Perhaps We Got Lactic Acid All Wrong

I think I got it wrong anyway. Remember the last time you pushed yourself way too hard while exercising? The buildup in lactic acid feels like a sharp, intense burning sensation in your working muscles. Your muscles feel really heavy, you quickly fatigue and you suddenly lose strength. This feeling goes away rather quickly when you slow down or stop.

What if we misunderstood what lactate (or lactic acid) is all this while? What if lactate does not slow you down but is actually a nutritional super fuel?

Yes, lactate has been accused to be the culprit behind behind 'burning' legs previously, but is now thought to be endurance sport's next nutritional breakthrough. 

Yomif Kejelcha used lactate gels (Spanish brand Santa Madre's Lactate 60) while finishing 2nd and also clocking sub 2 hours in the London marathon earlier this year. In fact, Tadej Pogacar has been trialing a Enervit 'lactate gel' (a gel with lactic acid) since 2024 when he won the Tour De France for the 3rd time. Pogacar recently won his 5th Tour De France this year.

Tadej Pogacar using Enervit's C2:1Pro Lactate Gel

So what are these new lactate gels and what is the science behind them? I was skeptical as I have been taught that lactate was the 'enemy', a by product that is responsible for burning legs and fatigue, not as a potential fuel source.

Going into Pogacar's jersey pocket

It all started in 2020 when Basque researcher Aitor Viribay first documented how 120 grams of carbohydrates an hour during exercise ignited the carbohydrate boom that was credited with helping cyclists, runners and triathletes race much faster. Viribay found that consuming more carbs promoted higher lactate availability in the body and thought that perhaps they can bypass the carbs and go straight to lactate utilization instead.

The original 'godfather' of lactate is Professor George A Brooks whose Lactate Shuttle Hypothesis in 1985 completely overturned the old belief that lactate (or lactic acid) is a "toxic waste product" of anaerobic metabolism, but an important energy source. 

When you exercise really hard, your fast twitch Type IIb muscle fibers produce lactate through glycolysis - the breakdown of carbohydrate. Brooks found that lactate does not just build up and fatigue, but is actually 'shuttled' (or transported) to slow twitch Type I muscle fibers, the heart and even the brain where it is converted into pyruvate and used to generate energy through aerobic metabolism.

Lactate also goes to the liver, where it is converted into glucose via the Cori cycle (a metabolic pathway where the liver and muscles work together to recycle energy during intense exercise). This newly formed glucose can be released into the bloodstream to help replenish energy supplies for working muscles or stored as glycogen when demand from working muscles is less.

The lactate does build up when exercising hard, and at some point the body cannot clear or reuse it, but it is the associated rise in hydrogen ions that slows you down and not lactate. 

This Lactate Shuttle Hypothesis by Prof Brooks provides the physiological foundation for Viribay's ExoLactate Gel (40 grams carbs with 1:1 ratio of glucose to fructose and 5 grams of lactate) and Enervit's C2:1Pro Lactate Gel used by Pogacar and UAE Team Emirates-XRG cycling team.

The gel works by sidestepping several metabolic steps so users enjoy an extra energy boost quicker by bypassing the glucose and frutose intestinal transporters at the heart of those 120 grams/ hour studies. Lactate is absorbed through a different transporter called monocarboxylate or MCT1.

Athletes that have reached a carbohydrate ceiling now has the potential of adding a complementary lactate energy boost without the 2 substrates (glucose and fructose) competing at the gut wall. One can then go faster for a longer time frame.

And there is more. Lactate is also a 'lactormone', a signaling molecule which kickstarts a variety of physiological responses to help the body adapt and grow back stronger. High lactate cranks up mitochondrial biogenesis (growth). 

Mitochondria are our cells' energy powerhouses. So more mitochondria means improved stamina, reduced fatigue and improved performance. 

It also means better cardiovascular function, insulin sensitivity and overall metabolic efficiency. This may even have implications beyond sports as increasing research links lactate to health and diseases. Ringer's lactate is already used in hospitals used to treat patient's low blood volume from trauma, surgery and burns. Gut microbiota that is more exposed to lactate from exercise are also healthier.

What about having a product that can mimic an exercise dose for someone who cannot move is a huge health potential. This is called 'exercise mimetics' where a drug mimics the biological effects without actually exercising. Kind of like a much healthier version of GLP-1 (Ozempic and Wegovy). Perhaps you can lose weight without exercising in the future. 

Will I try these new lactate gels? I am keen to try, but my first question is how they taste and what is it going to do to my stomach as gastrointestinal issues are one of the biggest concerns for endurance athletes when trying something new.

Will lactate gels offer similar breakthroughs similar to the high carb fueling trends we have seen? Is it for pros only or can most of us mortals also use them? You should already be training, sleeping and eating well, fueling correctly before exercising for best results, prior to trying. Those are the true pillars of performance.

Reference

Viibay A, Arribalzaga S, Mielgo-Ayuso J et al (2020). Effects Of 120 g/h Of Carbohydrates Intake During A Mountain Marathon On Exercise-Induced Muscle Damage In Elite Runners, Nutrients. 12 95): 1367. DOI: 10.3390/nu12051367.

Exolactate's version

Running Twice A Day?

Remember earlier in the year I wrote about how it wasn't really increasing total weekly mileage that caused running injuries. Instead, huge single session mileage increases known as "single-session paradigm" more likely caused injuries. That study (Frandsen et al, 2025) found that large jumps in a single-session distance predicted injuries much better than large jumps in weekly mileage.

The 5,205 runners were followed over 18 months and accumulated 588,071 run sessions. The authors found that instead of keeping your longest run to within 10 percent of your previous longer run, a 10-30 percent increase increased your injury risk by 64 percent. A 30-100 percent increase increased risk by 52 percent while more than 100 percent increase increased risk by almost 128 percent.

To increase mileage safely, instead of running say 10 km at a go, you can run 5 km in the morning and a second 5 km in the evening. Each 5 km run stays well within what your body can tolerate. Instead of doing one run further than what your body can normally handle, you can log more volume by running 5 km in 2 manageable sessions separated by many hours of recovery.

Moreover, a 5 km run definitely feels easier than the last 5 km if you are running the last 5km in a 20 km run. Your running form stays better, you have less fatigue and that second run may feel better after a stressful day at work.

When I used to race triathlons, I can run up to 15 km in the morning and then do another easy 5 km in the late afternoon. It allows me to log 20 km without needing to do all 20 km in the morning.

While it's not mandatory to run twice a day, it's probably one of the simplest and safest way to increase mileage compared to running as many days as you already can. Especially if that is your goal without getting injured.

Reference

Schuster Brant Frandsen J, Hlme A, Parner ET et al (2025). How Much Running Is Too Much? Identifying High-Risk Running Sessions In A 5200-Person Cohort Study? BJSM. 59 (17): 1203-1210. DOI: 10.1136/bjsports-2024-109380

Lots Of Volume Needed

A nice place to log some serious mileage

Previously I wrote that high mileage alone may not enough for you to run fast. Just because Sebastian Sawe clocked over 240 km a week leading to his sub-2 hour marathon does not mean you too have to clock huge distances to run fast. 

So this post is for serious runners. For runners who want and can log long distances. Runners who want to run fast and are prepared to spend lots of time running. The recommendations will not help weekend warriors who just want to complete a race or fitness influencers to quote this to their followers.

Here is what a comprehensive analysis of the training intensity distribution (TID) across runners from different performance levels looks like. Researchers looked at different training sessions from 16 weeks before 151,813 marathons (yes you read correctly), done by 119,452 runners.

TID was measured using a 3 zone approach (Z1, Z2 and Z3) where critical speed is defined the boundary between Z2 and Z3. Note that this IS different from the Zone 1-5 runners talk about. The Zone 2 most runners talk about is Z1 here and Z3 here is Zone 5 on that scale.

The transition between Z1 and Z2 was assumed to occur at 82.3 percent of critical speed. Critical speed is the maximum running speed you can maintain for 30 to 60 minutes without fatiguing rapidly. It is strongly correlated to your lactate threshold.The training characteristics and TID were reported based on the runners' marathon finish time.

Results show that training mileage was 45.1 ± 26.4 km each week. The fastest runners in the study group (marathon finishing time between 120-150 mins) ran greater than 3 times more volume than slower runners.They did not run fast often.

The amount of time spent training in Z2 and Z3 remained relatively stable across all performance levels, but the proportion of training time spent in  was progressively higher in faster runners.

More than 80 percent of the runners with faster marathon times had a pyramidal approach where the volume of training (mileage) decreases as intensity increases. Visually it forms a pyramid pictured below. A big base of easy Z1 running, a smaller middle section of moderate effort and a tiny peak of high intensity work. 

With regards to total mileage that the faster runners covered, the more time they spent in Z1 (really easy pace), the faster their marathon finish time (p < 0.01 - highly siginificant statistical finding, less than 1 percent chance this happened by coincidence). Moreover, R² ≥ 0.9, meaning over 90 percent of the variance in marathon finish times can be explained by looking at how much total volume the runner did and how much of it was in Z1.

The study also found that the more time a runner spent training at Z2 or Z3 intensities, the slower their marathon finish time. p < 0.01 and R² ≥ 0.85, at least 85 percent of the variance in slower finish times can be predicted by an over reliance on Z2 and Z3 training.

Focusing too much on hard and moderate efforts usually backfires. Why? Running too 'fast' on easy days and not hard enough on hard days means you are in the "grey zone". Not easy enough to get the aerobic adaptations needed and not hard enough to get the benefits of the high quality intervals.

Spending too much time in Z2 (moderately hard) causes higher fatigue levels without the beneficial effects of Z1 nor the high end fitness gains of Z3. 

The fastest runners in this study achieved their better times by increasing training volume mainly in Z1. They also ran less when they incorporated high intensity runs to allow for recovery. 

Is that true for all distances? What about a 5km or 10 km race? Will you still need to run lots of easy Z1 miles. If you want to simply finish the race, no. But if you consider that even a mile race of 5 km race is predominantly aerobic (pictured above) then you will understand why a large volume is needed to build a large base. 

Slower means more sustainable over time, you will not get injured so easily and hence more adaptation over time. That's how you will get stronger. 

Find more ways to increase your training volume with long easy runs. True aerobic developmnent is only possible from accumulating volume.  It allows you to recover and handle the key sessions. You cannot HIIT your way to the top. If you cannot get your hours in then it would be a lot more difficult to run faster.

Reference

Muniz-Pumares D, Hunter B, Meyler S et al (2025). The Training Insity Distribution Of Marathon Runners Across Performance Levels. Sports Med 55: 1023-1035. DOI: 10.1007/s40279-024-02137-7