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.
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.
More and more people are overweight or obese and at the same time more and more people do not sleep enough. Could there be a link? Scientists have studied this problem by asking participants to reduce their sleep, usually from 8.5h/day to 5.5 h/day. They then noted what and how much the participants ate, and measured any hormone or body weight changes. Most of them would now answer yes indeed, there is a link.
It is clear that nobody believes that you can sleep excess weight off, but not sleeping enough (less than 7 hours/day) can hamper your efforts to slim down or keep your weight under control.
At a first glance this looks unbelievable, as when you are awake for longer, you are going to spend more energy.
The energy you spend consists of 3 components:
1) what you need to keep your body going (your basic metabolic rate),
2) the amount needed to assimilate food,
3) the energy used for all kinds of exercise and activities.
When asleep, you will not eat or move and your basic metabolic rate is reduced by 20-30%. Scientists have calculated that sleeping 5.3h instead of 8h would increase the amount of energy you spend by 45 kcal/d.
However, it is here that your unconscious brain starts interfering. As we have seen in some previous posts (e.g. here or here), your brain wants to keep you safe and it therefore wants your energy balance to remain the same. The balance between the energy you take in and the energy you spend determines your body weight, and depends on genetic, psychological and behavioural factors. Even if it sets your body weight a bit too high for your health, your brain will be unwilling to change it, as anybody who has ever tried to lose weight knows only too well.
Experiments have shown that when you have not slept enough, your brain will stimulate you to eat more to compensate for the energy you have spent. Unfortunately, it will make you overdo it. It will do so by making food more rewarding, and the data show that you will tend to snack more and to choose more fatty and carbohydrate-rich food. This is easily done in our modern world where food is widely available.
It is easy to see how all this will put your best efforts to stay slim in jeopardy. Moreover, a study by Arlet Nedeltcheva showed that dieters who slept for only 5.5 h/day lost more lean body mass and less fat than dieters who slept for 8.5h. They also suffered more from hunger.
Researchers have also studied the effect of insufficient sleep on next day’s activities. Even though some of them have not observed any effect, most report more sedentary time and less vigorous workouts. The discrepancy might be due to the fact that some study participants were used to insufficient sleep, or to the short duration of some studies which could not capture the full effect on people who exercise a few times a week.
There are still plenty of questions to be answered, e.g. what is the effect of habit, is there a difference between men and women, is what scientists observe in a study the same as what happens in real life etc…We do not know either what the effect of physical exercise is: regular exercise improves your sleep, which would then influence your energy balance. Nevertheless, it is a good idea to make sure you have enough sleep!
Several studies have shown that television watching makes you snack more, which is very dangerous for your waistline, while others have found no effect. Could this discrepancy be due to the content of the programmes? If so, choosing your programs wisely would help you to keep your weight under control.
It is possible that your mood, in particular your level of boredom, could influence how much you are eating. To check this out, Colin Chapman and his colleagues compared how much 18 normal-weight women snacked when watching an engaging comedy program, with what they ate looking at a boring lecture or reading a boring text. The snacks consisted of grapes and M&M chocolates.
The women snacked significantly less during the engaging television program than during the boring one or while reading the boring text. There was no real difference between the amount snacked while reading or watching something boring.
Previous studies have already shown that obese people tend to eat more when bored, but now more and more researchers think that everybody does so. Moreover, if Colin Chapman is right it would mean that being bored by other means than television watching (in this experiment: reading) is just as bad.
The researchers also noted that when bored the women snacked more on grapes than on chocolates. When captivated however, they had relatively more chocolate. They suppose that when the women had more time to choose, they went for the healthy option. Even so, they took in more calories than when they were captivated.
Of course, this experiment was conducted in a lab and the women might behave otherwise when at home. The researchers did not check what the women ate after the experiment and we therefore do not know if there was any effect on the size of their meal.
We do not know either what the women were used to do. Habits are powerful, and if you are used to snack while watching television or if you associate snacking with having a good time, you will find it harder to control it.
Even so, if you want to keep your snacking under control, you should avoid boring stuff… Alternatively, you could make sure that there are no snacks available when you have boring things to do, which is probably a more realistic solution.
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!
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.
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.
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.
Nutritional science is fascinating, but difficult. Keep informed, stay critical and be prepared to change your mind.
What do you use as carbohydrates during long runs and marathons? I usually have gels or jelly beans but as they are highly processed foods, I would prefer a more natural source of carbohydrates.
I have experimented with portions honeycomb packed in cling film, but it was fiddly and sticky and therefore much too difficult. It is a pity, because I felt fine on it and I could obtain it locally.
Searching through the literature, I found an article describing an experiment whereby they used raisins instead of sport chews. Eleven male runners ran 80 minutes on a treadmill at 75% of their VO2max, followed by a 5 km time trial. They performed this workout tree times (on different days), once having water only, once having sports chews, and once having raisins. There was no difference in performance or gastro-intestinal comfort between the workouts with sport chews and the ones with raisins. Using water only, the runners performed less well.
The researchers also measured blood levels of glucose, insulin, free fatty acids and creatine kinase. The chews caused slightly higher insulin levels and more carbohydrate oxidation than the raisins, and creatine kinase was markedly higher in the raisin group. Elevated levels of creatine kinase are suggestive for muscle fibre disruption, and are used as a marker for delayed onset muscular soreness (doms), but the runners did not report more soreness when using raisins. The researchers could not explain this finding, which, I think, is a bit worrying.
I have not tried raisins out for myself, mainly because of the creatine kinase. Moreover, a marathon takes me so much longer than about 100 minutes of running, and therefore I am not sure that I will be fine.
Do you need to take in extra protein after a strength exercise session and, if so, how much?
Scientists are still debating this question. It is an important one, even for endurance athletes, as we all need strength to practise our sport properly and to perform well. In the May edition of Sports Medicine, Stuart Philips from McMaster University has summarised what we know about this question.
Muscle proteins are in a constant turnover: some are broken down, and other are synthesised. As long as you making more muscle proteins than you are breaking down, your muscles will grow (hypertrophy) and you will get stronger, your performances will become better and, crucially for endurance sports, you will be able to maintain good form for longer and therefore reduce your risk of injury.
Resistance exercise will stimulate muscle protein synthesis for at least 24 to 48 hours. Proteins are made of amino acids, and having more amino acids in your blood will further enhance muscle protein synthesis. After a meal you tend therefore to make more proteins than you break down. The effects of eating and exercising reinforce each other, and this is why it is beneficial to have a protein rich drink or meal after your strength training session.
However, as exercise stimulates muscle synthesis for at least 24 hours, researchers such as Brad Schoenfeld and Alan Aragon believe that timing your meals is much less important than having enough protein in each of them. They think that supplements immediately after training are unnecessary as long as you are having a healthy diet containing enough protein. I have blogged about their opinions before.
There are 20 different amino acids, but our bodies can synthesise only 10 of them. The others are called the essential amino acids, as we have to get them from food. Unfortunately, we can only synthesise muscle proteins if all the essential amino acids are available, which means that we need a well balanced diet. One of them, leucine, is particularly important, as it triggers the synthesis. Foods that contain plenty of leucine, such as whey, are therefore more effective than others to build up muscles.
Having too much protein in your food does not help. The maximal effective amount is 0.25g protein/Kg body mass in younger people. Ageing and inactivity makes it harder to get the process of muscle synthesis started, and it is likely that we need more leucine and protein in our food as we get older. Older people may need up to 40g protein/ Kg body weight.
The rate at which the amount of amino acids rise in your blood is also important: a low level or an almost continuous delivery is much less effective than a bolus every three hours or so, as you would get from meals and snacks during a normal day.
– As yet, there is no evidence that other amino acids such glutamine or arginine, help to build up muscle.
– Carbohydrates are important to replenish your glycogen stores, but there are no reasons to believe that they influence muscle synthesis, as long as you have enough protein in your food.
Try to have at least three well balanced meals and/or snacks a day, each of which should contain sufficient protein, and schedule your workouts so that you finish before a meal. Do not eat too much protein either, as this is probably just wasteful.
As you get older, you will need more protein, especially more leucine. You will find a list of foods containing leucine by clicking here.
Never give up exercising, as inactivity and ageing are a bad combination for your muscles.
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.
The Mediterranean diet has been linked to a longer and healthier life, but the reason why is not completely clear yet. It is likely to be due to a multitude of factors, such as plenty of fruit and vegetables, garlic, fish, a more outdoor lifestyle…Olive oil is a key component, and the latest publication from the Predimed study shows that the extra-virgin variety is the most beneficial, suggesting that the effects are mainly due to its phytochemicals.
We assumed for many years that the benefits of olive oil are due to its high content of mono-unsaturated fatty acids. However, many foods in a typical Western diet contain plenty of mono-unsaturated fatty acids, but do not seem to be as beneficial.
Olive oil also contains many phytochemicals such as polyphenols, phytosterols and vitamin E, which are anti-oxidant and anti-inflammatory. The amount depends on the kind of olive oil: extra-virgin is the first oil obtained by mechanically pressing olives, and contains much more phytochemicals than common or virgin olive oil. If the benefits of olive oil are largely due to its phytochemicals, extra-virgin oil should be much better for you than any other variety.
The Predimed (Prevencion con Dieta Mediterranea) is a Spanish study trying to understand which components of the Mediterranean diet are the most important and why. 7216 older adults at high risk of cardiovascular disease participated, and were randomised in three groups. They all continued with their usual Mediterranean diet, but one group added more olive oil, a second group consumed extra nuts, and the third group reduced the amount of fats. In their latest publication, the researchers looked at the effects of olive oil on cardiovascular disease. (I have blogged about the results concerning nuts previously.)
Sure enough, consuming more olive oil was associated with a reduced risk of cardiovascular disease, but the association was due to the use of extra-virgin olive oil: for each 10g/day more extra-virgin olive oil the risk of having cardiovascular disease was reduced by 10%, and the risk of dying from it by 7%. Using common olive oil did not have any benefits.
The researchers could not find a reduced risk of cancer, but they did not examine specific types of cancer. Other studies however, have shown that olive oil reduces the risk of breast cancer and some digestive and respiratory cancers.
We all know that we should have some carbohydrates and proteins to recover faster after a hard workout, but what happens if at the same time we have a few drinks to celebrate the achievement? How will that affect the recovery?
In 2003, Louise Burke and her colleagues studied the effect of alcohol on the rebuilding of glycogen stores after an exhaustive bout of cycling. They noticed that alcohol slowed down the glycogen storage during the first 8 hours, but after 24 hours there was no difference anymore. This means that if the early phase of recovery was poor, there must have been a period of catching-up. They also showed that the main problem with drinking alcohol is that it makes it unlikely that you are taking in enough carbohydrates to rebuild your glycogen reserves, and, as you cannot make glycogen from alcohol, you could be losing out.
However, recovery is not only about glycogen, but also about rebuilding damaged muscle fibres. To do so you need to make new proteins, and taking in high quality protein soon after your workout can help your body to do so.
In a study published in PloSOne, Evelyn Parr and colleagues showed that drinking alcohol during your recovery hampers the protein synthesis. 8 men performed a workout comprising resistance, continuous and interval exercise. Immediately and 4 hours afterwards, they had a drink containing protein, protein with alcohol or carbohydrate with alcohol. The study was constructed as a cross-over design, which means that each volunteer performed the workout three times, using each time a different drink at the end. The researchers took muscle biopsies before the exercise, and 2 and 8 hours afterwards.
As you can see from this graph from Evelyn Parr’s article, alcohol impaired protein synthesis by 24%, even if the athlete had enough protein during his recovery. In real life, it is likely that the athlete would not take in proteins, and that the situation would be at best similar to having the alcohol and carbohydrate drink. That would mean 37% less protein synthesis.
The athletes in this study had about 12 standard units alcohol in their drinks. This sounds awful, but according to the researchers it corresponds to the mean amount used by team athletes during a drinking binge (!). We do not know yet what a safe amount of alcohol would be, or if that exists. We need therefore more research. Until we have that, it is better to be careful…
A mounting amount of evidence shows that eating with smaller bites and keeping your food for longer in your mouth makes you take in fewer calories. However, as all these studies have been done under standardised conditions in labs, it is not clear how you could do this in daily life. How can you keep taking smaller bites and keeping food in your mouth for longer while chatting or watching television?
In her latest article on the subject, Dieuwerke Bolhuis suggests choosing harder foods, which will need more chewing, to achieve just that without having to think about it.
Bolhuis and her colleagues asked 50 volunteers to have a meal of harder foods and one of softer foods for lunch on two different days. The volunteers ate as much as needed to feel “pleasantly full” while the researchers filmed them to determine their bite size and the time it took them to chew and swallow the food. The volunteers were invited for dinner on the same day as they had lunch. They could again eat as much as needed, and the researchers calculated the amount of energy they were taking in.
Eating harder foods indeed forced the volunteers to take smaller bites and chew longer, and led to a 13% lower energy intake. They did not compensate for this at dinner, which means that had eaten substantially less over the day without noticing any difference.
If you could keep having about 13% less energy a day, you would quickly lose weight indeed. Moreover, the harder or chewier foods are often the healthier ones as well, as they are likely to be less processed or to contain more fibre. Unfortunately we do not know yet whether this can go on day after day: would your body end up compensating by eating more?
Anyway, it is certainly something to try out.
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.