UKC

Evening all,

I wonder if anyone has heard this TED lecture, now on YouTube, about the dangers of running long distances? It is convincing. I am hoping someone will say, no, that is not the full story, keep on running, the research is incomplete. I love running but am wondering if I should cut down the distances. Interested in your thoughts; thank you. Here is the link:

youtube.com/watch?v=Y6U728AZnV0&

In reply to thelostjockey:

You're more likely to die from not running than running.

I'd get at it.

(Disclaimer, I've not watched video and I am a total idiot)

In reply to thelostjockey:
No, that is not the full story, keep on running, the research is incomplete.

(Disclaimer, I've not watched it either!)

In reply to thelostjockey:

If it’s a TED lecture, it’s definitely true...

In reply to thelostjockey:

Started watching it but got out of breath after 2 mins and had to stop....

In reply to thelostjockey:
I believe your long distance running needs to be quite extreme from other sources. Are you a 100 mile plus / week type of runner?

In reply to thelostjockey:

If my running was just about health I might pay some attention to that. But it's not, it's about lots of other life affirming things like the joy of moving fast in difficult terrain, and sunsets and challenge and fellowship.

In reply to thelostjockey:

December's runner's world had a small article saying New research shows marathon do not lead to cardiac problems

In reply to RX-78:

Do runners world still do that really annoying thing of having numbers for citations as if there are references, but then not have any references – really annoying!

In reply to thelostjockey:

At the end of the day.....
Do what makes you happy, just don't train when you feel ill.

In reply to SouthernSteve:


That's not what the talk is saying. For those who can't be bothered to listen to a 18 min talk it is saying:

Running 10 - 15 miles a week spread over 2 -3 days at a moderate pace (6 - 7mph) is best for your health.

Running 25 miles + per week, running 6 or 7 days a week, or running at extreme speeeds (8mph +) significantly reduces the health benefits of running to the point where mortality is nearly the same as for non runners.

He doesn't present statistical evidence regarding extreme distance runners but does mention some anecdotal evidence to suggest that it can often be damaging to the heart although there is also evidence that this damage goes away when you stop the extreme exercise.

Before seeing this I did have my concerns about the current popularity of ultra running and ironman triathlons, I find two + hours of full intensity exercise hard work, draining and thought it was probably not doing me much good. But this is the first time I have seen scientific research that supports my feelings.

It sounds like there are more studies being done. I will have to try and find out more.

In reply to mountain.martin:


Gives you an excuse not to bother you mean?

In reply to DaveHK:

Well yes, if we can get maximum longevity benefit from exercising for 40 mins of cardiovascular 3 times a week that should be good news for lots of people who don't have the time or inclination to do more.

He was just talking about longevity, but I would imagine running 15 miles a week rather than 25 - 100 would also be kinder on the knees and hips and hence likely improve your quality of life in older age.

This talk was about running but I would infere that it could be the same time/intensity of any cardiovascular exercise.

In reply to mountain.martin:

I am familiar with the study and also some critisism of the methodology, basically the sample of runners doing 25+ miles a week was far too small, the error bars are very large, but this has been ignored.

I have got a minor congenital heart defect, so I have it checked regularly. I also run 50 miles a week, sometimes quite a lot faster than the "extreme" speeds described above. My heart is in far better shape now than when I didn't run as much.

In reply to mountain.martin:

Not the original critisism that I read, but interesting.

http://constantforwardmotion.blogspot.co.uk/2013/01/is-marathon-running-bad...

In reply to thelostjockey:

Very interesting link ! Thanks for posting.
I am advised that there is a time in people’s lives (and it will vary a lot) when personal bests should become a thing of the past because of what it can do to the heart. My dentist does ultras and my doctor does marathons and both have mentioned this. My dentist advises that if possible keep your heart rate to the level of 85% of 220 beats per minute less your age. However, it can be exceeded for a while but how long that is will vary person to person and depend on their fitness. The only way I imagine any of us can really know if we’re overdoing it is to have a heart scan every now and then. Keep running but less fast for most people.

In reply to The New NickB:

Thanks for the further info and glad to hear it has been good for you. I don't to high mileage but I do get into the high speed category (just).

When I was younger I used to go out and flog myself in both distance and speed. As I'm getting older I still like the challenge of trying to run as fast as I can over 5k, 10k or the very occasional half marathon, but have been thinking that for my long term health i should be doing less punishing exercise and more to maintain flexibility.

In reply to The New NickB:

Thanks for your link which I’ll finish reading tomorrow. Certainly makes me feel better about possibly overdoing things !

In reply to The New NickB:

Yes that is an interesting critic of the video, obviously a complicated topic with different ways of interpreting results.

In reply to mountain.martin:

I did have a bit of a pubmed read before originally answering where the longer distances were causing the bigger changes in the papers I found. The data from 2013 seemed to put this idea out into the public domain. It still seems to be a slightly undecided topic and various podcasts and articles I have reported extremes of opinion.

Looking at our running club more than 30% of runners are in the 25 miles / 6-7 days a week category with some running 120 miles a week for many weeks of the year with an average pace of 8 minute miles or just below. Most of these runners are not training for ultra-marathons, which is actually the domain of the slightly older and slower runner quite often in our group. This probably means that this question is not a minority issue and needs sorting out.

Personally as a VERY non-elite runner I find an ultra much less taxing than running continuously at marathon or even half marathon distances and I can usually walk properly within a couple of days. I cannot imagine, in my current state of health, not having 2-3 long target races a year and the training, anticipation and pleasure that that gives.

In reply to thelostjockey:

I'd class myself as an extreme ultra runner and I think it all comes down to the intensity of the exercise. This year I've completed 6 100+ mile events. Some of which I have walked away from with no adverse effects of fatigue and others where I know I was working harder I've had tell tale signs of stress going on in my body.

My body and hopefully my heart is accustomed and fit enough to cope with my normal level of exertion (I have been operating at this level for four years now) but the last long race I did (and won!) was particularly hard in terms of duration and exertion and my body showed physical signs of this during and after the event.

So I'm of the mind that it is exertion level that causes damage not distance.

But what do I know, I'm just a dumb ultra runner

In reply to thelostjockey:

I think, within reason, most of us must be aware that being extremely fit is not as good for your health as being adequately fit.
Obviously being a couch potato is bad, combine it with being obese and it is worse.
I think I'd sooner be too fit than the other way.
Saw an interview with an extreme fell runner who had issues with his circulation and heart due to all the extreme running he had done. Still kept on doing it though.

In reply to DubyaJamesDubya:

“Extreme fell runner”. Fell running is thankfully the antithesis of the kind of marketing which designates things extreme.

In reply to DubyaJamesDubya:


That pretty much sums it up. Most elite endurance athletes are insanely 'fit' but are not what anyone would call healthy. Still, its easier to ease off the intensity than it is to go from being a couch potato to being fit.

I'm in the 4-6 days a week, 40-60 miles per week category and I do really thrash it on short races so food for thought. But like someone said above, I don't run to be fit, I run because I love being outdoors in the mountains and experiencing nature and the freedom that running brings me, along with the opportunity to disconnect from a desk job.

In reply to The New NickB:


Perhaps so but the guys's exercise regime would have viewed as extreme by even keen runners (daily runs over big fells and long distances). I'll use a different word if it helps.

In reply to yorkshireman:



That's it for me too. If fitness and long life were a side product of the training I do to enable my goals, I'll be very happy, if it is of minor benefit or even of some harm I would continue in the same way we do other things we enjoy that are not always the best thing for our health.

In reply to The New NickB:

The word extreme is only bad when associated with Red Bull or Endurancelife events......in all other circumstances is should be judged on a case by case basis

In reply to mountain.martin:

If he thinks 8mph+ is an "extreme" speed then he's talking through an aperture that wasn't designed - either by evolution or God, depending on your point of view - for the purpose.

When I was training (for steeplechase) then I ran my track reps at 15mph+, short (200 metre) runs at 20mph (or thereabouts).
My easy runs, which were at up to 10 miles or so were at about 11mph, and even 15 mile runs were above his 8mph.

In reply to I like climbing:



I would be very wary of taking advice of someone who still uses 220 minus your age as a way getting your max heart rate.

In reply to The New NickB:

I vaguely remember seeing magazine articles and the like trying to promote fell running as an 'extreme sport' a few years back. Strangely enough it turned out that trying (and failing) to keep up with some skinny 60 year-old bounding up a hill, whilst feeling like your heart is about to burst out of your chest does not float the boats of those with an 'adrenaline junkie' mindset.

In reply to thelostjockey:
A subject ‘close to my heart’.

I’m now in my mid 50’s and hilll fit and active. I was extremely fit for a period of about 25 years, and would run, climb and cycle. The cycling took the form of ultra type events, overseas tours and a 50 mile commute most days.
I began getting heart problems which were diagnosed as atrial fibrillation. This took the form of long periods of fast abnormal heart beats and was very debilitating and put me at risk of stroke amongst other things. Six fairly major heart operations I was fixed (and thankfully remain fixed).
The input of various cardiologists on my condition was interesting.
Scans showed I had a heart the size of a football and a very slow resting heartbeat.
My heart was very good at long periods of exercise but not so good at sitting around when it would play up. I was informed that this was an increasingly common phenomenon.
I thought one Specalist put it very well..
He said in primeval times we were designed to not do much most of the time with short fairly intense periods of exercise (fighting, hunting and the like). A bit like a hunting pack animal for example. We were not designed to do 3-4 hours a day of quiet intense exercise. The systems cope but get out of balance.

Everything in moderation is a good idea.

In reply to fred99:

Sorry Fred I don't agree, you have obviously posted some very decent times and if you hang around and train with people on the same level you might think 8mph is a jog. But it is extreme for a big proportion of the population, even over shortish distances like 5k.

That's about 23.30 for a parkrun. I'm pretty sure that at least 90% of the general population couldn't do that, I know some pretty fit climbers and regular runners who can't do that.

In reply to fred99:


And how is your heart now?

In reply to mountain.martin:


Even if that is true and I’m not convinced it is. That isn’t really what extreme means in this context. The problem with the research here is that they may not be test what they think they are testing. To give a personal example, my heart rate can go up above 190 in certain circumstances, but running at 8 mph, it does go above 150. That isn’t extreme, better runners could provide examples of running at 10 mph with similar results.

In reply to The New NickB:

What I'm saying is that a large part of the population could not run at 8mph. So to them 8mph is an extreme speed. For quite a few runners maintaining around 8mph for 5k would max out their heart rate so would also be considered extreme in relation to the study.

Only a small % of the population could run 8mph for 5k and not think it was an all out cardiovascular workout.

In reply to mountain.martin:



The problem is, the people they are using as a benchmark, are probably in that %, whatever it actually is.

In reply to The New NickB:

Ok, I see what you mean. More detailed information on the study and the participants would be required to get a clearer interpretation.

In reply to spartacus:

Thanks. That’s very interesting.

‘Becoming increasingly common’

In reply to spartacus:

Thanks for this and sharing your views on it. Hoping you remain truly fixed.

In reply to bouldery bits:


In a similar vein remember article by old doctor, I think in London Hospital gazette, to effect that if he died of a heart attack in the hills it would be because he'd done too little mountaineering rather than too much.

In reply to spartacus:










This sounds very similar to the case I read about in my paper.
I hope all remains well with you.

In reply to nufkin:


After a few years of doing bugger-all, my resting heart rate is 54.
I'm just coming up to my 62nd birthday.
And I can still "outwalk" youngsters half my age.

In reply to mountain.martin:



Far too many people refer to themselves, or are regarded by others, as being "really fit" or "superfit".
I regard the overwhelming majority of these people as having an over enthusiastic opinion of their own ability - i.e. they are nowhere near as good as they think they are.
(I once saw a "superfit" 27-year old sports teacher, who ran and cycled every day completely thrashed over our local Fell race by a slightly overweight woman in her 70's - talk about embarrassment !)

And when someone presents "data" they should have some sense of what is fast and what is just plain low quality jogging. This person seems to have no real grasp of what pace a large number of club runners actually run at - it seems that anyone who is capable of making even the weakest team is some kind of superman by their estimates.

In reply to DubyaJamesDubya:



All good at the moment thanks. The symptoms may return but should be fixable.
Science involved is fascinating, atrial fibrillation is caused by electrical misfiring in heart wall. To fix it they map electrical activity and find anomaly. They then burn lines across the heart wall, the scar tissue prevents the extraneous electrical activity, stopping symptoms.
That sounds ok but the some of the operations were done while awake. They did a local anaesthetic in the groin and pass Catheters the size of bicycle cables through the femoral arteries up to your heart. At one point they pushed one through the heart wall between the upper chambers.
When they got the right location the effect of stopping symptoms was immediate return of normal heart function like cutting a cable.

I am hugely grateful to the Royal Brompton Hospital in London for a life changing result.

In reply to fred99:

Agreed, it would be better to know the criteria/context for fast/extreme. Fast for the general population could be slow/steady for many club runners. To be fair it was a 18 min ted talk. Hopefully more detail is available in his full paper.

In reply to fred99:


It'd be swell if I was anywhere approaching your level when I get to 62. But Spartacus' Wed 15:26 post does inject a note of concern too

In reply to nufkin:
I think everything in moderation is a good way to look at it. However it becomes a life style and a ‘fix’ which is more than a hobby. In some ways it’s an endorphin addiction, usually a positive addiction but an addiction none the less.

Generally running is a great thing to do and I’ve enjoyed being fit and all that goes with it including a sense of well being and reduced stress levels.

The difficulty lies in taking a detached strategic look at your lifestyle and deciding if it is actually ‘making you fit’. If you are carrying constant injuries, need drugs to allow you to carry it out or it is causing long term medical effects which are negative it may be time to take a hard dispassionate view on things.

I think we can all think of people who have overdone this balance. Save some of your worn out body for an old age walking in and enjoying the hills however you do that.

In reply to spartacus:





Great post.

In reply to SouthernSteve:

Yup, this paragraph had a '4' superscript

In reply to mountain.martin:

Most average runners could get to 8mph with some speed training. I've got short fat legs and not a 'proper' runner, and managed to get to 16 miles home in 1hour 40m with lots of speed work. If you want to run reasonably fast you have to train with fast intervals. This was when I was in my late forties, and then I took up hill running, which suits short legs.

In reply to thelostjockey:

I havent watched it but will try to.

Not too surprised but think there could be other factors, do high mileage/good runners have bigger hearts anyway which gets them into running but has risks etc.

I always said when I was running 90-100 miles a week for 100+ weeks in a row I felt it was bad for my health. I think the long term inflammation isn't good. But I wouldn't trade it.

I now run 60-70 miles a week, up to 100 in the summer but 60-70 is very manageable.

In reply to thelostjockey:

Totally anecdotal, but Ron Bentley (family friend, ultra runner and erstwhile holder of the 24 hour world record), has recently had to have heart bypass surgery.

In reply to Mark Kemball:

Think bypass surgery would be for something different to what we're thinking might be caused/contributed to by long/extreme runs though.

Bypass is for blocked coronary arteries, whereas the other thing is thick ventricular walls causing bad cardiac rhythms (AF mostly) right?

In reply to JayPee630:

I think there is a clear history of heath problems in ex professional cyclists who have to be one of the prime examples of ultra fit athletes. Without repeating it on here a simple check on the internet shows a large quantity of research into AF type problems in endurance athletes. I believe they have to train down over a period of time and not just stop all exercise.

Constant training enlarges the heart (as does many types of heart disease) and produces the same symptoms, AF and other electrical fault anomalies

Half an hour looking at research concludes, exercise is good for you and far outweighs any risks heart problems in almost all cases.

In reply to spartacus:

It is hard to disengage the heart problems from the drug abuse that was prevalent in cycling though.

I do not think it is the long durations of exercise that is the issue. It is the lake if recovery time between these durations. You also cannot really extrapolate professional athletes symptoms to the casual,athlete as the durations , intensities and other demands are different. As a percentage how many people would expect to develop heart issues anyway and how does that compare to the percentages in endurance athletes?

In reply to Lion Bakes:

There are several studies that say professional cyclists who raced during the periods when there was wide spread drug abuse live longer than average.

In reply to JayPee630:


AF, as I understand it, is not related to thick ventricular walls but to the tissue (the sinoatrial node) at the top of the heart or just outside in the vessels coming into the heart that creates the electrical pulse that starts the heart contractions. This spreads down through the atria which contract and finish the natural filling of ventricles. The electrical pulse is stopped briefly at the AV node and then the ventricles contract and close the valves and pump blood through the body and lungs. If the sinoatrial node is dysfunctional this pattern of organised contraction is broken and the ventricles may beat independently (ventricular escape - a slow heart beat) or at the wrong time in recognition of the chaotic information that they are receiving - irregular heart rate with incomplete filling of the heart. This is a really common disease in all people in the western world.

Although the heart has intrinsic rhythm, external influences including hormones and neurological information from the brain via the vagus help slow the heart. I suspect that for this reason as Spartacus says you need to train down if you are a super athlete to get adaptation. However the mileage discussed in the initial video was not really in that extreme place so I remain confused – although 25miles + is described as being bad the examples being given are of people doing vast amounts more exercise.

In reply to SouthernSteve:
Another cardiologist gave me a very interesting analogy in relation to understanding AF.

He said it was a bit like a crowd in a football stadium doing a Mexican wave, if all are in synchronised everything is good. If only 2-3 people stand up at the wrong time the system malfunctions and produces a defective electrical signal and quivering and uneven beats result.

The heart gives uneven beats and can fail to empty properly. This can result in clotting in parts of the upper chambers with the possibility of heart attack or more commonly stroke as a result.

If untreated AF strengthens as the false pathways become re enforced by repetition. I’m told it works in the same way as repeated activity in the brain, I.e driving a manual car takes effort to start with remembering order of the pedals, after time it is apparently done without thought because of familiarity (established pathways).
In my case AF still exists but cannot cross the scar tissue (see explanation above) I therefore am symptom free. My cure came with a note of caution that it may return as the body is adept at finding alternate routes to the AV node which then become established and the AF returns.

In reply to webbo:


Link to 4 of them please.

In reply to thelostjockey:

I do a fair amount of long distance stuff. The LDWA 100 miler, a couple of other ultras each year and a whole lot of longer moorland runs.

I am 52, recently ran a half marathon faster than the last one I entered at 18 years old.

My resting heart rate is down to 41. Following the same trend of rate reduction it will stop before I am 60!!! I think I will stick with running rather than taking up fags or drinking too much booze.

In reply to Lion Bakes:
Just google longevity of professional cyclists.

In reply to webbo:

Well that was good to read!

In reply to webbo:

The study that I have seen shows significantly increased longevity in cyclists who were TdF participants between 1930 and 1964. Obvious reasons why we have not got data to cover the blood doping and EPO eras of cycling, but don’t you think drug use pre-1964 was a very different beast to later times.

In reply to The New NickB:
I'm sure it was but I mentioned those study's as someone posted that professional cyclists were another group who had heart problems as a result of long and extreme endurance exercise.

In reply to thelostjockey:
I think a holistic approach is needed to extreme running. The effects on the heart are just one aspect. Wear and tear to the rest of the body are also relevant. Back problems worn our knees and hips are also a consideration if you want to keep going to the great outdoors in your decrepitude.
I would hate to be unable to get out to the mountains through muscular or skeletal problems.

In reply to webbo:

I’d also be interested in how much it was down to the abuse of carbohydrate which is a relevantly (last 30 years) phenomena. Saw a guy yesterday carrying 4 gels and a water bottle for a just about - sub 2 hour half marathon. In contrast I ran the whole thing on the previous night’s curry and didn’t stop for water.

In reply to webbo:

Maybe I’m conflating what other people are posting about drugs, with the point you are making. I think I agree with you, intense exercise is generally good for the heart.

In reply to DancingOnRock:

This need for food and drink whilst running is a modern fad.
When I was racing, it was actually against the rules for there to be a drinks station, or for that matter ANY drinks/food to be handed to a runner in a race if the course was not at least 20 miles. To do so would have been classified as assistance and would have meant immediate disqualification.
The use of designer water and gels whilst actually running seems to be more about hype than any actual benefit, at least unless you are (truly) running for over 2 hours.
Once the run was completed, that was when I (and my contemporaries) had our food and drink - in a much more relaxed manner.

In reply to fred99:


Fair enough if everyone has to stick to the same rule, but the physiological case against this seems sound*. Did you try eating during runs of this length/duration, and did it make a difference?


*ie The body carries around 2000kCal of glycogen - once used it needs to get energy from the fat reserves, which is less available. Consuming more easily converted sugars saves the need to use fats during activity, thus better ability to maintain greater intensity

In reply to nufkin:

All I ever did was take on water in the long races - only raced the full marathon once.
Trained over 15-20 miles quite often, and 13 miles was a normal solo sunday run.
I found that, as I built up to it, I never had any problems - frequently finished the race sprinting to the line to (hopefully) beat someone.
As I said, I'd have a relaxing repast afterwards - usually a pint mug of hot sweet tea, and whatever I felt like for a snack.

In reply to fred99:

Whilst I disagree with the 20 miles no water concept – I definitely start to wane at about 15 miles if have nothing, it always amuses/amazes and disappoints me that people feel the need to carry water when they are clearly only running around the block. In the hand it changes their upper body carriage and can't be good! Although if you were really hardcore you could carry massive bottles in both hands, but no drink any!

In reply to nufkin:

It depends how trained the athlete is as to how much glycogen they store and again it depends on how trained they are as to how easily they recruit fat for energy.

Our bodies are not evololve to process carbohydrates in huge pure quantities. Type 2 diabeties and heart disease has increase massively since the government drive on low fat diets. No proper real research was done and it’s highly likely that it was salt in the diet that was the main culprit. We took that out and replaced it with sugar and made the problem worse.

In reply to SouthernSteve:

I think it was 20miles no drinks, not no water. Im pretty sure they used to have an orange squash (barley water) drink at 20miles.

In reply to SouthernSteve:

In fact, I’ve just come back from an interval session with the club, a fairly hard 4.5 miles in total, and I’m not actually thirsty.

In reply to DancingOnRock:

I'll never be a good marathon or distance runner. I can't get my sweat rate below about 1.5-2l per hour, and hence over about 2h I really start to fade. I can absorb about half a litre an hour.

At a spin class there is a huge puddle underneath me, and generally no one else.

There is possibly a certain amount of self selection here. Athletes who sweat less have an advantage over longer distances and hence do those distances more.

In reply to Dave B:
When I'm cycling at a reasonable work rate I need a gel after 1 hour and every 30 mins after that otherwise I really drop off pace and HR. When running its about 1:20 and every 30 mins after that. For a half marathon I'll carry one gel, for a 4 hour bike ride I'll carry 6 .. gets expensive! I don't generally drink as I keep myself hydrated the rest of the time.

In reply to Dave B:


Never ever heard of that before......How on earth do you know how much your sweating?

In reply to Wonrek:


Weigh yourself, go for a run for an hour and drink and eat nothing, then weigh yourself again. I tried it a few times in the summer after reading about it because I suffer in the heat and wanted to work out the optimum fluid intake on hot summer ultras. I'm around 1.5L/hr rate as well when it comes to hot weather - I was very surprised.

In reply to yorkshireman:

Yep, that makes sense, never thought of that......but then although I 'run hot' I don't seat excessively. Probably because I avoid running in hot weather as much as possible. Interesting though, thanks!

In reply to DancingOnRock:


Of course - and the great thing about our bodies is that they are so adaptable. But the drawback seems to be that sometimes we aren't able to tell just what's going on inside - no dials or readouts to give precise figures about energy stores, fat burning efficiency, water levels etc:


Obviously it's not my place to say 'actually, you are', but I do wonder if sometimes in these situations we rely on the body's adaptability and overlook the objective needs. Of course, maybe you had a drink anyway, or maybe you didn't but that's what you're used to and could cope fine - but 'fine' isn't the same as 'perfect'.

On the other hand, there's probably no such thing as perfect performance since there's so many variables involved, and at any rate what's 'perfect' for me probably wouldn't be the same for you.

Now I'm not quite sure what my point is - and I don't mean to seem like I'm having a go. I suppose 'do what works and makes you happy, and maybe sometimes see if other things also might work'

In reply to nufkin:

No. I follow you. I had drunk during the day and an hour of sweating might lose me a litre of water. It’s not something I needed to replace during the session and I had water later in the evening.

My point was that it’s not something we need to be doing.

People are sabotaging their training by taking on large amounts of carbs. If your performance is suffering after an hour and a half it’ll be because you haven’t spent a large amount of time on those adaptions. What happens is someone joins a club, goes on a 30mile ride, loses energy, the other cyclists say, “take gels”, you take gels, they appear to fix the problem, so from then on you keep taking them and your body never adapts. But you’re not treating the underlying cause of why you didn’t have enough energy.

In reply to DancingOnRock:




My understanding is that it depends on pace and duration, even if you are a well adapted fat utilising athlete adding carbs (gels) during a session at race pace (or even tempo pace) can be necessary to sustain the effort without wrecking yourself.

In reply to JimR:

Sure. “Need”?

But what’s the long term effect of regularly pumping yourself full of sugar so that you can run faster or cycle faster?

In reply to Wonrek:

Science.

I do part in a dehydration experiment in Sports science dept at work.

Was very interesting.

In reply to JimR:

I eat little (and even train fasted) at low intensies, and use gels if I’m pushing it a bit or am after performance. I wouldn’t eat anything for rides under 2 hours though. You get the fat burning adaptations without hindering performance. It highlights the importance of doing a mix of training.

I do drink, inc electrolytes, all the time though.

In reply to Dave B:

From what I’ve read the gains/losses in performance are marginal unless you’re very dehydrated.

If your body is 60% water by weight and you lose 5% of that, you’re talking about 2 litres for a 70kg man before he becomes dehydrated enough to notice a drop in performance.

In reply to DancingOnRock:

It seems to be slightly less than 5% from what I can recall ...

Yes the work was looking at the water loss = lighter performer vs water loss = decreased performance.

Thousands of hours of testing (90 minute steady state run followed by a 5k time trial) with physiological measurements throughout (hr, lactate, blood composition, weight etc -- I can't remember them all)

The conclusion of the study was that drinking to thirst was about 45 seconds slower in the 5k compared to a forced drink strategy where all lost fluid was replaced in the 90 minute run. Not drinking at all was about a minute slower again. (I think...)
https://sportslabcccu.wordpress.com/2014/03/07/hydration-strategy-for-endur...

However, these are averages, not actuals for every human - some lose more and some lose less. I lose more...
With me losing 1.5 l an hour at my 'steady pace' I couldn't get the fluid in after about 2 hours and while I could run at a speed for time x I simply couldn't drink at that speed. I tend to start to vomit the water back up, irrepsective of 'training' myself. By 2h45/3hours I'm semi-done. in one marathon (3h23m) I lost about 7-9 minutes (I estimate) in the last half due to this dehydration. I then spent a whole day trying to rehydrate. A drip would have been nice at that point... Race day was a lot hotter than the training