The Four Systems

What makes Ironman racing so interesting and also so frustrating for many participants is that the better athletes don’t always finish ahead of less fit athletes. “How can this be?” they ask with anger and disappointment. “I trained harder, I have completed more Ironman’s and I am more physically fit than the person who just beat me,” is an often heard statement the day after a race when reviewing the final results.

What typically happens is that athlete exceeded their threshold on one of the four systems during the race, and as result, they did not race to their physical potential when it counted. The four systems that are critical in Ironman racing are:

1. The Aerobic System
2. The Muscular System
3. The Nutrition/Hydration System
4. The Cooling System

We have all heard the saying, “The chain is only as strong as the weakest link.” The four systems is a similar concept in that the athlete needs to understand very clearly where that threshold is on each of the systems during the race. Failure to stay on the correct side of those thresholds will end up with a less than desirable race. Further, these four systems are all integrated with one another. Making a mistake in one area will often impact another system which often leads to a downward spiral in race performance.

System #1 - The Aerobic System

The aerobic system is a complex network that ultimately delivers oxygen and fuel to our muscles via blood flow through our capillaries. Specifically to Ironman racing, the athlete must have an efficient aerobic system that was developed in training to sustain oneself at submaximal speeds for long periods of time (8 to 17 hours). As the athlete competing moves closer towards their maximal speeds and physical efforts in the swim, bike and run, they shift from using their aerobic system to their anaerobic system.

An important concept to understand about the aerobic system related to Ironman racing is that the aerobic system and the nutrition system are INVERSELY RELATED. As you put more stress on the aerobic system (moving towards anaerobic activity), your body’s ability to process fuel decreases. One way to measure the stress load of the aerobic system is your heart rate during racing. As heart rate INCREASES, the efficiency of the nutrition and hydration system DECREASES.

Why is this? Well, to begin the body must run a process called “glycolysis.” Glycolysis is basically the breakdown of glucose in the body to be used as fuel for our muscles. We eat carbohydrates that supply the body with glucose. The glucose is stored as glycogen in our muscles and liver for later use. However, this storage system has a maximum capacity of only storing enough glycogen for a few hours worth of physical activity. So how do we get enough energy to race for 8 to 17 hours if we can only store enough glycogen for a few hours worth of activity?

The way a body could keep moving for 8 to 17 hours at one time is by using fat as a source of energy for the muscles rather than glycogen. Most human beings (almost regardless of how skinny they are), have enough fat to fuel the body for days and days of activity. The key is to be able to tap fat as a source of energy.

Here’s the catch. In order for the body to use fat for fuel it must have a sufficient supply of oxygen. But if the exercise is too intense (i.e. you start moving into your anaerobic system) the cardiovascular system is unable to supply the muscle cells with enough oxygen and the body switches to carbohydrates as the fuel supply. Remember, the body can only store a few hours worth of carbohydrates, so if your heart rate (HR) is too jacked up for an extended period of time, you’ll simply run out of glycogen, won’t be able to tap fat as a fuel source and you’ll basically run out of gas. (READ – YOU BONKED BUCKO!!!) This is a good time to ask yourself, “How do I like walking during the Ironman marathon???”

So, what do we know? We know that in order to race for 8 to 17 hours, we need to tap fat as a fuel source because we can’t store enough glycogen in our liver and our muscles to fuel ourselves that long. If we race too intensely, our bodies automatically shift to burning carbohydrates (glycogen) as a fuel supply and we don’t use fat. Eventually, we’ll get passed my athletes whose main training consisted of mall walking but paced themselves more appropriately. Don’t get passed by the mall walkers…

Key Point #1 - What must we know from our training? We must learn what our threshold is for endurance activity where our body has the ability of burning fat as a fuel source rather than carbohydrates. What heart rate can we sustain over long periods of time where we still burn fat? It is different for each athlete. What is a ballpark way of estimating so that we could experiment in training? Most well trained age groupers can sustain a heart rate range of 85% to 90% of their lactate threshold. For example if an age group athlete has a lactate threshold of 152 bpm on the bike and 168 bpm on the run, they probably can hold in the range of 129 to 137 bpm on the bike and 143 to 151 bpm on the run and still burn fat as a fuel source. Certainly racing below these ranges will increase the odds of burning fat as a fuel source. Failing to recognize this and racing with a heart rate exceeding these thresholds without thoroughly testing yourself in training or in racing environments could lead to very negative consequences. Just remember, if heart rate goes up past a threshold, fat burning goes down and you don’t have the storage to make it last for 8 to 17 hours. Enjoy the 26.2 mile walk and wave to your family and friends as you go by. Don’t be surprised to learn that the mall walkers can walk faster than you at this point. Hopefully they will save some pizza for you at the finish line.

System #2 - The Muscular System

Muscular contraction is the essential physiological event that allows us to swim, bike and run for 8 to 17 hours. A muscular contraction is simply the event when a muscle cell lengthens or shortens to produce a locomotive effect to move our limbs allowing us to move forward.

As we train and race, we are placing substantial concentric and eccentric contractions on our muscular system. A concentric contraction is the type of muscle contraction in which the muscles shorten while generating force. An example would be our hamstrings shortening while pulling our foot strike through while running. In an eccentric contraction, the force opposing the contraction of the muscle is greater than the force produced by the muscle. In an eccentric contraction the muscle is not working to pull a joint in the direction of the muscle contraction but rather is acting as a breaking mechanism to slow the movement of a joint. The result is a lengthening of the muscle while the force is being applied. An example of eccentric contraction would be our quadriceps muscles in our leg helping act as a break to slow us down while running down a steep hill. The muscles aren’t necessarily being used to move us forward as much as they are being used to slow us down. Muscles undergoing heavy eccentric loading will result in greater muscular damage than concentric loading.

It doesn’t take us long to figure out that muscles become damaged by severe, prolonged exercise such as swimming 2.4 miles, cycling 112 miles and running 26.2 miles. Two particular events happen that effect our pacing when dealing with the muscular system. The first is peripheral fatigue which is basically the exhaustion in the exercising muscles. The second is a reduction in central neural recruitment dictated by our brain. Studies demonstrate that as we place significant strain on our muscular system our brain reduces the mass of muscle that can be recruited (a method of self preservation.) Simply put, our subconscious overrides our conscious to stop us from running ourselves to death.

Now an interesting physiological process happens with our muscular system whereby the total amount of work greatly increases as we move further away from maximal muscular output. Let’s use an easy example to understand this concept. Let’s say a weightlifter can bench press a maximum amount for one single repetition of 315 pounds. We can say that the total work output of the session then is 315 pounds (1 X 315 lbs). But if the weightlifter diminishes the weight by only 5% of the maximum amount (to 300 lbs.), the weightlifter would be able to do two repetitions. So the total work output of the session is now 600 lbs. (2 X 300). If we reduce the weight again to 70% of the maximum amount (to 225 lbs.), the weightlifter might be able to do twelve repetitions. So the total work output of the session is now 2,700 lbs. (12 X 225).

How does this relate to Ironman? The athlete must be aware of the limits that can be placed on the muscular system before significant fatigue, exhaustion and reduction of muscle recruitment takes place within the body. Crossing this threshold will result in a significant reduction of pace.

Keep in mind that the muscular system is independent of the aerobic system at this point. It’s possible and quite common to tax the muscular system while being within the limits of our aerobic system. Let’s imagine for example that an athlete was at a ¼ mile running track and had with them two 25 lb. dumbbells to carry. Now imagine that the athlete completed a loop of the track while doing walking lunges the entire way around the track. The athlete could take a little break between steps to ensure that the heart rate does not exceed aerobic limits. Once the athlete is done with a loop of doing walking lunges with 25 lb. dumbbells, the athlete is told to go and run a marathon. How would the athlete perform relative to their potential even though the athlete never crossed aerobic limits during the loop around the track? The athlete would have significant diminished results as the result of muscular fatigue.

Key Point #2 - What must we know from our training? We must learn what our threshold is for muscular output relative to our maximums where our body has the ability of sustaining muscular contractions for 8 to 17 hours. This becomes critical on the cycling leg of the Ironman. As we learned from the previous weightlifting example, the higher the athlete is relative to maximum single repetition output, the lower the total muscular work output is for the entire session. What is the most effective and accurate way of assessing this work output on the bike? A power meter can tell us this information exactly. If the athlete can push down on the pedal and generate 475 watts for a single repetition, the closer that athlete gets to that maximum output, the more impact it will have on the endurance of the muscle. Look at how much the total workout output increased when the weightlifter decreased the weight from 100% of maximum to 70% of maximum. It was a difference of 12 repetitions and 2,385 more total pounds lifted in the session. Let’s assume that an Ironman athlete will hold a cadence of 85 rpm during the 112 miles and that it will take the athlete 5 hours and 30 minutes to complete the 112 miles. That’s 85 reps per minute multiplied by the 330 minutes that it would take to complete the cycling portion for a total of 28,050 repetitions per leg. Now ask yourself, “How close to my maximum do I really want to be with the understanding that I need to complete 28,050 repetitions?”

System #3 - The Nutrition/Hydration System

The nutritional system is the body’s ability to deliver energy to the muscles and the brain. If we fail to deliver enough fuel to the muscles, the muscles run out of gas (literally and figuratively) and begin to shut down. If we fail to deliver enough fuel to the brain, our brain starts to shut down. Hence the athlete must balance the act of delivering enough fuel to the muscles but also maintaining adequate liver glycogen levels for the brain to function. The brain is dependent on glucose levels. Allowing blood glucose levels to fall results in a term called hypoglycemia. Hypoglycemia impairs brain functioning and will lead to exhaustion. Many of us have experienced the symptoms of hypoglycemia on long training days and especially in Ironman racing. Symptoms include but are not limited to an inability to think clearly, concentrate, a lack of coordination, a feeling of extreme physical weakness, and dizziness. Failure to address hypoglycemia will ultimately result in collapse.

We run into an interesting conundrum during Ironman racing. Our muscles are in constant need for fuel. The fuel source can come from two primary resources; carbohydrates and fat. The problem is that our bodies can only store a couple of hours worth of carbohydrate stores in the form of liver and muscle glycogen. One solution is to consume enough carbohydrates through eating to replace what our bodies need to burn. But it isn’t that easy. Physical exertion at race intensities won’t allow our bodies to eat, digest, distribute and burn the carbohydrates at adequate levels to keep us going for 8 to 17 hours.

We may have experienced the symptoms ourselves or have seen other athletes attempt this method of fueling; they continue to eat carbohydrates at a rate faster than the body can digest and distribute the glycogen. The result is bloating, undigested food in the digestive track which if left uncorrected usually resulting in vomiting. Vomiting empties the system and usually feels pretty good but creates another problem which is zero fuel in the digestive system which will lead to eventual failure (READ – BONK!)

Our success on race day will be dependent on our abilities to oxidize fat as a fuel source. Our bodies have plenty of fat reserves to get through an 8 to 17 hour event such as an Ironman. The key is to be able to tap into this fat reserve as the primary means of fuel. It’s worth repeating from the aerobic system section previously described at the beginning of this paper. In order for the body to use fat for fuel it must have a sufficient supply of oxygen. But if the exercise is too intense (i.e. you start moving into your anaerobic system) the cardiovascular system is unable to supply the muscle cells with enough oxygen and the body switches to carbohydrates as the fuel supply. Remember though, the body can only store a few hours worth of carbohydrates, so if your heart rate (HR) is too jacked up for an extended period of time, you’ll simply run out of glycogen, won’t be able to tap fat as a fuel source and you’ll basically run out of gas.

Here’s another saying that you may have heard before, “Fat burns in a carbohydrate flame.” Simply put, carbohydrates aid in fat metabolism. The fat oxidation process cannot take place without the presence of carbohydrates. So the purpose on race day would not be to consume enough carbohydrates and calories to replace what is being burned but rather to provide the body with enough carbohydrates to oxidize fat and to keep blood glucose levels at adequate levels to prevent hypoglycemia (i.e. that’s why we eat during the race.) Our goal is to supply enough carbohydrates to oxidize fat as opposed to eating to provide the actual calories for our body to burn as a direct fuel source.

Key Point #3 - What must we know from our training? We must learn what our range of caloric and carbohydrate intake must be per hour to allow our body to oxidize fat for muscle fuel and also keep blood glucose levels at adequate levels to prevent hypoglycemia. Intensities must be kept at appropriate levels during the swim, bike and run portion to allow the nutritional system to function properly for 8 to 17 hours. Many age-group athletes have had success consuming some carbohydrates about 15 minutes prior to the swim along with taking a gel at the half way point of the swim (easy to do on a two loop swim course by placing a gel in the sleeve of your wetsuit.) Most successful Ironman athletes consume between 250 and 500 calories per hour during the bike portion and 200+ calories per hour during the marathon. It is better to consume the calories in a steady and consistent manner (say 60 calories every 10 minutes on the bike) rather than taking in 360 calories at the top of the hour. In a perfect world we would have a steady supply of carbohydrates come in through an IV drip all day long.

The hydration system is the body’s ability to replace fluids that were lost primarily due to sweating but could also be due to urinating, vomiting and/or diarrhea. The consequences of dehydration from an Ironman race perspective is reduced physical performance as the effects of dehydration continue to increase within the athlete. As the state of dehydration increases, body temperature increases, heart rate increases, and mental/cognitive function decreases along with a reduction in physical performance. Dehydration, if left unchecked, can eventually lead to organ failure or even death.

Athletes that cannot regulate their hydration levels throughout the race day will experience an increase in heart rate yet will also experience a reduction in the heart’s output and stroke volume as well as the blood flow to the skin (impacting the body’s cooling system.) Dehydration also increases the amount of glycogen used within the muscle and increases the feeling of discomfort experienced during by the athlete.

There are two factors that must be taken into consideration when addressing the hydration needs during a race. The first is that humans can’t store fluid or electrolytes to reduce future dehydration (i.e. we are not camels). The second is that there is a limit to the amount of fluids that can be ingested and absorbed in the gastric/intestinal system to deliver those fluids into the body’s bloodstream. The body has a natural absorption rate of fluids within this system but research has also demonstrated that the rate of absorption is inversely related to the race or exercise intensity. As the intensity increases, moving towards VO2max, the rate of gastric emptying and intestinal absorption rates decrease. Athletes that attempt to drink at a rate faster than the body can absorb the fluids will ultimately be faced with bloating and left unchecked will lead to vomiting (Iron yaking ?.)

One common misconception of Ironman athletes is that you have to replace fluids at the same rate of fluid loss due to sweat and urine loss. This is not entirely true. Although it is critical that an athlete not lose a substantial amount of body weight throughout the race event (certainly not losing 10% of body weight during the day), some weight loss should not only be accepted but tolerated/accepted. The body is going to lose weight due to the metabolic process of burning fuels (using stored carbohydrates and the fat oxidation process). Water is also released from stored glycogen used during the race. In recent research studies, it was determined that during an event such as the Hawaiian Ironman, athletes with a weight loss of up to 3 kg (6.6 lbs.) of weight may not represent the actual amount of fluid loss that needs to be replaced for actual dehydration to be prevented.

What does all of this mean in practical terms? In practical terms, research indicates that most athletes need, and can absorb fluids in the range of 400ml to 700 ml per hour with the average athlete being 500ml per hour. If the athlete is exercising at proper race intensity and fails to take in an amount in this range, dehydration most likely will occur. If the athlete is either racing at intensities above an appropriate range or taking in fluids in excess of this range, it is likely that the fluids will begin to accumulate in the gastric/intestinal tract resulting in bloating and/or vomiting. For reference, one ounce of fluid is equal to approximately 29.5ml. So a range of 400ml to 700ml of fluids per hour is the equivalent to ingesting 13oz to 24oz of fluid per hour.

One last aspect regarding hydration is the electrolyte replacement and the potential for the athlete to self-induce a condition called hyponatremia. Our bodies have a need for electrolytes to function mentally and physically (sodium, potassium, calcium, magnesium, chloride, phosphate and hydrogen carbonate.) Athletes that consume large amounts of water can create an electrolyte disturbance called hyponatremia. Hyponatremia exists when the sodium concentration in the blood plasma falls below 135 mmol/L. Severe hyponatremia can result in death in humans. To prevent a loss of electrolytes that can result in severe consequences in addition to diminished athletic performance, athletes should be replacing sodium lost due to the sodium lost during the sweating process. If consumed as part of a sports drink, replacement should be in the range of 20 to 60 mmol per liter of sports drink.

Key Point #4 - What must we know from our training? We must learn what our range of fluid intake must be per hour to allow our body to replace those fluids lost from sweat and urination and to keep fluids at adequate levels to prevent dehydration. Intensities must be kept at appropriate levels during the swim, bike and run portion to allow the hydration system to function properly for 8 to 17 hours. Most successful Ironman athletes consume between 400ml and 700ml of fluids per hour during the bike and run portion of the race. (Note many age-group athletes feel that they consume about 10 gallons of fluid during the open water swim while being pounded into oblivion but we aren’t counting that in our calculations ?) It is better to consume the fluids in a steady and consistent manner (for instance 4 to 6oz every 15 minutes) rather than taking in 24oz of fluids at the top of the hour. In a perfect world we would have a steady supply of fluids come in through an IV drip all day long. Athletes must also account for sodium loss and should supplement sodium within our fluids at the rate of 20 to 60 mmol per liter and should not over consume water to avoid a very serious condition called hyponatremia.

System #4 - The Cooling System

The cooling system is a complex network that ultimately serves to keep the body within a narrow range of temperature despite environmental factors that lead to heat stress upon an athlete. Specifically to Ironman racing, the athlete must ensure that their cooling system is capable of functioning properly that will allow the athlete to sustain itself at submaximal speeds for long periods of time (8 to 17 hours). As the athlete competing moves closer towards their maximal heat limits in the swim, bike and run, they greatly increase the chances of declining athletic performance.

Human beings operate in a tight range of preferred internal body temperatures (typically between 35 to 42 degrees C which is 95 to 108 degrees F.) Humans can tolerate overcooling and have been shown to recover from long periods of hypothermia with body temperatures diving more than 20 degrees F below what is normal.

But humans have very little tolerance for even brief overheating as the brain malfunctions with changes in internal temperature barely a dozen degrees above normal. When competing in an Ironman, the muscles generate too much heat for the air to absorb. The same thing happens when the outside temperature climbs into the 90s. When this happens, the skin stops losing heat to the air and absorbs it instead. The body sweats to create an evaporation process which when working properly acts as a cooling agent to the skin and trickles down to the body’s core temperature.

Humidity reduces evaporation and the body responds to this by sweating more. A breezy/windy day enhances evaporation as does moving at quicker speeds on the bike vs. the run and makes skin cooler unless the air is so hot that the athlete absorbs the heat. A negative consequence of dehydration is the reduction of sweat production and thus a reduction in the body’s ability to cool itself. Sunburn has similar consequences as dehydration.

Individual sweat patterns vary from athlete to athlete. Factors that impact sweat rates and the ability to keep cool include, but are not limited to; age, sex, genetics, weight, and body mass index. Some people have fewer than two million sweat glands and some people have more than four million sweat glands. Heavy sweaters often have sweat glands that are five times average size.

As an athlete begins racing, the blood flow to the muscles is increased to create forward propulsion. The heart begins to pump more blood via a higher heart rate and this blood is diverted from nonessential organs toward the working muscles and the skin. As the blood makes its way through the muscles, the blood is heated and the heat is distributed throughout the body, particularly to the skin. As the heat makes its way to the skin, the skin sheds the heat through the process of convection (the body heats up the air around it). Thus any nearby object that has a temperature lower than the skin temperature such as the air, the ground, trees, or road surface will attract the heat away from the skin. Further, surface heat on the skin is lost when the sweat produced by the swat glands in the skin evaporates. The evaporation of the sweat into the surrounding air creates the cooling affect.

What Ironman athletes need to understand about heat is that as the intensity of racing increases more heat is generated by the body. The body also has a strange priority ranking for blood flow. The body could choose to either pump more blood to the muscles to create forward propulsion or to increase more blood flow to the skin to aid to the cooling system. When faced with these conflicting demands, the body tends to increase blood flow to the muscles rather than to the skin which escalates the chances of the body overheating. One would think that the body would have a central regulator preventing the athlete from continuing with racing which eventually results in dangerous overheating. However, as explained above, the body at times seems to allow athletes to continue racing at intensities that result in dangerous situations. Luckily the body’s internal thermostat typically recognizes the problem and as a result it will reduce the amount of muscular recruitment (i.e. you will slow down as a result of overheating but hopefully before it becomes too late.).

The skin temperature of the body at rest is about 91 degrees F (33 degrees C). If the athlete is racing in conditions greater than 91 degrees, heat cannot be lost by convection because the air temperature is higher than that of the skin. In this case, the situation is reversed, it is the skin that absorbs additional heat from the surrounding air. The body will attempt to compensate for this loss of convection with additional sweating. If the humidity is high, the sweat does not evaporate but rather the sweat drips from the body without evaporating. As a result, there is no cooling effect.

An athletes ability to cool itself is also contingent upon its body mass index which measures the ratio of the body mass (in weight) to height. Physiologically speaking, athletes with a lower body mass index are able to shed heat more effectively and efficiently than larger athletes. Interestingly, height (as in additional height) has a negative impact on the body’s ability to transfer heat. If there are two athletes with the same weight, the shorter athlete will be able to shed heat more efficiently than the taller athlete. If you are a larger athlete, you will need to heed notice that heat and humidity will have a much higher impact on you than your smaller competitors.

Key Point #5 - What must we know from our training? We must learn how to adjust race intensities downward in hot and humid conditions to prevent overheating. Intensities must be kept at appropriate levels during the swim, bike and run portion to allow the cooling system to function properly for 8 to 17 hours. Larger athletes with higher body mass indexes will be impacted by heat much greater than smaller athletes with lower body mass indexes. It does not matter how well trained the athlete is, how efficient their aerobic system is, how strong their muscular system is and how well they fuel themselves. If they overheat, they will eventually succumb to a reduction of muscle recruitment and will slow down. Athletes must be aware that the human body is slow to respond to overheating and will allow the athlete to push itself past the overheating point before responding. The effects on your race day may end up being catastrophic as you will not race to your potential based on your fitness.

For a fantastic scientific reference book that has researched many of the items discussed in this report, I would highly recommend “The Lore Of Running” by Timothy Noakes, MD.

Iron Quiz

Take the following true or false quiz to test your knowledge

Question #1 – The fastest athlete always finishes ahead of slower athletes in Ironman racing?

Answer – False. Slower athletes often complete Ironman races faster than others who are better trained and more physically fit because they raced with better execution relating to their four systems. Athletes that stay below their thresholds with the four systems will hold their pace for longer periods of time and will end up passing athletes that raced too hard, too early and end up slowing down later in the race.

Question #2 – The four systems all work independently and are not related to one another?

Answer – False. Athletes that exceed their aerobic thresholds may experience problems with their muscular system, their nutritional/hydration system and potentially their cooling system since their bodies cannot allocate enough blood flow and run all systems at high levels simultaneously.

Question #3 – As heart rate INCREASES, fat oxidation levels DECREASE.

Answer – True. If we race too intensely with too high of a heart rate, our bodies automatically shift to burning carbohydrates (glycogen) as a fuel supply and we don’t use fat as the primary fuel source.

Question #4 – The further we move away from our single maximum repetition limits, the greater the total workload we can produce.

Answer – True. Ironman athletes need to sustain muscular contractions for 8 to 17 hours. Having any muscular contractions that are close to maximum efforts will greatly impair our ability to contract muscles for any length of time.

Question #5 – The only thing we need to worry about is having enough fuel to deliver to working muscles.

Answer – False. The brain is dependent on glucose levels. Allowing blood glucose levels to fall results in hypoglycemia which impairs brain function and will lead to exhaustion.

Question #6 – The body is capable of digesting food at any level regardless of physical exertion.

Answer – False. As the rate of physical exertion increases our bodies ability to digest food decreases. Athletes that continue to eat at a rate faster than the body can digest will experience bloating and if left uncorrected will lead to vomiting (Don’t puke on your new race shoes…)

Question #7 – The purpose of eating carbohydrates during the race is to directly fuel our muscles.

Answer – False. The purpose of consuming carbohydrates during the race is to provide the body with energy to oxidize fat and to keep blood glucose levels at adequate levels to prevent hypoglycemia.

Question #8 – The body has a natural absorption rate of fluids and the rate of absorption is inversely related to the race/exercise intensity.

Answer – True. As intensity increases and moves towards VO2max, the rate of gastric emptying and intestinal absorption rates decrease. Athletes that attempt to drink at a rate faster than the body can absorb the fluids will ultimately be faced with bloating and if left unchecked will lead to vomiting.

Question #9 – Heat and humidity have no impact on athletic performance and athletes could race at the same pace and efforts regardless of temperature.

Answer – False. Humans have very little tolerance for even brief overheating as the brain malfunctions with changes in internal temperature barely a dozen degrees above normal. Athletes that attempt to race at the same efforts regardless of temperatures may want to tell their families to meet them outside of the medical tent and explain what “DNF” means prior to the race start.

Question #10 – Smaller athletes are able to shed heat more effectively and efficiently than larger athletes.

Answer – True. An athlete’s ability to cool itself is contingent upon its body mass index which measures the ratio of the body mass (in weight) to height. Athletes with a lower body mass index are able to shed heat more effectively and efficiently than larger athletes.