Jan 29, 2015
Ahead of the Pack

If you haven’t thought much about endurance training lately, you’re behind the curve. This author dissects the research and provides insight into training for stamina, in any sport.

By Dr. Guy Thibault

Guy Thibault, PhD, is an Associate Professor in the Kinesiology Department at the University of Montreal and a scientific advisor to the Canadian Cycling Association and the government of Quebec in Canada. His work, published mainly for French-speaking audiences, is dedicated to the interpretation of scientific knowledge for coaches, particularly those involved in individual sports. He can be reached at: [email protected].

Many myths and misconceptions surround endurance training. Popular magazines provide advice that is not always backed by science. And coaches who have “always done it” a certain way may not keep up with the latest research.

Anyone who trains athletes needing endurance does them a disservice by not knowing the latest research. In this article, I’ll explore three important topics in endurance training that are often misunderstood.


When an athlete fatigues, lactic acid is often blamed. For years, we have told athletes the reason they can’t push anymore is that lactic acid has built up in their muscles. But this is false, and there is much evidence disproving it.

Let’s start with a fact: at high intensity, muscles produce lactic acid, which enters the blood in the form of a salt called lactate. From this truth, many have reasoned that the more lactic acid accumulates, the more the muscle fatigues. However, if we examine the way energy is produced in the muscle during efforts of varying intensities, we find that lactate is not as detrimental as once thought.

The most convincing evidence for this conclusion is that it’s possible to observe muscle fatigue while the lactic acid concentration in the muscle remains low. Conversely, there can be an absence of fatigue when the lactic acid concentration in the muscle is high.

For example, at the end of a demanding bike ride of several hours in the mountains, the athlete’s fatigue level is quite high, but his or her blood lactate concentration is not much higher than in a resting state. Another example is found in people who suffer from McArdle’s Disease, which makes them incapable of producing (and thus accumulating) lactic acid. These individuals are very prone to suffering from muscular fatigue, even though there is no lactic acid accumulating in their muscles.

Now, let’s look at the opposite scenario. If an athlete performs an exhausting isometric effort with the quadriceps (for example, one study had athletes perform a chair exercise, with their backs leaning against a wall), fatigue will tend to reduce strength temporarily. The athlete gets to the point where he or she can’t continue the exercise and needs to rest. Two minutes after completion of the exercise, fatigue in the muscle is gone, and the athlete can once again produce his or her initial force.

However, during the recuperation period, the degree of acidity in the muscles lowers to normal rather slowly. At the two-minute mark, the degree of acidity remains very high. Thus, it is difficult to embrace the idea that an increase in lactic acid in the muscle causes fatigue, since a high degree of acidity without fatigue can be observed.

An athlete’s overall level of fatigue depends on a mixture of causes, which vary with different types of effort. Lactic acid or lactate is not the sole cause, nor even one of the major causes of muscular fatigue.

In fact, lactic acid build-up may be a positive. For an average sprinter, blood lactate concentration, which is about 1 mmol/l in a resting state, increases to about 18 mmol/l at the end of a 400-meter race. But, for an elite sprinter, it rises to 23 mmol/l. The extra lactic acid produced by the elite runner supplies his muscles with a greater amount of anaerobic energy, which means a better performance. Thus, in short efforts (under 10 minutes), higher blood lactate concentration helps to make elite runners elite.

It is wrong to believe that athletes training in anaerobic events learn to “tolerate” more lactic acid. Instead, they learn how to produce more, which means they develop a greater supply of energy.

Related to the lactic acid myth is the anaerobic threshold misconception. It says that among the vast range of exercise intensities, there is a threshold at which you start producing lactic acid at a much higher rate and cannot increase exercise intensity anymore. This seems to make sense: During a prolonged high-intensity run, you sometimes feel that it would be very difficult to increase your speed by even the smallest amount. In addition, popular fitness magazines frequently cite anaerobic threshold as if its existence is generally agreed upon.

However, current scientific knowledge refutes the anaerobic threshold theory. Studies have found that there is no power threshold below or above which the muscle does not produce lactate. Muscles constantly produce lactate, from the lowest work level to the highest.

During a ramp test, in which an athlete must exercise at an intensity that keeps increasing until exhaustion, blood lactate concentration never appears as a threshold. In fact, a curve comparing intensity level to lactate concentration shows no deflection.

The take-home message is this: There is no reason to consider lactic acid build-up or anaerobic threshold when designing your strength and endurance programs. Lactic acid and lactate—the scapegoats for the pain athletes experience—are not responsible for all the ills they are blamed for. They are not the cause of fatigue, cramps, or soreness. The anaerobic threshold is just as meaningless, and its importance has been vastly overstated.


Interval training is frequently chosen over continuous training because it enables an athlete to perform a greater amount of work at elevated intensity. And that is the key to boosting important physiological performance factors, such as anaerobic capacity, maximal aerobic power (MAP or power output when VO2max is reached), and endurance capability.

One key to effective interval training is planning the correct amount of work at the correct intensity. However, no model for determining the ideal duration, frequency, and intervals for this type of training existed.

In response, I designed one that relates the elements of an infinite number of interval training sessions, all of which are of the same level of difficulty. In fact, they are all very difficult, which means after doing any of these workouts, an athlete needs one or two days of easy training to recover before taking on another session.

My interval training model is represented by a graph (See Inteval Training Model). Each of the six curves corresponds to a relative intensity, from 85 to 110 percent of MAP in five-percent increments. The duration of each work interval is represented on the x-axis, and the number of repetitions on the y-axis. Each point on the curves of the graph represents an interval training session. The squares represent sessions in which work intervals are multiples of 30 seconds. The varying colors on the chart indicate the number of sets that should be used based on the number of repetitions chosen. The box in the upper right-hand corner provides the duration of active recovery between work intervals and between sets. It is assumed that recovery occurs at around 50 percent of MAP, a relatively low intensity.

For example, the session represented by point A on the graph consists of four sets of seven to eight repetitions (for a total of 30), each consisting of 1:30 minutes of work at 85 percent of MAP. One minute of active recovery is allowed between repetitions and three minutes between sets. The session represented by point B on the graph consists of one set of four repetitions, each consisting of six minutes of work at 85 percent of MAP, this time with five minutes of active recovery between repetitions. The session represented by point C on the graph consists of two sets of five repetitions (for a total of 10), with each consisting of 1:30 minutes of work intervals at 100 percent of MAP. Three minutes of active recovery is allowed between repetitions and 10 minutes between sets.

Coaches and athletes can also use this model to plan interval training sessions that are not as difficult. A session in which an athlete completes less than the number of repetitions called for by the model has a level of difficulty below the “maximum” level. For example, completing only five work intervals instead of 10 as prescribed by the model corresponds to a 50 percent level of difficulty.

The beauty of the model is that it helps coaches plan sessions and develop training programs for any sport in which anaerobic capacity, MAP, and endurance capability are performance factors. Feedback from coaches and athletes who use the model indicates that it has useful pedagogical and practical applications in organizing sessions and developing long-term training plans. It may also lead coaches to consider unexplored forms of interval training, thus enabling them to develop innovative workouts.

Athletes performing one to three interval training sessions every week based on this model improve their MAP by a margin almost impossible to achieve with a regular training program. I have often seen MAP improvements of more than two watts per hard interval training session. It truly takes the guesswork out of planning interval training.

To use this model, you must first answer some questions about your training goals. For instance, what is the physical quality you want to improve? If it is anaerobic capacity, then target intensity should be 105 or 110 percent of MAP. If you want to train MAP, then the target intensity should be 95 or 100 or 105 percent of MAP. For endurance, target intensity should be 85, 90, or 95 percent of MAP.

Also, do you want to put the emphasis on quantity or quality? If the answer is quantity, choose a session with more than 20 repetitions. If the answer is quality, choose a session with less than 10 repetitions.

Let’s say I want to improve MAP in “quantity” at a 75-percent difficulty level. Therefore I’ll train at 95 percent MAP (100 or 105 would also be okay), with each session consisting of 24 repetitions of one minute. Using three sets at a 100-percent difficulty level, I would do eight repetitions with two minutes of active rest between repetitions and five minutes between sets (see point D on the graph). But instead of doing all 24 repetitions, I’ll do only 75 percent of the 24, or 18 repetitions. That would translate into six reps in each set.

If I have a device that provides feedback on the actual intensity at which I exercise (such as a CompuTrainer), I can set the intensity if I know my MAP, which can be assessed with a progressive maximal test. If I do not have such a device, I have to pace myself as if I’d be doing 24 exhaustive repetitions even though I’m stopping at 18. In the latter case, even if I’m not exactly at the targeted intensity (95 percent MAP), I should be close enough to achieve my goal, in this case increasing MAP.


Exercise physiologists used to believe that it was not possible to improve performance through training the respiratory muscles. But now, a technique to strength train respiratory muscles (the diaphragm and intercostals) has been developed, and it shows great promise.

The principle is that by forcing the respiratory muscles to overcome mechanical resistance, they can be trained to work at a higher stamina. There are already products on the market for this—I have used POWERbreathe and PowerLung. The apparatus resembles a pipe with a small valve, which is placed in the mouth. While inhaling (inspiring), the athlete must create enough negative pressure to overcome a threshold load. About 30 repetitions are recommended, either all at once or in series of five to 10 breaths with a few seconds of rest in between. Obviously, the difficulty depends on the choice of resistance, which can be modified on most units.

The manufacturers claim that positive performance results appear after about six weeks of training. However, in general, two or three sessions are enough for the athlete to find intense aerobic exercise less constraining.

In one valuable study, 14 elite female rowers participated in a series of tests before and after an 11-week daily training program for the inspiratory muscles. Seven of the participants performed 30 repetitions each day against a resistance that corresponded to 50 percent of their maximum inspiratory pressure. During this time, the other seven participants performed 60 repetitions against a resistance too weak to significantly affect the inspiratory muscles (only 15 percent of their maximum inspiratory pressure). At the end of the 11 weeks, the two groups were tested on an indoor rowing machine: one all-out six-minute test and one simulated 5,000-meter race.

It was found that the experimental group improved its performance in the 5,000-meter race by an average of 36 seconds (a decrease of 3.1 percent), while the control group improved only by 11 seconds (0.9 percent). Analysis of the results delivered other interesting data, in particular, less fatigue of the inspiratory muscles at the end of the all-out test in the experimental group. (See “Training the Lungs”.)

A thorough review of all available research recently done by Alison McConnell, PhD, and Lee Romer, PhD, of Brunel University (Middlesex, England) backed up the validity of this study. After a critical analysis of all the available data, they concluded that this training technique was effective, especially in tests lasting between six and 60 minutes. Some data suggests this type of training also reduces the time needed to recover between sprints, which is good news for athletes and coaches in many sports.

One question remains: Should the expiratory muscles be trained as well as the inspiratory muscles? Obviously, different muscles are used to inhale and exhale. Most of the equipment on the market provides resistance while air enters the lungs, while the expiratory pathway is left alone. The belief is that expiration is passive during exercise of low and average intensity. Therefore, there would be no value in strengthening the expiratory muscles. This is also the opinion of McConnell and Romer.

However, I feel the training of expiratory muscles should be examined further. One product (PowerLung) provides resistance during both inspiration and expiration, and I asked athletes and coaches who regularly use it for their opinions. They all prefer to mix exercises for both expiration and inspiration instead of just the latter.

Gregory Wells, PhD, in the Department of Lung Biology at the Hospital for Sick Children in Toronto, is presently doing studies with elite swimmers and cyclists. So far, his studies show that the work performed by expiratory muscles increases proportionally to exercise intensity and can become very intense in certain circumstances. In a series of papers (submitted for publication), he concludes that elite athletes should train all respiratory muscles, both agonists and antagonists, just as they would for any other muscle groups.

Why is this training successful? It is quite possible that the ergogenic effect of respiratory muscle strength training can be explained through:

    1) decreased respiratory muscle fatigue,

    2) increased blood flow to the active muscles due to a lowered blood volume needed by the respiratory muscles, and

    3) a perceived decrease in respiratory effort.

Here is a sample respiratory muscle-training protocol if you want to try it yourself: Five days a week, twice a day, do three sets of 10 repetitions, with one minute of inactive rest between sets. Set the inspiratory and the expiratory restriction to a level that will make it difficult, but possible, to complete all three sets, inhaling and exhaling. Do not try for an elevated rhythm, but exert a maximal force at each repetition, so that the valve will be set open.

Some of the advice presented in this article may surprise you, as it contradicts long-held beliefs in endurance training. But by keeping our eyes open to the latest information and taking notice of new research, we can best help athletes improve their performance. Try the training suggestions I have provided, and I believe the results will speak for themselves.

Sidebar: Training the Lungs

A study of 14 elite female rowers showed the positive effects of a training program for respiratory muscles. The rowers were dived into two groups—one that trained heavily with respiratory trainers (the experimental group) and one that trained lightly (the control group). Here are the results:

Variable Experimental group Control group
Strength of inspiratory muscles

Virtual distance traveled in maximal test of six minutes

Time to perform 5,000-meter test

Fatigue index of inspiratory muscles









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