11/11/2019

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Hydration: From Lab Bench to Sideline Bench

Matthew S. Ganio, PhD, FACSM

Brendon P. McDermott, PhD, ATC, FACSM

Outline

• Physiology of water balance• Hydration and body temperature• Hydration assessment• Individualized hydration• Conclusions

Body Fluid Balance Terminology

Hypothalamus

Osmoreceptors

Baroreceptors

Nephrons

I’m thirsty!

AVP

AVP

Involuntary Dehydration

Drinking as much as sweating

Sweating more than drinking

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Influence of Hydration on Body Temperature Hypohydration and Body Temperature

• Peripheral/Skin blood flow decreases

• Sweat rate decreases

• Less evaporative cooling

• Temperature increases 0.15 –0.20°C per % body mass loss

• “…[Sports Medicine professionals] should be aware that core temperature is not necessarily associated with either percentage of dehydration or sweat rate”

Godek SF, Bartolozzi AR, Burkholder R, et. al. Core temperature and percentage of dehydration in professional football linemen and backs during preseason practices. J AthlTrain. 41;8-17:2006.

Field Study

Four 7.5 mile trials‐randomized counter‐balanced (ie. ½ DHY ½ HY):

– Trial 1: Race – Trial 2: Sub‐maximal – Trial 3: Sub‐maximal (pace feedback)– Trial 4: Race 

400ml of water given at 2.5 and 5 mile marks for HY group

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Caffeine• “If athletes choose to consume caffeinated beverages, they need to balance this with equal amounts of non‐caffeinated fluid”

Caffeine

• Replacing caffeinated fluids post‐practice

• Caffeine before and during exercise

• No differences in urine output

• Resting urine output (what’s in your bladder)

Fiala KA, Casa DJ, Roti MW. Rehydration with a caffeinated beverage during the nonexercise periods of 3 consecutive days of 2-a-day practices. Int J Sport Nutr Exerc Metab. 2004;14(4):419-429.

Silva AM, Judice PB, Matias CN, et al. Total body water and its compartments are not affected by ingestingA moderate dose of caffeine in healthy young adult males. Appl Physiol Nutr Metab. 2013;38(6):626-632.

Ergogenicity of Caffeine

• Performance increased when 3‐6mg/kg ingested prior to and every 30min during exercise

– Tested up to 9 mg/kg (That’s 630mg for me)

• Practice with this stuff

Hydration Assessment

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What does that spot check mean?

Cheuvront SN, Kenefick RW, Zambraski EJ. Spot urine concentrations should not be used for hydration assessment: a methodological review. IJSNEM. 2015;25(3):293‐297. 

Competitive Athletes• Sweat rate assessment 

– Determine individual needs

– Sweat rate varies from 0.5 – 3.9 L/hr

– Dependent on a number of factors

• Sweat‐electrolyte assessment

Individualized Hydration

• Consume fluids and electrolytes based on individual losses

• Should lose <2% body mass during exercise– Drink according to individual sweat rate

• Replace 125‐150% of losses following exercise• For the novice: drink according to thirst

– Avoids hyponatremia

• Sweat rate is 1.8L/hr• Practice is 2.5 hrs long• 4L = 2% body mass

• 3.9 L/hr sweat rate• Event is about 2 hrs• 1.3L = 2% body mass

Physically active are not so good• On average, about 65‐85% of athletes report to game or practice activities inadequately hydrated– NBA Study (78% dehydrated); Osterberg KL et al, JAT, 2009– Ice hockey players (<50% dehydrated); Palmer MS et al, Appl Physiol Nutr

Metab, 2010 – Youth football campers (~70% dehydrated); McDermott BP et al, JSR, 2009– High School football players ( 65‐85% dehydrated); Yeargin SW et al, JAT, 

2010

• Replace ~66% of sweat losses during activity

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Hydration & Performance Hydration, Temperature & Performance

• What happens if athletes are pushed beyond and not allowed to tank it?

– Overbearing coach, military, end of distance event, parents, teammates

• Decreased endurance exercise performance

• Decreased anaerobic performance

Hydration Assessment

• Urine color

• Urine specific gravity

• Urinary frequency

• Body mass changes

Urine Color

• Must be done in clear container or stream assessment

• Urine is always delayed 

– Indicative of 2 hours ago

Armstrong LE, Soto JA, Hacker FT, Casa DJ, Kavouras SA, Maresh CM. Urinary indices During dehydration, exercise, and rehydration. Int J Sport Nutr. 1998;8(4):345-355.

Urine Specific Gravity

• Compares density of fluid to that of distilled water

• Various devices

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Body Mass Changes

• 3‐day euhydrated weight as baseline

• Can detect subtle changes in hydration

• Cannot use 1‐day body mass as baseline

Baker LB, Lang JA, Kenney WL. Change in body mass accurately and reliably predicts Change in body water after endurance exercise. Eur J Appl Physiol. 2009;105(6):959-967.

● Weight● Urine (color/frequency)● Thirst

Sawka MN, Cheuvront SN. SSE#97: Hydration assessment of athletes. Sports Sci Exchange. 2005;18(2):1‐7.

Conclusions• Many student‐athletes are dehydrated

• They are decent during activity, but not good outside of activity

• Hydration assessment is not difficult. Use multiple measures. 

brendonm@uark.edumsganio@uark.edu

Delayed Thirst

How do measure hydration status?

• Stable isotope dilution• Neutron activation analysis• Bioelectrical impedance spectroscopy• Body mass change• Plasma volume change• Plasma/Serum osmolality • ADH level• Urine osmolality• Urine specific gravity• Urine conductivity• Urine color• 24‐hr urine volume• Salivary flow rate• Rating of thirst

Classifying Hydration StatusAdapted from Armstrong 2010

24‐hr fluid intake (L)

24‐hr urine 

volume (L)

Morning USG

24‐hr USG Morning Urine Osm

24‐hrUrine Osm

24‐hrUrine Color

Extremely hyperhydrated

>3.3 >2.3 <1.017 <1.012 <545 <377 <4

Slightlyhyperhydrated

2.6‐3.3 1.9‐2.3 1.017‐1.021 1.012‐1.014 545‐713 377‐475 4

Well hydrated 2.5‐2.6 1.5‐1.9 1.022‐1.023 1.015‐1.017 714‐817 476‐586 5

Euhydrated 2.0‐2.5 1.2‐1.5 1.024‐1.026 1.018‐1.020 818‐924 587‐766 5

Slightlydehydrated

2.01‐2.05 1.1‐1.2 1.027‐1.028 1.021‐1.024 925‐999 767‐880 6

Very dehydrated

1.4‐2.0 0.9‐1.1 1.029‐1.031 1.025‐1.027 1000‐1129 881‐1013 6

Extremely dehydrated

<1.4 <0.9 >1.031 >1.027 >1129 >1013 >6

(290 data points, 59 male test subjects). Data fit to normal curve

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Methods of assessing hydration

Nude Body weight pre‐ and post

70 kg baseline‐68 kg after exercise=2 kg

2 / 70 *100 = 2.86 % dehydrated