Understanding Lactate in Cycling: Energy Source and Metabolism

Cycling is unique as an endurance sport that demands high energy levels, endurance, and efficiency from the body. Cycling has long periods of low intensity riding along with periods of high intensity efforts. Whether you’re a casual rider or a competitive cyclist, understanding how your body fuels itself during cycling can enhance your performance and overall experience. One crucial aspect of this energy production is lactate, often misunderstood but vital for endurance sports like cycling. Let’s delve into how lactate works in the body and how it compares to other energy sources like fat and glucose.

What is Lactate?

Lactate is a byproduct of anaerobic metabolism. At low intensities, we burn fat and glucose to produce energy with aerobic metabolism in our slow twitch muscle fibers (type 1). The end products of aerobic metabolism are co2, water and a large amount of ATP (energy used by our cells). As exercise intensity increases, we start to recruit fast twitch muscle fibers (type 2a and 2x) as well. The 2a fibers also resorts to anaerobic metabolism to produce energy, but are aerobic too. The 2x fibers are only anaerobic. The anaerobic metabolism breaks down glucose without using oxygen, and produces lactate as a by product.

To this day, many people still think lactate is creating an acidic environment, which causes the burning sensation in our muscles and eventually makes us exhausted. That’s not true. Lactate is an extremely efficient energy source for our muscles and organs like the heart, brain and liver. In fact studies have shown that our muscles prefer lactate over glucose as a fuel. Lactate is also the only way for our body to transport energy from one muscle to another.

When a working fast twitch muscle produces an excess amount of lactate, it can pump it out through MCT4 transporters. It can either be pumped into the bloodstream, or it can be uptaken by slow twitch muscle fibers through the MCT1 transporters. The more capable our slow twitch fibers are at taking up lactate, the less will go to the bloodstream, which is an extremely important trait for a good cyclist.

The burning sensation in our muscles

When anaerobic metabolism burns ATP to make our muscles contract, there are 5 leftover types of molecules. One of these is lactate. Another one is Hydrogen ions (H+

Hydrogen ions are released during the conversion of pyruvate to lactate and contribute to the increase in acidity in the muscle cells. We don’t know all of the factors that contribute to overall fatigue. But these hydrogen ions, and the acidity they create, are an essential part of the burning sensation we feel in our muscles.

Hydrogen ions (H+) are transported out of the muscle and eliminated from the body through several mechanisms:

• Buffering: Within the muscle cells, buffering systems help to temporarily bind and neutralize hydrogen ions. Bicarbonate ions (HCO3-) and proteins act as buffers, reducing the immediate increase in acidity.

• Lactate Shuttle: Lactate produced during anaerobic metabolism can act as a buffer by taking up hydrogen ions. Lactate is then transported out of the muscle cells and can be used as fuel by slow twitch muscle fibers or other organs or converted back to glucose in the liver.

• Bloodstream: Hydrogen ions are released into the bloodstream from the muscle cells. They bind to plasma proteins like albumin or are transported by hemoglobin in red blood cells to the lungs.

• Lungs: In the lungs, carbon dioxide (CO2) is exchanged for oxygen (O2) during respiration. Some of the CO2 produced in the tissues combines with water to form bicarbonate ions (HCO3-), which can then release hydrogen ions. These hydrogen ions are expelled from the body when we exhale.

Kidneys: The kidneys play a crucial role in maintaining acid-base balance in the body. They filter and excrete excess hydrogen ions in the urine, helping to regulate the body’s pH.

Together, these mechanisms work to transport hydrogen ions out of the muscles and eliminate them from the body, helping to maintain pH balance and prevent excessive acidity that can impair muscle function and overall health.

Lactate in Cycling

In cycling, lactate plays a crucial role in energy production, especially during high-intensity efforts like sprinting or climbing. As you push yourself harder, your muscles require more energy quickly, leading to increased lactate production.

As we know, cycling has periods of both high and low intensity. During low intensity, lactate can be recycled by the body and used as a fuel source, especially by the heart and muscles. This recycling process, known as the lactate shuttle, allows lactate to serve as an additional energy source and delay fatigue. Following very high lactate levels, it can take as much as 15 minutes to get back to a normal level, depending on an athlete’s level to clear lactate and use it as fuel in slow twitch fibers.

Remember lactate is burned by the muscles for energy production, so keeping the pedals turning will help you clear lactate quicker. In fact riding close to that first lactate threshold is where you will have the best clearance capacity, because that’s where you consume the most amount of energy, but produce the smallest amount of lactate comparatibly.

But wait a minute. Why do we want to clear lactate if it’s a prime energy source ready to be burnt? Shouldn’t we just free ride as much as possible to preserve that energy for the next interval or attack? No, because lactate is inevitibly bound to those hydrogen ions. So clearing lactate will also get rid of the acidity in our body, and get our muscles back to homeostasis, ready to work at full force again.

How to use lactate as a training and performance metric

Lactate is the closest metric we have, in terms of measuring internal load or cost at a given external power output. Therefore, setting your training zones based on lactate levels is the closest thing we can come to getting zones that are individualized to you as a cyclist. However, the levels can still have a daily variability, so there is no golden model to rule them all. Measuring lactate levels on a daily basis is also highly inconvenient and can’t be used for all training intensities.

Getting a lactate test done is typically performed on an indoor bike where resistance can be controlled precisely. You start at a reasonably low wattage. Then the power increases in steps of around 30 watts (depending on your start point and expected end point). Each step lasts 5-7 minutes, because it takes time for your body to stabilize the lactate level. At the end of each step you take a blood sample from a finger or earlope and apply to a test strip, which you then measure in a lactate meter.

The goal of a lactate test is to establish your two lactate turnpoints. These are also referred to as lactate threshold 1 and 2. When you start the test, you sit at an easy pace. After the first steps, your lactate level might actually decrease a little. This is because we always produce lactate. At rest our blood lactate level is around 1 mmol/L. That might drop a bit during the first steps but at some point you will see an increase in lactate. This is your first lactate turnpoint or threshold. For the next steps, your lactate levels will also increase, but only to a level which you would keep stable at, if you carried on at that intensity. However, at some point you reach your second lactate turnpoint. Above this, is where if you remain at that intensity, your lactate level will keep on rising. You are no longer at a sustainable effort. So the second lactate threshold is the maximum effort you can sustain for a longer time.

Comparing Energy Sources: Lactate, Fat, and Glucose

1. Glucose:

• Source: Stored as glycogen in muscles and liver or derived from carbohydrates in the diet.
• Efficiency: Rapid energy production but limited storage capacity.
• Intensity: Primary fuel during high-intensity efforts due to quick energy release.

1. Fat:

• Source: Stored as triglycerides in adipose tissue.
• Efficiency: Provides long-lasting energy but requires more oxygen to metabolize.
• Intensity: Preferred fuel during low to moderate-intensity exercise and endurance events.

1. Lactate:

• Source: Produced from glucose during anaerobic metabolism.
• Efficiency: Rapidly produced and utilized, especially during high-intensity efforts.
• Intensity: Significant contributor to energy production during high-intensity exercise and can be recycled for prolonged endurance.

Optimizing Lactate Utilization in Cycling

Understanding the role of lactate can help cyclists optimize their training and performance:

• Training: Incorporate high-intensity interval training (HIIT) to improve lactate threshold and increase lactate recycling capacity.
• Nutrition: Maintain a balanced diet rich in carbohydrates to ensure glycogen stores are adequately replenished for energy production.
• Recovery: Active recovery and stretching can help clear lactate from the muscles, reducing muscle soreness and improving recovery.

Conclusion

Lactate is a dynamic energy source that plays a pivotal role in cycling performance. While glucose and fat are essential energy sources, lactate contributes significantly to energy production during high-intensity efforts and endurance events. By understanding and optimizing lactate utilization, cyclists can enhance their performance, endurance, and overall enjoyment of the sport. So, next time you hit the road or trail, remember the role lactate plays in powering your ride!