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Exercise and mortality

5797534694_a36e9d8b0dExercising helps you to live longer, whatever the amount you are doing. If you exercise a little, your risk of an early death drops and if you exercise a lot, it drops even more. This is the conclusion of a study published on April 6th in the JAMA.

If you plot “benefits” against “dose” on a graph, most biological systems will show an inverted “U”. Take food for example: if you eat too little, you might die, but if you eat too much, you might also die. If you take a medicine, you have to take the right amount, as taking not enough will have no effect and taking too much is toxic.

Is the same true for exercise? Everybody agrees that you need a minimum of exercise to stay healthy, but some people believe that too much is bad for you. The recent cases of sudden deaths during competitions and the findings of heart rhythm disturbances in older endurance athletes have fuelled the debate.

To answer this question, Hannah Arem and her colleagues have looked at the mortality rates and physical activity levels of 661 137 men and women over 14.2 years.

Sure enough, they showed that having the recommended amount of exercise (a minimum of 150 min of moderate intensity, or 75 min of vigorous intensity endurance exercise per week) resulted in a 30% lower mortality risk compared to not exercising at all. However, any exercise is much better than none, as people who did less than the recommended amount already reduced their mortality risk by about 20%.

Working out more is even better, and exercising 2 to 3 times the recommended amount reduces your risk by 37%, while doing 3 to 5 times more leads to a 39% reduction.

The researchers noticed that those who exercise 10 times or more the recommended amount did not reduce their risk any further, but they could not observe any evidence of harm either.

Can I believe this?

This is very large study, which makes it trustworthy. Moreover, the results are the same for both genders and all BMI ranges.

On the other hand, it is based on questionnaires, and participants can easily over- or underestimate what they are doing or change their habits. However, most population studies about exercise and mortality suffer from these same limitations.

If Hannah Arem is right, concerning exercise, there cannot be too much of a good thing. Even though I have never met anybody running marathons or participating in triathlons for health reasons only, it is good to know we are not harming our bodies.

Keep going, but make sure that you avoid overtraining and injuries!


Arem H, Moore SC, Patel A et al. Leisure time physical activity and mortality: a detailed pooled analysis of the dose-response relationship. JAMA Intern Med 2015; DOI:10.1001/jamainternmed.2015.0533. (Abstract)


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Do you need to exercise if you are healthy?

14022436150_97d48f6579Exercise improves your health, even if you are fit.

What is the importance of exercise if you are young, fit and healthy? Researchers in Finland have tried to answer this question by studying male identical twins. As these brothers are identical at the gene sequence level, any difference should be due to lifestyle factors.

They recruited 10 healthy male identical twins between 32 and 36 years old, of which only one brother had been exercising regularly for the last three years. They then measured their body weight and fat percentages, assessed their glucose levels and insulin sensitivity, and calculated the volume of their brains’ grey matter using magnetic resonance imaging.

The active twins had a higher VO2max and less visceral fat than their sedentary brothers, even though their body weight was not that different. Their glucose levels were lower and their insulin sensitivity* was higher. They also had a higher volume of grey matter in those areas associated with motor control.

The researchers concluded that even among healthy young adults exercise makes a difference. This is important, as lower fitness levels, more visceral fat and poor glucose metabolism are associated with chronic diseases later in life. Obviously, the negative effects of being sedentary begin early!

You might wonder if you have taken up exercise because you have a more favourable genetic profile than sedentary people. If so, you would be healthier whatever you do. This study suggests that this is not the case and that exercise makes a real difference, since identical twins should have the same genetic profile. This does not mean that genes do not matter. They are very important indeed, but you can influence them by your lifestyle.

This is only a small study. It would be great to confirm it with larger ones, but it must be very difficult to find a large group of identical twins of the same sex and age group with different exercise habits.

* Insulin sensitivity = how sensitive the body is to insulin stimulation. Low sensitivity is associated with higher risk of diabetes type 2.


Rottensteiner M, Leskinen T, Niskanen E et al. Physical acivity, fitness, glucose homeostasis, and brain morphology in twins. Med Sci Sports Exerc. 2015; 47(3): 509-518.


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A happy brain makes you run better

Fatigue during endurance exercise is a weird and complex phenomenon, and scientists are still discussing what influences it. Samuele Marcora’s group has just published an article in Frontiers in Human Neuroscience reporting two experiments studying the effect of visual cues related to happiness and motivation. They showed that such cues can make your unconscious brain think you are working out less hard than you actually are, and that therefore you will keep going for longer.medium_1734834072

Samuele Marcora’s theory about fatigue states that the moment you stop exercising is determined by perceived effort (how hard you think you are working) and potential motivation (the maximal effort you are happy to deliver). This means that you will stop when you are judging that the effort required has become larger than the effort you want to make. This theory is called the psychobiological model of endurance performance. To delay fatigue you could therefore do two things: make the effort seem less important, or increase your motivation.

Our unconscious brain takes in much more information than we realise, especially visually. Only a tiny amount of this information makes it to our conscious attention, but we process all the information unconsciously and it therefore influences our behaviour. To study the impact of the unconscious brain on perceived effort, the researchers therefore set up a study during which they could give participants subliminal visual cues.

In their first experiment 13 participants cycled for as long as they could (i.e. to exhaustion) while looking at a computer screen. They were shown happy or sad faces on a regular basis during the effort, but the images came and went so quickly (in 16 msec) that they did not realise they were seeing them. Every participant performed the experiment twice: once with happy and once with sad faces.

In the second experiment, a well trained competitive endurance athlete cycled 12 times to exhaustion while looking at a screen showing words extremely quickly. The words were encouraging (action, go, lively, energy) during 6 workouts and discouraging (stop, toil, sleep tired) during the other workouts.

In both experiments, the participants cycled significantly longer when exposed to happy faces or encouraging words, and rated the effort as less strenuous. Their mood was not different however, proving that the information had not reached their conscious attention.

Samuele Marcora and his team concluded that these experiments confirm their theory. They also think they provide evidence against the central governor theory of Tim Noakes.

The central governor theory states that your pace, and therefore your fatigue, is determined by your unconscious brain which has to make sure that you get safely over the finish line. According to this theory your pace will thus be determined by “calculations” of your brain based on signals from your body, (e.g. working muscles, glycogen reserves), the environment (temperature, altitude…), but also on messages from your central nervous system, such as motivation, encouragement, knowledge about the course, etc…If you brain is not sure that you will get there safely, it will slow you down –or even stop you- by making you feel tired and reducing the number of muscle fibres you can use.

I am not so sure that the experiments contradict the central governor theory. Is it not likely that subliminal cues would also influence how your brain determines what you can do? Please let us know what you think!

Whatever you think about these theories, it is a good idea to surround yourself by positive images and words, and to smile to every runner you meet.

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What should we eat?

If you want to create an animated discussion, start talking about what you should eat (or not) to protect yourself from cancer, cardiovascular disease, diabetes etc… Humans have been wondering which foods to eat since ancient times, but we still have more questions than answers!

© Skdesign | Dreamstime Stock Photos
© Skdesign | Dreamstime Stock Photos

Several large studies have shown that we should avoid excess calories, eat plenty of fruit and vegetables, reduce the amount of refined sugars and stay away from processed food, but everything else is still open for discussion. Why is this so?

Nutritional science is based on epidemiological studies, from which researchers try to determine what the effects of different foods or diets are. They can then perform interventional studies, whereby they ask half of the study participants to have more of a specific food or change their diet, and compare the effects with the other half of the participants (= the control group). In the Predimed Study for example, researchers examined the importance of olive oil and nuts in this way. Without good epidemiological studies however, researchers do not know what to look for.

I have just stumbled upon an article by Farin Kamangar and Parisa Karimi explaining how difficult it is to conduct such epidemiological studies, and here comes their list of possible errors and problems.

Measurement errors

The first problem Kamangar and Karimi mention is the way they obtain information about what you are eating. Traditionally this is done via questionnaires and interviews assessing your dietary habits over one year. It is clear that it is difficult to recall accurately what you have eaten over a year. Moreover, you might have changed your diet, and what you have eaten last year is therefore not necessarily reflecting your lifelong habits.

Some researchers ask you to write down what you have eaten for the last 24 hours. Even though you will be able to recall this accurately, it is not sure that you are having something similar each day.

Most questionnaires are really long (80 to 200 items), which can discourage even the most motivated participant.

These problems will hopefully be minimised in the future, as researchers are starting to use online self-assessment questionnaires.


Epidemiologists try to find an association between risk factors and diseases. Confounders are factors that independently affect the risk of developing the disease, and therefore falsify the results of the study.

A classical example is the association between coffee drinking and lung cancer. Previous studies suggested this, but as coffee drinkers were more likely to be cigarette smokers, the risk of developing lung cancer had nothing to do with coffee. Another example is the association between lying in bed and dying. As most people die in bed, you would conclude that beds are the most dangerous places on earth.

As confounders are usually unknown, it is easy to see how they can falsify the results. Researchers try to avoid them by comparing populations that are very similar except for the factor they want to study. With this in mind, Beth Taylor and her colleagues compared marathon runners with their non-competitive spouses to examine the effect of strenuous exercise on your arteries.

Variability of food products

Foods are typically grown and/or prepared in different ways in different parts of the world, which might affect their nutritional value. Kamangar and Karimi cite the example of brown rice, which is a healthier choice than white rice since it contains more fibre, but in the United States it has a higher arsenic concentration than white rice. Another example is the difference between grass-fed and grain-fed beef: grass feeding typically results in leaner meat.

The correct control group

As already mentioned above, finding a good control group is a challenge: it has to resemble the study group except for the factor the researchers want to study.

In nutritional science this is very difficult, as the study participants avoiding a specific food usually replace it by something else. For example, imagine what the study results would be if participants abstaining from a specific, probably unhealthy food use to replace it by something containing plenty of simple sugars.


Foods contain chemical substances that influence each other’s absorption and actions, and different foods can contain the same substance in different amounts and availabilities. These interactions are very complex, and researchers need large study groups to try to avoid them.

© John Valenti | Dreamstime Stock Photos
© John Valenti | Dreamstime Stock Photos

Multiple testing

Epidemiological studies about nutrition are typically large and expensive. Researchers want to use all the data and they therefore test several hypotheses at once. However, there is always a chance to come to a false conclusion by coincidence. Statistically, the probability to obtain such a false positive result is 20%, which means that if you test 20 hypotheses, you will get at least one false positive one.

And therefore…

Nutritional science is fascinating, but difficult. Keep informed, stay critical and be prepared to change your mind.


F Kamangar and P Karimi. The state of nutritional epidemiology: why we are still unsure of what we should eat? Arch Iran Med. 2013; 16(8):483-486.

BA Taylor, AL Zaleski, JA Capizzi et al. Influence of chronic exercise on carotid atherosclerosis in marathon runners. BMJ Open. 2014; 4(2): e004498. doi: 10.1136/bmjopen-2013-004498.

ME Van Elswijck and SH McNeill. Impact of grass/forage feeding versus grain finishing on beef nutrients and sensory quality: the US experience. Meat Sci. 2014; 96(1):535-40.


Active kids reduce their risk of cardiovascular disease later in life

We know that atherosclerosis begins in childhood, but are children with an unhealthy lifestyle invariably going to suffer from atherosclerosis as they get older? Nobody is sure…

© Alexk | Dreamstime Stock Photos
© Alexk | Dreamstime Stock Photos

A Finnish group of researchers has therefore started to follow-up risk factors in young people. The first survey was done in 1980, when they examined 3596 youngsters between 3 and 18 year old. The same group was then re-examined in 1983, 1986, 2001 and 2007. The researchers measured the usual risk factors such BMI, blood lipids and blood pressure, and asked about their diet and exercise habits.

In 2001 and 2007, the researchers also determined the wall thickness and elasticity of the youngsters’ arteries. Wall thickness and elasticity (or stiffness) are two different signs of vascular aging, and both of them are probably very early stages of the disease. As yet, we do not know which one is more important.

By comparing the evolution of arterial wall thickness and elasticity with risk factors, we can determine if a child’s lifestyle influences its risk of cardiovascular disease later in life.


In their latest article (April 2014) the Finnish group published their findings concerning the association of exercise in childhood or adolescence and the elasticity of the carotid arteries 21 years later. The carotid arteries are situated in the front of your neck and supply your head and neck with oxygenated blood. They are rather important, as your risk of stroke increases if they narrow due to atherosclerosis!

They noticed that exercise in children and adolescents was associated with an increased arterial elasticity in 30 to 34 year old adults. This was independent of other factors such as BMI, blood lipids or insulin levels. They concluded that it pays off to be an active kid.

Vigorous exercise

This confirms a similar study published in 2010 by Roel van de Laar and his colleagues. They followed 600 boys and girls during 24 years, and noticed that adolescent and young adults involved in vigorous physical exercise had more elastic arteries at the age of 36 than those who performed only easy or moderate workouts.

They also noticed that those who kept exercising vigorously in adulthood had a much better elasticity than those who slowed down. The difference in elasticity went hand in hand with other risk factors such as cholesterol levels, resting heart rate, cardio respiratory fitness…

They concluded that we should keep exercising vigorously as we get older to keep our arteries healthy.

Working Up Sweat (ID: 74747)
© Vlad | Dreamstime Stock Photos

Arterial thickness

The Finnish group also compared the classical risk factors (exercise, diet, BMI, cholesterol, blood pressure blood glucose levels…) with the thickness of the arterial wall. They noticed that childhood risk factors became non-significant compared to adult ones, except for physical activity and fruit consumption.

This means that if somebody has unfavourable cholesterol levels or is obese as a child, but corrects this as an adult, the arterial wall thickness is not worse than that of somebody who was not obese or did not have bad cholesterol levels as a child.

For fruit consumption and physical exercise however, this seems not to be true. Eating a healthy diet and exercising regularly as a child is thus important for your arteries.

What does this mean for me?

If you are lucky enough to have exercised and eaten a healthy diet as a child, your arteries are likely to be healthy. This is not a reason to stop taking care of yourself, as Roel van de Laar’s study shows that we should continue exercising vigorously.

Vigorous exercise is of course different for each of us. What feels like running hard for me is maybe only a jog for you. Only you can know what vigorous exercise is for you. Don’t forget either that nobody exercises vigorously every day. If you are in doubt, you should contact a health or fitness professional.

Even though exercising as an adult might not totally reverse the lack of exercise as a youngster, it will help you to keep all other risk factors under control. Moreover, your health depends on much more than the thickness or elasticity of your arterial walls. Exercise will reduce your risk of many diseases, such as diabetes, Alzheimer and some cancers. It is therefore never too late to start!

The Finnish study is ongoing, and that is a good thing as there are plenty of questions left. For example: what happens to those of us who are active as a child and adolescent,  abandon sport to raise a family, and start training again when life becomes less busy?

Disclaimer: this article is for general information only, and does not replace medical advice. It cannot be used to diagnose or guide treatment. If you have any concerns or questions, you should talk to a qualified health provider.


Juonala M, Viikaril J S A, Kahonen M et al. Life-time risk factors and progression of carotid atherosclerosis in young adults: the cardiovascular risk in young Finns study. Eur Heart J 2010; 31(14): 1745-1751.

Palve KS, Pahkala K, Magnussen CG et al. Association of physical activity in childhood and early adulthood with carotid artery elasticity 21 years later: the cardiovascular risk in young Finns study. J Am. Heart Assoc. 2014; 3(2): e000594.  doi: 10.1161/JAHA.113.000594.

Van de Laar RJ, Ferreira I, van Mechelen W et al. Lifetime vigorous but not light-to-moderate habitual physical activity impacts favorably on carotid stiffness in young adults: the Amsterdam growth and health longitudinal study. Hypertension 2010; 55(1): 33-39.

What do you need to become a top athlete: special genes or dedicated training?

P SPORT (Photo credit: Wikipedia)

Athletic success is the result of a combination of genes and training.

Your muscles and metabolism are very adaptive, and they respond to training by becoming stronger and better. They can only improve because training stimulates your body to produce enzymes and other proteins which are then used to make your metabolism more effective, and your muscles, bones and tendons stronger.

Even genes that code for the same protein can be slightly different between people. This is called polymorphism. They might therefore produce a slightly different protein, which does not matter in daily life but could make the difference between winning and losing during a race.

As your genes code for every protein your body makes, most scientists assume that the genetic profile you have inherited is at least partially responsible for the differences in athletic capabilities between people.

Sports Frau

On the other hand, we all know that you have to train hard and have the right lifestyle to improve, and therefore training and healthy living are likely to influence the activity of your genes. The question therefore is: what is more important: your training or your genetic profile as you have inherited it?

Studies on families and twins

Researchers have compared strength and muscle power between family members and twins, but their results are controversial. Genetic influences could be found in all studies, but their importance was very different from one study to another. Moreover, some studies suggest that genetic influences become less important as you get older.

VO2 max, or the maximal amount of oxygen that you can burn to produce energy, is a popular measure of your maximal work rate. It varies considerably between individuals, and studies have shown that high values run in families. You can increase it by training, but the extent to which you can do so is also inherited, probably mainly from your mother’s side.


If you want to perform at the highest level, you cannot afford to lose time due to injuries. Studies have shown that Achilles, rotator cuff and anterior cruciate ligament injuries run in families, and two genes have been linked to a higher risk of getting injured.

The perfect genetic profile

Athletic performance is associated with many characteristics, such as muscle strength, size of your heart, tendon elasticity etc…, and therefore with a large number of genes. As yet, 23 polymorphisms have been associated with endurance performance. According to studies, the chances to have the perfect profile are very low, less than 1 in 20 million. You have to add to this the odds of having the perfect psychological profile. Psychology is very important in sports, but as yet we know very little about its genetics.

It is unlikely that somebody will ever inherit the perfect or even a near perfect profile, but the chance that exceptional talents will be born increases as the population grows. It is therefore likely that records will continue to be broken.

Do we really need it?

In 2009, Spanish researchers looked at the 7 most important genes known to be associated with fitness in 46 world-class endurance athletes and compared it with the same genes in non-athletic controls and in the general population. All the participants were Spanish.

On average the genetic profile of the top athletes was only slightly better than that of the other groups. None of the elites had the perfect genetic profile and only 3 of them had a favourable polymorphism for 6 of the 7 genes. A top-3 finisher of The Tour de France had a profile comparable with the average Spanish population. This is remarkable as The Tour de France is one of the hardest endurance events regularly undertaken by competitors. They concluded that anybody with an average profile could make it to the top.

The importance of the right training in the right environment at the right time

In his book “Bounce”, Matthew Syed argues that athletic success is only the result of many hours (at least 10.000) of deliberate practise and training during optimal periods of life and has nothing to do with inheritance. He agrees Erickson who suggests that intense exercise activates dormant genes that we all have.

Unfortunately, this does not correspond to what we experience in daily life: who has never been beaten by a “newbie”? We can all name athletes who have progressed to the top in a minimal amount of time. Some people improve much quicker than the average, while others can handle a larger training volume, or have almost spontaneously a better technique.

Nobody will ever contradict that many hours of hard training are a must, but ignoring all the good science about inherited genes is probably a mistake, just as ignoring the importance of training would be one. Nevertheless, Matthew Syed has thought-provoking arguments and his book is a “must read” for everybody who is interested in this subject.

It is likely that our genetic profile, training and the interactions contribute to our performances. We need more research, as we probably have not found all the genes yet. We might not even have discovered the most important ones.

The Post-Exercise Window to Have Your Recovery Drink: myths and facts

Sports Drink for hubby

According to a review article by Alan Aragon and Brad Schoenfeld, you do not need to have your recovery drink within 20 minutes after your workout.


Over the past two decades or so, we have been told repeatedly that we should have our recovery drink within 20 minutes after our workout or race. Taking it two hours or more afterwards was considered much too late, almost useless.

To rehydrate as soon as possible feels indeed right, but to have a lot of carbohydrates and proteins on a still contracted stomach can be a bit over the top.

Alan Aragon and Brad Schoenfeld reviewed all the evidence in the latest issue of Journal of the International Society of Sports Nutrition, and concluded that a healthy diet and the usual eating habits are usually enough for a good recovery.

The theory


During a hard bout of exercise, you use your glycogen stocks and you disrupt muscle fibres, and as your glycogen stocks are getting empty, you start burning some proteins. During your recovery, you have to rebuild your reserves and repair the damage. Normally your body will “overdo” it, which means that your stocks will become slightly lager and the new muscle fibres stronger. Thanks to a correct balance between exercise and recovery you are becoming a better athlete indeed.

Immediately after a workout that has depleted your glycogen reserves, your muscles are craving for glucose, and they can take up much more than otherwise. During the first hour you are therefore able to rebuild your reserves much quicker than at any time afterwards. If you have your carbohydrates two hours later, the rate of glycogen rebuilding will be 50% slower.

Taking in glucose leads to an increase in blood insulin levels. Insulin is a hormone necessary for the uptake of glucose by cells. It also decreases muscle protein breakdown, and studies have shown that muscle protein breakdown can rapidly increase after exercise. Higher insulin levels are thus beneficial if you want to build up your muscles.


 Several studies have shown that adding a small amount of proteins makes the process even faster. It would also give you the opportunity to start rebuilding damaged muscles fibres. Proteins are made of amino acids and one of them, leucine, acts as a signal to start the re-synthesis process.

In practice


 You will have rebuilt your glycogen stocks within 24 hours, even if you have not been able to have a recovery drink within the first hour. Your new stocks will still be slightly larger than the previous ones; it will only have taken much longer to build them up. The advantages of replenishing them very quickly are not clear. It is certainly important for athletes participating in a multi-day event and for those who want to repeat the same exercise within about 8 hours, but it does not matter if you are taking at least 24 hours rest.


 The results of studies about the value of amino acids supplements after exercise are controversial. They are very difficult to interpret properly, because they all use different set-ups and products.

In theory, a recovery drink containing amino acids and carbohydrates (leading to high insulin levels) would promote protein synthesis and decrease its breakdown.

On the other hand, after a normally healthy mixed meal it takes insulin at least 3 to 6 hours to drop back to fasting levels, and the amino acids blood levels remain increased for about three hours. It is therefore likely that after your workout, you will still have everything you need in your blood to start your recovery. Having your next meal one or two hours later will be fine.

However, if you train more than three to six hours after your last meal, you will benefit from a carbohydrate-protein recovery drink.

And finally…

Further research is necessary to fully understand the interplay of pre- and post exercise meals.

Moreover, most studies have been carried out on untrained volunteers, and the needs of well-trained athletes might be different. Some studies even suggest that age also influences what you need for an optimal recovery.

What is your experience with recovery drinks?

Lactate: your best friend during a run

Lactate is a source of energy that your body can shuttle around. It is not a waste product, and it does nor make you sore.


Lactate: a valuable souce of energy

When you are running hard, you need a fast source of energy. Lactate is the end product of the glycolytic or anaerobic metabolism, which is a quick pathway to produce energy by breaking down glycogen or glucose without the need for oxygen. However, that is not the end of the story, because lactate can then be shuttled to other muscle fibres, your heart or your brain, and further broken down to produce more energy. Inactive muscles or the liver can even transform it back into glucose or glycogen and store it. Lactate is therefore a valuable molecule that allows you to move energy around.

Breaking down lactate requires oxygen and this is therefore called the oxidative or aerobic metabolism. It delivers much more energy than the glycolytic metabolism, but it is a slow process. That is why the lactate breakdown cannot follow the production when you are running hard. The clearance by other organs might not keep up either, and the concentration in your blood will increase. When that happens, you have reached your lactate threshold.

“Yes, but I thought lactate was created when my muscles do not have enough oxygen?” you ask. It is true that the glycolytic metabolism does not require oxygen, but the amount of oxygen is never so low that the oxidative energy metabolism has to stop. Lactate accumulates because the oxidative metabolism is much slower than the glycolytic, and the clearance cannot follow the production.

This should not change the way you train. Even though the lactate threshold is not exactly what you thought it was, it is still a good idea to do part of your training at that intensity.

Nothing to do with sore muscles

As lactate is not a waste product, you do not have to “flush it out”. It is taken out of the bloodstream and used even if you do not perform an active cooling down, and it is incapable of making you sore. Soreness usually develops in 24 to 48 hours, while lactate levels are back normal within 2 hours.

Scientists think that muscle soreness develops because fibres get injured by vigorous exercise. The injury is worse if you perform eccentric actions, whereby you contract your muscles while they are lengthened, as for example the quadriceps when you go downhill. You can therefore develop muscle soreness without increasing your lactate levels.

This does not mean that an active cooling down is a waste of time. It does indeed help, but it is not clear why. I you know the reason, please tell me.

Lactate and fatigue

During exercise, an increase in lactate levels coincides with fatigue, but it is still not clear if lactate is a cause or a consequence of fatigue.

It is possible that lactate is just the messenger. To stay alive, there has to be a balance between the chemical substances in your body. Rapidly rising lactate levels might be a signal for your unconscious brain that you could disrupt the balance by exercising too hard for too long, and that you should slow down. Your brain will then make you tired and reduce the number of muscle fibres you can recruit. This theory is still controversial, but it would explain why you cannot keep going hard by using the glycolytic system for very long.


G A Brooks. Cell – cell and intracellular lactate shuttles. J Physiol 2009; 587(Pt23): 5591-5600

R S de Oliveira Cruz, R A de Aguiar, T Turnes et al. Intracellular shuttle: the lactate aerobic metabolism. ScientificWorldJournal 2012, 2012: 420984

E Goes. Benefits of lactate during exercise. Suite 101 02/09/2012

A Philp, A L Macdonald and P W Watt.  Lactate – a signal coordinating cell and systemic function. J Exp Biol 2005; 208: 4561-4575

Why do we get tired during a run?

English: Dr. Tim Noakes at the Department of P...
English: Dr. Tim Noakes at the Department of Physical Education at West Point shortly before delivering a lecture on Exercise Induced Hyponatremic Encethalopathy (Photo credit: Wikipedia)

The classical theory to explain why we have to slow down during a hard run is that our leg muscles do not get enough oxygen anymore; therefore lactate builds up and further work becomes impossible. During longer, slower runs, the theory predicts that we run out of ATP (= the molecule that delivers energy), and that our cells become “poisoned” by by-products of our metabolism. Fatigue is thus seen as a “catastrophe” due to failure of our muscles.

Is that true?

As runners, we cannot help being sceptical. How can this be true if, at the end of a race, we manage to speed up when we see the finish? How is it possible that we run so much better if loved ones cheer us on? Why is motivation so important, even though there is no room for it in this theory?

If our leg muscles are too poisoned to work properly, what is happening to our hearts? Runners do not die from a heart attack at the end of a run, unless they have an underlying disease or abnormality.

Moreover, if this theory is correct, how did our prehistoric ancestors have the strength to defend themselves against wild animals after a hard day hunting?

To make matters even worse for the classical theory, scientific studies have shown that muscle cells still contain oxygen at their maximum work rate. In other words: they do not become “anaerobic” as the lactate concentration starts to increase. They have also demonstrated that athletes are not engaging all their muscle fibres at maximal effort, as you would expect according to the classical theory, but only about 30%.

Another theory

To solve all these contradictions, Prof Tim Noakes has come up with a new theory. He starts from the fact that a correct perfusion of our brains and hearts by oxygenated blood is essential for our survival. He thinks that we regulate unconsciously our running speed to make sure that our hearts and brains have enough oxygen. This means that there must be a “governor” who protects us from exercising so hard that we would damage ourselves. Tim Noakes therefore called his theory “the central governor model”.

The central governor model

At the start of the run, the unconscious brain chooses the pace by recruiting an appropriate number of fibres in the working muscles. Its choice is determined by the expected length and difficulty of the run, and by a long list of other factors, including fitness, fatigue, temperature, motivation, presence of spectators or competitors…

At each step it further adapts the pace according to information coming from the conscious brain such as the distance already covered, or the true difficulty of the terrain. It also uses information from the working muscles, such as the rate of glycogen consumption, and from other unconscious sources, e.g. amount of oxygen in the blood, loss of fluid, rise in core temperature, etc…

In that way the brain aims to prevent catastrophic changes in the body. It does so by reducing the amount of muscle fibres we are using and by making us feel tired. According to this model, fatigue is not just a physical event but an opinion of the brain. In other words: it is an emotion, which can be altered by other emotions and by physical factors.
This explains why we have some energy left for the final sprint, or to speed up when we hear friends and family shout our name.

A partnership between mind and matter

Some scientists find it difficult to accept this model, because the exact pathways and mechanisms are not well understood, but most runners find it very appealing. It indeed explains what we feel. It also makes it possible to be happy when we are tired: our brains are keeping us safe.


T D Noakes, A St Claire Gibson, E V Lambert. From catastrophe to complexity: a novel model of integrative central neural regulation of effort and fatigue during exercise in humans: summary and conclusions. Br J Sports Med 2005; 39: 120-124

T D Noakes. Fatigue is a brain-derived emotion that regulates the exercise behaviour to ensure the protection of whole body homeostasis. Front Physiol 2012; 3: 82

R S Richardson, E A Noyszewski, J S Leigh, P D Wagner. Lactate efflux from exercising human skeletal muscle: role of intracellular PO2. J Appl Physiol 1998; 85(2): 627-634

R S Richardson, S C Newcomer, E A Noyszewski. Skeletal muscle intracellular PO2 assessed by myoglobin desaturation: response to graded exercise. J Appl Physiol 2001; 91(6): 2679-2685

A St Clair Gibson, T D Noakes. Evidence for complex system integration and dynamic neural regulation of skeletal muscle recruitment during exercise in humans. Br J Sports Med 2004; 38:797-806

J P Weir, T W Beck, J T Cramer, T J Housh. Is fatigue all in your head? A critical review of the central governor model. Br J Sports Med 2006; 40: 573-586

Can running be bad for you?

We all know that physical activity is essential for our health, and it therefore seems logical that participating in extreme endurance sports such as marathon running is good for you.  Several studies have indeed shown that endurance athletes live longer and healthier than the general population.

As a keen runner, I have always believed this, even though running means much more to me than just a healthy habit.

However, there is now a mounting amount of evidence suggesting that lifelong endurance athletes suffer more from heart rhythm disturbances than the general population. In the largest study we have today, Dr Aizer and colleagues demonstrated that men who exercised hard 5-7 times a week had a 20% increased risk of rhythm disturbances than sedentary healthy people. They also showed that runners were at the highest risk. Could it be that some athletes are doing too much?

We are talking here about a small group of extreme endurance athletes. Most people do not exercise enough to be at risk. The affected athletes are typically in their forties or fifties, and have been involved in competitive endurance sport since their youth. On average they have trained for 36 years. On the other hand, very vigorous exercise could protect you against premature death, as recent studies have shown that Tour de France’s cyclists and cross country skiers live longer and healthier than the general population. This makes the occurrence of rhythm disturbances even more puzzling.

Cardiac magnetic resonance imaging (CMR) is currently the best imaging technique we have to evaluate the heart. It gives us clear images of its anatomy and function in real time, and if we use a contrast product such as gadolinium, we can look at its blood perfusion and diagnose areas of fibrosis. Recently, scientists have used this technique to examine runner’s hearts before and after completing a marathon.

These studies are small (CMR is an expensive examination!) but in general the results indicate that the right heart can become overworked. In some people, this leads to a dilatation of the right ventricle and atrium, which normalises in a week to a month. There was no relation between fitness (as measured by VO2 max), training mileage or marathon experience and right heart dilatation. It is thus likely that some people are more susceptible because of their genetic make-up.

A few years ago, Dr Breuckman and colleagues demonstrated areas of fibrosis in seasoned marathon runners, but they were not sure what the cause was. It was an important finding though, because fibrosis in the right heart muscle makes you prone to heart rhythm disturbances.  

In 2011, Dr Benito and colleagues published a study on rats which ran vigorously for up to 16 weeks. This corresponds to about ten years of daily intense training for humans. They noticed areas of fibrosis in the hearts of the rats who ran, and none in the sedentary ones. They concluded that lifelong intense endurance training can lead to fibrosis. Most scientists now believe that this could be explained by repeated dilatation and recovery of the right heart chambers. Interestingly, the fibrosis disappeared when the rats were allowed to stop running for eight weeks.

It is obvious that we need more research. For example, we do not know if and how we can diagnose the problem at an early stage, or if we can decrease the risk by altering the training regimen.

Exercise has many health benefits, but it is not because you are a very fit athlete that you are immune from heart disease or other health conditions. You still have to look after yourself.




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 F.  Breuckmann, S.Moehlenkamp, K. Nassenstein et al. Myocardial late gadolinium enhancement: prevalence, pattern, and prognostic relevance in marathon runners. Radiology 2009; 251(1): 50-57.

J. Grimsmo, S. Maehlum, P.Moelstad et al. Mortality and cardiovascular morbidity among long-term endurance male cross country skiers follower for 28-30 years. Scand J Med Sci Sports 2011; 21(6): e351-358

J. Karjalainen, U. M. Kujala, J. Kaprio et al. Lone atrial fibrillation in vigorously exercising middle aged man : case control study. BMJ 1998; 316(7147):1784-1785.

S. Moelenkamp, N. Lehmann, F. Breuckmann et al. Running: the risk of coronary events. Eur heart 2008; J 29 (15): 1903-1910.

F. Sanchis-Gomar, G. Olaso-Gonzalez, D. Corella et al. Increased average longevity among « Tour de France » cyclists. Int J Sports Med 2011; 32(8): 644-647

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