Sweat Rates

Question 1

What are some myths about fluids and hydration in athletes?

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 ecercise and perform at your best

Question 2

What is the approximate sweat rate of most people?

Answer 2

• ~1-2 L/hr
• Variation and factors can influence sweat rate
• Due to large variation some risks associated with giving broad recommendations because some athletes need tailored advice

Question 3

Why do we sweat?

Answer 3

Sweating cools the body!!

Question 4

How does sweating rate vary by sport?

Answer 4

• baseball, soccer, and basketball similar
• Biking high
• Football highest sweat rates
• Highly dependent on intensity and equpment! Body size can also contribute to more energy expenditure/heat generation

Question 5

What facrors can impact the variability of sweat rate?

Answer 5

• exercise intensity - working harder means more heat
• Body size
• Environmental conditions
  → temperature
  →humidity/humidex - heat + humidity
  →solar load - angle of sun, depends on geography
  →wind - can mask heat a bit
• Heat acclimatization
• Fitness - sweat more if untrained
• Clothing/equipment worn - dry fit vs wool
• Body composition
• Hydration status
• Age (maturation) - children not effective at sweating
• Genetics
• Methodology - way you measure

Question 6

Why is humidex so dangerous?

Answer 6

• Humidex = heat + humidity so get more sweating than if it was just one or the other
• Need lots of water, and cooling.
• Agressive hydration may still not even be enough to prevent dehydration

Question 7

What decreases and increases mass when it comes to hydration balance?

Answer 7

• Mass loss: sweat, urine, respiration (fuel oxidation, water vapor)
• Mass gain: drinking, eating

Question 8

What is the theoretical formula for sweat loss calculations?

Answer 8

Sweat loss = [Pre-Ex Body Mass - (Post-Ex Body Mass - Fluid and food + Urine and respiration)]

Question 9

What is the practical formula for sweat loss?

Answer 9

Sweat Loss = [Pre-Ex Body Mass - (Post-Ex Body Mass - Fluid and food + urine)]

Question 10

Why is the theoretical formula and practical formula for sweat rate calculations different?

Answer 10

Respiratory losses = 0.2g/kcal of energy expended during exercise. Because of the relatively small contribution of respiratory losses to total body mass loss and because energy expenditure is difficult to measure, this part of the equation is usually dropped for acute bouts of exercise

Question 11

What is the goal of sweat rate calculations?

Answer 11

• 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). Fine tune the 1-2L for each individual athlete

Question 12

What are the supplies needed when doing a sweat rate calculation (advanced approach)?

Answer 12

• Digital platform body weight scale with precision of 0.10kg or better
• Towels
• Clock or stopwatch
• Drink bottles
• Small digital scale
• Urine cup

Question 13

What are the instructions for calculating sweat rate (advanced approach)?

Answer 13

• Before exercise: ask athlete to use the restroom to void (weigh urine cup), weigh athlete wearing minimal clothing, weigh drink bottles and food (bars, ges, etc) if applicable
• During exercise: collect urine loss in cup and weigh, if applicable
• After exercise: ask athlete to towel dry, weigh athlete while wearing same minimal clothing, weigh drink bottles and food, if applicable

Question 14

What is the way of calculating seat rate (simple approach)?

Answer 14

• Weigh before and after
• Calculate amount of fluids drunk and the time of the activity then can calculated the sweat rate
• Sweat loss = deficit + fluid intake
• Sweat rate = sweat loss/time

Question 15

Kelly’s pre-exercise weight is 61.7kg, her post exercise weight is 60.3kg. She filled water bottle with 500mL (prefluids). Kelly had 200mL of water in her bottle at the end of her exercise session (post-fluids). She trained for 55 minutes. What is her sweat rate?

Answer 15

Question 16

What is the urine coloration chart and where should athletes aim to be?

Answer 16

• 1-3
• Body concentrates waste products when dehydrated = more concentrated color

Question 17

Calculate the athlete’s sweat rate

Answer 17

Question 18

Calculate the athlete’s sweat rate?

Answer 18

Question 19

What is the simplest way to assess hydration status?

Answer 19

• Acute body mass change can be used to calculate sweating rate and perturbations in hydration status when corrrected for urine losses, drink volume, and trapped sweat
• Other non-sweat factors (fuel oxidation and respiratory water loss) can overestimate sweating rate but do not require correction for <3 hr exercise)
• Therefore, using acute body mass changes to estimate hydration status is appropriate for most individual and team sports, since practices and games are typically <3 hrs

Question 20

How much is a pound decrease in water?

Answer 20

• Body weight changes reflect hydration status
• 1lb decrease (acutely) = 500m: (2 cup) fluid loss

Question 21

What simple recommendations would you have for an athlete?

Answer 21

• Have athletes track their body weight so that they can assess hydration-related changes
• Want body weight to remain consistent, DO NOT want major losses

Question 22

What is hydration status? How do you calculate it?

Answer 22

• Hydration status = % change in nude body mass
• Calculation: [(Change in body mass)/baseline body mass]x100
• E.g. 2% hypohydration = 2% body mass deficit through fluid loss

Question 23

What are the supplies needed to change hydration status?

Answer 23

• Digital platform body weight scale with precision of 0.10kg or better
• Towels

Question 24

What are the instructions for changing hydration status?

Answer 24

• before exercise: ask athlete to use restroom and void bladder and bowels, weigh athlete while they are wearing minimal clothing (e.g. compression shorts, sports bra)
• After exercise: ask athlete to towel dry thoroughly, weigh athlete while wearing the same minimal clothing as before

Question 25

What is the problem with using body mass to determine hydration status?

Answer 25

It becomes less accurate with long events. For example, during ultra endurance events greater than or equal to 2% body mass loss can occur through non sweat sources

Question 26

Calculate the athlete’s % change in hydration status after the match

Answer 26

Question 27

What urine color should athletes have and why? What are the practical recommendations?

Answer 27

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

Urine charts don’t work if they are taking vitamin or mineral supplements (e.g. vitamin C, beets)

Question 28

How can athletes self-assess before exercise?

Answer 28

Question 29

When should you use planned drinking versus drinking to thirst?

Answer 29

• Drink to thirst: short duration activities <60 to 90 minutes, cooler conditions, lower intensity. Plain cool water all you need
• Planned drinking: longer duration activities >90 minutes particularly in the heat, high intensity, high sweat rates, when performance is a concern, when carbohydrates intake of 1g/min

Start planned schedule of drinking right from the start 90-125mL of fluid every 10-15 minutes

Question 30

What are the recommendations for keeping hydrated?

Answer 30

• Begin exercise properly hydrated. All athletes need to 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 - Hyponatremia
• Consume sodium with fluids if exercise is >2hr in hot weather and/or if sweat electrolyte losses are very high (>3g)

Question 31

What is the ACSM Position Stand for fluids before exercise?

Answer 31

• 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
• ~5-7mL 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 32

What is the ASCM position stand for fluids after exercise?

Answer 32

• Consume ~1.5 L of fluid for each kg of body weight lost.
• Range = 1200-1500mL/kg ? until usual body weight is recovered and held
• Consuming beverages and snacks with sodium will help expedite rapid and complete recovery by stimulating thirst and fluid retention

Question 33

What is the ACSM position stand for fluids during exercise?

Answer 33

• If possible, individuals should develop customized fluid replacement programs that prevent excessive (<2% body weight) reductions from baseline body weight) dehydration
• Predicted sweat rates range from ~0.4 to ~1.8L per hr
• It is recommended that indiviuals should monitor body weight changes during training/competition sessions to estimate their sweat lost during a particular exercise task with respect to the weather conditions
• CHO consumption can be beneficial to sustain exercise intensity during high-intensity exercise events of ~1hr or longer, as well as intense exercise events sustained for longer periods
• If both fluid replacement and CHO delivery are going to be met with a single beverage, the CHO concentration should NOT excees 8% or even be slighlty less, as highly concentrated CHO beverages reduce gastric emptying (could cause nausea)