03/05/2020

Exercise and Hydration

Comprising of nearly two thirds water, the human body relies heavily on regular fluid intake (11). The demand for fluid intake further increases in hot environments and during physical activity when water losses through sweat and breathing increase (11). The amount of fluid we need to consume daily depends on the environmental conditions (temperature and humidity) (8), the level of physical activity (10) and our age (13). General daily guidelines for woman are 1.6L p/day (8 x 200ml glasses of water) and 2.0 L p/day for men (10 x 200ml glasses of water) (1). These guidelines do not include the fluid we get from consuming food, which usually provides an extra 20% to total fluid intake. Conversely, these guidelines do include all types of drinks, including water, coffee, tea, fruit juices, soft drinks, milk and alcoholic beverages. This can pose a problem as many drinks contain further calories, particularly in the form of sugar, often leading to a significant undetected calorie intake. Many energy drinks also contain a combination of huge quantities of caffeine which will cause further urination due to its diuretic properties (2).

Pre-Exercise Hydration

It has been accepted that the most common nutrition related problem around exercise is dehydration (12). Since exercise increases body temperature resulting in greater sweat losses, it makes sense to go into any training session well hydrated (euhydrated) (4). This is further supported by the available research that on most occasions fluid intake during exercise cannot match sweat losses (4). Unfortunately, research has found many individuals already begin exercise in a dehydrated state (5). This problem can be further enhanced in individuals on extreme weight loss or poorly constructed detox plans.
Pre-exercise hydration should begin 24 hours in advance to the training session (4). It’s important we stay well hydrated throughout the day, concentrating on water intake. Foods and drinks with diuretic properties should be eliminated around training such as alcohol and caffeine. The duration and the temperature need to be considered when drinking water in the hours before exercise. Any exercise sessions under 1 hour will only require 200-300 ml of water in the 2 hours before exercise (1). This can also be combined with CHO to further improve performance if that is the goal. In hot conditions it is recommended you consume 500-600 ml (2 large glasses of water) in the two hours before exercise (10). In the gym environment and in many sports, we can also take water during exercise. For exercise modes such as running and swimming, it is imperative we have adequate pre-exercise hydration status. For longer duration exercise, particularly in hot and humid conditions you will need to take on water during exercise.

During Exercise Hydration

In most exercise sessions, durations will consist of anywhere between 30-60 minutes. Only in specific endurance/strength programmes will you be advised to regularly engage in exercise durations of over one hour. For this reason, adequate hydration before exercise and immediately after is usually sufficient to prevent dehydration. However, many gyms have inadequate ventilation systems and are often set at too higher temperatures. This combined with hard training protocols, will result in considerable sweat losses. Therefore, water intake (200-300ml) during your 45-60 min sessions should be consumed (1). This should be in the form of a cool CHO electrolyte drink if the intensities are extremely high and muscle mass preservation is a priority. (3)

Post-Exercise Hydration

After exercise, our main priority should be to replace the water that has been lost through sweat and to a lesser extent the increased H2O through breathing (4). We also need to consider urination after exercise as well. For this reason, it is advised you consume 150% of actual water losses (10). The graph below shows a visual representation of this. Each of the 4 lines represents a different bolus of electrolyte drink in the post exercise period. As you can see, only 150% and 200% intakes keep us in a euhydrated state (normal amount of water in body) up to 6 hours after exercise.

The two other important factors we need to consider in a hydration drink both during and after exercise is the palatability of the drink and the electrolyte content (3). We are more likely to consume a drink that we enjoy consuming and have a cooler temperature. Research has also conclusively shown both sodium and potassium have a retention effect on total fluid balance (10). Therefore, drinks with additional electrolytes should be consumed when sweat losses are high.

Special Considerations

Hyperthermia

Research has proven dehydration combined with an increase in body temperature (hyperthermia) is more dangerous than either dehydration or hyperthermia alone (8). We should therefore aim to cool our body down at every opportunity using any water available and wearing the appropriate clothing.

Salt Losses

There is a genetic variability in the salt we lose in sweat (11). Many of us are ‘salty sweaters’ and need to use electrolyte drinks. A useful practical way to test if you’re a salty sweater is to wear black and do a prolonged session. If there are salty deposits left on the clothing, you are a salty sweater and will need to replenish the salts lost. However, electrolyte imbalances are rare in events anything other than ultra-distances. For this reason, water intake should be main priority.

Age

The thirst sensation decreases with age (13), making it more important to drink regularly. Many elderly individuals refrain from drinking in the belief that it will prevent them from frequent urination in the evening. This can further increase the risk of dehydration.

Hyponatremia

Although a rare condition, hyponatremia is a dilution of essential electrolytes in our body, caused by excessive drinking of water combined with salt losses (7). Although we need to prevent dehydration, we also need to use common sense with our hydration strategy. Hyponatremia is most common in cooler conditions, when salty sweaters usually with a smaller body mass consume very high amounts of water in the lead up/during an endurance event. The symptoms of hyponatremia are very similar to dehydration, which unfortunately has cost some people their lives, as they have continued drinking large amounts of water when all they need was to replenish salt losses.

Symptoms of dehydration (2-4% total BW loss)

  • Dark colour urine
  • Dizziness
  • Headache
  • Light-headiness
  • Dry lips (and eyes)
  • Infrequent passing of urine

Symptoms of severe dehydration (>4% total BW loss)

  • Confusion + extreme dizziness.
  • Severely lethargic
  • Weak pulse
  • Seizures
  • Not passing urine for > 8 hours

References

  1. American College of Sports Medicine (2007) Exercise and Fluid Replacement: A Position Stand.
  2. Armstrong, L. (2002) Caffeine, Body Fluid-Electrolyte Balance and Exercise performance. 12: 189-206.
  3. Burdon, C. Johnson, N. Chapman, P. O’Connor, H. (2012) Influence of Beverage Temperature on Palatability and Fluid Ingestion During Endurance Exercise: A Systematic Review. 22: 199-211/
  4. Burke, L, Deakin, V (2010) Clinical Sports Nutrition. Fourth Edition. McGraw Hill.
  5. Maughan, R. Merson, S, Broad,N, S, Sheriffs, S (2004) Fluid and Electrolyte intake and loss in elite soccer players during training. Int J Spor Nutr Exerc Metab. 14:333-46.
  6. Maughan, R. Watson, P. Evans, G. Broad, N. Shirreffs, M. (2007) Water Balance in Salt Losses in Competitive Football.  Int J Sports Nutr Exerc Metabob. 17: 583-594.
  7. Montain, S. Chevront, S. Sawka, M. (2005) Exercise Associated Hyponatraemia: Quantitative Analysis to Understand Aetiology. Br J Sports Med. 40; 98-106.
  8. Sawka, M. Cheuvront, S. Kenefick, R. (2012) High Skin Temperature and Hypohydration Impair Aerobic Performance. Exp Physiol. 327-332.
  9. Shireffs, S. Taylor, A. Leiper, J. Maughan, R(1996) Post Exercise Rehydration in Man: Effects of Volume Consumed and Drink Sodium Content. Med Sci Sports Exerc. Oct 28(10); 1260-71.
  10. Shirreffs, S. Aragon-Vargas, L. Keil, M. Love, T. Philips, S (2007) Rehydration After Exercise in the Heat: A Comparision of 4 Commonly Used Drinks. Int J Sport Nutr Exerc Metab. 17: 244-258.
  11. Shireffs, S and Sawka, M (2011) Fluid and Electrolyte Needs for Training and Competition. J Sports Sc. 29(S1); S35-46.
  12. Thom, W. (1813). Pedestrians, or an Account of the Performance of Celebrated Pedestrians. Aberdeen Chalmers.
  13. Yates, B. Eliis, L. Butts, C. McDermott, B. Williamson, K. Armstrong. L. (2018) Factors Associated with Pre-Event Hydration Status and Drinking Behaviour of Middle-Aged Cyclists. J Nutri Health Aging. 22(3); 335-340.
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