Too many long runs?

A few days reflection, a more detailed examination of my training logs, and an interesting discussion with Robert regarding nutrition in the comments on my recent post about the Robin Hood half marathon, have provided me with food for thought.  I think I have learned some useful lessons, but first of all, I should put that race into perspective.

Although I want to race well, and would like to once again run a creditable marathon, the underlying goal of my running is minimising the inexorable deterioration that accompanies aging.   Six years ago, I decided that I would train systematically for a half marathon.  I had been running regularly since the previous November, though averaging about only 8 Km (5 miles) per week.   At the beginning of March I started systematic training, initially building up volume on the elliptical cross trainer.  After 8 weeks my running pace at the second ventilatory threshold had increased from 6 min per Km to 5 min per Km.  I added increasing amounts of running and by mid-June, did a 5K time trial in 23:27.  I contemplated this ruefully in light of the times of my youth, but decided it was not too bad, and began to speculate whether a half marathon in 105 min might be possible.  I continued to do around 35 (equivalent) miles per week, including some elliptical sessions, and occasional longish runs of 15Km.  Then in August, the arthritis that had afflicted me in my 50’s made an unwelcome return.  At the time, we were on holiday in France, staying in a farm house and sleeping in the loft.  For a few days, I was forced to descend the steep steps from the loft each morning, shuffling on my bottom.   However, the storm abated as quickly as it had arrived, and about six weeks later, I ran the half marathon in 101:24.  That time remains my M60 PB.

This year, I have again been able to train regularly, disrupted only by an episode of arthritis early in the year. I have coped with a greater volume – about 46 (equivalent) miles per week over a period of 6 months.  However, by August, my pace at second ventilatory threshold was slower than 5 min/Km.  I did not attempt a 5Km time trial, but am certain that I would a have struggled to break 25 minutes.  A 105 min half marathon appeared to be an absurd goal.  However, based on previous experience I was hopeful that a few weeks of higher intensity, lower volume training would produce a major improvement.  On the day, this hope was partially justified by the fact that I was comfortably below the second ventilatory threshold while maintaining a pace 4:53 min/Km for the first two Km, on target for a time of 103 min.   But my legs were not coping well.   As described in my recent post, the pace ebbed away and I finished in 107:49, a little more than 6 minutes slower than my time six years ago.  Disappointing, but not really unexpected.  WAVA predicts a loss of a little over 1 minute per year for half marathon time at my age, so in fact I have deteriorated at almost the exact rate that WAVA predicts. Furthermore WAVA predictions are based on the performance of elderly runners who are not only naturally fast, but also are deteriorating less rapidly than average as they age. So this year’s evidence indicates that I have at least slowed my rate of deterioration over 6 years to match that of the WAVA standard setters.  However, the evidence provided by last years time of 101:50, which is my best WAVA graded performance of my 60’s, suggests that I could do better.

This year’s campaign has several other bright spots.  I appeared to cope reasonable well with a volume of  46 miles per week for 6 months.  This bodes well for my plan to train for a marathon next year.  Secondly, I was pleased to find that I can still muster a competitive edge even when nearly exhausted.   With one Km to go, the sight of the swishing ponytail of a young lady who had passed me about 16 Km earlier provided the focus.  I covered the final Km in 4:56, a little faster than I had managed for any Km between 5 and 20 Km.  Having overtaken the young lady with the ponytail with 300m still to run, I subsequently overtook at least four other runners, all younger men, in a spirited run to the line.

105 metres to run and the young lady with the ponytail is now well behind (2nd right). I am in the blue vest and now closing on four young men.

150 metres to run and the young lady with the ponytail is now well behind (2nd right). I am in the blue vest and closing on four young men.

Less than 100 m to go and I am not the only one with an ‘awesome race face’.  The competitive juices are flowing.

Less than 100 m to go and I am not the only one with an ‘awesome race face’. The competitive juices are flowing.

20 m from the line.  The 4 young men are now behind, but I can’t quite catch another young lady, just out of camera view.

20 m from the line. The 4 young men are now behind, but I can’t quite catch another young lady, just out of camera view.

It appears that I am still able to muster the type 2B (fast-twitch) anaerobic fibres when the chips are down.  Unfortunately, type 2B’s can only function at maximum capacity for about 10 seconds.   Nonetheless, at least for a brief period, my type 2B’s were twitching fast enough.  The foot pod recorded a peak stride rate of 216 steps per minute.  But my peak step length was only 118 cm.   Thus, the final sprint confirms that the capacity of my leg muscles to generate a strong eccentric contraction is poor.   This is clearly one of the major limitations imposed by age.   I suspect it is because accumulated fibrous tissue obstructs dynamic stretching of the muscles.  During static stretching I can achieve almost as great a range of motion as I could achieve 55 years ago.    How can I recover my former dynamic range?  As outlined in my previous post, I think hill sprints are probably the best option.

Long runs

But my training log provides further food for thought.  My performance was substantailly worse this year than last year despite a 10% increase in training volume in the final six months.  It is necessary to look at the type of running, not only the volume.   The really striking difference was in the number of long runs.  This year I did 32 runs longer than 15 Km in those six months, many of them in the range 18-21 Km, whereas last year I did 16 runs longer than 15 Km in the corresponding period.  The increase in long runs was the outcome of a deliberate plan to develop better endurance this year.  In fact, I did improve my endurance substantially.  Early in April, one month into my half marathon campaign, I maintained a pace of 6:15 /Km and a heart rate of 740 beats/Km during a typical 16 Km run.  Five months later, I did a 19 Km run at similar effort level and at a pace of 5:43 /Km, with a heart rate of 697 beats/Km.

But is it possible to do too many long runs, even at an easy pace?  Dudley’s well known study of rats training on a wheel for various durations and intensities, demonstrated that aerobic capacity increases with increasing duration of running, but only up to a certain limit, that depends on intensity.  The duration for optimal gain was greatest at low intensities, at paces where most of the work is done by slow twitch fibres.  But even at low intensity, there was no additional gain in aerobic capacity beyond about 90 minutes of training.    The physiology of muscle fibres in humans is quite similar to rats, though proportions of fibre types differ both within and between species.  Nonetheless, despite probable small differences, it is unlikely in either rats or man, that training beyond around 90 minutes will produce further improvement in aerobic capacity.  There might of course be other benefits, including conditioning of connective tissues and improving the balance between consumption of fat and glucose.  But could there be penalties?


For several years the debate between cross-fit enthusiasts and endurance runners has focussed on the potentially harmful effects of cortisol. In the short term, increase in cortisol mobilizes the body’s resources to deal with stress. In particular, it mobilizes glucose to fuel brain and muscle; and limits inflammation.  It should be noted that the brain is the higher priority; although blood glucose levels are increased, cortisol inhibits access to the glut4 transporter molecules in muscle cell membranes that transport glucose into the muscle, thereby ensuring preferential supply to the brain.   But perhaps more importantly for the rpesent discussion, sustained increase in cortisol has a range of harmful effects, including destruction of muscle and weakening of immune defences.  Cortisol rises steadily during long duration exercise.  Typically the level increases to around 220% of normal levels during a marathon.  The crucial issue is: how long is this increase sustained?  In a fit person, the level returns near to baseline within a few hours.  However, in the presence of other stresses, it can remain appreciably elevated for several days.  Until recently, the debate between cross-fitters and endurance runners has remained stalemated over the issue of whether or not typical endurance training programs produce a significant sustained increase in cortisol.

However in 2012, Skoluda and colleagues published the results of a thought-provoking study.  They measured cortisol levels in hair samples in athletes.  Levels of cortisol in hair, unlike levels in blood or saliva, provide a good index of sustained levels.  They found that in a sample of 304 endurance athletes, fairly representative of committed recreational runners, levels of cortisol, in hair were almost 50 % greater than in a reasonably well matched control group.   Furthermore the magnitude of the increase was greater in those with greater weekly training volume.  The increase was greater in marathon runners than in half marathoners, though both groups had values that were significantly increased compared with controls.  Typically a training volume of 70 Km/week (a little lower than my average of 74 Km/week) was associated with a 1.8 fold increase in sustained level of cortisol.  The health consequences of an increase of this magnitude are unclear though such an increase might plausibly result in greater risk of upper respiratory tract infections and even perhaps add to the risk of atherosclerosis and myocardial infarction.   There is evidence for increase in atherosclerosis among male multi-marathoners, as I have discussed previously.  Furthermore, the elevated cortisol levels might inhibit protein synthesis in muscles and limit any gain in strength.

It should be noted that increases in cortisol during exercise are usually less in well trained athletes, suggesting that problems due to cortisol might by ameliorated by a gradual increase in training volume. On the other hand, running in a glycogen depleted state would be expected to increase cortisol levels.  Therefore, I remain sceptical of the wisdom of training in a carbohydrate-depleted state.  In the discussion following my most recent post, Robert has raised some interesting points related to his positive experiences following changes in both the type and timing of his nutrition, including doing long runs without breakfast.  He is running very well at present, though it is perhaps noteworthy that his total training volume has been relatively low this year compared with previous years, and hence, sustained cortisol levels would not be expected.

Total volume or length of long runs?

Although Skoluda did not attempt to disentangle the effects of total weekly training volume from length or frequency of long runs, the evidence that cortisol rises steadily during a long run raises the possibility that it is the length and frequency of long runs that is the main contributor to sustained elevation of cortisol.  When taken together with the evidence that gains in aerobic capacity are likely to be small after 90 minutes of training, I think it is quite plausible that the large number of long runs in my program this year not only contributed to a relatively slow gain in aerobic fitness, but might also have produced a sustained increase in cortisol that impeded the development of strength.   Although I intend to prepare for a marathon next year, I will be more judicious in planning the frequency of long runs.

44 Responses to “Too many long runs?”

  1. Robert Osfield Says:

    Is there any easy way of measuring cortisol levels? I’m really curious at where I am during the day, especially before and after a run.

    Thoughts on cortisol and metabolism…

    With glycogen depletion there is the liver and the muscles to look at. After a fast but before exercise the liver may be become glycogen depleted before the muscles, then during a run one can steadily deplete the muscles stores.

    The rate of depletion will depend strongly on metabolism, if one is well adapted to fat metabolism then glycogen depletion will happen at a slower rate so increase in cortisol during runs will likely be at a lower rate.

    The next question would be what base level of cortisol would start with prior to a run. Fasting is likely to increase base level of cortisol if the liver is becoming depleted of glycogen.

    This then logical takes one to the question how would one encourage fat metabolism without depleting the liver and muscle glycogen stores, so the cortisol levels remain low. I believe keeping insulin levels low is key, insulin is the hormone that suppresses fat metabolism and induces glucose and fat storage. If we can keep insulin levels low for significant number of hours per day then our bodies naturally shift to fat metabolism without the need for increased levels of cortisol to balance blood sugar.

    Keeping insulin levels low can be done by eating complex carbs and combining meals that contain carbs with fats and fibre that help slow digestion and slow the release of glucose into the blood stream. Eating “naked” carb meals (i.e without fibre+fat) will induce an insulin spike and endanger subsequent a low blood sugar low and with it a spike in cortisol.

    I don’t mention protein in the mix here. Protein can work to slow digestion but it also can get converted to glucose by the liver which in turn can result in an increase in insulin levels. This means protein isn’t as good as food combiner as fats and fibre for avoiding an insulin spike.

    One thing you can also do is arrange your meals so that carbs are not consumed in quantity at all meals. Eating meals primarily of fats, protein and fibre will have modest impact on insulin levels and can be safely eaten without compromising the bodies fat metabolism. Avoiding snacks, particularly carb snacks will also help avoid insulin levels. Snacks high in fibre and fats will be fine.

    Another curious aspect of food is that non starchy vegetables take as much glucose to digest as they contain so are close to carb free. So filling up on non starchy vegetables is a great way of providing a filling meal without upping insulin levels and compromising fat metabolism.

    The key take home is that high fat metabolism doesn’t require glycogen depletion and high cortisol levels, it just requires a diet and way of eating that promotes fat metabolism and avoids spikes in insulin and other hormones like cortisol.

    • canute1 Says:


      Salivary measurements of cortisol are possible. Collecting the saliva at home is quite practical but the measurement needs to be done in a lab – more accessible to the general public in the US than in the UK.

      With regard to avoiding damaging chronic elevation of cortisol, being well adapted is likely to be the key. I agree that keeping insulin levels low without excessive increase in cortisol is likely to be crucial.

      At present my approach starts with breakfast consisting of Greek style yoghurt, rolled oats and a few nuts and raisins. I like the taste and it keeps me comfortably full for hours. I have this most mornings, and in a particular, that is what I consumed a few hours before the half marathon. In a HM I avoid anything other than water during the race, as it seems to me the risk of stomach upset while attempting to digest food while running outweighs any risk of glycogen depletion during the race, even when duration is over 100 minutes.

      I hope that by next year I will be better adapted to longer running, but nonetheless will avoid doing lots of very long runs.

      • Robert Osfield Says:

        Your breakfast sounds nice. Should be have a pretty low glycemic index. Yogurt is better than milk as the some of lactose sugars are converted into lactate acid that doesn’t case an insulin response when digested.

        I have been wondering if adapting to fat burning prior to upping training volume and intensity might be a good way of managing cortisol levels. So you adapt to fat metabolism while under less physical stress for a couple of months, then when you start your distance training your body won’t deplete glycogen stores as rapidly and avoid low blood sugar and elevated levels of adrenalin and cortisol, and high oxidative stress. If this works then one would be able to tolerate higher volume in training, as well as reaping the benefits when racing long distances.

        To qualify what I view as long distances, I’d say half marathon distance probably doesn’t stress the bodies glycogen stores so far adaptations are not crucial, but with 3 hour+ runs glycogen stores would ordinarily be heavily depleted so would benefit from being better adapted to fat burning.

        For training for a marathon or longer I believe being fat adapted will help significantly – both from physiological standpoint as well as personal one, as becoming better fat adapted looks to have help me.

    • canute1 Says:

      I certainly think that being adapted to using a higher proportion to fat to glucose is like to be good for both general health and for minimizing stress during endurance training and racing. Avoidance of insulin spikes is also highly desirable. Therefore I am quite convinced about the value of minimising intake of high glycaemic index foods, and intrigued about the question of other adjustments of amounts and timing of fats and carbohydrates.

      With regard to what length or duration of run leads to appreciably increased cortisol release, the increase depends on both duration and intensity but at moderate intensity, it is likely to be quite appreciable by 2 hours. For someone of my age and fitness this corresponds to a training run of around 20Km. In Skoluda’s study of cortical in hair samples, individuals whose main race distance was half marathon exhibited evidence of sustained cortisol level that was about 33 % higher that control values, whereas marathon runners had values that were 63% higher than controls.

      I think the crucial question is likely to be how quickly the cortisol level settles after the run. The scientific literature on the benefits of post-run nutrition is ambiguous, but maybe if one confined the studies to nutrition after long runs, the answers might be clearer. From what I have understood of your current diet, you consume a substantial amount of carbohydrate shortly after a long run. Maybe that helps lower the cortisol level and contributes to your recent successes. It is also likely that the presence of other sources of stress plays an important part in how quickly cortisol levels settle. So there are many factors to consider.

      Nonetheless many athletes experience fluctuation in performance and also fluctuations in the benefits they appear to derive from training. Fluctuation have causes. Although the causal processes are likely to be complex, I consider it is an interesting challenge to try to identify the major causal mechanisms. While recent research has revealed the vast complexity of biological cell signalling, I consider that the major catabolic and anabolic hormones, especially cortisol but also insulin, growth hormone and the anabolic steroids, are likely to play an important role.

      • Robert Osfield Says:

        After running I consume more food in general – rather than increasing intake of carbohydrates specifically. After a missing breakfast, then doing a pre-lunch run, then having lunch I have quite a bit of catching up to do calorie wise.

        Now that I’m burning more fat when training I actually don’t need to consume so many carbs in after run feasts. For instance this lunchtime I did a 9 mile hill run, had chocolate milkshake, showered, then for lunch at 2pm I had a four egg omlette + mushrooms, cheese and ham, cooked in oil oil and coconut oil. A also had a mid afternoon snack of a rice cake with liver pate. Not a huge intake of carbs, certainly as much if not more calories from protein and fats.

        My evening meal I had my main carbs for the day, I big helping of mash potato with butter and milk, prawns in cream sauce and peas (rather simply meal as we were all in a rush.) Followed up by ice cream with home made chocolate sauce (74% cocoa mass chocolate + cream). I prefer to focus my main carb meal in the evening to help with sleep.

        One thing mentioned either in the Perfect Health Diet book or on their website was that a study showed that growth hormone production post exercise was stimulated by an excess of overall calories rather than carb intake. So as long as you feast properly after a run you’ll get the desired training response.

        My approach can be summarised as:

        Fast, Run, Feast, Rest, Repeat 🙂

        Now that my injuries are on the mend I’m now able to up the training volume, so I’ve got back above 40 mile weeks for the last two weeks. Getting some regular training in will hopefully help me avoid the issues with cramp that have slowed me down in the Devil and the RAW – just over three weeks to go to the Jedburgh Three Peaks Ultra, should give me a bit more time for some proper long runs in (I had to make do with a max of 15 milers for the RAW and Devil.)

        As for complexities of exercise physiology, oh my, I only understand a tiny bit. I’m very grateful for your blog, I have learnt so much. I’ve learnt more about health and fitness in the last four years than I did in my previous forty!

    • canute1 Says:

      Robert, the variety of what you eat is similar to the range within my own diet apart from the fact that I include more cereal based food – mainly oats but a modest amount of wholemeal bread – and possibly a little more fruit and veg, but I eat less fat. Nonetheless, I do eat cheese, yoghurt and eggs, and am fairly liberal with olive oil on salads etc.

      Our greatest difference appear to be first, the timing: I rarely train before breakfast (usually oats and Greek yoghurt) and secondly, I have not yet abolished cereal, though in recent years I have tended to reduce cereal and increase fat.

      Good luck in the Three Peak ultra. I love the Eildons. Maybe one day I will do the Three Peak ultra, though simply running over the three peaks themselves would be the greatest attraction. I hope the banks of the Tweed are not too muddy this year.

  2. EternalFury Says:


    That’s what our bodies strive for.

    Run more than you usually do and your body will react with various hormonal responses. You might well experience elevated levels of cortisol, for instance.
    Run less than you usually do, and other responses will be triggered.

    Let’s go back to Ed Whitlock for a bit. After some 40 years slowly and gradually building up his training to 2-3 hours a day, this training regimen has become his NORMAL. That level of training is what constitutes for him homeostasis. In other words, even though this is a large volume of training, I would bet his cortisol levels are boringly normal. Because his body no longer needs to adapt to something he has been doing for decades.

    So, my advice would be: Stop measuring your training load in miles. Measure it in minutes or hours. Even if you were to increase your training by 30 seconds per day, you would achieve colossal results within 6 months.

    Secondly, consider what Robert has posted. I totally subscribe to what he posted, even though I am a fairly new convert and used to be a carb monster.

    I know this is totally contrary to what you intended to do, but I thought I would reply anyway.

    • canute1 Says:

      I agree homeostasis is what our bodies strive for. This explains apparently paradoxical effects such as the observation that high intensity exercise, which creates acidity that inhibits aerobic enzymes during that session, promotes the synthesis of aerobic enzymes (as discussed in my response to your comment on my previous post). However, it is possible to exceed the usual range of homeostatic responses. If you over-train, either through excessive intensity or excessive volume, you create a catabolic environment in which enzyme synthesis is prevented. The cell signalling mechanisms responsible for these effects is complex. Excessive training initially produces excessive cortisol, which exerts a catabolic effect (ie degrades enzymes and other proteins) but subsequently, the adrenal glands responsible for cortisol production become exhausted leading to a potentially dangerous and long term inability to produce adequate essential transient increases in cortisol in response to stress and to loss of fitness.

      I discuss what I consider are the five factors that contribute to Ed Whitlock’s amazing running ability in my response to your comment on my previous post. I agree that as a result of his genes and running history, which includes sub-elite racing in his youth, several years of high intensity training in middle age and several years of mainly low intensity training in old age (but even this was accompanied by intense racing up to 40 times per year) he has developed the ability to run for several hours each day, and to profit from this. I think it is very likely that his cortisol levels are not abnormal. It is likely that his cortisol level is moderately elevated by the end of each run, and probably return to normal levels by the next day.

      I increased my average daily training by about 10 minutes per day compared with last year, during the spring of this year, mostly at low intensity. My aerobic capacity did increase during this time, but less than during a similar period in recent years. Maybe I did too many long runs. All of them were slow.

      While some of what you suggest is contrary to what I plan, I am not completely opposed to the nutritional ideas that Robert has presented. I certainly agree that building the capacity to metabolise fats is very important for an endurance runner. I have never been a ‘carb monster’ and do not intend to become one. I eat what I regard as a good balance of carbohydrate fats and protein. While my diet tends to be flexible, I have two fairly strict principles: I avoid high glycaemic index carbohydrate as much as I reasonably can (even on race day), and I ensure I consume a moderate amount of oily fish to provide adequate omega-3 fats each week. At this stage, I remain cautious about training in a fasting state because of the risk that this will be too stressful, especially as I am aware of the need for an elderly person to build rather than destroy muscle.

  3. Ewen Says:

    Great photos Canute! You have plenty of basic speed, outsprinting those youngsters.

    With the Dudley rats study, did they find that there was no aerobic improvement beyond 90 minutes per day, or a 90 minute weekly long run? If the former, that’s quite a significant volume — for a young elite runner doing easy runs at 4 minute ks that’s around 160 km per week.

    The Skoluda cortisol study is interesting. Are cortisol levels affected by the intensity of the exercise or just the volume? I’m finding that MAF heart-rate runs and easier don’t feel stressful at all until the length gets beyond 15k.

    Regarding the frequency of long runs in marathon training, my friend Andy had a short build-up in long runs prior to Melbourne in 2012. He ran about 5 or 6 ‘long’ runs from 25 to 30k, some of these finishing fast, near 5 minute ks. He ran 3:25 and is in the 50-54 age-group. He ran about 4 or 5 times a week so total volume (and cortisol?) would have been low – 60-65 km per week perhaps. He usually ran 1 weekly race (about 26mins for 6k) and 1 interval session, so some intensity there but also good recovery with the days of rest. Do you think long runs every second week (or every 12 days or so) would be a good method to keep cortisol levels low?

    • canute1 Says:


      You raise a good point about the weekly training volume of Dudley’s rats. They ran 5 days per week. There were 19 different combinations of intensity and daily duration. For rats running at the lowest intensity (10 metres/minute) the development of aerobic enzymes did not increase beyond 60 min/day. 10m/min is pretty slow even for a rat. An ‘ordinary’ rat can maintain 60 m/min for over 10 minutes, so 60 m/min might be equivalent to 2.5 min/Km for a man, while 10 m/min is probably equivalent to something slower than 7 min/Km. Thus, 10 m/min for 60 min 5 days a week would be equivalent to 5 hours at a pace slower than 7 min/Km (43 Km per week). Rats who ran at higher intensities exhibited a greater increase in aerobic enzymes than the slow rats. The greatest increase in enzymes occurred in rats who ran at 30m/min for 60 min per day. On the assumption that 60 m/min for a rat is equivalent to 2.5 min/Km for a man, 5 days /week at 30 m/min for 60 min per day would be equivalent to a weekly volume of 5 hours at 5 min/Km for a man. That is 60 km per week. I suspect that with a training program that involved various different intensities, it might be possible to produce beneficial increases in aerobic enzymes with somewhat greater training volume, but overall, Dudley’s data suggests that runs of greater than 90 minutes will not produce greater increase in aerobic enzymes, though there might be other benefits.

      Both intensity and total volume contribute to the increase in cortisol. HIIT actually produces greater rise in cortisol than typical endurance training, so I think HIIT should be done sparingly. However it s probably sustained cortisol that is damaging, and this is perhaps more likely with high volume training that includes fairly frequent long runs. Andy’s program sounds great.

      • Ewen Says:

        Thanks Canute. If your rat:human calculations are close I’d have to aim for more than 60km per week. For me, 5 days of 12km in an hour would be impossible as that’s my ‘hard tempo’ pace. 10 or 11 km in an hour is relaxed for me, so perhaps 70 or 80 km per week for me would generate the same maximal aerobic benefit as 60km at 5 minute ks.

      • Robert Osfield Says:

        While the rate study is interesting, I can’t help but feel making anything other than very general conclusions about implications for humans rather stretching things.

        Prior training, diet, sleep, stress, many many factors are so wholly different, let alone the genetic differences. There is enough variation between humans in all of these factors that extrapolating from one human study to ourselves is fraught with problems. As I’m sceptical about applying all human studies to my own experiment of 1, I don’t think rat studies are going to make my short list for training guides.

        Training techniques used by top coaches is probably a better source of understanding what may be most appropriate for us, but even then one needs to think about our own personal profile.

    • canute1 Says:


      Perhaps those rats were a bit younger 🙂

      Of course those rat : man numbers are at best approximate, but your comment does raise the issue of how to adjust the training program as the years go by. Should we increase the duration as we get older? Ed Whitlock has succeeded with very long duration training runs, but as discussed before, there are several different factors that probably contribute to his success.

      On the whole, I am inclined to think that a mixed palette of training is the best option – a modest amount of high intensity; a much larger amount of medium and low intensity: be cautious about too many very long runs: and pay attention to recovery. And when increasing either intensity or volume, build up slowly. Lydiard said many things similar to this 50 years ago, though I think we can now reframe Lydiard’s views on the basis of greater knowledge, and maybe the HRM adds an important additional source of information not widely available in the 1960’s

    • canute1 Says:

      I agree that the conclusions drawn from Dudley’s rats should be general, and in particular that we need should be very cautious is extrapolating actual values of the optimal duration of training for aerobic development, from rats to humans. However the basic physiology of rat muscle and human muscle is similar, and I think that general principles are worth noting. The two main conclusion Dudley drew were that there is an optimum duration beyond which the benefits in aerobic development are only slight, and secondly, that at higher intensity, optimum benefit is achieved at shorter duration. These observation in rats fit my own observations and indeed fit the astute observations of Arthur Lydiard. Arthur recommend three long runs per week during base building but typically, only one of those exceeded 90 minutes. He was clear that the optimum training durations and intensity depended on age and experience. As far as I can establish, the recommendation of two runs of 90 minutes and one of two hours were for trained males in the prime of life – perhaps more similar to you than me.

      However, it is also noteworthy that despite Lydiard’s famous dictum that miles make champions, he considered that excessive weekly mileage was harmful. For males in the prime of life he recommended 100 miles per week (plus additional jogging).

      While I think that the two main conclusions reached by Dudley had in fact already been deduced thirty years previously by the most successful endurance coach of the twentieth century, there is a third observation in Dudley’s data which he did not emphasise: the greatest overall benefit for aerobic capacity (at east over an eight week period) is achieved at relatively high intensity (30m/min for rats – which is the pace the rats could maintain for 90 minutes, and possible reflects something a little below lactate threshold. It is therefore Interesting to note that Lydiard recommended ‘a good aerobic pace’ which as far as I can estimate from his description is a bit below lactate threshold. Lydiard believe that gains could be made at slower paces but progress would be slower.

      I do not think that either Lydiard nor Dudley’s rats provide all the answers, but I believe both are very informative

      • Robert Osfield Says:

        Although my training hasn’t been consistent this year due to injury, I have tried to follow Lydiard’s principles and I feel they worked well for me.

        In the first two months this year I was able to run consistently and did mostly 1 hour easy or tempo runs with long runs either an hour and half at the start of the year, rising to two hours by the end of February. It required a bit of belief in avoiding really long runs for aerobic fitness during training as fellow Scottish Ultra runners were all racking up 4hr+ training runs by the end of February.

        Finding the “good aerobic pace” was a bit illusive, but I found that the principle of rating runs as 1/4 for recovery, 1/2 for easy, 3/4 for harder runs (be it speed or duration) useful, in that I could run 1/2 runs consecutive days week in week out, but 3/4 runs I’d follow with 1/4 run to ensure adequate recovery.

        My longest daily distance in training this year has been 15 miles in one run, followed by an evening 3 mile recovery. I did this just 9 days before the Devil.

        I do feel that I didn’t do enough long runs though. It’s not just aerobic fitness you are building, you are building strength and resilience, to achieve this you do need to push your muscle fibres occasionally and fatigue them.

        I’m now back nearer into proper training for two weeks and have changed my diet. I’ve had one run of 2:10 minutes, most around 1 hour, and few around the 1:30 mark. I’m doing them all fasted except for one 4 mile easy run at the weekend that I did in the afternoon, after having pigged out on home-made pancakes for breakfast and a pasta dish for lunch (our girls had sleep overs so I was catering for the masses and pigged out with them.) For all my runs except the non fasted 4 miler I felt strong throughout, no dips in energy, the 4 miler, my shortest and flattest run for a few weeks and I felt crap and hypoglycaemic at mile 3.

        Wrapping this personal experience up, I’d say that really long runs still need to be done but to build strength, but should only done once you have built the aerobic fitness and fat burning capabilities to handle them without hitting the wall. Regular (several times a week) long runs are good for you, but long being 1 and half hours to two hours, rather than 3+. How long these regular runs can be depends upon fitness level and how well one burns fat. You need to build it up.

        For a new runner I wouldn’t be surprised if more than an hour run would be pushing it for a long run. For an experienced runner well in the building their aerobic base will be able to cope easily with regular longer runs. I now can cope with hilly 2 hour runs and for it to still be just a 3/4, so as long as I take it easy the next day I’ll be fine to go out the next day and bang out another. My 1/4’s have also gone from a 4 mile recovery run to a 6 mile recovery run.

        I haven’t yet tried a 3+ hour training run this year, but plan to do one this week as part of the build up to Jedburgh Ultra at the end of October. I’ve had cramp in the last few hours of each of my last two ultras, I’m pretty sure this is down to lack of doing really long distances in training – the aerobic fitness and fat burning capabilities are there but muscles simply couldn’t handle the level of fatigue that one gets when running for three times longer than ones longest training runs.

    • canute1 Says:

      Your experiences and conclusions echo much of my own, though, as Lydiard emphasized, one must allow for differences between individuals in capacity to cope with the demands of exercise. For me, age is the crucial factor. The intriguing question is the extent to which a gradual build up might overcome the effects of age. Any up-slope is gradual and the trajectory is towards a lower plateau; maybe I am already reaching the point where the up-slope is being overwhelmed by a downward sloping degeneration but I am not willing to accept this without trying to find some new tricks.

      The aspect of your experience that differs most from mine is the effect of fasting before running. This issue also presents an intriguing question. There is good evidence that race performance can be enhanced by prior ingestion of carbohydrates. But the goals of training differ from racing. Research provides mixed evidence regarding the issue of whether training in a fasting (or carb depleted) state produces increased gains in fitness. My own experience is similarly mixed. A few years ago I did failry intense training daily before breakfast for two weeks. I felt strong and appeared to gain fitness, but pulled a hamstring in the third week. When the hamstring recovered I was at what appears to have been the peak of my fitness in middle age. I suspect that the balance between catabolic and anabolic hormones is the major issue. As outlined previously, my current practice is a low GI breakfast before both training and racing – though this often clashes with the other demands of my schedule, and training must be deferred until evening.

      • Robert Osfield Says:

        From tracking my HR/Calories per mile my body seems to respond to both adding longer runs, adding hill sprints and adding tempo runs. Part of this might be just an increase in blood volume, but could also be an change in efficiency/muscle tuning or an improvement in muscle strength and metabolic efficiency.

        Something else I have noticed is if I haven’t done tempo runs for a while then my first few tempo run I’ll see quite low efficiency compared to slower paces, but this then improves to I become for efficient at faster paces. I’ve noticed the converse as well, adding in more slow recovery runs has helped my efficiency at slow paces.

        My change in diet and running fasted doesn’t seem to have helped my HR/Colories per mile when running an hour, but when running two hours plus I see a huge difference. I really don’t know if I now training for 10k I’d see improvements here with the new diet+fasting. However, I already have see improvements in my ultra’s, with my energy levels and ability to eat in the second half of races much improved.

        If I were to go from just my short distance efficiency I probably wouldn’t have known about how much better my efficiency at ultra’s had become – in fact my performance at the Devil was an hour better than my optimistic expectations that I pegged based on my shorter hour training runs. I very much doubt the studies look at this aspect to training response, i.e. what happens when you go run an ultra.

        I expect these improvements also are helping me recovery quicker from the 2hr+ training runs and likely make them more beneficial for my aerobic fitness, so the 1 and half hour rule for seeing aerobic fitness improvements has been lifted up a notch.

      • EternalFury Says:

        Here is a log of my Sunday long run:

        I ran in a fasted state, no drink or food during the run. This being said, I limited myself to be slower than 8:45 pace throughout.

        12 hours later, I feel more than well recovered. I could have never said that with previous nutritional approach.

      • Robert Osfield Says:


        Nice steady long run, good to see you were able to do it fasted without problems and that your recovery is swift. It’s a good sign that you are well on the road to burning a good % of fat.

        Going for 18 miles without water is probably at the limit of what I’d do. If you find yourself feeling thirsty then you probably need to take some water, if not then you are probably fine.

        I used to worry about taking water on longer runs, but I found that as long as I don’t push the pace on I can keep cool and don’t loose an excessive amount of water. When running at the higher end of aerobic zone I certainly do sweat significantly though, and running a marathon race I would need to drink.

        I’m my ultra’s I typically drink around 300ml an hour, of water or milk shake. I don’t want to risk getting too dehydrated when running for many hours as ones performance can suffer, it’s a bit different from training where I don’t worry too much about getting a little dehydrated.

        In the book “The Art and Science of Low Carbohydrate Performance” by Jeff S. Volek PhD and PhD, Stephen D. Phinney MDm they suggest drinking a glass of water five minutes before going for a run as it helps top up blood volume. I’d suggest adding this practice in before your long runs.

    • canute1 Says:

      I would certainly expect that increased utilization of fats relative to glucose would have it’s most pronounced effects during longer runs (eg 2 hours or more). The crucial issue for the ultra runner (and to a lesser extent, the marathoner) is what is the best way to increase the fat/glucose utilization ratio. Training is a fasted state might be the key. Alternatively, the balance of different nutrients and or the effects of different amounts and type of training might be the key factors. But perhaps it is most likely that all three (timing of nutrition/type of nutrition/amount and type of training) matter. The good news is that you seem to have found a balance that works for you well at present. I hope it continues.

    • canute1 Says:

      Thanks. That is impressive. I can see why you are a convert to training in a fasted state. What do you eat, if anything, before racing?

      • EternalFury Says:

        Ah, I started that scheme 8 weeks ago. I could not believe the reports I was reading. I could not believe how Tim Noakes had suddenly changed his stance on carb loading. I could not understand how Joe Friel had become a disciple of the Paleo diet. Etc.
        So, I decided to give it a try for 4 weeks. I was so impressed with the results that I decided to keep up with it!
        I won’t say the first 3 weeks were easy, but I will say it is totally unbelievable how our bodies are capable to adapt. It is also unbelievable how little we need in terms of food to perform very well.
        I know you are concerned about muscle loss and I was too. So, I included 2 strength training sessions in my weekly training: Upper body on Monday for about 45-60 minutes ; lower body on Thursday for about 45-60 minutes.
        The dietary changes I made called for more protein and also called for less carbohydrates beyond the 30 minutes-3 hour window immediately after exercise. So, I didn’t know how my muscle mass would evolve, but I used the strength training sessions as controls.
        I am pleased to say my strength has slightly increased over the past 8 weeks. Mind you, I am not trying to bodybuild, so I do not keep increasing the amount of weight I lift, but I can certainly say I could lift more if I wanted to.
        I really do not understand how all of this is possible. It’s contrary to dozens of books I read on the matter. Yet, it works for me. It also apparently works for Robert here and quite a few other people out there.

        Now, to come back to your questions about racing.
        Well, that’s a problem, my next race is the California International Marathon. What will eat before the race? What will I eat during the race, if anything?
        Honestly, I do not know. I am concerned that if I eat the same thing I ate previously, my body will react strangely. On the other hand, it sounds outright crazy (to my old self at least) to run a marathon without fueling along the way.
        I am going to do more research on the matter, and I am going to experiment during my next long runs.

        Clearly, I best have an answer before race day comes around.

      • Robert Osfield Says:


        I believe Canute used to run marathons on just water in his earlier days and did some very fast marathons. If I were to run a marathon now I would mostly just consume water. The biggest risk is getting gastric stress/stomach cramps when working hard.

        One thing you can do is use a carbohydrate drink as a mouth wash – just take some in your mouth, then spit it out. A study has found that this fools the body into thinking sugar is on it’s way and seem to release the brakes on the central governor. I’d just leave this for the final miles though.

        As for eating before hand, try out different things before long runs to see what works for you. In my last two ultra I’ve had scrambled eggs cooked in coconut oil, salad and beetroot juice drink, this has worked well for me. Eating too much carbs in morning tends to my blood sugar crash just when it’s time to race, while a meal of protein and healthy fats keeps me burning fat efficiently without noticeable dips in blood sugar.

        I would suggest making sure your muscle glycogen stores are well stocked in the days leading up to the race. Drastically lowering your training mileage in the week before the race will help towards giving your body the time to restock without you needing to focus on carb loading. Just adding a bit more carbs (like rice or potato) to evening meals would probably be fine.

        What you want to make sure is that you avoid too much carbs in the 12 to 24 hours before the race, you want you insulin levels low to allow fat burning to naturally rise up. When you do eat carbs in the last 24 hours make sure they are complex carbs and eaten with a meal with plenty of fat to slow digestion down and avoid an insulin spike.

      • EternalFury Says:

        Thanks, Robert. I appreciate your advice as I am in unchartered territory with this.

    • canute1 Says:

      Yes, I only consumed water during marathons in my younger days, but I doubt that this was wise, especially as I used to run marathons at a pace faster than 16 km/hour, where carbohydrate usage was almost certainly quite high. I suspect I would have finished more strongly if I had consumed carbs during the race.

      On the other hand, the final few Km were never a disaster. I suspect tthat I was moderately well adapted to utilizing fats in those days because much of my training was done is a state of mild carb depletion.

      Someone as well adapted to utilise fats as Caroline McKay (and I presume you also by this time) would probably get about half the required energy from fat at marathon pace and therefore glycogen reserves would probably last for 42 Km without refuelling, provided the reserves were reasonably well topped up at the start.

      • EternalFury Says:

        6:00/mi is definitely carb territory, unless you are an elite marathoner, and even then! Good job there!

        As I said, the trick with being fat-adapted, and consuming a very low GI diet, is that I must re-learn how to fuel in races.

        I fear that consuming things like gels and other nearly-pure-glucose foodstuffs would cause an extraordinary insulin response.

        But then again, if I go back to Lore of Running, or any of the other 30 books on the topic I have on my shelves, they pretty much all say insulin response is suppressed during even moderate-intensity efforts. So, consuming high-GI foodstuffs during races should not impact fat metabolism.

        This being said, so much of the stuff I read has been proven to be bad science that I will have to listen to those who have tried it before me (such as Robert) and conduct my own experiments to find out what works for me.

    • canute1 Says:

      The release of insulin during exercise depends on the intensity of the exercise. At low and moderate exercise levels , adrenaline (epinephrine) suppresses insulin release, while also promoting breakdown of glycogen and release of glucose from the liver. However at high intensity exercise (>80 VO2max) the rate of glucose release from liver can exceed rate of glucose utilization and the insulin is less likely to be suppressed. I think it is quite possible that for a person who is not adapted to preferentially utilize fats, running a marathon at an intensity high enough to ensure plentiful release of glucose from the liver (at a stage before depletion of the glycogen store) I would expect that ingestion of a substantial glucose load might well trigger an appreciable rise in insulin and further suppress fat metabolism. However I do not know of any data directly demonstrating this.

      I suspect things would be different in a person who was well adapted to metabolising fat as a result of a low carb diet. At least in rats, low carb diet tends to result in impaired glucose tolerance (in the non-exercising state) presumably due to a lesser insulin response, so perhaps in a person on a low carb diet would be less likely to increase insulin in response to glucose ingestion. Therefore, for such a person, I suspect that ingestion of a similar glucose load would be less likely to trigger an insulin surge. On the other hand, provided the runner had started the race with adequate stored glycogen, they would have less need to consume the additional glucose.

      But the regulation of metabolism is sufficiently complex that prediction based on general principles can only provide an approximate guide, and must be weighed up alongside experience.

      • Robert Osfield Says:

        One of the aspects of diet that book “Art and Science of Low Carbohydrate Living” suggests is that there may be a link between too much Omega-6 consumption compromising the cell walls resulting in increased insulin resistance.

        The book also suggests that in some people going low carb can improve the insulin resistance and once fixed can re-introduced more carbs into the diet without problems, while others simply can’t tolerate carbs and have to stick to a low carb diet to remain healthy. This advice is primarily for diabetics and those with metabolic syndrome rather than those with otherwise healthy like ourselves.

        To me this suggests there may be factors in different diets that can effect insulin resistance, it may not be simply the amount of carbs one eats, but the whole diet. Some low carb studies have been compromised by having the subject consume fats high in Omega-6 so produce results that aren’t representative of diets with a better balance of healthy fats. It could the case the the rat study was low carb, but high Omega-6.

      • EternalFury Says:

        Yes, my worst nightmare scenario is this one:

        My body learns to metabolise fat very very well. Consequently, my muscles start to carry less and less glycogen.
        Comes marathon day, I consume GU packets and my insulin levels spike, signalling to my body to use glucose before fat. Alas, there isn’t as much glycogen there as there used to be. I hit the wall.

        That’s my nightmare right now.

      • Robert Osfield Says:

        Hi EF,

        I don’t believe I now store less glycogen in my muscles – or at least not not noticeably less. What is the big difference is that I burn more fat and dip far less into my glycogen reserves. At the end of long run, even a tough one, I still have plenty of “carb” juice in the tank to up the pace or power up a hill when I want.

        If your experience is similar to mine then you simply won’t need to consume as much carbs if any when doing your marathon. The best thing to do would be to try a race pace half marathon and try out different foods, but don’t stress eating lots, aim for 50 to 100 calories an hour and you’ll be fine.

    • canute1 Says:

      I agree. The complexity of the system is one of the major problems, and perhaps explains why deciding on healthy diet has remained such a vexed question. Genuine debate remains about many issues, especially the relative merits and dangers of carbs and fats. On the other hand, there is an increasing consensus, based on evidence, about some important things. Of these, I think the most important is the growing acceptance that high GI foods are harmful in many circumstances. There is also widespread acceptance that diet should include a modest amount of omega 3 fats. I therefore have adjusted my diet recent years according to the principles.

      Other issues, such as the healthiness of a low carbohydrate diet simply remain unresolved on account of conflicting evidence. It might well be that covert factors (eg the composition of the fats in the diet) is the key to resolving some of the debate. Is it the addition of olive oil and tomatoes that accounts for the healthy features of the Mediterranean diet despite the fairly high carbohydrate content? It is also likely that individual differences, in either genes or life history, lead to individual differences in dietary needs. In his statement in Runners World in 2012, Tim Noakes was careful to emphasise that he only advocates a ‘Paleo’ type diet for individuals who have what he described as carbohydrate resistance.

      So many of the questions about healthy diet are difficult to answer. Fortunately, the general principles of regulation of metabolism during running are reasonably well understood. Nonetheless, the marathon presents a special challenge because the pace is high enough to result in substantial glucose utilization, and the duration is long enough to deplete glycogen stores. For a typical person, the answer is simple: a modest amount of carb intake is usually beneficial provided it does not upset the stomach. The answer is not so clear for a person who has adapted to preferential use of fat at marathon pace, but I also think that the issue is probably a less serious problem in that case.

      • Robert Osfield Says:

        Part of the difficulty in getting a clear message on what is a healthy diet is the role of big multi-nationals in the food industry and their influence on research and national institutions, and plain inertia. Good research can be buried and forgotten, while long discredited studies still have an influence on national guidelines.

        W.r.t eating on the run, I only have done this during ultra races, not in training, but what I have found is that I can now comfortably consume 200 Cals/hour all the way through a 7 hour race, while before I could last fours but then would begin to suffer gastric stress. I really don’t know if this improvement will apply to the higher intensity of a marathon but I suspect it will to an extent.

        What I do have confidence about now is that I don’t need to pile in 200 Calories/hour to perform well, so would confidently run a marathon distance without eating, and a race might consume a little, perhaps aim for 50 to 100 Calories and hour. This would keep me well below the danger zone of getting gastric stress.

    • canute1 Says:

      The scientific community has become better at acknowledging that there are subtle pressures that bias judgement, though this still remains a problem. Having been actively involved in science for decades, my own view is that holding a strong conviction about a particular theory is often a stronger source of bias than involvement with industry. On the other hand, holding a strong conviction is a powerful driver for creative research. Perhaps our best protection against the pressures from ‘conviction scientists’ is the fact that scientific debate usually reflects conflicting view-points and ultimately there is a respect for quality and strength of evidence. Review organizations such the Cochrane Collaboration have introduced a very high level of rigour into the debate.

      I think the review by Eilat-Adar and colleagues is a good illustration of the level of current debate. (Nutrients 2013, 5, 3646-3683; doi:10.3390/nu5093646; available via Open Access). In the disclosures section, two of the authors report delivering lectures sponsored by a diverse range of food companies. Examination of the list of foodstuffs might suggest a bias towards cereals and milk products, and this needs to be borne in mind when reading their paper. There might be hidden biases in their selection of topics for discussion, but within the range of topics they discuss, they employ high standards of academic rigour. They conclude that all five diets they review, including a low carbohydrate diet, are supported by good quality evidence of at least moderate strength. The diet that has the strongest support from high quality evidence is the DASH diet, which was specifically developed by scientists to promote low blood pressure.
      This is what they conclude about the DASH diet:

      ‘The DASH diet is recommended to prevent hypertension and lower blood pressure. The diet should be accompanied by lifestyle changes such as: weight reduction in overweight people, increased physical activity, sodium restriction, and alcohol avoidance.’

      This is what they conclude regarding low carbohydrate diet:

      ‘In the short-run, low-carbohydrate diets lead to a greater weight loss compared to low-fat diets. Some studies have shown that this advantage is retained at 2 years but not at longer follow-up periods Low-carbohydrate diets are preferable to a low-fat diet in reducing TG levels and increasing HDL-C
      blood levels. It should be emphasized that carbohydrates should preferably be replaced by unsaturated vegetable fats. Low-carbohydrate diets, which include 30%–40% of calories from carbohydrates and are low in saturated fat and high in monounsaturated fat, were found to be safe in healthy and overweight individuals at follow-up up to 4 years.’

      Their main reservation appears to be lack of evidence for long term health benefits. Their recommendation to replace carbs by mono-unsaturated vegetable fats differs from the recommendations of advocates of the Paleo diet.

      This is what they conclude about low fat diet:

      ‘Low-fat diet with restricted calories may present a healthy alternative to the typical Western diet. It may improve quality and life expectancy in healthy people, as well as in patients with overweight,diabetes, and CVD.’

      They also conclude there is good evidence for increased life expectancy in healthy people with the Mediterranean diet, and overall draw more positive conclusions regarding the Mediterranean diet. They conclude:
      ‘Mediterranean diets are preferable to a low-fat diet in reducing TG levels, increasing HDL-C blood levels, and improving insulin sensitivity.’

      • EternalFury Says:

        I am from the South of France and I literally grew up with my feet in the Mediterranean.
        I would say our diets are high in natural fats and low in starchy foods. Lots of butter and olive oil. Lot of green leafy vegetables. Alcohol. Lots of meat products. We basically eat every part of any animal we kill for food. And it does gross out a lot of people. 🙂
        When I was young, it was a well-accepted fact that you had to avoid white bread, pasta, pastries and beer to keep a reasonable weight. Nowadays, the population has lost touch with its nutritional origins.
        I don’t like the “low carb” blanket label, because there is a great difference between avoiding refined carbohydrates and consuming a “low carb” diet.
        I don’t believe there are foods that are inherently bad, except for those that were engineered in labs instead of through thousands of year of evolution.

      • canute1 Says:

        Thanks for those details.
        The Mediterranean diet characteristic of the studies reviewed by Eilat-Adar and colleagues is similar to what you describe. It includes a relatively high fat intake (40%–50% of total daily calories), of which saturated fats contribute ≤8% and mono-unsaturated fats 15%–25% of calories. There is a high omega-3 fatty acid intake from fish and plant sources and a low Omega-6:Omega-3 ratio of 2:1–1:1. It consists of seasonal, local, fresh vegetables, fruits, whole bread and grains, legumes, nuts, and olive oil. Moderate intake of dairy products as well as eggs, fish, and chicken are allowed, while red meat is avoided. Small to moderate quantities of wine with meals are encouraged.

        In one study adding additional extra-virgin olive oil (in one group) and extra nuts (in another group) to the Mediterranean diet both led to a significant reduction in serious cardiac events over a period of 5 years.

    • canute1 Says:

      If I were you I would not worry too much. I think that being adapted for preferential utilization of fat is almost certainly an advantage for a marathon runner.

      I doubt whether a few months of training in a carb depleted state will have made a very serious reduction in the capacity of your liver to store glycogen, especially of you have been consuming carbs after training.

      My own experience from many years ago is that having done a substantial proportion of my training in a mildly depleted state, I raced pretty well without consuming any carbs during the race, but I think I would probably have done a bit better with a modest intake of carbs.

      • EternalFury Says:

        Yes, and the fact that digestive capacity during high-intensity exercise is greatly reduced is undeniable. Consuming easily absorbed foods should be the way to go. So, if my insulin response remains typical (suppressed) during the marathon. I should be able to consume glucose without sending my body into a sugar binge.

  4. Robert Osfield Says:


    If measuring Cortisol levels requires a lab to measure, so not practical for anything other than a controlled study, is there any way we can use our own senses to gauge when our Cortisol levels might be elevated, or other symptoms that we get that may be a indicator of high Cortisol.

    Am I correct is broadly saying that the body uses Cortisol when blood sugar levels are low to signal the body to use gluconeogenesis to restore blood sugar levels. So if it’s low blood sugar that is trigger than feeling hypo-glycemic is a sign that Cortisol is likely to be active.

    My next question would what is the latency between the body getting low blood sugar and the Cortisol levels being raised, and how what is the latency on the body lowering Cortisol once blood sugar stabilises.

    Another question would be what happens if your body is working hard to maintain blood sugar with high Cortisol levels then eat a high GI food source and the blood gets flooded with glucose from the gut as well as from gluconeogenesis. I presume insulin levels will need to ramp up quickly to bring the blood sugar back. What happens then to the Cortisol level?

    The simplest thing from a training perspective might be to just avoid the blood sugar even getting too low, and ever getting it too high. Avoiding running too far, too fast would certainly be one way of avoiding blood sugar getting too low. Avoiding high GI foods the later.

    The other approach is to simply burn more fat, but do so without first exhausting the liver glycogen stores. This is where I think a carefully managed higher fat, modest carb diet can be useful.

    Another thought, if blood sugar level is getting low because the liver glycogen stores are depleted then perhaps short fast intervals can help via the cori cycle. Using the lactate generated from working hard effectively releases glycogen from the muscles into the blood stream, some of which can be used by the liver to top up it’s glyocgen levels which is in turn can prop up blood sugar levels.

    Again questions of latency of lactate release and how quickly the cori cycle in liver can top up glycogen in the blood might be of interest w.r.t what happens with Cortisol levels. Could a quick sprint or two mid run be of use at avoiding low blood sugar levels?

    • canute1 Says:

      Cortisol has many functions in the body and I doubt that there would be any reliable subjective experiences that allow us to identify the acute rise in cortisol during running. Chronic elevation in cortisol is associated with many symptoms but most are non-specific features of malaise. Mood is one of the most reliably affected subjective experiences and The Profile of Mood States is one of the best established indicators. Some coaches use an abbreviated version of POMS to detect over training. It is possibly a more consistent marker of over-training than HR and HRV measures, but is less popular because it appears more vague.

      With regard to the latency of rise and fall of cortisol during exercise, the rise lags behind the increase in work rate by a matter of about 10 minutes. At the end of 75 min at 75% of VO2max, cortisol has already reached its peak and remains at this level for 15 minutes before falling back to baseline after about 3 hours. See for example Ronson et al Am J Physiol Cell Physiol. 2002 283(6), C1612-1620).

      The release of cortisol is controlled by the hypothalamus, via a signalling system known as the hypothalamo-pituitary adrenal axis (HPA axis). Various different physical and mental triggers give rise to signals that eventually reach the hypothalamus and initiate release of corticotrophin releasing hormone (CRH) which is turn triggers the release of adrenocorticotrophic hormone (ACTH) from the pituitary. ACTH triggers release of cortisol from the adrenal cortex. Hypoglycaemia is only one of several things that might be responsible for increase in cortisol levels during running. Ingestion of glucose duirng a run might reduce the rate of rise of cortisol but I doubt that it would arrest it entirely.

      As cortisol rises failry steadily during a long run, I would be dubious about the wisdom of a quick sprint to avoid low sugar levels, I suspect the sprint would trigger an addtional surge of cortisol, but I doubt that this would add appeciably to the rate of gluconeogesis. .

  5. EternalFury Says:

    By the way, Robert, The Trossachs appear to be an amazing place to visit. I hope to go there one day! What time of the year is best to visit? Where do tourists usually stay? Where should they rather stay to experience the real thing?

    • Robert Osfield Says:

      Spring/Early summer tends to provide the best chance of good weather… but it really can be wet and windy any-time, so you need to enjoy what ever the weather the mountains and Atlantic throw at you. It’s always beautiful though.

  6. EternalFury Says:

    I was due for a Lactate Threshold Test at this point in my training cycle, so I did one this morning on an empty stomach (I had 20 oz of water beforehand, though)…here are the results:

    I think my current training cycle is on track and I am quite surprised at how well one can perform in a fasted state.

    • canute1 Says:

      That is impressive. Maintaining a steady 1000b/mile from 3 to 7 miles at around 6:50 /mile indicates that your aerobic fitness is good and also that you are not accumulating much stress. Clearly you maintained a high enough blood glucose level to keep your brain comfortable. 7 miles isn’t enough to seriously challenge the fuel supply, but nonetheless, this is encouraging.

  7. anabolic one Says:

    Fabulous, what a weblog it is! This web site presents
    useful information to us, keep it up.

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