There are numerous research papers that show the more you sweat without replacing those lost fluids leads to a more drastic performance drop.

What causes these performance declines when you race in the heat? This is based on a combination of effects the heat has on your thermal, cardiovascular, metabolic and central nervous systems. A drop in blood flow to the muscle, skin and brain; a decrease in blood pressure; and a decrease in oxygen delivery to the working muscles all cause an earlier onset of anaerobic metabolism and hyperthermia-induced fatigue, which slow you down.

So, how much should we be drinking?
Generally, exercise scientists agree that we need to rehydrate at a rate not exceeding our rate of fluid loss. The human stomach can only hold 900 to 1,300mL and can only empty about 800mL/hr while exercising. Research also tells us that it’s crucial for us to drink large volumes of water early in our long distance events, because there’s a 40 to 60 minute lag time for it to clear the gastrointestinal tract and get to where it is needed in the body’s cells and plasma.

How frequently should we drink?
It’s important to keep drinking at regular intervals during your triathlon at a rate that replaces fluid loss, around 400 to 800 ml of fluid per hour. This averages out at roughly five to seven ounces, or 250 ml of fluid, every 15 to 20 minutes.

Post-Race and Post-Training Rehydration
Many studies show that carbohydrates consumed immediately after and two hours after exercise enhance muscle glycogen restoration. This is most effective if ingested from fluid, as fluid is absorbed faster. Many studies also show that electrolyte balance is restored almost to pre exercise levels when an electrolyte beverage is drunk immediately after exercise.

Tips for Surviving High Heat and Humidity and Maintaining Performance Intensity

Training Advice

  • Drink lots of cold water before, during and after your training efforts. Select running routes that have water fountains along the way. Drink 200-500 mls 15 to 20 minutes before starting and drink at least one cup of water every 20 minutes during your activity. Carry a water bottle.
  • There is nothing macho or intelligent about the archaic practice of shunning water on your training efforts thinking that it will toughen you up-it could kill you.
  • Post training or post triathlon rehydration: Weigh yourself before and after your race or training effort. Make sure you drink that weight back on within an hour or two of finishing. Choose carbohydrate rich fluids such as juices that replace both water losses and muscle glycogen. Juices contain more carbohydrates than sports drinks, so drink your fill of your favourite fruit juices.
  • About 450mg of sodium per hour is the minimum amount required to maintain plasma volume and slow the decline in plasma sodium concentration that can accompany prolonged exercise.

Triathlon Racing Advice

  • On hot, humid days don’t push your pace beyond your current level of fitness. Above all, do not be tempted to go out fast from the start. Early dehydration invites disaster. Realize that your performance in heat and humidity will be substandard and accept this.
  • Never drink sports drinks in a trathlon without having experimented with them previously on your longer training runs.
  • A brief break combined with drinking cold fluids, and taking a sponge bath, provide great relief in the middle of the running section of your triathlon. The cooling effect more than compensates for the few seconds you’ve taken to do this in terms of recovery time.

General Advice

  • Food digestion interferes with the blood flow to the working muscles, so avoid large meals before running in the heat.
  • Electrolyte sports drinks with sodium have been found to help endurance athletes retain water in their system, so you’re well advised to try them. Avoid the imposters that are loaded with sugar and no better for you than soft drinks. If electrolyte drinks make you feel nauseated, they’re too concentrated, so dilute them 100 percent or more. Avoid alcohol-its diuretic effect causes you to dehydrate quicker.
  • You’ll be able to tell whether you are hydrating adequately by the color of your urine. Dark yellow indicates low hydration, and pale to light yellow is good. The old adage of eight glasses a day of fluid is not quite right. You should ingest ½ ounce of fluid per pound of body weight if you are running in hot conditions. 80 to 100 ounces of fluid covers almost every runner.

 Dehydration Numbers:

 Here are some of the statistics studies have shown about dehydration:

  • With a temperature above 20 degrees Celsius and exercise lasting longer than 90 minutes, performance is impaired. Even 60 minutes of running in 31 degree temperature is enough to cause your body a sweat loss of two percent of body weight, enough to impair performance seriously.
  • For each liter of sweat lost, exercise heart rate increases by eight beats per minute and cardiac output decreases by one liter. Another found that water loss of four to five percent of body weight impairs physical work capacity and function.
  • With a fluid loss of 4.3 percent of body mass, athletes take 48 percent less time walk to exhaustion and their VO2 max (oxygen processing ability) was reduced by 22 percent.
  • Another study found that a reduction in body weight of two percent resulted in decreased endurance performances of 22 percent and a reduction in VO2 max of 10 percent.

Sport Drinks:

Hundreds of studies have found that carbohydrate and sodium in sports drinks have beneficial effects. Carbohydrate solutions help maintain your energy levels during races by replacing your depleted muscle glycogen stores. The sodium in sports drinks helps your body retain water and prevents low plasma sodium.

If you notice that sports drinks cause gastric distress to you, try experimenting with various sports drinks during your extended triathlon simulations. If you find that your sports drink is delaying fluid absorption, try another sports drink or dilute the one you are using with water until you get it right. This is often all that is needed to make it tolerable to your system. Some research indicates that the fluid should be cooled for maximal absorption.

A study by Millard-Stafford found that a seven percent carbohydrate-electrolyte drink increased 5K running performance in the heat compared with an artificially sweetened placebo. Another study by Tsintzas concluded that a 5.5 percent carbohydrate solution improves marathon-running performance.

  • A study by Below showed the importance of preventing dehydration and providing carbohydrate while cycling. Subjects cycled for 50 minutes at 80 percent of VO2 max, then ending with a sprint finish. Performance was improved by six percent when 80 percent of their sweat loss was replaced, and by another six percent when they drank 79 grams of carbohydrate, compared with when they drank fluids with no carbohydrate, for a total improvement in performance of 12 percent.
  • A further study by Byars found that carbohydrate feeding improves performance when exercise lasts longer than 90 minutes at 70 percent of VO2 max. Desbrown concluded that exercise duration needs to be longer than two hours at an intensity of 70 percent of VO2 max for carbohydrate solutions to be effective-and the triathlon definitely fits these criteria.

This article contains information taken from Ray Stevenson’s 2011 story, a TMC contributor.

Roy Stevenson has a master’s degree in exercise physiology and coaching from Ohio University. He teaches exercise science at Seattle University in Washington State and has coached hundreds of serious and recreational runners and triathletes in the Seattle area. As a freelance writer, Roy has over 200 articles on running, triathlons, sports, fitness and health published in over forty regional, national and international magazines in the U.S.A, Canada, England, Scotland, Ireland, South Africa, Australia and new Zealand. Formerly from New Zealand, Roy competed in NZ Championships on track, road, and cross-country. He held the NZ under-20 marathon record in 1974 when he ran his first marathon in 2:42:28.

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