Hydration in Endurance Sports

Melanie Ramos 7 min. of reading Running Leave a comment

Hydration in endurance sports is almost vital and is key for optimal exercise performance as well as maintaining health

Index

1 Water Loss Through Sweat
2 Overhydration and Hyponatremia
3 Carbohydrate Influence
4 Fluid and Electrolyte Replacement for Health and Performance
5 Supplements for Fluid and Electrolyte Replacement
6 Recommendations
7 Sources
8 Related Posts

Water Loss Through Sweat

Many ultra-endurance athletes often don’t meet their fluid needs during exercise

For hydration in endurance sports, it’s important to consider all factors that influence changes in body weight, besides fluid loss, and all sources of water intake.

Higher ambient temperature and humidity can increase sweat rate by about 1L/h.

Depending on individual variation, exercise type, and intensity, sweat rates can range from extremely low values to more than 3L/h

Overhydration and Hyponatremia

Overhydration, although not common, can also cause problems, as can inappropriate fluid composition

Excessive hydration in endurance sports or fluid needs during long-duration exercise in heat with low or negligible sodium intake can lead to reduced performance.

Sometimes, hyponatremia (very low blood sodium concentration). Therefore, with high fluid intake rates, even just to meet fluid needs, sodium intake is vital and a higher concentration in drinks (30 to 50 mmol/L – 1’7 to 2’9g NaCl/L) can be beneficial.

If you take an insufficient amount of fluids during exercise, performance can drop

Also, sodium is needed during recovery to reduce urine production and increase the rate of fluid balance restoration

Carbohydrate Influence

Glucose Oxidation

Adding carbohydrates to a drink can affect the net rate of water absorption, and it’s also important to supplement endogenous stores as fuel for muscles during ultra-endurance activity.

To improve water absorption, glucose and/or glucose-containing carbohydrates (like sucrose, maltose) at concentrations of 3 to 5% weight/volume are recommended.

Carbohydrate concentrations above this can be advantageous for glucose oxidation and maintaining exercise intensity, but won’t add any extra benefit.

If they’re hyperosmotic (high solute to water ratio), they’ll actually reduce the net water absorption rate

Gastric Emptying

Fluid loss rate can exceed the gastrointestinal tract’s capacity to absorb fluids. Gastric emptying may be slower than fluid loss rate, so individual tolerance can dictate the max fluid intake speed.

There’s a lot of individual variation in gastric emptying rate and tolerance to larger volumes

Training to drink during exercise is recommended to increase tolerance

Improving Water Absorption

Water, electrolytes, and carbohydrates are essential nutrients for maintaining normal physiological function and optimal exercise performance.

As exercise duration and intensity increase, fluid and electrolyte losses and compartmental imbalances increase, unless losses are compensated by appropriate intake.

Not just volume, but composition is key to ensuring whole-body fluid homeostasis (intracellular and extracellular, vascular and interstitial).

Carbohydrate intake during prolonged exercise can help performance, not only through increased glucose oxidation but also, indirectly, through better water absorption

Fluid and Electrolyte Replacement for Health and Performance

Physiological Responses

With increasing muscle contraction rate and growing active muscle mass, metabolic demands rise along with heat production

Compensatory physiological responses include increased circulation and redistribution of blood flow. In particular, blood flow increases to muscle and periphery (skin) and decreases to the abdomen (hepatic and portal vein).

Besides these cardiovascular changes, sweat production increases, whose evaporation provides the most efficient heat loss method available to humans.

Importance of Hydration

Sweat Losses

During intense and/or long-duration exercise, sweat losses can substantially reduce body water

There’s practically no water storage in the body, except maybe water stored with muscle glycogen (needed for glycogen metabolism), and in the bladder, which isn’t available to meet fluid needs.

It also increases during exercise mainly through increased breathing and evaporation of fluid from the respiratory tract

Most water loss during exercise is due to sweating

Cooling Mechanism

If fluids are consumed in amounts sufficient to offset fluid losses, endogenous cooling mechanisms are maintained.

However, if fluid deficit occurs during exercise, plasma volume and stroke volume decrease.

Heart rate increases and cardiac output decreases at some point, due to heart rate’s inability to compensate for reduced stroke volume, and core temperature rises.

Fatigue During Exercise

In contrast, with fluid intake during exercise, these responses are lessened

Several authors have shown that blood flow to exercising muscles decreases with dehydration during exercise. They also showed that fatigue linked to dehydration during exercise is highly correlated with high body temperature.

There seems to be a critical internal body temperature where fatigue happens regardless of initial body temperatures or the rate of heat storage

However, the threshold lowers with dehydration during exercise

Supplements for Fluid and Electrolyte Replacement

The relative importance of carbohydrate and fluid supplements during exercise can vary due to differences in sweat rates and carbohydrate use.

External factors like environmental conditions, exercise type, intensity, and duration influence these needs

In cooler conditions, with lower sweat rates and prolonged moderate to intense exercise, glycogen stores may become limiting before dehydration is significant.

Conversely, in hot and humid conditions, when sweat rates are high, fluid deficit can limit performance before carbohydrate stores become limiting.

As a result, not only fluid but also carbohydrates can limit performance in a given ultra-endurance effort, so supplementation should address both needs to ensure proper hydration in endurance sports.

Sweating results not only in water loss but also in electrolyte losses.

Electrolytes, especially sodium levels, vary drastically in sweat and increase with sweat rate and decrease with acclimation and training adaptation

Recommendations

Individual Needs

The fluid volume to ingest should be determined individually and adjusted to tolerance, aiming to meet needs.

These individual needs should be assessed by changes in body weight, correcting fluid intake and adjusting metabolic losses of body weight and metabolic water production when feasible.

Test Before Competition

To ensure optimal hydration in endurance sports, drinks should be tested during training to make sure they don’t cause any issues, since trying them in competition could hurt performance if they don’t agree with you.