Posted: February 28, 2005

Science of Sport: Fatigue, Dehydration and Replacement Drinks

By Bill Gookin, GookinAid.com

The Science of Fluid Replacement

There are three kinds of fatigue: (1) anaerobic fatigue, not enough oxygen getting to the muscles and brain, the kind that hits you when you run up stairs at full speed and has you gasping for breath at high altitudes, (2) hypoglycemic fatigue, "low blood sugar" when you've exhausted the glycogen supplies in the liver and muscles, your arms and legs feel as if they are made of lead, you mind is numb and, if you try to increase your efforts, you go into "tunnel vision", and (3) dehydration fatigue, the loss of water and/or electrolytes resulting in fatigue in the usual sense of "just plain tired", muscle cramps and soreness and heat exhaustion among other symptoms and conditions. The first two kinds of fatigue are usually self-limiting; your body won't let you keep going any harder and you'll recover when you have to slow down.

However, when you are dehydrated, as you keep going you become even more dehydrated no matter how much you slow down and the only way to recover is to replace the fluids you are losing. The more serious symptoms of dehydration are classified as "heat exhaustion" and usually result from losing sweat in physical exertion. Sweating is the body's response to the build-up of heat from exertion or hot conditions. Without mechanisms to dissipate the heat, your body temperature can reach a fatal 45oC (114oF). Although some heat can be lost via radiation, convection and conduction from the skin, the most effective cooling is from the evaporation of sweat.

Athletes and industrial and farm workers lose 1 to 2 liters (about 1 to 2 quarts) of sweat per hour during normal work and as much as 4 liters per hour in high or low humidity and heat. Serious symptoms of heat exhaustion, including vertigo, fatigue and muscle cramps, develop as fluid losses exceed 2% of your body weight. As the loss increases to 4% of your body weight (3 quarts in a 150-lb. person), your condition becomes life-threatening unless fluids are quickly replaced.

Sweat is more than plain water; it also contains dissolved salts ("electrolytes") that gives sweat its salty taste, some vitamin C and traces of amino acids and waste products of cell metabolism. The first "activity" or "sports" drinks made to try to replace the sweat lost contained water and salt plus sugar to supply energy and to make the drink more palatable. Even then most athletes realized that potassium, along with calcium and magnesium, were more vital than sodium in muscle activity and recovery.

In a resting muscle cell there is a greater concentration of potassium ions than in the extracellular fluid while the reverse is true for sodium. As the muscle cell contracts, potassium ions diffuse out of the cell and sodium ions migrate into the cell. For the muscle to return to its relaxed condition, each cell needs to pump potassium into the cell and the excess sodium out of the cell, requiring energy and enough water and potassium in the cellular environment.

In a similar manner, the movement of calcium and magnesium ions is involved in nerve-muscle interactions and these and other ions in the activities of every cell of your body.

Meanwhile, water and these extracellular electrolytes are being lost in perspiration and are not available to be returned to the muscle cells. More and more cells are unable to relax and will cramp; the next day they will be sore and aching. As you become more dehydrated, entire muscle groups will fatigue and become cramped.

Plain water would replace the fluid loss but not the electrolytes so vital to cellular function and, if you continue the exertion long enough while drinking only water, you are losing both water and your own electrolytes in sweat and urine and can end up with serious electrolyte depletion ("hyponatremia" ... which actually means "low sodium" but when you're low in sodium, you're low in all of your electrolytes). Each year many hikers in the Grand Canyon, in Canyonlands and on Mount Rainier have flushed out enough of their electrolytes while staying hydrated with just water to require emergency evacuation and many die. Marathoners and ultramarathoners run the same risk, especially if they try to "pre-hydrate" with as much as a gallon of water the day before their race as did a woman who died in the 2001 Chicago Marathon and Rob deCastella, the world's top marathoner at the time, when he did poorly (for him) in the 1984 Olympic Marathon and then collapsed in the Rome World Championships.

Early efforts to replace the salts lost in perspiration consisted mainly of taking salt tablets with water and, even now, almost all "sports drinks" contain more sodium than potassium. Since ratios of these electrolytes lost by the kidneys and sweat glands are fairly constant, the loss of the sodium pulls other electrolytes along with it. This seriously lowers systemic potassium levels (hypokalemia) which results in accelerated fatigue and muscle cramps for workers and athletes who are pushing themselves in prolonged efforts and has resulted in many cases of permanent heartbeat irregularities.

Even though athletes have long been aware of the importance of potassium in muscle relaxation and avoiding cramps, most exercise physiologists have long insisted that not enough potassium was lost to be of concern. As early as 1967, exercise physiologists at the University of Stockholm found that if athletes were exercised to exhaustion on bicycle ergometers, there was a sharp drop in serum potassium levels that coincides with the onset of exhaustion: the stroke becomes erratic, muscles cramp and the subjects are unable to continue. Most of the other studies have not been as stressful and did not show the drop in potassium reserves which may be why so many sports drinks have so much more sodium than potassium.

Electrolyte Concentrations (mg/100 ml) source sodium potassium calcium magnesium sweat (conditioned athletes) 18-37 31-47 3-6 3-8 GatoradeTM 46.6 12.8 0 0 CytomaxTM 21.0 23.1 0 0 Gookinaid HydralyteTM 32.4 42.1 4.0 4.3 PoweradeTM 23.3 12.8 0 0 PedialyteTM 104.0 78.0 0 0 Cytomax is a trademark of CitoSport Inc., Gatorade is a trademark of Gatorade Co., Powerade is a trademark of Coca Cola Co., Pedialyte is a trademark of Abbott Laboratories.

Many activity drinks also contain magnesium and potassium for muscle activity and recovery and may have other electrolytes and supplements helpful in day to day conditioning and well-being which can usually be obtained in sufficient quantities in your daily diet. They also contain one or more sugars and other carbohydrates for sweetness and energy. Those called "energy drinks" have high concentrations of sugars and glucose polymers as short- and long-term energy sources. However, all of these carbohydrates except glucose must be digested in the small intestine, changed into glucose, before they can be absorbed. Some, especially the glucose "gels" are more concentrated than your body fluids ("hypertonic") and must be diluted before they can even leave the stomach into the intestines.

This dilution and digestion not only delays absorption into your circulation, but it pulls water from your muscles into the digestive system. Some of these drinks advertise that they are "isotonic" and "rapid stomach emptying"; "isotonic" means that the solution has the same concentration of particles, molecules and ions, taken together, as body fluids. When the stomach contents have been broken down and diluted to this point, they will be able to empty from your stomach into your small intestines for additional digestion and, ultimately, absorption. Glucose is the only sugar that can be absorbed directly from the stomach or intestines and the digestion of all other carbohydrates (sugars, glucose polymers and starches) into glucose requires water from the body. Even fructose, which is the same size as glucose but a different structure, must be changed into glucose to be absorbed.

This digestion and dilution pulls water from your muscles into your digestive system, further dehydrating your system and, if you are close to being dehydrated enough to have your muscles start cramping, this systemic dehydration can tip the balance. A classic example is that of Amy van Dyken, the youngest swimmer on the U. S. Olympic Team in 1992: in their first event, the 4 x 100-m relay, she came from behind on her anchor leg and won the event but was so fatigued by the effort that she had to be helped out of the pool and, after showing a replay of the event, the camera turned to Amy. She was lying on the deck on her back, her hand was like a claw and you could see that her trapezius and quadriceps muscles were cramped like boards. She said that she had taken a couple of swallows of the "official energy drink" of the Olympics and in less than three minutes it had pulled enough water from her muscles into her stomach to cause "every muscle in my body" to cramp up" ... and they hurt!

Sugars In Replacement And Activity Drinks source sugars and glucose polymers g/ 8 oz. GatoradeTM high fructose corn syrup, sucrose, fructose 14 CytomaxTM maltodextrin, polylactate, fructose, amylopectin 31 Gookinaid HydralyteTM glucose, <0.5% fructose in some flavors 10 PoweradeTM high fructose corn syrup, maltodextrin 19 PedialyteTM dextrose, sucralose, <2% fructose 6

Even if you aren't so dehydrated that you are on the verge of cramping, digesting and diluting the stomach contents, whether it is an activity drink, fruit juice, soft drinks or food, will delay absorption of the water you need by twenty to forty minutes. Because "energy drinks" are usually so concentrated, they may pull a lot of water into the intestines, giving you a heavy feeling in your abdomen during your event and even diarrhea ... as some world-class marathoners and triathletes have discovered. In activities of an hour (2-1/2 hours if you have "carbo-loaded") or more you will need to consume energy bars or drinks or bananas, etc., to maintain glycogen and blood sugar levels. Be sure to drink an equal volume of water or, preferably, an isotonic electrolyte drink to dilute the energy drink or 8 ounces for each energy bar or banana to help avoid muscle cramps or intestinal problems.

Although glucose is the only sugar that can be absorbed directly from your stomach into your circulation, it, with the electrolytes and other dissolved substances in the drink, must be at the right concentration (isotonic) and molecular form for this to happen. If the concentration and the ratios of electrolytes are just right, most of the water, electrolytes and other essential dissolved substances can be absorbed in just a few minutes even during an all-out effort.

Effects of Drink Concentration on Absorption from the Stomach

Some drinks and water are more dilute than body fluids (hypotonic) and it was long assumed that they would be absorbed into circulation most rapidly but it turns out that, as the cells of the stomach lining absorb the water, they swell up, blocking more absorption for some time. Drinking more water makes you even more uncomfortable, as you may recall after "drinking your fill" when you are really thirsty. Finally, hydrostatic pressure of all that water in your stomach forces the water out of the stomach and into the blood vessels in the stomach wall, diluting the blood in them. As this blood passes through the kidneys, they very efficiently remove the excess water ... and some of your electrolytes with it. And you are still thirsty!

The hypothalamus, located on the underside of your brain, detects changes in concentrations of body fluids and is the source of the sensation of thirst when you get dehydrated by about 3% of your weight. No matter how much you drink of a hypotonic or hypertonic beverage, you will still feel thirsty until enough fluid is absorbed into the circulatory system increasing blood volume and letting the hypothalamus detect the return to normal systemic fluid concentration.

Hypothalamus Triggers Thirst Reflex

Because athletes would get stomach cramps after drinking water, coaches had them suck on a lemon or tart candy or chew gum to stimulate salivation and psychologically override the thirst reflex so you wouldn't think that you were thirsty. Even electrolyte replacement salts in water and hypotonic replacement drinks like PedialyteTM will take a long time to be absorbed and can cause nausea and stomach cramps when exercising strenuously unless the solution is made isotonic with just the right concentration of glucose (40 g. per liter).

Because the brain is the most sensitive organ of your body, the first symptoms are mental affecting reactions, judgment and clarity of thought before you have become dehydrated by even 2% of your body weight. This means that you may not even think about being thirsty and doing something about it, especially if you are focusing on a task whether it be working at at a computer, in an intense athletic competition or part of a search team making a difficult rescue. It is important to be able to recognize the symptoms of dehydration in yourself and your teammates and coworkers before you or they get dangerously dehydrated.

The causes of dehydration are not often as obvious as exertion in hot, dry and/or humid conditions. Cold air is even drier than hot and the primary cause of hypothermia is dehydration in cold conditions, Air conditioning is very dehydrating, especially in airplanes. Alcohol, antihistamines and decongestants function by dehydrating you, which is why airline pilots cannot use any of these before flying ... they don't want to affect their reactions, judgment, quick decisions or clear thinking.

How does being even slightly dehydrated affect your performance at home or work and in sports or recreation?

What kind of drink, then, is going to be effective at preventing and relieving dehydration? Researchers have found that a dilute electrolyte and glucose solution is absorbed more quickly and completely than water alone and the correct ratio of potassium and sodium ions can speed up the absorption even more.

These studies were initially done between 1967 and 1974 and have been continually confirmed by research and the experiences of thousands ever since. Instead of hundreds of effective products based upon these findings, there is a multitude of sugar-laden, tart and flavorful energy drinks "validated" by the laboratories of the companies marketing the product to the general public.

There is one that has the proper balance of electrolytes, glucose and buffers to be absorbed almost as fast and effectively as an IV, without gastric discomfort. Before most of this research was done, it was formulated by biochemist and marathoner, Bill Gookin, after he got sick on an electrolyte drink during the 1968 Olympic Trials Marathon. He formulated his drink to be innocuous in his stomach and replace the electrolytes in the same proportions he was losing and it worked so well in the 1969 U. S. Marathon Championships that the other runners asked him what he was drinking and wanted to buy some for themselves. One of the runners who asked what the drink was had a bottle of GatoradeTM and Gookin replied "Mine's 'Gookin-aid'", intending to be funny, but the name, with "E.R.G." (for Electrolyte Replacement with Glucose) appended, stuck for more than 30 years.

In clinical tests, changes in blood volume and chemistry can be detected in the fingers within three minutes after drinking a pint of his "Gookinaid"; only an IV is faster, yielding similar changes in 11/2 minutes. However, as many search and rescue and emergency response teams have pointed out, it takes one to three hours to perfuse a liter of IV solution while two liters of Gookinaid can be absorbed from the stomach increasing blood volume and restoring normal blood pressure in just twenty minutes!

Because it is absorbed so quickly and doesn't upset the stomach, Gookinaid was used to help prevent and alleviate nausea and speed recovery from the flu, morning sickness, hangovers, altitude sickness and many other medical and nutritional conditions as well as for sports, industry, recreation, sports and emergency response teams. This has prompted the staff to change the name to one that is more marketable in pharmacies and health stores and to be used in medical facilities; the name "Hydralyte" meets this need, although you will see it as "Gookinaid Hydralyte" for a few years to maintain continuity and not confuse long-time users too much.

In the final analysis, the effectiveness of an electrolyte replacement drink must be evaluated by the individual using it. Understanding what the body actually needs and can use, what is really happening within your body and what each drink contains and is intended for should assist in this evaluation. Try and compare Gookinaid Hydralyte whenever you need to replace water and electrolytes to stay hydrated to keep feeling and functioning better!

Reposted with permission from GookinAid.com