Article - Fatigue: RFE Model

The Race Focus Energy Fatigue Model

Before reading this article, I encourage you to read the article titled "Training for Ultras", as it provides a bit of background to this article on the Race Focus Energy Fatigue model.

This article will attempt to provide an explanation into the many factors that influence ultra trail, and trail marathon race performance, through an illustration of my Race Focus Energy Fatigue Model. Hopefully my fatigue model will find some agreement with your experiences of race fatigue, and hopefully lead to a greater understanding of things to consider in order to improve trail marathon and ultra running performances.

First a little background into what causes fatigue during endurance running. Well as I have highlighted within the “Training for Ultras” article, very little is actually known in terms of what causes fatigue. Over recent years, the simple homeostatic failure model of fatigue, (homeostasis refers to remaining stable, or specific to the human body, functioning within a normal range) i.e. fatigue at the periphery within the muscles due to lactic acid, glycogen depletion or muscular damage/fatigue, has been clearly shown to be too simplistic! Many observations such as: the finishing spurt, different pacing strategies for different race durations, lack of glycogen depletion/lactic acid within muscles when fatigued, and how interventions that solely act on the brain affect performance, all confirm that the simple homeostatic failure model (either peripheral fatigue or catastrophic central/brain failure) , is flawed. Therefore the need for a new model!

Probably the most significant change over recent years is the increased acceptance that the brain needs to play an extremely important role within any endurance fatigue model. The Central Governor Model proposed by Professor Tim Noakes, author of the Lore of Running, is probably the most commonly known alternative fatigue model. The key feature of this model, shown above, is that it is an anticipatory-regulatory model, where the brain anticipates a future failure and so modifies behaviour specifically to ensure homeostasis is protected. This modified behaviour is a decrease in the number of motor units recruited in the exercising muscles, or what I refer to as a change in the level of muscle activation. Noakes and others have demonstrated that there is a decrease in muscle activation initiated by the brain when fatigued, They have identified some of the factors that lead to this reduced muscle activation, but haven't really explained how. My Race Focus Energy Fatigue Model introduces a novel way to look at endurance fatigue and proposes a number of factors that influence the rate at which fatigue develops.

Race Focus Energy (RFE) could be thought of as concentration or mental effort. It relates to the concept that it requires mental effort/concentration in order to remain focused whilst racing, in order to keep on running hard, out beyond one’s comfort zone. (The term 'race' doesn't have to mean racing other competitors, it simply means that the run is a special occasion, where you are extending yourself, trying to run to achieve a certain goal.) Fatigue will occur when your supply of Race Focus Energy is depleted so it is no longer able to recruit exercising muscles above a ‘threshold’ level. Or when the brain anticipates that at your current rate of RFE usage, depletion of RFE is imminent so alters the level of muscle activation to preserve the limited supplies of RFE. The basis of the RFE fatigue model is that RFE is required in order to activate the exercise muscles above a threshold level. At low levels of intensity, e.g. at a slow jog when 'fresh', it does not take any RFE to maintain the easy pace. A slow jog when fresh is below the RFE threshold. However as the race progress, as the body physiologically becomes less efficient, e.g. muscles fatigues, glycogen levels decrease, heart rate increases due to cardiac drift, to maintain a slow jog now may require RFE as the intensity, albeit rather low is now above the RFE threshold.

At the start of an endurance race, each runner has a limited supply of RFE, although this limited supply can be added to/topped up slightly during the race, however, the greater the supply of RFE at the start, the better the performance. This therefore leads directly onto Training Principle No. 1 – Maximise the size of the RFE tank prior to race start.

The size of the RFE tank is determined by a number of factors including: Research on the Race, Research on Oneself, and the Surrounding Environment leading up to and immediately prior to the race. Or to put it simply, the size of the tank is determined by one’s attitude to and expectations of the race; expectations to what will be encountered during the race and an expectation of how one will respond to these challenges. My TOTAL preparation in order to maximise the size of my RFE tank on the start line is to spend many hours researching the race. What are the demands of the race?: Total Time, Distance, Profile, Terrain, Daylight/ Darkness, Navigation, Possible Weather, Temperature, Clothing, Feed Stations, Food, Dehydration, Backpack, Fellow Runners, Loneliness, Support, Family/Friends. I also spend many hours researching myself: WHAT do I WANT? WHY do I WANT IT? HOW MUCH do I WANT IT? Are these WANTS realistic, based on what evidence?

I suggest above that the amount of RFE one has on the start line is influenced by one’s confidence in that they will respond positively to the expected challenges that the race will create. Yes, self confidence leading up to the race has a large effect on the level of RFE within the tank, and also the rate at which RFE is being consumed during the race. One factor that largely determines one’s self confidence is their recent physical training. If the physical training has been going well, then confidence is usually increased. How one determines whether physical training has been going well is an important issue, which I will return to, as are a number of other benefits from physical training.

The size of the RFE tank is also determined by the Surrounding Environment leading up to and immediately prior to the race. What I mean here are things like other stresses within your life, whether work related, family related, stress, tiredness, feeling drained, worn-out, stale etc. All of these factors will have a negative effect and reduce the amount of RFE at race start. Finally your surrounding environment prior to the race can, even at the last minute, reduce or increase the level of RFE within the tank. If you are surrounded my highly motivated people and there is a real buzz then this can add that little bit extra to your tank. Similarly if there is negativity, conflict, prior to the race, e.g. an argument with your partner, or having to listen to whinging and moaning from runners about injuries, or how tough it will be etc. Then this can have a decreasing effect on the level of RFE.

Maybe you are beginning to think, nothing really novel above. Apart from the term Race Focus Energy, there isn’t really anything to get excited about. Possibly true, but I think the real revolutionary feature of my RFE fatigue model is what happens DURING the race. Hopefully I can explain with the use of the following three figures, which include three important concepts; Rating of Perceived Exertion (RPE), Race Focus Energy (RFE), and Muscle Activation.

Rating of Perceived Exertion (RPE) is a common measure used within Sports Science research. While doing physical activity, subjects are asked to rate their perception of exertion. This feeling should reflect how heavy and strenuous the exercise feels to them, combining all sensations and feelings of physical stress, effort, and fatigue. They are then asked to look at the rating scale while they are engaging in an activity, and to choose the number, between 6 - 20, that matches the description that best describes their level of exertion. Research on running to exhaustion has shown that RPE is a better predictor of the time to exhaustion than any physiology measures. RPE is influenced by many factors, not just physical, and involves the integration and processing of multiple signals – feedback and feed-forward! There is an increase in RPE when there is a mismatch of expectations to what’s encountered.

One can therefore interpret that not only does extensive research of the race and oneself within the TOTAL preparation increases the level of RFE on the start line, but if there is poor preparation in terms of visualising what one is likely to encounter during the race, then this increased likelihood of there being a mismatch of expectations to what’s encountered will increase RPE.

Looking at the figure above, you see that the level of RPE determines the about of Race Focus Energy that is required in order to provide the muscle activation to run at the demanded race pace. A higher RPE will increase the amount of RFE required to activate the muscles. The greater the RFE usage, the sooner it will be before your RFE tank is emptied, which results in decreased muscle activation, and hence a decrease in running pace. The key to endurance running performance is therefore to reduce the rate at which RFE is being consumed!

The first obvious way to decrease the rate or RFE usage is to getting physically fitter. Everyone knows that as you get physically fitter, it feels easier to run at the same pace as before, and therefore there is a decrease in RPE. This concept matches most previous models, and is why there is such a massive emphasis on physical training. However the novel aspect of the RFE fatigue model is that there is not a DIRECT link between RPE and RFE, as shown in the above figure. The level of RFE being consumed for a set level of RPE can vary, and is dependent upon the amount of positivity or negativity that is being experienced at that moment of time. The two figures below illustrate this; if you are experiencing positivity, this will cause the arrow relating RPE to RFE to rotate downwards, resulting is a lower RFE consumption for the same RPE. So even though you know you are working really hard, i.e. at a high RPE, it doesn’t take much mental effort, it just feels easy, i.e. it is using less than normal RFE. Similarly in experiencing negativity, the RPE – RFE linking arrow will rotate upwards, causing an increase in the rate at which you use the RFE. In this situation, even though you know that the intensity isn’t very high, i.e. a low RPE, it just feels harder than usual, a real struggle!

The key to TOTAL preparation in order to maximise endurance performance is recognising that receiving positivity and ignoring/rejecting negativity whilst racing can have a large effect on overall performance. It is not just the final 1- 2 %, e.g. the icing on the cake. This positivity/negativity has a SUBSTANTIAL effect on endurance performance. Realising this, accepting that your race performance isn’t preset by your level of physical fitness is essential. The next step is then to identify what factors can contribute to positivity and negativity, and be prepared to accept/reject these. Listed below are a number of factors that affect me, but factors that affect you may be different. This is where race reflection is so important. Where you reflect back, to learn from what went well, what factors seemed to be related to running well, or related to achieving less than the ideal performance.

LIKELY sources of POSITIVITY - Racing / the competition, overtaking others; Internal feeling of satisfaction, i.e. running well, positive time splits, perception of speed, running non-stop to top of hill; Puffing and blowing hard; Feeling proud, support, family, friends, others; Being excited, unique experience; Feeling refreshed, sponge, water, food, break; Feeling easy yet running well, relaxed, ‘flying by’; Scenery, sunshine, warmth, dry feet, tail wind.

LIKELY sources of NEGATIVITY - Anxiety, doubt, lack of confidence/self belief; Getting tired, finding it hard/tough - counting down the miles; Muscle soreness, blisters - focus of attention!; Going slower than expected - a ‘bad day’!; Going faster than expected - will ‘pay’ for it!; Going off course - frustration, angry; Difficulty in taking on fluid/fuel; Being overtaken, slowing at a great rate; Conditions: rain, cold, heat, mud, wind, scenery.

Whilst racing there are often difficult moments where extensive preparation in terms of research on oneself, i.e. race goals/aims, e.g. what do I want, why do I want it, and how much to a want it comes into play. If one has these goals/aims clearly ingrained within one’s subconscious and conscious, then within a race when one is so close to achieving their clear goals, likely results in the RPE - RFE arrow rotating downwards, which allows for an increase in running pace, causing an increase in RPE, but yet for the same level of Race Focus Energy.

Whilst racing ultras and trail marathons, one thing I have noticed is that the brain’s subconscious anticipation of exhaustion of one’s’ Race Focus Energy appears to not only be influenced by the actual RFE usage rate at the present moment, but also the extent of the recent increase in RFE usage. Therefore if one is running at a reasonably comfortable pace, with this being not at too a higher level of RFE, to then immediately to go to extremely high levels of RFE leads to the insufficient muscle activation needed to maintain the increased running pace, due to the subconscious anticipation that RFE levels will soon deplete..

Time to sign off with some words related to this article;

“Often it is too easy to accept a less than satisfying performance due to an acceptance that physically you are not capable of better, however, as soon as there is the realisation that simply the way you think and respond to the challenges that you encounter during the race can alter one’s performance, one is capable of achieving so much more!” Stuart Mills, 2011.

All the best with your interpretation of my model.

A Bit More on the Race Focus Energy Fatigue Model

Part two of this article will expand a little bit more on my Race Focus Energy Fatigue Model, which personally I feel has a lot of merit, and helps to understand what factors contribute to fatigue during endurance running, but more specifically the model provides some guidance on what training is needed to perform well in endurance trail races.

When I first posted my Race Focus Energy model on UltraStu, a comment from left stating that my model sounded similar to the "Anticipatory Regulation" mechanism or specifically the Anticipatory Feedback model proposed by Dr Ross Tucker in 2009. I hadn’t heard of this model, so I immediately searched for it within the literature. Due to copyright laws I am unable to paste the complete article, however, pasted below is his model.

Tucker 2009 Anticipatory Feedback Model

The overall article is quite interesting, and I find myself agreeing with most of his comments, i.e. it is sensations within the brain that cause fatigue, although I feel that his model has one fundamental flaw. His model is based on the idea that fatigue occurs, i.e. you slow down during endurance events, when your RPE (rating of perceived exertion) reaches maximal levels. It is surprising that his model is based on this concept, as there is research out there that shows that as the duration of the exercise to exhaustion increases, the RPE at exhaustion decreases, e.g. for an exercise duration of 94 minutes the RPE at exhaustion was only 87% of the maximum RPE value obtained for the same subjects during a maximal test, and for the duration of 45 minutes the RPE at exhaustion was only at 98% (Pires, et al, 2011). Whilst searching the literature I also came across another newly developed model by another well respected sport and exercise science Professor Guillaume Millet (2011).

Millet 2011 Flush Model

Like Tucker’s model, Millet’s model, titled the Flush Model, also has the point at which the maximum RPE is obtained as the point at which fatigue occurs. Again it is surprising that he uses this flawed concept! Maybe their lack of understanding of fatigue during endurance events is due to that maybe they haven’t raced a long ultra trail event. (I have since been informed that Guillaume Millet has finished in the top ten at UTMB!)

I think every runner who has run an ultra trail race will confirm, that during the latter stages, even though they are running at nowhere near maximal levels of RPE, they are fatigued, they cannot run any quicker, barely any faster that a walk/very slow jog, even though there is a strong desire to run faster. So the idea that it is the attainment of a high RPE that causes fatigue is clearly flawed, hence why my model has a different concept that causes fatigue during endurance events, i.e. Race Focus Energy (RFE). It is once you have depleted your ‘tank’ of RFE, that you are then unable to maintain a running pace that is above your RFE threshold, hence why you have to resort to a walk/very slow jog.

To help explain my model in a little more detail, I have pasted below a number of the key slides from one of my presentations I have given to runners. (slightly modified, i.e. with a bit more text). If there are aspects that are confusing or need explaining, please leave a comment / zap me an e-mail.

Following the slides are my responses to a number of questions that I have been asked either via comments, e-mail, or during presentations.

The Overall Model with the RPE-RFE Arrow Pointing Up or Down

The RPE Portion of the Model

The RFE Level Portion of the Model

The Muscle Activation Portion of the Model

A Summary Slide Illustrating the Integration of the Body and Mind (Physical and Mental)

The first question: "How do you ensure your RFE is as high as possible when you may be going into a race with 1 or 2 individuals who have shown some fantastic race form and are on paper more likely to perform at a higher level?"

Remember the RFE Fatigue has three key aspects to it to improve performance: (i) ensuring your RFE tank is large/full prior to the race and topping it up during the race, and (ii) reducing the level of RPE for the required running pace, and (iii) reducing the demand of RPE on RFE.

For (i) the key aspect is to focus on yourself. Your goals should be worded/structured in that they are something you have control over. Having a goal of winning a race is not a good goal as it is largely out of your control. If Killian Jornet or Liz Hawker turns up at your race, you are not going to be able to achieve your goal. So the goal should be something like 'performing to your best'. Yes, very vague, but you then need to define what your best means, either in terms of remaining totally focused and positive throughout the race, or in terms of prior to the race, based on various bits of positive evidence you can access, your expected finish times for the overall race and for each leg.

Please note that although it is useful to formulate these positive split times / race time prior to the race, if possible I would encourage you not to focus on them during the actual race. The split times / race time strategy is there in order to allow some information about the likely demands of the race to enter your sub-conscious level. I have become to realise that having these times ready at your conscious level and focusing on them during the race in the majority of times leads to negative thoughts. Either that you are going slower than expected, or that you are going faster than expected, so then slow yourself down, or maintain the same quick pace but are then waiting for / expecting to 'blow up'! It takes quite a bit of confidence to not focus on the split times as you have spent quite some time and effort formulating them. However worth giving it a try. Try not to look at the times during the last few days. You will find that you are not totally running blind as during the race you will recall the approximate time that you were scheduled to pass the checkpoint, however, without the knowledge of the exact time, the negativity seems to be 'kept at bay'.

Both before and during the race it is possible to top-up your energy tank, but also possible to top-up your opponent's energy tank, simply through expectations. If you have this expectation that your opponent / fellow competitors are better / more capable than you, then you simply thinking this will be 'picked up' by them. You don't have to say anything, they will just feel your thoughts, the way you look at them, the way you position yourself around them, the way you run next to them or behind them. Even though on paper, it may appear that they are more capable than you, as mentioned in the above paragraph focus on yourself, focus on what you are planning to achieve.

I will have two examples to illustrate this boosting / not boosting the RFE tank of fellow competitors. The first example is based on my experience at the 2011 IAU World Ultra Trail Champs in Connemara Ireland. On paper I was the fifth ranked member of the five man Great Britain team. On the UK Athletics website, the team was even listed in ranking order, with me at the bottom, rather than I think the more acceptable alphabetical order! However, preparing for the race I focused on my capabilities, my strengths, my race goals. Not focusing on the fact that I was fifth ranked GB. Then I clearly remember just prior to the start, leaving the rest of the GB team, wishing then well as I headed off to the front of the field, ready to do my usual rapid race start. The feeling I sensed from my other team mates boosted my RFE tank. It felt as if even though my planned fast start was most likely perceived as foolish, they seemed to respect my determination or foolishness to give it a try. Either way I interpreted their subconscious response as a confidence boost, and if you have seen the video of the race on You Tube, you will see that my fast start paid off, with me finishing 15th overall and first GB runner across the line.

The second example is from chatting with Jono Wyatt (multiple world mountain running champion) and kiwi Kim Rodley who lives in Austria, who both happen to be running club mates from my running club back in New Zealand, Hutt Valley Harriers. I recall back in 2004 whilst staying with Kim for a week while at the same time as Jono, chatting about the pre-race atmosphere at the races that Jono raced at within Europe. At the time Jono, I think had been unbeaten in an uphill only mountain race for around 5 years, and Kim commented how it appeared that all of the other competitors simply looked up to and treated Jono like a 'running god'. Not only this, Kim really noticed how come race day Jono's confidence would dramatically rise, even if his confidence had been a bit down due to less than ideal training. Around 2003/2004 Jono was spending quite a bit of time training and racing whilst staying with Kim, as Kim's location was ideal, within the Leutasch Valley in Austria at around 1200 metres altitude. So Kim observed this boost to Jono's RFE tank immediately prior to the race on many occasions. One day I remember discussing this phenomenon with Jono. Although he didn't directly agree with the description of 'god like' status he was being given my fellow competitors, he did acknowledge that the manner in which the fellow competitors responded to his presence was definitely aiding his performance. I remember thinking way back then, that perhaps his massive unbeaten streak was perhaps partly due to the fact that the other competitors just expected to be beaten by him, and at the time back in 2004, I was your typical runner who thought race performance was all to do with physical genes and training. So unfortunately those 'out of box' thoughts disappeared for and didn't resurface for around another 3 - 4 years, when I started spending more time questioning the whole running performance aspect!

I could go on a bit more about how during the race your expectations can be sensed by other runners, but I think time for the next question:

"While I think I understand your model, my question relates to your mileage. I note that compared to other ultra runners your mileage is relatively low. Do you have any particular reason for this? I.e. belief that it is better/best? Do you believe that if you ran more mileage that you’d be a better/stronger runner? Lastly (in this regard) how do you do your mileage? Do you train in different (HR) zones? Or always fast or slow?"

Firstly my mileage is low relative to other ultra runners as I believe my RFE Fatigue Model clearly demonstrates that ultra trail running performance is determined by so much more than physical training. I was recently asked approximately how much time do I spend of my training doing traditional physical training and how much time do I spend doing other training, what most people classify as mental. I try not to separate the two, as I see it all as TOTAL training, but if I had to, I would say it would be around a 40 : 60 split, with the 40 being physical. So on paper it appears that my weekly training mileage is low, typically around 40 miles per week. If you take into account that this represents only 40% of my training, then in reality I am equivalent to a 100 mile a week mileage trainer, which I think would make some other runners feel more comfortable, as I sometime sense that sometimes other runners feel uncomfortable in the way that I seem able to perform on such limited training. Hopefully now, taking on board all the other training I do, to contribute to my TOTAL training, there won’t be a sense that somehow I am 'cheating the system'! What does this other training consist of? Well I haven't got time to explain in this article, but mainly research on the race and on myself, including extensive visualisations of all possible race expectations.

Would running more mileage make me a better/stronger runner? I have given this quite a bit of thought over the last two years. As much as I believe my ideas are sound, it does take a lot of confidence to not just follow everyone else. No other ultra trail runners, performing at a level similar to me, appear to be doing such minimal physical training. So in some ways, I have 'conceded' that maybe more is needed, with my weekly mileage leading up to each 100 mile key race in 2009, 2010 and 2011 increasing from 34.5 to 46.3 to 51.7 miles per week respectively. Has my performance improved? I would clearly say no. I would consider my 2009 UTMB result easily my best performance out of my key race for the year over these three years.

Why is physical training not so important then? Well if you look at my RFE Fatigue model, you will see that physical training only inputs into the model in one place, this being to the left of the model, as being one of the key factors that determines one's rating of perceived exertion (RPE). Yes, RPE is a key component of the model, and the lower the RPE due to improved physical fitness the better the overall performance. But when you look at all of the other factors / variables within the RFE Fatigue model you become to appreciate, that this physical fitness just isn't the 'end all' factor determining ultra trail run performance.

Then if one looks a little bit 'deeper' into what physical training actually achieves, hopefully you will begin to understand why I train the way I do. Simply put, there are three physical variables that contribute to physical fitness: VO2 max, lactate threshold, running economy. A quick review of any literature will clearly show that VO2max initially improves during the initial years of endurance training, reaches a level, and then stays constant regardless of what further training one does, and more importantly regardless of how much better the running performances become. Paula Radcliffe is probably the best example to illustrate this. There have been some really interesting articles written by Professor Andy Jones, her physiologist for nearly 20 years, now at Exeter University, but formerly from Brighton University. He has demonstrated that over the years her VO2max has not changed at all, even though her performances massively improved, to record the absolutely amazing 2:15 marathon time back in 2003! So to summarise, it doesn't really matter what physical training you do, your VO2 max won’t change much, as long as you keep on doing sufficient training.

The second component, won’t take long to explain; i.e. lactate threshold, this has absolutely nothing to do with ultra trail race performance, as the race intensity is way below all athlete's lactate threshold for the vast majority of the race. So not even worth typing any more words on this aspect.

The third and final variable is running economy. Now what is the best training to improve this? Well within the literature, apart from the fact that running economy continues to improve year after year, therefore indicating that it has something to do with the total number of miles every run, very little else is actually known regarding what training is most beneficial. So the interesting point is that the more miles you have totally run the better your running economy. This would seem to suggest that you should then perform mega mega miles per week, the more the better. However, not that easy, as this is likely to overstress the body and mind, and deplete the RFE tank prior to the race. My approach is to let my increase in running years be an advantage. Having been a runner for 34 years, I am getting close to 40,000 miles in total. Whether I run 2000 miles a year (40 miles per week, or 5000 miles a year (100 miles a week), within that actual year it won’t make much difference to my overall mileage, i.e. 42,000 versus 45,000 miles. I guess the difference is around a 6% difference, but I doubt the increase in running economy is still linear with mileage increases after this many miles run. As with most variables, the curve has probably pretty well plateaued out!

Just one last aspect to finish on, the pace/intensity of the miles I run? Well as highlighted above, very little is know within the literature on what intensity is most beneficial for improving running economy. My 'gut feeling' and that is all it is, simply a gut feeling from 34 years of running, is that running economy is best improved my running relaxed, rhythmically, easy, within a flow, with minimal tension, no forcing, no fighting. Hence why the majority of my runs are just this, usually around 8 - 8:30 minute mile rate. This isn't every run, I do do the occasional quicker run or sections of runs at 6:00 minute mile rate. But this is more a technique requirement, needed to remind myself how to actually run fast. And remember if we are talking about fast, for ultra trail running, a pace of 8 minute mile rate for 100 miles will win every ultra race, beating everyone including Killian Jornet or Liz Hawker! So in terms of race specific training maybe my easy relaxed rhythmical training pace has some actual merit. Definitely worth giving it some thought.

Well, yes another ultra effort! Just remember that you can log reading this article in your training diary. Hopefully heaps more effective than 'fighting' repeatedly up some hill, or 'red lining it' on some tempo run!
Time for a quick signing off quote. "Never accept the normal as correct, always question rather than follow!" Stuart Mills, 2011.

Hopefully my Race Focus Energy Fatigue Model is a little clearer.


  1. Nice article Stu.

    I agree with your main argument regarding RFE. Last year with three miles to go at the end of a 50+ mile ultra I was told that the team behind mine were only 20 minutes away which actually meant a 10 minute advantage due to a split start. At that instant all the fatigue evaporated from my legs and I set off like it was the first three miles of the race. In the end the message was wrong and we won comfortably but the immediate necessity for pace made a massive material difference.


  2. Hi James, I'm pleased that my RFE model is in agreement with your ultra trail experiences. Stuart

  3. Hi Stu,

    Great article and great blog. Loved your interview on Talk Ultra and the approach you are taking. As a marathoner turned ultra runner on similar weekly miles I have always felt the benefits of quality over quantity. I've also noticed that whether you run a marathon at 7min/mi or 7:30min/mi they both still hurt in the end!

    I did have a question about your lactate threshold training comment though. I'm curious why you think it is such a non factor in Ultras. Clearly the overall pace of an Ultra is no where near threshold but if we say take UTMB or another Mtn Ultra with lots of vertical, many of the best runners must approach their thresholds on the climbs and are forced to power hike. If they weren't near their threshold wouldn't it be easy for them to run the whole way up?

    And even if they near their thresholds for only brief periods before backing off, isn't this multiple accumulation of time right at high sub-threshold worth training? Kind of like the thought of raising your training ceiling gives you more room to work within before fatiguing.

    Curious on your thoughts that's all. Keep up the great writing and stimulating discussions!