Best Way To Train For Hyrox

Photo by CNA/ Marcus Mark Ramos

Yesterday I had a patient who's training for her second Hyrox competition coming up this November.  She has been going to the gym and participates in their Hyrox training program 5 times a week. The sessions are mostly strength sessions with simulated practices of lunges, farmers walk, wall balls and other strength training. There is very little running, rowing or cardio during these sessions. I mentioned 8 km of running is involved and I suggested that being able to run well when tired will allow her drop her time significantly. 

I also shared with her an article that was published last year that analyzed, in depth, the physiological responses and performance factors in Hyrox (Brandt et al, 2025).

Here are the numbers that matter and the requirements needed. On the rate of perceived exertion (RPE) on the Borg scale, participants rated it as 18 out of 20 difficulty. Average time the study participants took was 1 hour 26 and half minutes. 

Average heart rate during the event was 171 beats per minute. That's very high, easily above the 90 percent of maximum heart rate for probably everyone. In fact during 79 percent of the whole event, participants are competing at intensities of 90-100 percent of their maximum heart rate.

What set apart the better performers? VO2 max showed a strong relationship with finishing time. Spearman's rank coefficient was p = -0.71. It explains how critical an athlete's aerobic fitness is to their race success. Yes you read correctly, it's aerobic fitness, not strength. In exercise science, a correlation of 0.71 is considered strong. It proves that aerobic capacity (or fitness) is not just a minor factor, but a primary driver of performance.

In contrast, neither hand grip strength (a good predictor of work efficiency and fatigue management during sled pull, farmers carry and sandbag lunges) nor muscle mass percentage were good predictors. Hand grip strength also correlates with strength in other muscle groups and is used as a predictor for total muscle strength.

While variables like strength, pacing and transition speed matter, your raw capacity to absorb and utilize oxygen (VO2 max) is one the most reliable predictors of how fast you will finish the Hyrox event.

The negative sign indicates an inverse (or opposite) relationship, as an athlete's VO2 max increases, their race time decreases. This means they finish faster.

Recommendations for training?

According to the authors, endurance training should be emphasized at moderate intensities as well as forms of HIIT (high intensity interval training) to improve both aerobic and anaerobic capacity. Since 8 km of running is involved, a substantial amount of training volume needs to be dedicated to running based sessions. 

Since excessive running mileage can increase injury risk, a strategy would be to replace or combine running with Hyrox specific endurance activities like rowing or skiing. Combining running with other Hyrox requirements should be an integral part of Hyrox training to improve running economy in a pre-fatigued state and will help with ability to transition between different metabolic demands.

Even though strength appears to be less important, participants still need to be able to move external weights as per competition standards. Previous research indicated that endurance and weight training may interfere with each other if done together, affecting adaptations. To minimise interference, separating strength and endurance into distinct sessions. If both are done together, the more important aspect should be trained earlier.

It is not enough to run fast in isolation. Not enough to just be strong either. You have to be able to keep running fast after you have rowed, pushed the sled, done wall balls and lunges etc. And to repeat it over and over again.

Your aerobic (or cardiovascular) engine, running and the ability to maintain performance while fatigued is crucial.

"More running?" My patient said. Definitely I said, at least more than what you have been running so far, since you have doing lots of strength training previously.

Reference

Brandt T, Ebel C, Lebahn C et al (2025). Acute Physiological Responses And Performance Determinants In Hyrox- A New Running-Focused High Intensity Functional Fitness Trend. Front Physiol. 16:1519240. DOI: 10.3389/fphys.2025.1519240

What About Peptides?

Yesterday I had a patient, a medical doctor, who asked me about peptides. She asked whether I knew if my patients are using them. She was not the first person asking me about peptides. If you asked someone about peptides a few years ago, it would probably not ring any bells. Now, peptides is the latest buzzword in wellness and longevity.

Earlier this year, Singapore authorities warned against peptides sold online to help one grow muscles while helping with weight loss.

BPC-157 (body protection compound, or more famously known as the Wolverine) has been circulating around gyms and fitness spaces ever since fitness influencers like Joe Rogan touted its benefits. The muscle recovery effects are so popular that people have even injected their dogs to support their dog's health. Others are using a number of different peptides to improve cognition, longevity, sleep duration and revive sexual libido.

Peptides do occur naturally in our bodies. A peptide is a short chain of amino acids (which are building blocks for proteins), usually 2 to 50 amino acids linked together by chemical bonds called peptide bonds. If amino acids are individual lego bricks, and you put a few of them together, they become a peptide. If you link more than 50 of them, you build a protein. Since they are smaller, they are more easily absorbed by the body than full sized proteins.

While proteins are best known for building muscles, they have other important functions. We have millions of natural peptides in our bodies. Peptides act as messengers throughout the body. They regulate hormones, regulate inflammatory responses and boost our immunity systems. 

Since they are so versatile, artificial versions of peptides are used in medicine. These are lab grown chains of amino acids that mimic fragments of natural peptides. Insulin and GLP-1 (Ozempic and Wegovy) are 2 well known examples of FDA (food and drug administration in USA) approved synthetic peptides.

In late July 2026, the FDA voted to add 6 popular peptides to an approved list. BPC-1, KPV, TB-500, MOTs-C, Epitalon and Semax. Pharmacies in USA are allowed to use these peptides to make custom medications.

BPC-157 was approved as a treatment for ulcerative colitis, an inflammatory bowel disease. It is a synthetic peptide derived from a protein in human gastric juice. Very popular among athletes and gym rats after animal studies show that it could help heal fractures, tendon ruptures and ligament tears as well as reduce knee pain. However, these benefits are not confirmed in human studies. Almost entirely anecdoctal evidence from athletes self reporting faster recovery.

TB-500 is another trending peptide among athletes. This peptide was originally marketed for veterinary use in race horses and greyhounds. It has been marketed online for helping with tissue repair and regeneration, improving flexibility and boosting the immune system. Similar to BPC-157, TB-500 is promoted for healing muscle injuries, treating chronic diseases and inflammation. Human research is still lacking.

KPV is a peptide made of 3 amino acids, lysine (K), proline (P), and valine (V). A 2007 animal  study found that it can be a therapeutic agent for inflammatory bowel disease. Most research has been conducted in labs on mice. Another 2017 study tested a topical  KPV on human cadaveric skin  and found that it did not permeate well through skin and "could limit the systemic toxicity of KPV applied topically to the skin."

MOTS-c is created from mitochondria DNA to help with obesity and osteoporosis. Again, most findings have been limited to animal studies. 

Semax is a synthetic peptide developed in Russia and studied for its effects on the brain, including its effects on Alzheimer's disease. Evidence in humans remain limited. The FDA is evaluating how it can treat migraines, cerebral ischaemia and trigeminal neuralgia.

Epitalon is a pineal polypeptide extract from cattle and a 2025 study demonstrated high (or long) telomere lengths which are associated with longevity. Researchers are checking if they can improve sleep by increasing melatonin production and for insomnia treatment.

I think some people trying peptides may have exhausted conventional options and are bypassing quality checks if they buy and self administer based on information off social media. Others may want a 'short cut' to achieve their weight loss or training goals.

The world of synthetic peptides may be promising for sure, but there are dangerous side effects and some may even cause cancers. Do your research if you really want to try some of these peptides. Be aware of the side effects before you give them a go.

Reference

Mayfield CK, Bolia IK, Feingold CL et al (2026). INjectable Peptide Therapy: A Primer For Orthopaedic And Sports Medicine Physicians. AJSM. 54(1): 223-229. DOI: 1177/03635465251357593

Previous Treadmill Incline Guidelines May Be Wrong

I have written before that running on a treadmill indoors is easier than running outside and that research shows that setting your treadmill at 1 percent incline simulates outdoor running (Jones and Doust, 1996). This is especially so if you run at speeds of 12-17 km per hour. Under 12 km an hour, no need to set the incline up as the difference is small.

However a new study (Shahidi et al, 2026) found that the energy cost of running outside is still about 4 percent higher than running inside on a treadmill at 1 percent incline.

The researchers had 12 trained runners (21.3±‍2.4 years, 176±‍6.8 cm, 67.8±‍5.9 kg) first tested for their VO2 max. They subsequently ran 3 minutes at speeds between 8 to 15 km/hr both indoors on a treadmill and outdoors on a 400m track. Gas analysis was averaged over the final 60-90 seconds of each stage to determine steady-state VO2. 

The results (pictured above) show that running economy was significantly higher while running outside on a 400m track compared to running indoors on a treadmill. Especially as you run harder and closer to your limit (70-100 percent of the ventilatory threshold or VT2). Running outdoors requires much more energy than running on a treadmill.

At slower recovery paces, the physical effort between the 2 feels amost identical. Once your intensity hits the high effort zones, the treadmill becomes easier than the track.

Regardless  of how fast or slow the runners ran, running outside always used more total energy per kilometer than running on a treadmill.

The findings suggest that the commonly used 1 or 1.5 percent treadmill grade correction does not fully replicate the energetic demands of running outside. 

So, you will burn more total calories running 5 km outdoors than running 5 km on a treadmill if you go at the exact same pace. Your heart and lungs have to work slightly harder every single second you are outside to cover the same distance. Since the energy cost is higher across all speeds, an outdoor longer run will always leave you more physically spent than an identical treadmill long run.

Note that this is a small sample size study with only 12 national level trained subjects. Will the results apply to the rest of the population? Also they were made to run with the apparatus pictured above to measure exchange of gases. The runners may have to breathe harder outdoors.

In Singapore, the temperature and humidity affects us enormously when exercising outdoors, air conditioning while running indoors mitigates that.

One can run by heart rate and/ or time running on a treadmill and perhaps not worry about pace since the treadmills may not be properly calibrated as well.

May I also suggest running more outdoors if you are training for a road race/ marathon rather than solely indoors on a treadmill since the treadmill is softer and will not mimic the road conditions that you race on. Specificity is key. The gym environment is temperature controlled unlike outdoors. So if the race location is hotter and more humid then you will be less able to handle it.

References

Jones AM and Doust JU (1996). A 1% Treadmill Grade Most Accurately Reflects The Energetic Cost Of Outdoor Running. J Sports Sci. 14(4): 321-327.

Shahidi SH, Can R, Paca FM et al (2026). Overground Running Incurs A Higher Energetic Cost Than Treadmill Running At A 1% Grade: A Comparison Of Running Economy, Oxygen Cost Of Transport, And The Energy Cost In Endurance Athletes. PLoS One. 21(8): e0355988. DOI: 10.1371/journal.pone.0355988

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

Run Faster With Zero Drop Shoes

And we thought zero drop shoes were 'dead'. Zero drop shoes were all the rage after Christopher McDougall wrote about the Tarahumara Mexican Natives in his book, 'Born To Run', in 2009. Remember those Vibram shoes? Now, Vibrams I will classify as barefoot type and then there were minimalist type running shoes (or racing flats). Maximalist shoes have since replaced minimalist zero drop running shoes.

The research article I read was to determine if shoe heel-toe drop affects running economy. The researchers studied how shoe heel drop affects metabolic energy (total energy usage) in runners during running. 

20 runners were recruited for the study. Running speed was 3.5m/ sec (or 12.6km/ hr) in custom footwear that only differed in heel-toe drop of 0, 10, 20 and 30 mm. Running shoe and weight of the shoe were fixed with a US size 10, Air Pegasus. The heaviest shoe mass was the 30 mm shoe at 260 grams. Small weights were attached to the exterior heel of the shoes with the lower heel drops (pictured below).

During the research, the runners first did a standing 5 minute test and then ran for 5 minutes in their own running shoes at 3.5m/ sec (or 12.6km/ hr) on a force measuring treadmill (Treadmetrix). Each runner then completed a 5 min running trial at 3.5m/ sec in each of the 4 heel-toe drop shoe conditons in a randomized order. Participants rested at least 5 minutes between the runs.

To measure metabolic energy (or total energy usage), open circuit expired gas analysis was done to record oxygen and carbon dioxide uptake. Normalized net metabolic power (W/kg) was derived by subtracting the participants's corresponding standing metabolic power from each running trial and divided by their masses.

The results show that higher heel drop shoes increased plantar flexion in the ankles and knee flexion during ground contact. This we know from past research since runners who previously had knee pain had decreased knee forces and knee pain when they switched to zero drop running shoes.

Higher shoe heel-toe drop also increased metabolic power by 0.08W/kg per 10mm of heel-toe shoe drop.

One limitation in the study was that they only had one relatively large shoe size (US 10) which resulted in only one female participant in their study. Future studies may be warranted to test for potential effects between male and female runners.

Based on the researchers findings, they concluded that decreasing shoe heel-toe drop from 20mm to 0mm elicits a 1.6 percent more economical running which is predicted to improve total marathon performance by 1-3 minutes. 

Perhaps we will see the carbon plated maximalist running shoes come with zero heel-toe drop next?

Reference

Renninger K, Beck ON (2026). Shoe Heel-Toe Drop Affects Running Economy. J Appl Physiol. 141(1): 280-290. DOI: 10.1152/japplphysiol.00886.2025