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Water, Hydration, and Exercise :

Water, Hydration, and Exercise

Water, Hydration, and Exercise:

Water, Hydration, and Exercise Body Water or hydration status is of critical importance. Even when dehydration is subtle, it can lead to reduced endurance and premature fatigue. Dehydration can result in reduced power and strength for athletes in football, soccer, ice hockey, tennis and weight-lifting. Some athletes such as body-builders and wrestlers intentionally manipulate body water for reasons of aesthetics or weight reduction.

Water, Hydration, and Exercise:

Water, Hydration, and Exercise The human body is mostly water - ~ 56-64% of the weight of the average adult. But, water is not evenly distributed throughout the body. Water is found in all tissues of the body, but varies from tissue to tissue. ~2/3 of body water is found within cells as the basis of intracellular fluid. The remaining extracellular fluid includes: Interstitial fluid – the fluid between cells Plasma portion of blood. Water flux - Water moves through the body through the forces of: Hydrostatic pressure – such as blood pressure – a “pushing force” Osmotic pressure – a “pulling force” – movement down its concentration gradient.

Properties of Water:

Properties of Water Water is an excellent solvent because it is a polar molecule. Although it has no net electrical charge, there is uneven sharing of the electrons which leads to partial negative and positive charges around the H and O atoms. This allows water molecules to electrically interact with other water molecules and with, electrolytes, glucose, and amino acids/proteins. Water has a relatively high specific heat (the measure of the calorie energy required to raise a gram of a substance by 1º C. Water has a specific heat of 1.0 compared to 0.83 for the entire body of an adult male – the lower overall figure is due to the presence of proteins, fats, and other substances. The contribution of water helps slow the rise in body temperature in hot environments or during periods of greater heat production such as exercise Therefore, water is known as a heat buffer. In addition, the high specific heat of water minimizes the amount of sweat needed to dissipate surplus heat from the body – thermoregulation

Plasma Water:

Plasma Water Roughly half (1/2) the total blood volume is water. Electrolytes, mainly sodium and chloride, play a significant role in determining the osmotic properties of the blood. Another influential factor in determining plasma water volume is protein level. Plasma protein exerts a powerful effect on plasma water. For instance, if plasma protein levels decrease, plasma water volume decreases in response.

Skeletal Muscle and Adipose Tissue:

Skeletal Muscle and Adipose Tissue Roughly 72-73% of the mass of skeletal muscle is water. Comparatively, only about 10% or less of adipose tissue is water. Because men tend to have a greater percentage of skeletal muscle and a lower percentage of fat compared to women, they generally have a greater percentage of body water. Muscle fibers are concentrated with protein, glycogen, creatine phosphate, and amino acids – collectively these create a significant osmotic force which pull water into muscle fibers.

Roles of Body Water:

Roles of Body Water Body temperature regulation – through sweating Provides the basis for blood pressure basis for digestive juices basis for excretory fluids basis for fluid found within joints Dehydration may promote glycogen and protein breakdown in tissue such as skeletal muscle


Sweating Hyperthermia, a rise in core body temperature, leads to changes in enzyme activities and other cellular irregularities that can disrupt homeostasis. Sweat glands are found in skin tissue covering the entire body. As body core temperature increases stimulation of sweat glands increases.

Sweat Composition:

Sweat Composition Primary sweat is similar in composition to blood plasma and includes sodium and chloride. The rate of flow through the tubule is dictated by the rate of primary sweat production which is in turn dictated by stimulation. Reabsorption of sodium and chloride by the cells lining the tubule depends on the flow rate. As water is reabsorbed the remaining solutes in sweat become more concentrated…these solutes included lactic acid, urea, and potassium. If sweat flow through the tubule is rapid, then the reabsorption of sodium, chloride, and water is reduced and more reached the skin surface.


Urine Urine is a composite of water, electrolytes, urea, creatinine, and trace amounts of glucose, amino acids, and proteins. During rest, the kidneys receive ~20-22% of cardiac output - ~ 1 L of blood per minute. Efficient urine formation is crucial in removing nitrogen waste and excessive amounts of electrolytes and other substances in the body. Urine production decreases during exercise with dehydration but will not cease as waste must still be removed.

Blood Pressure:

Blood Pressure Because water is the predominant component of blood, it is fundamentally involved in establishing blood volume – which influences blood pressure. Several systems regulate blood plasma. Two influential hormones are: Antidiuretic Hormone (ADH/Vasopressin) – when extracellular fluid increases solute concentration, the hypothalamus releases ADH and initiates thirst. Aldosterone – promotes sodium reabsorption – helps stabilize blood volume by osmotically attracting water. In symbiosis with the release of renin which promotes vasoconstriction – thereby increasing blood pressure.

Water Balance:

Water Balance The average adult may lose as much as 4% of body mass from water in a typical day. Water is brought into the body by ingesting both fluids and solid foods. ~ 2/3 by water and fluids ~ 1/3 by moisture in foods See Table 8-2 p. 239 Water Content of Various Foods Water is a product of the combustion of energy nutrients so as activity increases so too does water production in cells.

Water Balance:

Water Balance Total water loss for an adult is typically 2-3 L /day Sweat Urine Feces Exhalation of air humidified in the lungs. Could be higher than avg 200-400 ml/day in arid environments General recommendations are 2-3 L/daily for adults to balance losses. The hypothalamus is the thirst organ and controls thirst intensity …. An individual must be slightly dehydrated in order for thirst to be evoked. Table 8-3 p. 239 Effects of Body Water Loss on Physiological Performance OVERHYDRATION – cell hydration status may influence the metabolism of carbohydrate and protein.

Exercise and Body Water Distribution:

Exercise and Body Water Distribution During exercise, reduction in blood volume reflects a flux of water from the plasma in the interstitial and intracellular fluids in active skeletal muscle. This flux leads to “the pump” sensation of transient swelling of muscle during strength and power exercise bouts. Hemoconcentration - the increased viscosity of blood makes it more difficult for blood to travel and deliver O2 as well as to dissipate heat…therefore plasma volume must be stabilized. This is accomplished by a balancing of hydrostatic and osmotic forces as well as hormones affecting water and sodium loss (aldosterone/ADH). CLIMATE INFLUENCES In warm environments, stabilization of plasma volume may not occur due to increased degree of sweating.

Exercise Induced Sweating:

Exercise Induced Sweating Breakdown of energy nutrients to fuel muscle contraction generates excessive heat. Higher humidity levels make it difficult for sweat to evaporate Therefore potential for heat related complications increase as humidity rises. Lower Sweat rate of children – increased surface area ratio – rely more on non-sweating techniques such as convection, conduction, etc..– therefore children have greater heat intolerance than adults. Apparel – Materials – dark colors, breathe-ability Land vs Water Competition – heat release methods and sweating

Hydration and Performance :

Hydration and Performance Thirst is a symptom of dehydration and may not be perceived until body weight has been reduced by 1% due to water loss. Additionally, thirst sensitivity may be blunted during strenuous exercise. Without recovery of electrolytes (NA/CL), thirst can be alleviated prior to complete rehydration.


Dehydration In a dehydrated state, the body is less able to absorb and transport heat from muscles and the body core. Result is an increase in body core. HYPERTHERMIA – some research suggests that this is the main factorunderlying early fatigue. HYPONATREMIA – a state in which the concentration of sodium in the blood is below 130 mmol – causing disturbances in the nervous system and muscular systems

Cardiovascular Consequences of Dehydration:

Cardiovascular Consequences of Dehydration Stroke Volume is reduced Heart Rate is accelerated Figure 8-12 p. 241 Physiological Effects

Metabolic Consequences of Dehydration:

Metabolic Consequences of Dehydration Dehydration influences substrate utilization May lead to Increased use of Carbohydrate and reduced use of Fat by working muscle Blood flow is reduced and therefore glycogen breakdown is increased along with lactic acid buildup


Hypohydration Wrestlers, bodybuilders Effects of dehydration at onset of activity Long term can have kidney and heart failure


Hyperhydration Can potentially benefit athletes during endurance exercise in a warmer climate Applicable to soccer, distance running, tennis

Athletes and Water:

Athletes and Water All athletes are encouraged to drink 13-20oz 2-3 hours prior to exercise…allows for equilibration of ingested water through various body compartments. General recommendation is 6-12oz every 15-20 minutes during competition. 16.5-33 oz (500-1000ml) during the first 30 minutes post-exercise and 1 L every 1-2 hours after until consumption has matched 150% of weight loss. Carbohydrates and electrolytes promote the recovery of nutrients in the body Aid recovery of glycogen stores through electrolytes CARB DRINKS ARE MORE EFFICIENT THAN WATER ALONE