Running Economy Part II

The Biomechanics of Running Economy

Today sees Part II of our series on Running Economy. After spending the first two posts introducing the concepts and discussing the results from the Zersenay Tadese study, today we move onto some fundamental concepts of running economy - the physiology and biomechanics of running economy explained (partly, we hope!)

I say "fundamental" with some caution, because the more one digs into this particular topic, the more you realise that the science, and our knowledge of how to put running economy into practice, is still a long way off where it should be. I know that our good friend Amby Burfoot is fond of reminding us that science is actually a long way from understanding running physiology, and he's quite right. In the words of Sir Roger Banister, the first man to crack the 4-minute mile and who then went on to become a respected neurologist:

"The human body is centuries in advance of the physiologist, and can perform an integration of heart, lungs and muscles which is too complex for the scientist to analyse"

Running economy is one such 'integration". And with that in mind, let's get to it!

A fundamental paradigm - running economy: one of many explanations?

The first point that I have to make is that we should be careful not to over-emphasize the importance of running economy to performance. Yes, it is important. And yes, any coach, scientist or runner who is dedicated to training and improving performance needs to be aware of running economy and possible means to improve it. And yes, it has been relatively "forgotten" by science in recent times, hence our relatively limited understanding of it. But regular readers of The Science of Sport will also know that we're not particular fond of "magic potion", "silver bullet" training methods or science principles! So we must approach running economy for what it is - one of many explanations for performance.

So when we look at the East Africans, we note that they have a better running economy than the European runners. We also note that the best runners tend to be the most economical, that certain physiological characteristics predispose runners to be more economical, and that certain types of training improve running economy more than others (more on that in our next post, by the way). This is only partly relevant to you as you read this, because ultimately, you must not "lose sight of the wood for the trees", and become so stuck in the running economy analysis that you forget to worry about performance! And let running economy take care of itself...

Factors influencing running economy

Running economy, to repeat, is an integration of numerous systems and characteristics, biomechanical, and physiological factors. It would take a month of articles to cover all of them in detail, so we'll skim the list quite substantially, and discuss these three categories very broadly.

Biomechanical factors influencing running economy

The Zersenay Tadese article attributed his incredible running economy to the small size (and thus lighter weight) of his calves, compared to the European athletes. That is, he is carrying less weight at the extremities than they were, since his calf circumference was a good deal smaller than the Spanish runners he was compared to.

I suspect that this is only part of the answer, and possibly a very small part. As mentioned in Part I, Tadese's economy is much lower than the Kenyan runners tested before him, who probably do not have quite as much of a disadvantage as far as the calf muscle goes. So while the difference between Tadese and the Spanish might be calf-size related, there is more to it than just this.

According to an excellent review article from 2004 (by Saunders, published in Sports Medicine, 2004), the following biomechnical factors are important for running economy:

• Height: Slightly smaller than average is better for men, while slightly taller is better for women - I must confess that I don't have an explanation for the difference!
• Somatotype: Ectomorphic physique demonstrates best running economy. An ectomorph is generally long-limbed, thin, has shoulders that are about the same width as the hips! Think Paul Tergat, or just about any Kenyan long distance runner!
• Body fat: Low percentage, because body fat represents additional weight that must be carried, increasing the oxygen cost of running
• Leg morphology: Most of the weight distributed closer to the hips. In other words, if you have mass, carry it in the quads and not the calves! This agrees with the suggested reasons for Tadese's economy
• Pelvis: Narrow
• Feet: Smaller than average
• Shoes: Lightweight but well cushioned. There is evidence that cushioning improves running economy, possibly because it reduces the work required by the muscle to absorb and cushion the landing (that's the theory, anyway)
• Stride length: Freely chosen. This is interesting, because there is evidence from research that if you chop your stride to try to increase the cadence, your running economy worsens. We touched on this in our series on Pose running recently, and a lot of people find that they chop their stride when trying to use the method. According to the economy research, this would be undesirable. Having said that, if you are overstriding, then it's just as bad, if not worse, because a great deal of energy is lost in braking. This factor, perhaps more than any other, emphasizes that "Practice makes Perfect" and that running is a skill which must be practiced and learned. It happens naturally, yes, but it must be learned.
• Kinematics: A few things here - first of all, low vertical oscillation of the centre of mass. What does this mean? Well, it means don't waste time going up and down if you don't need to. The less you waste on vertical braking forces, the better. It was always rumoured that the most economical runners were effectively "rolling" their legs along beneath their hips - this is in fact a premise of Pose Running, as we discussed once before. There is nothing new to this at all (despite the fact that it was packaged as 'revolutionary', because we've known for a long time that a relatively flat trajectory is more economical.
• Secondly, minimal possible movement of the arms. That's not to say zero movement, because the arms play an important role in providing some rotational stability, but the movement must not be excessive. On this note, you see some absolutely bizarre arms carries among the elite runners, which you'd have thought would be corrected, but that only re-inforces that this is not an exact science.
• Third, a more acute knee angle during the swing phase. In other words, when your trail leg is coming through (eg. your right foot is planted on the ground and your left leg is catching up), then it's better to have that knee fully bent than straight. The reason for this is physics, relating to rotational torque and the force that is required of the muscles to bring the leg through. But the practical point is that the hamstrings come into play to reduce running economy, because they contribute to the flexing of the knee. One practical issue here is that when running slowly, it's almost impossible to bend the knee more than a few degrees - you'd be working so hard to bend your knee, the effect would be increasing your cost, not reducing it! So this is largely influenced by running speed.
  

Then there are a couple of other factors, which we'll touch on as we develop our discussions further in the next few posts.

But what is important to take out of the above list is that if you are a tall, skinny man, weighing next to nothing, with hips as wide as your shoulders, short arms, no body fat, and you wear a well-cushioned pair of size 6 shoes, you might have a good running economy!

The most important thing that jumps out from the above list is that there are some factors that one is born with (narrow pelvis, foot size, height, distribution of weight on the legs) and others that are improved with training and preparation, such as the kinematics like vertical oscillation and arm carry. Point is, great runners are born, and then trained. But everyone can run, and so as you read this, there is probably a great deal that you can do to improve your running economy, which would then translate into improved performance. But we'll discuss that in a separate post, later in the week.

Join us then!
Ross

Running Economy Part I

The Zersenay Tadese study - the most economical runner ever?

Yesterday we introduced a new series, Running Economy, inspired by this study, which was published just last week in the British Journal of Sports Medicine. It makes a great start to a series that we'll build on next week, looking at the importance of running economy to performance.

We must of course make the disclaimer that just as VO₂max does not by itself guarantee performance, so too running economy is one of many possible variables, both physiological and psychological, that come into play when one tries to understand just what is goes into determining performance. But it certainly seems to be an important one...we spoke yesterday of the growing awareness of running economy as a crucial determinant of performance, and of how little is known about it.

So it is perhaps fitting to begin our series with the very latest work, and then we'll deconstruct the theories as we progress.

The Zersenay Tadese Study

The title of the research article that was published last week was "The key to top-level endurance running performance: A unique example". The researchers, based in Madrid, Spain, had access to Tadese, the World Cross Country champion who put an end to the reign of Kenenisa Bekele earlier this year. He then followed this up with a win in the World Half-Marathon championships, where he beat world record holder Sammy Wanjiru, running 58:59, in a race where some time may have been lost due to tactical manoevuring in the middle part of the race!

Zersenay Tadese is a class act. Regular readers will know that I (Ross) am a particular fan of his, and recently picked him to be the next world record holder in the marathon, when he eventually makes the move up from the track. I think he might even have a more successful marathon career than Bekele. And if he gets the preparation right, Beijing 2008 might also see him challenge Bekele on the track. So it was with some personal interest that we discovered this article, courtesy George.

Looking at the study, it is always remarkable to have access to such a uniquely talented athlete, clearly at the peak of his 'game'. It's always been one of the big barriers to understanding the 'eternal mystery' of the dominance of the Kenyans that they've never really been studied in their prime. Most of the published work done on the East Africans comes from the labs of Bengt Saltin, and while those runners were certainly talented, they were by no means the best Kenyans in their best condition. And of course, there's a potentially crucial difference between the Kenyan who can run 27:30 for 10k compared to the one who runs under 27 minutes! So the fact that Tadese was tested during the month leading up to the World Cross Country Championships, and that he allowed the results to be published is a great coup for the researchers.

So let's take a look at the results...

Blood hematocrit

The first finding of interest is the hematocrit, measured one week before the Championships. It was "only" 43.7%. I say "only" because in another endurance sport, cycling, I suspect that many riders would not even get out of bed on pull on their jerseys if it was this low! In fact, the value of 44% is pretty much in the normal range, considering that he was doing a moderate to high volume of training at the time of testing (about 150km/week).

The authors suggested that this measurement, together with other findings we won't go into here, indicates "no manipulations to artificially increase blood oxygen transport capacity", and "no artificial stimulation of erythropoiesis". I'm sure sceptics are out there (they'd hardly report it if his hematocrit was 58%, would they!), but we'll go along with that one. Let's get onto running economy.

Running economy

We introduced the concept of running economy yesterday, but it bears repeating. Running economy is a measure of how much (or little, as the case may be) oxygen the runner uses for a given, sub-maximal speed. In theory, two runners can have the same maximal capacity for oxygen use (called VO2max), and then the one who is more economical at the sub-maximal speeds is likely to be the better runner.

So there are two measurements we need to look at here. The first is the MAXIMUM - the VO2max. The second is the oxygen use at sub-max, which tells us how economical Tadese is.

VO2max

Zersenay Tadese's VO2max was reported as 83 ml/kg/min. This is a very high measurement, but that's expected of a world class long distance runner. When compared to other world class athletes, Tadese's value 'disappears' into the crowd. In otherwords, if we lined up a group of athlete's VO2max values and asked you to pick the the two-time World Champion based on VO2max alone, there's a good chance you'd be wrong! Just as you would have been completely wrong when you had to guess that Derek Clayton could run a 2:08 marathon with his VO2max of "only" 69 ml/kg/min.

Of course, when it comes to VO2max, there's a lot of hype around the measurements. It has become something of an urban legend, much like the size of the fish you caught on your last fishing expedition which gets larger every time you re-tell the story! So depending on who you believe, Greg Lemond had a VO2 max of 92.5ml/kg/min, the Cross-Country skier Bjorn Daehlie was at 96 ml/kg/min in the off-season, and the physiologist who tested him predicted that he'd be above 100 ml/kg/min when he was "fit"! We're pretty sure you can relate your own stories of this super-human measurement!

Incidentally, while we're talking super-human, the Siberian huskies who take part in Alaska's Iditarod Sled Dog Race have been reported as having VO2 max values of 240 ml/kg/min! Eat your heart out, Bjorn!

Running Economy

So now we move onto running economy.

First things first – we have to understand what they are measuring. They have measured running economy as the total volume of oxygen needed to run 1 kilometer. This is really important, because there is evidence, shown in the Figure below, that this total volume does not vary too much with running speed. In otherwords, regardless of how fast you run, you use more or less the same volume of oxygen to run 1 kilometer! Of course, there will be individuals who don’t quite follow this trend, and so some runners will become more or less efficient as they run faster, but in general, it stays similar.

Figure showing schematic values of oxygen cost to run 1 km in three
different population groups. Note that the data are schematic only,
and represent pooled values for the three groups. Note also the general
absence of a change in economy as running speed increases.
Redrawn from Foster and Lucia (2006)

Now this might be confusing at first (certainly took some figuring out from our side – it has major implications for our understanding of fatigue, actually), because you’ve no doubt heard that the faster you run, the more oxygen you use. And this is still true – the trick is to understand the units that economy is being reported in. This is illustrated in the following example:

Take a runner who runs along at 4min/km, and uses about 200 ml/kg of O₂ to run 1 km. If we look at his O₂ use per minute, then we work out that he is using 50 ml/kg/min (because it takes him 4 minutes to run that kilometer and use those 200ml/kg of oxygen). If our runner increases his speed to 3min/km, if we assume that his total oxygen to run 1 km remains 200ml/kg (again, we acknowledge that some people will differ, but generally, as the figure above shows, this is the case). But now, he’s only taking 3 minutes to run the kilometer (and hence use those 200ml/kg of O₂). Therefore, his actual use of oxygen PER MINUTE is now 67 ml/kg/min!

So in fact, the use of oxygen PER MINUTE goes up with running speed, but the use per kilometer remains relatively constant. This is important (and has MASSIVE theoretical implications, but that is for another day). The other thing about this figure is that it creates a number of questions – why are the East Africans lower than the Caucasians, for example? But that’s all for the later posts in this series. Let’s get back to Tadese.

Tadese has one of the lowest total volumes of oxygen to run 1 kilometer ever reported. In the article, the authors report the following “normal” values for running economy, measured as ml/kg/km (that is, volume used to run 1 km)

• Frank Shorter – 192 ml/kg/kilometer (running at 3:06/km)
• Elite Kenyans (including Olympic medallists) – 192 ml/kg/kilometer (running 3:00/km)
• Elite Caucasians (Spanish runners) – 211 ml/kg/kilometer (running 3:09/km)

• Zersenay Tadese – 150 ml/kg/kilometer (running at 3:09//km and at at 2:51/km)

The size of this difference is astounding. We do have reports of runners who have been tested in this range, but we just need to get permission to publish the results (we’re working on that!). But let’s put this into context:

• Tadese is running along at 3:09/km, which is a 2:13 marathon pace.
• He is using 150 ml/kg of Oxygen to cover each kilometer.
  
• If we now convert this to a volume per MINUTE, we work out that he is using 47.6 mlO₂/kg/min. This is absolutely astonishing for how low it is!
  

We cannot emphasize just how significant this is – quite what it means, and the implication thereof is something we will tackle in another post, possibly even another series (we don’t want to go off on a tangent here!).

What is wrong with this picture?

But just think about something for a moment – Tadese has a VO2max of 83 ml/kg/min, and he runs at 3:09/km using only 48 ml/kg/min. Therefore, he is using only 57% of his “maximum” at this speed.

There is good evidence that athletes are able to run for 2 hours at about 80% of their VO2max. Now, if Tadese did this, he would be able run at 66 ml/kg/min. Given his Running Economy of 150 ml/kg/km (which is 'relatively' independent of speed - see Figure, and was similar for Tadese in the two speeds he was tested at), this would mean he could cover each kilometer in 2 minutes 18 seconds! Even if his running economy worsened quite a lot and he used up 180 ml/kg/km (a 20% increase), he'd still have it in him to run 2:45/km!

Quite clearly, this is not possible. So either Tadese becomes MUCH LESS efficient as running speed increases (which is somewhat out of the ordinary, as the figure demonstrates - slight changes, sure, but not so large), or something else is going on - there's something wrong with this picture. We need to address this, but as I've said, that's another can of worms!

The inevitable disclaimer...

I have no doubt that people will attack some of the assumptions we’ve made, and so we might as well declare right now – “We know, we've made some assumptions here, the key one being that economy (as measured per kilometer) doesn't change with speed, but we use this to illustrate a potentially profound point for our understanding of what limits exercise performance”. Think about it – if you’re running along at 80% of VO2max, then you have the capacity to use more oxygen. Yet you don’t. So how then, can oxygen be limiting, as you’ve probably read many times? Interesting one that…but that’s for another day…

Explaining Tadese’s extra-ordinary running economy

So now we move onto a mechanism – how do we explain this unbelievably low use of oxygen? Well, the authors put a few things out there:

• Very efficient utilization of oxygen by working muscles
• Training
• Muscle fibre distribution
• Genetic Factors
• And then the big one, anthropometric characteristics. That is, they measured the mass and size of the calf and found that Tadese had a significantly smaller calf muscle than the Caucasian runners, who had Running economies of 211 ml/kg/km.

With that, which I’m sure many of you are thinking is a very generic set of reasons and mechanisms, we’ll sign off today! But that’s on purpose, because in our next post on the series, we’ll look at what factors contribute to running economy in more detail – what is training, muscle fibre distribution, genetics? And then we can all compare ourselves to Tadese and work out why we’ll never be that economical!

Bye for now!

Ross

Running Economy Introduction

Zersenay Tadese - the most economical runner in history?

Well, a provocative headline for sure, but that's pretty much what a SCIENTIFIC study has suggested after measuring the oxygen consumption and running economy of the World Cross Country and Half Marathon champion recently! The study, published just the other day in the British Journal of Sports Medicine, and performed by Carl Foster and Alejandro Lucia, found that Tadese has one of the best (if not THE best) running economies ever measured. That is, he uses LESS oxygen at the measured running speed than any runner reported before him.

I would not question the study for a second (well, not too critically, anyway), as Foster and Lucia are both excellent scientists, with great records in the field. Foster is famous for his modeling of pacing strategy and performance, while Lucia has been one of the leading researchers in cycling performance, doping and the physiology of performance. So some credible names, and a fascinating paper, for sure!

We are always on the lookout for interesting news stories here at The Science of Sport, and we do our best to take sports news and exaplain the science behind it. But this particular story is both newsworthy and science-worthy at the same time, and we say thanks to George (a self-described devoted reader of the blog) for bringing it to our attention!

Introduction of a new series - running economy

What we would actually like to do before we analyse this paper (and Tadese's new claim to fame) in tomorrow's post, is to use this really great story to introduce a new series and discussion around this concept of running economy. I seem to recall that about three months ago, there was a whole spate of articles on running economy - for some reason, it suddenly shot to prominence and a number of widely read newspapers started writing about it as though it was the very latest thing, even though we've known about its importance for about 30 years. And even back then, we considered the prospects of some posts about running economy, but they got kind of swept away by the heat of Chicago and the racing in New York. Well, no time like the present to go back there!

Running economy 101: What is the big deal?

To begin with, running economy in humans is probably analogous to cruising-efficiency in a car (not entirely, but we'll get there!). If you think of a human, we can measure the maximum volume of oxygen that can be used, and this is called the VO2 max or VO2 peak. The problem is, for most running events (certainly above about 5000m), runners don't use this "maximum" amount - they are sub-maximal. And so therefore, a more important measure becomes the volume of oxygen that is used up when the runner is going at a sub-maximal speed.

So to return to our fuel analogy, it's saying that the car is cruising along at a speed lower than maximal, and we're interested in how much fuel it uses per kilometer.

Now, there is plenty of reason to think that running economy is very important. There used to be a perception, which still exists in many circles, that the be-all and end-all of running performance was the VO2 max value. In other words, you'll still find people who think that the runner who has the highest VO2 max is the guaranteed winner. Many runners who have been tested wear their VO2 max like a badge of honour if it's high, whereas they hide it away if they think it's low, such is the importance that has been placed on this measurement.

And of course, it is still crucial that a world class runner have a higher than average maximum ability to use oxygen. So you'd be very hard pressed to find any world-class runner who has a VO2 max lower than about 70 mL/kg/min (this is the unit for VO2 max, by the way - it's a volume in mL, expressed relative to body weight over time). Your typical moderately fit male, weighing about 80kg, would have a VO2 max of about 50 to 60 mL/kg/min, and a fairly well trained athlete might hit the mid 60's, with the better ones being higher than this, into the 70's and 80's. So there is a "GENERAL" trend for the fitter, more highly trained athlete to have a higher VO2 max (although we would argue that is a consequence and not a cause of performance).

But then there's a catch - Maximum is not the deciding factor

The reality however, is that you don't always get this nice, uniform increase in performance with an increase in VO2 max - often times, a guy with a VO2 max of "only" 75 ml/min/kg will beat a runner whose VO2 max is "superior" at 85 ml/min/kg. And so clearly, there is more at play than simply the size of your lungs, your heart and the muscles maximum ability to use oxygen.

Intuitively, you recognized that this makes sense - as we pointed out above, because 10000m races are run about 90% of VO2 max, and marathons are run at 80 to 90% of VO2 max, there is room for difference because it's the runner's ability to use the oxygen most efficiently that contributes a substantial amount to performance.

So that's where running economy enters the equation. Whenever you read a book on this subject (be it Lore of Running, or any other text), you always see the concept of running economy introduced in this way - it's the excuse for the "little guy" (in terms of maximal oxygen use, anyway), beating the big guy!

Considering how important running economy seems to be, it's apparently been ignored in the literature. Last year, in October, a seriously high-powered gathering of exercise physiologists and scientists gathered in Chicago for a conference on Marathon Medicine and Physiology.

And at that conference, Carl Foster, one of the authors of the Tadese paper, discussed the role of running economy in performance. He suggested that the science has "ignored running economy" to date, despite knowing about it for 30 years, and as a result, relatively little is known about the topic.

It therefore seems like a nice, juicy and interesting topic to tackle in a series, and so what we'll do over the next couple of weeks is take a look at running economy. We'll begin with an analysis of the study on Zersenay Tadese, which began this post, then we move onto the importance of running economy, the factors determining running economy, and methods that you can use to improve your running economy, and hopefully performance.

So join us over the next few weeks as we get into what could be a very interesting discussion!

Ross

Fukuoka Marathon 2007

Sammy Wanjiru's debut party goes as planned

This past weekend saw the 61st running of the Fukuoka Marathon, which until a few weeks ago promised an epic dual between the seasoned veteran Paul Tergat and the up-and-coming Sammy Wanjiru. Unfortunately Tergat pulled out, leaving no one who could, on paper at least, touch Wanjiru's potential.

Wanjiru has been devouring competitors in the half-marathon since 2005, when he set his first world record over that distance (59:16 at Rotterdam). He lost that record to Gebrselassie in January 2006, only to break it again in February of this year in Ras Al Khaimah (UAE) with a new time of 58:53. However that record was not ratified as no EPO testing was carried out at the race. Undeterred, he promptly lowered that time to 58:33 in March at the Fortis City-Pier-City Half Marathon in Den Haag. He later committed to Fukuoka as his marathon debut and had all eyes upon him this weekend---could be break Evans Rutto's debut record of 2:05:50?

The race: Wanjiru never in trouble

It was a typical race of attrition as the pace setters did their job and one by one runners dropped off the pack. By 20 km only 15 runners remained in contention, and five km's later only 10 remained. At 30 km the rabbits' job was complete, leaving just two other runners to challenge the novice Wanjiru. At that point he and Japanese national Atsushi Sato tightened the screws and ripped off a few fast splits:

31 km: 2:58
32 km: 3:01
33 km: 2:57
34 km: 2:58
35 km: 2:52

It was Wanjiru himself who attacked during the 35th km, breaking Sato and leaving only Deriba Merga of Ethiopia. Wanjiru then toocontrol as he surged again to break Merga:

36 km: 2:56
37 km: 3:04
38 km: 2:57
39 km: 3:11

Merga was dropped, but hung on to smash his own PB by over six minutes and also borke the prvious course record and finished only 11 seconds behind the debutante Wanjiru. A stellar run by Wanjiru, to be certain, but very brave running by the young Ethiopian who showed class and form by clinging to Wanjiru for so long and losing by a relatively small margin.

The official splits for Wanjiru as he broke the course record by 12 seconds :

5 km	15:04
10 km	30:02
15 km	45:06
20 km	1:00:11
21.1 km	1:03:30
25 km	1:15:04
30 km	1:30:05
35 km	1:44:49
40 km	2:00:03
42.2 km	2:06:39

What is next for the young star?

So everything appears to be going exactly as planned for Wanjiru. He seems to be connecting the dots one by one from a very young age and turning in big performances along the way. Wanjiru claims to have Olympic Marathon aspirations, and so far has met his goal of debuting with a 2:06 marathon. His next goal is to run 2:05 in a spring marathon, perhaps London, in hopes that a feat of that magnitude will secure him a spot in Kenya's Olympic Marathon team. Another performance like this in London will signal his arrival on the Big City marathon scene. This past weekend, although matched against the best Japan has to offer, he did not run against such a stellar field. London's ability to secure both the fastest runners and best racers is legendary, and Wanjiru must prove he can beat the experience of guys like Felix Limo, Evans Rutto, Jaouad Gharib, Daniel Njenga, Robert Cheruiyot, Paul Tergat and Gebrselassie, among others. For now, though he owns the course record in Fukuoka and remains on a larger path to more success.

Muscle Cramps: Part V

What all this means for you

We have now run the entire gamut in this series on cramps, and it has been quite a ride. This series generated the more reader interest than any of our other posts or series, and let us say again how grateful we are for your participation in the debates and discussion. As academics, we hold fast to the old adage that there is no such thing as a stupid question, and all of us, expert or novice, must ask questions to learn and advance our own knowledge. And this was a complicated series, so we really thought it might be a good time to try to summarize what, exactly, does all of this mean for you the athlete?

Who experiences cramps?

There does seem to be a predisposition cramps. To date no one has even tried to identify the gene(s) that might predispose one to cramping, but even a general survey of the active population will reveal that some people cramp both at night and during exercise, while others never cramp. So you might indeed be a "cramper" before you even toe the line!

What causes them?

We have presented two models for the cause of cramps. The first model tries to explain them based on electrolyte disturbances and dehydration. The second model is based on neural activity and muscle excitation and relaxation. So which one is correct?

The short answer is that we do not know exactly what causes cramps, and it will likely be many years (perhaps even decades) before someone presents a more definitive model that better explains their cause. As we mentioned in a recent post, science is like watching one chess square and trying to create hypotheses based on observations of that one square. We have presented the available scientific evidence, and have drawn our conclusions based on that evidence. Does that make our conclusions correct? To be certain, "No not necessarily!" It merely represents our interpretation of the data.

The bottom line here is that it is a complicated mechanism, like so many others in the body. Also, just as our many different systems are affected by a vast array of factors and circumstances, so is the cause of cramps, and until we have a reliable laboratory protocol that can reproduce cramps in a predictable manner, we cannot really test the models further.

Ok, so I am a cramper. . .now what do I do?

There are a couple of key points here:

1. Regular stretching will help reduce the incidence of your cramps. This is because, as we explained in Part III, stretching will reduce the alpha motor neurone activity, and thus reduce muscle contraction---which is all a cramp is anyway, an uncontrolled contraction. Therefore stretching often is recommended especially if you know you are a cramper.
2. "I swallow an electrolyte pill and my cramping stops." This is a comment we hear often, and although we cannot explain this physiologically, the more important message is that you have found something that works for you. We cannot stress how important this is! All the science in the world can point to something, but if what you are doing works for you, then you are better to stick with that technique. We invest so much time and energy (i.e. blood, sweat and tears!) into our training, and if you know that taking some supplement---providing it is legal, of course---will prevent a cramp during your marathon, then by all means you must take it.

But wait. . .I am not a cramper, how can I reduce my chances?

Fatigue appears to be a common factor in cramps, and so preventing fatigue or delaying its onset is crucial. However, we can hear you all the way in Chicago and Cape Town saying, "Great! if only it were that easy. . why didn't you just say so?"

First of all, "Out running" your training could be a likely contributor to cramps. By this we mean that you know good and well that you have done the training for a 3:30 marathon, but in spite of that you decide you are going to go out at 2:55 pace. You feel great for about two hours, and then all hell breaks loose, the wheels fall off, and you are left in a crumpled heap with 5-10 km to go. Therefore we would suggest trying to race closer to your abilities in an effort to reduce the amount of fatigue you acquire during the event.

Second, progressive training is something else that we can all practice that will likely help reduce the chances that we cramp. Don't go from "zero to hero" and make large increases in your training from week to week. As many of you might already know, rest is just as important as all the intensity and distance work you do, because it is during rest periods that your body actually makes the adaptations. Therefore small and incremental increases in training with appropriate rest will provide your body with the maximum time to make the necessary adaptations, and it is those adaptations that will delay the onset of fatigue.

Physiology is a complicated topic, and the available evidence on cramps is sparse. To really advance our knowledge we need solid lab studies that help us identify exactly what is going on and why the cramps occur. In fact, just creating a reliable and reproducible lab protocol would be a major step in identifying what causes the cramps in the first place. However cramps tend to be unpredictable in most people, and even in the known "crampers" it is difficult to bring them in the lab and make them cramp 100% of the time. So the beat of science marches on, and we can only hope that even as you read this, some PhD student out there is hard at work dreaming up a thesis that investigates this issue and tries to advance our knowledge!

Sports drinks, sweat and electrolytes

The actual data from the lab and the field

In the last post we introduced you to Randy, our imaginary 70 kg average male runner, and we created some potential scenarios regarding his fluid and sodium losses and replacement. The biggest take home message was to listen to your body and to drink to thirst, as this has been shown again and again in the field and the lab to keep people from drinking either too little or too much. We have received tons of feedback and discussion, and as we stated in the comments to that post we are pleased that so many of you are participating in the discussion, sharing your stories, and asking relevant and insightful questions.

Just as we will admit that field studies are not the perfect experiment but play an important role, it is the same with prediction equations. We can predict all we want from imaginary scenarios, and some times the equations are pretty accurate, but there is no substitute for the real thing, and many readers wanted to see more actual data and references that demonstrated why sodium ingestion is not necessary, and how both sports drinks and water will can cause a fall in sodium concentration. So while it is important to go through the exercise in the prior post, the next logical step is to look at the actual data.

Baker LB, Munce TA, Kenney WL. "Sex differences in voluntary fluid intake by older adults during exercise." Med Sci Sports Exerc. 2005 May;37(5):789-96

This study examined ad libitum fluid ingestion in older adults during intermittent exercise in the heat. Basically, they had continual access to water in one trial and Gatorade in another, and they had to cycle for 15 min and then rest for 15 min. The total time of each trial was two hours (four work/rest bouts) followed by an additional 30 min recovery period. A number of variables were measured, but we will focus on the sodium concentrations. One limitation of this study for our purposes here is that it was performed in older adults, and there is a well-documented effect of age on the thirst mechanism so that as you become older you become less sensitive to thirst. That is, your plasma osmolality rises higher before thirst kicks in.

According to the authors, their main findings were (and we quote):

1. When cool palatable fluids were readily available, active adults aged 54–70 yr drank enough to match sweating rates and maintain their body mass;
2. Their fluid intake behavior was repeatable;
   
3. CES [note: Gatorade] promoted greater voluntary fluid intake and restored PV losses faster than water;
   
4. There were sex differences in the fluid intake behavior of older active adults, with women drinking more water per kilogram of BM than men

As we tried to explain in many of our prior posts, the ingestion of any hypotonic fluid in excess of thirst will cause a fall in the sodium concentration. In this case "in excess" means drinking more than to your thirst. This occurs even though sports drinks contain some sodium because they still have much less when compared to the body fluids. Therefore the end result is a fall in sodium concentration. The data from this study show that these older adults, even when drinking to thirst, experience a fall in sodium concentration when ingesting water or Gatorade:


What we see is the time on the x-axis and the sodium concentration on the y-axis. The black dots represent the Gatorade trial, and the white (open) dots represent the water trial. All the subjects started with a sodium concentration of 142 mM per Liter, and in both trials the average concentration fell over time to approximately 139-140. There were no differences between the groups, and the symbols you see on the graph means that those values are significantly (statistically) different from the baseline value. So water and Gatorade ingestion produced a similar effect, and so Gatorade did not prevent a fall in sodium concentration in these subjects.

However one female subject ingested 2.8 L of water and 2.7 L of Gatorade in the respective trials. She gained weight in both instances, indicating an excessive fluid ingestion, and here are the data that support the conclusion that ingesting Gatorade will not prevent hyponatremia:


The problem is that the authors herald this as proof that ingesting Gatorade is much better than water:

"Furthermore, this woman’s data support the notion that a CES [Gatorade] is superior to water in limiting reductions in serum sodium during exercise-heat stress. During the CES trial, this female subject consumed 2.7 L and had a final serum sodium of 131 mmol per L . Therefore, although she consumed similar amounts of CES and water, serum sodium was maintained above that of symptomatic hyponatremia during the CES trial."

While the authors are entitled to their interpretation of the data, we disagree and conclude that both fluids are producing a steady fall in sodium concentration, and that the 131 value in the Gatorade trial is just marginally outside the symptomatic range (< style="font-weight: bold;">ingesting either water or Gatorade produced a nearly identical fall (~2-3 mmol) in the sodium concentration.

The take-home part: Sports drinks do not prevent hyponatremia

In fact Jonathan tried to apply this finding to a more "real world" situation in a letter to the British Journal of Sports Medicine. In that letter he argued that since the mean finishing time of women marathoners in America is five hours, and if the ingestion of Gatorade at rates similar to those found in the study is advocated by races, coaches, scientist, etc., then there would likely be many women (and probably men, too) presenting with hyponatremia. These data demonstrate that sports drinks do not prevent this condition as their ingestion in these subjects and at these rates causes a fall in sodium concentration.

Again one limitation to this study is it was done on older subjects, who are less sensitive to thirst, and what we might see in younger subjects would be a slight rise in sodium concentration when ingesting Gatorade and a maintenance of sodium concentration when ingesting water. The evidence for that statement comes from a 1992 study by Robert Cade, the inventor of Gatorade who incidentally died this week at the age of 80. In that study three groups of runners completed a marathon. One ingested Gatorade, another "half-Gatorade" (50% water, 50% Gatorade), and the third group water:

So in fact ingesting Gatorade to thirst in younger subjects results in a rise in sodium concentration, which is why you drink more---you never lower your osmolality below the thirst threshold and therefore are thirstier when ingesting a sports drink, whereas with water you maintain the osmolality right around the thirst threshold and drink and abstain as your thirst comes and goes. With sports drinks you instead just get thirstier, which seems kind of ironic since their slogan is "The thirst quencher!"

So those are some of the data that support our conclusions, and we hope that helps to clarify some of our interpretation(s) and conclusions. We will still post a "wrap-up" for the series on cramping in which we will try to briefly summarize the main points but more importantly leave you with some practical advice on this complex topic!

Sports drinks, sweat and electrolytes

A look at sweating, drinking and the role of electrolytes in sports drinks

Today is a pseudo-Part V of our series on Muscle Cramps - I was tempted to call it Part V, but it's a little bit of a departure from what we've been talking about. In our next post, which we will be calling Part V, we'll wrap up this really challenging series and try to summarize all your comments and our posting into one post.

But today, we build on the arguments from yesterday. In yesterday's post, we looked at how hypothesis creation in science must be evaluated with observation, and if the measurement or observation contradicts or fails to agree with the hypothesis, then the theory requires revision!

Well, today, we want to apply that analogy to the issue of fluid and electrolyte replacements. It's an issue that we've touched on before, and even dedicated a post to, but it comes up so often in comments and questions, that we thought we should dedicate another post to it, and throw out some real figures, to prove a point.

So today's post looks at two key concepts:

1. Are low sodium levels the result of a LOSS OF SODIUM in sweat, or is it the result of excessive fluid intake?
2. How much difference would it make to drink sports drinks that contain electrolytes? After all, they tell you that they "replace the vital salt your body loses during exercise, which can contribute to hyponatremia and cramp" (ala the marketing and promotional material of those sports drink companies!)

Let's tackle that issue, with the aid of a regular runner - we'll call him Randy.

Some assumptions we must make about Randy

In order to do these calculations, we have to make some assumptions about our imaginary runner:

• The first, and most important assumption, is that we will have to treat Randy somewhat 'non-homeostatically'. I cannot stress just how important it is that we recognize that during exercise, the body is a finely tuned system, and is able to call on a number of different strategies for regulating its internal situation (this is called homeostasis). This is why we often measure things that are not predicted by equations - there are simply too many variables to factor in. For example, we often find that people do over drink, but they manage to regulate their body's sodium levels - this happens because they have other sources of sodium - hormonal regulation, renal function, and maybe even release of sodium from bone!

The point is that we have to look at the body a little bit "coldly" in order to evaluate these arguments - when we consider what is actually happening, then it becomes EVEN MORE APPARENT that the supposed failures and problems like dehydration and cramps are unlikely to happen! In other words, we will present a number of scenarios where Randy would run into trouble. In reality, that would not even happen, because the body is so well regulated.

• We must assume body weight - we have assumed that Randy weighs in at about 70 kg. This means that his total EXTRACELLULAR FLUID VOLUME is 17 L.

• We also assume that Randy is what Gatorade would call a "salty sweater" - this is someone who has higher than normal sodium levels in their sweat. Gatorade themselves can't define exactly what this means, but we've assumed that Randy's sweat has a sodium concentration of 100mM. Note that a fit, well-acclimatized person probably has sodium concentrations of about 20 mM, so Randy really is a "salty sweater"!

• We also assume that Randy runs for two hours, during which time he sweats at a rate of 1 L per hour (so Randy is running at moderate speed, hence the high sweat rate).
  

Now, let's take a look at some of the possible outcomes....

Scenario 1 - Randy does not drink at all

In this scenario, shown in the table below, we assume that Randy does not drink at all during his two-hour session. He therefore loses both sodium and water - 2 L of water to be exact, and given his very salty sweat, a total of 200mmoles of sodium (a mmol is a unit for measurement of amount, by the way - for ease of comparison, I've included the mass of sodium in grams as well)



As you will see, Randy's sweat, despite the fact that it's much saltier than most people's, is still very low on sodium compared to his starting sodium concentration (which was 140mM). As a result, his sweat is HYPOTONIC, and the end result is that his sodium concentration GOES UP - it ends at 145mM. Note that it is normal, though on the high side. In fact, when we analysed Comrades runners during our research studies in 2005 and 2006, we found that most runners finished the race with a sodium level between 140 and 145mM, and they were fine. So this scenario is actually pretty good!

Note here that in a "homeostatic system", Randy would simply become thirsty, and therefore drink - this would bring his sodium levels back down, even closer to the starting value. But that's what we look at in our next scenario...

Scenario 2 - Randy drinks WATER, and replaces 50% of his sweat losses

The table below shows the predictions for what would happen if Randy drank 500ml per hour - this is a reasonable rate for someone who drinks to thirst, though it does depend on the conditions.

What you see from this table is that now, the sodium concentration will still be in the normal range of 135 to 145mM. Note that this scenario is again IDEAL - his sodium level is in the normal range, he's been drinking to thirst (approximately) and his physiological situation is 100% normal. In fact, the ideal and most common scenario in reality is probably somewhere between Scenario 1 and Scenario 2 - about 30% to 50% of sweat losses replaced would see you finishing in a "normal" range.

Scenario 3 - Randy drinks WATER, and replaces 100% of his sweat losses

The next scenario we consider is that Randy follows Gatorade's advice to the milliliter and drinks TO REPLACE HIS SWEAT LOSSES EXACTLY. In order to do this, he weighs himself dilligently, works out that he is going to sweat at 1L per hour, and so he drinks 1 L per hour too. The table below shows the predicted changes:

You will notice from the last line of the table that Randy is now HYPONATRAEMIC - his sodium levels have fallen below 130 mM. This is usually going to land Randy up in the medical tent and could even have fatal consequences - people have differing sensitivities to a fall in sodium, but a value of 129 mM would be consider dangerously low.

Quite apart from this, Randy has managed to drink 2 L in two hours, and so depending on how quickly he was running, he might feel very ill just from the strain of drinking that much - I would challenge you to drink this much, unless you are running fairly slowly and it's a hot day!

Therefore, two things can be noted from these examples:

1. Sweating causes some sodium loss, but because the sodium content of sweat is so low relative to body fluids, your sodium concentration will rise. And it is the concentration that is important, since this controls fluid shifts in the body. It is NOT possible, even for a "salty sweater" like Randy in these scenarios, to LOSE sodium through sweat.
2. Rather, we have demonstrated that the only possibly theoretical way that the sodium level can fall is if Randy drinks too much. If he drinks more than he sweats, then he will really be in a lot of troube. For example, if Randy took Gatorade's earlier advice and drank 40 Oz per hour (1.2 L), then his sodium levels would fall to 125mM - OVERDRINKING can be FATAL.

Now, some of you may be wondering what would happen if Randy drank SPORTS DRINKS instead of plain water? The theory (and the marketing by the sports drink companies) will tell you that the sports drinks are critical because they contain sodium, which replaces what you lose. Let's look at these scenarios....

Scenario 4 - Randy drinks A SPORTS DRINK, and replaces 50% of his sweat losses

The first point we have to make is that Gatorade has a sodium concentration of 18mM - this is only 13% of what the body fluid concentration is, and only 18% of the sodium concentration of the sweat in our examples. It does not take a mathematician to work out that you cannot replace the losses if your replacement fluid is different from the original! But let's play with the numbers and see.

First, we consider what might happen (in theory, remember), if Randy replaces 50% of his sweat losses with Gatorade:


So, what this table shows is that Randy sweats out 2L in his run, and loses 200mmol of sodium. However, because he is putting some of those electrolytes back, his overall sodium loss is 182 mmol - this equates to about 4.2g of sodium.

You may recall from scenario 2 that if he drank just water, his sodium loss would have been 4.6g - the difference is therefore 0.4 grams! When you consider the volume of 17L that this is going into, then you begin to realise that the sports drinks are making a tiny, tiny difference to the body's sodium concentration! In fact, the difference is only about 1mM - Randy's sodium level would have been 136.4 mM with plain water, and it's predicted as 137.4mM on sports drinks!

That difference is absolutely minimal - in fact, it's negligible. A few people wrote in wondering whether a 1 or 2mM difference might be important - I can assure you that it's not. If it were, then in the time you have taken to read this, you would have seen your sodium levels shift by this "critical" amount! So the bottom line - sports drinks simply DO NOT help prevent the fall in sodium levels caused by potential overdrinking.

Scenario 5 - Randy drinks A SPORTS DRINK, and replaces 100% of his sweat losses

For our final scenario, consider what happens if Randy now drinks to replace all his sweat losses, but he drinks sports drinks instead of water. You may recall from scenario 3 that if he drank only water, his sodium level would be predicted to fall to 128.6mM - a level associated with hyponatremia.


The table above shows that if he drinks sports drinks, then his sodium level will fall to 130.6 mM - this is a difference of 2mM compared to drinking only water.

Again, this is a minimal, and negligible difference - the fact of the matter is that whether Randy drinks water or sports drinks, he still becomes hyponatraemic and could be running the risk of death as a result. Again, I have to emphasize - this difference of 2mM is insignificant - both final values are dangerously low, regardless of what he drank during exercise - and this was only in a two-hour run!

To illustrate this, if Randy ran a full marathon and took 4 hours, following this same pattern of drinking to replace all his sweat losses with a sports drink, then his final sodium concentration would be 121 mM - he would almost certainly end up in hospital. Why? Because he drinks too much of a sports drink that is hypotonic and unable to defend the body's sodium concentration.

So what is Randy to do? What is the best strategy?

So, having run through these five scenarios, I hope it's quite apparent that if your sodium level drops, it is NOT because you are losing salt, it's because you are over-drinking! I hope it is equally apparent that drinking a sports drink does nothing to change this situation.

So what to do? For our imaginary runner, the answer would seem quite obvious - don't overdrink! That only seems obvious because we get ourselves into terrible states of confusion by talking about what overdrinking means, and should we also supplement with salt?

The reality is that most people will finish exercise with a normal or slightly elevated sodium concentration - this is in fact the normal, and desired response. In otherwords, of the scenarios we have looked at here, the "ideal" probably lies somewhere between not drinking, and drinking about 50% of fluid losses. If you do this when you exercise, your sodium level will not change substantially - it will be neither too high or too low.

But let's simplify this as much as possible - ALL YOU NEED TO DO IS LISTEN TO YOUR BODY AND YOU WILL BE FINE. In otherwords:

• If you are thirsty, then drink!
• If you are not thirsty, then don't drink!
• Don't waste money on salt tablets - you don't need them!

Because we're too stupid to think for ourselves

The problem that we (as a sports community) find ourselves in today, with this huge confusion, is the result of allowing ourselves to be treated as stupid. Yes, that's right - the companies that sell sports drinks think that you are too stupid to drink when you should, and that your body is too stupid to realise when it needs salt! Our species learned how to make fire, put a man on the moon, and created a communication system that allows you in Colorado (or wherever you are in the world) to read the words I am typing in Cape Town! But when it comes to drinking - we're just not capable! Surely that doesn't make sense!

The reality is that your body is designed perfectly to regulate its internal environment unless you have some disease or potentially critical problem (being lost in the desert without food or water for a week is one that springs to mind!). Yet for some reason, every animal in the animal kingdom EXCEPT for humans is able to drink when they need to, eat the right foods and get the right nutrients when they need to!

So forget the salt tablets, forget trying to work out what you need to eat and drink when you exercise, and just listen! Your body knows better!

Conclusion

In this post, we've tried to illustrate some of the theoretically possible outcomes when you drink plain water during exercise compared to drinking sports drinks, which contain electrolytes.

What we have shown is that the electrolytes in sports drinks make a very tiny difference - not enough to prevent hyponatremia from developing and certainly not enough to back up the marketing claims made by the companies who tell you that you NEED the electrolytes.

We have used these mathematical scenarios to illustrate the theoretical point - I just want to point out again that in reality, when you do drink water and sports drinks, your body makes adjustments that prevent your sodium level from falling (up to a point - eventually, your poor physiology would be over-stressed and you would start to run into trouble!). So the reality is that even if you do make the mistake of drinking too much, your body does the best possible job of protecting you anyway.

One example of such a mechanism is that when your sodium level begins to fall, you are no longer thirsty, and the body is actually even able to release less sodium into the sweat, just so that you conserve it! It's just as well that our bodies are so 'smart', because if we did not have these regulatory mechanisms, can you imagine how many people would be in serious trouble because they did not simply listen to the body and drink to thirst?

So bottom line - drink to thirst, don't worry too much about what you drink, but just make sure you are getting enough ENERGY in - the one thing that the sports drinks provide that is required is glucose, and so plain water is unlikely to be sufficient for longer than about 2 hours of exercise.

Looking ahead - a wrap of cramping tomorrow

So that's it for today's little 'diversion' from our series. Tomorrow we will wrap up the cramp series, and put our minds to what lies ahead!

Ross