Module 6 lecture 2 Sweat Rate Calculations and Monitoring Fluid Status in Athletes

Question 1

Fluids and Hydration in Athletes Myths

Answer 1

• The body can adapt to dehydration (lack of body water)
• Thirst is a good indicator of fluid requirements in athletes
• Water-based athletes (e.g. swimmers, divers) don’t need to worry about staying adequately hydrated
• You can “cure,” dehydration during exercise and perform at your best!

Question 2

What does sweating do?

Answer 2

Cools the body
* sweat rate ~1-2 L/h

Question 3

Factors impacting the variability in sweating rate

Answer 3

• Exercise intensity
• Body size
• Environmental conditions (Temperature, humidity/humidex, solar load, wind)
• Heat acclimatization
• Fitness
• Clothing/equipment worn
• Body composition
• Hydration status
• Age (maturation)
• Genetics
• Methodology

Question 4

What factors are dangerous in determining sweat rate?

Answer 4

HEAT AND HUMIDITY ARE DANGEROUS
* More heat = more sweating!
* More humidity = more sweating!
* Humidex = Lots more sweating!

Question 5

What is the difference between the theoretical and practical formula for measuring sweat rate?

Answer 5

The theoretical include respiratory losses however this contribute very little (0.2 g/kcal) so typically dropped in the practical for acute bouts of exercise.
* theoretical: Sweat Loss = [Pre-Ex Body Mass – (Post-Ex Body Mass – Fluid & Food + Urine & Resp)]
* practical: Sweat Loss = [Pre-Ex Body Mass – (Post-Ex Body Mass – Fluid & Food + Urine)]

Question 6

What is the goal of sweat rate calculations?

Answer 6

Calculating sweat losses allows the sport dietitian to develop individualized fluid replacement goals for each athlete.
* Sweat Losses (mL/hr) = Target for fluid replacement during sport (ml/hr)

Question 7

Advanced approach for sweat rate calculations

Answer 7

Question 8

What is considered hydrated BW?

Answer 8

1, 2 or 3 is considered within 1% hydrated BW

Question 9

How can hydration status be monitored?

Answer 9

Body weight changes reflect hydration status
* 1 lb decrease (acutely) = 500 ml (2 cup) fluid loss
* Have athletes track their body weight so that they can assess hydration-related changes.

Question 10

2007 Fluid Replacement Position Stand on monitoring hydration status

Answer 10

Acute body mass change can be used to calculate sweating rate and perturbations in hydration status when corrected for urine losses, drink volume, and trapped sweat for activites <3 hours.
* Other non-sweat factors (fuel oxidation and respiratory water loss) can overestimate sweating rate but do not require correction for < 3 h exercise.

Question 11

% change in nude body mass

Answer 11

hydration status

Question 12

[(∆ body mass) / baseline body mass] x 100

Answer 12

hydration status calculation

Question 13

How to collect data for changes in hydration status

Answer 13

Question 14

How does using BW as a measure of hydration status change over activity duration?

Answer 14

Using change in body mass to determine hydration status becomes less accurate with longer events
* For example, during ultra endurance events ≥ 2% of body mass loss can occur through non sweat sources:

Question 15

What is another method for measuring hydration status?

Answer 15

Urine color can be used as a reliable marker of hydration status whereby mean urine color of 3 provides a reasonable assurance the athlete is hydrated but athletes with a urine color of 5 on a urine color chart are 6 times more likely to be hypo-hydrated
* Urine color can be monitored by the athlete or by the ATC
* Post urine color charts in bathrooms

Question 16

How can hydration status be self-assessed prior to a workout?

Answer 16

Question 17

When should planned drinking be implemented over drink to thirst?

Answer 17

Question 18

What are fluid reccomendations for staying hydrated?

Answer 18

• Begin exercise properly hydrated (should meet the basic AI for water AND add sport requirements on top)
• Use a personalized fluid intake strategy based on sweat test results, exercise duration, and environmental conditions
• Drink enough fluid to prevent >2% dehydration, especially in warm weather
• Do not overconsume fluids during exercise
• Consume sodium with fluids if exercise is >2 h in hot weather and/or if sweat electrolyte losses are very high (> 3 g)

Question 19

ACSM position stand on fluid before exercise

Answer 19

Pre-hydrating with beverages, if needed, should be initiated at least several hours before the exercise task to enable fluid absorption and allow urine output to return toward normal levels.
* ~5-7 mL/kg per body weight
* Consuming beverages with sodium and/or salted snacks or small meals with beverages can help stimulate thirst and retain needed fluids.

Question 20

ACSM position stand on fluid during exercise

Answer 20

• develop a fluid replacement strategy to keep <2% BW changes and prevent dehydrations
• monitor body weight changes (Predicted sweat rates range from ~0.4 to ~1.8 L·h)
• Consuming CHO for activites >1h
• If CHO is a part of beverage it should not exceed 8% concentration, or be less

Question 21

ACSM position stand on fluid after exercise

Answer 21

Consume ~1.5 L/ kg BW lost.
* Range = 1200-1500 ml/kg until usual BW recovered and held.
* Consuming beverages and snacks with sodium will help expedite rapid and complete recovery by stimulating thirst and fluid retention.