Category Archives: Uncategorized

A Day That Will Never Be Forgotten

L-Jay Health

Boston

This is probably the most depressing blog topics that I have written about in two years. As many of you are aware, two explosives were detonated at the finish line during the Boston Marathon today 04/15/2013. I am not writing this blog to report the news and give you politics or the facts, however I am writing this to express my condolences to those that are no longer with us and those who are severely injured. All of our prayers and thoughts at LJay Health goes out to families of the victims, the Boston community, running family and the nation as a whole.

The Boston Marathon is like the Super Bowl for many runners and everyone works very hard to get there. Unfortunately the glory and victory was taken away from the athletes who ran the marathon today. Who would have ever thought that someone would intentionally plant explosive devices…

View original post 246 more words

Advertisements

Should you Take Carbohydrates during a Race?

Time Trial
Time Trial (Photo credit: davharuk)

A new review study shows that taking carbohydrates during shorter races is useless.

We have all been told that taking carbohydrates during an endurance race will boost our performance. Numerous scientific studies have indeed shown this effect but unfortunately the set-up of the experiments did not always correspond to what most of us do.

Many researchers asked elite athletes to exercise at a fixed intensity for as long as possible. They then compared how long it took the athletes to get exhausted with and without taking carbohydrates. These tests are called time-to-exhaustion tests. The problem is that they do not mimic a real event; in real life you typically try to cover a fixed distance as quickly as possible. A time trial would therefore be a better test.

Moreover, the athletes usually performed their test after an overnight fast. Scientifically this makes sense, because it is easier to compare two fasted individuals than two fed ones, as not everybody digests and absorbs food in exactly the same way. However, this is not a realistic situation as nobody would race without a pre-race meal.

In the last issue of Nutrition Journal Paolo Colombani and his colleagues reviewed studies that have tried to mimic real-time events by studying recreational athletes (as most of us are) performing time trials 4 to 2 hours after a meal. They concluded that taking carbohydrates does not lead to significant improvements during races shorter than 70 minutes. For longer races, the picture is a bit more complicated, as 10 of the 17 studies showed improvements up to 13%.

You can therefore gain some time by not having carbohydrates during shorter races (I always have to slow down when I am having a drink or a gel). Concerning the longer ones however, you will have to experiment to find out what is best for you.

Your gut micro-organisms are essential for your health

Lactobacillus acidophilus

A large and dynamic bacterial community lives in your gut, and its interactions with your cells are essential for your health. In exchange for food, it influences your metabolism, promotes the growth of your gut cells and helps to protect against infections. However, this microbiota is a delicate ecosystem and if it is altered, it can affect your health.

Metabolic functions

Colonic micro-organisms metabolize non-digestible carbohydrates (e.g. cellulose, pectin, or gums) and transform them into short chain fatty acids, which are then absorbed by the colon and used as a source of energy. This system allows you to get up to 10% more energy from your food. However, the short-chain fatty acids are much more than just additional energy. They promote the growth of your gut cells, stimulate the absorption of minerals and water and have a beneficial influence on your glucose and fat metabolism.

The microbiota also metabolizes proteins to produce short chain fatty acids, but during this process potentially toxic substances such as ammonia and amines are formed as by-products.

It also provides you with vitamins, such as vitamin K and B12.

Immunity and infections

The surface of your guts is the main interface between your immunity and the external world, and the interactions between you and your colonic micro-organisms shape and develop your immune system. Our modern lifestyle, with its sterile, processed food and overconsumption of antibiotics, damages the microbiota and disrupts these interactions. As your immune system does not have the necessary bacterial contacts anymore, it becomes dumb and badly adapted to do its work correctly, which puts you at a higher risk of allergies and immune diseases.

Bacteria compete for food and for attachment sites on intestinal cells. A well-balanced microbiota will reduce the chances of infectious bacteria to find food, attach and multiply in your gut. It can also produce substances which can kill or neutralise pathogens.

Intestinal micro-organisms and chronic disease

An unhealthy microbiota is called dysbiosis. This can be due to a change in the relative amounts of the bacteria, a reduced diversity or a decrease in their activity. Scientists think that a dysbiosis puts you at a higher risk of diseases such as colon cancer, inflammatory bowel disease, obesity, metabolic syndrome or diabetes, as it is typically found in patients suffering from these conditions.

Causes of dysbiosis

Antibiotics, stress and dietary factors are the best known factors that can disrupt the normal microbiota.

Antibiotics

Antibiotics do not only kill pathogens but also beneficial bacteria, and they have therefore a huge impact on the intestinal micro-organism. Their effect depends on their activity, dosage and length of administration. Recent studies have shown that the effect lasts much longer than previously believed. In one study it was seen up to 16 months.

Obviously, nobody takes antibiotics unless it is necessary, but more research is needed to find how and when to supplement them with live beneficial bacteria.

Stress

Studies have shown that physical and psychological stress can lead to a decline in the Lactobacillus population.

Stress also results in a decreased immunoglobulin A (Ig A) production. Ig A is crucial for our defence against pathogens and stressful events could therefore lead to an overgrowth of pathogens. Scientists also think that noradrenaline, a hormone which is typically secreted during stress, can promote the growth of some pathogens.

During competitions or periods of hard training, athletes suffer more often from infections than the general population. This might be partially due to stress. Recent studies suggest that yoghurt containing Lactobacillus might help to protect them.

Diet

A diet that contains too many processed and sterile products does not provide the microbiota with enough food to keep them healthy. Moreover, consumption of a high protein diet, such as the typical Western diet, increases the production of toxic bacterial metabolites, and eating too many simple sugars slows down the colon transit time. A slower transit time increases the bowels exposure to toxic products.

Probiotics and prebiotics

To make your microbiota stronger and healthier, you can increase the number of beneficial bacteria or stimulate the existing ones.

Probiotics are live micro-organisms that are beneficial for our health when taken in adequate amounts with food, usually as yoghurt. Lactobacillus and bifidobacillus are the most common types used.

As the gastrointestinal track is a harsh environment, many bacteria die before they reach a spot in the colon where they can develop. Scientists are therefore developing capsules to protect them during the journey.

Prebiotics are food ingredients that stimulate the growth and activity of beneficial micro-organisms. Jerusalem artichoke, soybeans and unrefined wheat contain large amounts of them, but you will find them in smaller quantities in thousands of plant-based foods. A healthy diet should provide you with enough prebiotics to keep your microbiota happy.

Probiotics and prebiotics could become important forms of treatment, but we need further research to know exactly which doses and combinations to take. In the meanwhile, it is good idea to prefer whole food over refined and processed products.

Disclaimer: This article is for general information only, and cannot be used to guide diagnosis or treatment. If you have any questions or concerns, you should talk to a qualified health provider.

References

K Brown, D DeCoffe, E Molcan et al. Diet-induced dysbiosis of the intestinal microbiota and the effects on immunity and disease. Nutrients 2012; 4(8):1095-1119.

F Guarner and J-R Malagelada. Gut flora in health and disease. Lancet 2003; 361: 512-519.

J A Hawrelak and S P Myers. The causes of intestinal dysbiosis: a review. Altern Med Rev 2004; 9(2): 180-197.

Y K Nakamura and S T Omaye. Metabolic diseases and pro-and prebiotics: mechanistic insights. Nutr Metab (Lond) 2012; 9: 60.

S Resta. Effects of probiotics and commensals on intestinal epithelial physiology: implications for nutrient handling. The Journal of Physiology 2009; 587:4168-4174.

K A Tappenden and A S Deutsch. The physiological relevance of the intestinal microbiota – contributions to human health. J Am Coll Nutr 2007; 26(6):6795-6835.

What happens to my bowels when I’m running?

Stomach colon rectum diagram.
Stomach colon rectum diagram. (Photo credit: Wikipedia)

20 to 50% of athletes complain of gastrointestinal problems while running, especially during hard training sessions and races. Women, novices and younger athletes are most affected.

It is not completely clear what is happening, but it is likely that during intense exercise your digestion gets hampered, because most of the blood is diverted from your bowels to your working muscles. During running, bouncing and compression of the gut can aggravate the situation.

If that is true, the best thing that you can do is to reduce your bowels’ workload:

  • Eat your last meal at least 2 hours before the race and avoid fatty and high-fibre food. Consider having a liquid meal, such as a meal replacement drink, as that is quicker and easier to digest.
  • Keep hydrated during the run, but do not overdo it: drink to your thirst. Sport drinks are much easier to digest than juices or soft drinks.
  • Some people cannot digest milk and dairy products during exercise, even though they can at rest. Experiment with avoiding dairy products for 24 to 48 hours before the race.
  • Caffeine can give you a boost during a race, but sometimes it leads to gastrointestinal symptoms. Try out how it works for you during training sessions.

Do not forget that exercise is good for your bowels: physically active people reduce their risk of bowel cancer by up to 50% and suffer less from gallstones or diverticular disease. Some researchers have even shown that runners are less likely to be constipated than the general population. Even so, it is not because you are a really fit athlete that you are immune from disease: contact your doctor if you have any concerns, if your stool habits change or if you see blood in it.

References

C Riddoch and T Trinick.Gastrointestinal disturbances in marathon runners. Br J Sports Med. 1988; 22(2): 71–74.

 

RW ter Steege and JJ Kolkman. Review article: the pathophysiology and management of gastrointestinal symptoms during physical exercise, and the role of splanchnic blood flow. Aliment Pharmacol Ther  2012; 35(5):516-28.

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.

References:

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

Is drinking beetroot juice helpful for runners and cyclists?

The beetroot, also known as the table beet, ga...
The beetroot, also known as the table beet, garden beet, red beet or informally simply as beet, is one of the many cultivated varieties of beets (Beta vulgaris) and arguably the most commonly encountered variety in North America and Britain. (Photo credit: Wikipedia)

Drinking beetroot juice has become very popular between runners and cyclists. It might indeed be the right thing to do, because it contains dietary nitrate, which can reduce the oxygen cost of exercise. Whenever you want to produce power, you need oxygen, and if you need to go harder you need more oxygen.   If your body can produce the same power with less oxygen, you have the possibility to go faster and longer.

Scientists have therefore wondered if consuming nitrate-rich food, such as beetroot and leafy green vegetables, could help competitors, and in 2009 a study showed indeed that drinking 0.5l of beetroot juice reduced the oxygen cost by 20%. This is phenomenal, and it sparked a real rage.

However, the initial results were obtained in volunteers who ate a nitrate-free diet, and in 2010 the same group demonstrated that people who had a normal Western diet decreased the cost “only” by 5%.

Our normal diet does not contain that many nitrate rich vegetables, and the whole story reminds me of vitamins and minerals: if you have a real deficiency, a boost will help you, but if not, you are much better off with a healthy diet. If this is the case here as well, could we obtain the same effect by changing slightly the kind of vegetables we eat? That would be the safest, cheapest and easiest solution.

To make matters even more complicated, a recent study could not notice any improvement in elite athletes.

Would this mean that as you get fitter and/or exercise more, dietary nitrate becomes less beneficial? Or is the other way around, and would very fit athletes need more to see an effect?

There are many more questions, such as: should we take it during training as well, so that we can work harder and therefore (hopefully) perform better at races? Or is it better to train without it to make our bodies used to work hard without help, and only take it during the last week before a race?

The most important question is probably this: could it reduce the benefits we get from exercise in the long-term?

As long as these questions are not answered, I will not spend my money on beetroot juice, but I am going to eat more nitrate-containing vegetables all year round…

Does anybody have experience with this?

If you want more details about the effects of beetroot juice, you can read my article in Suite 101.

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.

References

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.

                       

 

References:

A. Aizer, J.M. Gaziano, N.R. Cook et al. Relation of vigorous exercise to risk of atrial fibrillation. Am J Cardiol 2009(1);103(11): 1572-1577.

B. Benito, G. Gay-Jordi, A. Serrano-Mollar et al. Cardiac arrhythmogenic remodeling in a rat model of long-term intensive exercise training. Circulation 2011; 123:13-22.

 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

J. E. Trivax, B. A. Franklin, J. A. Goldstein et al. Acute cardiac effects of marathon running. J Appl Physiol 2010; 108 (5): 1148-1153.

 

How your body keeps cool when you are running

As runners, we are always looking for a challenge. In the heat however, our performances are markedly reduced. If we want to know what we can do about this, we first have to understand what is happening.

Our bodies are divided into an inner core (brain, vital organs such as heart and liver) and an external shell (skin and underlying structures).  The temperature of the core is regulated within narrow limits while that of the shell depends on the environment and on our need to lose or conserve warmth. The thickness of the shell can therefore vary from one centimetre in warm conditions to several centimetres in the cold.

The amount of heat your body generates is roughly proportional to your body mass and size. Women produce slightly less heat than men, probably because their bodies contain a higher proportion of fat.

The core loses heat by conduction (transfer between tissues that are in contact with each other) and convection (transfer of heat into air or liquids, in this case blood which carries it away to the shell).

Most of the heat exchanges between the body and the environment happen at the skin surface. The skin can dissipate heat into the air by convection, especially if the air is cooler than the skin and if there is wind, but sweating is more efficient. To cool you down, sweat has to evaporate. If it drips off from your body, it is useless.

Exercising in the heat

When you exercise, your muscles generate heat. An increased temperature in your muscles allows them to produce more power (that’s why you warm up!), but your core needs to stay cooler than 40C. Moreover, exercise and thermoregulation impose competing demands on your body. Your muscles need a large increase in blood to perform well, but to cool your core down you need to direct blood to your skin.

As the blood flow through the skin increases, large superficial vessels dilate and blood pools in them. This reduces the blood available to fill your heart chambers. The amount your heart pumps around at each beat therefore decreases, and to maintain the same intensity of exercise your heartbeat has to increase. Moreover, if the fluid lost through sweat is not replaced, your plasma volume will decrease, making the situation even more difficult. To help out, your body reduces the blood flow through your bowels and kidneys. Nevertheless, if you continue to generate more heat than you can dissipate, your core temperature will go up.

As the brain realises that the core temperature is rising, it will slow you down by preventing some muscle fibres to contract and making you feel tired. Fatigue is therefore triggered by the rate of core temperature increase, and not by its absolute value.

This is a safety brake to keep your core temperature below 40C. It is clearly not an “all or nothing” mechanism, but a gradual phenomenon. If it does not work and your core temperature continues to increase, you will suffer a heatstroke.

 Acclimatisation

To be able to go harder and for longer in warm conditions, you need to become better at dissipating heat.

A full acclimatisation will take up to 14 days, but after a few days of training in warm conditions your plasma volume will have expanded, your heart rate reduced, and your blood flow more efficiently redirected to your skin and working muscles. Your sweat rate will increase, and sweat production will start earlier and become more important on your limbs than on your torso. Your sweat becomes dilute, allowing you to save salt.

Your core temperature at rest will have decreased by 0.2 0r 0.3C, which means that it will now take longer to reach 40C.

You can only acclimatise correctly by exercising in the heat: just resting is not enough. You will not be able to train hard during that period and this can be a problem, as you might lose fitness.

Fitness

As you can see, physically fit people have already many of the necessary adaptations, and training in the heat will further enhance them. You will therefore have an advantage over your sedentary counterparts, and you will also acclimatise quicker than them.

However, as you are fitter you are able to exercise harder and therefore generate more heat. Even though fitter people are better at dissipating heat, you might produce more than you can dissipate. In shorter races (e.g.: 10 Km), faster runners are therefore more at risk of heatstroke than slower ones. On the other hand, if a group of individuals are working out at a set intensity or pace (e.g. team sport or work activities), the aerobically unfit ones will suffer most.

What you can do

Scientists have shown that dehydration makes it more difficult for your body to keep the core temperature down, but drinking more than you need is useless and dangerous as it puts you at a higher risk of hyponatremia (too little salt in your plasma). Make sure that you are well hydrated when you start and simply drink to your thirst.

Other risk factors for heatstroke include sleep deprivation, recent infections, alcohol use, some drugs and a lack of physical fitness.

Do not forget to sponge yourself on a regular basis when exercising. Sponging your limbs will make the dilated veins contract and therefore reduce blood pooling.

Interval training will be harder than continuous work, as your heat dissipating mechanisms take some time to respond while the sudden bouts of intense exercise produce a large amount of heat. In non-acclimatised and untrained people the heat dissipating will start even slower.

What you cannot change

The heat your body produces depends on its size. Smaller people will thus generate less and, as they have relatively more skin surface, are better at dissipating it.

Some people are more vulnerable to heat illness than others.

Disclaimer: This article is for information only, and cannot be used as a guide for treatment or diagnosis. If you have any questions or concerns, talk to your health care provider.

References

T Kuwahara, Y Inoue, M Abe et al. Effects of menstrual cycle and physical training on heat loss responses during dynamic exercise at moderate intensity in a temperate environment. AJP-Regu Physiol 2005 (288); 5: R1347-R1353

L Nybo. Hyperthermia and fatigue. Journal of Applied Physiology 2008 (104); 3:871-878

R  Mora-Rodriguez. Influence of aerobic fitness on thermoregulation during exercise in the heat. Exercise & Sport Sciences Reviews 2012(40); 2:79-87.