Lactate: Friend or Foe?
Overview of lactate; is it really the runner's enemy?
When you’re mid-sprint and your quads start burning, is it because you’re “lactic”? In the final 200 meters of an 800, when you’re digging deep but the burn is overwhelming, can that be pinned on lactate? Athletes and coaches throw the word around all the time, often as a warning:Watch out for the lactic acid. In my own years as a distance runner, I’ve learned to fear “lactate” and the feeling that comes with it. But here’s the twist: what if lactate isn’t the villain at all? What if it’s actually part of the solution, a source of energy that helps us run faster? Let’s break it down.
What Lactate Really Is
At its simplest, lactate is just a byproduct of your body’s effort to keep producing energy when the demand has skyrocketed. During running, many muscles rely heavily on glycolysis, the breakdown of glucose into pyruvate, to generate the body’s energy currency, ATP. When oxygen is plentiful, usually when you’re running sub lactate threshold, the pyruvate is able to enter mitochondria within muscle fiber cells, which yields the maximum amount of ATP; this is known as aerobic respiration.
But if you crank up the pace, let’s say a sprint, running at 5k pace, or a surge in a marathon, your body suddenly cannot deliver enough oxygen to cells at the needed rate, this is called VO2 max. Rather than letting pyruvate back up, which would slow energy production, your body calls in the enzyme lactate dehydrogenase (LDH) to convert pyruvate into lactate.
This step does two big things:
Keeps glycolysis running by regenerating NAD⁺, a key molecule without which ATP production would grind to a halt.
Buys time for your aerobic system to catch up.
Far from being waste, lactate is workaround that keeps you moving hard when oxygen supply is limited.
Lactate Shuttle System
Once produced, lactate isn’t left to fester in your muscles. Your body has an entire distribution network for it; called the lactate shuttle. Fast-twitch muscle fibers, which are recruited heavily during hard efforts, churn out lactate when glycolysis outpaces oxygen delivery. These fibers are excellent at generating energy quickly, but they aren’t as strong at burning lactate once it’s made. So instead of letting it accumulate, your body sends it away to tissues that can handle it better.
Through the bloodstream, lactate travels to:
Slow-twitch (oxidative) muscle fibers, which have dense mitochondria and can easily convert lactate back into pyruvate for aerobic use.
The heart, which actually prefers lactate over glucose during heavy exercise because it’s a quick, high-energy fuel.
The brain, which can run on lactate just as well as it runs on glucose, especially when exercise intensity is high.
Think of it like a logistics system in a city.
One neighborhood (your fast-twitch fibers) produces more goods (lactate) than it can use. Instead of letting them sit in a warehouse, a fleet of delivery trucks (your blood) carries them to neighborhoods (slow-twitch fibers, heart, brain) that have the factories (mitochondria) to use them efficiently.
Even the liver plays a role, taking in lactate to convert it back into glucose through a process called the Cori cycle. That glucose can then re-enter the bloodstream and fuel the muscles again.
The lactate shuttle is not just cleanup, it’s an energy recycling loop that keeps high-intensity performance going longer. Without it, lactate would build up in the producing fibers, pH would drop faster, and you’d be forced to slow down much earlier.
If It’s Not Lactate, Why The Burn?
That sharp, searing sensation you feel when you push deep into the red, the one that makes your quads feel like they’re on fire, has long been blamed on “lactic acid.” For decades, the story went like this: run hard, produce lactic acid, muscles fill with acid, you slow down. But the real culprit is more nuanced, and lactate is actually playing the role of an under appreciated helper, not a villain. When you run at high intensity, your body’s glycolytic pathway (breaking glucose into pyruvate) is working at maximum speed to supply ATP. This rapid turnover of energy comes with a biochemical cost: it releases hydrogen ions (H⁺) into your muscle cells. These hydrogen ions lower the muscle’s pH, making it more acidic; a condition known as metabolic acidosis.
Acidosis disrupts muscle performance in several ways:
It interferes with the proteins responsible for muscle contraction, making each contraction less forceful.
It impairs the enzymes needed for further energy production, slowing ATP resynthesis.
It increases the perception of effort, making the work feel disproportionately harder.
So where does lactate fit in? In the process of converting pyruvate to lactate, the enzyme lactate dehydrogenase (LDH) actually consumes one hydrogen ion. This reaction helps slow the pH drop, a small but important buffering effect. In other words, lactate isn’t adding to the acidity problem, it’s helping contain it.
The confusion comes from the old term “lactic acid”, which doesn’t exist in meaningful amounts inside working muscle. In the pH range of the human body, “lactic acid” dissociates almost instantly into lactate and hydrogen ions. The lactate is neutral, the hydrogen ion is the acidic part, but decades ago, researchers lumped them together and blamed the whole bundle on “the burn.”
Why Training At Lactate Threshold Works
Think of your lactate threshold (LT) as the tipping point between sustainable discomfort and unsustainable suffering. Below LT, your muscles produce lactate at a rate your body can clear and reuse efficiently. Above LT, the production rate outpaces clearance, hydrogen ions start to build up faster, and the steady state begins to unravel.
Training right at, or just under, this point teaches your body to work at higher intensities without tipping over that edge. Physiologically, this type of training sparks a set of targeted adaptations:
More mitochondrial density – Mitochondria are the “power plants” of your cells. Increasing their number and size means more capacity to fully oxidize lactate and other fuels for energy, reducing reliance on fast glycolysis.
Enhanced lactate transport – Special proteins called monocarboxylate transporters (MCTs) act as the molecular buses that move lactate across cell membranes. LT training upregulates both MCT-1 (bringing lactate into oxidative muscle fibers to burn) and MCT-4 (moving lactate out of glycolytic fibers). The more transporters you have, the smoother and faster the lactate shuttle system runs.
Improved buffering capacity – Regular LT sessions improve your muscles’ ability to bind and neutralize hydrogen ions, delaying the onset of acidosis. This lets you hold a harder pace without the burn forcing you to slow.
The payoff? Your lactate threshold shifts to a faster pace or higher power output. In racing terms, that’s the difference between hanging on at 10K pace for only 3 miles vs. cruising at that pace for the whole distance. In the marathon, it means your “comfortably hard” pace is suddenly 10–15 seconds per mile faster without extra effort.
From a performance standpoint, LT training is like widening the shoulder of the highway, you can run faster for longer before hitting traffic. For a distance runner, that’s gold.
Verdict
Lactate isn’t the problem, it’s part of the solution. Far from being a waste product, it’s a versatile fuel and a key player in endurance performance. By understanding how your body produces, shuttles, and uses lactate, you can train smarter, push harder, and recover faster. Instead of fearing it, learn to work with it. Because in running, lactate is more friend than foe.
When you’re mid-sprint and your quads start burning, is it because you’re “lactic”? In the final 200 meters of an 800, when you’re digging deep but the burn is overwhelming, can that be pinned on lactate? Athletes and coaches throw the word around all the time, often as a warning:Watch out for the lactic acid. In my own years as a distance runner, I’ve learned to fear “lactate” and the feeling that comes with it. But here’s the twist: what if lactate isn’t the villain at all? What if it’s actually part of the solution, a source of energy that helps us run faster? Let’s break it down.
What Lactate Really Is
At its simplest, lactate is just a byproduct of your body’s effort to keep producing energy when the demand has skyrocketed. During running, many muscles rely heavily on glycolysis, the breakdown of glucose into pyruvate, to generate the body’s energy currency, ATP. When oxygen is plentiful, usually when you’re running sub lactate threshold, the pyruvate is able to enter mitochondria within muscle fiber cells, which yields the maximum amount of ATP; this is known as aerobic respiration.
But if you crank up the pace, let’s say a sprint, running at 5k pace, or a surge in a marathon, your body suddenly cannot deliver enough oxygen to cells at the needed rate, this is called VO2 max. Rather than letting pyruvate back up, which would slow energy production, your body calls in the enzyme lactate dehydrogenase (LDH) to convert pyruvate into lactate.
This step does two big things:
Keeps glycolysis running by regenerating NAD⁺, a key molecule without which ATP production would grind to a halt.
Buys time for your aerobic system to catch up.
Far from being waste, lactate is workaround that keeps you moving hard when oxygen supply is limited.
Lactate Shuttle System
Once produced, lactate isn’t left to fester in your muscles. Your body has an entire distribution network for it; called the lactate shuttle. Fast-twitch muscle fibers, which are recruited heavily during hard efforts, churn out lactate when glycolysis outpaces oxygen delivery. These fibers are excellent at generating energy quickly, but they aren’t as strong at burning lactate once it’s made. So instead of letting it accumulate, your body sends it away to tissues that can handle it better.
Through the bloodstream, lactate travels to:
Slow-twitch (oxidative) muscle fibers, which have dense mitochondria and can easily convert lactate back into pyruvate for aerobic use.
The heart, which actually prefers lactate over glucose during heavy exercise because it’s a quick, high-energy fuel.
The brain, which can run on lactate just as well as it runs on glucose, especially when exercise intensity is high.
Think of it like a logistics system in a city.
One neighborhood (your fast-twitch fibers) produces more goods (lactate) than it can use. Instead of letting them sit in a warehouse, a fleet of delivery trucks (your blood) carries them to neighborhoods (slow-twitch fibers, heart, brain) that have the factories (mitochondria) to use them efficiently.
Even the liver plays a role, taking in lactate to convert it back into glucose through a process called the Cori cycle. That glucose can then re-enter the bloodstream and fuel the muscles again.
The lactate shuttle is not just cleanup, it’s an energy recycling loop that keeps high-intensity performance going longer. Without it, lactate would build up in the producing fibers, pH would drop faster, and you’d be forced to slow down much earlier.
If It’s Not Lactate, Why The Burn?
That sharp, searing sensation you feel when you push deep into the red, the one that makes your quads feel like they’re on fire, has long been blamed on “lactic acid.” For decades, the story went like this: run hard, produce lactic acid, muscles fill with acid, you slow down. But the real culprit is more nuanced, and lactate is actually playing the role of an under appreciated helper, not a villain. When you run at high intensity, your body’s glycolytic pathway (breaking glucose into pyruvate) is working at maximum speed to supply ATP. This rapid turnover of energy comes with a biochemical cost: it releases hydrogen ions (H⁺) into your muscle cells. These hydrogen ions lower the muscle’s pH, making it more acidic; a condition known as metabolic acidosis.
Acidosis disrupts muscle performance in several ways:
It interferes with the proteins responsible for muscle contraction, making each contraction less forceful.
It impairs the enzymes needed for further energy production, slowing ATP resynthesis.
It increases the perception of effort, making the work feel disproportionately harder.
So where does lactate fit in? In the process of converting pyruvate to lactate, the enzyme lactate dehydrogenase (LDH) actually consumes one hydrogen ion. This reaction helps slow the pH drop, a small but important buffering effect. In other words, lactate isn’t adding to the acidity problem, it’s helping contain it.
The confusion comes from the old term “lactic acid”, which doesn’t exist in meaningful amounts inside working muscle. In the pH range of the human body, “lactic acid” dissociates almost instantly into lactate and hydrogen ions. The lactate is neutral, the hydrogen ion is the acidic part, but decades ago, researchers lumped them together and blamed the whole bundle on “the burn.”
Why Training At Lactate Threshold Works
Think of your lactate threshold (LT) as the tipping point between sustainable discomfort and unsustainable suffering. Below LT, your muscles produce lactate at a rate your body can clear and reuse efficiently. Above LT, the production rate outpaces clearance, hydrogen ions start to build up faster, and the steady state begins to unravel.
Training right at, or just under, this point teaches your body to work at higher intensities without tipping over that edge. Physiologically, this type of training sparks a set of targeted adaptations:
More mitochondrial density – Mitochondria are the “power plants” of your cells. Increasing their number and size means more capacity to fully oxidize lactate and other fuels for energy, reducing reliance on fast glycolysis.
Enhanced lactate transport – Special proteins called monocarboxylate transporters (MCTs) act as the molecular buses that move lactate across cell membranes. LT training upregulates both MCT-1 (bringing lactate into oxidative muscle fibers to burn) and MCT-4 (moving lactate out of glycolytic fibers). The more transporters you have, the smoother and faster the lactate shuttle system runs.
Improved buffering capacity – Regular LT sessions improve your muscles’ ability to bind and neutralize hydrogen ions, delaying the onset of acidosis. This lets you hold a harder pace without the burn forcing you to slow.
The payoff? Your lactate threshold shifts to a faster pace or higher power output. In racing terms, that’s the difference between hanging on at 10K pace for only 3 miles vs. cruising at that pace for the whole distance. In the marathon, it means your “comfortably hard” pace is suddenly 10–15 seconds per mile faster without extra effort.
From a performance standpoint, LT training is like widening the shoulder of the highway, you can run faster for longer before hitting traffic. For a distance runner, that’s gold.
Verdict
Lactate isn’t the problem, it’s part of the solution. Far from being a waste product, it’s a versatile fuel and a key player in endurance performance. By understanding how your body produces, shuttles, and uses lactate, you can train smarter, push harder, and recover faster. Instead of fearing it, learn to work with it. Because in running, lactate is more friend than foe.
When you’re mid-sprint and your quads start burning, is it because you’re “lactic”? In the final 200 meters of an 800, when you’re digging deep but the burn is overwhelming, can that be pinned on lactate? Athletes and coaches throw the word around all the time, often as a warning:Watch out for the lactic acid. In my own years as a distance runner, I’ve learned to fear “lactate” and the feeling that comes with it. But here’s the twist: what if lactate isn’t the villain at all? What if it’s actually part of the solution, a source of energy that helps us run faster? Let’s break it down.
What Lactate Really Is
At its simplest, lactate is just a byproduct of your body’s effort to keep producing energy when the demand has skyrocketed. During running, many muscles rely heavily on glycolysis, the breakdown of glucose into pyruvate, to generate the body’s energy currency, ATP. When oxygen is plentiful, usually when you’re running sub lactate threshold, the pyruvate is able to enter mitochondria within muscle fiber cells, which yields the maximum amount of ATP; this is known as aerobic respiration.
But if you crank up the pace, let’s say a sprint, running at 5k pace, or a surge in a marathon, your body suddenly cannot deliver enough oxygen to cells at the needed rate, this is called VO2 max. Rather than letting pyruvate back up, which would slow energy production, your body calls in the enzyme lactate dehydrogenase (LDH) to convert pyruvate into lactate.
This step does two big things:
Keeps glycolysis running by regenerating NAD⁺, a key molecule without which ATP production would grind to a halt.
Buys time for your aerobic system to catch up.
Far from being waste, lactate is workaround that keeps you moving hard when oxygen supply is limited.
Lactate Shuttle System
Once produced, lactate isn’t left to fester in your muscles. Your body has an entire distribution network for it; called the lactate shuttle. Fast-twitch muscle fibers, which are recruited heavily during hard efforts, churn out lactate when glycolysis outpaces oxygen delivery. These fibers are excellent at generating energy quickly, but they aren’t as strong at burning lactate once it’s made. So instead of letting it accumulate, your body sends it away to tissues that can handle it better.
Through the bloodstream, lactate travels to:
Slow-twitch (oxidative) muscle fibers, which have dense mitochondria and can easily convert lactate back into pyruvate for aerobic use.
The heart, which actually prefers lactate over glucose during heavy exercise because it’s a quick, high-energy fuel.
The brain, which can run on lactate just as well as it runs on glucose, especially when exercise intensity is high.
Think of it like a logistics system in a city.
One neighborhood (your fast-twitch fibers) produces more goods (lactate) than it can use. Instead of letting them sit in a warehouse, a fleet of delivery trucks (your blood) carries them to neighborhoods (slow-twitch fibers, heart, brain) that have the factories (mitochondria) to use them efficiently.
Even the liver plays a role, taking in lactate to convert it back into glucose through a process called the Cori cycle. That glucose can then re-enter the bloodstream and fuel the muscles again.
The lactate shuttle is not just cleanup, it’s an energy recycling loop that keeps high-intensity performance going longer. Without it, lactate would build up in the producing fibers, pH would drop faster, and you’d be forced to slow down much earlier.
If It’s Not Lactate, Why The Burn?
That sharp, searing sensation you feel when you push deep into the red, the one that makes your quads feel like they’re on fire, has long been blamed on “lactic acid.” For decades, the story went like this: run hard, produce lactic acid, muscles fill with acid, you slow down. But the real culprit is more nuanced, and lactate is actually playing the role of an under appreciated helper, not a villain. When you run at high intensity, your body’s glycolytic pathway (breaking glucose into pyruvate) is working at maximum speed to supply ATP. This rapid turnover of energy comes with a biochemical cost: it releases hydrogen ions (H⁺) into your muscle cells. These hydrogen ions lower the muscle’s pH, making it more acidic; a condition known as metabolic acidosis.
Acidosis disrupts muscle performance in several ways:
It interferes with the proteins responsible for muscle contraction, making each contraction less forceful.
It impairs the enzymes needed for further energy production, slowing ATP resynthesis.
It increases the perception of effort, making the work feel disproportionately harder.
So where does lactate fit in? In the process of converting pyruvate to lactate, the enzyme lactate dehydrogenase (LDH) actually consumes one hydrogen ion. This reaction helps slow the pH drop, a small but important buffering effect. In other words, lactate isn’t adding to the acidity problem, it’s helping contain it.
The confusion comes from the old term “lactic acid”, which doesn’t exist in meaningful amounts inside working muscle. In the pH range of the human body, “lactic acid” dissociates almost instantly into lactate and hydrogen ions. The lactate is neutral, the hydrogen ion is the acidic part, but decades ago, researchers lumped them together and blamed the whole bundle on “the burn.”
Why Training At Lactate Threshold Works
Think of your lactate threshold (LT) as the tipping point between sustainable discomfort and unsustainable suffering. Below LT, your muscles produce lactate at a rate your body can clear and reuse efficiently. Above LT, the production rate outpaces clearance, hydrogen ions start to build up faster, and the steady state begins to unravel.
Training right at, or just under, this point teaches your body to work at higher intensities without tipping over that edge. Physiologically, this type of training sparks a set of targeted adaptations:
More mitochondrial density – Mitochondria are the “power plants” of your cells. Increasing their number and size means more capacity to fully oxidize lactate and other fuels for energy, reducing reliance on fast glycolysis.
Enhanced lactate transport – Special proteins called monocarboxylate transporters (MCTs) act as the molecular buses that move lactate across cell membranes. LT training upregulates both MCT-1 (bringing lactate into oxidative muscle fibers to burn) and MCT-4 (moving lactate out of glycolytic fibers). The more transporters you have, the smoother and faster the lactate shuttle system runs.
Improved buffering capacity – Regular LT sessions improve your muscles’ ability to bind and neutralize hydrogen ions, delaying the onset of acidosis. This lets you hold a harder pace without the burn forcing you to slow.
The payoff? Your lactate threshold shifts to a faster pace or higher power output. In racing terms, that’s the difference between hanging on at 10K pace for only 3 miles vs. cruising at that pace for the whole distance. In the marathon, it means your “comfortably hard” pace is suddenly 10–15 seconds per mile faster without extra effort.
From a performance standpoint, LT training is like widening the shoulder of the highway, you can run faster for longer before hitting traffic. For a distance runner, that’s gold.
Verdict
Lactate isn’t the problem, it’s part of the solution. Far from being a waste product, it’s a versatile fuel and a key player in endurance performance. By understanding how your body produces, shuttles, and uses lactate, you can train smarter, push harder, and recover faster. Instead of fearing it, learn to work with it. Because in running, lactate is more friend than foe.