fluids and electrolytes: hydration for physical activity...

Fluids and Electrolytes: Hydration for Physical Activity and Sport

Advanced Module

1

Learning Objectives of the Course

After completing this module, participants will be able to Understand significance of water in the human body Explain the process of thermoregulation during exercise Describe the sweat mechanism and reason for electrolyte losses

in the water of sweat Recognize and reduce the risk of heat illnesses by stating the

symptoms, contributing factors, and strategies for prevention Estimate appropriate fluid replacement needs and hydration

strategies Discuss several specific concerns and apply strategies to help

prevent their occurrence during exercise in the heat – Dehydration – Hyponatremia

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Hydration of the Human Body

Is the body nearly 75% water as often stated? – In fact, lean tissue (fat-free mass) is about 73% water – The whole body is roughly 50% to 65% water

• Leaner individuals having the higher water percentage • Fat mass contains very little water

– The more adipose tissue, the lower the water percentage The roles and significance of water in the body

– Gives form and substance to body – Lubricates joints – Transports nutrients and waste (eg, blood is nearly 80% water) – Provides a medium for metabolism – Is a reactant in or product of metabolic reactions – Is a major factor in heat dissipation

• Cardiovascular system – cardiac output • Thermoregulation – skin blood flow and sweat

3 Casa DJ, et al. J Athl Train. 2000;35(2):212-224.

Thermoregulation

4

Nadel ER, et al. Ann N Y Acad Sci. 1977;301:98-109. Wilmore JH, et al. Physiology of Sport and Exercise 4th edition. Champaign: Human Kinetics Publishers; 2008: pp 252-268.

Effect of Exercise Increases metabolism and body heat production

Response to Exercise: Maintenance of Homeostasis

Heat removal is required Means of doing so include • Conduction (Cd) • Convection (Cv) • Radiation (R) • Evaporation (E, via sweat)

Cv

R

E

Cd

Quantifying the Change in Heat

Heat balance = M ± Cd ± Cv ± R – E

Where − Metabolic rate (M) contributes to heat gain − Conductance (Cd) is considered to be zero in application and is typically

not used − Convection (Cv) and radiation (R) can be positive or negative (adding to

or subtracting from metabolic heat gain), depending on environmental temperature vs the body

− Evaporation (E) is always negative (subtracting from metabolic heat gain), reducing body temperature

5

Nadel ER, et al. Ann N Y Acad Sci. 1977;301:98-109. Wilmore JH, et al. Physiology of Sport and Exercise 4th edition. Champaign: Human Kinetics Publishers; 2008: pp 252-268.

Evaporation of Sweat

Critical body cooling mechanism for most physical activities – 1 liter of sweat evaporated off the skin dissipates 580 kcal of heat – Must evaporate off the skin

• No dissipation occurs when sweat drips off the body

6

Costill DL. Ann N Y Acad Sci. 1977;301:160-174. Cheuvront SN, et al. Cur Sports Med Rep. 2003;2(4):202-208.

Routes to Initiate and Discontinue Sweating

Exercise increases heat production – Temperature of blood ↑ – Thermoreceptors sense ↑ temperature

Input to CNS control center, preoptic anterior hypothalamus, via – Circulation of warmer blood temperature – Afferent signals thermoreceptors

Hypothalamus stimulates response via the SNS – Sweat glands secrete fluid – Arterioles in skin dilate

Thermoreceptors detect a reduced skin temperature, provide neural feedback to hypothalamus

7

Abbreviations: CNS, central nervous system; SNS, sympathetic nervous system. Crandall CG , et al. J. Acta Physiol. 2010;199:407-423. Shibasaki M, et al. Front Biosci (Schol Ed). 2011;2:685-696.

Sweat Rate: A Function of Several Factors

Environment – Temperature – Humidity

Fitness Heat acclimation Gender Genetics Exercise intensity Clothing and equipment

Average sweat rates, L/hour

Swimmers 0.3 Motor-car athletes 1.1 Yacht athletes 1.3 Junior hockey 1.5 NFL players 2.1

8

Brearley M, et al. Int J Sports Physiol Perform. 2007;2(2):182-191. Godek SF, et al. J Athl Train. 2010;45(2):128-135. Neville V, et al. Scand J Med Sci Sports. 2010;20(3):475-484. Maughan RJ, et al. Int J Sport Nutr Exerc Metab. 2009;19(6):598-606. Palmer MS, et al. Appl Physiol Nutr Metab. 2010;35(3):328-335.

9

Sweat Composition: More than Just Water

Sweat Minerals Range, mmol/L1

Sodium 20 - 80

Chloride 20 - 60

Potassium 4 - 8

Calcium 0 - 1

Magnesium < 0.2

Factors affecting sweat electrolyte concentration include sweat rate, state of heat acclimatization, genetics, and gender.

1. Data from Maughan RJ. J Sports Sci. 1991;9 Spec No:117-142.

Electrolyte Loss in Sweat Sweat gland function

– Draws water from plasma volume to make sweat • Proteins, other large

compounds remain in blood • Minerals move with the water

– Reabsorbs minerals for conservation

– Reabsorption is not 100%

When rate and duration of sweat loss are extensive, replacement of water and electrolytes is increasingly important.

10

H2O Na Cl K

High flow rate Na Cl K

Heat dissipation Final Na+, Cl–, K+, other minerals in sweat

Low flow rate Na Cl K

Sweat Droplet

Duct

Secretory coil

Abbreviations: Na, sodium; Cl, chloride; K, potassium. Sato K, et al. J Am Acad Dermatol. 1989;20(4):537-563.

Clothing: Barriers to Heat Dissipation Clothing such as gear and uniforms in sports

– Retards the evaporation of sweat for heat dissipation – Adds insulation to increase heat retention – Adds weight that can increase work and heat production

Rec

tal T

empe

ratu

re, °

C

36.5

37

37.5

38

38.5

39

39.5

Clothes only

Weighted Backpack

Wearing Gear

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After 30-minutes’ rest in uniform, temp still above peak during exercise in t-shirt

Mathews DK, et al J Appl Physiol. 1969;26(5):611-615.

In a classic study, – 30 minutes of moderate intensity

exercise on treadmill and 30 minutes of recovery showed • Temperature increases during

exercise with increasing weight and clothing − T-shirt and shorts (Clothes only) − Clothing + Weighted Backpack − Football uniform (Wearing Gear)

• Baseline temperature returns slower with increasing weight and clothing

Outcomes When Heat Production Is Not Offset During Exercise

Rapid increase in core temperature ↑ Risk of heat illnesses

– Heat cramps – Heat syncope – Heat exhaustion – Heat stroke

12

Wilmore JH, et al. Physiology of Sport and Exercise 4th edition. Champaign: Human Kinetics Publishers; 2008: pp 252-268. American College of Sports Medicine. Med Sci Sports Exerc. 2007;39(3):556-572.

Heat Illnesses

Factors contributing to episodes of heat illnesses – Intensity of exercise – Heat acclimation – Fitness level – Medications – Supplements with ephedra

or other stimulants – Environment – Recent illness – Hypohydration or dehydration

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Caution: Heat stroke can occur with little warning or few associated factors being present


Heat Cramps (Exercise Associated Muscle Cramps) Definition: involuntary contractions and spasms of skeletal muscle in

association with intensity of exercise in the heat Symptoms

– Twitching or tightening precedes the cramp – Fatigue – Possibly nausea

Contributing factors – Muscle fatigue – Large losses of fluid and electrolytes (particularly sodium) – Multiple and/or prolonged competition within a day

Treatment – Stretching – Rest – Replace fluids and electrolytes (orally or by intravenous infusion depending on

severity)

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Heat Syncope

Definition: orthostatic hypotension and collapse in the heat, occurring as a result of heat exposure, vasodilation, and lack of movement Symptoms

– Unconsciousness after standing or stopping movement in a hot environment

Contributing factors – Prolonged heat exposure, possibly while wearing excess clothing – Not necessarily large fluid losses

Treatment – Elevate legs to restore blood flow to head – Rest in a cool area to reduce body temperature – Possibly oral fluids, if dehydration appears to be a factor

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Heat Exhaustion Definition: inability to continue work or exercise in the heat Symptoms

– Fatigue, weakness – Irritable – Headache – Nausea or vomiting – Chills – Low blood pressure and rapid pulse – Core temperature may be elevated, but <40° C

Contributing factors – Excessive sweat and electrolyte loss – Prolonged exercise in heat – Pre-existing dehydration

Treatment – Rest in cool area, elevate legs if victim feels faint – Fluid and electrolyte replacement orally or intravenously – Monitor vital signs

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Heat Stroke (HS) Definition: extreme core body temperature increase due to failure of the brain

to function normally and sustain cooling – Other organ systems also failing

Symptoms – Rectal temperature > 40° C is the definitive sign – May have hot pale skin – Confusion or irrational behavior – Hyperventilation (rapid breathing) – Vomiting – Loss of consciousness – Seizures – Coma Contributing factors

– Intense exercise in or exposure to the heat – Recent illness – Use of certain medications – Dehydration is likely, but not necessary

for HS to occur Treatment

– Immediate cooling such as in an ice bath or ice packs – Treat as a medical emergency—call 911

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Medications thought to increase risk of heat stroke

• Diuretics • Drugs having diuretic actions

- Ephedrine-containing medication - Ephedra herb - Alcohol - Possibly caffeine and theophylline


Effect of Dehydration on Physiology Study involving 8 endurance-trained cyclists, with 4

sessions each Cycling at constant work load (~65% peak VO2) for

2 hours in heat (32.7o C) Randomized to different fluid replacement treatments

– No fluid (–4.2%) – 20% of sweat loss (–3.4%) – 50% of sweat loss (–2.3%) – 80% of sweat loss (–1.1%) Thermoregulation and

cardiovascular responses follow in the next slides

18 Montain SJ, et al. J Appl Physiol. 1992;73(4):1340-1350.

Thermoregulatory Response to Replacement Fluids: Temperature

36

36.5

37

37.5

38

38.5

39

0 20 40 60 80 100 120

Esop

hage

al T

empe

ratu

re, °

C

Time, minutes

No fluid20% of sweat loss50% of sweat loss80% of sweat loss

Reprinted from Montain SJ, et al. J Appl Physiol. 1992;73(4):1340-1350.

Thermoregulatory Response to Replacement Fluids: Blood Flow

10

11

12

13

14

15

16

17

0 20 40 60 80 100 120

Fore

arm

Blo

od F

low

, m

L/10

0 m

L/m

in

Time, minutes


-4.2%

-1.1%


Cardiovascular Response to Replacement Fluids: Heart Rate

130135140145150155160165170

0 60 120

Hea

rt R

ate,

bea

ts/m

inut

e

Time, minutes


-1.1%

-4.2%


Cardiovascular Response to Replacement Fluids: Cardiac Output

15.516

16.517

17.518

18.519

19.5

0 60 120

Car

diac

Out

put,

L/m

inut

e

Time, minutes


-1.1%

-4.2%


Summary of Dehydration Effects

Impaired cardiovascular function1

Impaired heat dissipation2

Elevated ratings of perceived exertion2

Starting at 2% dehydration,2-7 – Physical endurance is reduced – Cognitive function is impaired

23

1. Crandall CG, et al. J. Acta Physiol. 2010;199:407-423. 2. Murray B. J Am Coll Nutr. 2007;26(5 suppl):542S-548S. 3. Lieberman HR. J Am Coll Nutr. 2007;26(5 suppl):555S-561S. 4. Grandjean AC, et al. J Am Coll Nutr. 2007;26(5):549S-554S. 5. Casa DJ, et al. J Athl Train. 2010;45(2):147-156. 6. Gopinathan PM, et al. Arch Environ Health. 1988;43(1):15-17. 7. Judselson DA, et al. Sports Med. 2007;37(10):907-921.

Thirst Mechanism Defends Against Dehydration Fluid loss from plasma volume

– Reduces blood pressure – Increases plasma osmolality

Nervous system detects changes – Baroreceptors sense drop in pressure – Chemoreceptors sense rise in osmolality

Receptors in CV system signal hypothalamus – Registers as “thirst” – Stimulates behavior to drink and restore plasma volume

Replacement is not perfect – For reasons yet unknown, humans typically stop drinking during exercise before

replacing 100% of fluid lost – Potential reasons for gap in drinking response

• Allows humans to override the thirst response when other physical danger is imminent

• Inadequate response may help prevent acute hyponatremia

24 Greenleaf JE. Med Sci Sports Exerc. 1992;24(6):645-656.

Hyponatremia

25

Defined as – Plasma blood sodium level < 135 mmol/L – Normal range, 136 to 142 mmol/L

Symptoms – Headache – Coma and/or death from shifts in water into brain cells

Risk Factors • Over drinking, weight gain during exercise • Small body mass • “Back-of-the-pack” runner • Female • Drinking fluids containing no sodium

Almond CSD, et al. N Engl J Med. 2005;352(15):1550-1556. Francesconi RP, et al. J Appl Physiol. 1987;62(3):1271-1276. Maughan RJ, et al. Eur J Appl Physiol Occup Physiol. 1995;71(4):311-319. Montain, SJ, et al. Br J Sports Med. 2006;40:98-106. Speedy DB, et al. Med Sci Sports Exerc. 1999;31(6):809-815. Vrijens DMJ, et al. J Appl Physiol. 1999;86:1847-1851.

Mechanisms of Hyponatremia During Exercise

Exercise-associated hyponatremia linked to – Over drinking of water – Inappropriate arginine vasopressin (AVP) secretion – Cytokine production by damaged muscle – Excessive sodium loss

Non–exercise-associated hyponatremia linked to – Mental disorders – Post-surgery complications

26

Beltrami FG, et al. Br J Sports Med. 2008;42(10):796-801. Francesconi RP, et al. J Appl Physiol. 1987;62(3):1271-1276. Montain, SJ, et al. Br J Sports Med. 2006;40:98-106. Noakes TD, et al. Med Sci Sports Exerc. 1985;17(3):370-375. Rahman M, et al. Neurosurgery. 2009;65(5):925-935. Siegel AJ. Harv Rev Psychiatry. 2008;16(1):13-24.

Fluid-Need Estimate for Exercise

Weigh yourselfa

– Before exercise – After exercise

Record duration of exercise in hours Estimate fluid volume intake (16 oz = 1 lb) Account for urine loss, if relevant (8 oz = 0.5 lb)

ΔBW + drink volume – urine volume = Sweat rate, lb/hour Exercise duration, hour

aMethod is relevant and precise for 1 to 2 hours of exercise. During longer events, depletion of carbohydrate may account for some of the change in body

weight and is not associated with fluid loss.

27 American College of Sports Medicine, et al. Med Sci Sports Exerc. 2007;39(2):377-390. Maughan RJ, et al. J Sports Sci. 2007;25(7):797-804.

Difference = Δ body weight (BW) in pounds (lb)

Fluid-Need Estimate for Exercise - Metric

Weigh yourselfa

– Before exercise – After exercise

Record duration of exercise in hours Estimate fluid volume consumed Account for urine loss, if relevant

– Use units of milliliters and divide by 1,000 for Liters ΔBW + drink volume – urine volume = Sweat rate, L/hour Exercise duration, hour

aMethod is relevant and precise for 1 to 2 hours of exercise. During longer events, depletion of carbohydrate may account for some of the change in body

weight and is not associated with fluid loss.

28

Difference = Δ body weight (BW) in kilograms (kg)

American College of Sports Medicine, et al. Med Sci Sports Exerc. 2007;39(2):377-390. Maughan RJ, et al. J Sports Sci. 2007;25(7):797-804.

Estimating Fluid Intake Needs During Exercise

Repeat procedure for estimating fluid intake in various weather conditions Calculate estimates for

– Hot and cooler days – Different amounts of clothing – Different intensities of exercise

Apply appropriate sweat rate as part of strategy during training and competition

29 American College of Sports Medicine, et al. Med Sci Sports Exerc. 2007;39(2):377-390.

Strategies to Maintain Hydration

Estimate rate of sweat loss Anticipate volume needs

– Use guidelines for replacement

30

American College of Sports Medicine et al. Med Sci Sports Exerc. 2007;39(2):377-390. American Dietetic Association, et al. Med Sci Sports Exerc. 2009;41:709-731. Burke LM, et al. Sports Med. 1997;24(1):38-54. Maughan RJ, et al. Scand J Med Sci Sports. 2010;20(suppl 3):40-47.

Fluid Intake Guidelines: US Volumes

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2007 ACSM Position Stand Recommended replacement

during exercise – Volume to prevent acute loss of

>2% of body weight – Don’t drink in excess

• No demonstrable benefits of over hydration

• Increases risk of hyponatremia

Provides specifics on fluid formulation to optimize safety and performance

Recommended volume to ingest every 15 min to minimize dehydration

Expected sweat rate, lb/hour

oz/15 min to replace

80%


90%


100%

0.5 1.6 1.8 2.0 1.0 3.2 3.6 4.0 2.0 6.4a 7.2 8.0 3.0 9.6 10.8 12.0 4.0 12.8b 14.4 16.0 5.0 16.0 18.0 20.0 6.0 19.2 21.6 24.0 7.0 22.4 25.2 28.0

lb, pound; oz, ounce. a At this rate, a 121-lb female experiences only 0.3% dehydration (<1% body weight loss). b At this rate, a 154-lb male experiences only 0.5% dehydration (<1% body weight loss).

American College of Sports Medicine (ACSM), et al. Med Sci Sports Exerc. 2007;39(2):377-390.

Fluid Intake Guidelines: Metric Volumes

32

2007 ACSM Position Stand Recommended replacement

during exercise – Volume to prevent acute loss of

>2% of body weight – Don’t drink in excess

• No demonstrable benefits of over hydration

• Increases risk of hyponatremia

Provides specifics on fluid formulation to optimize safety and performance

Recommended volume to ingest every 15 min to minimize dehydration

Expected sweat rate, L/hr

mL/15 min; 80% replaced



0.25 50 56 62

0.50 100 112 125

1.00 150a 169 188

1.50 200 225 250

1.75 300 338 375

2.00 400b 450 500

2.50 500 562 625

3.00 600 675 750 L, liter; mL, milliliter. a At this rate, a 55-kg female would experience only 0.4% dehydration (<1% body weight loss). b At this rate, a 70-kg male would experience only 0.6% dehydration (<1% body weight loss).

American College of Sports Medicine (ACSM), et al. Med Sci Sports Exerc. 2007;39(2):377-390.

Strategies to Maintain Hydration

Estimate rate of sweat loss Anticipate volume needs

– Use guidelines for replacement1-4

Make it easy to get to fluid – Sports bottles – Sidelines – Belts with bottles – Time-outs/breaks for fluids Use fluids that promote adequate volume intake

and encourage drinking

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1. American College of Sports Medicine, et al. Med Sci Sports Exerc. 2007;39(2):377-390. 2. American Dietetic Association, et al. Med Sci Sports Exerc. 2009;41(3):709-731. 3. Burke LM, et al. Sports Med. 1997;24(1):38-54. 4. Maughan RJ, et al. Scand J Med Sci Sports. 2010;20(suppl 3):40-47.

Characteristics of Appropriate Fluids Used During Exercise Encourages drinking behavior

– Light flavor system – Moderate sweetness

Stimulates adequate drink response – Contains sodium

Helps replace electrolytes, retain fluid – Contains electrolytes/minerals

• Sodium and chloride are critical

Promotes absorption of fluid and substrate – Contains transportable nutrients

• Combination of monosaccharides • Limited absolute amounts for tonicity

Sustains performance in physical and cognitive efforts

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Recommended Oral rehydration solutions Sports drinks

Acceptable, in some cases Water

Not recommended Energy drinks Fruit juice Soft drinks – diet or regular Beverages with alcohol

Passe, DH. In: R. Maughan and R. Murray (eds). Sports Drinks: Basic Science and Practical Aspects. Boca Raton: CRC Press; 2000: pp 45-88.

Limitations of Conventional Fluid Replacement Options Issue Excessive salt loss

Indigestion/heart burn

Large sweat losses

Limitation Sports drinks with 100 to 110 mg sodium/8 oz

are on low end of that in human sweat (110 to 440 mg/8 oz of sweat)

Calorie content and presence of acidity may delay gastric emptying and provoke indigestion in those at risk

May be difficult to match volume ingested with sweat rate – Particularly if sodium content is low and

carbohydrate (CHO) is relatively high (ie, exceeds 60 g CHO ingested/hour—too many calories)

Athletes experiencing these issues should select rehydration solutions with

sodium content of > 660 mg/quart (> 30 mEq/L), low CHO content of ~ 20 to 40 g/quart (20 to 40 g/L), and/or

possibly devoid of citric acid.

35 R. Maughan and R. Murray (eds). Sports Drinks: Basic Science and Practical Aspects. Boca Raton: CRC Press; 2000: pp 45-88.

Objective Monitoring of Hydration Status

Day-to-day body weight – Should restore at least 80% of weight lost from prior day workout

Urine – Color is an approximate for hydration status

• Intense yellow, small volume indicates dehydration • Clearly and almost colorless with adequate volume indicates normal hydration

– Specific gravity (USG) or osmolality can be used as quantitative index • USG should ≤ 1.20 • Osmolality should be < 900 mOsm/kg

Thirst – Alone, thirst is a poor indicator particularly during exercise – Combined with acute change in body weight and urine index, thirst is a valid

predictor

36

American College of Sports Medicine, et al. Med Sci Sports Exerc. 2007;39(2):377-390. American Dietetic Association, et al. Med Sci Sports Exerc. 2009;41:709-731. Burke LM, et al. Sports Med. 1997;24(1):38-54. Maughan RJ, et al. Scand J Med Sci Sports. 2010;20(suppl 3):40-47. Shirreffs SM, et al. Med Sci Sports Exerc. 1996;28(10):1260-1271.

Other Strategies to Defend Against Heat Stress

Environmental awareness Clothing adjustment

– Light weight, reflects light – Porous – Holds fluid for evaporation

Modifications in training sessions – Location: out of the heat – Time of day: cooler hours

and less direct sunlight

Heat acclimation

Wet bulb globe temperate

(WBGT) meter for monitoring environmental stress from humidity, air temperature, and radiant heat of the sun

37

American College of Sports Medicine, et al. Med Sci Sports Exerc. 2007;39(2):377-390. American Dietetic Association, et al. Med Sci Sports Exerc. 2009;41(3):709-731. Burke LM, et al. Sports Med. 1997;24(1):38-54. Maughan RJ, et al.. Scand J Med Sci Sports. 2010;20(suppl 3):40-47.

Heat Acclimation

Acquired within a 10- to 14-day period of training by – ~100 minutes per exercise session – Heat exposure – Reduced training intensity

Effects – Expanded total body water and plasma volume – Sweating response

• Distributed more evenly across entire body • Initiated sooner, at a lower rise in core temperature • Higher rate of sweating

– Lower concentrations of sweat electrolytes (conservation) – Reduced body temp, less CV stress when training at same intensity – Attenuated rate of rise in core temperature

38

Abbreviation: CV, cardiovascular. Wilmore JH, et al. Physiology of Sport and Exercise 4th edition. Champaign: Human Kinetics Publishers; 2008: pp 252-268. Montain SJ, et al. Int J Sports Med. 1998;19(2):87-91. Sawka MN, et al. J Appl Physiol. 1985;59(5):1394-1401.

Well hydrated, but not acclimated Well hydrated and acclimated

Time, minutes

Cor

e Te

mpe

ratu

re, º

C

Sawka MN, et al. Int J Sports Med. 1998;19(suppl 2):S108-S110.

Core Temperature Benefits of Acclimation During Submaximal Exercise

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Summary Thermoregulation during exercise includes convection, radiation, and evaporation

− Evaporation of sweat is key to keep athletes cool during exercise, particularly in the heat • Sweat consists of water and salts (electrolytes) • Total amounts of water and salts lost are dependent on sweat rate

Heat cramps, heat exhaustion, and heat stroke are the 3 main risks of overheating during exercise – All 3 are related to intense exercise in the heat – Key factors are dehydration and not tailoring the exercise session for heat

Dehydration is the loss of body fluid – At > 2% of body weight, dehydration can result in reduced performance and risk of illness

Fluid intake needs should be estimated to replace sweat loss – Estimation should consider temperature, clothing, and exercise conditions – Hydration status should be monitored

Strategies to promote safety and exercise performance under hot conditions – Fluid intake containing appropriate sodium and carbohydrate concentrations – Clothing adjustments – Modify exercise session – Heat acclimation

40

Appendix 1: Bibliography Almond CSD, Shin AY, Fortescue EB, et al. Hyponatremia among runners in the Boston Marathon. N Engl J Med.

2005;352(15):1550–1556. American College of Sports Medicine, et al. Position Stand: Exertional Heat Illness During Training and Competition.

Med Sci Sports Exerc. 2007;39(3):556-572. American College of Sports Medicine, et al. Position Stand: Exercise and Fluid Replacement. Med Sci Sports Exerc.

2007;39(2):377-390. American Dietetic Association, et al. Position Stand: Nutrition and Athletic Performance. Med Sci Sports Exerc.

2009;41(3):709-731. Beltrami FG, Hew-Butler T, Noakes TD. Drinking policies and exercise-associated hyponatraemia: is anyone still

promoting overdrinking? Br J Sports Med. 2008;42(10):796-801. Brearley MB and Finn JP. Responses of motor-sport athletes to v8 supercar racing in hot conditions. Int J Sports

Physiol Perform. 2007;2(2):182-191. Burke LM, Hawley JA. Fluid balance in team sports. Guidelines for optimal practices. Sports Med. 1997;24(1):38-54. Casa DJ, Armstrong LE, Hillman SK, et al. National Athletic Trainers’ Association position statement: fluid

replacement for athletes. J Athl Train. 2010;35(2):212-224. Casa DJ, Stearns RL, Lopez RM, et al. Influence of hydration on physiological function and performance during trail

running in the heat. J Athl Train. 2010;45(2):147-156. Cheuvront, SN, Carter R 3rd, Sawka MN. Fluid balance and endurance exercise performance. Cur Sports Med Rep.

2003;2(4):202-208. Costill DL. Sweating: its composition and effects on body fluids. Ann NY Acad Sci. 1977;301:160-174. Crandell CG and Gonzalez-Alonso J. Cardiovascular function in the heat-stressed human. Acta Physiol.

2010;199(4):407-423. Francesconi RP, Hubbard RW, Szlyk PC, et al. Urinary and hematological indexes of hydration. J Appl Physiol.

1987;62:1271-1276. Godek SF, Bartolozzi AR, Peduzzi C, et al. Fluid consumption and sweating in National Football League and collegiate

football players with different access to fluids during practice. J Athl Train. 2010;45(2):128-135. Gopinathan PM, Pichan G, Sharma VM. Role of dehydration in heat stress-induced variations in mental

performance. Arch Environ Health. 1988;43(1):15-17. Grandjean AC and Grandjean NR. Dehydration and cognitive performance. J Am Coll Nutr. 2007;26(5 suppl):549S-

554S. 41

Appendix 1: Bibliography (2) Greenleaf JE. Problem: thirst, drinking behavior, and involuntary dehydration. Med Sci Sports Exerc.

1992;24(6):645-656. Hunt JN and Knox MT. The slowing of gastric emptying by four strong acids and three weak acids. J Physiol.

1972;222(1):187-208. Judelson DA, Maresh CM, Anderson JM, et al. Hydration and muscular performance: does fluid balance affect

strength, power and high-intensity endurance? Sports Med. 2007;37(10):907-921. Lieberman HR. Hydration and cognition: a critical review and recommendations for future research. J Am Coll Nutr.

2007;26(5 suppl):555S-561S. Maughan RJ. Fluid and electrolyte loss and replacement in exercise. J Sports Sci. 1991;9 Spec No:117-142. Maughan RJ, Dargavel LA, Hares R, Shirreffs SM. Water and salt balance of well-trained swimmers in training. Int J

Sport Nutr Exerc Metab. 2009;19(6):598-606. Maughan RJ and Leiper JB. Sodium intake and post-exercise rehydration in man. Eur J Appl Physiol. 1995;71(4):311-

319. Maughan RJ and Shirreffs SM. Dehydration and rehydration in competitive sport. Scand J Med Sci Sports.

2010;20(suppl 3):40-47. Maughan RJ, Shirreffs SM, Leiper JB. Errors in the estimation of hydration status from changes in body mass. J

Sports Sci. 2007;25(7):797-804. Mathews DK, Fox EL, Tanzi D. Physiological responses during exercise and recovery in a football uniform. J Appl

Physiol. 1969;26(5):611-615. Montain SJ and Coyle EF. Influence of graded dehydration on hyperthermia and cardiovascular drift during exercise.

J Appl Physiol. 1992;73(4):1340-1350. Montain SJ, Sawka MN, Wenger CB. Hyponatremia associated with exercise: risk factors and pathogenesis. Exerc

Sport Sci Rev. 2001;29:113-117. Montain, SJ, Cheuvront SN, Sawka MN. Exercise associated hyponatraemia: quantitative analysis to understand the

aetiology. Br J Sports Med. 2006;40:98-106. Montain SJ, Sawka MN, Latzka WA, et al. Thermal and cardiovascular strain from hypohydration: influence of

exercise intensity. Int J Sports Med. 1998;19(2):87-91. Murray B. Hydration and physical performance. J Am Coll Nutr. 2007;26(5 suppl):542S-548S. Nadel ER, Wenger CB, Roberts MF, et al. Physiological defenses against hyperthermia of exercise. Ann NY Acad Sci.

1977;301:98-109. Neville V, Gant N, Folland JP. Thermoregulatory demands of elite professional America's Cup yacht racing. Scand J

Med Sci Sports. 2010;20(3):475-484. 42

Appendix 1: Bibliography (3) Noakes TD, Goodwin N, Rayner BL, et al. Water intoxication: a possible complication during endurance exercise.

Med Sci Sports Exerc. 1985;17(3):370-375. Palmer MS, Logan HM, Spriet LL. On-ice sweat rate, voluntary fluid intake, and sodium balance during practice in

male junior ice hockey players drinking water or a carbohydrate-electrolyte solution. Appl Physiol Nutr Metab. 2010;35(3):328-335.

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Appendix 2: Unit Conversions Work or heat: Kilojoules (kj) to kilocalories (kcal)

– Multiply kj value by 4.186 to obtain kcal Temperature: Celsius (C) to Fahrenheit (F)

– Multiply the C value by 1.8 and add 32 to obtain F Concentrations: mmol/L to mEq/L

– Conversion is one-to-one if electrolytes are univalent (single charge) – Multiply mmol by the charge on the electrolyte if divalent or greater than one.

Particles to mass: milimoles to milligrams – Multiply mmol value by the atomic weight of the element

Metric to English volumes: milliliters (mL) to ounces (oz) – Divide metric volume by 28 ml to obtain ounces

Volume to mass: liters (L) to mass (kg) or oz to pounds – One to one conversion for L to kg (assumes fluid density of 1.00) – Divide ounces value by 16 to get pounds (lb)

Mass to force: kilograms (kg) to pounds (lb) – Divide kg by 2.2 to obtain weight in lb

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Appendix 3: Environmental Awareness and Guidelines A wet bulb, globe, temperature meter (WBGT) or a sling psychrometer can be

used to monitor environmental conditions

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Abbreviations: EHS, exertional heat stroke; F, Fahrenheit. a EHS can still occur due to other factors. American College of Sports Medicine. Med Sci Sports Exerc. 2007;39(3):556-572. Adapted from Casa DJ, Eichner ER. Exertional heat illness and hydration. In: Starkey C, Johnson G (eds). Athletic Training and Sports Medicine. Boston; Jones and Bartlett; 2005: pp 597-615.

fluids and electrolytes: hydration for physical activity...

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