Heat WILL Slow You Down: How to Minimize the Slow

After the 2018 Ironman Boulder, the biggest complaint I heard from athletes was the heat and its relation to a high Did Not Finish (DNF) rate. We are all aware that heavy exercise in high temperatures can lead to medical emergencies such as heat stroke, but so many tend to brush this off as something that could happen but won’t happen to them. So instead of focusing on heat illness, I’d like to discuss a heat related issue that should catch any athlete’s ear:

Your performance will be diminished

Yes, if your body overheats, you will not be able to race at your full potential.

Athlete Story: Ironman Boulder second-timer Andrea Greger hit the start line prepared to annihilate her previous course time. The day started off well with a 15min PR on the swim leg, but by mile 30 of the bike, she knew she was in trouble. It was hot, she couldn’t eat and her pace suddenly slowed. After stopping three times to vomit, Andrea considered pulling from the race. With encouragement from teammates she kept pedaling, finishing well behind her target pace. As she started the marathon it quickly became clear that running wasn’t an option. No cooling effort could bring her core temp down, and she vomited five more times. Although the task felt monumental, Andrea was determined not to quit and continued to march her way towards the finish. She says, “I remember at mile 25 of the run, a lady told me I was almost there, and I wanted to kill her! It was another 20 minutes.” Although it wasn’t’ the race she expected, Andrea learned a lot that day—about herself, about racing, and about the toll of heat.

Negative Effects of Heat on Performance:

First, a quick physiology refresher. One of blood’s primary jobs during exercise is to carry oxygen to muscles. To cool the body, blood flow is shifted from muscles to the skin in an effort to dump heat. This reduces the oxygen available for muscles to perform their work.On top of that, sweating profusely dehydrates the body, and the loss of water makes blood thick. Thick blood transports less oxygen, so there is now exponentially less available to muscles.

With reduced oxygen on site, the metabolic system used for muscle-fueling must then shift from aerobic to anaerobic metabolism, and VO2Max will be reduced. The aerobic metabolic system is most efficient as the aerobic system of glycolysis uses 1 glucose molecule to yields a net total of 6 molecules of the muscle fuel ATP. Glycolysis Anaerobic metabolism, on the other hand, yields only 2 ATP per molecule of glucose. In short, an athlete’s low-effort, sustainable-for-hours pace now has an expiration date closer to that of a hard tempo or threshold effort. The body burns through glycogen faster than you can process it in a race, so when it’s out, it becomes very difficult to continue. This is the dreaded bonk that can drastically slow pace, make racing miserable and lead to a DNF (Did Not Finish). And let’s not forget that heat illness IS an issue and a serious risk.

In short, heat can lead to:

  • Wasted Energy

  • When the body gets too hot, you sweat excessively. The energy spent running your cooling system on overdrive is energy that could be spent elsewhere.

  • Stomach Issues & Gastric Distress

  • To dissipate extra heat, your body will increase blood flow to your skin as a cooling process, and decrease blood flow to your GI track. This shift away from the gut can lead to the dreaded stomach issues faced by many endurance athletes.

  • Decreased Muscle Endurance & Cramping

  • Cramping occurs and muscle endurance is decreased because the body will burn through its limited glycogen stores more quickly with less oxygen available for metabolic processes.

Made even shorter, the body’s negative response to heat will slow you down.

Minimize the Slowing

Fortunately we are not doomed when the weekly forecast is showing temps in the 90’s or above. There are things an athlete can do leading up to and during a race to help maintain body function. In extreme heat, you WILL slow down, but you can help minimize the slowing of pace through heat acclimation training. To illustrate, an athlete unaccustomed to the heat may slow by 15% of capability while an athlete who has practiced heat acclimation techniques in training may slow by only 5%. (Note that these percentages are for illustration purposes only and are not derived from a study.)

It is important to be realistic about your heat acclimation and adjust pace accordingly. “Pushing through” is likely race mismanagement and can lead to disappointing results or, more likely, to a dreaded DNF.

Athlete Story: Age-group athlete Michael Stanley reflects that including hot yoga as part of his training regime helped him in his heat acclimation efforts. “That was a big help in preparing for the heat. I also scheduled rides and runs in the middle of the day to help prepare my body for the heat. All in all I had a great day at Boulder, and though it was hot, I felt I was well prepared for the day.”

Preventative Measures-Preparation in Training:

  • How Heat Acclimation Works

  • With consistent exposure, your body begins to sweat at a lower temperature but with expend less loss of the electrolytes contained in sweat.

  • Additionally, the body becomes better able to absorb liquid and calories in the heat.

  • Negative physiological heat responses begin to return to normal

  • It takes just 7-10 days to build heat acclimation, but only 5-7 to lose it. Once acclimation has occurred, maintain it by two short heat training sessions per week.

  • Heat Acclimation in Training

  • Doing long or hard training sessions in the heat of the day can jeopardize the integrity of the workout by not allowing the body to perform at its full potential, but active recovery or shorter sessions can help the body adjust to the heat.

  • Outside of training, avoid overly cooled environments, but don’t allow your body to get too hot either. You want your body to become accustomed to the heat without zapping your energy.

  • Heat Acclimation with Sauna or Steam Intervals for humidity or dry heat

  • 2 weeks prior to an event, begin doing “intervals” in the sauna (or steam room if preparing for humidity)

  • On the first day, sit in the sauna for 2-5 minutes. Step out and cool down for several minutes, taking a cold shower if possible. Go into the sauna again for a few minutes less than the first time.

  • Repeat this process for 7-10 days, gradually increasing the intervals each time.

  • Make sure to hydrate, consuming your normal electrolytes while in the sauna or steam room.

  • While this is a great way to prepare your body for racing in the heat, do so at your own risk, and listen to your body! You do not want to end up unconscious on the sauna floor!

  • Learn Sweat Rate to Counteract Dehydration

  • To know how much fluid you need to be taking in, you need to know how much you expend during exercise. To calculate this:

  • Weigh yourself undressed before a workout. Afterward, dry yourself off and weigh yourself undressed again. Take the weight lost and to it any fluid you drank during the training session. The number you are left with is how much you lost in sweat. To get a sweat rate, divide this number by the length of the workout in hours.

  • Example:

  • Pre-exercise weight: 150lbs

  • Post-exercise weight: 146lbs

  • Liquid consumed during exercise: 16oz (1lbs)

  • Total Sweat lost: 3lbs (48oz)

  • Sweat Rate: (ounces lost ÷ hours exercised).

  • Ex: 48oz ÷ 2 hours = 24oz

  • Repeat this process several times and in different conditions to get a sense of how much sweat you lose on average

Race-Day Cooling Methods:

  • Start using cooling techniques BEFORE you are overheated

  • Douse body with water

  • This will aid in evaporative cooling so that the cooling process isn’t relying 100% on sweat. This is easier on the body, preventing it from spending so much energy on sweating as a cooling mechanism.

  • Cooling Fabrics

  • Cloth ice-rolls around neck

  • White hat, fill with ice at aid stations

  • Fluid and Electrolyte Replacement

  • Using your calculated sweat rate, plan your hydration strategy appropriately. You will also want to experiment with electrolyte supplementation to find the correct balance for you.

Athlete Story: Ironman first-timer Jeff Bosch says, “I think it’s best to take the time to get extra water on the bike. It seems much like nutrition: if you get behind in cooling you can never seem to catch up.” Jeff refilled or topped-off bottles at ever aid station on the bike course, spraying himself with any leftover water from the hand-up that wouldn’t fit in the bottles. He also strategically sprayed himself mid-ride, especially before descents and faster sections where the passing air would be highly effective in assisting evaporative cooling.”

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