Hydration Flashcards
What are the hourly sweat rates for runners??
When humidity is high, sweat rates are typically 0.75L/HR more.
Sweat losses more than 1L/HR are not uncommon
Dependent greatly on intensity of exercise.
Discuss the sweat loss work from Patterson et al (2000)???
Water loss from the plasma = reduced plasma and blood volume. Sweat is hypotonic therefore plasma osmolality increases.
Measured sweat from 10 men after 90 minutes 45% Vo2 max cycle, plasma NA+ decreased from normal levels of 135-145mmol to 24+-15
Discuss the work of Chevront et al (2010)??
Stated the best static assessment of hydration in plasma osmolality (typically 275-290mOsm/kg)
Best dynamic measure is urine specific gravity, where an individual is euhydrated at 1.003-1.035u, water =1.000 (ACSM suggests below 1.025). And body mass change in energy balance.
Stated a 99% change of dehydration if Posm/mmol/kg=13, Usg =0.014, Bm % =3.5
Discuss Kenefick et al (2010)??
Showed the impact of dehydration on aerobic performance, and illustrated the 27C threshold, after which every 1C warmer skin temp , performance on a TT reduced by a further 1.5%.
Discuss the effects of dehydration on performance (Shirrefs and Sawka, 2011)
1-2% BM loss - minimal impact
2-3% BM loss - may degrade aerobic performance, and reduced cog function with heat stress
>3% BM loss - impaired cog function even in temperate conditions
3-4% loss - minimal impact on muscle strength and power.
Variation does occur.
Discuss the ACSM guidelines for hydration??
24h prior to ex - drink adequate fluids, balanced diet
2-4 hr pre event - 5-7ml/kg BM (more if dark urine)
During event - sufficient fluid to limit body mass losses to 2% and limit excess electrolyte imbalance (0.4-0.8l/h cool flavour). If >2h then add sodium, add CHO >1h.
Post exercise - for rapid recovery (i.e. <12h)’consume 1.5L for each kg lost and sodium. For longer, resume normal practices and extra water.
Why should we take sodium?? (Shireffs and Sawka, 2011)
Pre exercise - fluid retention
During exercise - limit electrolyte loss and to stimulate thirst
Post exercise - restoration of sodium and fluid balance
Discuss Shirreff et al (1996) ??
Stated that sodium of 61 mmol/L must be consumed to maintain a neutral fluid balance .
See methods.
How do you do define a CHO-E solution?? (FSA, 2011)
Should supply CHO as main energy source
Energy: 80-350kcal/L from CHO, >75% of energy from CHO that induce a high glycaemic response
Sodium: 20-50mmol/L
Tonicity: must be between 200-300 mOsm/kg water, can be described as isotonic if between 270-330mOsm/kg water
Below et al (1995) showed the effect of CHO and water is additive, how so??
Had 8 cyclists cycle at 80%vo2max then a 10 min performance test.
Gave LV of 6% CHO, or water. Gave SV of 40% CHO, or water.
CHO was sig faster for performance test than no CHO, LV water faster than SV water.
Fastest together, the beneficial independent effects were additive.
Discuss Newell et al (2018)??
Looked at the dose-response of CHO-E (0%/3.7%/6.1%/7%) on endurance performance
6.1% and 7.0% CHO were significantly superior (for % improvement ) to water only and 3.7%CHO.
