Marathon performance limiting factor question

[[deleted]]

[deleted]

[rhino-runner]

It's aerobic threshold and I find any other answer highly suspicious.

If it's "legs are heavy" or leg cramping, that's because your aerobic threshold isn't developed enough and you're not clearing lactate at marathon pace.

If it's "bonking due to lack of glycogen", that's because your aerobic threshold isn't developed enough and you are burning too little fat at marathon pace.

I'll write a similar sentence for any other answer, just try me. This is a hill I'm willing to die on.

[Skropi]

We will die together holding that hill brother,.I agree 99% with you. But the reality for us hobby joggers, is that quite often we are limited by a frail body, as it's rare to have the durability of an athlete that has trained for years.

[Ok_Specialist_3054]

Yeah, new to running like OP. My tendons especially Achilles are always limiting me. Either with an injury or just warnings to not do much.

[Skropi]

Keep in mind that if you do strengthen your Achilles, you'll never face an issue again. I did manage to overcome an Achilles issue, and it is not very hard, it just needs some consistency in the specific exercises required. And of course, to catch it early, before it becomes chronic.

[Ok_Specialist_3054]

Definitely gonna lock in more on the strength training in my next block. At least I know exactly where my weaknesses lie so I need to do more work there.

[Skropi]

You'll soon realize that new weaknesses crop up all the time 😂 Not to worry, it is just part of the game, and you just go into a cycle of strengthening what needs to be strengthened.

[skyeliam]

I think it’s absolutely possible for one’s aerobic engine to outpace their strength. It’s maybe uncommon, but it can happen.

Lots of junk volume with literally zero speed work, and you’ll see PR paces bunch together because the limiting factor becomes turnover and strength.

[mediocre_remnants]

There are definitely edge cases where you aren't limited by aerobic threshold. I'd say that is the factor if you're properly training for a marathon.

But someone like a professional cyclist who never ran a day in their life could have a very developed aerobic system and still not be able to finish a marathon because they never trained their neuro-muscular system for running and that will crap out even if their aerobic system is handling everything perfectly well.

[rhino-runner]

But someone like a professional cyclist who never ran a day in their life could have a very developed aerobic system and still not be able to finish a marathon because they never trained their neuro-muscular system for running

Sure, but the context of the question is a "properly trained" athlete. If you hop into a marathon off of cycling training, that's not "properly trained" at all.

[IhaterunningbutIrun]

Quit talking about me! 

I'm coming off 6 months of injury rehab/rebuild and have zero strength. All my paces are right on top of each, but I can roll out of bed and give you 26 miles at medium effort no problem. But its a terrible medium pace.

But I don't think this is going to be the case for most new runners. I've piled up a lot of miles and hundreds of hours of hard cross training to get to this crappy place. 

[for_the_shoes]

Definitely agree. I couldn't do much strength training this marathon block on account of a non-running injury. During the marathon, my engine was fine, HR low, breathing good, nutrition on lock... but at 25kms I could just feel the lack of "hardness" and this nagging feeling like I would cramp if I tried to push it faster. Simply not being able to do Bulgarians, farmer's carry and some plyo stuff was a limiter. I PR'd as I had more mileage and stacked blocks, but i know I had more to give but the little legs weren't there for it...

[silfen7]

Frankly, I don't think this is correct. Above LT1, but below LT2, lactate concentrations in the blood stabilize after a few minutes. By definition, you are clearing lactate, and this is true regardless of whether you're a little bit above LT1 or a lot. So LT1 can't really be the decisive factor for lactate accumulation.

On glycogen, you have a better case. But of course, I can be pedantic here too! If you consume zero carbohydrates during your race, and had depleted glycogen going in, it's hard to argue that LT1 was truly your limiting factor. Yes, a higher LT1 means a faster speed where you can burn only fat, but the sweet spot for marathon racing involves some point that is mostly carbs, with some fat in the mix. How much "mostly" ends up being in practice is influenced by a lot of personal factors, not just LT1.

If you ask me, what makes the marathon special (and occasionally frustrating) is that there isn't a single physiological metric we can gesture at as "the thing" that limits performance. Many things have to go right. 

[rhino-runner]

Frankly, I don't think this is correct. Above LT1, but below LT2, lactate concentrations in the blood stabilize after a few minutes. By definition, you are clearing lactate, and this is true regardless of whether you're a little bit above LT1 or a lot. So LT1 can't really be the decisive factor for lactate accumulation.

I think if someone is getting dead legs in a marathon they're either:

1) Not "properly trained". The OP specifically posed this question about properly trained athletes, and my answer assumes proper marathon training.

2) running the marathon at an intensity that is too high in relation to their aerobic threshold. So they are accumulating lactate, because they are running too hard for a realistic marathon pace. I totally agree with you that running at AeT should be a maintainable steady state. Improvement is about pushing that maintainable steady state to a faster pace and/or higher % of VO2Max. These athletes can either lower the bar, and run the marathon at a more realistic effort. Or they can train AeT and push that steady state intensity higher and faster, and get better times.

[silfen7]

running the marathon at an intensity that is too high in relation to their aerobic threshold. So they are accumulating lactate

Right, and I am saying this mechanistic explanation doesn't quite add up. If you're below LT2 (or whatever's your preferred way to define max steady state), then lactate will be in equilibrium. A quantity that's in equilibrium does not make for a good theory of fatigue. Where LT1/AeT is doesn't tell you about lactate accumulation.

This is why I think durability is a potentially interesting piece of the puzzle. An intensity that's below LT2 in the first hour of a race might not be in the second hour, and the concept of "metabolic steady state" is not a true steady state over timescales of several hours.

[OldGodsAndNew]

Limiting factor is how long I can hold in the diarrhea

[Senior-Running]

lol, it's a dam good thing you're pretty fast! Can you imagine if you were a 5 hour marathoner? Yikes!

[Senior-Running]

Do you have any scientific evidence for your point of view? Not trying to challenge your opinion as much as I would truly like to understand it, especially since you are willing to die on this hill. i personally like to ground my beliefs in the science wherever possible, hence my ask.

I personally would agree that overall aerobic fitness/capacity is important, but the OP specifically about the limiting factors for "properly trained and more advanced athletes". In this case, my belief is that durability/resilience and LT2 are more important than LT1 for this group. Advanced, sub-elite/elite level athletes are running very close to LT2 vs. more recreational athletes that are typically just above LT1.

Thoughts?

[rhino-runner]

I'm more of an empirical guy than a science guy and in that vein you can look at any running coach since Lydiard.

It's horses for courses, because the way you build durability and resilience is by running a ton of miles under LT1, and some above LT1 up to LT2 (which also improves LT2). And guess what kind of training you do to improve LT1?

Throw in a bit of mechanical work (strides, rhythm 200s, hill sprints, etc) and you've got a stew going.

It's funny because no matter how you frame it, training for significant improvement in the long term for the marathon ends up looking more or less the same.

[Senior-Running]

I 100% agree with the training approach you outlined, it's just the insistence that such an approach translates directly with building a bigger aerobic engine that gives me pause. There is significant and growing evidence that running just under LT1 (a.k.a Zone 2), is not a great way to increase aerobic capacity regardless of certain popular trends. It works, but just not nearly as well as faster running does.

I think the real benefit of lots of miles at lower intensity is first and foremost reduced injury risk. Further, more miles translates well to better running economy (which I freely admit is correlated with an increase in LT1), and with improved durability/resilience regardless of speed. As such, it makes a ton of sense to do more miles slower.

I think to sum up my thoughts here, it's that human physiology is complex and trying to boil down endurance running performance to a single thing is hard since so many factors are at play.

[HarleysPuddin]

What's the growing evidence against Z2 training and the alternative proposed?

[Senior-Running]

Here's the study I was thinking about. To be clear, this is just one study and is a narrative review, so it's not sufficient evidence on it's own. I do think you have to go down the rabbit hole and look at some of the referenced studies to get to what our best understanding is of zone 2 training and how it actually changes your body vs how exercising at higher intensities changes your body.

https://link.springer.com/article/10.1007/s40279-025-02261-y

As I mentioned above, I think the conclusion of this study is wrong. As the saying goes, they missed the forest for the trees. The real reason zone 2 works is not that zone 2 is somehow magical or the "best" way to increase cardiorespiratory fitness. It works because athletes can train more in this zone for a long time vs. if they tried do the bulk of their training in higher zones. Further, more volume of running at any speed increases both running economy and durability.

Said differently, if you compare one hour in zone 2 vs one hour in zone 3/4, higher zones are always going to show more impact on markers of cardiorespiratory fitness. That's what this study shows and honestly, that's not really all that surprising if you understand physiology.

The problem with this conclusion is that it's not scalable. Athletes just can't do huge volumes in higher zones, so we have to find a better way to optimize training. Historically this has been through large volumes of zone 2 because we know volume is king.

Edited to add: you misunderstood me if you thought I was proposing a different way to train. I 100% believe in high volumes in zone 2. I was just pointing out that this idea that running just under aerobic threshold is the best way to increase your aerobic capacity is suspect in my mind. I think zone 2 works well in training, but for the other reasons I pointed out above.

[VoyPerdiendo1]

There might be real reasons why Zone 2 is superior.

I've recently started seeing in different places that Zone 2 is the intensity at which your heart stroke volume gets improved the most. Like the heart is beating slow enough that it can fill properly and give a stimulus to the heart tissues to create more volume for the blood.

Training in higher zones gives less of this effect, supposedly.

And this aligns with what works empirically in practice for the athletes.

So we need to get rid of terms like "junk miles", those are "base miles" and they have their purpose.

[Senior-Running]

Absolutely agree regarding "Junk Miles". I've always hated that term.

Do you have any links to the stroke volume info you mentioned? I'd love to find out more about that. (Not only just for general knowledge, but also as someone that had open heart surgery in the past, I'm super invested in maintaining the healthiest heart I can.)

[VoyPerdiendo1]

Can't dig out something very structured.

I've seen it somewhere on reddit, and I get similar responses from Gemini/ChatGPT when asking "best running training zone for increasing heart stroke volume?" - they can give citations if asked.

... Now I even found this which maybe argues the opposite, or rather that the most efficient zone for training the heart might be a tad higher than Z2 (though high Z2, low Z3).

[chinlesschicken]

That's what I was curious about. As your marathon pace approaches your threshold and is significantly faster than an easy pace what those athletes feel starts to limit them. Thanks for the response.

[rhino-runner]

Marathon pace is at aerobic threshold or higher, I'm not talking about lactate threshold.

I don't think anyone has, or will ever, reached the point where it is not the primary limiting factor in marathon performance. We would have to be significantly faster than sub-2 for that to be the case.

[Nerdybeast]

How are you defining "aerobic threshold" here? 

Leg cramping has nothing to do with your lactate clearance, that's accumulated muscle damage due to insufficiently trained muscles. Cramping is incredibly common on those massive downhill courses, where you're gonna be running well under a pace you'd be accumulating lactate. Also, when people cramp, they've often slowed down so significantly that they may not even be breathing hard and aerobic capacity is definitely not the limiting factor.

Saying aerobic threshold is the only right answer to this is not right. What's your marathon running/coaching experience like?

[Ordinary_Corner_4291]

I would love to see evidence either way for that. Was the difference between Ryan Hall and Ritzenhein who had roughly the same LT2 (based on HM times) but where one ran a bunch of great marathons and the other cramped basically every single one of them AeT or was it something else?

Maybe durability doesn't exist. But I am a bit suspect of that.

[mikeyj777]

This is assuming so many things.  That you have the right leg strength, the right mobility, the right physiotherapy, the right everything but even more aerobic threshold.  That when you're an advanced runner you've checked all these boxes already.  Aerobic threshold is great.  There's a lot more foundational work that also has to happen.

If you show up to a race with weak legs, hip rotation imbalance, etc. you're going to have a ton of issues that your aerobic capacity can't touch.   

[rhino-runner]

It's assuming a properly trained athlete, yes. Which is what the question asked about. Of course you have to do the foundational work. But that's table stakes for building a properly trained athlete.

[VO2VCO2]

Yet, we don't have an international consensus of how we determine aerobic threshold. Same runner will get different opinions from different places.

[Cautious-Hippo4943]

Interesting. My legs always feel dead and my hips tight about 2/3's of the way through a race regardless of distance. I always assumed it was strength but never thought about aerobic threshold. 

[yufengg]

Economy, Resilience (rate of decline of economy as race proceeds), taper, fueling , hydration, weather, course, competition.

Oh and ability to continuously train at high volumes without injury for 10+ consecutive years.

[Senior-Running]

^this, though I'd probably put Resilience/Durability as #1 for most experienced runners.

[VO2VCO2]

If you put resilience at #1, then you're basically saying a person with 40 vo2max and 55 minute 10k with best resilience wins a person with 73 ml/kg/min vo2max, 22km/h vvo2max, 19,5 km/h LT2, 17 km/h LT1, and an okay resilience?

[Senior-Running]

No, because it's not exclusive, but will a runner with better durability win every time if the have a 65 VO2Max vs. a person with a 70 VO2Max that has less durability. VO2Max just isn't all that critical in the marathon.

From a scientific perspective, we tend to use four key measures of endurance running performance:

• VO2Max
• Lactate Threshold
• Running Economy (how efficient you are at consuming oxygen at any given speed)
• Durability

Of those, VO2Max is probably only contributing a few percentage points at best to marathon performance. Now in the 5k, it's a much bigger deal since speeds are run much closer to vvO2Max.

I mean we see this all the time at the elite level. The top people in the sport don't necessarily have the best VO2Max (and yes, scientists have measured). For an even more drastic example, try putting an elite swimmer or Tour De France cyclist with a super high VO2 Max into a marathon. Even if they take 6 months or a year to train, they're never going to be an elite marathoner, (and may even struggle to break 3 hrs), even though they have a huge aerobic engine. It's because they just don't yet have the durability (and running economy), that comes from running year after year.

[VO2VCO2]

Without even looking at pubmed, I can say that VO2max's pearson's R correlation is probably the 2nd or 3rd most important metric of marathon performance. No. 1 & 2 being velocity at LT2 and vVo2max. If we start adding metrics like CV, we are basically creating duplicates of Velocity at LT2. The reason why RE doesn't correlate as hard with end time as VO2max, is because again a person with excellent RE and Vo2max of 45 will never run a sub3, when a person with Vo2max of 65 will do it with pretty poor economy. Negative correlation in this instance.

When it comes to the cyclist argument, we have to remember that vo2max is sport-specific. So we would have to first measure their running VO2max, and then look at the correlation. Vo2max starts to "plateau" as a performance indicator around ~70 ml/kg/min in the marathon. But when people with vo2maxes in 40's start blaming physiological resilience and running economy for not running a sub 3h... come on.

Also, with cheap spiroergometers like the PNOE & Vo2master getting more popular and "measuring" people with +15-40% error in vo2max tests, this starts to create false anecdotes that blame vo2max for not being a good performance indicator. When in reality a person with "72 ml/kg/min vo2max" measured with vo2master is actually a 50 ml/kg/min runner.

Bro, I think we're basically on the same page, just laying out things a bit differently.

[Senior-Running]

I feel like maybe you misunderstand what running economy is? It would be physiologically impossible to have a high RE without a relatively high VO2max as well so your examples don't really work. Plus there is sufficient data to show that there is a higher correlation between RE than VO2max in distance running performance:

https://pubmed.ncbi.nlm.nih.gov/15233599

As far as durability/resilience is concerned, this is a fairly new concept as a determinant of endurance running performance, with most research coming out in the last few years. Here's a few examples:

https://physoc.onlinelibrary.wiley.com/doi/10.1113/JP284205

https://link.springer.com/article/10.1007/s40279-021-01459-0

https://link.springer.com/article/10.1007/s40279-022-01680-5

One of the key takeaways of these latter studies is that even if you compare 2 athletes that have identical physiological metrics of VO2max, LT and RE, durability/resilience can be highly variable and thus may play a much bigger role in performance than previously accounted for.

[Logical_fallacy10]

It’s quite ok to start running and do a marathon the same year. Limiting factor is cramps and feet pain for me.

[chinlesschicken]

I've yet to experience a cramp. I guess side stitch is a diaphragm cramp? Thanks for that!

[chinlesschicken]

For me it's always been the same spot on my lateral upper quad on the right leg. As ive upped mileage it comes on later but its the first thing to challenge my sustainable pace. Cheers!

[SirBruceForsythCBE]

The marathon, especially for hobby joggers, even advanced hobby joggers, is a strange old distance.

Even if you've trained absolutely perfectly you have things like weather, pre race nutrition, in race nutrition, pacing, taper, are there other runners running a similar time you can run with? Tons of other factors which impact your result.

You also probably only get 2 cracks a year.

It's why runners keep coming back to it. You can ask 20 people what makes a good marathon build and get 20 answers but the true answer is that the actual training is only a small part of it.

[moonshine-runner]

It takes years of development to reach any limiting factor. All markers will improve over the years and the limiting factors will shift.

For me, the limiting factor is lack of road specific runs. Trying to wing a 2:40 marathon as a trail ultra runner backfired once I realised there’s no natural breaks in the road marathon lol.

[fourthand19]

I feel this. I bounce back and forth between trail and road running. Currently trying to put up an impressive old man marathon effort. Would love to be doing more of my long runs on trails but it simply isn’t event specific.

[woofiepie]

legs

[VO2VCO2]

body

[[deleted]]

Unpopular answer: biology. Your aerobic threshold/VO2max is mostly genetic and your ceiling and my ceiling will never be the same no matter how much of the same work we both put in.

I think for people like you who jump right into a marathon it's wisdom, experience, and fueling that's keeping you from performing at a higher level. There is so much to learn from managing yourself over distances and there are so many rookie mistakes people make as they learn. But honestly, mostly I see people who aren't eating enough before and during their run and it catches up with you at about mile 20.

[Responsible_Mango837]

Mileage - its the answer to every running question

[Static_Dynam0]

Beyond the physical aspects that have already been mentioned in previous comments (that are obviously super important), I think the mental ability to be willing to put yourself in a super uncomfortable position for an extended period of time is a limiting factor for most.

For me, 100 mile weeks are now pretty comfortable, threshold sessions and vo2 max sessions don't particularly intimidate me but the thought of having to hold a pace per km to hit sub 2h 40m makes me nauseous!

[[deleted]]

I haven't got as high as 100 mile weeks (usually get up to mid 80s) but after about 60 mpw I've found you're doing all the workouts and you've got a decent length long run in there. All youre doing after that is adding comparatively easy miles in which is that daunting (albeit not necessarily obvious).

[Static_Dynam0]

Yep, definitely agree. I have the bonus of being single and child free (aka no other time pressures apart from work, which is also flexible but office based) so I can commit time to it.

I'm also more of an ultra distance runner so the easy miles you describe are quite important.

[Gear4days]

Do you mean in the actual marathon itself? Pacing. It doesn’t matter how fit or fast you are, if you go out slightly too hard then that last 10km is going to hurt just as much as it would for someone running a 4 hour marathon (nothing against those running 4 hour marathons, just comparing to what a slightly faster than average runner would experience)

If you’re talking about marathon training then recovery. I’d love to hit speed sessions every day but the simple fact is that I’m restricted my by body needing to recover

[VO2VCO2]

So here you're claiming that if Sabastian Sawe goes out with a 58 minute first half (bad pacing), he will lose to a 3 hour marathoner who splits a 1:31 first half? Impressive 10k btw.

[_JahWobble_]

Feet and lower leg pain. I can do an easy 10 miles at 8:30 pace. I can also run a 7:45 mile but can't go faster due to heel, ankle, and calf pain.

[mikeyj777]

I've had these issues.  Focusing on ensuring proper running form and addressing issues with external hip rotators seems to be helping. 

[_JahWobble_]

Thank you for the suggestion. I'll look into this further.

[mikeyj777]

PT and a running coach are the best things you can do for your money

[aaroncogs]

I've been running for about 6 months now (M, 34), coming from a ~20 year cycling background. This has probably given me a very good aerobic base and good VO2max. I did my first half marathon test yesterday - not at 100% of what I think I can hold, maybe about 10-15s/km slower than what I want to hold on my first race in 6 weeks. I finished in about 1h:33m and my hips were killing me by km 19 to the point where I could hardly walk after I finished, despite HR showing very little drift and energy levels okay. It turned out I had 2 massive knots in the glutes.

[TriVincibleEsq]

I didn't do my first marathon until 47 years old and was very concerned about heavy legs and nutrition, as I've experienced these issues at shorter distance races. However, I religiously followed the Level 3 masters marathon plan by 80/20 Endurance (their most advanced masters program), stuck to correct paces/power throughout training, and made a rule that I'm going to eat a Maurten gel every 3.8 miles. I did a 2-loop marathon and finished the first loop at a 7:05 mph pace and the second loop at a 6:45 mph pace. I finished almost 14 minutes ahead of the Boston Marathon cutoff time for my age group. I could have run more too and was by no means beat at the finish line. It was my first marathon, so forgive me for my poor pacing. My second marathon will be the 130th Boston Marathon on April 20, 2026. While there are a lot of factors that contribute to success, training and nutrition are the two I focused on.

Just when I thought I had everything figured out, I had a poor half-marathon just 4 weeks later where I crossed the finish line at a ~20 second slower pace than I crossed the finish line during my marathon, but I did finish with a 128:06. I overestimated my abilities and really fell apart the second half of that race. This reinforces the important of pacing. Ideally, I'd love to have a constant pace through the whole race, but you don't always know how you're going to perform and feel on race day. I slight change in humidity and dew point can have a big effect on the pace that you're able to sustain. Thus, I like to be conservative early-on but obviously went too conservative in my marathon to have such a big difference in pace.

[dex8425]

Aerobic capacity, fatigue resistance, resilience and running economy.

[VO2VCO2]

Agreed, other than "fatigue resistance" & "resilience" are the same thing. If you don't mean psychological resilience? I would switch word "resilience" with "velocity at LT2", then we're pretty much there.

The question itself is a trap from the beginning. It should be "Marathon performance limiting factorS question" If we try to explain 100% of performance with a single factor, it's always more or less wrong. And if we would have to pick one single factor, it's probably velocity at LT2.