Exercise in the Cold: Part II

A physiological trip through cold water exposure

While we are all still thinking about the incredible video of Kayoko Fukushi's marathon finish, we thought we would carry on with our series on exercise in the cold. Most of us are still firmly in the depths of the northern-hemisphere winter, and so we hope you found Part I of this series relevant---it was meant to introduce some basics of heat loss and temperature regulation, and also look at some of extreme stories such as the runner who "won" an ultra-marathon by being the only one to complete the race in below-freezing temps. The price of victory? Losing two toes!

Water vs. air exposure

In tackling this series on exercise in the cold, we differentiate between cold AIR and cold WATER exposure - the key difference is that the heat LOSSES in water are so much greater than on land, that you're far less likely to develop any kind of hypothermia (low body temperature) on land. In fact, water conducts heat about 25 times better than air. So when water moves across your skin you will lose heat more quickly compared to air simply because of its physical properties.

As as we said in Part I, the key to managing exercise on land is simply through appropriate clothing. But the introduction of some water to the mix ('Just add water') makes the situation far more complex and challenging and that's what we'll tackle today!

Too much heat to cool down - why hypothermia is the least of your worries

Perhaps the first, and maybe the most surprising fact about cold water physiology, is that your body has too much heat to become hypothermic within about 30 minutes, no matter how cold the water is! In other words, it is not possible to get so cold that you're in danger unless you are in the water for more than about 30 minutes. The graph below shows this:


So from this graph, you can see that even at water temperatures of 0 degrees celsius, 30 minutes falls within the marginal zone, not the lethal zone. Many would probably survive for close to an hour - this is demonstrated by shipwreck victims, who have survived freezing water for this long.

The implication of this is that if someone is immersed in cold water, and dies, the cause of death is unlikely to be hypothermia unless that person has been exposed for a long time! Hypothermia is often wrongly blamed for death in people exposed to cold water - getting too cold is actually the least of your worries! We'll take a look at the main challenges a little later, but first, a key discussion about body composition and its effect on your ability in the cold.

Lessons from English Channel swimming

Perhaps the best forum in which to examine the physiology of cold-water swimming and immersion is English Channel swimming. The great British Exercise Physiologist Lawrence Griffiths Pugh performed a series studies in this area on the channel swimmer Jason Zirganos. Zirganos died from exposure to cold water while attempting to cross the Irish Channel, but his legacy was to leave behind a solid understanding of cold-water physiology.

The importance of body fat - 'fatter = warmer'!

The first important point about cold-water exposure is that body composition has a profound effect on core temperature during immersion. Pugh demonstrated this when he compared himself---the scrawny scientist type---to Zirganos, the chubby cold-water swimmer type. When just sitting in 16 C water the rectal temperature of both men fell, but after approximately 80 min Zirganos was sitting a full one degree higher than Pugh. The more dramatic difference was when swimming in the same water, though. Zirganos was able to maintain his temperature at around 38 C for nearly two hours while Pugh's temperature began to plummet after just 30 min until he exited the water after about 70 min, when his temperature was less than 34 C.

This early research from the 1950's pioneered this area of physiology, and today we have a substantial body of evidence that demonstrates both the effects of cold-water immersion and how we adapt to this stress.

The cold-shock response - the biggest challenge to survival in the cold

One of the first things you experience when submerging yourself in cold water is something called the "cold-shock response." This is characterized by an uncontrollable gasp for air, followed by a prolonged period of hyperventilation - more rapid breathing. In fact, this response is one of the most likely causes of death in most cold-water immersions such as when one falls out of a boat into icy water. It's not difficult to see that if the timing of that "gasp" is slightly wrong, you'll take in a huge lungful of air, and one or two gasps while underwater is all it takes to drown.

The other big 'killer' is a heart attack, which can result when the temperature of the blood returning to the heart is suddenly cooled - this can affect the electrical conduction within the heart, causing fibrillation. So it is these two possibilities - drowning and cardiac arrest that are most likely the cause of death. However, as we said, most times, people blame hypothermia for death, when in fact the body temperature does not need to fall for an unlucky 'swimmer' to perish in the cold.

Swimming in the cold - a problem of breathing and muscle weakness

Once you've overcome that problem, however, the next thing to worry about is swimming. And again, the hyperventilation that happens in the cold has a profound effect on the ability to swim in an efficient manner. The graph below, from a paper published by Eglin and Tipton in 2005 (EJAP) shows the breathing response of a swimmer exposed to cold water. It shows the BREATHING RATE in breaths per minute against time in a person who stands in a cold shower at 10 C.


So the rate of breathing goes up from about 16 breaths per minute to 75 breaths per minute, within the first 20 seconds. It then stays up at 40 breaths per minute for the next few minutes. It is not difficult to see how that would affect your ability to swim, because your stroke rate would have to change substantially to allow you just to breathe!

Next problem - the "DiCaprio" problem - a cold muscle, and cold skin, equal a weak muscle

The next problem is equally significant - when the muscle and the skin are cooled, the muscle becomes weaker! So the cold water on the skin will make a powerful swimmer incapable of swimming, simply because his skin is cooled. There is evidence from studies that shows that the ability of the muscle to produce force is as much as 25% lower immediately after exposure to water at 10 degrees celsius - this would only drop in even colder water. Then we add to that the fact that as you get cold, your body's natural response is to shiver. But when you shiver, your co-ordination is affected, making it even more difficult to swim!

This obviously has profound implications on ability to swim. And for all those who watched in despair as the character played by Leonardo DiCaprio could not swim to safety in the movie Titanic, you now have a physiological explanation - he simply could not swim, because his skin and muscles were too cold to contract normally! (Far be it for us to suggest that Hollywood portrayed that accurately!). The principle remains, however - a good swimmer in warm water will be an average swimmer in the cold. And a weak swimmer in the warm...well, that's a recipe for trouble.

The good news - adapting the cold shock response

So that is the bad news. . .but the good news is that humans are adaptable organisms, and just like we make adaptations to things like marathon training, we also make adaptations to stressors such as cold-water immersion. The data show that exposures to cold water as short as three minutes in a 10 C shower will attenuate the cold-shock response by as much as 20-30%. In the graph below, you can see the same data we showed above (Eglin and Tipton, 2005, EJAP), but this time, we've added in a comparison with the breathing rate AFTER six 3-minute long exposures to the cold water.

So you can see that only six exposures is enough to reduce the cold shock response by 20%. If you have even longer exposures, you can bring it down by 50%. That is obviously a significant reduction, and the implication is that swimming will be far easier if you are simply adapted to the cold.

The second important adaptation has to do with blood flow and heat loss. When at rest your muscle tissue actually acts as in insulator. This changes when you exercise because now you are pumping lots of blood to the working muscles, and it is the blood that transports heat around the body. Therefore when you start to swim in cold water you send more blood to the muscles, and all this does is increase your heat losses as now the blood----and the heat it contains----it close to the surface of the body and the cold-water. Since water conducts heat very well, the heat from your body readily moves to the water. . .and the consequence of this is a decrease in core temperature even though you are producing some heat with your muscle contractions.

Decreases in sh-sh-sh-shivering

Another big change that occurs with repeated cold-water exposures is that we lower our "shivering threshold," or the temperature at which we begin to shiver. The bonus of with shivering is that we produce heat as our muscles are contracting, although involuntarily. The bad news is that when trying to perform a complex movement such as swimming (or any dynamic activity), shivering can really foul things up. So we adapt by lowering the temperature at which we begin to shiver, and the result is that you can swim for longer before being hampered by shaking limbs and uncontrolled movements.

Evidence for non-shivering thermogenesis?

Finally, there is evidence that humans actually increase their core temperature either acutely or chronically in response to repeated cold-water exposures. The net effect of this response is that they can then remain in a cold environment for much longer before suffering any detrimental effects of the exposure, such as decreased nerve conduction velocity and then shivering (and a loss of coordination as a result of that shivering). Simply put, they have more heat in their bodies, and together with the other adaptations we mentioned above it means they reach a critically low temperature much later than someone who is not adapted to the cold.

So the take-home message here is that cold-water exposure is just like any other "stressor" or training stimulus. Our physiological response to these stimuli is to make adaptations that allow us to cope better with the , which in this case is cold-water immersion.

That wraps up Part II of this series, but stay tuned for Part III, when we will examine how the cold actually affects exercise performance!

Amazing marathon video

Kayoko Fukushi's debut - an amazing video of what happens when the marathon goes wrong

In our most recent post, we looked at some really interesting stories from the indoor athletics and tennis worlds.

But here's one that I felt should be added to this, and it includes a video which I found through the Let's Run website (great source of news).

The story, and the video, come from the Osaka Marathon over the past weekend. The full story of the race can be read here.

But the real story, from our point of view, anyway, was that of a Japanese runner, Kayoko Fukushi, making her debut in the marathon event.

Fukushi is Japan's national record holder over 3000m, 5000m and the half-marathon. Considering how many brilliant female athletes Japan has produced in the marathon, when one of their runners with such speed over the shorter distances steps up to the marathon, it is bound to cause a stir.

And so, at the Osaka Marathon, Fukushi lined up for her first marathon knowing that no Japanese woman had ever run faster than her over the half-marathon - a great source of confidence, no doubt.

But too fast too soon, and the price is paid

Perhaps a little too much confidence, in hindsight, because Fukushi set out at a pace of sub-2:20, leaving the entire field behind from the very first kilometer! According to reports, she ran about 3:20/km for the first 25km - just about on pace for 2:20. But by 32km, she had slowed substantially, run 3:42 for that kilometer. The rest of the field caught and passed her at about the 35km mark - she lost a lead of about 4 minutes within about 5 km! So the wheels had really come off.

Just how much did they come off? Well, take a look at this video (available also on YouTube), and you'll see her final kilometer, complete with frantic and excitable Japanese commentary, and a very enthusiastic crowd - it's quite an entertaining package and a courageous run, which we describe a little more below. The video is just under four minutes long.

Fukushi enters the stadium, falls flat on her face, stands up and soldiers bravely on. I timed her final 300m at 2 minutes and 21 seconds - a pace of 7:50/km! That includes two falls in the final 200m.

For more insight into this pacing strategy, the graph below shows the pace per 5km interval during her race. The blue line represents her pace (in min/km), and the maroon blocks are added to give an indication of the pace - they project a 10km time based on each 5km interval.


What is interesting as an observation is that she's not showing any mental symptoms like confusion (though she is smiling, which some would possibly say is a mental sign considering her physical state!). One of the main symptoms of hypoglycemia (running out of glycogen and hence your blood sugar levels fall) is deliriousness and confusion. Fukushi is running in a straight line (albeit slowly), at least. It's quite apparent that her physiology has basically shut down - she could not pick up the pace even if she wanted to. It would be really interesting to speculate just what percentage of her total muscle she's actually using. Is she using ALL the muscle? It hardly seems like. Rather, it looks as though something has put a brake on her running speed. This "central fatigue", characterised by poor co-ordination (she falls over repeatedly) and often, confusion (not apparent here) was recognised by scientists as a key indication that the fatigue was NOT simply in the muscles, but also in the brain.

It's also an illustration of just how badly things can go wrong if the early pace is too ambitious. Having reached half-way in 1:10.32, Fukushi covered the second half in 1:30.32! That's still a pretty respectable half-marathon time for many people, no doubt! It's all relative of course...

But then Fukushi's final 7.2km took her 40:25 (pace of 5:37/km), and her final 2.2 km was run at an average of 7:06/km, and includes that section from the video above! A courageous run by Fukushi, no doubt. One really interesting thing to debate is whether this is an "intelligent" act to continue. Just how much do the final 10km take out of her? Is there a chance that this effort will affect her future marathon running performances? Of course, it's just as easy to argue that she'll be stronger for it, and back for that 2:20 some day! Again, time will tell...

The moral of the story - patience, aim rather run a negative split, especially in your first marathon, and remember, you might pay heavily for a fast early pace!

Cheers
Ross

Sports news - athletics and tennis

Signals of intent for the athletics season and a Grand Slam without Federer down under

Just a quick filler news article today, to comment on some very interesting sports performances from the past weekend. First, we look at some results from the distance races at the Reebok Indoor Athletics meeting from Boston - Ethiopian women in fine form and Craig Mottram signalling his intent for 2008.

Then we look briefly at the Men's final of the first Grand Slam of 2008, the Australian Open. As from tomorrow, we'll resume our series on Exercise in the cold.

Craig Mottram - sign of things to come?

Last year, heading into Osaka, we (and others) picked Craig Mottram's battle with the East Africans in the 5000m final as one of the possible highlights of the Championships. How wrong we were! Mottram never featured, eventually finishing 13th out of 14 runners, in what was the slowest 5000m race in the history of the IAAF World Champs. So having begun the season with great promise, Mottram failed on the biggest occasion. In the aftermath, it emerged that Mottram had been struggling with a hamstring injury, which curtailed his training leading up to the race.

Well, 2008 has begun much the same was as 2007 did - Mottram looking mighty impressive. In Boston, he ran the fastest time ever on American soil for an indoor 3000m - 7:34.50. He won the race going away, with a final 400m of 59 seconds. The time is only 2 seconds slower than Mottram's best ever OUTDOOR 3000m performance, and given that indoors, the time is expected to be 3 or more seconds slower, Mottram is clearly in great shape.

So what will be interesting to see in the next few months is whether he is able to remain injury free and whether he can sustain the level of performance all the way through to August. In terms of the injury, Mottram has said that he's not travelling full-time with a physio, specifically to work on the risk of injury.

In terms of performance, things might be a little trickier. With six months to go until Beijing, Mottram will need to maintain his current form through the indoor season, and then on the tracks of Europe, which will be a tough task. He's clearly got great speed right now - to have speed sufficient for a PB at a shorter distance like 3000m indicates that at some stage in the next six months, he'll have to pull back and reassess before sharpening again for Beijing - a tricky task. It might require very frugal racing in Europe, perhaps even none until about July. Mottram enjoys racing though, and so to maintain good speed all the way to August will be very tough. But hopefully he's got the timing right and will be in his best shape to mix it with the Africans come Beijing.

The Ethiopian women - dominant distance running performances

Meseret Defar and Turinesh Dibaba are only 24 and 22 years old, respectively. But they are well on the way to being the best middle and long distance athletes in history. Dibaba has four world track and four World Cross Country titles, and Defar was the Women's World Athlete of the Year in 2007, is an Olympic and World Champion, and makes a habit of breaking world records by seconds.

And this past weekend, Defar added another to her collection. Admittedly, it was a soft record - the women's 2 mile record. The old time was held by Regina Jacobs, at 9:23. Defar cleaved 13 seconds off it with her winning time of 9:10.50 - that's how soft it was! But the performance was still remarkable. The halfway point was reached in 4:38.4, which means the second mile was covered in 4:32! This suggests there is more to come, for a negative split this large is not optimal in this length of event. Not that Defar will get the opportunity soon - the 2 mile is too rarely run. But that kind of sustained speed over the second half suggests that a 3000m time very close to 8:20 later on this year, and her 5000m PB of 14:16 (the World Record) may also be under threat this year.

Unfortunately for us, it does not look as though the race with Turinesh Dibaba will happen any time soon. In Boston, we had the bizarre scenario where Defar ran 2-Miles and Dibaba ran the 3000m - basically, the same race. So it does provide a nice comparison, but would have been far more exciting to see them race head to head. That was denied to us last year in Osaka, after Dibaba withdrew from the 5000m after winning the 10000m title. And it seems unlikely that they will race again in Beijing, since Dibaba will surely focus on the 10000m event, and with the heat, it's unlikely she'll have the appetite for two 5000m races after.

In any event, Dibaba was an impressive, not spectacular winner of the 3000m race. Her time was 8:33.37. Quite a nice comparison is possible by looking at the time taken to cover the second half of the race - Dibaba reached 1 mile in 4:36.1, which means the final 1400m was covered in 3:57.2 (give or take a few meters). Defar's final mile of 4:32 equates to a 1400m pace of 3:56.7. So they are seemingly as inseparable as ever.

Of course, this comparison is somewhat shaky, and that's why the best solution would be to have them race one another. Unfortunately for the sport, this kind of situation often develops, where two high-profile athletes avoid one another for all but one or two races per year, if that. We had Powell vs. Gay (on, off, on and off again), and numerous others in the past. One can't blame the athletes for not wanting to race unless the right "carrot" is offered, but it certainly would give the sport a boost to have a great head-to-head contest for meeting promoters to hype up and promote.

Tennis action - new faces and new prospects

Moving onto tennis, and exciting times for the men's game. For the last four years, Roger Federer has so dominated the tennis world that everyone else in the Grand Slams was vying for the title of runner-up. With the exception, that is, of the French Open, where they were all hoping for a semi-final, right before Rafael Nadal disposed of them on the red clay!

And a month ago, we looked into our crystal ball and predicted more great Federer-Nadal contests. Well, the year's first Grand Slam is over, and amazingly, neither of these two even made the final, let alone against one another!

Instead, it was Novak Djokovic and Jo-Wilfried Tsonga who fought out an absorbing, if error ridden contest. In the end, Djokovic won in four sets, and claimed his first Grand Slam title. That after disposing of Federer in the semi-final. Tsonga, for his part, destroyed Nadal and if he can keep up his level of play, then 2008 promises at least four awesome performers, and that does not include a number of other prospects.

On the note of Djokovic, I was a big fan of his before this tournament, but what I have seen in the final week has only undermined that opinion. Djokovic comes across as petulant, supported by his family of four cheering him on with T-shirts emblazaned with letters spelling out N-O-L-E, which I'm told is his nickname.

But in yesterday's final, and in the match against Federer as well at times during previous games, Djokovic displays a petulant arrogance, even going so far as to shout and gesture aggressively towards fans. At one point during the final, someone in the crowd shouted "Stop" when Djokovic bounced the ball about 15 times before serving (Djokovic has this very annoying ball bounce routine, which has seen opponents complain to umpires, including in the final). In response, Djokovic angrily told the umpire to ask for quite (still acceptable). And then on winning the subsequent point, Djokovic first gestured aggressively to his family, and then turned specifically in the direction of the unruly fan and gave a very angry fist-pump, shouting something at him. It was a taunt more worthy of a drunken soccer fan, not a soon-to-be Grand Slam champion.

This kind of behaviour leaves a bad taste in the mouth, and it was not the first time. On many occasions, on winning a competitive point, Djokovic pumps his fist for the fans' benefit, posturing and preening, almost expecting their adulation. Unfortunately, in this final, he didn't get it - instead, Tsonga, who is all heart and spirit, was the fans' favourite. And whether this unsettled Djokovic, I don't know. But it seems quite clear that he has an attitude of disrespect towards the fan - yes, they are wrong to shout out as he's about to serve, but a great champion recognizes that the bad must be taken along with the good, and is gracious and humble enough to roll with these 'blows'. Instead, Djokovic shouts at fans to 'shut up', gestures angrily towards those who don't support him, and postures like a prize-fighter or WWE wrestler waiting for the respect and admiration.

Perhaps he can take a lesson from the man he beat in the semi-final, for Roger Federer has dominated with humility. Djokovic, on the other hand, is a new kid on the block, and has displayed little of the respect that Federer clearly has.

And sadly, it would be wishful thinking to suggest that Djokovic's support group and family will advise him in this regard, for it would seem that they encourage it. I have often seen people wearing T-shirts with slogans or letters that spell out the name of their favourite player. Usually it's the fans. But when the family of the player resort to that, I have to wonder. At one point early in the tournament, one of the four family members (it's him father, mother and two brothers) failed to stand up and cheer - the result was that their shirts spelled N-O- -E, rather than the intended N-O-L-E. In response, his mother turned and gestured rather angrily to her son to stand up, as he clearly wasn't doing his bit. Well, that seems somewhat unhealthy to me.

And in a world of tennis, where the parents of the players often court controversy and negative press more than the players (think of Pierce, Sharapov and Dokic), I'd prefer to see Djokovic just play tennis, rather than perpetuate this rather perverse affinity to a family that is only spurring on a WWE wrestling attitude on court. If any sports psychologists are reading this, please do weigh in and give your take on this behaviour that seems especially typical of tennis players...

Nevertheless, it's great for the game that Djokovic, and hopefully Tsonga, are so competitive, beating Federer and Nadal. It makes for a fascinating 2008, and a mockery of our crystal ball!

The week ahead

So that's it for the Weekend Sports wrap. This coming week, we'll get the series on Exercise in the cold moving. So do join us then!

Ross

Exercise in the Cold: Part I

Introduction to HYPOthermia and survival in the cold

As promised (a while back, admittedly), today we kick off a series on exercise in the cold. A challenging one to write, mostly because most of you reading this will (hopefully) never be exposed to conditions that are so extreme that your physiology is challenged to the point where it can't cope. Because most of you reading this are runners or cyclists, and it's only when you get into the water that a potentially lethal drop in body temperature is a real possibility. For the most part, exercise in the cold on land is limited by sensation and perceptions, which are of course controlled by wearing appropriate clothing. The biggest dangers of exercise in the cold on LAND? Frost-bite and other medical conditions, and not actually hypothermia.

But, there are still some fascinating studies and insights into exercise in the cold, and it is one of the most amazing areas of physiology to discuss. As I mentioned yesterday, Jonathan and I both worked with the polar swimmer Lewis Pugh when he prepared to swim 1km in the Arctic Ocean in 2005. Jonathan subsequently worked on his trip to the Antarctic as well. So we have a tendency towards COLD WATER physiology, which will make up the first couple of posts. Then we'll move onto the studies of running, cycling and muscle function during cycling and running.

So bear with us as we move through the series in a few parts:

1. How cold is cold? What are the limits to survival in the cold? Some stories of cold exposure in sport
   
2. The physiological responses to cold water immersion
3. The effects of cold temperatures on performance during swimming, cycling and running
4. Practical recommendations and insights

To begin with, how cold is "cold"?

In terms of body temperature, let's begin with a few basics - your body temperature as you read this is somewhere between 36 and 38 degrees - most textbooks will tell you 37 degrees celsius (or 98.6 Farenheit). As with exercise in the heat, the regulation of body temperature within a fairly narrow range is critical, not only for performance, but for health and survival. When we exercise, the body temperature very quickly rises to about 39 degrees celsius - one of the most remarkable questions in physiology, in my opinion, is why the body would allow this when it has the ability to lose the heat? It can reach 40 degrees celsius with few ill-effects, as found by numerous studies by the Danish group of Nielsen and Nybo.

The body regulates this temperature in a number of different ways. When we wrote about heat, we spoke of sweating, sending blood to the skin etc. In the cold, the opposite happens - you shift blood away from the skin, you shiver and release hormones that help keep the temperature up. The body is naturally insulated by skin, muscle and fat, and it's no co-incidence that on land and in water, the lean athlete, with low body fat percentage, is likely to get colder sooner!

What determines whether hypothermia happens ON LAND?

A drop in body temperature in recreational athletes is rarely seen ON LAND, even in quite cold conditions, provided they are not forced into prolonged exposure (discussed below). Rather, the main factor predicting body temperature is metabolic rate, and so provided you are exercising, your body temperature will rise, regardless of how cold it is...up to a point.

Remember that your body temperature will only fall if you lose heat faster than you produce it. When you are exercising in cold conditions, the fact is that you're usually:

• Dressed very warmly and therefore not likely to lose heat too rapidly - in this case, your body temperature is a function of heat production; or
• Dressed very inadequately, with skin exposed, or not waterproof. In this case, you'll FEEL so cold within minutes of starting, that you're likely to be unable to run altogether. You'll turn home and get warm in no time!

The point is, the SENSATION of the cold, mediated through your skin, precedes any fall in body temperature. So, by extension, provided you have free-will (and choose to exercise it - see the story of Andrew Wells below!), you'll be able to get warm without any complications. If, however, you're unlucky enough to get caught out, either because you're underdressed, far from shelter, or forced to spend a good deal of time in the cold (injury on the run/ride, getting lost etc. - think Polar explorers!), then your physiology really will be challenged, and that's what we'll tackle in subsequent posts!

Interestingly, in water, the situation is quite different. Because as we'll see tomorrow, you actually lose MORE HEAT when you exercise in the water than when you don't! So it's in water that hypothermia becomes a real threat - hypothermia, incidentally, is a fall in body temperature below about 35 degrees celsius - by this time, you'd be shivering uncontrollably.

But for today, we'll look at survival in the cold, and just what the risks are.

Some stories of cold exposure

In 1964, during the Four Inns Walking Competition in Derbyshire, England, tragedy struck when 3 hikers died as a result of cold conditions combined with poor preparation and planning for the cold. In this race (which is described by Pugh and later Noakes), competitors set out in temperatures between 0 and 4 degrees celsius, with wind speeds of about 45km/hour.

Seven hours into the event, the first reports of hikers in distress were received. In total, three hikers died as a result of the extreme cold and wind. In an analysis of these events, the following three characteristics were common to all three deaths:

• Inadequate clothing, which was not water-proof. As a result, when it began to rain, the water, combined with the cold and wind would have meant zero insulation for the hikers
• All the hikers had low body fat percentages. This was insufficient to make up for the loss of insulation by clothing once the clothes were wet
  
• The three hikers fatigued within a few hours of starting. As a result, they were walking very slowly, often collapsing, and hence unable to keep their rates of HEAT PRODUCTION high. The hikers who survived were those who finished faster.

These three points demonstrate the principles of exercise in the cold ON LAND - make sure you're dressed well, and make sure you are not forced to stop exercise or remain exposed for any longer than is necessary (unfortunately, this is not a choice we always have!)

In marathon running - evidence of hypothermia

The story above deals with hikers, exposed to snow, rain, wind and cold for days at a time. What about marathon runners? There is some evidence of hypothermia in marathon running. And perhaps surprisingly, it doesn't take temperatures below freezing to cause this. For example, in Scotland in 1982, in the Aberdeen Marathon, temperatures were about 12 degrees celsius, it was quite windy (25 to 30km/hour), but there was no rain, and yet 4 out of 59 runners finished with temperatures lower than 37 degrees! Similarly, in South Africa in 1985, during a 56km race, a temperature of 19 degrees combined with wind and rain was enough to see 8 runners taken to the medical tent with body temperatures below 37 degrees celsius!

Once again, in these cases, the likely cause is a combination of inadequate clothing, combined with low heat production as the athlete becomes fatigued. One of the body's responses to cooling is to shiver, and use more energy in an attempt to keep your temperature up. This is hardly conducive to performance and so the exercise intensity drops and body temperature tends to fall. Also, most of the time, athletes, particularly in South Africa, would expect reasonably warm conditions - they'd dress for these conditions, wearing little more than running shorts and a vest, completely inappropriate for wet, cool conditions, once the wind starts blowing. The same would apply to cycling, perhaps even more so, since the higher air speeds move heat away from the body more rapidly.

Having been in the medical tent at the last three Comrades Marathon events (90km race), I can also testify that towards the end of the day (around 4 or 5pm), when temperatures have fallen to the low teens (not cold, by any means), many runners report to the medical tent feeling very cold, shivering uncontrollably. And a big part of it is that they are fatigued, exhausted from the preceding 80km. They walk more, which causes heat production to fall. At the same time, they are underdressed, and then unable to do two jobs at one time - provide energy for exercise and for keeping the body warm. So the athlete often pays by cooling down and feeling very cold.

More recently - a high cost for winning a race

So we've seen that on land, the biggest danger is that you'll be caught underdressed and unable to keep exercising hard enough to keep your rate of heat production up. Provided you combat these two potential problems, your risk of hypothermia is actually relatively low. However, there is still a risk of frost-bite, demonstrated as recently as this past weekend by the case of one Andrew Wells. Wells won the Frozen Otter Ultra Trek, a 64-mile trek on what is called the Ice Age Trail in the Northern Kettle Moraine State Forest.

Wells won the race not because he finished the 64 miles first, but because he was the only competitor to actually reach the fifth check-point of the race. Only two competitors reached half-way! That's how severe conditions were - it was nearly 15 degrees below freezing at times!

But Wells clearly kept warm enough to avoid the potential for hypothermia. But unfortunately, he was not as lucky when it came to frostbite. This quote comes from this news story on the race:

Wells said he never noticed the frostbite set in. "My feet were obviously frozen, so I couldn't feel them," he said. "And it was too cold to take my shoes off to check my feet. On my hands, I had mittens on, and just to take them off for 30 seconds, my hands got really cold, painful. I thought my toes were OK."

It turns out that Wells competed in only running shoes, one pair of wool socks and a pair of waterproof socks! He'll now have two toes amputated! This story demonstrates that the danger of hypothermia may be lower, but frost-bite is a real possibility. Interestingly, none of the other competitors had this problem, because most, it is reported, bailed from the race when they'd hd enough. Wells, on the other hand, pushed past the initial pain until numbness set it. So it certainly is possible to voluntarily exercise into health problems, but for most, the sensation determines the safe limit.

But the record belongs to...

However, all these stories pale into insignificance when compared to the record for LOWEST SURVIVED body temperature. This report, published in Lancet in 2000, reports the remarkable story of a skiier, who holds the distinction of record cold-survivor:

“A twenty-nine year old woman fell while skiing (18h20), and was trapped and partially submerged under a waterfall. After 7 min, emergency rescue was summoned and, after 40 min struggling in the ice water, she stopped moving. The rescue team arrived (19h39), commenced cardiopulmonary resuscitation, and transported her to Hospital…Her Tc, 14.4oC at the start of rewarming, dropped to 13.7oC (afterdrop), and then returned to near normal after 3h. She recovered to normal function…”

Remarkable survival, but I'm sure you can appreciate, a one in a million story, and most are not nearly so fortunate (she did have numerous complications requring many years of rehabilitation afterwards).

So these stories and situations are obviously what we all wish to avoid! And in our next post in this series, we'll look at what happens to the body when it's suddenly exposed to a very cold environment - we'll look specifically at water immersion.

So join us then, and in the meantime, if you're in the Northern hemisphere, remember, it's all in the clothing!

Ross