HYDRATION For Cyclists
In July 1994, a well-conditioned athlete entered a 1/2-Ironman distance ride with hopes of putting in her best performance. She was well trained and had raced in the heat before. It turned out to be a very hot west Texas day. Things were going well until the run. After one mile, she experienced diarrhea and painful quadriceps muscle cramps. By mile 6 1/2 she had headaches and had stopped sweating. She managed a slow, painful finish, tried to hydrate, but became delirious. The medical staff was called. Intravenous fluids were started, but she deteriorated and began vomiting. After transfer to the hospital she had seizures. She experienced widespread muscle breakdown, severe electrolyte disturbance, kidney damage, and her lungs filled with fluid. She was placed on artificial life support and was given a 50:50 chance of survival.
Fortunately, she lived.
Proper hydration is one of the key elements in cycling performance. Over 60 percent of the human body is water.
In the bloodstream, water helps serve as an energy supply line to deliver oxygen and nutrients that allow your muscles to perform at their peak.
Water is also the primary element in your body’s cooling system. During cycling, your body loses fluids as it works to maintain a healthy temperature. Your muscles generate eight to 10 times more heat when you work out than when you’re at rest. High-intensity cycling can cause you to lose 2.25 litres or more of body fluid per hour! And if you don’t replace that fluid, you’ll suffer from dehydration.
Dehydration has a dramatically negative impact on cycling performance, and this can happen long before you get thirsty. At the extreme, dehydration is a dangerous condition that can lead to severe cramps, exhaustion and heatstroke.
Humidity is not your friend
The rate of perspiration is higher in humid conditions (such as here in Singapore) but the cooling is less. The reason is that because the air is already very saturated with water, sweat can’t evaporate. Sweat that beads up and rolls off doesn’t function in the cooling process. However, this “futile sweat” does deplete the body of vital water and salt. As dehydration progresses cooling becomes more difficult. Performance drops and heat injury becomes a real threat.
Recognizing symptoms of heat injury
There are three stages to heat illness; heat cramps, heat exhaustion, and heat stroke — listed in order of increasing severity. Often the border between them is blurred into a continuous spectrum. Heat cramps are due to muscle spasms and often occur in the arms, legs, or abdomen. They are thought to be caused by dehydration and loss of salt and other electrolytes. Heat exhaustion is due to more profound loss of water and electrolytes. It is characterized by generalized weakness, disorientation, nausea, headache, dizziness, low blood pressure, elevated pulse, and temperature elevation as high as 40 degrees C.
There is only one remedy when this happens; stop cycling, find a shady spot to rest under, and drink plenty of fluids, preferably a mixture of plain water and an isotonic drink. (The isotonic drink assists the stomach to absorb the water faster, plus it contains salt and minerals which are also lost in the sweat but which water alone cannot replace).
Heatstroke is a life threatening condition and represents severe dehydration, high body temperature, and a shutdown of the cooling mechanisms. The sufferer may be delirious or comatose, and half of the victims have stopped sweating. The pulse is rapid and weak, the blood pressure is low and body temperature is greater than 40.6? C. The oral temperature is notoriously inaccurate in these circumstances. Damage to the brain, heart, lungs, kidneys and other organs may occur. Sometimes despite the best medical care, death is the end result.
|Emergency trail-side treatment of heatstroke
? Call 995 – clearly stating location and giving directions to location if necessary. If in remote locations, arrange to meet the ambulance at a more accessible/recognizable landmark and guide the medics in to the casualty, or move the victim out to the landmark.
? Remove the patient from direct sunlight
? Remove the patient’s clothing
? Wet the body surface and fan to promote air movement and evaporation
The following table and graph relate % body weight loss (via perspiration) to performance and symptoms.
Relating % loss of body weight to symptoms and performance in the heat from Nutrition for Cyclists, Grandjean&Ruud, Clinics in Sports Med. Vol. 13(1);235-246. Jan 1994
· 0% — normal heat regulation and performance
· 1% — thirst is stimulated, heat regulation during exercise is altered, performance begins to decline
· 2% — further decrease in heat regulation, increased thirst, worsening performance
· 3% — more of the same
· 4% — exercise performance cut by 20 – 30%
· 5% — headache, irritability, “spaced-out” feeling, fatigue
· 6% — weakness, severe loss of thermo-regulation
· 7% — collapse is likely unless exercise is stopped
To avoid becoming a victim of heat injury, a proper program of hydration has to be made part of your cycling routine
· Drink before, during, and after the ride
Hydrate thoroughly the day before the ride. How do you know if you are drinking enough? A good sign of hydration is the output of large volumes (having to go at least 6 times a day) of clear, dilute urine.
just before the start of the ride. Experts say you need 500 ml (16 ounces) of water two hours before you ride and 8 to16 ounces 30 to 60 minutes beforehand as well.
· Drink during the ride
Don’t rely on your thirst to signal you to start drinking. By the time you’re feeling thirsty, it’s already too late. Drinking 150 – 250 ml (5 – 8 ounces) every 10 – 15 minutes is probably the best way to attempt to stay hydrated while riding. For some people, drinking a lot causes discomfort and a feeling of being “bloated”. Thus guzzling a liter once per hour will likely cause problems. Also realize that the more dehydrated you get the harder it is for your gastrointestinal (GI) tract to absorb what you drink. Dehydration also causes a variety of GI symptoms (nausea, cramping, and diarrhea).
It is all too easy to forget to drink as you get caught up with the ride, so you must determine and plan you hydration strategy ahead of time.
· After the Ride
Drink as much as you can manage immediately after the ride to kick-start your body’s re-hydration, and top up with smaller drinks thereafter.Based on pre and post exercise body weight, drink liberal quantities of fluid (150% of the loss in body weight). This is to replace fluid losses in the post event phase (i.e. when you’re sitting there sweating away, talking about the ride)
A major telltale sign of dehydration is the color of your urine; if it’s anything other than clear or pale yellow, you’re dehydrated and should increase your water intake.
Choice of fluid – Water, Gatorade, or Heineken
For rides lasting less than 1 hour, water alone is adequate.
(Quote from “The Waterboy” – Water sucks, Gatorade is better) For longer rides, you will need to replace sodium and carbohydrate. There are many commercially available sports drinks. The most important features are taste, carbohydrate (fuel for the MTB engine) and sodium content.
Taste is important, because if you don’t like it you won’t drink it.
Carbohydrate content in the range of 4 – 8% is best for endurance rides. Levels above 10% are poorly absorbed and can cause diarrhea.
Most sports drinks have a sodium content in the range of 10 – 20 mmol/liter (Gatorade is 23 mmol/liter = 1.3 grams of salt per liter). Higher levels are better for salt replacement, but tend to be less palatable. There doesn’t appear to be any advantage gained from adding other electrolytes (e.g.. potassium, magnesium) since the diet is usually adequate to replace these.
Avoid drinks with fructose since it can upset the stomach.
Many people cut out alcohol entirely in the training period and if you are really serious about your performance this is probably a good idea. But if you are simply doing this for fun, then one or two drinks socially will not do you any harm. Do avoid drinking 24 hours before a big ride though. Alcohol dehydrates you and also messes up your ability to make and store glycogen, all-important over long distances.
Alcohol should also be avoided after a heavy ride because of its dehydrating effect.
Know your body
There is large variability between individuals with respect to net water loss while exercising in the heat. This depends upon perspiration rate, rate of fluid ingestion, rate of gastric emptying, type of fluid ingested, percentage body fat, and many other variables. Because of this there is no simple answer for which fluid to drink, how much, and how often. So how do you know what is right for you?
To get an accurate reading you need to weigh yourself, preferably nude, before your cycling session. Then, after the session, you weigh yourself again to see how much weight you have lost.
Say that, after an hour of cycling, you lost one pound or 0.45 kg of body weight. This would be equivalent to 16 ounces of water loss. Therefore you would need 8 ounces of water every half an hour of cycling.
OVERHYDRATION – Don’t overdo it!
This will tend to affect you only on longer rides. Over-hydration can be as dangerous as dehydration.
The problem arises when you drink too much water on a long ride. Your body loses sodium as well as water through sweat, but if you only drink plain water, you will only be replacing the water lost, but not the sodium.This results in a dilution of the sodium levels in your body.
Failing to replace salt during the ride can result in hyponatremia.
What is it? Dr. Mark Steckel says, Hyponatraemia means “low concentration of sodium in the blood”. Sodium is an important electrolyte, which plays a role in water balance and muscle contraction. Sodium is required to draw water through the permeable membranes in the body and thereby distribute fluid throughout the body. When you perspire, you loose water and salt, and salt is made up of sodium and chloride. A lot of sweating means you are depleting your sodium stores in your body. If your sodium levels get too low, you will no longer be able to move water across these permeable membranes and you will become dehydrated – even if you are drinking enough water. You can drink all the water you want, but if you don’t have sodium present to move it from the gut to the bloodstream, you don’t stand a chance.
The signs and symptoms of hyponatremia include bloating, upset stomach, nausea, headaches, cramps, disorientation, slurred speech and confusion.
Experts recommend that athletes ingest an average of 1 gram of sodium per hour for hot rides lasting longer than 4 hours. (2.5 grams of sodium chloride has 1 gram of sodium and 1.5 grams of chloride. One teaspoon of salt weigh approx. 6.6 grams) It is also advisable to increase salt intake for several days before a long ride. Aim for between 10-25 grams of salt per day pre-ride (one teaspoon of table salt has approximately 2.65 grams of sodium) To ingest 1 gram of sodium from sports drinks alone, you would have to drink 2.18 litres of Gatorade. You can’t drink (or carry) that much per hour for the duration of a long ride. So, even if you drink sports drinks during a hot ride it is very likely that you will perspire out more salt than you can replace. You will need to replace salt specifically. This can be accomplished by either eating salty foods or taking salt tablets.
There are pros and cons to both:
Salty Foods will taste good and the fact that you are ‘tasting’ the salt will help to trigger a thirst response that will make you drink more. But, you will need to eat a lot of salty food to get in enough sodium. One gram of Sodium equals 2.5 grams of table salt. Now, one tablespoon of salt weighs about 6.6 grams, so you will need less than half a tablespoon (per hour), but if you are trying to ingest that from pretzels or crackers, that’s a lot of food you’ll have to carry.
Salt Tablets are convenient little ‘pills’ made up of sodium and chloride (some electrolyte tablets may have other ingredients, but basic salt tablets are just table salt) which are easy to carry and ingest. But, because they don’t stimulate a thirst response you will have to make sure that you are drinking enough during the ride. The nice part about ingesting salt while you ride is that it allows you to drink plain water for a change from the sports drink of the day.
As mentioned, hyponatremia is only likely to bother you on really long epic rides. For most rides, even longer ones, you should be able to get by with salt replacement from Salty Food. Salt Tablets tend to be more for the really extreme whole-day-sweating-in-the-sun sagas or for “salting-up” on the pre-ride day.
There are a couple of other important things to remember when discussing hyponatremia:
? The signs and symptoms of hyponatremia are very similar to dehydration, and that’s what makes it dangerous, for it is commonly mis-diagnosed. As a result, the sufferer keeps drinking more water in a mis-directed attempt to fight dehydration, and in reality making his hyponatremia worse by further diluting his sodium levels with the water he consumes. Untreated, hyponatremia and dehydration can lead to collapse, convulsions, and sometimes even death.
? It is possible to become hyponatremic without sweating out all your salt. Over-hydration in a cooler climate can cause low sodium concentrations in the blood. Some athletes actually consume too much water, which dilutes the sodium in their system thereby causing hyponatremia. Remember, it is the concentration of sodium that we are concerned with, not the absolute amount.
? Medication such as Aspirin (ASA), Ibuprofen, Non-Steroidal Anti-Inflammatories (NSAIDs), and Tylenol (Acetaminophen) interfere with kidney function and may contribute to hyponatremia. Taking such medication while exerting strenuously is simply foolish.
To summarize, it is important to increase your salt intake in the days leading up to the ride, to drink an amount of fluids which is appropriate to the ride climate, and to ingest salt during the ride if the day is hot and the ride long.
The above is aimed at being informative to a social group of riders. The author does not claim any credit or merit for the content, and does not intend to infringe any copyright laws or to commit plagiarism. Whilst every effort has been taken to ensure the information contained herein is accurate, the author is NOT a trained medical professional and cannot vouch for its accuracy