Which consequence of dehydration contributes to reduced performance during heat stress?

Which consequence of dehydration contributes to reduced performance during heat stress?

• A. Increases blood viscosity and impairs CNS function
• B. Reduces blood viscosity
• C. Improves cognitive function
• D. Increases sweating efficiency

Answer: (A)

Dehydration lowers plasma volume and concentrates the blood, making it thicker (increased viscosity). This raises the resistance the heart faces to pump blood, so stroke volume tends to drop and the heart must beat faster to maintain output. In the heat, that cardiovascular strain reduces skin blood flow and sweating efficiency, worsening heat dissipation and raising core temperature. At the same time, reduced cerebral perfusion and electrolyte disturbances can impair brain function, increasing fatigue and deteriorating decision-making and coordination. Taken together, the thicker blood and compromised CNS function are key factors that degrade performance during heat stress.

The other ideas don’t fit: dehydration does not reduce blood viscosity, it increases it; cognitive function is not improved with dehydration, it is impaired; and sweating efficiency is not increased by dehydration—in fact cooling ability is diminished.