Greetings Dr Kaufman, Thank you for sharing your professional knowledge and contributing to the site in the interest of rider safety. Please start us off by telling us what is hydration and dehydration?
My Pleasure. "Hydration" is simply a term coined to describe a person's ability to manage water, On the other hand, Dehydration is a term defined by the American College of Sports Medicine as weight loss exceeding 1% of a person's body weight. Simply put, the term dehydration simply implies a deficit of water in the body.
Could you tell us about the importance of hydration during strenuous and often intense conditions such as when riding a motorcycle off-road or on a closed course?
The importance of hydration is to avoid dehydration which can result with a number of symptoms. In many instances adequate hydration can reduce the frequency and severity of symptoms which can include weakness, muscle cramps, general malaise and suboptimal racing performance. The worst case scenario is the dehydrated military recruit who collapses during Basic Training from Exertional Heat Illness (EHI) which is among the leading causes of death in young athletes including some racing motorbikes.
Ok, Is there any advice one should follow for administration of fluids and electrolytes during strenuous exercise (ie; riding a dirt bike)?
Much has been written on the importance of drinking water to maintain hydration levels during exercise in order to
prevent dehydration. However, most of this literature is based on observations of athletes during marathon foot races and "endurance" events typically lasting upwards of several hours in duration where an athlete may be swimming, cycling and running.
Extrapolating from this data to the dirt bike racer in a sense calls for "comparing apples and oranges", as the footraces are generally longer and require a different type of training program than that of a motorcycle competitor. Nonetheless, some basic principles of fluid management can be applied to a sport such as off-road motorcycling, which demands sustained physical exertion, often in a hot environment while wearing protective gear which reduces the bodies ability to cool itself and exacerbates the need for maintaining proper body fluid levels.
With the previously mentioned caveats in mind, what should a motorcyclist do to optimize fluid balance so as to prevent dehydration?
Of foremost importance is to be proactive and take in enough water to prevent dehydration, not waiting for it to develop. For this purpose, thirst is unreliable and will usually underestimate fluid needs reinforcing what you have likely heard about "If you're thirsty, you're already dehydrated". Likewise, simple adages such as "drink all you can" present a risk of vomiting or over-hydration and the possibility of water intoxication. An individual simply can't rely on empirical data because there are none befitting their particular situation. There are just too many variables influencing water loss which will occur in varying degrees from urine, sweat, and the respiratory tract.
Factors that may contribute towards dehydration include ambient temperature, humidity, fitness of the individual, duration of the event, etc. Yet, to optimize hydration levels requires at least an educated guess as to what water losses are likely to be.
How do you recommend a competitor or a rider in training predict their water loss which is likely to occur?
The approach I recommend is to simply use changes in body weight during a race to estimate water losses expected during subsequent races. Every pound of weight loss represents 14 ounces of water. With this in mind, replacement fluids can be determined accordingly.
To ensure the greatest accuracy the rider should subtract the weight of any fluid consumed during the event to obtain the actual rate of fluid lost.
Additionally, The rider should urinate to empty his / her bladder and wear the same gear both before and after a race or long ride.
To ensure optimal hydration when beginning a race or a long ride the rider should "Pre-hydrate" by drinking enough water to turn the urine from the usual amber to a light straw color about an hour before the start of a race or a ride. (12-16 ounces should suffice for an average size person.) Usually water losses of less than 0.5% of body weight don't need replacement during the race or ride. However, when predictions exceed this value, hydration during the race or ride is advisable and can be easily accomplished with a hydration pack which will allow a person to remain well hydrated in the most adverse conditions throughout a race or any off-road adventure.
Example of A MX Setting:
A 25 year old dude named Joe enters a motocross race, which on average may range from 15 minutes to just over 30 and of which are often conducted on hot summer days. In preparation for Joe's race which is expected to last roughly 20 minutes Joe completes Pre-hydration (16 ounces of coffee and orange juice) an hour before the start of the race. 20 minutes later he empties his bladder and records a weight of 170 pounds wearing a full racing outfit.
On the track, Joe is lapping some of his competitors and sweating like anyone else holding off a gate full of competitors during the race which takes him nearly 20 minutes to complete. After the race his weight is 169 pounds indicating water losses of about 14 ounces which represents approximately 0.6% of his body weight and indicates that water replacement during the subsequent similar races is optional.
Alternatively, In An Off-Road Environment;
Joe may be riding an off-road discipline such as a local hare scramble. Before the race Joe weighs himself, then he Pre-hydrates with 16 ounces of fluid. Since this event is expected to take about 90 - 120 minutes to complete and based on previous experience Joe anticipates water loss of approximately 32 ounces so he knows to fill a drinking bladder with one one quart of water, which he will likely consume during the ride.
After the race Joe steps on the scale and realizes he lost 1/2 pound during the race which he replenishes with 8 ounces of the latest sports drink. However, reading the product label peaks his curiosity and he questions the value of using sports drinks.
Now Joe's girlfriend maintains that only a small knowledge of dietetics is needed to answer this important question as she points to the sodium content of 1 liter of Gatorade which depending on flavor ranges from 8.5mg to 430 mg.
If Joe's girlfriend is as knowledgeable as some on basic nutrition she would also know that many people eat over 4 grams of sodium daily but how do these quantities compare to sodium losses that can be expected in sweat?
This calculation requires two assumptions. (1) Sweat rate of 1-2 liter per hour (Wikipedia reports maximum sweat rates of twice this amount). (2) Sweat sodium concentration of approximately 1 gram per liter (Wikipedia reports normal sweat sodium levels of 690-1500 mg per liter). These values predict sweat sodium losses of up to 1 to 2 gram per hour. Replacing these estimates of sodium loss with Gatorade Perform 02 would require drinking approximately 2-4 liters per hour which exceeds the human ability to swallow and excrete.
Our subject has now encountered a fundamental problem with trying to correct or prevent salt depletion using a solution containing very little sodium compared to normal dietary intake. The result is likely to be vomiting and/or water intoxication well before salt deficits could be corrected.
Alternatively, water losses can be replaced with plain water during the event while relying on dietary intake for sodium repletion after the event. In practice this approach seems to work well. The issues are similar with potassium. Sweat losses of this important mineral can range from 100-200 mg per hour which is tiny compared to total body stores of 130-140 grams in an average sized person. For potassium depletion to occur requires prolonged strenuous activity on a daily basis coupled with a diet deficient in fruit, vegetables, meat, and other potassium rich foods. A "healthy" diet will provide 1500-3000 mg of potassium per day which renders a potassium content of sports drink pretty insignificant. (10 liters of Gatorade Perform 02 contains 1300 mg of potassium which is less than most people eat each day.)
In summary, serial measurements of body weight obtained before and after practice sessions and races can provide guidance for water replacement needed to prevent dehydration during off-road motorcycle events. For this purpose "sports drinks" are of limited value compared to plain water and a diet rich in potassium and sodium will supply a more than adequate quantity of these important electrolytes.