Sports Drink Science
Why I like sport drinks over gels and concentrates
Nearly all the bio-chemical reactions that occur in body cells depend on water and electrolyte (sodium, potassium, calcium, chloride, phosphorous, magnesium etc.) balance. These balances are not only vital to maintaining life but also affect physical and mental performance.
Water is the most abundant component of the body (60% + by weight). I believe it was Mike Colgan of the Colgan Institute who referred to the body as a "Hairy protein bag full of water". This bag of water has many holes which allow for leakage. These holes include skin pores which allow for perspiration (skin leakage) the kidney / bladder system which expels wastes carried by water and the respiratory system which must be moist or breathing would be very dry and painful.
Adequate hydration is very important in the maintenance of body temperature. When muscles contract they generate heat which must be dissipated from the core to the body surface and adequate water to maintain adequate blood volume is vital.
Sports drinks are widely used during exercise to avoid the onset of dehydration and delay the depletion of the body's carbohydrate stores. It is this popularity and the many mistakes I see many athletes practicing and marketers promoting that prompted me to write this explanation of sport drinks.
It is well established that sports performance can be impaired by many causes but the dominant factors leading to premature fatigue are:
- the depletion of the body's carbohydrate stores
- the onset of dehydration resulting from the loss of water and
the loss of electrolytes through perspiration.
The main purpose of sports drinks is to prevent dehydration, to supply energy, and to replace electrolytes. Sports drinks are said to be some of the best researched food items in the market place today. In the sport science community and their published research, there is a consensus about the optimal composition of such drinks: sports drinks should contain water, carbohydrates as an energy source, and the electrolytes listed above.
All of this must be in a defined osmolality consistent with optimal gastric emptying. In other words, the water, sugars and the electrolytes must be in a concentration that allows for the free flow of the drink from the gut to the blood.
Some of the most thorough research on this topic was reported by Dr. Ethan Nadel of Yale University in American Scientist in 1988 when he was lead physiologist for the Daedalus Project (man powered flight from the Greek Island of Crete to the island of Santorini across the South Aegean Sea). This work was followed by Dr. John Greenleaf at the NASA Ames Research Centre in California and reported in several Technical Bulletins from NASA in 1992.
Please be aware that recovery drinks serve a different purpose and are based on the science of glycogen storage and amino acid replacement. Also be aware that "energy drinks" are not sport drinks and were never designed as such. They are fundamentally liquid candy that is caffeinated, and sometimes fortified with a few vitamins.
It's All about Osmolality
The effectiveness of pre-mixed commercial sport drinks, powdered ingredients that must be mixed in water, the convenience packed Gel products and "home-made sport drinks" is dependent on the OSMOLALITY of the product. Here is where the most of the mistakes are made. Imbalances will inhibit gastric emptying, intestinal fluid absorption, blood flow, and induce side effects such as fever, and cramping.
Osmosis, to review your high school science, is described as the movement of a solvent (water) through a semi-permeable membrane (gut wall and blood vessel wall) from a less concentrated solution to a more concentrated one. If water existed on both sides of the membrane there would be no net flow and the two solutions would be considered isotonic.
Similarly, if the concentration of particles in the gastric fluids was the same as it is in the blood, there would be no net flow of water in either direction. However if the gastric fluids are primarily water (meaning very few particles and a very low osmolality) there would be a net flow of water into the blood in an attempt to equalize the osmolality.
This low osmolality of the gastric fluids would be defined as hypotonic (less concentrated than the blood). On the other hand, if the gastric fluid were more concentrated (meaning more particles and a high osmolality) than the blood, there would be net flow of water from the blood to the gut and this would be known as a hypertonic solution.
The osmolality of blood hovers around 280-290 mmoles/kg (that's how they measure osmolality) so the best sport drinks have osmolality measures near or below these values. Maugghan, reported in the Canadian Journal of Applied Physiology in 1999, after a thorough review of the science that the optimal osmolality for sports drink to be defined as in "the slightly hypotonic range between 200 and 250 mmoles/kg".
The carbohydrate content of the drink seems to exercise the greatest influence on osmolality (electrolyte content also contribute) and that is why you see most Physiologists recommending 6 - 8% carbohydrate solutions (see the most popular grocery store sport drinks). This usually results in a solution of 12 to 16 grams of carbohydrate (50 to 60 Calories).
However there are a few drinks that are 10 -12% carbohydrate and containing up to 25 grams of carbohydrate (100 Calories). This can make a big difference in the glycogen sparing action during an Ironman or Ultra-marathon race.
Even mild dehydration -1% of body weight - which would represent approximately .75 to 1 litre of water (1% of 75 Kg = 750 ml.) can create a reduction in muscle performance and start to show dehydration symptoms.
If the dehydration is 2 - 3 %, serious performance inhibition occurs. Dr. David Costill (of Ball State University) demonstrated that at these low levels of dehydration 1 - 3% even the time for 1500 meters was inhibited. The time for a competitive 10 K was reduced by 2.5 minutes which is serious in a 30 min 10 K.
So how can there be such a variation in carbohydrate content if osmolality is to be maintained? The answer is - not all sugars are created equal.
Not All Sugars Are Equal
Osmolality is influenced by the concentration of particles in solutions. That is the number of particles and not the size of the particles.
Glucose (also known as Dextrose) is a monosaccharide or single molecule sugar, and sucrose is a disaccharide or two molecule sugar and maltodextrin is a glucose polymer or polysaccharide or multiple molecule sugar. Therefore a single molecule of glucose or sucrose or maltodextrin will have the same osmotic effect, but these single units will have been of different sizes and therefore supply different amounts of calories from carbohydrate.
So the grocery store sport drinks are primarily sucrose and maybe glucose and therefore can deliver fewer grams of carbohydrate than the more sophisticated drinks made form maltodextrin. Maltodextrin is defined as a chain of glucose (usually 8-10 but could be more) molecules "loosely" linked and therefore easy to digest. It is known as complex carbohydrate but still has a very high glycemic index that allows for rapid consumption. Hence the better sport drinks can deliver more energy without upsetting the osmolaltiy.
Dr. Sam Mettler of Zurich a reviewed the osmolality and pH of 35 sports drinks and 53 other drinks commonly used by athletes and reported the results in a Swiss Journal of Physiology in 2006. Among commercial sport drinks the osmolality varied from 210 to 391 mmoles / kg and the carbohydrate grams varied from 4.1 to 15.1 grams. Only 3 were considered in the ideal range. Fruit drinks and sodas all tended to have very high (hypertonic) osmolality.
This review also included several "gel" products that create some unique problems. I always tell my clients that using a gel or a syrup concentrate while performing requires you to "play biochemist" on the run.
An average gel provides 20 to 30 grams of carbohydrate (and few if any are made with maltodextrin) and that means a very specific amount of water must accompany a gel in order to avoid upsetting the osmolality.
In addition they may contain milk products, gycerin, carnuba wax or gelatin, all of which will affect the osmolality and the glycemic index. If the average gel contains 25 grams of carbohydrate you would require 1.7 cups of water for a 6% solution and 1.2 cups for an 8% solution. When someone says they carry gels "just in case because they would be better than nothing", they don't understand how sport drinks work. They may not be better than water alone if you don't drink enough water at the exact same time as you ingest the gel.
So for optimal performance and optimal protection from dehydration I recommend you use a reputable scientifically based product (mix according to directions) and avoid playing biochemist on the run. Long endurance challenges require more than just water. The delivery of energy and electrolytes is also critical to avoid fatigue and health problems.
Published in the 2010 May/June Multisport Issue of IMPACT Magazine as "Smart Sipping: Sports Drink Science". Illustration by Fred Rix.
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