The Repeated-Bout Effect

Picture from Iwannaburnfat

Those of you who are preparing for races with long downhills (like Boston) or trail races may want to know this. Or even personal trainers and strength coaches getting their athletes to do eccentric exercises.

If the long descent (or an eccentric exercise) is unaccustomed, it can cause muscle damage, soreness and a loss of strength (or delayed onset of muscle soreness - DOMs). However, repeating the same activity causes far less damage the second time. This protection is known as the repeated-bout effect. It is not commonly known how long the protection lasts. Let's see what the latest research found.

48 young males were recruited for this study. They did 2 identical exercise sessions where 5 sets maximal knee extension (straightening) exercise was peformed. Each set consisted of 15 repetitions at 60°/ sec.

4 independent groups performed the second bout of exercise 3, 6, 9 and 12 weeks after the first bout of exercise. 

Range of motion, delayed onset of muscle soreness (DOMs), muscle thickness (swelling), isometric torque (strength), echo intensity (tissue quality/ fluid accumulation), creatine kinase and high sensitivity C-reactive protein (hs-CRP) were assessed before, 2 and 4 days after each exercise bout.

Since the participants started with different levels of strength, soreness and blood markers, the researchers measured the subjects at baseline and then adjusted future data points based on their starting numbers. This allows the resarchers to evaluate how much strength each participant lost or recovered, rather than their raw strength.

The repeated bout effect was still present after 3 and 6 weeks across most outcomes and certain markers were still detectable after 9 weeks. At 12 weeks, all the protective effects were gone.

Please note that this study was done on young men performing isolated knee extension on a machine so some differences in timeline can differ in downhill running, for women and older runners.

So those of you preparing for races with long descents should ideally run a downhill-specific session every 3-4 weeks so your repeated-bout effect protection is intact. After a 3 month break or more or after the off-season, the first downhill session should be treated like a new first session. 

Picture from Iwannaburnfat

For strength coaches or personal trainers planning eccentric strength training cycles (like Nordic curls) to build injury resilience, you need to repeat the exercises within 6 weeks to maintain the protective adaptations. 

Reference

Theodorou AA, Margaritelis NV, Karyofyllidou et al (2026). The Duration Of The Repeated-Bout Effect After Eccentric Exercise. Scan J of Med & Sci Sp. e70381. DOI: 10.1111/sms.70381

Exercise Within 30 Minutes After You Eat?

Walking after a meal

I see patients before and after lunch 6 days a week. This reduces the chance of me sitting down and being stationary after a meal. I've been trying to walk a little after dinner especially after I read an article by Borror et al (2018).

This article investigates the effects of exercise on glucose (or sugar) control in people with Type II diabetes.

12 studies met the inclusion criteria in this systematic review. There were a total of 135 participants (108 males, 20 females, 7 unknown). The included studies varied greatly with respect to timing of exercise, duration, intensity, modality of exercise and glucose measure.

Exercise after meals was shown to decrease short term glucose (sugar) spikes. Most consistent benefits were seen in long duration (≥45 min) of moderate intensity exercise. Short term sugar levels decreased by up to 27 percent and 24-hour hyperglycemia decreased by up to 65 percent.

Strength training (or resistance training) was also effective. Those figures were cut by up to 30 percent for short term blood sugar levels while 24-hour hyperglycemia decreased by up to 35 percent.

The authors recommend that individuals with Type II diabetes focus on increasing energy expenditure after the largest meal of the day.

If you are like me, with the largest meal of the day being dinner, there is very little chance of me going out for a 45 minute aerobic/ cardio exercise or even a strength training session after. Granted, I definitely do not have Type II diabetes, but to minimise the spike in sugar levels, light exercise like walking is definitely doable. Hence the walk to the supermarket nearby or volunteering to collect a parcel from the Shoppee collection point near our house.

Most blood sugar advice suggest diet or medications. I feel one of the easiest way is to simply walk. A light 'exercise' after you eat. Muscles will use and "pull" the glucose out of the bloodstream when they work. That will help blunt the post meal sugar spike. Even a 10 to 15 minute walk helps. Much easier than going for a 45 minute bike or run session or doing weights.

Reference

Borror A, Zieff G, Battaglini C et al 92018). The Effects Of Postprandial Exercise On Glucose Control In Individuals With Type 2 Diabetes: A Systematic Review. Sporst Me, 48(6): 1479-1491, DOI: 10.1007/s40279-018-0854-x

Negative Split For Your Next Race

Still on Vince Mauri, he started fast at the Chicago marathon and then dropped a 14:28 min 5 km split (2:53 min/km or 4:39 min/mile) from 20-25 km. He was on course to run a 2:04 hrs race, enough to break the American record of 2:04:43 hrs. 

However he was running on his own in no man's land, behind the race leaders but in front of his fellow Americans, Clayton Young and Charles Hicks. Then Mauri faltered. He basically tried to bank in time early. Most runners know that the best way to approach a race is to run a negative split. A negative split means running the second half of the race faster than the first half.

Runners know that how you pace yourself at the start is critical in a race, especially in a marathon. If you ran like Mauri, you are doing a positive split, a faster first half of the race followed by a slower second half.

However a review of pacing physiology found negative splits improve glycogen sparing, thermoregulation and cardiovascular drift compared to a fast start. These benefits contribute to delayed fatigue (by sparing glycogen usage) and greater efficiency in the later parts of the race. 

If one wishes to race well in a marathon, you need to have enough muscle glycogen. Starting too fast in a race hastens the rate of glycogen breakdown and leads to fatigue inducing metabolites like lactate and hydrogen ions. A negative split pacing strategy allows for more gradual glycogen utilization (since you are going slower) and preserve energy for the later stages of the race.

When you start slower, a higher proportion of your energy are derived from using your fat stores, thus sparing glycogen stores. When glycogen stores are depleted, runners are forced to rely on slower, less efficient energy systems. You experience hypoglycemia-induced fatigue or "hitting the wall".

Glycogen sparing also helps sustain neuromuscular coordination and delay central and peripheral fatigue, both are essential for maintaining biomechanical efficiency in the later stages of a marathon.

This approach is consistenty associated with superior race outcomes (Sha et al, 2024). For example, Eliud Kipchoge's sub-2 hour marathon involved a highly controlled pace with subtle acceleration in the final stages, a textbook example of even to negative pacing.

Remember my post on warm weather making me eat more during my 3 hour Saturday rides? Starting at a conservative pace reduces metabolic heat generation during the early stages as well. Thermoregulation plays a vital role in endurance performance especially in a marathon where progressive effort leads to progressive heat accumulation. 

When core temperature rises, the central nervous system initiates protective mechanisms to limit further exertions, known as "central fatigue". A negative split strategy allows for a more controlled rate of heat production early on, helping to delay the onset of thermally induced fatigue.

Moreover, better thermoregulation helps to improve cardiovascular stability. In hot conditions, blood supply is partly directed to the skin for cooling purposes. Meaning your running muscles may not get as much blood flow.

As you sweat more, your blood volume drops causing your heart to beat faster just to maintain cardiac output (or cardiovascular drift). A conservative start minimizes early sweat loss, preserving your blood volume for the final push.

How do you execute a negative split for your race? The authors suggest doing progressive long runs to simulate negative split pacing. Begin at easy pace and gradually increase to race pace or faster in the closing kilometers allowing you to practice the metabolic and mental transition from conservative to assertive effort. Other strategies include tempo runs with a fast finish, negative split intervals and controlled progression runs to develop pacing control and late race strength.

Perhaps using heart rate monitors, GPS pacing, etc is necessary for some runners to achieve pacing awareness.

To run a negative split, you need to have confidence, patience and a tolerance for initial 'underperformance'. You need to resist temptation to "bank time" early and trust your ability to finish strong. 

You can practise visualization, goal setting and self-talk to help reinforce a conservative start and maintain focus before the crucial end part of the race.

Reference

Grivas GV. The Physiology And Psychology Of Negative Splits: Insights Into Optimal Marathon Pacing Strategies. Frint Physiol. 16: 1639816. DOI: 10.3389/fphys. 2025.1639816

Lane 8 Distance On A Track

Picture from SacKenny

I probably would never run as long and as fast as Vinny Mauri on a treadmill. The longest I've ran on a treadmill is probably slightly more than an hour in Birmingham, UK. This was when it was windy and rainy outside. I was traveling with the Singapore Badminton team then. They were taking part in the All England Open Badminton Championships.

I did run many laps at the old National Stadium where I worked previously. I would also run on the grass outside lane 8 of the track to cover more ground. 

I never really knew the exact distance for every lap I did. I just 'guesstimated' the distance when I recorded it in my training log book. 

I just saw the above picture of the distance you cover depending on which lane you run in. So if you need to run many laps on a track, see the exact distance in the picture above.

Give Him A Treadmill

Mauri after his debut marathon in Toledo

I had a patient who told me that while training the marathon segment of the Ironman triathlon event, she would often go to the old Kallang Practice Track and and run 50 rounds (20 km). She could focus on running and not have to worry about traffic lights, pedestrians or spraining her ankle on an uneven pavement.

Meet Vinny Mauri, who ran a 2:05:54 hrs in his marathon debut in April this year at the unheralded Glass City marathon in Toledo. The race had less than 1,300 finishers, no pacers and a previous course record of 2:19:31 hrs. 

He also does most of his training on a Planet Fitness treadmill. 6 months ago, 25 year old Mauri was largely unknown. However, at the Chicago marathon next week (11/10/26), he has a good chance of breaking the American record of 2:04:43 hrs set by Connor Mantz at the same race last year.

Mauri has what many consider an abnormal training routine. He runs the majority of his miles on treadmills at one of two Planet Fitness gyms near his hometown of Warren in Northeast Ohio.

He rarely runs slower than 6:00 min /mile (or 3:44 min/km) for any of his runs. He regularly reaches 30 miles (48 km) at under 5:00 min/mile (or 3:06 min/km) pace.

He runs very little in carbon plated shoes. In fact he only just signed a shoe contract with Asics last week. He does all that while working more than 15 hours a week at a running store. 

On June 28th this year, he earned 611 kudos after his effort on Strava post went viral for running 26.39 miles (42.7 km) on a Planet Fitness treadmill in 2:20 hrs. Impressed?

Only a week later, he ran 29.16 miles (46.66 km) even faster at 2:15 hrs marathon pace again on a treadmill. Or 5:09 min per mile (3:20 min/km).

He clocked a total of 1,223 miles (1957 km) in his last 10 weeks of training. All at an average pace of 5:38 per mile (3:30 min/km).

If you look at Conner Mantz's same 10 week training block leading up to his American record of 2:04:43 hrs set in Chicago last year, Mantz ran 1,182 miles (1891 km). His average pace of 6:35 min/mile (4:05 min/km) was almost a minute a mile slower than Mauri's.

For 4 straight Tuesdays from 25th August to September 15th, Mauri ran 4 godzilla sets of double workouts. On each of those Tuesdays, he ran 36 miles, with at least 27 of those miles at 4:56 min/mile (3:04 min/km) pace or faster. 

On 8th Septemeber, he ran 36 miles at an average pace of 4:56 min/mile (3:04 min/km). 2x50 minutes in the morning, 4x20 mins in the afternoon. That's 36 miles at 2:09:09 marathon pace. If you include his warm up and cool down runs, he logged 45 miles (72 km) that day (pictured below). 

If you include his 28 miles long run and a 13 miles "easy" run at 6:00 min/ mile (3:44 min/km) pace across the previous days from 6th-8th September, Mauri ran 86 miles in 3 days at an average of 5:27 min/mile (3:23 min/km).

He ran the fastest debut marathon in American history on a day the marathon world was watching Sabastian Sawe break 2 hours in London. In one race, he went from being a virtual unknown to 4th fastest of all time on the US marathon list.

Why does he run so much on a treadmill? Perfect weather, no need to worry about wind, snow or ice in winter or heat/ humidity in summer. He likes the convenience, gels and drinks always at hand and the bathroom is nearby if needed.

He also runs on a treadmill to protect himself as he has a natural tendency to pick up the pace during runs outside. In a 60 min recovery run outdoors recently, he wanted to run a 6:10 mile/min (or 3:55min/km), he averaged 5:25 min/mile (3:22 min/km) and was running sub-5:00 min/mile (3:00 min/km) at the end.

The Planet Fitness treadmills stop automatically after an hour, and Mauri has to stop and start the machine again once or twice per session, usually during his rest periods. The treadmills also max out at 12.4 miles/hour (20km/hr) or 4:50 min/ mile (3:00 min/km), meaning he cannot go faster than that, thus holding him back to prevent going too fast. That's slower than his marathon race in Toledo 2:05:54 hrs which is 4:48min/ mile (2:59 min/km).

Can he beat the US record next week? You can get good training on a treadmill, but it does not quite equal to racing outdoors. The race in Chicago next week will require one to know which moves to respond to when the pack goes out too fast or slow and how to adjust to the temperature and wind etc.

Mauri says he feel's fitter than before his race in Toledo. His entire buildup is documented on Strava (pictured above), yet so unorthodox, and does not include tune up races.

I don't know how it will translate to the streets of Chicago. Everything about Mauri's build up to Chicago is superior to Toledo. Longer buildup, significantly more miles at a much faster pace. He will also be racing against a stacked field.

I will definitely be cheering him on. The treadmill companies should give him a faster treadmill (than his race pace) to train at home.

PS *Mauri finished the race 10th overall and 3rd American in 2:06:45 hrs. He ran a 14:28 min 5 km split (2:53 min/km or 4:39 min/mile) from 20-25 km, on course for a 2:04 hrs pace. Alas, the oppressive humidity came back to bite him as he had to stop and stretch his hamstrings twice. 

Even though he was reeled in by Clayton Young, Charles Hicks and Japan's Akira Akasaki, he stayed at or near the front of that group as long as he could. Young would finish 7th overall in 2:05:23 hrs as the first American, Hicks was the 2nd american and 8th overall in 2:05:35 hrs, just 12 seconds behind Young.

Mauri is definitely not a one hit wonder.

Improve Your Running Economy Durability

Remember my post for runners who want to log long distances so that they can race well? Here's another benefit for running longer.

Runners with regular long runs tend to hold their form and keep their running economy better late in a run. Running economy durability becomes better.

If you have high running economy, your body uses less oxygen and burns less carbohydrates when running at 6 minutes per kilometer pace. If you have low running economy, your body is less efficient and has to work harder and burn through more carbs to maintain that same 6 min / km pace. 

When you start running, your body is fresh and highly efficient. As the minutes and miles go by, your muscles fatigue, your running form deteriorates and your systems have to work harder. Running economy durability is your resistance to this degradation over time.

Consider the following study by Zanini et al (2026). Two groups of 13 male runners were recruited as long distance training (LDT) or short distance training (SDT) runners. The LDT group of runners had regular long runs ≥ 90 mins while the SDT group had all their runs under 70 mins.

Both groups of runners were first assessed to determine their lactate threshold and maximal oxygen uptake. On another day, they then did a 90 minute run at lactate threshold. Lactate threshold here is the running pace (or exercise intensity) where lactate begins to accumulate in your bloodstream faster than your body can clear. It represents a boundary line between sustainable effort and unsustainable exhaustion.

Respiratory gases were collected and assessed every 15 minutes. Isometric squat peak force and counter movement jump values were assessed before and after the run.

When matched for 10 km performance, the LDT was faster (39:00 versus 39:10 min), had higher maximal oxygen uptake (58.9 versus 56.6 mL kg⁻¹ · min⁻¹). The LDT runners lost 3.1 percent running economy over 90 minutes versus 6.0 percent for the SDT runners. 

Results show that SDT runners had greater losses in running economy, isometric squat force and jump power compared to the LDT running group of runners. Running economy durability also correlates significantly with weekly training volume and length of the weekly longest run rather than muscular fatigue.

This study shows that long runs and higher training volumes positively affect running economy durability and protects a runner's aerobic efficiency over time. So even if there are 2 runners who can run a fast 10 km at the exact same pace, the runner who skips or does not do as many long runs will burn through significantly more energy and experience drastically higher muscle fatigue as the duration of an event stretches past the one hour mark.

Want to run a personal best in a marathon (or any long event), make sure you do your long runs regularly and race pace training.

Reference

Zanini M, Folland JP, Blagrove RC. (2026). Regular Long Runs And Higher Training Volumes Are Associated With Better Running Economy Durability In Performance Matched well-Trained Male Runners. Med Sci Sp Ex. 58(1): 162-173. DOI: 10.1249/MSS0000000000003840.

Why We Ask If You Drink Alcohol?

One of the questions we always ask our patients when they see us for the first time is whether they smoke or drink. This past week, I had a patient who gave me a 'none of your business' kind of look when I asked that question. 

I told him actually it is none of my business whether he smoked or drank. The only reason we ask that in our clinic is that both can affect tissue healing. Smoking dries and dehydrates our interstitial spaces and connective tissues. Alcohol has an inflammatory effect and damages articular cartilage.

Surprised? Consider a prospective Osteoarthritis Initiative study that studied 2,846 participants (between 45-79 years old) and most importantly had no radiographic (or x-ray) evidence of knee osteoarthritis (OA) in at least 1 knee at baseline. These participants were followed for 96 months.

The researchers investigated for incident cases of radiographic knee OA as Kellegren-Lawrence grade changing from zero or one to ≥ two during the follow-up period. Incident symptomatic OA was defined as radiographic knee OA with knee pain worsening. 691 knees with incident radiographic OA knees were identified and 496 knees with symptomatic OA were found among the subjects.

Baseline information on alcohol consumption were obtained using the Block Brief Food Frequency Questionnaire. 

Drinking 30 grams of alcohol a day or more (about 2-3 drinks) was associated with a 93 percent higher risk of radiographic knee OA and 61 percent higher risk of symptomatic disease versus non drinkers. A similar result was observed for liquor spirit consumption (pictured above).

The underlying mechanism between between alcohol consumption and OA onset is still controversial. An animal study demonstrated that chronic alcohol consumption increased the articular cartilage breakdown enzymes (MMP-13, ADAMTS-5) in both shoulder and knee joints in mice. They also suppressed the molecules that protect articular cartilage.

The authors concluded that excessive alcohol consumption (≥30 grams/ day) was significantly associated with an increased risk of developing both knee structural changes and clinical knee joint pain. Light to moderate drinking showed no measurable negative impact on knee OA development in this study.

Light to moderate drinking data was mixed for other factors. What we know is not mixed is alcohol also disrupts sleep, triggers inflammation, adds empty calories which affects every other healthy knee arthritis habit.

Now you know why we ask about smoking and drinking. Especially if you have knee pain.

Reference

Liu T, Xu C, Driban JB et al (2022). Excessive Alcohol Consumption And The Risk Of Knee Osteoarthritis: A Prospective Study From The Osteoarthritis Initiative. Osteo Cartilage. 30(5): 697-701. DOI: 10.1016/j.joca.2022.01.011

And there is an article on drinking less alcohol in the Sunday Times today too.

Rotator Cuff Tear

A patient sent me a message yesterday regarding her shoulder. She had slept poorly and woke up with some shoulder discomfort. After seeing her doctor, he referred her for a scan. Her MRI shows a tear in the supraspinatus muscle (part of the rotator cuff) and some osteoarthritic changes in the joint. She was worried about the tear. It got scarier when her friends told her that if she did not "fix it" the tear would become worse and her shoulder would wear out.

I told her about a recently published study done where 602 participants had  scans done on both shoulders. (Ibounig et al, 2026). Median age of the participants was 59 (range from 41-76 years old) and 52 percent were female. 

Rotator cuff abnormalities were found in 98.7 percent of painful shoulders. There were 25 percent with tendinopathy, 62 percent partial thickness tears and 11 percent with full thickness tears (FTT).

More importantly, rotator cuff (RC) abnormalities were seen in 96 percent of pain free shoulders. Full thickness tears of the RC were in 7 percent of shoulders that did not hurt. 

The prevalence and severity of abnormalities increased with age, but did not differ between sexes. 

Only FTT were more prevalent in painful shoulders (14.6 percent) than in non-painful shoulders (6.5 percent). However this difference decreased after "adjustment" (absolute difference, 0.8%; 95% CI, -3.4% - 6%). This means that once the researchers accounted for age, the apparent link between having shoulder pain and a FTT vanished.

At first glance, FTT looked more common in painful shoulders (14.6%) versus non-painful shoulders (6.5%). However, older people are more likely to have shoulder pain and a FTT just from normal aging.

"Adjustment" is a statistical technique that levels the playing field as it allows reserachers to compare painful and non-painful shoulders of the exact same age. When they did this, the true difference was just 0.8 percent. This is a very tiny margin, meaning the presence of a tear does not reliably explain why a shoulder hurts.

95% CI, -3.4%-6%. When the confidence interval (CI) crosses zero (goes from a negative to positive number), it means there is no statistically significant difference. The negative side means it is statistically possible that FTT are actually less common in painful shoulders by 3.4 percent.

The positive side means it is statistically possible FTT are more common in painful shoulders by 6 percent.

The math proves that one cannot look at a FTT on an MRI an automatically assume it is the cause of someone's shoulder pain. A person with a painful shoulder is statistically no more likely to have a full thickness tear than a person of the same age with completely pain free shoulders.

I told my patient that her 'abnormalities' on the scan were actually just aging. What matters most for her (and others) is function. Is there weakness and/ or pain when she moves her shoulder?

Can she sleep without pain and can she play pickleball without pain? If all her answers are no, she most likely will NOT need an operation. Just because abnormalities are seen on MRI does not mean it can cause pain or needs to be fixed.

Reference

Iboinig T, Jarvinen TLN, Raatikainen S et al (2026). INcidental Rotator Cuff Abnormalities ON Magnetic Resonance Imaging. JAMA Intern Med. 186(4): 406-414. DOI: jamainternmed..2025.7903

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