BEAT THE HEAT

in World Athletics Road Races

CONTENTS

2

Are you prepared? Calculator.

pg.4

How is body temperature maintained?

pg.5

How does heat affect performance?

pg.6

What temperature does our body reach?

pg.7

How to best prepare to compete in the heat?

pg.8

How much can performance be improvedby heat acclimatization?

pg.10

How does hydration impact performance?

pg.11

How much to drink?

pg.12

What to drink?

pg.13

What about pre and per-cooling?

pg.15

PREPARED TO COMPETE IN
THE HEAT? GIVE ME FIVE!
ARE YOU PREPARED TO
COMPETE IN THE HEAT?
2 weeks of heat acclimatization/acclimation+ 4 points

1 week of heat acclimatization/acclimation+ 3 points

Coming from a warm country+ 3 points

Hydration plan

+ 2 points

Pre-cooling+ 1 points

Per (during)-cooling+ 1 points

Clothing limiting sweat evaporation– 1 points

Previous history of heat illness– 1 points

I am taking approved medicationthat can reduce my heat tolerance– 1 points

SCORE AT LEAST 5 POINTS ON THE ABOVE LIST!

3BEAT THE HEAT
Out of the several thousands of road races that take place every year, manyof them are held in hot and humid environmental conditions.
Hot and humid ambient conditions limit heat dissipation capacity during
exercise, thus impairing endurance performance and increasing the risk ofexertional heat illness such as heat cramps, heat exhaustion, and heat stroke.
The risk of heat illness can be reduced by adopting countermeasures such asheat acclimation/acclimatization. This document addresses some Frequently
Asked Questions about performing at athletic events in hot and humid
ambient conditions and provides recommendations to optimise performanceand reduce the risk of heat illness.

4HOW IS BODYTEMPERATURE MAINTAINED?
When resting in temperate environmental conditions:- core body temperature in humans is around 37ºC
- muscle temperature is approximately 35ºC
- skin temperature is approximately 31ºC
During physical exertions such as running, muscle contractions produce a
considerable amount of heat, inducing a large increase in muscle temperature,
which drives an increase in core body temperature.
The heat produced by the body is dissipated to theenvironment via the skin primarily in the form of sweating.

THE ATHLETE’S
THERMAL ENVIRONMENT
Radiation(direct and reflected on theground or any other surface)
Sweat evaporation(main avenue for heat dissipationin exercising human)(minimal heat loss byradiation from the body)

Metabolic production(¼ of the energy is transformed
in mechanical work, ¾ is heat)

Convection(requires air flow at a lower
temperature than the skin)5

Change ni performance >250C versus <250C(%)

HOW DOES HEATAFFECT PERFORMANCE?
1,5
1
0,50-0,5800m
100m

200m

1500m

5,000m 10,000m Marathon

400m-1-1,5-2-2,5-3-3,5THE EFFECT OF TEMPERATURE
ON RUNNING PERFORMANCE
An increase in muscle temperature (e.g. through warm-up) has several benefits
for explosive athletic performance such as sprints, jumps or throws. However,endurance events in the heat can be negatively affected by high body coretemperature. The increase in body core temperature has a direct impact on
the cardiovascular strain that, when significant, increases perception of effort
and this will inevitably impact the exercise capacity (e.g. reduce speed).
In summary, hot ambient conditions may benefit performance during shortduration explosive events, but progressively impairs performance during
longer duration events.

6

WHAT IS THE BODYTEMPERATURERESPONSE DURING
EXERCISE?
Body temperature increases after a
few minutes of exercise. If the heatstress is not effectively compensated,core temperature will keep rising
unless heat production is reduced(e.g. reduce speed).
Depending on the intensityand duration of the exercise, astabilization in body temperature
may occur anywhere around 38.539ºC when exercising in temperateenvironments. However, athletes canachieve a core body temperature
above 41ºC when competing
intensely in hot ambient conditions.

Maximal body coretemperature whencompeting in the heatCore body temperature
can reach ~39-41°C

VISIBLE BODY
ADAPTATIONS TO
REPEATED HEAT TRAINING:• Increased sweat rate
• Decreased heart rate at a given intensity• Better retention of electrolytes• Decreased body core temperature
7

HOW TO BEST PREPARETO COMPETE IN THE HEAT?
Train in the heat. Heat adaptation is achieved via repeated exerciseheat exposure that increases body core and skin temperatures as wellas induces significant sweating. This can be achieved using hot ambientconditions (acclimatization) or by simulating hot ambient conditions by using
environmental chambers or improvised “hot rooms” (acclimation).
14 days is the preferred adaptation period. Most adaptation tends tooccur within 7-10 days, but 14 days is optimal for most. It is therefore
recommended that athletes train in a similar environment to the one in which
competition will occur for two weeks prior to competition.
Initial heat acclimatization camp can enhance rate of adaptation. Conducting
an initial acclimatization camp several weeks before the target event may alsoenhance the rate of adaptation in a follow-up pre-competition camp.

ADAPTATIONS TO REPEATED TRAINING IN
THE HEAT FOR UN-ACCLIMATISED ATHLETES
125
120
Adaptation (%Day 1)

115
110
105
Plasma Volume

100

Heart Rate

95

Core Temperature

90

Skin Temperature

85

Sweating Rate

80
75

Thermal Comfort
012345678

9 10 11 12 13 14

Days of Heat Acclimation

8Exercise Capacity

HOW MUCH CANPERFORMANCE BE IMPROVEDBY HEAT ACCLIMATIZATION?
Heat acclimation is far more important than other performance enhancing
strategies such as altitude training when competing in the heat. Heatacclimatization will also reduce the risk of heat illness. Therefore, heatacclimatization should be a priority before any event where hot and/or humid
conditions are likely or expected. Indeed, heat acclimatization does not impair
performance in cooler environment and may even enhance performance undercertain conditions.

HOW TO HEAT ACCLIMATISE
IN A COLD COUNTRY?
There are a wide variety of approaches that can increase core and skintemperature and stimulate sweating. These are:•Train for 60-90 minutes a day in the same ambient conditions as theupcoming competition for 2 weeks. However, if not possible, mostadaptations can be acquired by artificially simulating heat during indoor
training (i.e. use of a purpose-built environmental chamber if available,
or even using heaters and boiling water to artificially create hot andhumid ambient conditions). If not possible, other alternatives should
be considered like using passive heat acclimation techniques such as
hot water immersion or sauna bathing for 30-40 minutes pre- or posttraining but overall benefits of passive heat acclimation will be less thantraining in hot ambient conditions. Water temperature should be around
40ºC in order to cause adaptation while remaining tolerable (this can beeasily measured with a floating pool thermometer).

Collectively, artificial techniques aimed at inducing heat adaptation are called
heat acclimation. Although not as specific as exercise heat acclimatization,
heat acclimation can be used before travelling to a hot environment to reduce
the time required for acclimatization upon arrival.
9THE DIFFERENT HEAT ACCLIMATIZATION METHODSACCLIMATIZATION
Natural environment(outdoor/field training)Self-paced exercise

ACCLIMATION
Artificial environment(indoor/laboratory training)

HEAT

Constant work rate

Controlled
hyperthermia

Controlled intensity

Passive heating

Activity

Activity

Activity

Activity

Activity

Football, running etc.

Walking at 6 km/h
running at 12 km/h
cycle ergometer at
185 W, etc.

Cycle ergomoeter
at 65% Vo2max, heart
rate (e.g. 145 bpm)

Work +/- Rest
to maintain coretemperature at38.50C

Water immersion,or sauna bating

Conditions

Conditions

Conditions

Conditions

Conditions

Indoor(400C,40%RH)

Indoor(400C,40%RH)

Water 40-420C, or
Sauna 70-900C

Outdoor (variable)
Outdoor (variable)
Indoor (400C,40%RH) Indoor (400C,40%RH)
Duration

Duration

Duration

Duration

Duration

60-90 min60-90 min60-90 min60-90 min

45-60 min, orintermittent for 30 min

EXAMPLE OF HEAT ACCLIMATIZATION STRATEGIESDEPENDING ON TRAVEL REQUIREMENTS
2 weeks acclimatization before travelling

Acclimatization in advance + maintenance 1 session/week

Pre acclimation + 1 week acclimatization upon arrival

2 weeks acclimatization upon arrival-7-6-5-4-3Weeks

10-2-1Competition

HOW DOES HYDRATIONIMPACT PERFORMANCE?
Heat dissipation relies on sweat evaporation. However, profuse sweating maylead to progressive dehydration if fluids are not sufficiently replaced. Severe
dehydration accelerates the rise in body temperature and impairs prolonged
exercise performance. Therefore, a sufficient intake of fluids before, during
and after exercise is necessary for athletes to perform well and stay safe whencompeting in hot and humid ambient conditions.

DEHYDRATIONLEVEL WHEN
COMPETING
IN THE HEAT

Dehydration
can range
between 2-8%

11

HOW MUCH TO DRINK?
Drinking to thirst is adequate forexercise lasting less than 1-2 h incool environments.
Planned drinking may enhancesporting performance during
activities lasting more than 90
minutes, particularly during highintensity exercise in the heat thatelicits high sweat rates.
Beware of overhydration. It is also
important to recognise that hydration
regimens should never result insignificant over-hydration, as this canhave serious health consequences (socalled “hyponatremia”, an imbalanceof the salts in the body) that can be
more severe than dehydration andeven result in death.
Simple techniques such as measuring
body mass before and after exercise
or evaluating urine colour in themorning (first void) can help athletes
assess fluid losses through sweatingand estimate hydration needs andstatus.
Prepare in advance. It is of paramountimportance that athletes establish
their optimal personal drinking
strategies during training and wellbefore arriving at the competition.

WHATCOLOURIS YOUR
URINE?

Well hydrated
Well hydrated
Fairly well hydrated
Dehydrated
Dehydrated
Very dehydrated
Severely dehydrated
Severely dehydrated

It is also important torecognise that hydration
regimens should neverresult in over-hydration.

DO NOT OVERDRINK

12

WHAT TO DRINK?
Sodium (salt) supplementation during exercise lasting longer than 1 h isrecommended for heavy and “salty” sweaters. Sodium intake may be increased
before and after hot-weather training and racing. Electrolyte tablets or somesalt (a pinch of salt at a time) may be used by athletes during training andcompetition by those who tolerate it. It is also advisable to include 30–60 g/h
of carbohydrates to drinks for sporting performances lasting about 1 h and up
to 90 g/h for longer events. These recommendations can be achieved througha combination of fluids and solid foods. After training or competition in theheat, recovery drinks should include sodium, carbohydrates and, if necessary,protein to optimise recovery.
The preferred method of rehydrationis through the consumption of fluidswith foods, including salty food.

HYDRATION INDEX (I.E. AMOUNT OF WATER RETAINED AS
COMPARED TO STILL WATER) OF COMMON BEVERAGES
Skimmed milk
Full fat milk
Orange juice
Cola
Diet Cola
Cold tea
TeaSports drink
Sparkling water
Still water
Lager
Coffee0130,20,40,60,81

1,21,41,61,8

WHAT ABOUT PRE
AND PER-COOLING?
Before the start of the event, it is advisable to:•Minimise unnecessary heat exposure, athletes should therefore warmup in the shade if possible;•Consider external (ice-vests, cold towels, or fanning) and internal (coldfluid or ice slurry ingestion) pre-cooling methods, or a combination ofboth. One option is the use of commercially available ice-cooling vests
during warm-up, which can provide effective cooling without affecting
optimal muscle temperature and function.

During competition, athletes should:

14•

Protect their eyes, by wearing UV ray blocking sunglasses in a dark tint
(i.e. grade 3)•

Protect their skin by using non-greasy sun-screen (water-based sunscreen should be preferred to oil-based sun-screen that may affectsweating).

•

Wear lightly coloured clothing that can also minimize the effect of thesun’s radiation, but clothing should not impair sweat evaporation.

•Self-dousing water or other cooling techniques that are commonly
adopted are less evidence-based but may offer some psychologicalbenefit.

•Any cooling method should be tested and individualised during training
and not in competition, to minimise disruption to the athlete.

DURING WARM-UP, CONSIDER USING:

ICE
VESTS

ICE
SLURRYCOLDTOWELS

DO MEDICATIONS HAVE AN IMPACT ON
HEAT STRESS DURING EXERCISE?
The use of prescribed or over-the-counter medication can have a significant
impact on the body capacities of dissipating heat. The following medications
have been demonstrated to have a direct effect on central temperature
control and heat dissipation:•Diuretics (such as furosemide, acetazolamide, amiloride, bumetanide,torsemide, hydrochlorothiazide, spironolactone and metolazone);•Non-steroidal anti-inflammatory drugs (NSAIDs, such as aspirin,ibuprofen, naproxen and ketoprofen);•ADHD medications (such as methylphenidate anddextroamphetamine-AMP);•Selective serotonin reuptake inhibitors (SSRIs, such as fluoxetine,sertraline, paroxetine and citalopram);•Ephedrine containing medications.

Individuals taking these medications should be aware of their potential
increased risk of heat-related illnesses during exercise and should consult
their physician prior to conducting any form of exercise. Especially when
exercise will be conducted in an extreme environment such as heat.

15

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www.worldathletics.org@worldathletics

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