Inigo Mujika

James Spragg is a young South African exercise physiologist who has carved out an interesting niche for his research. It is based on the idea that the fastest athlete on fresh legs is not necessarily the fastest athlete on fatigued legs, which is an important distinction, as in most endurance races, it is better to be the guy or gal who is fastest on fatigued legs. Yet conventional fitness testing protocols ignore this reality, which is a problem, because it has the potential to skew athletes’ training too far in the direction of improving fresh-legged performance.

In one of his early studies, Spragg teamed up with several other researchers, including Iñigo Mujika, whose name you might recognize from his work related to the 80/20 intensity balance, to compare power profiles in nine members of a U23 cycling team and five professional cyclists. Interestingly, they found that the U23 riders were able to generate as much power as the pros on fresh legs. Had this experiment been limited to non-fatigued performance testing, we would have been left to wonder why the U23 cyclists were not also on professional teams. But what Spragg and his collaborators also found was that, in U23 cyclists, achievable power outputs began to decline after 1,500 to 2,000 kilojoules (about 3,600 to 4,800 calories) of prior work was completed, whereas in professional cyclists, performance fell off only after 3,000 kJ of pedaling.

What’s more, a later study by Dutch and South African researchers found that, among top-tier professional cyclists, those able to do the most work before their power output capacity dropped off performed best in races. So, it appears that the ability to ride fast on tired legs is a key factor separating the best from the rest, both between and within echelons of cycling.

Spragg’s recent study is also his most ambitious to date. It involved collecting power data from every training ride and race completed by 30 U23 professional cyclists over three years. The aim was to determine how individual cyclists’ fresh and fatigued power profiles changed over the course of a competitive season and how these changes related to their training. The main findings were as follows:

  • Fresh power profiles remained relatively stable throughout the season.
  • Fatigued power profiles changed over the course of the season.
  • The difference between fresh and fatigued power profiles also varied as the season unfolded, indicating that the two phenomena are independent.
  • More time spent at low intensity in training predicted better 2-minute power on both fresh and fatigued legs.
  • A shift away from moderate intensity toward high intensity was associated with a stronger fatigued power profile (i.e., a smaller delta between fresh and fatigued power)

An important implication of these findings is that, depending on the type of event an athlete is training for, performing fitness testing in a fresh state may be of limited value. If you specialize in the 400m freestyle event or the 1500m track event, then perhaps testing in a fresh state has greater relevance. But if you’re training for a marathon or an Ironman 70.3, I would imagine that fatigued fitness testing would tell you more. In a narrative review published in October 2021, Spragg, Mujika, and three other colleagues provide detailed recommendations for incorporating fitness testing into training for road cycling events, one of which is to “avoid single effort prediction trials, such as functional threshold power.” As a running and triathlon coach, I personally lean toward using regular workouts to assess fitness. For example, tacking a fast finish onto the end of a long run serves as a good measure of fatigued performance capacity in a marathoner while also functioning as a relevant fitness-builder for the marathon.

Another interesting finding from Spragg’s 2022 study is that cyclists who maintained their peak training load through the late season also maintained their fatigue resistance, whereas those who reduced their training load during this period lost fatigue resistance. This finding is consistent with other studies reporting a correlation between training volume and fatigue resistance/endurance. One example is a 2020 study byThorsten Emig of Paris-Saclay University and Jussi Peltonen of the Polar Corporation, who collected and analyzed training and racing data from devices worn by more than 14,000 runners for a combined 1.6 million exercise sessions. For the purposes of this experiment, endurance was defined as the percentage of VO2max running velocity that a runner could sustain for one hour, and the data showed a strong positive correlation between training volume and endurance thus defined.

I wish all of this science had been available when I wrote 80/20 Running back in 2014. It would have bolstered the argument I made therein about how the typical exercise science study design puts a thumb on the scale in favor of HIIT-focused training when compared against the type of training elite endurance athletes do. It’s less of a problem nowadays, but back then it was common to use fresh-legged VO2max tests as the basis for such comparisons. But we now know that a VO2max test performed after extensive prior exercise is likely to yield different results that are more relevant to real-world race performance, and that high-volume, mostly low-intensity yields better results in pre-fatigued fitness tests.

Oh, well. That’s what second editions are for, right? In the meantime, you can check out our cycling plans here – some are built to improve your FTP and can be used in your off season.

If the fastest swimming, cycling, and running you do is in races, you’re not training right. Every triathlon training program should include speed work, or efforts that exceed race intensity. Speed work not only changes your perception of race intensity, making it feel more comfortable, but it also enhances fitness in ways that slower training does not.

There are right and wrong ways to incorporate speed training workouts. Doing speed work the right way is not difficult. A top triathlon training tip is to copy how professional triathletes go about it (which is not to say you should try to go as fast as they do!). Incorporating speed exercises all comes down to obeying these three simple rules.

Rule #1: Do some speed training workouts year-round.

Speed training workouts can be done year round

The term “periodization” refers to the practice of dividing the training process into phases and assigning a distinct fitness objective to each. Traditionally, the first phase, known as the base phase, is all about building general aerobic fitness and endurance through large and increasing amounts of low-intensity training. Speed work is excluded from this phase because maximizing overall training volume is easier when intensity is kept low.

These days, however, most elite triathletes include a small amount of high-intensity swimming, cycling, and running in the base phase, and you should too. The reason is that when speed work is completely eliminated from training, the athlete loses the dimension of fitness that comes from speed work and makes it harder to get it back in later phases.

Just one small dose of high-intensity swimming, cycling, and running per week during the base phase will enable you to avoid digging this all-too-common hole. I recommend doing very short efforts at or close to maximum intensity, such as 8 x 25-yard sprints in the pool and 8 x 20 seconds uphill on the bike or the run.

Rule #2: Keep your total volume of speed training workouts low.

After the base phase of training comes the peak phase. During this period, which should begin 6-12 weeks before a race, you will want to increase your volume of speed work while keeping your overall training volume steady. But even at this time, speed work should account for no more than 10 percent of your total training volume.

Again, let the pros be your guide. In 2012, Iñigo Mujika of the University of Basque Country monitored the training of elite triathlete Ainhoa Murua as she prepared for the London Olympics (where she placed seventh). He found that she spent 10 percent of her total swim training time, 2 percent of her cycling time, and 7 percent of her running time at high intensity. These numbers are normal for elite triathletes and they should be the norm for you too.

While a little triathlon training for speed goes a long way, more than a little is counterproductive. This was shown in a 1999 study involving elite middle-distance runners. For the first several weeks of the study period the runners completed six runs per week, all at low intensity. Then they switched to a schedule of five low-intensity runs and one high-intensity run per week for a few weeks. Finally, they switched to a schedule  of three low-intensity runs and three-high-intensity runs per week. The runners produced the best results in a fitness test when they were doing one run per week at high intensity and got the worst results when they did speed work three times per week.

Here’s an example of a sensible breakdown of training intensities during the peak period of training:

Monday: Rest

Tuesday: Swim 1500 yards w/ 3 x 200 at moderate intensity

Wednesday: Bike 50 minutes w/ 8 x 1 minute at high intensity

Thursday: Run 45 minutes w/ 6 x 3 minutes at high intensity

Friday: Swim 1500 yards at low intensity

Saturday: Bike 70 minutes + run 10 minutes at low intensity

Sunday: Run 10 miles at low intensity

Rule #3: Make your speed work increasingly race-specific as the training process unfolds.

swimming for speed training workout

The format of your speed workouts should evolve from week to week as the training process unfolds. The idea is to make your high-intensity sessions increasingly race specific. What does this mean exactly? It means that your intervals should become longer and slower (while remaining faster than race speed). The reason is that the true goal of speed work is not to make you faster—it’s to increase your fatigue resistance at higher speeds.

In the pool, I suggest starting with 25-yard sprints and moving step by step from there up to 200-yard repetitions. You should include longer intervals in your training as well, but these don’t count as speed work. On the bike and on the run, start with 20-second hill sprints and transition incrementally to intervals of 3 to 5 minutes. Don’t completely give up the really short stuff, though. Sprinkle in a few sprints even during the last few weeks before a race to maintain your highest gear.

Love it or loathe it, speed work is a critical component of effective triathlon training. But there are right and wrong ways to go about it. Now you know the right way.

A few months back, the following tweet from triathlon legend Dave Scott caught my eye:

It always amazes me how folks fear a new paradigm for sports nutrition. Unless you own a sugar-based nutrition company, why WOULDN’T you experiment w/ #LCHF It works when implemented properly … even at high intensities.

I’m not sure whether Dave meant this question rhetorically (after all, there’s no question mark), but I took it literally and personally. As a competitive endurance athlete who takes seriously the role of diet in endurance performance, I had to ask: why haven’t experimented with a low-carbohydrate, high-fat diet?

The answer, I decided, could be distilled to a single word: risk. I believe that switching from my current way of eating to LCHF would carry an unacceptably high risk of causing problems. For me, a better question than the one Dave asked is, why would I experiment with LCHF? My current diet does not limit my athletics in any way that I can identify. When I train harder I get fitter and when I rest I recover. I feel good physically pretty much all day every day. At age 47 I am as lean as I was when I was 27. If it ain’t broke, as they say. . .

Meanwhile, on the other side of the equation are a host of negatives outcomes, some guaranteed, others likely, that are associated with jumping onto the LCHF bandwagon. Nearly all athletes who do so feel like crap initially and experience a significant decline in training capacity and performance. Some come out the other side eventually, others don’t. The diet is extremely restrictive and monotonous and socially isolating. (“Hey, Brad! Do you want to come out to dinner with us? We’re going to that Italian place.” “Uh, well, you see. . .”) And the physiology is inescapable: Eating LCHF will make your muscles better at burning fat and much worse at burning carbohydrate, hence more dependent on fat, which requires greater amounts of oxygen to metabolize, thereby increasing the energy cost of moving at any given speed.

Those are the guaranteed outcomes. The potential outcomes that seem to affect some but not all LCHF eaters include unfavorable changes in blood lipids, mood disturbances, vertigo, skin problems, caffeine intolerance, and panic attacks. The long-term health effects of eating in this extremely unbalanced way are largely unknown, but a recent, large epidemiological study found that, on average, men and women who get less than 40 percent of their daily calories from carbs die four years younger than do those who get between 40 and 70 percent of their calories from carbs.

Elite endurance athletes don’t shy away from this diet because they are afraid of news things. To the contrary, no group is more eager to gain a competitive advantage through early adoption of new methods. Instead, the vast majority of pros choose to keep their diet carb-centered because, with their livelihood depending on their performance, they can’t afford to try “new” things with such an obviously poor risk-reward ratio as LCHF.

A recent case study indicates they are wise to do so. For a period of 32 weeks, a professional triathlete who switched from his normal, lacto-ovo vegetarian diet to LCHF was monitored by Spanish exercise physiologist Iñigo Mujika. Within the final third of this period, the athlete raced three times, finishing 18thin a half-Ironman with his worst time ever for that distance, then finishing 14thin a full Ironman with his second-worst time ever for that distance, and then DNF’ing his next race. Having had enough of LCHF by this point, the athlete went back to his normal diet. Just five weeks later he took second place in an Ironman.

This case study challenges several tenets of the LCHF doctrine. One of these is the notion that only athletes who, as Dave Scott suggested, fail to implement the diet properly fail to benefit from it. But Mujika’s subject was an experienced and knowledgeable professional athlete with all the attending resources and scientific support. Mujika reported 95 percent compliance with the diet’s strictures across the 32-week period. LCHF advocates also like to explain away the disasters that so commonly befall athletes who try it by claiming they didn’t give it enough time. I’m sorry—if 32 weeks isn’t long enough, then forever isn’t long enough.

The primary reason this particular athlete switched to LCHF was that he suffered from debilitating GI issues during races, and it is another popular tenet of the diet’s doctrine that it cures these issues. The subject of the case study experienced no improvement in GI symptoms during races on LCHF. This shouldn’t surprise anyone, as the two main causes of GI distress during long endurance events are the stress of the events themselves and a genetically-rooted susceptibility, neither of which can be changed by any diet.

Here is where LCHF advocates predictably say, “But this is just a case study. We’re talking about one athlete!” The problem with this objection is that each of us is one athlete with only one body to care for and limited opportunities to compete each year. If LCHF works best for 90 percent of athletes, it is remarkably unlucky that the athlete chosen for this case study was among the few for whom it doesn’t work. Is this the assumption you want to make as an athlete who cares most about your fitness and performance? I think it’s far more reasonable to see this case study as yet more firm evidence that LCHF is risky.

This was not intended to be another one of my rants against LCHF for endurance athletes. The point I want to make in referencing it is that, although this way of eating does appear to work okay for some athletes, it is high0risk. So are a lot of other diets and nutritional measures that endurance athletes try in pursuit of better performance. Reflecting on Dave Scott’s tweet caused me to realize that the approach to endurance nutrition that I advocate is really a risk-minimization approach.

If you adopt and follow the five habits of the Endurance Diet, you will not and, indeed, cannot go off the rails in the way that so many LCHF athletes, plant-based athletes, and other athletes who choose unbalanced diets of one kind or another do. To refresh you memory, these habits are:

5 Habits of Endurance Diet


Consistently including all of the major food types in your diet minimizes your risk of being taken down by one of the nutritional holes that open up when things like meat/fish and grains are eliminated.


This habit is about centering the diet on unprocessed, natural food types (e.g., nonfried vegetables) and limiting intake of processed foods (e.g., refined grains). Many LCHF eaters pay no attention to quality, loading up on processed animal products such as cured meats and mayonnaise that have proven negative health consequences.


It’s just a fact: The safest place to start with your macronutrient balance, if you’re an endurance athlete, is carb-centered, which simply means including high-quality carbohydrate-rich foods in most meals and snacks. Lots of LCHF eaters claim they switched to this way of eating because a carbohydrate-centered diet didn’t work for them. This claim never stands up to scrutiny. It was sweetsand refined grainsthat didn’t work for them, not carbs in general. I’ve never dealt with an athlete who couldn’t make a carb-centered diet work for him or her by combining it with Habit #5 (below).


This habit is about relying on the body’s built-in appetite signals to regulate the amount of food you eat instead of counting calories. In my experience, calorie-counters are at much greater risk of eating too little, which is far more detrimental to endurance performance than eating too much.


Most extreme diets are one-size-fits-all. The Endurance Diet is not, and this is another way in which it manages risk. Do grains generally not agree with you? Fine. Then practice Habit #3 (“eat carb-centered”) by getting most of your carbs from fruit and starchy vegetables. Forcing yourself to eat exactly like every other follower of whichever named diet you choose to follow brings with it great risk of forcing yourself to do something that doesn’t work for you individually.

Woven into these five habits are two further principles that also serve to minimize risk in eating for endurance. Framed as edicts, they are (1) Keep things as simple as possible and (2) don’t change anything in your diet that you don’t both want and need to change. The more unnecessarily complex you make your eating habits (e.g., intermittent fasting) and the more things you change (e.g., completely tossing out your current habits and going all-in with LCHF or some other unbalanced one-size-fits-all) diet, the likelier it is that you will create a health- or fitness-harming new problem that did not exist previously.

A certain amount of risk is inherent in endurance athletics. You have to train hard to attain peak fitness, and hard training brings with it the risk of injury and the risk of illness. Don’t let your diet compound these risks unnecessarily.

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