Thermoregulation and hydration

Question 1

How are we acclimatized for heat vs cold?

Answer 1

For the heat: we have powerful acclimatization (sweat loss, vasodilation, nude body). Behaviour
For the cold: Poor acclimatization (Vasoconstriction, shivering). Behaviour but mostly exercise or clothing

Question 2

What are the four ways for losing heat?

Answer 2

1. Convection (moving air removes radiated heat)
2. Evaporation (sweat respiration)
3. Radiation (emission of electromagnetic radiation)
4. Conduction (direct transfer by contact)

Question 3

How to measure heat balance, taking into account all factors?

Answer 3

Metabolism = indirect calorimetry (VO2 vs VO)
Storage = change in body t
Radiation - difference Tskin and ambient
Convection = air flow (wind)
Conduction = difference T skin and ambient (very limited)
Evaporation - BW change, corrected for fluid loss

Question 4

Pre-cooling can be an advantage for the first X minutes, because..

Answer 4

20 mins
After pre-cooling, there is much more space for heat storage because the core is cold. In the initial stage, they sweat less.

Question 5

When is a person considered dehydrated?

Answer 5

Lose >2% of BW as fluid

Question 6

Symptoms of severe dehydration?

Answer 6

Nausea, vomiting, headache, dizziness, muscle cramping.

Decreased endurance performance, less effect on short-term HI exercise (muscle strength, power)

Question 7

1 goes down, 2 goes down, 3 goes up, 4 to skin

Answer 7

1 cardiac output
2 stroke volume
3 Heart rate
4 less blood flow

Question 8

Fluid balance during exercise is highly individual. It can be different due to ..

Answer 8

 Evaporation (sweat rate)
sex
 Respiratory loss
 Environmental conditions
● Heat acclimation
● altitude
 Intensity/duration
 Fitness level
 Body composition (%BF)
 Medication (diuretics)

Question 9

Sweat is not only water, it also contains..

Answer 9

 Electrolytes
● Sodium and Chloride main electrolytes
● Sweat is hypotonic (lower than blood) -> interindividual variation
● Extreme conditions up to 7 gram salt loss
(Acclimatization reduces Na loss)

Question 10

Pre-exercise glycerol hyperhydration: ‘expander’, allow the body to keep a higher water content.

Two downsides?

Answer 10

However, when blood volume increases, can more easily introduce hyponatremia (maybe you should add a bit of salt to the water). Also increase of body weight.

Question 11

What is advised to drink after exercise?

Answer 11

150% drink of fluid loss + sodium added is advised

Question 12

Why add sodium to the drink after exercise?

Answer 12

plain water will dilute plasma -> lower osmolality and plasma Na content (sodium is
main electrolyte in plasma) -> stimulation of diuresis + suppressing thirst -> impaired fluid retention, poorer net fluid
balance.

Adding sodium will prevent this dilution, and improves fluid retention due to less diuresis.
The sodium concentration for maximal fluid retention is quite high (ORS !), but lowers the palatability
of drink . Commercial sport drinks therefore don’t have the optimal Na level for rehydration.

Question 13

Advice for volume and pattern of ingesting these types of sodium drinks?

Answer 13

• amount greater than sweatloss (150%)
• not too rapid rehydration
• small boluses better than large amounts

Question 14

Caffeine and alcohol: recommended for hydration?

Answer 14

No clear evidence, alcohol not recommended

Question 15

During exercise: advice?

Answer 15

Strength/power athletes: drinkt to sweat loss, endurance: drink to thirst or prevent >2-3% BW loss
cold drink (thermoregulation)