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Exercising in the Cold of Winter by Allen Lim

Posted on January 17, 2013 by Skratch Labs

So far, every time I’ve gotten on a plane this year, I’ve flown to somewhere colder than where I was previously. I started the year in Los Angeles, leaving LAX at a nice balmy 70˚F, before heading back home to Colorado where temperatures were a cold but manageable 40˚F. Unfortunately, things started really getting tough when I headed out to spend the week in Verona, Wisconsin for the Cyclocross National Championships, where we brought the Skratch Lab’s kitchen trailer to cook for racers and spectators. I knew it was going to be cold heading out, but working in 20 to 30˚F temperatures all day was a harsh reminder of all of the challenges and risks associated with exercise and exposure in sub-freezing temperatures.

While I’ve spent a large part of my career thinking about how to improve performance in hot weather conditions, the reality is that humans are extremely well suited to cope with the heat. When it gets hot, we easily and effectively redirect blood flow to help dissipate heat to the skin, we sweat to help cool that skin, we make quick hormonal adaptations that increase our ability to hold and store water, and we become more efficient at this whole process the more we are exposed to the heat. 

In stark contrast, humans have very few and fairly unsubstantial responses to the cold. Blood vessels can clamp down to help keep warm blood at the core, we might shiver to increase our metabolic rate, and for some individuals, after consistent exposure to the cold an increase in the core temp during exercise or an input of heat into the core can cause blood flow to increase to the hands and feet helping to keep the extremities warm despite the cold – something known as the “Hunter’s Reflex.”  These responses, however, do little to actually keep us from losing precious body heat. Unlike some animals, our fur is limited and we can’t just burn fat to create heat, so our only real option for preventing hypothermia or other cold weather related injuries like frostbite or exercise-induced bronchoconstriction depends on our behavior and technology.

When we exercise in the cold, we might be creating extra heat, but the combination of sweat, movement, and an increased ventilation rate can create some real problems. Ironically, one of those problems is the loss of even more heat and the risk of getting too cold once we stop exercising because of excess moisture from sweat. In fact, Eric Larssen, who we supported on his recent attempt to ride to the South Pole, faced temperatures in Antarctica that were so cold that he had to find an exercise intensity that was just hard enough to keep his bicycle moving, but easy enough that he would minimize any sweat production or risk freezing when he stopped.

That extra heat production from exercise and the ease at which we can lose that heat in the cold also puts extra strain on our fuel stores. In particular, when exercising in the cold, we preferentially rely on carbohydrate in the form of stored glycogen. A lot of that is due to an increase in our fight or flight response – activation of our sympathetic nervous system that works in the background without conscious attention to keep us charging under stress. Cold as a basic stress causes our sympathetic nervous system to light up which can cause us to waste precious energy, especially carbohydrate, making it a lot easier to bonk or hit the wall in the cold. Despite having ample fat stores available to us, once we run out of carbohydrate, we risk becoming hypoglycemic (low blood sugar). Since our nervous system and brain rely solely on glucose (i.e., sugar or carbohydrate) we can get really loopy when that happens. While becoming hypoglycemic at any temperature is bad enough, becoming hypoglycemic and hypothermic can be even worse since in and of itself, hypothermia can also lead to a host of issues like confusion, apathy, irritability, and cardiac arrhythmias. Thus, making sure we have plenty of food available, especially simple sugar, can be a lifesaver when it’s cold or when we get cold.

            This increase in sympathetic tone can also result in something known as cold diuresis. Essentially, when we’re cold or exposed to the cold we pee – a lot. As our sympathetic tone increases, it causes our blood vessels to stiffen which increases our blood pressure. At the same time, the cold causes blood vessels in our skin and periphery to constrict which drives more blood to our central blood volume further increasing blood pressure. This ultimately causes our kidneys to respond by pushing out dilute urine into our bladder and inadvertently dehydrating us even if we previously drank enough.

Another issue is that cold air is extremely dry air, which can damage our delicate lungs which function best when the air we breathe is brought up to 100% humidity and to body temperature (37.0˚C / 98.6˚F).  This is easily done at warm temperatures, but at a given relative humidity, the colder the temperature the less water the air holds. As an example, at 100% relative humidity, there is 44% less water in the air from 0˚C compared to 10˚C (5 grams of water per liter of air versus 9 grams of water per liter of air). So when people say “it’s too cold to snow” it probably is too cold to snow since the air can’t hold the moisture. The net result is that as the temperature drops, we lose more water and heat through our lungs to humidify and heat the air we breathe. Specifically, depending upon the humidity, at 0˚C (32˚F), we can lose anywhere from 20-30% more water through our lungs compared to 20˚C (68˚F), and from 40-50% more water compared to when the temperature is at 30˚C (86˚F).

At rest, when our ventilation rate is only about 5 liters of air per minute, the amount of water we lose through our lungs is fairly insignificant - about 10.5 ml of water per hour at 0˚C and 6.5 ml of water per hour at 30˚C. But this small amount can become a really big deal when we are exercising and ventilation rates can be as high as 100 to 150 liters of air per minute. At a ventilation rate of 100 liters per minute, we can lose as much as 211 ml of water in an hour at 0˚C through our lungs versus 132 ml of water in an hour at 30˚C. This difference isn’t trivial since in many cases, our lungs can’t actually keep up with this differentially and the air we breathe isn’t fully brought up to temperature and humidity in the lower airways. This can lead to inflammation, damage to our airway structure, and a higher prevalence of exercise-induced bronchoconstriction and asthma in the cold winter season – something that can be worsened by dehydration or inadequate fluid replacement in the cold.

 The question, however, is if all of this actually adds up to real dehydration in cold weather. While there are obvious risks of not getting adequate fuel and hydration in the cold and while there is a good rationale for how one might be at risk for becoming dehydrated in cold environments, there’s not too much research on hydration status in cold temperatures. This may be due to the fact that it’s not actually a problem and not something that we either worry about or study. But, that lack of attention may also be a problem in and of itself. In fact, in a recent study examining hydration status and sodium balance in a group of junior women’s soccer players in a cool environment, the players did not drink enough or consume enough sodium despite very low sweat rates (Gibson, et al. 2012). In another study, that examined water turnover and core temperature on Mt. Rainier, researchers found that hydration demands during the ascent in a group of seven novice climbers was elevated and that the climbers lost a significant amount of fluid despite not showing an elevation in core temperature (Hailes, et al. 2012). In both situations, dehydration occurred despite a lack of a heat stress and perhaps because of a lack of drive to drink due to the cold. Because, even a small amount of dehydration can hurt performance (Yoshida, et al. 2002), it stands to reason that staying focused on hydration, even in the winter, can help improve one’s performance.

With all of this in mind, it’s obviously important to first and foremost do everything you can to stay warm when temperatures are cold. For the most part, much of this comes down to our behavior – to being prepared and having the right gear if you’re planning to head out and exercise in the cold. Investing in the right clothing is obviously the first place to start – a high quality and tight wicking base next to the skin, an insulting wool over that, high loft materials for extra warmth as another layer of defense, and a final barrier to stop the wind on top. Add to that gloves, a good neck gaiter, something to cover your face and create a barrier to help maintain moisture lost through breathing, good head protection and booties to keep your feet warm.  Also, instead of putting air activated toe and hand warmers around your feet and hands, try putting them next to your chest and see if that “Hunter’s Reflex” works for you.

Beyond the right clothing, it’s just as important to focus on your food and hydration in the winter as it is anytime of the year with some subtle differences. First and foremost, realize that your need for carbohydrate at any given intensity is probably going to be higher when it’s cold. So don’t forget to eat and to bring those simple sugars outdoors with you. Next, just because you may not sense that you are losing a lot of fluid or you may not feel that you need to drink, making sure you stay on top of your hydration, especially with something warm. It’s a lot easier to keep your core temperature up from the inside out than it is from the outside in, so having an insulated bottle and keeping some warm hydration product can be a small but significant thing. This is one of the main reasons we decided to develop our Apple and Cinnamon exercise hydration drink mix. We wanted something that would taste good hot and that would remind us to bring something hot out with us that had some calories and electrolytes in it for exercising in the cold.

Finally, use common sense. Sometimes it’s best to just stay indoors and go to the gym, get on a treadmill, or ride the trainer. Be smart out there and use your head. In cold weather, it’s really our best tool.

For more on the topic, check out the references below:

Gibson, J. C., Stuart-Hill, L. A., Pethick, W., & Gaul, C. A. (2012). Hydration status and fluid and sodium balance in elite Canadian junior women’s soccer players in a cool environment. Appl Physiol Nutr Metab, 37(5), 931-937.

Hailes, W. S., Cuddy, J. S., Slivka, D. S., Hansen, K., & Ruby, B. C. (2012). Water turnover and core temperature on Mount Rainier. Wilderness Environ Med, 23(3), 255-259.

Kippelen, P., Fitch, K. D., Anderson, S. D., Bougault, V., Boulet, L. P., Rundell, K. W. et al. (2012). Respiratory health of elite athletes - preventing airway injury: a critical review. Br J Sports Med, 46(7), 471-476.

Marek, E., Volke, J., Muckenhoff, K., Platen, P., & Marek, W. (2013). Exercise in cold air and hydrogen peroxide release in exhaled breath condensate. Adv Exp Med Biol, 756, 169-177.

McMahon, J. A., & Howe, A. (2012). Cold weather issues in sideline and event management. Curr Sports Med Rep, 11(3), 135-141.

Sue-Chu, M. (2012). Winter sports athletes: long-term effects of cold air exposure. Br J Sports Med, 46(6), 397-401.

Yoshida, T., Takanishi, T., Nakai, S., Yorimoto, A., & Morimoto, T. (2002). The critical level of water deficit causing a decrease in human exercise performance: a practical field study. Eur J Appl Physiol, 87(6), 529-534.

(2011). Update: cold weather injuries, U.S. Armed Forces, July 2006-June 2011. MSMR, 18(10), 14-18.

This Week at Skratch Labs

Posted on October 25, 2012 by Skratch Labs

Well, it finally happened.  We got our first snow of the year here in Boulder and, try as I might, there’s apparently no amount of denial that can convince me that summer is not truly over. I suppose it had to happen eventually.  And while I know the colder days and longer nights will make it a bit tougher to keep putting in the miles, I’m determined to not let it stop me entirely.  Who knows, with winter coming, maybe we’ll even slow down a bit here at the offices and get a chance to catch our breath.  But if the past nine months are any indication, I probably shouldn’t count on that.

A couple folks I know for sure won’t be getting a break any time soon are our founder, Allen, and Ian, our CEO.  Allen’s been jetting around the country doing super cool stuff as per usual as you'll see below, so no rest for him, and Ian happens to be in his final semester of engineering school while also running our company, so I’m guessing there won’t be much respite in the near future for him either.  Talk about having a full plate...

Allen took a quick trip to Chicago to meet Michaela Kiersch, one of our new ambassadors earlier in the week.  He spent the day getting to know her, watching in awe as she displayed her unique version of urban “rock” climbing by conquering all sorts of structures on the south side of Chicago, and, if this was the same Allen I’ve known for twenty years, waxing philosophic about life, love and everything in between.   We’ll share more about Michaela and let her tell you her story in the months to come.  We’re all very proud to have her as one of our first ambassadors and we’re excited for you to meet her.

After that stopover in Chicago, Allen met Biju in Atlanta to help hydrate and feed the Dempsey Racing Team and their crew at the Le Petit Le Mans auto race.  They clearly passed over into the Bizarro world because Patrick was asking to take pictures with them.  Is it me or does that seem a little backwards?  

After that, Allen was off to North Carolina to consult with the gang at Joe Gibbs Racing.  And if you think auto racing is just about driving really fast in a circle, well, Al can tell you there is heck of a lot more to it than that.  The British Cycling Team has McClaren for research and development?  Fine.  We’ve got NASCAR.  Sounds nuts, right?  We’ll see.

Back at home it was business as usual for the most part.  Orders came in, orders went out.  We do our very best to get everything out the same day it comes in so you don’t have to wait any longer than necessary for your Skratch.  (Quick tip- if you can have your order shipped to a commercial address, you’ll save as much as 25% on shipping via FEDEX Ground.)   Our events manager Jon brought his new puppy, Penny, in.  She is, what’s the word I’m looking for… adorable.  We had our daily Knockout games on the basketball court out back which are typically won by order packing expert Julian and, sadly and as usual, Jason kept clobbering me at Ping Pong.  Just another day at the Skratch Labs office. 

Remember up top how I said I’m determined to not let the cold and the dark stop me from getting my miles in?  So far, so good.  I’ve been taking the long way to and from work a few days a week on my cyclocross bike. Here’s the thing about the CX bike:  Funnest. Thing. Ever.  A straight shot on the bike path would be about three miles each way, but I usually rack up between fifteen and twenty as I explore as many different routes as I can find.  Dirt trails, levees, alleys- all are fair game on the CX bike. My rule is that I never take the same way twice.  And now that I'm riding home in the dark, even the same old routes seem completely different.

And look, if Tim Johnson is going to leave his Sweet Ride (Cannondale SuperX Hi-Mod Disc!!!) at the Skratch Shop for two weeks while he’s in Europe, then I'll just have to assume it’s because he knows it’s my size.  But that’s a story for another day.  Ok, I gotta get ready to ride to work in the snow tomorrow. Please don’t tell Tim. 

Aaron

Skratch Labs

How sweet is this ride?

Pretty Sweet.