Hydration (wk 5) Flashcards
(26 cards)
What are the body water basics?
- Adult body = 50-60% basics. Lean body tissues = ~75% water and Fat mass = ~5-10% water
- Functions = Nutrient transport, protection, temperature regulation, biochemical reactions and medium for reactions
What is the distribution of water in young 70kg man?
-Intracellular fluid - 40% of body mass
-Extracellular fluid - 20% of body mass
-Interstitial fluid - 15% of body mass
-Blood plasma - 5% of body mass
Draw the daily body water balance for a sedentary adult
-In fluid (water) balance (euhydration)
Draw the daily body water balance for an active adult
-Negative fluid (water) balance (dehydration, hypohydration)
Draw the daily water balance for an active adult
-In fluid (water) balance (euhydration)
What is the net body water balance?
-> Net body water balance is the difference between fluid water grain (intake + production) and fluid loss. Typically, well maintained on a day-to-day basis (within 1% of body mass) – thirst and hinger drives. Net body water balance can be challenged during periods of high sweat rates.
What is dehydration?
-> Referred to as hypohydration, is defined as a body water deficit greater than normal daily fluctuation. Change in body mass provides the most sensitive and simplest measure to determine acuate changes in body water. Acutely: >2% body mass reduction = 90% chance that body weight deficits are sufficient to be classed as dehydration.
What is the assessment for dehydration?
- The best static physiological index of hydration status is the measurement of plasma osmolality.
- Osmolality – a measure of the total dissolves particle concentration (in mOsm/kg)
- Typically 275-295 mOsm/kg
- Dynamic dehydration assessment can be tracked well with ->
- Body mass change (in energy balance)
- Plasma osmolality
- Urine specific gravity (Urine density relative to water (water = 1.00) and Euhydrated at 1.003-1.035 U(Eu)
What are hourly sweat rates for runners at different paces and heat stress conditions?
-> There is a consistent increase in sweating rate in ‘hot and humid’ and ‘cool and dry’ conditions
Why do we sweat?
- Heat production during exercise – For every L of oxygen consumed 4kcal of heat is produced and only about 1kcal is used to perform mechanical work. Most of this heat is passed to the body core. Hypothalamus senses increase in body (and skin) temperature. Responds to increase blood flow to skin and initiate sweating response
- Sweating is the body’s principle means of preventing excessive rises in body temperature during exercise (hyperthermia). Normal body temperature is 36-38 C and during exercise is 38-40 C
- Evaporative cooling – 1L sweat evaporated will remove 573kcal of heat from the body
Average running speed/ finish time against post-race dehydration:
-> During periods of high sweat rates, ad libitum drinking will often lead to body water deficit (i.e. negative net water balance). Most deficits >2% initial body mass loss.
What is sweat loss?
-> Water loss from the water component of blood (plasma) = reduce plasma and blood volume. Sweat is hypotonic as compared to plasma, therefore plasma osmolality increases.
Does hypohydration impair performance?
-1-2% -> minimal impact
-2-3% -> may degrade aerobic performance, deterioration in sport-specific skills and minimal impact on sprint running
->3% -> impaired cognitive function (even in temperature)
-3-4% -> minimal impact on muscle strength and power
-Important to note considerable individual variability in performance responses to hypohydration
What is the impact of ‘blinded’ dehydration on aerobic performance?
- Blinded dehydration impairs endurance performance
- Similar performance decline with blinded vs unblinded dehydration
What are the potential mechanisms of impaired aerobic performance in warm-hot conditions?
- Cardiovascular – Blood pressure and blood flow, oxygen delivery, metabolite removal
- Central nervous system – Brain metabolism, brain temperature
- Peripheral muscular factors – Temperature, metabolic, afferent feedback
- Psychological – Thermal comfort, perceived exertion
- Respiration – Breathing sensations
+Dehydration exacerbates these proposed mechanisms, although cardiovascular strain (high skin blood flow + reduced blood volume) is likely a critical primary factor
Dehydration and performance:
-> Inadequate maintenance of fluid balance and the development of hypohydration can negatively impact physiology and exercise performance in some, but not all exercise contexts. The mechanisms by which hypohydration affects performance are multifactorial, although cardiovascular strain appears to be the most prominent. Environment can play a big role in the impact of hypohydration.
Draw the ACSM guidelines for 2-4hr pre-event, during exercise and post-exercise:
*Situations where hydration may impact performance. **Accounting for urine losses and drink volume
Describe sodium for hydration:
-> Sodium helps with reabsorption of fluids in the body and helps to maintain the hydration status. Other electrolytes, though lost in sweat – do not seem critical for hydration.
Draw the pre-exercise, during-exercise and post-exercise hydration status
Explain hydration during exercise:
-> Pre and post weighing can be used to measure hydration status in the body. Sufficient fluid to limit body mass losses to <2%. Sweat losses variable between sports and between individuals. Maintain plasma sodium levels through exercise with electrolyte drinks consumed during exercise.
How do you calculate sweat rate?
How do you characterise CHO-E solution?
-> A CHO-E should: Supply CHO as the major energy source and Be effective in maintaining hydration status. Energy: 80-350 kcal/L, >75% of energy from CHOs that induce high glycaemic response e.g. glucose, glycose polymers, sucrose. Sodium: 20-50 mmol/L (460-1150mg/L)
What is the sodium content of sports drinks?
-> Lucozade: sodium = 50mg/100ml. ‘Fit water’: sodium = 21mg/100ml.
Describe sodium:
-Sodium plays a critical role in ensuring effective maintenance or reassumption of fluid balance. It is important to not overdrink during exercise so that the individuals weight increases and the body mass should be maintained the whole time during exercise.
