Racing a Hot and Humid Ironman
My intent with this post is to provide an outline for racing and Ironman in hot and humid conditions. I’m sure there are major elements and tactics that I have not covered or have not occurred to me. I hope the resulting thread with input from our experience and amazingly smart team can then be redrafted into some set of best practices for the Wiki.
Racing a Hot and Humid Ironman (one man’s view 
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) Racing an IM in the heat and humidity makes a challenging day even more difficult. As we race in our BOX there are many elements that can be managed to make the best of difficult conditions. At the macro level the key objective is keeping your body’s core temperature under control. As we swim, bike and run our bodies are roughly 25 % efficient. We produce a ton of heat that has to level the body or the core temp will rise. Due to this challenge, typically a normal marathon running race won’t start if it’s above 72 degrees. Once the body’s core temperature rises to ~104, our brain begins to significantly reduce muscle activation levels, we slow down dramatically and if core temp continues to rise we effectively stop moving forward.
So the whole idea is to keep your core temp under control. As the environmental temperature gets closer to normal body temperature it becomes increasingly difficult to cool the body. If the effective ambient temp moves into the upper 90’s, just walking the marathon without smart cooling measures may be too much to ask of yourself.
Here are a couple of key things you can expect your body to do in the heat. Your heart rate will be higher at the same level of work. The heart is working to pump large amounts of blood to the skin in an attempt cool the body. With your muscles needing their heavy supply of oxygen-rich blood, and now more blood being diverted to the skin, your digestive system is the one that loses in the mix. This increases the risk of a nutritional problem during the day. Sweat levels will increase significantly and in high heat and humidity conditions a 30% increase is sweat rate yields a 10 % cooling impact. Your battle is to keep the core temp low while not dehydrating.
Below, in my view, are the elements we can manage in the battle to control our core temp on a hot and humid day. Descending relative impact:
Pacing
Hydration
Fitness level
Heat Acclimatization level
Nutrition
On the course cooling practices
Clothing
Pacing:
The rate at which your body produces heat is a function of your pace. Faster creates more heat to be removed from the body. On the bike in extreme conditions, expect your power levels to be impacted. Some TT research data shows for a 30 min TT at 90 degrees expect a 6.5% power loss, at 100 degrees expect 16-18 % power loss. We don’t bike an IM at our FTP level, but to be conservative, dial in a power level reduction. Last year in the hot at IMLOU, I dialed my target watts down from an IF of .70 to .68 and was able to execute at that level.
Steady pacing is even more critical on a hot day. Hammering up a hill can create enough heat to “put you in the ditch in the fetal position underneath the shade tree”. For the run use the pacing from the EN Heat pacing app for the run. The faster and fitter you are the less the pace impact. The longer you are on the course the more you have to slow down in extreme conditions. Also, smaller bodies have an advantage over larger bodies. The smaller person has proportionally more surface area to dissipate the heat they are producing.
Hydration :
Use the data from your sweat tests to set a plan for fluids for the day. Each person has some upper limit of fluids that their digestive system will absorb per hour. Numbers in the 32-50 oz per hour are typical. See if you can determine your level on your long runs and rides. If your swim is non wet suit temps, then do a sweat test for the swim. (I lost 4 lbs fluid in my test in 1:10 for the 2.4m). Stay hydrated the days before and the morning of the race. I drank 30 oz of coldwater in the wait to start the swim.
Cold fluids are absorbed quicker than warm fluids, plus they help lower the core temp. Don’t carry hours worth of fluids on the bike that will get warm (nutrition is another challenge). Get cold fluids often. If given the choice of riding for 3 aid stations with fluid on the bike or picking up fresh cold fluid at each aid station, go for fresh cold fluids at each station. Plus you have less weight to carry up hills. The bit of time lost by hitting the aid stations is the least of your worries in these conditions.
Expect to see your HR rise as the day moves along, this will be due to the likely increasing temperatures and the rise in your core temperature. If you see a noticeable rise in a short period and your effort has not changed, this may be an indication that you are getting dehydrated. Slowing for 5- 15 min, get fluids in (if not blotted) and see if the HR comes back down.
Be aware there is a significant danger in drinking too much water which can result in Hyponatremia. This condition can be very dangerous.
Fitness Level:
The EN training plans have us covered on this front. Note the closer you are to the pointy end of the spear, you will be slightly less impacted by the heat. The common thoughts are better overall bike and run mechanics and muscle efficiencies play a role in this.
Heat Acclimatization:
Proper acclimation to heat and humidity can drive some significant physiological changes. These include the following:
·Decreased core temperature
·Decreased heart rate
·Decreased psychological perception of perceived effort (RPE)
·Increased exercise tolerance time
·Increased plasma volume
·Increased sweating rate with decreased sodium chloride (loose less electrolytes)
A good overview article fitbricks.com/new-articles/heat-acclimation-article/
Heat acclimation takes 1-2 weeks
Also worth a look www.irunfar.com/2010/04/heat-acclim...nners.html
The following is an excerpt from the above link
Heat Acclimation Methods and Considerations
The work needed to achieve the benefits heat acclimation is reasonable. Most heat acclimation protocols have athletes spend about 1 hour a day in a heat chamber for 7-10 days. Importantly, this needs to occur as close to the time of the competition as possible, as the adaptations conferred by acclimation decay rapidly without ongoing exposure. So there’s no point in spending 2 weeks in a heat chamber a month before the race – the effects will decay in 1-3 weeks.
The work needed to achieve the benefits heat acclimation is reasonable. Most heat acclimation protocols have athletes spend about 1 hour a day in a heat chamber for 7-10 days. Importantly, this needs to occur as close to the time of the competition as possible, as the adaptations conferred by acclimation decay rapidly without ongoing exposure. So there’s no point in spending 2 weeks in a heat chamber a month before the race – the effects will decay in 1-3 weeks.
Loss of Acclimatization
As previously mentioned, the benefits of heat acclimation decay rapidly if you do not maintain heat exposure. Estimates vary, but it’s possible that you could lose half of the benefit in 10 days without ongoing heat exposure. This raises some logistical problems for athletes living in cold environments who are attempting to acclimate for a hot weather event. To benefit maximally from acclimatization, the heat training sessions should occur as close as possible to the event. That seems pretty straight forward. The problem is that acclimation is quite physically demanding, and most athletes attempt to taper in the week(s) prior to a big race. So, if you want to acclimatize optimally, it needs to occur during your taper – which may cause overtraining, or at least minimize the benefits of tapering.
The following is from this link www.sportsci.org/encyc/heataccl/heataccl.html
The physiologic adaptations to exercise training in a cool environment are lost after several weeks or months of inactivity. In contrast, heat acclimatization adaptations may vanish after only a few days or weeks of inactivity (i.e., 18-28 days). The first adaptations to decay are those that develop first: heart rate and other cardiovascular variables. The rate of decay of adaptations is affected by the number of heat exposures per week, the number and format of training sessions, and the degree to which core body temperature is elevated. Athletes with high VO2max usually will lose heat acclimatization adaptations slower than individuals with low VO2max.
If you want more this is a bit of a heavier read - Heat adaptation: Guidelines for the optimization of human performance
Also note that lack of sleep can diminish the heat acclimatization benefits.
Nutrition:
After improper pacing, this is the easiest place to blow your race up on a hot day. The digestive system has a sizable challenge during a normal temperature IM. On a hot and humid day the blood supply to the gut is reduced even more in the attempt to cool the body. It becomes even easier to take on more calories than your stomach can process. You can start a spiral down process just by taking a gel and washing it down with perform rather than water. The gel / perform mix will be too concentrated to process so the stomach will have to take water from the body to dilute it. While this process is happening fluids aren’t being process into your body, you are sweating like mad and start to dehydrate. The dehydration process results in lower blood plasma volumes and now even less blood is going to the gut and the process spirals out of control until you stop and allow it to reset. (Yes I simplified many things here). So target the lower levels of calories per hour that has worked for you, also go liquid whenever possible. If you can use cold liquid then that would be better.
Sodium – let’s treat as a subset of nutrition. You need to find what works for you. We are all different and the research is inconclusive at best. See following excellent resource by our very own Dr. Kitma: http://members.endurancenation.us/R...ion+Status
On the course cooling practices:
Swim - Before the swim start keep your body temp as cool as possible, elevating the body temp at this point is giving up work capacity later. Drink cold fluids. Consider putting Ice down the speed suit.
Bike
- Liberal and frequent application of cold water to the face, head and arm coolers if you have them on. Practice getting water into the vents on your aero helmet as this is a bigger challenge than a standard helmet.
- Take advantage of shade on the course where you can. Direct sun can add 15 degrees to the ambient temperatures.
- I put a single use cold pack in my special needs bag. It goes under the jersey on the neck and under the aero helmet. 20 min of cold on the back of the neck is a nice pick-me up at that time of the day.
Run
- Ice sponges and Ice at every aid station. I get 5 sponges at each aid station, into the upper chest area,2 on the shoulders and 1 under the hat.
- Cold water in the face, and ice down the jersey.
- Run with a cup of ice in your hand, eat the ice, swallow some for fluids and the added cooling to the core.
- Pick your run line to use shade when you can.
- Half -way through to the next aid station, squeeze a couple of the sponges to rewet your head.
- I have tried the single use cold pack on the run. It’s hard to keep stable in any location. If you use a fuel Belt it will keep a pack from sliding out the back of your jersey. Cold on the small of the back - Nice!
Clothing:
During the day you will sweat gallons off fluid, plan on being wet the entire day. The core of the on course cooling practices above is to whenever possible/practical get cold water onto your face and head. I wear the same tri kit from start to finish. If I was going to take the added time in transition to put on dry gear, the new gear will be soaked in 10 min.
I find arm coolers or the wings to offer a real benefit on the bike and the run. First they keep the sun’s radiation from directly hitting the skin and raising the body temp. Being white they reflect much of the radiation back. Also the new fabrics do seem to provide an evaporative cooling factor. The impact of wetting these with cold water seams to last longer than bare skin.
On the run I wear a white DRIFIT fabric hat with a large bill that is black on the underside. I can fill it up with ice and put it on my head I place of an ice sponge.
I run with socks and know they will be soaked with sweat, melting ice and splashes of water within the first few miles. I use shoes that have drain holes in the bottoms so I’m not standing in a puddle all afternoon.
Final thought:
On extreme hot and humid days slower is faster 
Matt
PS - All inputs are welcome and please corrections where I have stated something not quite right.
PSS - Take the time to look at the reference links on heat acclimatization tagged above. The is much more information that I have given in this high level view.
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Comments
Thanks Matt for taking the time to put this together. Well worth the read. Must be immortalized in the wiki as all should read this over and over to let it all sink in.
Paul
Thanks for all the hard work you put in to this post. It's solid gold for any endurance racer, not just the IM crew.
Chapeau!
Jason - sorrry I was not clear, rathr than an ice pack , I should have said a single use cold pack. Thes are chemical packs that when you crush them them make cold for ~20 min. They are often used for first aid. I get mine from Wallgreens. Make sure they don't create a temp below 32 for risk of frost bite. I will edit the post.
Obviously this strategy isn't easy to do for an IM, because I have no way to keep them frozen before I get to them on the bike, but it could help in training.
On hot days one may want to lower their tire pressure a bit. Rolling along on 130+ degree asphalt will raise the tire pressure. I found a reference from Bicycling Magazine - For each 10-degree-Fahrenheit increase in the temperature, your tire pressure increases by about 2 percent. So if the temperature rises from 80 degrees Fahrenheit to 130 degrees Fahrenheit, you will gain about 10% or 12 PSI. So if you start with your tires at 120 in the AM you will be at 132 on the hot roads.
Unless you are riding on extremely smooth roads high tire pressures create added roll resistance. Most IMs are not those kind of roads. If my IM is hot, I’m going to split the difference and drop my cold tire pressure by 4-6 psi depending on heat and if overcast.
The article you wrote up is very informative and being a newer member here I have learned much the last 7 months. For example the above quote, I always thought to inflate the tire to its highest PSI and roll with that.
I rode with a friend up at IMLP for a loop and he reduced PSI by 10 lbs because " that's the way I roll ", I figured to try it too.
It provided for a more comfortable ride one and two I didn't know rolling resistance with an increased PSI could slow you down and just training in Placid for a day I could have used all the help I could get.
I've been here almost 2 years and I still learn something everyday! I also wasn't aware just how much the hot roads would affect the tires. Thanks Matt!
Great post Matt, as hot as it is this year we can use all the suggestions you wrote. You are right, the tire pressure is really important especially when you go to transition on race day and check the psi. I use SRAM S80's with clinchers on race day and learned that they are very touchy when it comes to too much air, I have blown the front tire twice by inflating the tire to 125psi which is the recommended max. The hot roads will make for a bad day if you dont consider the temp.
Thanks again Matt, see you in a few weeks.
Tires, like stated, increase pressure with high temps, plus tires being a mass-made commodity (mostly), aren't all uniform. When one might explode at 130psi, another might explode at 110 psi - it's a crap shoot! So, don't let them sit there and chance exploding overnight (temps vary, in/out of direct sunlight while sitting, etc), adding to your race day stress when you hit transition the next morning.
HOLY CRAP!!
Friggin' AWESOME resource!
For me, keys are:
The clothing stuff, as well as the hat, five (5!!) sponges, etc all new to me. Gonna seriously consider the ice pack on the grape placed under the aero helmet at BSN if it's a crazy hot day. That's money! And I have a pair of Desoto arm coolers, will start to wear them and keep them wet, to see if they work for me.
Awesome stuff!
Hey Coach Rich....I gotta tell ya' thats two posts that you have left today that made me feel good about my own habits....1st...high bike cadence...and 2nd "32oz. of coffee"! I have always maintained that coffee is indeed a fluid.
Matt, is the "Heat Pacing App" in the wiki, or maybe called by another name? I tried searching for it there and in the forums and couldn't find it. Thanks.
Ok Coach, I gotta ask - *why*? And, to be clear, are you advocating this as a future strategy for others?
Good question. I'll have two cages on the bike:
My routine (used this for many races) is to grab a bottle of water at the aidstation, drink half of it (about 12oz?), dump the rest on me and toss the bottle. If I feel the need to carry an extra bottle (ie, hot day), can do that on the downtube cage or I've found I can also jam the cheap plastic, Costco-type water bottles they hand off between my elbow pad and the torpedo mount.
Lately, the aerodynamics of a bottle bolted to my $$$$$ downtube has been getting inside my head...but not enough to put myself in the med tent about it = I'll still have two bottle cages on the bike but plan to only use 1 of them if I can get away with it.