or duration increases also known as fatigue resistance/durability
Performance metrics such as VO2max and FTP are not strongly correlated with enhanced fatigue resistance/durability
Nutrition such as the intake of carbohydrates helps to preserve anaerobic performance and is positively correlated ie the greater the glycogen depletion in muscle, the greater the decrease in anaerobic performance (W Prime). Carbohydrate intake during exercise helps to fuel blood glucose and spare muscle glycogen.
In the next blog post, we will delve deeper into researching fat oxidation and how it impacts performance. Stay Tuned
Any help with further questions, discussions, consultations, or coaching? Please don't hesitate to reach out to darrin@thethreshold.coach
@darrinjordaan
@wattfarming
Train Hard and Prosper!
Darrin Jordaan
MSc (Med) Biokinetics WITS
HMS (Hons) Sports Science UP
BK 0016934
CSCS
UCI Level 1 Cycle Coach
IronMan certified coach
References:
Valenzuela PL, Alejo LB, Ozcoidi LM, Lucia A, Santalla A, Barranco-Gil D. Durability in Professional Cyclists: A Field Study. International Journal of Sports Physiology Performance. 2022 Dec 15,18(1): 99-103
Clark IE, Vanhatalo A, Thompson C, Joseph C, Black MI, Blackwell JR, Wylie LJ, Tan R, Bailey SJ, Wilkins BW, Kirby BS, Jones AM. Dynamics of the power-duration relationship during prolonged endurance exercise and influence of carbohydrate ingestion. Journal of Applied Physiology. 2019. Sep 1;127(3):726-736
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