Marathon and Beyond

Sport Science Research

by Mel Williams, Ph.D.

Can It Improve Your Marathon Time?

The human body is beautifully designed to run.

Over the eons, the human body developed energy systems to run very fast for short distances, a necessity when sprinting to safety from the impending attack of some saber-toothed creature. The human body also developed energy systems to run long, a necessity in tracking and catching prehistoric mammals as a food source. As civilization progressed with diminished necessity to run fast for safety or to run long for sustenance, various types of organized play eventually evolved into high-caliber international sport to serve as an outlet to demonstrate one’s ability to run fast or run long.

Running is the purest form of athletic competition, and just as the 100-meter dash became the criterion for the world’s fastest sprinter, so too has the marathon evolved as the principal marker for the world’s greatest endurance runner.

Although the first marathon was organized primarily for international-class athletes competing in the 1896 Olympic Games in Athens, other marathons soon blossomed for the masses, such as the Boston Marathon in 1897. During the past century of marathon competition, about an hour has been shaved from the original world men’s record, and similar improvements have occurred during the shorter history of women’s marathon competition. During the early years of marathon competition, runners used various “scientific” techniques in attempts to enhance performance, but these “scientific” techniques were based primarily on theory and anecdotal evidence, trial and error, or inappropriate research. As an example of the latter, scientists in the 1890s were involved in the field of work physiology and were primarily interested in means whereby industrial work productivity could be enhanced. In one such study, alcohol was found to decrease fatigue in the small group of muscles that move the thumb. Such information was subsequently, albeit improperly, applied to sport, and marathon runners reportedly consumed champagne, cognac, or rum before and during competition; wine was served at the fluid replacement stations in the 1924 Paris Olympic marathon.

Distance running has always been popular, but it became increasingly so during the years following World War II as Olympic and other international sport competitions were commercialized. In particular, the popularity of running in the United States surged in the late 1960s, partly in response to the publication of Aerobics, by Dr. Ken Cooper. Several years later, Frank Shorter won the marathon at the 1972 Munich Olympics, an event that seemed to serve as the catalyst for the popularity of the marathon as a major sporting event in the mid-1970s and beyond. Thousands of runners took to the marathon, and most wanted to improve their time for one reason or another, particularly to qualify for the Boston Marathon.

The advent and growth in popularity of the marathon coincided with the development of the science of sport and exercise, which will be referred to here as “sport science” and its researchers as “sport scientists.” The baby-boom generation was coming of age for both college and marriage. Colleges needed to prepare for this influx of new students, increasing the demand for professors with doctorates. In particular, professors were needed to prepare public school teachers for the subsequent children of the baby-boom generation. At that time, physical education was an integral part of public school education, so major universities with doctoral programs in physical education needed to increase their Ph.D. productivity to meet the expected demand for physical education teachers and coaches.

Although there are various tracks in Ph.D. programs in physical education, several are based on the underlying science of human movement, particularly physiology, biomechanics, and psychology. To earn a Ph.D., one must produce a doctoral dissertation, which involves a concerted research effort over the course of a year or so. Many of the students were former athletes and entered these doctoral programs with the intent of simply teaching or coaching at the college level. However, some became very interested in sport science research, conducting sophisticated studies.

With the concomitant surge in marathon running and the unique energy demands of the sport, many of these sport scientists focused their research efforts on various scientific aspects of marathon running. Several of the early key researchers who have contributed significantly to our understanding of running, particularly marathon running, include Dr. Dave Costill at Ball State University, who focused on the physiological aspects; Dr. Peter Cavanagh at Pennsylvania State Univer-sity, who focused on the biomechanical aspects; and Dr. William Morgan at the University of Wisconsin, who focused on the psychological aspects. During the 1980s and 1990s, sport science became increasingly popular as a career goal, and many departments of physical education incorporated new terms to describe their degree offerings, such as kinesiology, human movement, exercise science, or sports science. More universities offered graduate degrees combined with other fields of study, such as nutrition, and research efforts increased accordingly.

Sport science has evolved to the point that many nations devote considerable research to prepare athletes for major international competition. For example, many nations have Olympic training centers where athletes may not only experience top-notch coaching but also receive the latest information and treatment from various sport scientists, including physiologists, biochemists, biomechanists, psychologists, nutritionists, physicians, chiropractors, physical therapists, athletic trainers, and masseurs.

Such scientists have conducted research with marathon runners at all levels of ability, from the elite to the beginner level. They have attempted to identify the variables that contribute to successful marathon running and also have explored various means to enhance these variables to maximize performance. Over the years they have accumulated a significant knowledge base, from which advice that may help you improve your marathon time can be extracted.

Determinants of Marathon Run Performance

Your ability to produce energy is the key to improving your marathon run performance. Your body can produce energy for running in a variety of ways, and over the years, sport scientists have deciphered three key pathways of energy release in the muscles, the machines that move your body.

In brief, the principal energy substrate for human muscle is adenosine triphosphate (ATP), a high-energy compound whose breakdown converts its chemical energy into mechanical energy, or muscle contraction. ATP is essential for the muscle to contract, but muscle stores of ATP are very limited, enough for a second or two at the most. For the muscle to continue to contract, ATP must be replenished. The speed at which you can run and continue to run depends on your ability to replenish ATP in your active muscles.

In general, sport scientists have classified three distinct human muscle energy pathways ranked in order of their ability to replenish ATP.

1. The adenosine triphosphate-phosphocreatine (ATP-PCr) energy pathway is designed to replace ATP very rapidly. Phosphocreatine (PCr) releases energy to synthesize ATP very rapidly, but like ATP, PCr content in the muscle is also limited. The ATP-PCr energy pathway is predominant in very short duration, high-power events such as sprinting a 100-meter dash.

2. The lactic acid energy pathway, more technically known as anaerobic glycolysis, involves the rapid breakdown of muscle glycogen (glycolysis) under conditions when oxygen supply is limited (anaerobic). It replenishes ATP less rapidly but in greater quantities than the ATP-PCr energy pathway and is the predominant energy pathway in more prolonged sprints, such as 400 meters. Accumulation of lactate (lactic acid) in the blood induces muscle fatigue, so the endurance of this energy pathway is somewhat limited.

3. The oxygen energy pathway involves the aerobic metabolism of either carbohydrate (aerobic glycolysis) or fat (aerobic lipolysis), producing substantial quantities of ATP but at a slower rate than the other two pathways. The oxygen energy pathway predominates in more prolonged aerobic endurance events. Although both carbohydrate and fat may be used as fuel sources for the oxygen energy pathway, carbohydrate is the more efficient fuel. Carbohydrate produces more ATP per unit of oxygen than does fat.

Running involves all three energy pathways at the same time, but marathon running depends primarily on the oxygen energy pathway, whose optimal functioning during a marathon is dependent on multiple body systems.

For example, the digestive system is essential to provide fuel for muscular energy before and during the marathon. The endocrine system secretes hormones such as insulin and epinephrine that influence fuel supply to the muscle. The integumentary system, which includes the skin, is involved in temperature regulation, particularly important under warm environmental conditions.

However, the two key system combinations involved in the oxygen energy pathway are the neuromuscular and cardiovascular-respiratory systems. The neuromuscular system (nervous and muscle systems), which consists of the brain, peripheral nerves, and muscles, generates the muscular energy to run with the appropriate speed and efficiency. The cardiovascular-respiratory system (cardiovascular and respiratory systems), which consists of the heart, blood vessels, and lungs, provides oxygen, the keystone to the oxygen energy pathway.

The interaction of the neuromuscular and cardiovascular-respiratory energy systems determines several of the key components of running potential. Maximal oxygen uptake (V.O2max) represents the ability of the cardiovascular system to deliver and the neuromuscular system to utilize oxygen during running. The lactate threshold, often referred to as the anaerobic threshold, represents the level of running intensity at which energy production becomes increasingly anaerobic, leading to lactate accumulation in the blood and predisposition to fatigue. Running economy refers to the ability of the neuromuscular and cardiovascular-respiratory systems to maximize oxygen efficiency, obtaining the highest running speed for the amount of oxygen used. Speed represents the ability of the neuromuscular system to maximize energy production for running. In general, improvement in any of these components will enhance your marathon running performance. However, marathons are normally run at a pace just below the lactate threshold, so improving your running economy, which is an increase in speed at a given oxygen uptake, may be the key element. A scientifically based training program may be your best means to improve your marathon performance.

Scientific Training

How fast can you run a marathon?

Your ultimate limit is determined by your genetics, the level to which you inherited the physiological, psychological, and biomechanical characteristics that underlie successful aerobic endurance performance. Using molecular biology research techniques, sport scientists have identified various inherited physiological characteristics, such as heart volume, muscle fiber type, mitochondrial density, and enzymic activity, that are inherent to the oxygen energy pathway.

Psychological characteristics such as brain neurotransmitters and biomechanical characteristics such as overall anatomy and body fat that are important to marathon running capacity are also inherited. We all inherit these characteristics but to different degrees. Jon Entine, in a recent issue of Marathon & Beyond (September/October 2002), notes that the world’s best marathoners come from East and North Africa, and he makes a strong case for genetic characteristics, along with appropriate training, as why these athletes dominate international competition.

You can’t do anything about your inherited genetic characteristics that influence your marathon running performance (although with genetic therapy you may be able to do so in the future), but through proper scientific training you will be able to optimize your genetic potential. As one geneticist has noted, nature deals the cards, but you play them. Train scientifically to be all that you can be.

More than 50 years ago, most distance-running coaches, and athletes like Emil Zatopek, developed successful training programs primarily through trial and error. Later, as sport science developed, several former international-class athletes who studied sports science applied their knowledge to coaching. One of the best known is Dr. Jack Daniels, whom Runner’s World has recognized as the world’s best running coach. In his book, Daniels’ Running Formula, Dr. Daniels has developed a scientific training program for distance runners, including marathoners.

Science underlies Dr. Daniels’s training program, which is designed to improve two critical physiological characteristics underlying aerobic endurance.

First, training is designed to improve the cardiovascular system to transport blood and oxygen. Increases in heart pumping capacity, total blood volume, and capillarization of muscle tissues are principal changes induced through proper training.

Second, training is designed to improve the ability of the muscles to effectively use oxygen by converting carbohydrate and fat into ATP. Increases in the size and number of mitochondria, oxidative enzymes, and myoglobin in oxidative muscle fibers represent desired changes. Collectively, these beneficial adaptations to training will (1) improve aerobic capacity (V.O2max); (2) improve the lactate threshold, so it is attained at a faster running speed; (3) improve running economy by lowering the energy demand of running; and (4) improve speed, or the ability of the neuromuscular system to maximize energy production for running. Dr. Daniels’s scientifically based training program is based on five different running intensities. Easy long runs are designed to improve muscle cell adaptation necessary to optimize utilization of fat and carbohydrate stores for energy. Marathon-pace runs represent the pace at which you wish to run the marathon, promote muscle cell adaptation to optimal energy usage, and also provide specificity of neuromuscular efforts for your desired pace. Threshold-pace runs are designed to increase the lactate threshold. By increasing the lactate threshold, you increase the running pace at which lactate begins to accumulate and contribute to fatigue. Interval-pace runs are designed to increase V.O2max. Repetition-pace runs are designed to increase running economy and speed.

Runners often question why they should do speed intervals or repetitions if they are going to run the marathon. Such training, by increasing your running economy and speed, will help you run faster at distances shorter than the marathon and subsequently run faster marathons. For example, an excellent prediction formula for your next marathon is to multiply your recent 10K time by 4.67. Thus, if your recent 10K race time is 40:00, the formula predicts a marathon time of 3:06:48, give or take a minute or two. The formula assumes you have been doing your long runs as well. Improving your 10K time by one minute will improve your marathon time by 4:40. A scientifically based training program may be one of the best means to improve your marathon running performance if you are not currently using such a program. The details of such training programs are beyond the scope of this article, but several excellent books, such as Daniels’ Running Formula, are commercially available to help you individualize your marathon training program based on your current running ability.

Dr. Daniels notes that there are also other goals of training, including the psychological goal of enhanced self-confidence and the biomechanical goal of optimal body weight and composition, but these benefits normally will occur with effective training of the physiological systems. However, there are various psychological strategies, such as mental imagery, mental dissociation, and thought control, that may benefit the marathon runner. Such strategies, whose discussion is beyond the scope of this article, need to be practiced in training if they are to be effective in competition. Several biomechanical strategies, including an optimal body weight, are discussed next. Additionally, although proper training is the most effective means to improve your marathon time, sport scientists have investigated the effectiveness of various performance-enhancing substances theorized to enhance aerobic endurance.

Sport Biomechanics

How can biomechanics help the marathoner? Most of us who have run a marathon have used a simple biomechanical strategy. When running into the wind, we have drafted off another runner or, better yet, a group of runners. In doing so, we have reduced the adverse effects of air resistance, or drag. When we draft, the oxygen cost of running is reduced dramatically, improving running efficiency and saving energy for the latter part of the race.

The goal of the sport biomechanist is to improve movement efficiency, mainly by maximizing propulsive forces and minimizing resistive forces, and thus provide the athlete with a mechanical edge. Using high-speed cinematography, the biomechanist can analyze a runner’s form and detect problems in running form that may be inefficient, such as overstriding, and that may waste energy. Although most elite and experienced marathoners have developed efficient running styles, even a small improvement in running efficiency may make a significant difference over the duration of a marathon.

There are several biomechanical strategies you can use to improve your marathon time. One involves selecting the right sportswear, and the other is optimizing your body weight and composition.

Running Sportswear

A uniform and shoes are the only sportswear equipment the marathon runner normally uses. Well-fitting uniforms should be selected to minimize wind resistance without retarding sweat evaporation. Most uniforms (shorts, singlets, socks) in use today are very lightweight and of such composition as not to interfere with proper body temperature regulation. The shoe is the most significant piece of sportswear worn by the marathoner, particularly its weight. The oxygen cost of accelerating each foot an average 90 times per minute over the course of a marathon may influence energy efficiency. Ed Frederick, a biomechanist at the Nike Sports Research Laboratory in the early 1980s, calculated that use of a racing flat weighing approximately 4 ounces less per shoe than a regular training shoe can save approximately 2.5 to 3.0 minutes over the course of a marathon.

Body Weight

Sport scientists have calculated the energy cost of running, a weight-bearing sport activity. If we disregard the normal resting oxygen consumption, according to a formula developed by the American College of Sports Medicine, the energy cost of horizontal running is 0.2 milliliter of oxygen per kilogram of body weight per meter per minute (ml O2/kg/m/min). The more you weigh, the more oxygen, or energy, it takes to run at a given speed.

Optimizing your body weight may be a very effective means to improve your marathon performance. V.O2max may be expressed in several ways, including total V.O2max in liters per minute (L O2 /min), or based on body mass (ml O2/kg/min). If your total V.O2max is 4.0 liters/min (4,000 ml/min) and if you weigh 80 kg, then your V.O2max is 50 ml O2/kg/min (4,000 ml O2 /80 kg). If you lose 5 kg (11 pounds; 1 kg = 2.2 lbs) to 75 kg and maintain your V.O2max at 4,000 ml/min, then your V.O2max increases to 53.3 ml O2/kg/min, a 6.6 percent increase.

Let’s apply this body-weight change to marathon running. To run a marathon in four hours, you would need to maintain a pace approximating 176 meters per minute (42,200 m/240 min). Again, disregarding the resting O2 in the ACSM formula, the oxygen cost to run a four-hour marathon approximates 35.2 ml O2/kg/min (0.2 ml O2 3 176 m/min). For an 80-kg runner, this totals about 2,816 ml O2/min (which is running at about 70 percent of V.O2max). If this runner would lose 5 kg of body fat (about a 6 percent loss), the oxygen cost would drop to 2,640 ml O2/min, a savings of about 176 ml O2/min (over 6 percent). Since the cost of running each meter for our 75-kg runner is 15 ml O2 (0.2 ml O2 3 75 kg), the speed of running would increase approximately 11.7 m/min (176 ml O2/15 ml O2) to a speed of 187.7 m/min. This would improve the marathon running time to 3:44:50, or an improvement of about 15 minutes (about 6 percent faster).

In general, for every 1 percent loss of body mass, primarily as body fat, there will be an approximate 1 percent increase in running speed. Most elite marathon-ers are most likely at an optimal body weight and composition. However, other marathoners who are carrying excess body weight, primarily body fat but also excess upper-body muscle, may enhance performance by losing the excess weight. If you decide to undertake a weight-loss program, a general guide is to lose no more than a pound a week. If you have difficulty losing weight, see a sports health professional, such as a sports dietitian with an R.D. (registered dietitian) degree.

Excessive weight loss, however, may impair the health and performance of marathon runners. There is a fine line between optimal body weight for marathoning and excessive loss of body mass. Excessive weight loss may adversely affect performance if muscle tissue function and energy stores are impaired. Health may also be impaired. For example, the female athlete triad involves disordered eating patterns and weight loss affecting hormonal disturbances that may predispose the athlete to premature osteoporosis.

Performance-Enhancing Substances: Drugs

Pharmacological agents (drugs) theorized to enhance performance have been used by various athletes, including marathoners, for many years. However, because of the potential health risks, the use of performance-enhancing drugs has been prohibited by the International Olympic Committee (IOC) and other sports governing bodies since 1968. Nevertheless, there are some exceptions that may benefit marathon running performance.

Caffeine

Caffeine is a drug, a stimulant whose use is restricted by the IOC but not completely prohibited because it is found naturally in a variety of beverages, particularly coffee, that are consumed by athletes. Numerous studies using various doses of caffeine have evaluated its effect on a wide variety of running events but particularly on distance running.

Caffeine may enhance marathon performance in several ways. First, caffeine may stimulate the central nervous system and help prevent mental fatigue. Second, caffeine stimulates the release of epinephrine (adrenalin) from the adrenal gland, which may enhance cardiovascular functions and fuel utilization. In particular, caffeine may help spare the use of muscle glycogen by increasing the use of free fatty acids for energy during the early stages of the marathon, leaving more of the muscle glycogen for the latter part of the marathon to help you maintain an optimal pace. Terry Graham and Lawrence Spriet, from Guelph University in Canada, are two of the principal sport scientists who have evaluated the performance-enhancing effect of caffeine. In several recent reviews of the available scientific laboratory research, they concluded that caffeine could enhance aerobic endurance performance in elite as well as amateur runners, even when taken in legal doses approximating 5 milligrams of caffeine per kilogram of body weight. They noted that although the underlying mechanism has not been clearly identified, it could involve muscle glycogen sparing. However, they also noted that the beneficial effects of caffeine have been documented mainly under laboratory conditions and not during competition. Thus, although one would theorize that the beneficial laboratory findings would be applicable to field competition, it is possible that the natural excitement of competition may provide a stimulation effect to override that associated with caffeine.

Nevertheless, in a recent issue of Sports Medicine, an international review journal of sport science research, several reviewers calculated that caffeine could enhance performance in a 40K cycle time trial by 55 to 84 seconds. If extrapolated to marathon run performance, the enhancement would approximate 135 to 210 seconds, a savings of several minutes.

If you want to experiment with caffeine, take about 5 milligrams of caffeine per kilogram of body weight, or about 300 to 400 milligrams of caffeine. Most over-the-counter stimulants such as Vivarin contain about 200 milligrams per tablet, so two tablets should suffice. Taking more than this amount has not provided additional benefits. Although caffeine is a relatively safe drug, some individuals may experience adverse reactions such as nervousness, trembling, anxiety, and even heart palpitations, especially when taking larger doses.

Erythropoietin

Erythropoietin (EPO) is a hormone produced naturally by the kidneys in response to decreased blood oxygen content. For example, if you go to high altitude, such as the Rocky Mountains in Colorado, the lowered barometric pressure and decreased oxygen content will stimulate your kidneys to produce EPO. The EPO will then stimulate the bone marrow to produce more red blood cells (RBCs) and hemoglobin, increasing the capacity of your blood to transport oxygen.

One of the most effective techniques to enhance marathon run performance is blood doping. The autologous technique has been most studied, involving blood withdrawals and appropriate storage. Once the athlete has regenerated blood levels back to normal about six to eight weeks after withdrawal, the blood is infused with the intent of increasing the RBC and hemoglobin concentration and the associated oxygen-carrying capacity.

Several studies involving both laboratory and field studies with blood doping have revealed improved running speed in aerobic endurance events approximating eight to 10 seconds per mile. Although blood doping bypasses the use of natural EPO to increase oxygen transport, the end result is the same. Blood doping was used by international-class athletes during the 1970s and 1980s, but it was banned by the IOC in 1985. In the late 1980s, recombinant erythropoietin (rEPO) was developed by the drug industry, and its use enhanced the quality of life for individuals whose kidneys were diseased and unable to produce EPO naturally. Sport scientists eventually researched the performance-enhancing effects of rEPO and found that it mimicked the beneficial effects of blood doping. However, as it does for blood doping, the IOC prohibits the use of rEPO for performance enhancement, and techniques have been developed to detect its use. Moreover, excessive injections of rEPO may be very dangerous, as they may make the blood very viscous and impair circulation, allegedly contributing to the premature deaths of several elite young cyclists during its early years of availability.

Producing EPO naturally may be just as effective and safer. The technique of “living high, training low” involves living at high altitude but training at low altitude. Living high will stimulate natural production of EPO. Training low will help to avoid the problems of exercising at high altitude, primarily the decreased exercise intensity because of the decreased oxygen availability. There are several ways you can live high and train low.

One technique involves living at high altitude and traveling down to a lower altitude to train, which is feasible if this is geographically possible where you reside. Another technique involves living in a special high-altitude house designed to mimic the barometric pressure at altitude and to train outside at sea level. Many national Olympic centers have constructed such houses. [See “Live High, Train Low,” Marathon & Beyond, January/February 2003, pp. 77-88.] Research using these techniques in both elite and average runners has revealed increases in EPO, RBC, and hemoglobin concentration; maximal oxygen uptake; and aerobic endurance running performance. Although these two techniques may be feasible for some, they may be geographically or financially infeasible for most of us. Another option, less expensive than building an altitude house, is use of a high-altitude tent canopy for sleeping at night; such tents are available commercially and have been advertised in running journals. Although this technique would seem to stimulate endogenous EPO production during seven to eight hours of sleep each night and provide associated benefits for the endurance athlete, no research has been uncovered evaluating its use. It is important to note that some athletic governing bodies, such as the International Cycling Union, mandate that the athlete’s hematocrit (concentration of RBCs) cannot exceed an established level, such as a hematocrit of 50 for males and 48 for females.

Performance-Enhancing Substances: Nutrients

Other than training, what you eat and drink could have the most significant effect on your performance. A deficiency of any essential nutrient associated with human energy systems may impair performance. For example, iron is an essential nutrient for the formation of hemoglobin. The American College of Sports Medicine, the American Dietetic Association, and the Dietitians of Canada, in their joint position statement regarding nutrition for athletes, note that female distance runners should be screened periodically to assess iron status.

Sport nutritionists indicate that a diet stressing variety, balance, and moderation will provide the nutrients needed by most athletes. A diet rich in fruits, vegetables, whole grains, lean meats, and low-fat dairy products will provide adequate calories, carbohydrate, essential fats, protein, vitamins, minerals, and water. In general, the diet that is optimal for health is also optimal for sports performance. In particular, marathon runners in training should focus on a healthy diet rich in carbohydrates, polyunsaturated fats, protein, iron, and calcium.

Various nutritional strategies and dietary supplements marketed to endurance athletes have been evaluated, and although the vast majority of such strategies and supplements have not been shown to enhance endurance performance when added to a healthful, balanced diet, several may possess ergogenic properties for endurance athletes. Adequate carbohydrate and fluid intake, both before and during the marathon, are the two dietary strategies most proven to enhance performance.

Carbohydrate

Carbohydrate is the primary dietary energy source for high-intensity aerobic endurance exercise (> 65 to 70 percent V.O2max), but endogenous supplies of muscle and liver glycogen are limited and may become suboptimal within 90 minutes of intense aerobic endurance exercise. John Hawley, a renowned sport nutrition scientist, has noted that carbohydrate loading (consuming 400 to 600 grams of carbohydrate several days before a marathon) may elevate endogenous muscle and liver glycogen stores, postponing fatigue and improving performance in which a set distance is covered as quickly as possible (such as a marathon) by 2 to 3 percent. For a four-hour marathon, carbohydrate loading could improve performance by about five to seven minutes if it helps prevent premature depletion of muscle glycogen.

Sports Drinks and Water

Various factors may contribute to fatigue during prolonged aerobic exercise, but dehydration and depleted carbohydrate stores are most common, particularly when exercising in warm or hot environmental conditions. Sports drinks are designed to delay the onset of fatigue by providing both fluids and carbohydrate. Sports drinks were developed in the early 1960s and were modeled after medicinal oral rehydration solutions. Although water is the main ingredient, carbohydrate content approximates 5 to 10 percent; the type of carbohydrate also varies, including glucose, sucrose, fructose, and glucose polymers, depending on the brand. Caloric content ranges from about six to 12 kilocalories per ounce. Most sports drinks include electrolytes, mainly sodium, chloride, and potassium. Some sports drinks contain other substances as well, such as miscellaneous vitamins and minerals, protein, herbals, and caffeine. However, the key ingredients for the marathoner are water and carbohydrate.

Water ingestion is essential to help optimize body water balance and body temperature regulation during exercise under warm environmental conditions. Rehydration, about 6 to 8 ounces every 10 to 15 minutes, during exercise in the heat, has been shown to decrease physiological stress as evidenced by a decreased heart rate response, lesser rise in the core temperature, and increased endurance performance. Hyperhydration, such as consuming a pint of fluid before exercise, may also be helpful, but it has not been shown to be as effective as rehydration. When compared to consuming only water, numerous studies have shown that consuming carbohydrate, approximately 60 grams per hour, significantly increased performance in prolonged aerobic endurance exercise tasks.

In a recent Sports Medicine review, several sport scientists concluded that sports drinks with carbohydrate concentrations less than 10 percent are among the few nutritional food products that may enhance sport performance in exercise tasks where performance may be impaired by dehydration and depleted endogenous carbohydrate reserves. Other sport scientists concluded that sports drinks may decrease the time to complete a 40K cycle time trial by 32 to 42 seconds, which would approximate 80 to 105 seconds if extrapolated to running a marathon.

Glycerol

Glycerol has been marketed in some sports drinks. Glycerol-induced hyperhydration (approximately 1 gram of glycerol per kilogram of body weight with 20 to 25 milliliters of water per gram of glycerol), when compared to water hyperhydration alone, has been shown to increase total body water, including blood volume, to a greater extent. The extra water retention associated with glycerol ingestion would increase body weight. Several studies have shown that glycerol-induced hyper-hydration improves cardiovascular responses, temperature regulation, and cycling exercise performance under warm/hot environmental conditions.

However, other research has shown that both glycerol and carbohydrate supplementation improved cycling endurance compared to a placebo solution, suggesting that carbohydrate supplementation was as effective as glycerol supplementation as a means to enhance performance. Recent reviews have reached different conclusions regarding the ergogenic efficacy of glycerol supplementation, with one review suggesting glycerol improves tolerance to exercise, another concluding that glycerol is ineffective, and a third suggesting that additional research is needed to resolve the current equivocal findings. The latter review appears most reasonable, particularly so in sports in which the extra body mass needs to be moved, such as distance running.

Creatine

Creatine is a nitrogen-containing substance, found naturally in small amounts in animal foods. Creatine monohydrate has been manufactured commercially since the 1980s and has been studied extensively as a means to enhance exercise performance. Creatine loading (20 to 25 grams of creatine monohydrate for four to seven days) has been reported to increase muscle supplies of phosphocreatine (PCr), as noted previously a high-energy compound essential for rapid restoration of ATP. Numerous studies and several major reviews have reported a positive performance-enhancing effect of creatine supplementation on short-duration, repetitive, very high-intensity exercise tasks such as sprinting.

Creatine has been marketed in Runner’s World magazine for endurance athletes, but there are limited scientific data evaluating its effect on endurance performance. In general, creatine supplementation research does not support a performance-enhancing effect on aerobic endurance performance, and some research has shown an impairment in endurance running, possibly because creatine loading may increase muscle water retention and body mass by 2 to 5 pounds, imposing a biomechanical disadvantage where the body mass must be moved.

However, one study has shown that creatine loading could improve interval training performance in 300- and 1,000-meter repeats. If creatine supplementation improves interval training, endurance performance subsequently may be improved, but studies are lacking to support this hypothesis.

Summary

As runners, we all have the ability to complete a marathon, but our ability to set a personal record (PR) is determined primarily by our inheritance of genetic traits that set the limits of our aerobic endurance exercise capacity. To attain this genetically based PR, we must train scientifically to maximize our genetic potential. To obtain our PR we can also fudge a little bit, maybe by choosing a downhill course such as the Las Vegas Marathon or a point-to-point course with a high possibility of a tailwind, such as the Anthem Bay Bridge Marathon in Virginia Beach, Virginia.

But we can also apply other scientific strategies to improve our chances to run a PR. Losing excess body fat, wearing lightweight racing flats, consuming adequate carbohydrate and water, and taking caffeine have all been shown to enhance performance in prolonged aerobic endurance exercise and thus may shave minutes off your marathon time if used judiciously.

Although there is a science, there is also an art to running a marathon. The art is applying the science to the individual runner. Although many of the scientific strategies discussed here have been shown to enhance endurance performance when tested on groups of subjects, not all individuals may benefit. You may become overtrained and stale if you try to train too intensely. You may lose too much body weight, and your running performance may actually suffer. You may suffer an injury because lightweight racing flats do not provide sufficient support or cushioning. You may have an adverse reaction to caffeine or dietary supplements that impairs performance.

So, become a sport scientist yourself. If you decide to experiment with any performance-enhancing strategies or substances, keep detailed records of your daily training and your competitive races to see how your performance is affected. Your performance varies naturally, dependent on a number of circumstances, such as the daily weather. However, effective strategies such as losing excess body fat should show a progressive improvement in performance until you reach your optimal body weight. Keeping track of your progress provides an excellent means to evaluate the efficacy of various performance-enhancing strategies.

General Book References

Antonio, J., and Stout, J. Sports Supplements. Philadelphia: Lippincott Williams & Wilkins, 2001.

Bahrke, M., and Yesalis, C. Performance Enhancing Substances in Sport and Exercise. Champaign, Ill.: Human Kinetics, 2002.

Daniels, J. Daniels’ Running Formula. Champaign, Ill: Human Kinetics, 1998.

Maughan, R., ed. Nutrition in Sport. Oxford: Blackwell Science, 2000.

Williams, M. H. Nutrition for Health, Fitness and Sports Performance. 6th ed. Boston: McGraw-Hill, 2002.

This article originally appeared in the May/June 2003 issue of Marathon & Beyond. For information about reprinting or excerpting this article or any other M & B article, contact Jan Seeley via email or at 217-359-9345.