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Hydration and thermoregulation.pdf
1. EXSS3071: Nutrition for Exercise and Health
Hydration & Thermoregulation
Miss Sheran Guo, APD
Acknowledgements:
Dr Janelle Gifford
Assoc Prof Helen O’Connor
Ms. Alison Miles
Mr. Kenneth Daniel
2. Basic Overview
§ Basic concepts
§ Plasma volume and hydration
§ Thermoregulation
§ Effects of hypohydration
§ Prevention of hypohydration and
recommendations
– When to drink?
– How much to drink?
– What to drink?
Free Pickit image
The University of Sydney Page 2
3. Hydration Terms & Physiological Effects
Dehydration:
¯ of body
water
Hyperhydration
Hypohydration
Euhydration
BODY
WATER
CONTENT
‘normal’ body water
content
body water content
excesses
body water content
deficits
The University of Sydney Page 3
Variations %BW occur
across population groups
e.g., est. infants (~75%) VS
elderly (~55%)
Dale A Schoeller, Changes in total body water with
age, The American Journal of Clinical Nutrition,
Volume 50, Issue 5, November 1989, Pages 1176–
1181, https://doi.org/10.1093/ajcn/50.5.1176
Additional terms to be familiar with:
• Total body water
• Osmolality
• Hyponatremia
• Hypertonic / hypotonic
4. Fluid distribution: intra- and extracellular compartments
Folkow & Neil (1971),
cited in Fox, SI (1993),
Human Physiology,
Fourth ed. Dubuque:
Wm. C. Brown
Publishers
The University of Sydney Page 4
25% heat load
regulation
(~0.52 mL/kcal)
“Typical” net
loss of ~1
mL/kcal REE
5. Absorption of sodium and water, secretion of water
Cell model for the absorption of sodium and water
Bahn, A. Water, electrolytes, and acid-base balance. In Mann, J and Truswell, AS (eds), Essentials of Human Nutrition (5th Edition). Oxford
University Press: Oxford, pp113-130. See also https://www.youtube.com/watch?v=I1MZG6508IM for explanation of cell transport.
The University of Sydney Page 5
6. The University of Sydney Page 8
Negative feedback control of blood volume and osmolality
STIMULI
Dehydration
(¯ blood volume) Salt ingestion
Blood osmolality
NEGATIVE FEEDBACK RESPONSE
blood volume
¯ blood osmolality
Osmoreceptors in
hypothalamus
posterior pituitary gland thirst
ADH
water retention by kidneys drinking
Redrawn from Fox, SI (1993), Human
Physiology, Fourth ed. Dubuque: Wm.
C. Brown Publishers
7. The University of Sydney Page 9
Angiotensin II
NEGATIVE FEEDBACK RESPONSE blood volume
Angiotensinogen Angiotensin I
Redrawn from Fox, SI (1993), Human
Physiology, Fourth ed. Dubuque: Wm. C.
Brown Publishers
STIMULI
¯ blood pressure
¯ blood flow to kidneys
Juxtaglomerular apparatus
in kidneys
Renin
Converting
enzyme
Aldosterone
Adrenal Cortex
Vasocontriction
arterioles
Salt and water
retention by kidneys
blood pressure
Negative feedback control of blood volume and osmolality
8. Hypohydration
• 9 subjects (8 M, 1 F)
• Randomized cross over:
• 3-day water restriction (1L/day including
food and fluid) OR
• 6.8L fluid/day
• Fixed Na & K intake
• Outcomes measured:
• Plasma osmolality (Posm)
• Urine osmolality (Uosm)
• Arginine Vasopressin (AVP or ADH)
Shore AC, Markandu ND, Sagnella GA, Singer DR, Forsling ML, Buckley MG, Sugden AL, MacGregor GA. Endocrine and
renal response to water loading and water restriction in normal man. Clin Sci (Lond). 1988 Aug;75(2):171-7. doi:
10.1042/cs0750171. PMID: 2970362.
9. General Water Requirements
• TBW fluctuations broadly estimated ± 1% BW (600 – 900 mL/day)1
• Factors influencing water requirements of a population:
• Metabolic activity
• Environment
• Diet
• Adequate intake of fluids:
• Replace water lost
• Sufficient for excretion of solutes
• Amount of water consumed alone does not necessarily determine
euhydration 2
1. Cheuvront SN, Kenefick RW: Dehydration: physiology, assessment, and performance effects. Compr Physiol 4:257–285, 2014..
2. Perrier E, Vergne S, Klein A, Poupin M, Rondeau P, Le BL, Armstrong LE, Lang F, Stookey J, Tack I: Hydration biomarkers in free-living adults with different levels of habitual fluid consumption. Br J Nutr 109:1678–1687, 2013.
AI water intake (NNS 1995)
Adult men 3.4 L/day (fluid 2.6 L/day)
Adult women 2.8 L/day (fluid 2.1 L/day)
10. Temperature & Sport
• Average temperature ~ 37 °C for
homeostasis
• “Core” temperature > abdominal,
cranial and thoracic cavity
• “Shell” temperature > skin, muscle,
subcutaneous tissue
• Heat accumulation occurs when heat
generation > dissipation
• Age, sex
• BMI
• Environment & clothing
• Training
• Prior fluid intake
Source: Lim CL, Byrne C, Lee JK. Human thermoregulation and measurement of body temperature in
exercise and clinical settings. Ann Acad Med Singap. 2008 Apr;37(4):347-53. PMID: 18461221.
Rüst CA, Knechtle B, Rosemann T. Changes in body core and body surface temperatures during prolonged swimming in water of
10°C-a case report. Extrem Physiol Med. 2012 Nov 1;1(1):8. doi: 10.1186/2046-7648-1-8. PMID: 23849461; PMCID: PMC3710093.
11. Temperature & Sport
• Average temperature ~ 37 °C for
homeostasis
• “Core” temperature > abdominal,
cranial and thoracic cavity
• “Shell” temperature > skin, muscle,
subcutaneous tissue
• Heat accumulation occurs when heat
generation > dissipation
• Age, sex
• BMI
• Environment & clothing
• Training
• Prior fluid intake
Source: Lim CL, Byrne C, Lee JK. Human thermoregulation and measurement of body temperature in
exercise and clinical settings. Ann Acad Med Singap. 2008 Apr;37(4):347-53. PMID: 18461221.
Rüst CA, Knechtle B, Rosemann T. Changes in body core and body surface temperatures during prolonged swimming in water of
10°C-a case report. Extrem Physiol Med. 2012 Nov 1;1(1):8. doi: 10.1186/2046-7648-1-8. PMID: 23849461; PMCID: PMC3710093.
Source: Tipton M, Eglin C, Gennser M, Golden F. Immersion deaths and deterioration in
swimming performance in cold water. Lancet. 1999 Aug 21;354(9179):626-9. doi:
10.1016/S0140-6736(99)07273-6. PMID: 10466663.
12. Core Temperatures under Cool Conditions
Source: Veltmeijer MT, Eijsvogels TM, Thijssen DH, Hopman MT. Incidence and predictors of
exertional hyperthermia after a 15-km road race in cool environmental conditions. J Sci Med Sport.
2015 May;18(3):333-7. doi: 10.1016/j.jsams.2014.04.007. Epub 2014 Apr 26. PMID: 24930073.
Source: Macaluso F, Di Felice V, Boscaino G, Bonsignore G, Stampone T, Farina F, Morici G. Effects of
three different water temperatures on dehydration in competitive swimmers, Science & Sports 2011;
26(5): 265-77. https://doi.org/10.1016/j.scispo.2010.10.004.
13. metabolic heat
sweating
Exercise
Hydrostatic pressure in
capillaries
Force water from
plasma to interstitial
fluid
¯ Plasma volume
metabolic wastes within
the muscle
intramuscular osmotic
pressure
The University of Sydney Page 13
Muscle Contractions
14. Hyperthermia and HYPOhydration
— Hyperthermia
— Heat production in exercise 15-20 times higher
— Can core body temp by 1°C every 5mins if no heat removed
— Muscle generated heat faster than heat dissipation
— As body temp removal of heat via sweat is increasingly important
(Wilmore and Costill (1994), Physiology of Sport and Exercise. Human Kinetics, Champaign)
— Fluid deficits > 3-5%BW→ ¯ sweat production, ¯skin blood flow
Heat dissipation is reduced
• Hypohydration → ¯ exercise performance, decreases time to exhaustion,
increases heat storage
ACSM. Position Stand: Exertional Heat Illness during Training and Competition. Med. Sci. Sports Exerc.
39(3):556-572, 2007
The University of Sydney Page 14
15. Hyperthermia: motorsports
Walker SM, Ackland TR, Dawson B. The combined effect of heat and carbon monoxide on the performance of motorsport athletes. Comp Biochem Physiol A Mol Integr Physiol 2001;128(4):709-18.
The University of Sydney Page 14
16. Heat Illnesses in Sport
• 1996 Atlanta Olympics
• ~80% humidity, temperatures 19-35°C
• 12.8% of admissions to hospital treated for
heat related injuries throughout event:
• Heat cramps
• Hypohydration
• Heat syncope
• Heatstroke
• Prevalence audience & volunteers > athletes
• <<< 2020 Tokyo Olympics
https://www.youtube.com/watch?v=KzerHULhZ64
17. • Heat Illness
= heat exhaustion OR heat stroke
• May be caused by inadequate fluids before, during, and
after exercise
• Prevention
– adequate fluids before, during, and after exercise!
– recovery of loss may be assisted by electrolyte replacement
• See Sport Medicine Australia (SMA) Hot Weather Guidelines
available at
http://www.sma.org.au/pdfdocuments/Hot_Weather_Guidelines.pdf
• See also Racinais et al (2015), Concensus recommendations on training and
competing in the heat. Sports Med 45; 925-938.
http://themeatandpotatoesoflife.com/
Heat illness, fluids
The University of Sydney Page 17
18. • Heat Illness
= heat exhaustion OR heat stroke
• May be caused by inadequate fluids before, during, and
after exercise
• Prevention
– adequate fluids before, during, and after exercise!
– recovery of loss may be assisted by electrolyte replacement
• See Sport Medicine Australia (SMA) Hot Weather Guidelines
available at
http://www.sma.org.au/pdfdocuments/Hot_Weather_Guidelines.pdf
• See also Racinais et al (2015), Concensus recommendations on training and
competing in the heat. Sports Med 45; 925-938.
http://themeatandpotatoesoflife.com/
Heat illness, fluids
The University of Sydney Page 18
19. Exercise-associated hyponatremia (EAH)
Definition:
EAH is the occurrence of hyponatremia in individuals engaged in prolonged
physical activity and is defined by a serum or plasma sodium concentration
below the normal reference range of the laboratory performing the test; for
most laboratories, this is a [Na +] <135mmol/L.
Mechanisms
– Over-drinking
– Water intake in excess of the kidneys excretory capacity
– Behavioural or psychological factors
– Inappropriate ADH secretion
– Some impaired kidney diluting ability
– Failure to suppress ADH in face of in TBW
The University of Sydney Page 19
20. Exercise-associated hyponatremia (EAH)
Definition:
EAH is the occurrence of hyponatremia in individuals engaged in prolonged
physical activity and is defined by a serum or plasma sodium concentration
below the normal reference range of the laboratory performing the test; for
most laboratories, this is a [Na +] <135mmol/L.
Mechanisms
– Over-drinking
– Water intake in excess of the kidneys excretory capacity
– Behavioural or psychological factors
– Inappropriate ADH secretion
– Some impaired kidney diluting ability
– Failure to suppress ADH in face of in TBW
The University of Sydney Page 20
CLINICAL MANIFESTATIONS:
Headache
Irritability
Nausea and vomiting
Confusion
Disorientation
Stupor/coma
Convulsions
Respiratory arrest
21. Fluid needs
— Hypohydration
— heart rate
— body temp
— ¯ physical performance
— ¯ mental performance
— ¯ gastric emptying
(exertional heat stress can also ® gastrointestinal syndrome, see McCubbin C, et al. . IJSNEM, 2020; 30: 83-98).
— nausea/vomiting, heat illness
— Needs vary individually
— *genetics, body size, fitness, environment, intensity of exercise
— develop awareness of individual losses in different circumstances
— develop fluid replacement plan
*AIS website Fact Sheet: Fluid - who needs it? at http://www.ais.org.au/nutrition/documents/FactFluid.pdf
Jeukendrup, et al, Competition
fluid and fuel. In Burke and Deakin,
2015, pp376-419.
The University of Sydney Page 21
22. Hyperthermia: effect on sports
McCubbin AJ, Allanson BA, Odgers JNC, Cort MM, Costa RJS, Cox GR, Crawshay ST, Desbrow B, Freney EG, Gaskell SK, Hughes D, Irwin C,
Jay O, Lalor BJ, Ross MLR, Shaw G, Périard JD, Burke LM. Sports Dietitians Australia Position Statement: Nutrition for Exercise in Hot
Environments. IJSNEM, 2020; 30: 83-98 .
The University of Sydney Page 22
23. Hypohydration: endurance
– Temperate climate (20-21°C), 1-2% dehydration, <90min exercise
– performance effects insignificant (Cheuvront, et al, Curr Sports Med Rep, 2003; 2: 202–208)
– Temperate climate (20-21°C), >2% dehydration, generally
>90mins exercise
– impairs performance
– Hot climate (31-32°C), 2% dehydration, >60mins exercise
– significantly impacts performance
– Pre-exercise hypohydration ≥ 1.7% bw (Deshayes TA, et al. Sports Med. 2020; 50: 581-96).
– significantly impairs performance – running/cycling ≤ 60mins
– variety of environmental conditions (19-40°C)
– Possibly impedes VO2peak – magnitude related to extent of hypohydration
Shirreffs, SM, et al. J Sports Sci, 2011; 29(suppl): S39-S46.
The University of Sydney Page 23
24. Hypohydration: sprint/power/ strength
— Running
— 2-3% ¯ body mass may → no effect sprint performance
(See Judelson et al, Sports Med 2007; 37: 907-921, Watson et al MSSE 2005;
37:1168-1174; Folgelholm et al, MSSE 1993; 37:1168-1174)
(few studies address the independent effects of heat and hydration on repeated
sprint/intermittent sprints (Girard O et al. Scand J Med Sci Sports. 2015;25 Suppl 1:79-89.))
— Jump
— 1-3% ¯ body mass may → no effect jump power/ht
(See Cheuvront et al, Eur J Appl Physiol, 2010; 109: 1163-1170, Watson et al, MSSE
2005; 37:1168-1174; Hoffman et al, IJSM 1995;16:214-218; Gutiérrez et al, IJSM
2003; 24:518-522)
— Strength
— 3-5% ↓ body mass does not ↓ strength
(See Sawka et al (2007) MSSE 37:377-390)
— Mod-severe hypohydration ↓ bench velocity & vertical
jump in combat athletes (See Pallarés et al (2016) Journal of the
International Society of Sports Nutrition, 13:1, DOI: 10.1186/s12970-016-0121-3)
https://commons.wikimedia.or
g/wiki/File:Running_icon_-
_Noun_Project_22889.svg
https://commons.wikimedia.org/
wiki/File:High_jump_pictogram.s
vg
https://en.wikipedia.org/wiki/File:
Weightlifting_pictogram.svg
See also Shirreffs, SM, et al. J Sports Sci, 2011; 29(suppl): S39-S46.
The University of Sydney Page 24
25. The University of Sydney Page 22
Hypohydration: repeated sprints
RPE
Power - mean Power - peak
Mean sprint time
above 90RPM
Kraft JA, Green JM, Bishop PA, Richardson MT, Neggers YH, Leeper JD. Effects of heat exposure and
3% dehydration achieved via hot water immersion on repeated cycle sprint performance. J Strength
Cond Res. 2011; 25: 778-86.
26. Hypohydration: water sports
— Surfing
— 0.9 – 1.2% ¯ body mass → no effect on performance. Nylon wet
suit ↑ generation of heat and should be considered
(See O'Neill B et al, The Effects of a 2-hour Surfing Session on the Hydration Status of
Male Recreational Surfers. Int J Exerc Sci. 2022 Jan 1;14(6):1388-1399.)
(note: small sample size n=6 males >5 years of surfing experience)
— Swimming
— Dependent on hypohydration, no perceived benefit at
~0.42% dehydration
(See Briars G L et al, Swim drink study: a randomised controlled trial of during-
exercise rehydration and swimming performance. BMJ Paediatr Open. 2017 Oct
25;1(1):e000075. doi: 10.1136/bmjpo-2017-000075.)
— Water Polo
— Fluid balance changes much lower than other land-based sports
(e.g., training -0.26%, competition -0.35%), exercise intensity a
major predictor. Potential implications on accuracy and power.
(See Cox GR et al,. Body mass changes and voluntary fluid intakes of elite level water
polo players and swimmers. J Sci Med Sport. 2002 Sep;5(3):183-93. doi: 10.1016/s1440-
2440(02)80003-2. PMID: 12413035.)
27. The University of Sydney Page 24
Accuracy
and
speed
• 30 Sri Lankan cricketers – 22YO
• 28-32C temperate; 77% humidity
• Fluid rate
• Fluid provided – 12-15ml/kg/hr –
4.2-4.9lt in 4hrs
• Fluid restricted – 4ml/kg/hr – 0.9-
1.1lt in 4hrs
https://www.youtube.com/watch?v=TXNDtDtDyCw
Gamage et al, Int J Sport Nutr Exerc Metab. 2016
Dec;26(6):531-541.
Speed Accuracy
28. Hypohydration: cognitive performance
Wittbrodt MT, Millard-Stafford M. Dehydration Impairs Cognitive
Performance: A Meta-analysis. Med Sci Sports Exerc. 2018;50(11):2360-8.
The University of Sydney Page 28
29. Before exercise
Goal = to start physical activity euhydrated and with normal
body electrolyte status
• Initiate several hours before exercise
• 5-10mL/kg in 2-4 hours prior to exercise
• achieve pale yellow urine
• provide time for voiding
• Consume beverages and/or small amounts of salted snacks
or sodium containing foods at meals
ACSM. Position Stand: Exercise and Fluid Replacement. Med. Sci. Sports Exerc. 2007; 39: 388-90.
Goulet ED. Dehydration and endurance performance in competitive athletes. Nutr Rev. 2012;70 Suppl 2:S132-6.
AND/DC/ACSM Nutrition and athletic performance. Med Sci Sports Exerc 2016; 48: 543-568.
The University of Sydney Page 29
30. Starting exercise in a euhydrated state: combat sports
Does this happen in practice?
• ‘Making weight’/‘weight cutting’ in combat sport
athletes
• Rapid weight loss with dehydration strategies eg
• Restricting fluid ingestion
• Increased exercise
• Sauna
• Training in ‘sweatsuits’
• Even diuretics
• Rehydration will depend on time available
between weigh-in and competition
• 89% prevalence of hypohydration on the morning
of competition day
Pettersson S, Berg CM. Hydration status in elite wrestlers, judokas, boxers, and taekwondo athletes on competition day. Int J Sport Nutr Exerc Metab 2014;24(3):267-75.
The University of Sydney Page 30
31. The University of Sydney
Goulet EDB, De La Flore A, Savoie FA, Gosselin J.
Salt + Glycerol-Induced Hyperhydration Enhances Fluid
Retention More Than Salt- or Glycerol-Induced
Hyperhydration. Int J Sport Nutr Exerc Metab. Page 31
2018;28(3):246-52.
Pre-exercise hyperhydration
– useful prior to substantial fluid loss
– ‘set point’ of water regulation
– glycerol loading (+salt?)
– ‘priming’ the stomach
http://pngimg.com/uploads/drops/drops_PNG13515.png
32. Creatine Monohydrate
• Acts by drawing water into muscle
cells
• No clinical evidence of ↓ heat
tolerance & hydration1
• ↑ TBW, storage potentially favouring
intracellular fluid (ICF)
• ↑ Body mass (maintenance phase)
• Stable USG with short term
supplementation 2
• ↓ core temperature post training
• May work in combination with
other hydrating agents e.g.,
Glycerol 3
• ↓ perception of effort
1) Lopez RM, Casa DJ, McDermott BP, Ganio MS, Armstrong LE, Maresh CM. Does creatine supplementation hinder exercise heat tolerance or hydration status? A systematic review with meta-analyses. J Athl Train. 2009 Mar-Apr;44(2):215-23. doi: 10.4085/1062-6050-44.2.215.
2) Ropero-Miller JD, Paget-Wilkes H, Doering PL, Goldberger BA. Effect of oral creatine supplementation on random urine creatinine, pH, and specific gravity measurements. Clin Chem. 2000 Feb;46(2):295-7. PMID: 10657393.
3) Easton C, Turner S, Pitsiladis YP. Creatine and glycerol hyperhydration in trained subjects before exercise in the heat. Int J Sport Nutr Exerc Metab. 2007 Feb;17(1):70-91. doi: 10.1123/ijsnem.17.1.70. PMID: 17460334.
33. During exercise
Goal
– to prevent excessive (>2% body weight loss from
water deficit) dehydration
– to prevent excessive changes in electrolyte
balance
ACSM. Position Stand: Exercise and Fluid Replacement. Med. Sci. Sports Exerc. 39(2):388-90, 2007
AND/DC/ACSM Nutrition and athletic performance. Med Sci Sports Exerc 2016; 48: 543-568.
The University of Sydney Page 33
34. – Drink periodically (as opportunities allow) during
exercise
- (e.g.) On bench, between quarters/halves, time-out
- Use opportunities to your advantage
- Prime stomach
– Due to considerable variability in sweating rates and
composition between individuals, individualised fluid
replacement programs are recommended.
ACSM. Position Stand: Exercise and Fluid Replacement. Med. Sci. Sports Exerc. 39(2):388-90, 2007
AND/DC/ACSM Nutrition and athletic performance. Med Sci Sports Exerc 2016; 48: 543-568.
The University of Sydney Page 34
During exercise
https://www.youtube.com/watch?v=8aLW-VX0fnc
35. Factors influencing emptying*
energy density
osmolality
volume
*Refer to
• Rehrer, N (1996), Factors influencing fluid
bioavailability. AJND 53(4 Suppl): S8-S12.
• Maughan, R (2006), Third Ed. In L. Burke and
V Deakin, Clinical Sports Nutrition. Roseville:
McGraw-Hill Pty Ltd, pp385-414.
• Leiper, JB (2015), Fate of ingested fluids:
factors affecting gastric emptying and
internal absorption of beverages in humans.
Nutr Rev 73(S2): 57-72.
hypohydration, hyperthermia
temperature
stress
carb concentration
exercise type/
intensity
The University of Sydney Page 35
36. After exercise
– Goal = to fully replace fluid and electrolyte
deficits
– Plan determined by:
– speed with which rehydration is needed
– magnitude of fluid/electrolyte deficits
– Time available for consumption of meals and snacks
ACSM. Position Stand: Exercise and Fluid Replacement. Med. Sci. Sports Exerc. 39(2):388-90, 2007
The University of Sydney Page 36
37. Complete hydration
— If time permits, consumption of normal meals
and drinks will restore euhydration.
— Substantial dehydration + short recovery
period (<12 h) ®aggressive rehydration
plan required.
—drink ~1.25-1.5 L of fluid per kg of
body
weight lost.
— Recovery of sodium balance is a
prerequisite of recovery of fluid balance
Merson et al Eur J Appl
Physiol (2008) 103:585–
594
ACSM. Position Stand: Exercise and Fluid Replacement. Med. Sci. Sports
Exerc. 39(2):388-90, 2007
AND/DC/ACSM Nutrition and athletic performance. Med Sci Sports Exerc
2016; 48: 543-568.
The University of Sydney Page 37
38. Post-exercise Rehydration Considerations
Maximize rehydration • Supply of fluids – palatable, suited for athlete needs and the condition
• Aim to rehydrate target volume within 2-4 hrs
• Spread intake instead of a large bolus (↓urine losses and GI discomfort)
• Replace electrolytes – beverages with added electrolytes or salty snacks
• Avoid excessive alcohol – diuretic, counterproductive to recovery goals
Suitable choices • Choose a different flavour training vs recovery – taste fatigue
• Temperature – cold in warm weather, reverse in cool weather
• Consider total energy need in selecting an appropriate beverage
• Other – CHO? Protein?
Timing • Post session, < 8 hrs
Adverse reactions • ↑ energy intake, potential weight gain
• GI discomfort & ↑ urination, potential impact on sleep
• Overconsumption of salt above guidelines
When is post-exercise
hydration expendable
• Before bed > interruption to sleeping patterns
• Mild fluid losses and next bout in cool conditions
Adapted from: Burke LM, Mujika I. Nutrition for recovery in aquatic sports. Int J Sport Nutr Exerc Metab. 2014 Aug;24(4):425-36. doi: 10.1123/ijsnem.2014-0022. Epub
2014 Jun 5. PMID: 24901517.
39. Alcohol & Hydration
• Alcohol consumption can be common
post-event/exercise
• Social expectations particularly in team sport
• Source of water, CHO (3-7 g/ 100 g), sodium
(~ 0.5 – 1.5 mmol/L) and potassium 1
• Alcohol intake ↓ arginine vasopressin
(AVP / ADH) independent of osmolality 2
• ↑ urine output, especially when EtOH > 4%
• Milder effects < 2% EtOH, blunted with
exercise induced hypohydration 1
• ? Impairments to thermoregulation 3,4
• ↑ blood flow to skin & ↑ sweat rate
• ↓ core temperature
1. Shirreffs SM, Maughan RJ. Restoration of fluid balance after exercise-induced dehydration: effects of alcohol consumption. J Appl Physiol (1985). 1997 Oct;83(4):1152-8. doi: 10.1152/jappl.1997.83.4.1152. PMID: 9338423
2. Eggleton MG. The diuretic action of alcohol in man. J Physiol. 1942 Aug 18;101(2):172-91. doi: 10.1113/jphysiol.1942.sp003973. PMID: 16991552; PMCID: PMC1393383.
3. Yoda T, Crawshaw LI, Nakamura M, Saito K, Konishi A, Nagashima K, Uchida S, Kanosue K. Effects of alcohol on thermoregulation during mild heat exposure in humans. Alcohol. 2005 Jul;36(3):195-200. doi: 10.1016/j.alcohol.2005.09.002.
4. Desruelle AV, Boisvert P, Candas V. Alcohol and its variable effect on human thermoregulatory response to exercise in a warm environment. Eur J Appl Physiol Occup Physiol. 1996;74(6):572-4. doi: 10.1007/BF02376775. PMID: 8971501.
5. Wijnen AH, Steennis J, Catoire M, Wardenaar FC, Mensink M. Post-Exercise Rehydration: Effect of Consumption of Beer with Varying Alcohol Content on Fluid Balance after Mild Dehydration. Front Nutr. 2016 Oct 17;3:45. doi: 10.3389/fnut.2016.00045..
48. Factors impacting fluid losses during
training/competition
• Body size and composition
• Fitness level
• Genetics
• Temperature
• Wind
• Humidity
• Clothing & equipment
• Time of day (noon vs early morning vs night)
• Location (indoor vs outdoor events)
• Exercise structure (intensity, duration, number of sessions/bouts)
Source: Tennis Australia. AO Heat Stress Scale a Grand Slam first. 2018. Accessed 14
September 2021. <https://ausopen.com/articles/news/ao-heat-stress-scale-grand-
slam-first>
Page 48
49. Belval LN, Hosokawa Y, Casa DJ, Adams WM,
Armstrong LE, Baker LB, Burke L, Cheuvront S,
Chiampas G, González-Alonso J, Huggins RA,
Kavouras SA, Lee EC, McDermott BP, Miller K,
Schlader Z, Sims S, Stearns RL, Troyanos C,
Wingo J. Practical Hydration Solutions for
Sports. Nutrients. 2019 Jul 9;11(7):1550. doi:
10.3390/nu11071550. PMID: 31324008;
PMCID: PMC6682880.
50. Sport
Availability of Fluid Environment Intensity Hypohydration Risk
Training Competition Training Competition Training Competition Training Competition
Tennis High Mod Mod Mod High High Mod Mod
Wrestling High High Mod Mod High High High Low
Gymnastics High High Low Low Mod Low Low Low
Running (<1 h) Low High Mod Mod High High Low Low
Running (1–2 h) Low High Mod Mod Mod Mod Mod Mod
Running (>2 h) Low High Mod Mod Low Mod Mod Mod
Cycling (<1 h) High High Mod Mod High High Low Low
Cycling (>2 h) Mod Mod Mod Mod Mod Mod Low High
Swimming High High Low Low High High Low Low
Triathlon (<2 h)
Swim Low Low Low Low Mod Mod Low Low
Bike Mod High Mod Mod Mod Mod Low Low
Run Low High Mod Mod Mod Mod Low Low
Triathlon (2–5 h)
Swim Low Low Low Low Mod Mod Low Low
Bike Mod High Mod Mod Mod Mod Low Low
Run Low High Mod Mod Mod Mod Low Low
Triathlon (5–9 h)
Swim Low Low Low Low Mod Mod Low Low
Bike Mod High Mod Mod Mod Mod Mod Mod
Run Low High Mod Mod Mod Mod Mod Mod
Triathlon (>9 h)
Swim Low Low Low Low Mod Mod Low Low
Bike Mod High Mod Mod Mod Mod Mod Mod
Run Low High Mod Mod Mod Mod Mod Mod
Belval LN, Hosokawa Y, Casa DJ, et al. Practical Hydration Solutions for Sports. Nutrients. 2019;11(7):1550. Published 2019 Jul 9. doi:10.3390/nu11071550
51. Summary of Hydration Strategies
Before
• Start exercising in a well-hydrated state (not necessarily over hydrated)
During
• Aim to rehydrate during official break periods or stoppages
• Consider an individualized hydration plan, and having appropriate amounts of
fluids (excess hydration => urination, GI upsets)
• Consider type of fluids used (cold vs hot, electrolytes, glucose, etc.)
• Strategies selected should be well practiced
After
• Fluid losses continue post-exercise, so aim to continue hydration recovery
strategies post event.
• Consider combining fluid intake with salty/savory snacks
• Consider other dietary components e.g., protein, glucose
Page 51
52. What to drink?
Sports Drinks
• Replenish fluids, electrolytes, and provides an energy
source (CHO)
• CHO 30-60 g/hour for events 1 – 2.5 hours long
• Up to 90 g/hour for events > 2.5 hours
• CHO % ≤ 8 to maximise gastric emptying
• 10-35 mmol/L Na (230-805mg/L)
• 2-5 mmol/L K (20-30mg/L)
• Consider temperature, flavour, duration of exercise
Water?
• Replenish fluids, neutral flavour
Burke, et al, Supplements and sports foods. In Burke and Deakin, 2012, pp419-500
Maughan, Fluid and carbohydrate intake during exercise. In Burke and Deakin, 2012, pp330-357
ACSM. Position Stand: Exercise and Fluid Replacement. Med. Sci. Sports Exerc. 39(2):388-90, 2007
Page 52
54. 54
McCubbin AJ, Allanson BA, Odgers JNC, Cort MM, Costa RJS, Cox GR, Crawshay ST, Desbrow B, Freney EG, Gaskell SK, Hughes D,
Irwin C, Jay O, Lalor BJ, Ross MLR, Shaw G, Périard JD, Burke LM. Sports Dietitians Australia Position Statement: Nutrition for
Exercise in Hot Environments. IJSNEM, 2020; 30: 83-98 .
55. Additional Resources and Optional Readings
• Belval LN, Hosokawa Y, Casa DJ, et al. Practical Hydration Solutions for Sports. Nutrients.
2019;11(7):1550. Published 2019 Jul 9. doi:10.3390/nu11071550
• Burke LM, Hawley JA. Fluid balance in team sports. Guidelines for optimal practices. Sports Med.
1997;24(1):38-54. doi:10.2165/00007256-199724010-00004
• Garth AK, Burke LM. What do athletes drink during competitive sporting activities?. Sports Med.
2013;43(7):539-564. doi:10.1007/s40279-013-0028-y
• ACSM Resource for Exercise in Hot and Cold environments. https://www.acsm.org/docs/default-
source/files-for-resource-library/exercising-hot-cold-environments.pdf?sfvrsn=1b06c972_4
• AIS Sports Supplements Framework Sports Drinks (Carbohydrate Electrolyte Drinks)
https://www.ais.gov.au/__data/assets/pdf_file/0009/998802/36194_Sport-supplement-fact-
sheets-Sports-drinks-v4.pdf
• Sports Dietitians Australia Fact Sheet on Sports Drinks
https://www.sportsdietitians.com.au/factsheets/fuelling-recovery/sports-drinks/
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56. The University of Sydney Page 56
Lecture Objectives
1. Understand the processes of absorption and excretion of sodium.
2. Describe concept of thermoregulation in achieving thermal balance and thus factors effecting
sweating rate
3. Describe fluid balance measurement and assessment of sweat rate and water loss. (practical)
4. Define dehydration and expression of dehydration
5. Describe performance effects of dehydration.
6. Describe methods of pre-exercise hyper-hydration
7. Indicate the general effects - undesirability - of dehydration in exercise and heat stress
8. Be aware of commonly available and consumed beverages and water
9. Demonstrate a thorough knowledge of the nutritional composition of a range of beverages
10. Explain drinking behaviour during exercise, the concept of ‘voluntary dehydration’ and other
limitations to maintaining hydration during strenuous exercise and heat stress.
11. Define recommendations for fluid intake before, during and after exercise.
12. List and describe factors affecting gastric emptying of fluids.
13. Describe factors affecting fluid intake.
14. Define sports drinks and their benefits.
