If you want to start a debate in a group of runners, mention lactic acid and lactate threshold. The topics are two of the most confused and misunderstood in the running world. For the last few decades, lactate was presumed to be all bad–causing only muscle soreness and dashing dreams of personal records.
But that’s only half the story.
Lactate threshold is the exercise level at which lactic acid builds up in the blood. This accumulation of lactic acid is associated with fatigue, and most people assume the burning sensation of hard exercise is caused by lactic acid.
Endurance athletes specifically focus on lactate threshold as a measure of efficiency and fitness. For many, the goal of training is to maintain increased power and speed without crossing over this threshold. Most athletes want to stave off blood lactate accumulation, training so they clear it faster and produce less.
That’s why lactate is generally considered a four-letter-word, thought to be a waste product linked to muscle fatigue.
Research on the issue makes muddy waters more clear: producing and burning lactate provide essential fuel for cells throughout the body when oxygen is depleted.
Lactate & Lactate Threshold Basics
There’s a nuance to lactate responsible for its bad rap.
Lactate: More Protons, More Problems
Lactate can be produced throughout the body naturally.
Glucose is the body’s most readily available fuel, easily transported around the body and broken down to support short bursts of intense exercise. Glucose gets metabolized by a process called glycolysis, resulting in pyruvate. There are two possible uses for pyruvate: anaerobic or aerobic energy production.
When there is plenty of oxygen, pyruvate is turned into energy in the form of ATP through the aerobic pathway. Without enough oxygen present, pyruvate has another fate: anaerobic conversion to lactate. So all that huffing and puffing during intense exercise is used (among other things) to fuel the metabolic reactions that make our muscles work.
The majority of lactate released into the blood is mopped up in the liver where it can be converted back into glucose via a process called gluconeogenesis, and then released back into circulation.
Lactate itself isn’t at all that bad for the body. The bad part is the acid associated with it.
Lactate caries a proton (an acid) when it’s released, and the build up of protons decreases the pH of the blood. When the body gets more acidic, function becomes compromised because the protons interfere with energy production and muscle contraction.
All this time, athletes have been blaming lactate like it’s a referee. But they should be blaming those protons.
Still, generally, lactate is pretty much always associated with protons, so there is a strong relationship between high lactate and fatigue.
Lactate Threshold: Recycling is the Name of the Game
Blood lactate levels rise gradually as one exercises. The harder the exercise, the higher it climbs; this is an indicator of a shift in our energy production from aerobic (lots of oxygen) to anaerobic (less oxygen).
Before reaching the lactate threshold, blood lactate concentrations increase gradually. But upon arriving at the lactate threshold, the blood concentration of lactate begins to exponentially increase. Usually that intensity hovers around 80% of an athlete’s maximum heart rate, or 75% of their maximum oxygen intake–but you can also link it to speed or power.
Recycling lactate is true north of endurance training, which aims to maintain an intensity below the lactate threshold. When the recycling process can’t keep up, lactate produced by the exercising muscles begins build up in the bloodstream.
Well-designed training programs target both sides of the lactate threshold; there should be some training sessions working at or above LT. These sessions are harder on the body, but this forces adaptations that ultimately increase speed on race day.
Why Does Lactate Build Up Happen During High Intensity Exercise?
Lactate buildup is a result of the rapid anaerobic breakdown of carbohydrate.
Cells break down carbs and fats from our food to produce a molecule called ATP (the body’s energy currency), which is then used as energy by exercising muscles. ATP is produced from carbs through a three-step process: Glycolysis, Krebs Cycle and Electron Transport Chain (ETC). Products from Glycolysis feed Krebs which feeds ETC.
ETC is what generates most of our ATP. Energy generated from ETC is effective enough to sustain moderately-intense exercise...but the process doesn’t happen fast enough to keep up with the energy demand of high-intensity exercise. This means rapid-release energy from glycolysis is required to keep going. Glycolysis increases to supplement the difference but, as we know, this leads to lactate production.
Oxygen delivery rate also becomes limited during high intensity exercise. The ETC absolutely relies on oxygen for its function. We can’t breathe enough, or pump blood fast enough to our muscles when they are in overdrive to keep the ETC going. This necessitates oxygen-free energy production via glycolysis and lactate production.
That extra lactate (along with its acidic proton) ends up in the blood and decreases our pH. Our brains aim to keep a steady state of pH, and sensing this imbalance in pH, cause us feel nauseous. This leads to a feeling of fatigue, then a decrease intensity, then decreasing ATP demand, then glycolysis slows, leading to a better match between oxygen demand and oxygen delivery. Ultimately, this match allows lactate clearance from the blood.
Exercise above the lactate threshold can only be sustained for a limited amount of time: the body runs out of glycogen (stored carbs) to convert into lactate, and the increasing acidity of the blood causes fatigue.
Better athletic performance comes from training with LT in mind, geared to a higher production of speed or power at the lactate threshold.
How to Figure Out Lactate Threshold
Testing protocols to determine lactate threshold are sport-specific. Many consider the running speed at lactate threshold (RSLT) to be the best indicator of running fitness and the most reliable barometer of endurance performance.
In cycling, step-tests (where power is increased at regular intervals until you are exhausted) are the gold standard for measuring physiological performance markers, such as lactate threshold.
Upon completing the test and finding a personal lactate threshold, one can begin incorporating lactate threshold training to target specific adaptations for the body to make.
There are a few different ways to test for a personal lactate threshold, and factors to consider when doing so. It’s important to remember everyone is different, and lactate threshold changes in response to training (or sadly, de-training).
Lab Testing: Accurate But Expensive
The most concrete way to determine lactate threshold is to take a series of blood samples as exercise is conducted at increasing intensities. This type of lactate testing occurs at an exercise physiology laboratory, and tends to be expensive (but worth it).
In a lactate threshold test, athletes exercise on a treadmill or stationary bike while increasing intensity every few minutes until exhaustion. A blood sample is taken during the each stage of the test–similar to testing for ketones, through the fingertip or earlobe–illustrating blood lactate readings at various running speeds or cycling power outputs. Results are then plotted on a curve to show the speed or power at which the lactate threshold occurs.
However, lactate threshold changes as more training is done to build your aerobic base. So in order to maintain an updated understanding of your lactate threshold, you’d have to visit the lab again after a block of training.
During her time on the Great Britian Rowing Team, H.V.M.N. Research lead, Dr Brianna Stubbs, did lactate threshold testing every 2-3 months. She recounts the collective effort to find lactate threshold.
"The gym even got gory on step-test days, with athletes dripping blood from the testing holes in their earlobes."
"Seeing results change over time was interesting," she said. "I recorded my highest power at lactate threshold toward the end of the winter training block, which made sense because that’s when we did most of our endurance work."
Do-it-Yourself Field Test: You Have a Few Options
Many endurance athletes choose to estimate their lactate threshold by measuring heart rate and/or VO2 max at different training zones (there’s even a portable lactate blood analyzer some use to further cement results).
There are several different methods to estimate running speed at lactate threshold:
VDOT (or VO2 max) Chart
- A VDOT chart is an adjusted VO2 max chart (created by esteemed running coach Jack Daniels) that uses some of your most recent run times (at max effort) to identify training pace that will maintain your lactate threshold. There are two corresponding chats that work together to illustrate max effort and training paces for different distances (we've simplified it above)
- For example, running at a 7:49 mile pace at max effort corresponds to a VDOT number of 36. That VDOT number illustrates the pace at which training should be done to maintain lactate recycling: 8:55. For a more in-depth analysis of interval training and different distances, refer to these charts here
- Using a heart rate monitor set to a five second recording interval
- Begin running and increase speed every 200 meters until exhaustion. The goal isn’t to maintain a steady state of exercise, instead increasing incrementally to test yourself
- Plot heart rate against speed; the deflection point in the graph (where your heart rate goes up much more than your speed) roughly corresponds to speed at lactate threshold
Time-Trial Method / 30-Minute Test
- Research has shown that doing a 30 minute flat out time trial is one of the most accurate ways to find your lactate threshold without using fancy equipment
- Start by warming up
- Then, on a track or treadmill, run for 30 minutes at the fastest sustainable pace. 10 minutes into the run, obtain and note your heart rate. Then, after the final 20 minutes of the test, obtain and note your heart rate again
- Add your heart rate at the 10-minute mark to heart rate at the 30-minute mark, then divide by two—that's your lactate threshold heart rate. And your average pace for the entire 30-minute test (assuming it was steady) is your lactate threshold pace
Both elite athletes and weekend warriors can benefit from understanding personal lactate threshold to maximize results. However, lactate threshold is impacted by training and changes over time. So keeping regular on these types of tests will indicate an improving lactate threshold through focused training.
Optimizing Lactate Metabolism
Lactic acid gets blamed for muscle soreness, but the production of lactate is an important metabolic process. The idea that lactate is pure waste and leads to fatigue is somewhat outdated. Nevertheless, a higher speed or power at lactate threshold is still one of the key goals of aerobic training.
Different strategies can help minimize lactate buildup during exercise.
Warming Up: As Important as Cooling Down
Warming up is important to reducing risk for injury and minimizing potential lactate buildup. During a warm-up, heart rate increases, and blood vessels dilate, meaning there is more blood flow and more oxygen reaching your muscles.
When exercise intensity picks up the pace, there’s less mismatch between oxygen needs of the muscles and blood. Therefore, you don’t need to do as much anaerobic respiration, and you don’t build lactate early in the run.
Equally, cooling down and stretching immediately after a workout is especially important. Gentle exercise (slow jogging or spinning on a bike) or using a foam roller can help clear lactic acid buildup from the muscle by stimulating blood flow and encouraging lymphatic drainage.
Nutrition and Supplements: Replenishment is Key
The key to dealing with high lactate production is dealing with the acid associated with it (that pesky little proton). Two “buffer supplements,” sodium bicarbonate and beta-alanine, work by mopping up that proton. This means lactate levels can go higher than before without triggering fatigue because the proton is taken care of.
Beta-alanine works inside the muscles to clean up protons before they affect muscle contraction. Compounding effects of beta-alanine powder (~5g per day) happen after several weeks, but studies show around a 2-3% performance boost.
Sodium bicarbonate is better for short-term boosts in proton buffering. Bicarbonate is the main buffer usually binding protons to stop blood from becoming too acidic. About an hour before exercise, taking bicarb powder dissolved in water, at 0.3kg per body weight, has shown to improve performance.
Lactate can only be produced by breaking down carbs. Sustaining an exercise intensity that is producing lactate means the depletion carbohydrate stores (glycogen). When the glycogen gas tank reads empty, we hit a wall.
Exogenous ketones can lower lactate production. By drinking pre-workout exogenous ketones, your body can use the ketones for energy instead of carbohydrates–glycolysis decreases and therefore, so does lactate production.
Having ketones as a whole new source of fuel means the body doesn’t need to dip into its existing carb and protein stores: athletes using exogenous ketones show a decrease in the breakdown of intramuscular glycogen and protein during exercise, compared to carbohydrates alone.
Exercise: Training Toward Adaptation
Regular training forces the body to adapt; what once felt like an unsustainable pace becomes easy. And adopting a training plan helps accelerate how that adaption will progress.
Looking at the whole body, the heart muscle gets stronger, building more small blood vessels. These small blood vessels mean more oxygen-rich blood can be transported to the muscles, requiring less demand for anaerobic respiration and lactate production.
On a muscular level, cells can produce more mitochondria, which are the site of aerobic respiration. This helps increase reliance on that energy system. Muscle cells also express more of the transport proteins for lactate, so lactate doesn’t build up inside the cells and compromise their function.
Lactate threshold training switches up workout intensity, optimizing the body’s lactate response.
Peter Broomhall, who has been running ultramarathons for seven years, started incorporating lactate training into his regimen with his coach.
"I’ve trained with lactate threshold in mind this year more than any other year. It takes time to build up that threshold, but things like recovery become quicker. It compliments every aspect of training."
For runners, one way to work on lactate threshold is to breakdown a run into mile sections: the first mile or two should be run at a pace just below lactate threshold, while the proceeding mile section should be slower, thus allowing the body to process the lactate. Active recovery is more effective at clearing lactate than passive recovery.
Lactate, A Misunderstood Villain
Next time your running club gangs up on lactic acid, maybe you can remind everyone of its important role in helping our bodies produce energy quickly when oxygen is short.
We do know the combination of high lactate (and the associated increase in protons in the muscles and blood) can impact our ability to maintain peak athletic performance. But we now have a deeper understanding of blood lactate (and how to optimize it), thanks to monitoring tools outside the lab, structural training regimens and recovery techniques.
We’re altering how the body responds to lactate with nutrition supplements like exogenous ketones and bicarb gels. And in the process, we’re rewriting the old story about lactic acid.
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