Heat & the runner continued...

It is beginning to get hot and sticky and while you maybe had an excuse before that it was too cool – you are now beginning to develop another one – that it may be too warm. Fear not because we discussed in the last entry that there is no bad weather, only poor clothing choices and we’ll cover some tricks for all climates to get you through this. You should also know that our bodies have some truly unique adaptations which allow us to run, slowly, better than just about any other animal on the planet. Don’t take my word for it – read Dr. Dan Lieberman’s studies on the subject as they are very educational. [http://www.fas.harvard.edu/~skeleton/danlhome.html]

One of these amazing adaptations is that we can dump heat, fast and effectively if we are smart about it and keep up with our bodies’ adaptations. Your body will begin adapting and acclimatizing to the hot weather in only a few days but it will take several weeks to fully be able to thrive in higher temps. Ease into this w/ a slower pace as you adapt. While you are adapting lets think about heat and how you are going to control this variable.

When two objects of different temperature are placed in contact with each other heat moves from the warmer object to the cooler object. You need to know this – because it will work to your advantage, like when you run early in the morning and you are hotter than the air around you. The larger the temperature gradient, the faster heat will move into the air and away from you. Have you ever seen your coffee steam in the morning? This is a micro example of a temperature gradient. Do you know how Gore-Tex rainwear works? On a temperature/moisture gradient also – so if the weather is humid and hot – your Gore-Tex jacket accumulates perspiration and you do not feel as dry. So remember this above law and think about gradients as energy or fluid or material moving from high concentration to low concentration. Here are the primary ways heat moves or terms to define how heat is lost into the environment:

Conduction – immersion in water, tongue on a lamp post, lying on the ground – heat goes into the cooler object
Convection – wind pulling the warm air away from your body, a breeze of a fan help with this and the winter wind does this when you do want it to…
Radiation – heat moving into space, rising from your attic, your head or elsewhere – watch the heat radiate from the road sometime in shimmering waves seen from a distance
Evaporation – high evaporation = high cooling, like wet burlap on the cooler or wet fabric on skin, sweat leaving the skin – carries heat w/ it.

So you want to understand this basic terms and properties because they present real world opportunities for you to avoid overheating. At the cellular level half of the energy you burn is heat production, you’re warm and you can’t help it, but as I said you can work with it.

Do not stress about the heat. We are among the most well developed mammals on the planet for running in this weather. How does the body cool itself? Radiation, Convection and evaporative cooling are the primary means – respiration a secondary means and we have a large skin surface area to vasodilate blood vessels and dump heat. We are able to sweat and provide a large area for convection & evaporative cooling. The faster you have heat carried away the better, as high core temps equate to difficult running. Quick cooling; via evaporation, a breeze, skin in contact with open air to draw off heat these processes all accelerate the cooling process.

You must be hydrated and stay that way in order to run in the heat. Drink plenty of fluid on the days you run & sip water during your runs (16-32oz per hour of exercise or 3-6oz every 15-20 minutes.) How much to drink varies by your weight, metabolism, adaptation, climate and other factors. Until you know your fluid loss/sweat rate just remember what a bag of IV fluids does – steadily drips… You will need a steady drip of fluid replacement in order to perform at your best. We just read that evaporative loss has profound results in cooling you, and if you are not drinking almost as fast as you are sweating, you need not be an accountant to see deficits ahead.

So how fast am I sweating at a given temperature? The SWEAT TEST: You can weigh yourself nude before going out on the run. Weigh yourself nude after the run (sounds obvious but those clothes are full of water, so you do not weigh them.) Convert the number of ounces lost on your scale into ounces of fluid lost. If you had a drink on your run add that number to the total amount lost. You can then estimate, for those conditions, how much fluid you need on a run. So I start the run at 155 pounds and return weighing 153 pounds, meaning I lost two pounds. I had 16 ounces to drink and yet I still lost two pounds so I add that 16oz (one pound) to the total lost = 3 pounds. That means I need about 42 ounces (16oz X 3 pounds) of fluid to replace what I lost out there and get back to my regular weight. I was not sweating fat – I have to replace that lost water. Lost water is lost blood volume and that blood volume keeps me from getting dizzy, delivers oxygen and groceries to my recovering muscles, and takes out the garbage or lactic acid and metabolic waste from muscle efforts. I must know what I generally loose and I need to put it back in order to recover well – dehydrate athletes do not recover well, in fact they do not even digest food very well.

I use a calculator I found at Runners World as a comparison to my
weigh-in calculations for fluid needs. http://www.runnersworld.com/article/0,7120,s6-242-302--10084-2-1-2,00.html

Based on the above calculator a 180lb person would need the following quantity of fluid (in ounces) ea. hour as a minimum for the temperature 50F=5.4oz, 60F=5.7oz, 70F=5.9oz, 80F=6.5oz, 90F=7.3oz, 100F=8.4oz and for temperature I would use the “feels like” temperature the weather man uses – rather than your window thermometer - as this “feels like” includes the heat index calculations.

Research and the medical community seem to mostly agree that you do not want to lose more than 2% of your mass during a run. For example: a 130-pound woman can lose no more than 2.6 pounds. After that your brain does not thermoregulate as efficiently, low blood volume affects perfusion, and you do not generally work as well. Many folks experience mental status changes at this stage of fluid volume loss or may not pass the “tilt test”. This refers to the idea that they get dizzy when they change positions quickly; there is not adequate blood volume to keep up with all your efforts. Drugs can also affect your body’s response to heat and thermoregulation. If you are using amphetamines, thyroid medication, antipsychotics, excessive caffeine (above 500mg daily) or alcohol, you may respond differently to heat stress.

Listen to your body while running. Nausea and light headedness, cramping, irritability, dry & flushed/red skin, low urine output &/or dark urine, or a body that stops sweating is showing critical signs of stress. STOP running and cool off in the shade while getting help. Your body knows more than you do & heatstroke can kill you. Body Temps of 102-104 are survivable with emergency assistance while 107 will be critical but do not pull out a thermometer and read it. Instead remember that the longer someone is at a high temperature the more severe the long term effects. Chill immediately.

Remember that heat injuries affect the “level of consciousness” first. If your running partner seems unaware, confused or more combative than usual it may be the first sign of a problem.

Remember the “chill vest” you saw in the Beijing Olympics? Think about a run that includes a spin through the sprinkler, dip in the stream, or a shower every other lap. Try to keep your shoes dry to prevent blisters but keep your core temperature low so that the blood used to power your legs is not reallocated to cooling your body.

This low core temp concept is another strong argument for going out slow. You need to do your fast running, if any, closer to the end of your workout so that you can then cool down properly. Fast running early will leave you hotter and more sluggish throughout the workout.

Running very early or very late in the day is a big help. Consider night runs with reflectors and a flashlight as one way to beat the heat. Our area has several parks and a bike trail where you can run cool and not be concerned with traffic. While mornings may see the highest humidity levels, temperatures are lower and so the heat index is tolerable for many. Notice that many desert cultures cover themselves completely with light colors and loose clothing that allows air circulation. If you choose to bare the skin to speed cooling, wear your sunscreen.

Conduction cooling: many folks freeze a hat or bandanna and wear it to provide additional cooling. Some even stash a cooler out on the route for a second frozen hat or ice water. Dumping one cup of cold water over your head while drinking the other at aid stations may help. Choose shady routes and plan to slow down; one study has shown that 54 degrees is perfect for running and that we can expect each 7 degree increase above this temperature to slow runners one minute/mile.

HEAT INDEX the NWS provides these numbers for reference – when temperature & humidity meet or exceed these combinations you need to find a treadmill in the AC. Again our area has several great facilities for air-conditioned running and both enjoy brand new treadmills.
Temp Humidity

86 90
88 80
90 70
92 60
94 55
96 45
98 40

Research has shown that you can absorb as much as one liter/hour of fluid. Your minimum daily allowance of fluids is 8-10 glasses a day (64oz) but 128oz is even better for runners or folks who engage in an hour or more of exercise daily. You can “pre-hydrate” yourself on days you know you are running in the heat which is preventative because you can, after adapting to the heat, easily sweat 2 liters/hour during heavy exertion. You will benefit from the additional fluid volume for cooling the body as long as you do not drink more than you can absorb right before a run, which may lead to sloshing while you run. As long as you are eating a normal diet you will not need additional salt or electrolytes to adapt to heat and added salt may prove to be a stressor. Keep it simple with water and it’s cheaper – as well as always available. Sugars generally slow the absorption of fluids so while some may need sweeteners/drink mix to make water appealing to drink – be careful not to create a problem with gastric emptying pre-run.

Think about a water bottle, hydration pack, fanny pack or fuel belt that you can use to carry fluids during these very hot months. I do not target a lot of gear recommendations because every one likes their own style on this kind of thing, but something to keep you hydrated will make your runs safer and more enjoyable.