18. Temperature & fluid balance during exercise Flashcards
What happens to most of the energy from metabolism during exercise?
Most energy from metabolism during exercise is dissipated as heat, which must be removed to prevent critical hyperthermia.
How is heat lost?
- radiation
- conduction (contact)
- convection (movement of air)
- evaporation of sweat (primary mechanism)
Cardiovascular responses to exercise in the heat
& what happens with pre-exposure to heat?
CO will increase with higher heat
- **Pre-exposure to heat:
- maximal HR remains the same
- max SV decreases
- hence decrease in CO and VO2 with pre-exposure
What are the consequences of heat stress?
Heat stress increases glycogen utilisation during exercise (higher muscle temperatures = sped up reactions).
Heat stress impairs exercise capacity (unable to get rid of heat = impairs capacity).
Heat stress impairs exercise performance (power output is reduced in “hot trial” - interaction between central NS & contracting muscle).
What is the effect of lowering core temperature on time to fatigue?
Lowering core temperature = greater capacity for heat storage, hence you can go longer before you reach “critical temperature” (if that exists).
Describe the factors of exercise heat stress that contribute to “central fatigue”.
Increased rating of perceived exertion
Reduced voluntary activation of muscle
Reduced cerebral blood flow, but increased VO2
Hyperprolactinaemia - increased prolactin coming out of brain during exercise, can have possible effect on NTs?
How does hyperthermia influence neuromuscular performance? What happened with pre-heated trial?
Reduces it.
In preheated trial, there is greater decrease in activated muscle. High heat causes reflex to limit muscle activation as muscle is a source of heat.
What are strategies to enhance exercise performance in the heat?
Heat acclimatisation (adaptations that improve cardiac & metabolic function)
Pre-cooling
Fluid ingestion
How does heat acclimatisation enhance performance?
lowers HR & core temperature during exercise
What are the physiological & metabolic adaptations to heat acclimatisation?
- increased blood volume
- reduced HR
- lower core & skin temperatures
- increased sweat rate & earlier onset
- more dilute sweat
- reduced muscle glycogen use (lowered body T, muscle T, plasma adrenaline levels)
How does pre-cooling enhance exercise performance?
Cooling the brain/carotid arteries to the brain can cause brain to think that the body is cooler than it is, so you can go longer but there is the potential risk of overheating for your muscles that have not been cooled.
What parts of the body does exercise-induced dehydration affect?
All body fluid compartments
- plasma
- interstitial
- intracellular
What does fluid ingestion attenuate during exercise?
Fluid ingestion attenuates cardiovascular drift.
-with fluid there is better maintenance of plasma volume & therefore SV & CO at a lower HR.
It also attenuates hyperthermia.
-major determinant of core T is exercise intensity though, but can blunt the rise over time with fluid ingestion.
What are the benefits of fluid ingestion?
Increased blood volume Decreased HR Increased SV & CO Lower core temperature Lower plasma [Na+] & osmolality Reduced muscle glycogen use Enhanced exercise performance
Increased plasma renin & aldosterone promote…
fluid & salt retention!
Sodium & fluid losses impair performance.
Relying on only fluid balance means that you only regain water with regained sodium balance.
