|
|
|
|
Beverages / FluidsAlthough water does not contain Calories, adequate hydration is at least as important as food in maximizing your athletic performance. The single biggest mistake of many competitive athletes is their failure to replace the fluid losses of exercise. And this is especially true in cycling as rapid skin evaporation leaves the impression of minimal fluid losses (even though sweat production and loss through the lungs can easily exceed 2 quarts per hour). For your best performance, it is key that fluid replacement begin early continue throughout the ride. A South African study compared two groups of cyclists (one rehydrating, the other not) exercising at 90% of their maximum and demonstrated a measurable difference in physical performance as early as 15 minutes into the ride. Back to topFluid losses during exercise can result in a decrease in the circulating blood volume and the water content of muscle cells. As fluid losses mount, there is a measurable effect on physical performance. Unreplaced water losses equal to 2% of body weight will impact heat regulation, at 3% there is a decrease in muscle cell contraction times, and when fluid losses reach 4% of body weight there is a 5 to 10% drop in overall performance which can persist for up to 4 hours after rehydration takes place, emphasizing the need to anticipate and regularly replace fluid losses. Maintaining plasma volume is one of the hidden keys to optimal physical performance. For those who practice the philosophy of "if a little is good, a lot is better", there are risks associated with overcorrecting the fluid losses of exercise. There have been numerous reports of hyponatremia (low blood sodium concentration) leading to seizures in marathon runners who over replaced sweat losses (which contain both salt and water) with pure water alone. This is rarely if ever a problem for cycling events of less than several hours duration (except under extreme environmental conditions of heat or humidity) and generally becomes an issue only for longer events (more than 5 hours). If you want a measure as to how effectively you are rehydrating during your workout, weigh yourself before and after your long rides (without clothes to avoid inaccurate weights from sweat soaked clothing). This will help you to tailor YOUR OWN replacement program. A standard water bottle (20 ounces) weighs about 1 1/4 pounds or a pound of weight equals 16 ounces (1 pint) of fluid. Under normal conditions, you should be drinking a minimum of 4 to 5 ounces of fluid every 15 minutes and should aim for 1 to 2 standard water bottles per hour. When extreme conditions of heat and humidity are anticipated, the following strategy may be of additional benefit:
Back to top
Back to topDo electrolyte drinks (those containing minerals such as sodium and potassium) provide an advantage over pure water alone? Not for rides of 1 to 2 hours. When two groups were exercised for 2 hours at 67% VO2 max (with average fluid losses of 2300 ml) there was no advantage to electrolyte drinks over pure water alone. However, the fact that large fluid volumes were needed for rehydration reinforces the fact that palatability and digestive tract tolerance are important in the selection of replacement fluids, and for some riders electrolyte drinks are easier to consume on a regular basis. For longer rides, especially over 5 hours in duration (100 miles), or in conditions of extreme heat and humidity, using electrolyte sports drinks for sodium replacement is important to prevent dilutional hyponatremia.How about carbohydrates? When do I need to think about using a sports drink? It also appears that 2 hours is the point at which carbohydrate supplements will improve your overall ride performance by supplementing your internal glycogen stores. Cyclists can drink large volumes during competitive events, and in extreme events, such as the Tour de France for example, competitors were able to replace 50% of their daily energy expenditure by using 20% carbohydrate solutions and drinking 2 to 4 quarts an hour. You can calculate your exact Caloric replacement needs based on the duration and average speed of you ride. For those interested in a rough estimate, you need approximately 1/3 gram of carbohydrate per pound of body weight per hour to replace Calories expended. If selected wisely, liquids can be quickly emptied from the stomach with the sugar they contain quickly absorbed into the bloodstream. This carbohydrate is then delivered to the muscles where it is available as an alternative to muscle glycogen as an energy source. Drinks using glucose polymers (increased Calories while remaining iso-osmotic) deliver additional Calories per ounce of fluid. Back to topThe temperature of replacement fluids MAY impact the rate of stomach emptying - with colder liquids emptying more slowly and increasing the risks of nausea and a delay in getting the contents (electrolytes, water, glucose) into your system. On the other hand, cooler fluids may be more palatable and help to keep you cool (a positive for a ride in extreme conditions). The balance point for drink temperature will depend on your personal physiology and the ride conditions, so no absolute recommendations on the "best" temperature can be made. The same considerations apply to post ride drinks. If you are under time constraints to get back to work, a cool fluid can help you cool down more quickly and cut down your "sweat time". NO studies have confirmed a benefit of fruit drinks (which contain the sugar fructose) over glucose drinks. Although fructose requires less insulin to enter muscle cells, this does not appear to provide a performance advantage for cycling performance. Taste alone is the only advantage. For many years it was believed that a 2.5% concentration of glucose or glucose polymer molecules was the maximum tolerated without slowing stomach emptying and causing nausea. However a recent study in cyclists demonstrated normal gastric emptying with 6 to 8% solutions, and nausea occurred only when concentrations were pushed above 11%. The old standbys - apple juice and cola drinks - have a sugar concentration of around 10% and, although the glucose polymer sports drinks can provide more Calories per quart at the same overall concentration, controlled studies have failed to demonstrate performance advantage of these newer complex carbohydrate drinks over the simple sugar drinks alone. The major advantage of the polymers is the absence of a sweet taste and the nauseating properties of high concentration isocaloric glucose drinks, which can be a barrier to maintaining a high fluid intake. The stomach does have volume limits and for most riders this is around 800 ml (approximately 1 quart), particularly when pushing your aerobic limits (gastric emptying diminishes as exercise approaches 100% VO2 max). If larger volumes are forced, nausea and abdominal distention may result. A regular water bottle is 1/2 quart (16 ounces or 480ml) and the large ones are 3/4 quart so you should be able to drink at least 2 bottles per hour. Back to topIn summary, drinking plain water at a rate of 1 to 2 quarts per hour is adequate for rides of 1 1/2 to 2 hours. For longer rides, where the body's glycogen stores will be depleted, carbohydrate supplements in your water bottle will take on increased importance (glucose containing liquids can deliver Calories from the mouth to the muscles in as little as 10 minutes as compared to solid foods and energy bars which empty more slowly from the stomach). In most individuals, an 8 to 10 % concentration is the maximum tolerated. Glucose polymers, however, give you the ability to increase total Calories per quart without risking the side effect of an unpalatable, sweet taste. Aside from palatability and there is no proven advantage over simple sugar (glucose) drinks. Although there are many commercial drinks available, the old standbys such as apple juice and cola drinks are probably the least expensive per Calorie provided. In the pre and post ride period, the high Calorie, easily absorbed, glucose polymer sports drinks do offer an advantage for rapidly building (or restocking) glycogen stores. For those of you interested in saving a few £, take a look at this site for some ideas on homemade energy drinks. For longer rides, don't forget about the risks of overdoing rehydration with pure carbohydrate drinks alone. If you plan to ride more than two or three hours, it's worth considering a commercial electrolyte containing drink, and if you are going to be riding 5 hours or more, it is essential to pace your fluid replacement rate (and keep an eye on your weight during training rides to be certain you are not overcompensating). Back to topCommercial sports drinks are the easiest, but are pricey. Often times complex carbohydrates can be purchased in a health food store and mixed at home with a flavor of your choice or used to supplement a current favorite drink. Maltodextrin is a corn starch molecule which has been broken down into glucose polymers (chains of glucose molecules). When added to water or other drinks, it increases the energy content without the disadvantage of an extremely sugary taste and creating a highly concentrated solution which will delay gastric emptying. Thus it is useful during exercise or as a post ride supplement, but does not make sense as an alternative to breads, cereals, grains, etc. as a regular daily energy source. Directions are usually available from the container, but can vary from 1/2 cup in 8 pounces to 3/4 cup in 32 ounces. You may need to experiment to find the best concentration for your personal physiology. But if you look at the calculations, a 16 ounce water bottle (480 cc) of a 7% sugar solution at 4 Cal per gram of carbohydrate will contain about 136 Calories. If you add 1/2 cup of Carboplex (a commercial maltodextrin) you will add another 220 Calories almost tripling the energy density (concentration) of your drink with minimal chances of nausea or other side effects. There have been some encouraging studies on the use of glycerol to minimize the negative impact of dehydration on performance. For those interested in a commercial product, try the internutria website. Except under extreme conditions, electrolytes (particularly sodium chloride or salt) do not need to be replaced along with fluids. Back to top |
|
This site was last updated on Sunday, 12 October 2008 16:22
If you find any problems with this site please contact the webmaster Copyright © 2008 Sid Valley Cycling Club. All rights reserved |
