Training Intensity Distribution

this is science of ultra the knowledge resource for achieving your ultra endurance best train and perform smarter and now your host dr sean bearden training intensity distribution the relative amount of exercise you do at different intensities is called your training intensity distribution if you spend 75 percent of your time running easy 15 percent running somewhat hard and 10 percent running very hard then you have a 75 15 10 training intensity distribution there's a lot of interest in identifying the optimum distribution for each sport and each athlete the optimal distribution will depend upon many factors including just genetics training history capacity for recovery and adaptation nutrition event demands and timing in the training progression when we look at the practices of successful athletes there are some patterns that emerge elucidating and curating the training of top athletes provides useful insight into the training that generated sufficient adaptations for those individuals to be successful this approach however when espoused as the likely best approach for unsuccessful or pre-successful athletes is an application of survivorship bias it ignores all of the people who trained that way and were not successful it also fails to capture the likelihood that underlying biomechanics physical build and fiber type among others all layer into the research and development of the training and development of the training and development of response equation what helps athletes who are predominantly slow twitch which we can assume of all elite endurance athletes may not be the best approach for amateurs who may have a higher percentage of fast twitch fibers and no chance of reaching the world stage but who do wish to achieve their personal best for example someone with a sprinter phenotype is not necessarily going to optimize their endurance potential by training like someone with a marathon phenotype nevertheless it is useful to understand the training intensity distributions of top athletes because when patterns emerge these are likely to serve as actionable starting points for athletes to adopt if those athletes have similar potential we begin with the foundation of endurance training and that is volume you will not become a great endurance or ultra endurance runner by running 30 to 40 miles per week you might get away with 30 to 40 miles per week sometimes but at some point in your career you're going to have to put in quite a bit more volume if you're going to really get good at ultra marathons or long endurance running and if you're putting down 80 mile weeks for example you're going to have to put in quite a bit more volume if you're going to really get good at ultra marathons or long endurance running and if you're going to really get good at ultra marathons or long endurance running you can't tolerate running most of those miles at your 10k race pace that's not sustainable i laid the groundwork for this thought experiment in recent episodes dedicated to discussing mileage and volume we begin our exploration of training intensity distribution then with the understanding that we have to run significant mileage and most of that mileage has to be easy or modest to be able to run a significant amount of mileage and most of that mileage has to be easy moderate effort running small mileage isn't enough and running a lot of miles very fast isn't sustainable so this obvious observation results in a training intensity distribution for ultra marathon runners where the majority of the training is easy to moderate intensity so what do we do with the rest one option is to do more of the same make all of the training easier or moderate a lot of people will do pretty well on that program this approach will give you most of the endurance capacity you need to complete ultra marathons over time it will even help you get a little bit faster at running them but the evidence shows that athletes benefit from adding some faster or high intensity running into their program and while some high intensity running is beneficial doing more is not better and may even be detrimental especially if it takes time away from more running at lower intensities in the laboratory we can measure two transitions in metabolism that occur as we progressively increase output like running faster and or greater inclines one of these transitions occurs at the transition from what bioenergeticists call the moderate domain to the heavy domain it can be identified by a rise in blood lactate from resting levels to higher values and occurs roughly at two millimole blood lactate on average it can also be identified as an increase in exhaled carbon dioxide relative to oxygen consumption or as a rise in oxygen consumption above the average level of oxygen it can also be identified as an increase in oxygen consumption or as a rise in oxygen consumption above the average level of oxygen apparent in lower work rates that last method is a little wordy and heavily scientific but it's actually the one i like and use the most to put into into easier terms it's where you begin consuming more oxygen per unit of work output than you did at lower efforts which is why i've dubbed it the economy threshold now the higher transition is the one above which a relative steady state is not achievable and it's synonymous with critical power we can call this the fatigue threshold because fatigue arrives at a highly predictable moment for any higher pace if some of the physiologic capacities have been properly measured for that athlete these two transitions define the bounds of three bio energetic domains called moderate heavy and severe exercise is sustainable for many hours in the moderate domain some hours to less than an hour in the heavy domain and less than 30 minutes if we're clearly in the severe domain it becomes tricky to equate these domains with race distances because sustainable paces don't line up perfectly with the underlying measures of these bioenergetics across the entire spectrum of athletes from novice to elite said another way a recreational runner or short distance specialist may finish a marathon with high lactate levels while an elite may run the entire race and never get much above two millimole per liter despite running much faster and at a higher percentage of their max small aerobic capacity but as a very rough guide and averaging heavily the first transition that is from moderate to heavy may be roughly at marathon race pace and the second that is from heavy to severe at roughly 10k race pace and i give these not as guides for you to try to implement but only as a way of helping you to get the most out of your life and to get the most out of your life helping to map what we're talking about onto some tangible metrics you'll be familiar with so roughly the moderate domain is below marathon pace heavy is marathon to 10k and severe is faster than 10k again any individual may differ significantly from these estimates they become more accurate in a population average but it gives you something rough to anchor on for the rest of this episode this recap of intensity domains is useful because these are the three domains that have been used most often when quantifying training intensity distributions if we accept that most of our training will be in the moderate domain the question is how much of the rest of our training will be distributed in the heavy and severe domains the possibilities are running most of it in the heavy domain and less in the severe domain something called pyramidal training because the graph of the pyramidal training intensity distribution slopes like one side of a pyramid or we could run a little or even not at all in the heavy domain and most are all of it in the severe domain that's called pyramidal training polarized training where the graph of your training intensity distribution looks like an inverted There is one other major type of training intensity distribution worth mentioning. It's called threshold training. This is where the largest amount of running is in the heavy domain, with less in both the moderate and severe domains. Threshold training intensity distribution graphs look like an upside-down V or an upside-down U. It may be useful for those running marathons or half-marathons for some of the peaking weeks, but threshold training is not really sustainable because running a lot of mileage at threshold puts you at high risk of eventual overreaching. Now, you've probably heard one of those patterns talked about a lot because it's been popular lately, polarized training. One of my goals today is to show you why the evidence for polarized training has been misunderstood. It's not how most top endurance athletes train, and it's not how most people should be training most of the time. The underappreciated factor in early papers that popularized a polarized training intensity distribution is that the studies quantified training by a session-goal approach, and not by training time or distance. In these studies, each training session counted once, regardless of the duration or distance of the session. Each workout was assigned a training intensity for the entire session, based on the main goal intensity within the session. For example, a two-hour easy run counts as one moderate domain session, and a one-hour run with 30 minutes of intervals at half-marathon pace would be counted as one heavy domain session. A track workout with 15 minutes of 400-meter fast repeats would count as one moderate domain session. A three-hour training session would count as one moderate domain session. You can see immediately that the session-goal approach tells you the number of sessions aimed at hitting intensities in the three domains, but it doesn't tell you about the amount of training time or distance that athletes actually spend in each intensity. One of the first and most cited early studies to do this was by Seiler and Kirkland. In 2006, which I call the study that launched a thousand misunderstandings. When you read the abstract of that paper, all the authors tell you is that the intensity distribution of training sessions was 75-8-17, which means that 75% of sessions were moderate, 8% had some heaviness, heavy domain bouts, and 17% of sessions included severe domain intervals. That word sessions is the key, and it's the word that has gone unappreciated by most of what I see and hear in the general running public when polarized training intensity distribution is recommended. When you read the paper, you have to dig deep into the results, and then you discover the outcome. The actual training intensity distribution of those athletes was 91-6.4-2.6 by time using heart rate records. Those are massive differences. 75-8-17 by sessions, but 91-6-3 by time. If you, like so many, simply gloss over that word sessions in the abstract, you come away thinking that you're supposed to spend about 20% or so of your time in the heavy or severe domains with most of that above 10k race pace, when in fact, the athletes in that study spent only 6.4 and 2.6% of their time. That's 9% total at heavy and severe domains. They spent less than 3% of their time running fast. Not 17%, like you might glean from the session approach. As we explore more studies, we find another failing in communicating the science to the general public. Upon closer analysis, the majority of what has been counted as severe, severe domain training, was around 90% of maximum heart rate. Roughly 88-92%. Which is approximately the heavy to severe border. Approximately critical power. Or the fatigue threshold. It's a misapplication to use those findings to recommend severe domain training because most listeners of that message will run out of time. And they'll run their faster workouts too fast. Like 5k pace. Rather than near 10k pace. Which is more consistent with the research data. If you want only one take-home message, it's this. Based on more than 15 years of research studies, the training intensity distribution that seems to produce great endurance performance, based on time or distance, is a pyramidal approach. Where the clear majority of running, often more than 85 or 90%, is moderate. That's slower than marathon pace. Most of the rest is in the heavy domain. That's roughly up to 10k pace. And only a few percent is faster than 10k pace. If you graph your time or distance spent at all intensities over the course of a week or more of training, using, say, heart rate or power, for example, this will look like a line or curve where more time is spent at any lower value when compared to any higher value. Now, we'll explore the nuances and studies to date, beginning with studies of runners, then moving on to other endurance disciplines, and finally, on to reviews and meta-analyses. I'll come back at the very end and repeat that take-home message. In 1999, Billott et al. studied eight subjects who performed four weeks of normal training with one session per week, doing some intervals at the lowest velocity, that would elicit VO2 max, that's just barely into the severe domain. They followed this training with four weeks of overload training, where they did the interval session three times per week. The conclusion was that intensification of training did not improve factors associated with performance. In other words, one hard session per week was enough to maximize gains. In 2001, the same group reported that top-class marathon runners ran, about 78% of their weekly kilometers, slower than marathon pace, 12% at marathon to half-marathon pace, 6% at 10k pace, and just 4% at 3k pace. This is a pyramidal training intensity distribution. I've actually seen this study cited as evidence supporting polarized training by those who promote session-based training intensity distribution. Why? Because if you're a marathon runner, if you don't pay attention to the time or distance spent training and only bin each workout based on the top speeds of each session, that goal approach thing, then there are more sessions with very fast running than with just somewhat fast running. But as I've just given you the numbers, you can see that these athletes run less at faster paces than any slower paces. In 2005, Esteve Laneo and colleagues showed that regional and national class runners training was pyramidal, with 71-21-8 distribution of their training time. Two years later, the same group reported that increasing the amount of time spent in the middle, the heavy domain, from a training intensity distribution of 81-12-8 to 67-25-8, 5, 8, did not enhance performance. So in other words, adding more in the middle by taking away from the moderate or easier running doesn't help once you've got, in this case, 8% in the more severe intensities. In 2012, Stellingworth published case studies of three elite Canadian international marathon runners over a 16-week period before a marathon race. Based on subjective ratings of perceived exertion, the distribution of sessions was 74-11-15, which is polarized, but the actual time spent in each domain reveals a pyramidal training intensity distribution. This difference is because athletes report. perceived exertion for a session with a bias to the harder parts of the session, and we get a skewing of outcomes when we count each session as one intensity anchored on the hardest parts. In 2013 and 2014, Tjeltla reported a pyramidal training intensity distribution for top runners in two studies across all time points of training, which spanned up to two years. In 2014, Munoz et al. studied 30 recreational runners who performed either polarized, 77-3-20, or threshold, 46-35-19 training, for 10 weeks. Now, that's a near threshold, because notice I said 46-35-19, and true threshold training puts more in the middle. But both groups improved 10K. And the improvement was not statistically different between the two groups, though the authors say that the polarized distribution was more beneficial statistically when they excluded the polarized group athletes who did the least amount of training. Unfortunately, there was a large difference in the amount of moderate domain training between the two groups. In other words, the threshold wasn't pyramidal. I include mention of this study because it may well be that the threshold was not parametral. However, the training intensity distribution matters less when the runners are less well-trained to start. Remember, these were recreational runners, and that's important to consider if you are relatively new to running or otherwise would consider yourself recreationally trained. In 2015, Manzi and colleagues reported the training intensity distribution of seven recreational marathon runners, which was 76-17-6. This is pyramidal training. And what I found more interesting is. There was a significant correlation between total time spent in Zone 1, meaning the moderate domain, and the improvement at running speed of 2 millimole lactate. This is important for ultramarathon runners because ultras are run at an average output that is roughly this intensity, especially the longer ones. They found that the amount of time spent running slower than that intensity. was significantly correlated with improving speed at it. There's a common misconception that I regularly hear. It's this notion that to enhance a physiological capacity, ability, or measure, you have to train harder than it and accumulate time above it. But there's no evidence to support that notion. It may be that you can enhance some capacities or measures by training harder than them. But there's no evidence that doing so is required for improvement. I'd like to further illustrate this point using an example of just one factor that supports enhanced endurance capacity. Capillary density. Which is the number of capillaries, the tiniest blood vessels, in contact with each muscle fiber or within a voxel of muscle tissue cross-section. Given the architecture of microvascular control. relative to motor unit dispersion, it is predictable that easy exercise generates sufficient shear stresses to increase capillarity, even to fast-twitch fibers, despite fast-twitch fibers being recruited less at lower intensities. Specifically, arterioles control flow into capillary beds that serve fibers from multiple motor units. Which includes adjacent slow and fast muscle cells. One need only recruit slow fibers sufficiently to generate arteriolar dilation to increase shear stresses in the capillary beds that also serve fast fibers and thereby create a stimulus for angiogenesis to fibers that may not even be recruited. Because the shear stress signal may have a minimal duration effect, a need to be on for a period of time before new capillaries will result, short, high-intensity exercise is less likely to add capillaries than longer, total durations of low-intensity exercise. This is a long way of explaining how longer duration of moderate running can improve blood flow delivery capacity even to those fibers that are relatively less aerobic. and thereby improve support for long endurance performances where those fibers become necessary late in a race. This is one reason why high-intensity interval training cannot substitute for long runs at moderate paces, and why a larger volume of your training for endurance performance should be at easy to moderate efforts. In 2017, Esteve Laneo and Kostas Kostasov, who are both in the medical field, said, and colleagues published another study, this time comparing the training of marathoners and full-distance triathletes. They found that marathon runners' training was in a pyramidal approach of about 75, 16, and 9 of the time across those three domains. In 2019, Perez et al. studied the effect of two different training intensity distribution programs on measures in ultra-endurance runners. So why do I mention a study if it was so badly done as to not even have comparable groups? Because the training was in advance of a 93-kilometer ultramarathon, at which neither group performed better than the other. This may be another case of almost any training being equal to any other in recreational athletes, or it may reflect the realities that there are many other factors, that have a large impact on performance in ultras beyond the training intensity distribution. Said another way, once we're consistent with our training and do enough overall volume, with most of it at easy to moderate intensity, the distribution of remaining percentages between a bit above or below roughly 10k pace may not have a significant impact on ultramarathon performance, at least for recreational athletes. In 2020, Festa and colleagues studied 38 recreational runners who trained for 8 weeks in a polarized or threshold program, that is, 77-320 or 40-50-10. Both groups improved the velocity at VO2max, running economy, ventilatory threshold, respiratory compensation threshold, and 2k running time. No differences were found between the groups, on any parameter investigated. But it's important to note that the threshold group trained 17% less overall time. If you're unfit and you have limited time, it might be just as useful to split your time between easy, moderate, and moderate-somewhat-hard intensities, with just a bit of fast-for-you running, according to this study. Also in 2020, Keneally et al. published a training intensity distribution analysis of seven world-class middle-distance, that is 800-1500 meters, and long-distance, that is 5,000 meters to 10,000 meters, runners over 50 weeks, using two different approaches to organize training intensity distribution zones. These were based on individual, specific race pace, and based on physiologic parameters. Training volumes for the three domains, rounded off, were 89, 7, and 4% for race pace-based approach, and 87-6-7 for the physiological approach. They wrote, quote, The approach based on race pace zones produced pyramidal distributions in both middle and long distance runners across all phases of the season. The physiological approach produced polarized and pyramidal distributions depending on the phase of the season in the middle distance runners and pyramidal type distribution across all phases of the season in the long distance runners. Specifically, in the short competitive micro cycles of the year, middle distance runners adopted a slightly polarized training intensity distribution. And I say slightly because the difference was less than 1%. Otherwise, all training was pyramidal and all training at all times was pyramidal for the long distance runners. It's routinely reported that the fastest athletes run the most mileage. From the 2001 paper by Billott to a more recent big data analysis in Nature Communications that I've mentioned on the podcast before, faster athletes run more per week than slower runners. The differences seem to be caused by something more than just the obvious fact that faster athletes run more per week than slower runners. The differences seem to be caused by something more than just the obvious fact that faster runners can cover more ground than slower runners in the same amount of training time. And it's reasonable to question whether this trend manifests from other aspects of physiology. For example, the best endurance athletes will tend to be more slow twitch, and they can likely handle lots of low-intensity mileage. Indeed, they may even need it for optimal training stimulus. The effect of this trend is that the effect of different training intensity distribution programs aimed at enhancing endurance capacities is also complicated by the starting glycogen levels. The external stress may be the same for two identical runs, but the internal strain and its impact on adaptive responses such as, say, mitochondrial adaptations may differ depending on the finishing glycogen concentration. This was the main topic we covered in episode 1, 19, with Drs. Morton and Louis, titled Finish Low. Elite and pro runners who train for distances up to the marathon may train up to 13 times per week, with two sessions on most days of the week. They have sessions that are essentially all intervals, for example. They don't run for 90 minutes, with 4x5 minutes hard in the middle. Instead, they'll do the interval session, and then they'll run easy miles in a different session. Most amateur athletes run only once per day, and often blend harder efforts within the context of running slower miles. The total time or distance in each intensity zone is what we should be looking at, not the number of sessions binned by the highest intensity of those sessions. It takes two weeks for the recreational athlete to get in as many training sessions as the elite or professional athlete does in one week. Thus, the session goal approach used by Seiler and colleagues in 2006 and since, which has formed the foundation of the current craze in polarized training, may not be relevant for the once-per-day athlete. Moreover, the reality that polarized training approaches are only for the one-day athlete, are only supported when using the session goal approach, has gone underappreciated. Even the highly referenced 2006 study by Seiler and Kierland found a non-polarized time distribution. There are at least a dozen studies in sports other than running. In 1999, Lucia et al. reported a pyramidal training intensity distribution of 70-23 seconds. In 2007, during the Tour de France, based on the heart rate time-in-zone method, over 22 competition days. Five years later, Fiskerstrand and Seiler published data from a survey of Norwegian international-level rowers across three decades, 1970 to 2001. The data clearly shows a pyramidal training intensity distribution in all decades, except in the 1970s where there was more over-speed training, but still not polarized. In 2009, a study of world-class rowers reported a 95, 2, and 3 percent distribution, which is mathematically polarized, perhaps, but the actionable message is that nearly all training, 95 percent, was easy or moderate, and about 5 percent distributed among the higher outputs. In 2013, Neal et al. found that six weeks of polarized training was more effective than a threshold distribution of 90 percent. In 2014, several studies shed more light on the topic of distribution of training. Ori et al. published results from an analysis of 38 years of training intensity distribution in Olympic speed skaters. The distribution of successful male Dutch Olympic speed skaters in four Olympic seasons from 1972 to 2010, assessed by interviewing the coaches and athletes, was based on threshold in 1972, although it wasn't exactly threshold, it was 40-40-20, but transitioned to a pyramidal approach by 2010, which was 80-12-8. A threshold training intensity distribution approach was also supported by a study in 2019 by Salas-Perez et al., who reported that training time in Zone 2, that is, the heavy domain, was related with better performance on a half-Ironman race in amateur athletes. So, while we might begin to theorize that a threshold training intensity distribution can be useful in recreational athletes and possibly even more effective than polarized approach in some well-trained athletes, top performers have transitioned to a pyramidal approach in more recent years. Muñoz et al. quantified the training distribution of nine recreational Ironman triathletes. They found a greater percentage of training done in the middle zone was strongly correlated with worse performance, while more training at low intensity was correlated with better Ironman performance. Clearly, not all studies will agree, which is likely due to more subtle factors in the study design. On aggregate, however, it is a consistent finding that more time spent at easy and moderate intensities consistently correlate with the best performances. Moreover, programs with 90-95% of training time in those zones are practiced by most of the athletes and most of the best endurance athletes across numerous disciplines most of the year. Stogl and Sperlik studied the training of 48 healthy competitive endurance athletes from Austrian national teams who participated in cross-country skiing, cycling, triathlon, or running. Unfortunately, this time, they did not provide time or distance in zone data, but only the session maximum, which, unsurprisingly, was polarized. The study methods stated that the athletes wore heart rate monitors throughout training sessions so they should have all the data to report time or distance at various intensities. To that extent, that heart rate reflects those relative intensities. So, I emailed Dr. Stogl. He told me that they did record the data, but did not store it and could not make those determinations, though it was likely the athletes did train in a pyramidal distribution by time or distance. And he followed up by confirming that the discrepancy in training intensity distributions by the two methods, as he put it, was, quote, huge, and that the majority of research demonstrates that top and successful endurance athletes, by and large, employ a pyramidal training intensity distribution, not a polarized one. So, it's not just a randomized training intensity distribution when assessed by time or distance of training at intensity. In 2017, Soli et al. published an interesting study of the training characteristics of the world's most successful female cross-country skier, Marit Björgen. Her training was more than 90% easy to moderate. The remainder was pyramidal early and only became more severe in the final preparation phase before competition. where severe intensity bursts would be required. So indeed, when we see a polarized training intensity distribution in endurance athletes' regimens based on time or distance, it seems to be only in the final preparation phases before competitions and when there will be a requirement for those brief but very high-intensity bursts in the competition. For example, in 2020, Mayak and Chenko et al. found that international-level cross-country skiers and biathletes increased the percentage of time at race pace and intensities as they neared competitions but that, quote, all teams employed the pyramidal model of intensity distribution, end quote. Also in 2020, Rorkin et al. conducted an intervention study in 15 moderately trained triathletes assigned to polarized or a, what they called, moderate distribution, which had no severe intensity training at all, and concluded that, quote, polarized training intensity distribution in moderately trained athletes did not prove to be superior compared to a more moderate distribution. My overall take from all of this research is that, A, a polarized training is uncommon and only employed for brief periods and in specific phases for specific events. B, most amateur athletes will benefit similarly from any training intensity distribution as long as total volume is sufficient and the emphasis is placed on easy-to-moderate intensities. And C, some time or distance. Spend at efforts at half-marathon pace or half-marathon pace. These are likely beneficial for ultramarathon runners but need not be more than a maximum of maybe 5-8% of training time and can probably be even as low as 2-3%. I've reviewed studies on running and studies on non-running sports. The next and last section here of this episode is of review papers that synthesize multiple studies. The first was in 2008 by Seiler and Tonneson. And along with another review by Seiler in 2010 explains that, across endurance sports, successful top athletes tend to have a pyramidal training distribution by time or distance, but have a polarized distribution in terms of training sessions. So by this point you understand this to be true. But even then, there is an especially important wrinkle in the fact that, the severe domain intervals are not all-out, but rather low zone 4 of a 5-zone model or just barely into zone 3 of a 3-zone model. Again, this is somewhere close to 10k pace on average. I think most runners have gotten the idea that they should be running their hard sessions or intervals harder than is true. The consensus view from the data is that, extremely little running needs to be much faster than 10k race pace when training for ultramarathons. In 2018, Keneally et al. published a paper titled, The Effect of Periodization and Training Intensity Distribution on Middle and Long-Distance Running Performance, a systematic review. They wrote, According to the results of this analysis, pyramidal and polarized training are more, more effective than threshold training, although the latter is used by some of the best marathon runners in the world. Despite this apparent contradictory finding, this review presents evidence for the organization of training into zones based on a percentage of goal race pace, which allows for different periodization types to be compatible. So the conclusions are consistent with the observation that top athletes, may adopt a polarized distribution as they get into competition phase, and when the competitions contain high-intensity output requirements, like rowing that may only last seven minutes, or cross-country skiing that has short uphills with downhills that are effectively high-intensity interval performances. Applying the consensus observation of this systematic review to training for ultramarathons indicates a pyramidal distribution is right. In 2019, Rosenblatt et al. published Polarized vs. Threshold Training Intensity Distribution on Endurance Sport Performance, a systematic review and meta-analysis of the randomized controlled trials, where they wrote, quote, The pooled results demonstrate a moderate effect favoring the polarized group over the threshold group. These results suggest that polarized may lead to a greater improvement in endurance sport performance, than threshold. Only three to four studies made it into quantitative and qualitative analyses, and pyramidal training intensity distributions was not part of that review. And finally, in 2019, a very thoughtful narrative by Bourgeois et al. titled Perspectives and Determinants for Training Intensity Distribution in Elite Endurance Athletes includes an evolutionary perspective. That suggests humans are likely most sensitive to training that mimics how we lived during our evolution as hunter-gatherers, which is mostly easy, with some brief spurts of high intensity, and little or no in the middle. They write, quote, We speculate that type 2 oriented endurance athletes, for example 65% type 1 and 35% type 2, and thus more anaerobically oriented, will have a faster force development pattern and a higher movement velocity as compared with type 1 oriented endurance athletes, for example 85% type 1 and 15% type 2 fibers, thus aerobically oriented, and will induce more adaptive benefits from pyramidal training. On the other hand, type 1 oriented endurance athletes might benefit from more polarized training, since a higher volume of threshold in pyramidal versus polarized can have a negative impact on the autonomous nervous system as well as on glycogen homeostasis as compared with polarized. We also assume that total training volume in polarized used by type 1 oriented endurance athletes can be higher in pyramidal, used by type 2 oriented athletes. With regard to the biological training age of an individual, which will also have an impact on the planning and periodization strategy, the lower total training volume of young athletes will allow a higher contribution of zone 2, or heavy, and zone 3, severe. As athletes develop toward elite level, the training volume will increase, and thus the contribution of zone 1 will be more pronounced. They continue, up to now, we can only speculate that a large volume of low-intensity training, more than 70%, combined with a low proportion of threshold and high-intensity training, is paramount. It's worth wrapping up by exploring a 2015 review. In 2015, Stoegl and Sperlich published The Training Intensity Distribution Among Well-Trained and Endurance Athletes. This is the same Stoegl who previously published with Seiler, who reports session goal rather than time at intensity. And now we get to see Stoegl's take on the field without that constraint. The findings of that review indicate that elite endurance athletes spend a high percentage of their training intensity distribution in a high percentage of their training intensity distribution. in a parametral shape. That is, great portions of high-volume, low-intensity training with 84-95% in moderate, 2-11% at heavy, and 2-9% at severe. Depending on the competition calendar, the training intensity distribution during the pre-competition phase may vary between endurance disciplines. The shifts were toward a larger emphasis on race paces, which resulted in parameter or polarized depending on the events. They also wrote, quote, overdoing threshold by more than 20% through reducing high-volume, low-intensity training may exert a negative impact on the autonomic nervous system with no further adaptation. In fact, threshold training places greater demands on carbohydrate fueling, leading to restricted training time due to low-intensity training. to limited glycogen storing. However, threshold may be more applicable for untrained and or recreational individuals. End quote. But I'll add, the race preparation phase if the performance is at threshold paces, such as in the marathon. So I think this is a useful assessment in summary. Nearly all of your training should be easy to moderate, with 0 to 15 percent of your time or distance spent running faster than marathon pace, with generally less of that at progressively faster paces. In other words, a pyramidal training intensity distribution. You might spend 5 to 10 percent of that time in higher intensity training as you get closer to race day, but only if you're doing a short event that will require those redlining efforts. I'll finish by repeating the take-home message. Based on 15 years of research studies, the training intensity distribution that seems to produce great endurance performances based on time or distance, is a pyramidal approach, where the clear majority of running, often more than 85 or 90 percent, is moderate, slower than marathon pace. Most of the rest is in the heavy domain, roughly up to 10k pace, and only a few percent is above 10k pace. If you graph your time or distance spent at all intensities over a week or more of training by, for example, heart rate or power, this will look like a line or curve where more time is spent at any lower value when compared to any higher value. Now this has been a whole lot of information. I hope the take-home message, though, is straightforward and simple, and helps to relieve you of any stress or anxiety you might have in how you will do best in distributing your training intensities over a week or a month or even a year. If you're training for long endurance events, remember that programming all of this distribution of your movement isn't enough and isn't sufficient to optimize your overall training, because how you sleep, think, eat, and move all play a role in helping you become your ultra-best.