A new study suggests that cramps during exercise have nothing to do with electrolytes or dehydration, but are simply due to muscle fatigue.
For decades we have been told that cramps during long runs are due to dehydration and loss of electrolytes. It is tempting to think so indeed, as patients with disturbed electrolytes due to illness suffer from cramps. However, these patients are usually severely ill and have cramps all over their bodies. Runners on the other hand, typically have them in the working muscles and often only later in the race. Moreover, they might be tired but they are not ill!
Scientists now suspect that cramps in runners (or in any athlete) might be something different. Indeed, there is more and more evidence that cramps are due to muscular fatigue, and the latest study by Martin Hoffman and Kristin Stuempfle suggests this as well.
They studied 280 runners during a 161 km ultra-marathon by measuring their body weight before, during and after the race, and they determined their sodium and CK (= a measure of muscular damage) levels by a blood sample after the race. The runners also completed a questionnaire about cramping, “near” cramping (= controllable, not full blown), drinking strategies and the use of electrolyte supplements.
14% of the participants reported cramping, and 28% near cramping. There was no difference in changes in bodyweight or sodium levels between those suffering from cramping or near cramping and the others. Those who cramped or near cramped however, showed higher CK blood concentrations and were more likely to have suffered from them in the past.
The researchers concluded that cramping was associated with muscle damage, which confirms other studies suggesting that it is due to fatigue.
This is important for all of us, because if they are right, there is no need to take electrolyte supplements. It could then be more beneficial to review our training, build up our muscle strength and see if our technique needs improving.
KW Braulick, KC Miller, JM Albrecht et al. Significant and serious dehydration does not affect skeletal muscle cramp threshold frequency. Br J Sports Med. 2013; 47(11): 710-4.
MD Hoffman and KJ Stuempfle. Muscle cramping during a 161 km ultra-marathon: comparison of characteristics of those with and without cramping. Sports Med Open. 2015; 1 (1):8.
MP Schwellnus, EW Denman and TD Noakes. Aetiology of skeletal muscle “cramps” during exercise: a novel hypothesis. J Sports Sci. 1997; 15(3):277-85.
MP Schwellnus. Cause of exercise associated muscle cramps (EAMC) — altered neuromuscular control, dehydration or electrolyte depletion? Br J Sports Med. 2009; 43(6):401-8.
Have you ever wondered which exercise would be best to keep you healthy as you get older? I guess the answer is “the one you like”, but Pedro Angel Latorre-Roman and his colleagues wanted to investigate this further and compared master long distance runners with athletes engaged in gym work and sedentary people.
47 long distance runners and 49 bodybuilders from local clubs volunteered for the study, and were compared to 47 sedentary people. All the participants were male, and between 35 and 60 years old. They were divided in groups according to their age (35-40 year, 40-50 year and 50-60 year old).
The researchers calculated their BMI, measured their body fat percentage, and analysed their quality of life using a questionnaire. The participants performed countermovement jumps and had their hand grip measured to test their strength.
Unsurprisingly, the long distance runners as well as the bodybuilders maintained their strength much better throughout aging than the sedentary people, even though muscle mass was decreased in all the older participants compared to the younger ones. The runners showed healthier BMI values and body fat percentages, and scored better in the quality of life questionnaire than both other groups. However, they lost more muscle mass than the bodybuilders as they grew older.
This study confirms a previous study by Williams, which showed that running is much more effective in keeping your body fat percentage healthy than other sports. Williams compared the BMI and waist circumference of 33,374 runners with the kind and amount of exercise they were doing. Most runners do not only run, but are also engaged in a wide variety of different sports, such as cycling, walking, swimming… He noticed that those who ran more were leaner, even if the total amount of energy spent exercising was the same.
Both studies are off course observational, which means that they can only show an association between two findings. It does not mean that one leads to the other, as there might be a third factor which explains the association. For example, there is an association between lying in bed and dying, as most people die in bed, but this is explained by disease and injury.
It is also possible that lean people are more often tempted to take up running than other people.
The same could be true concerning the results of the quality of life questionnaire: are you happy because you are running, are you running because you are happy or is there another explanation?
A study by Henny Solleveld on soccer players suggests that poor oral health increases the risk of sports injuries and muscle cramps. As soccer players run a lot during a match, these results are probably important for runners as well.
Sports injuries are common, not only between runners but also between soccer players. The risk factors can be intrinsic or extrinsic in nature. The extrinsic factors include interactions between players, and the intrinsic ones comprise health, previous injury, age, fitness, stress, anxiety…In this study, Henny Solleveld and her colleagues show that oral health should also be included in the intrinsic factors.
They questioned 184 premier league and 31 elite junior soccer players about re-injuries, muscular cramps, oral health, age, player position and psychosocial factors (stress and anxiety).
They noticed that poor oral health was associated with cramps and all kinds of injuries, even if they controlled for age, player position, diet or stress and anxiety.
Of course, it is not because there is an association between two factors that one leads to the other. There might be a third factor that leads independently to poor oral health and injuries, or it might just be a coincidence.
However, it is possible, as theoretically there is a mechanism. Poor oral health leads to an increased amount of inflammatory factors in your blood which make your muscles more easily fatigued and increase oxidative stress. Muscular fatigue puts you at a higher risk of injury as you lose good technique and as your coordination deteriorates. It can also lead to cramps.
This study is based on questionnaires and, as we all know, participants can get the answers wrong. Moreover, it is only a small study. It would therefore be good to see it repeated on larger groups. In the meanwhile, it is good idea to see your dentist regularly!
Exercising 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)
Most people still use the terms “aerobic” and “anaerobic” exercise to name intensity levels, referring to the way your body produces the required energy. However, the way you produce energy is one big continuous chain of reactions, and categorizing exercise in this way can lead to misunderstandings.
In an article in March 2015, Kamir Chamari and Johnny Padulo suggest using the terms “explosive efforts”, “high intensity efforts” and “endurance intensity efforts”.
Energy production: a complex chain of reactions
When you exercise, your body transforms glycogen, glucose, fats or some proteins into a specialised molecule called ATP (adenosine triphosphate), which can then be used by your muscle fibres.
There is some ATP available for immediate use to perform very intensive bouts of exercise, e.g. sprinting, which we should call “explosive efforts”. After about 6 sec however, it is gone and your body therefore immediately starts topping it up.
Glycogen or glucose is first broken down in the cytoplasm of the cells into pyruvic acid, producing about 3 molecules of ATP. This might not sound as very much, but the system is quick. It does not need any oxygen, even if oxygen is available, and it is therefore often called “anaerobic”. It is everything you need for short, intense bouts of exercise which Chamari and Padulo suggest calling “high intensity efforts”.
Pyruvic acid is then used by the mitochondria of your cells to produce about 32 molecules of ATP in a complex series of reactions. This part of the energy production chain is very productive but it is rather slow. As it requires oxygen, it is often called “aerobic” and the exercise intensity at which you rely most on it is “endurance intensity exercise”.
The bottle neck between high intensity and endurance intensity levels
As the first part of the chain is fast (up to pyruvic acid, without the need for oxygen) and the second slow, there will be a bottle neck between the two of them. If you go harder, the bottle neck will become bigger, and more of your energy will have to come from the first “anaerobic” part of the chain, even if there is plenty of oxygen available.
Whatever the intensity you are exercising at, you will always be using energy from both parts of the chain. The relative amounts will differ, obviously, but will be determined by the intensity of the effort and not by the presence or absence of oxygen. Labelling a workout as “aerobic” or “anaerobic” is therefore incorrect, and can lead to confusing and misunderstandings.
If you are going hard, pyruvic acid will be accumulating in your cells due to the bottle neck. It changes then into lactic acid and moves out of the cell. As lactic acid can very easily change back into pyruvic acid, which can used to produce a lot of energy, it is eagerly taken up by other tissues. It is therefore not a waste product at all, but a very important molecule.
However, if you produce more lactic acid than your tissues can take up, the amount in your blood will increase. Your brain uses this rise as a signal that you are going a bit too hard and it will slow you down by making your muscles ache.
As you can have this feeling even if you are doing an endurance workout, it is clear that you are getting energy via every part of the chain.
Exercise 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.
A number of physiological parameters, such as VO2max and lactate threshold, describe your ability to run well. Most of them decline as you get older, except for running economy. Running economy is the energy you spend to run at a given speed, in other words: it corresponds to what it costs your metabolism to make the movements.
Studies have shown that older runners are just as economical as younger ones. Walking economy on the other hand becomes worse in people who use to walk for exercise just as it does in sedentary people. A paper published in PloSOne by Justus Ortega now suggests that running will allow you to keep the cost of walking down.
This is much more important than you might think because keeping the ability to walk easily is essential if you want to live independently in your old age. Moreover, there is a correlation between losing this ability and getting ill, showing how important it is for your life expectancy.
To find out what you can do to keep the cost of walking down, Justus Ortega and his colleagues compared the cost of walking of 15 older walkers with that of 15 older runners. (You can read the article for free if you want to know how they did it exactly.) They showed that the older runners’ cost of walking was much better than the older walkers’ and, of course, than sedentary older people’s. It was just as good as that of young sedentary adults.
What influences running/walking economy?
Your muscles and tendons have to be able to store and release elastic energy, they have to fire at the right moment and work together effectively to support your body weight, do the work, maintain your balance and allow the leg swing.
Your economy is also determined by the ability of your muscles to produce energy, such as the number and efficiency of your mitochondria and their enzymes.
Why older runners keep their walking cost low is not clear, but Justus Ortega and his colleagues suggest that the intensity of exercise is crucial. They think you might have to exercise harder, longer or more frequently if you want to keep your cost down. This would confirm a previous study, where elderly women performing high intensity walking workouts improved their economy by about 20%. On the other hand, a year-long fitness program including strength and balance exercises did not have any effect.
Can I believe this?
This is an observational study, and just like any other observational study it does not prove cause and effect. In other words: the runners might have a better walking economy for reasons not related to running at all. Maybe they have become runners instead of walkers because their exercise economy was better due to a more favourable genetic profile.
Furthermore, this is a small study, and the results might simply be due to chance –or bad luck- while in de general population there is no difference.
It is clear that we need further studies, but in the meanwhile it is a good idea to have a healthy balance between high and low intensity exercise.
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
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.
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.
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.
Many long distance runners perform at least some of their long runs in a fasted state (for example before breakfast, without taking anything), hoping that this will teach their bodies to become more effective at using fats for energy production. Even though it is not sure that it helps on race day, studies have shown indeed that you become better at burning fats if you train your body to do so.
The next question is then: would it help you to lose weight? In other words: would you lose more fatty tissue when you exercise in a fasted state than after a meal? Brad Schoenfeld and his colleagues have investigated this and concluded that it does not seem to make a difference. They published their study in the Journal of the International Society of Sports Nutrition in November 2014.
They divided 24 young female volunteers in two groups. One group exercised in a fasted state and the other after consuming a meal replacement shake. They all worked out on a treadmill three times a week at 70% of their maximal heart rate and followed the same diet with the aim to slim down. The women who started by exercising had their shake immediately after the workout.
After four weeks, all the women had lost weight, but there were no differences between the groups concerning amount of weight lost, waist line, lean or fat mass.
The researchers therefore concluded that it does not matter whether you exercise before or after a meal.
Schoenfeld explains the findings by citing previous research showing that our bodies change what they use as fuel, depending on what is available. If you burn more fats for a while, you will use more carbohydrates later in the day, and you have therefore to look at much longer periods than just a few hours.
You might understand their findings better if you think about the First Law of Thermodynamics, which states that energy does not get destroyed or created, but only changes from one form into another. What matter is therefore to get rid of the excess energy, whatever the form it is in.
A study with a negative result?
It is true that reading a study with a negative result is always slightly disappointing, and that is why in the past they did not get published. It is great that this now changing, because it might avoid repeating the same studies over and over again and it might also help us (I hope!) to avoid doing useless things.
Disclaimer: this article is for general information only, and does not replace medical or coaching advice. It cannot be used to guide treatment or training. If you have any concerns or questions, you should talk to a qualified health provider.
Many people exercise in order to lose weight or to keep it under control, but does this make sense? It is beyond doubt that regular exercise will improve your health and well-being, but could it make you hungrier, and therefore make you eat more? If so, it would not make any difference for your waistline…
In the November 2014 issue of Nutrients, Stephanie Howe and her colleagues published a review article discussing what we know today about this subject. There are still plenty of questions left, especially concerning women, as most studies have been done on men. Studies on women are indeed much more difficult to conduct since oestrogen influences appetite, and researchers therefore have to control for the menstrual status.
Stephanie Howe and her colleagues explain how hormones influence our appetite, and how exercise influences these hormones. They then discuss several studies which have investigated this problem, and finally they look at the impact of diet.
They come to the conclusion that if you are sedentary, an acute bout of exercise is likely to make you overeat. However, as you become well-trained, your body becomes better and better at matching your energy intake with your expenditure.
They also note that as intense exercise suppresses your appetite more, you have to pay attention to what you are having after hard workouts: you could be tempted to eat too little or too late, which will delay your recovery.
Their article is free for all to read, and I will just try to make a summary in lay terms.
What determines your appetite?
Appetite is very complex and influenced by a long list of factors, such as gastric motility, the status of your energy reserves, temperature, dehydration… Your brain receives all this information via hormonal and neural signals, integrates them and then stimulates or suppresses your appetite.
The involved hormones can roughly be divided into two types: tonic circulating and episodic hormones.
The tonic circulating ones reflect your energy reserves and suppress your appetite when your energy stores are full, and are thus more involved with long term regulation. The best known ones are insulin and leptin.
The episodic hormones on the other hand are involved in short term appetite. Most of them are gut hormones and are released when you are eating or just before a meal. They suppress appetite, except for ghrelin, which makes you feel hungry. As their levels depend on what you are eating, it is easy to see why some diets make you feel fuller than others. Foods rich in fibres for example, will allow you to take in fewer calories without feeling hungry.
As mentioned earlier, oestrogen and progestogen also influence appetite, which explains why many women tend to gain weight during the menopause.
All these hormones act on the hypothalamus (an organ in your brain), which integrates the information and controls your appetite. Despite this sophisticated system, other factors, such as the sight and smell of food, cultural and social elements or the time of the day, also influence your desire to eat and can even override the hormonal influences.
Researchers who want to study the influence of exercise on appetite therefore have to measure the amount of the appetite hormones in your blood as well as your desire to eat. The first can easily be done by a blood test, and the latter is often done using a visual analogue scale (VAS) or by measuring what the participants eat at a buffet in the research centre. A visual analogue scale typically consists of a series of numbered boxes (e.g. from 1 to 10), where the first and the last ones correspond to the extremes (e.g. “I’ve never been so hungry” and “I couldn’t eat anything at all”). You can then mark the box that corresponds best with how you are feeling.
Appetite hormones and exercise
A bout of aerobic exercise decreases your appetite by influencing your gut hormones. This effect is more pronounced in weight baring and more metabolic demanding exercise, such as running, than in non weight baring exercise.
Intense exercise influences the hormones more than moderate exercise. This suppression is only temporarily, but it can be enough to interfere with your next meal, and therefore with your recovery. This explains why it is so hard to eat anything solid after a race!
Resistance exercise on the other hand, does not seem to have an influence.
Are you really eating less?
It is not because your hormones are suppressing your appetite that you will eat less. As I am sure you know by experience, you can override your appetite if the food looks nice or if you believe you have good reasons to eat (e.g. I have spent a lot of calories, I need some comfort after all this hard work…).
Most studies looking into energy intake after exercise do so by measuring what the participants eat at a buffet offered by the researchers. This does not necessarily simulate real life and might therefore lead to false conclusions. Even so, there is evidence that trained people are able to match their energy intake to what they have spent, and can therefore maintain a healthy weight. Sedentary people however, are more likely to overeat after an acute bout of exercise.
Most athletes are health conscious and will choose a diet rich in fruit, vegetables, whole grains etc…Such a diet will contain fewer calories per volume than an unhealthy one. It will also make you feel full much earlier. For the vast majority of us this is excellent news, but the combination of a low calorie diet, intense exercise and appetite suppression can become a trap for some athletes. It can lead to a chronic negative energy balance, and is more often seen in women engaged in sports for which being lean is an advantage, such as long distance running. It can lead to menstrual disorders with all their complications: poor bone health, injury, illness…
If you want to recover quickly, you have to refuel as soon as you can. This can be difficult if your appetite is suppressed. Other factors such as fatigue, dehydration, an elevated core body temperature or gastrointestinal problems can make things even trickier. A good recovery drink can help you out though, as drinking is much easier than eating.