Download Water as an ergogen

Cardiac Output
• Q = HR x SV
– Q = cardiac output
– HR = heart rate
– SV = stroke volume
Regulation of Stroke Volume
• end diastolic volume (EDV) - volume of
blood in ventricles at the end of diastole
– Frank-Starling Law
– increase in contractility increases volume
pumped per beat
– venous return
• average aortic blood pressure
• strength of ventricular contraction
Components of Blood
• Plasma
– Liquid portion of blood
– Contains ions, proteins, hormones
• Cells
– Red blood cells
• Contain hemoglobin to carry oxygen
– White blood cells
– Platelets
• Important in blood clotting
• Hematocrit
– Percent of blood composed of cells
Hematocrit
• hematocrit is the percentage of whole blood
which is composed of solid material
– cells, platelets etc
• the blood is composed primarily of water
(~55 %) called plasma
– the hematocrit would be 45
• can vary between 40 and 50
Cardiac Output during Exercise
• Q increases in direct proportion to the
metabolic rate required to perform task
• linear relationship between Q and VO2
• remember... Q = HR x SV
Stroke Volume and Heart Rate
during Exercise
• in untrained or moderately trained
individuals stroke volume plateaus ~ 40%
VO2 max
• at work rates > 40% VO2 max, Q increases
by HR alone
• See fig 9.17
Changes in Cardiovascular Variables
During Exercise
The Fick Equation
• VO2 = Q x (a-vO2 diff)
• VO2 is equal to the product of cardiac
output and arterial-mixed venous difference
• an increase in either Q or a-vO2 difference
will result in an increase in VO2max
Redistribution of Blood Flow
• Increased blood flow to working skeletal
muscle
• Reduced blood flow to less active organs
– Liver, kidneys, GI tract
Changes in Muscle and Splanchnic
Blood Flow During Exercise
Redistribution of Blood Flow During
Exercise
HR, SV, and CO During
Prolonged Exercise
Prolonged Exercise
• Cardiac output is maintained
– Gradual decrease in stroke volume
– Gradual increase in heart rate
• Cardiovascular drift
– Due to dehydration and increased skin blood
flow (rising body temperature)
.
Heat Exchange Mechanisms
during Exercise
Increases in Temperature
• Receptors on skin first sense changes
– receptors also located in spinal cord and
hypothalamus respond to core temp changes
• Stimulates sweat glands - increases
evaporation
• Increases skin blood flow - vasodilation
Changes in Heat Production and Loss during
Exercise
Take Home Message
• During exercise, evaporation is the most
important method of heat loss
• Heat production must be matched with heat
dissipation or hyperthermia will ensue
• Metabolic heat production increases in
proportion to the exercise intensity
• Convective and radiative heat loss do not
increase with intensity as temp gradient
between body and environment does not
change significantly
Hyperthermia
• Increased core temperature to the point that
physiological functions are impaired
• Contributing factors
– dehydration
– electrolyte loss
– failure of cooling mechanisms to match heat
production
Exercise in Hot/Humid vs. Cool
Environment
Other factors related to hydration
• Water as a solvent
– Ionic concentration
• Neuro-muscular coordination
• Contractile function
– Reactions
• Macronutrient formation
– Glycogen
• Proper digestion and waste removal
Amount of fluids ingested
• Small amounts of fluid ingestion do not
entirely attenuate
– Elevation in core temperature
– Elevation in heart rate
– Rating of perceived exertion
Moderate and Large fluid
intake resulted in
significantly different
responses than No or
Small fluid intake
Small = 300 ml/hr
Moderate=700 ml/hr
Large=1200 ml/hr
From Coyle SSE #50 GSSI
Effects of dehydration on
cardiovascular parameters
versus % body weight loss
From Coyle SSE #50 GSSI
Recommendations
• Drink as much as can be tolerated up to
1250 ml/h for 68 kg/150 lb individual
• Drink should contain 4-8 % CHO to
optimize absorption
• Adjust volume per body weight as ratio of
68 kg
– E.g. 50 kg> 50/68 * 1250 = 925 ml/hr