In another study, athletes repeated a challenging interval workout involving 6-second sprints on successive days.23 The athletes who followed a high-carbohydrate diet during the 24-hour recovery period were able to perform with greater power during the first 20 minutes of the second-day’s session than those who consumed a low-carbohydrate diet. Performance was not significantly greater for the high-carbohydrate athletes during the final 40 minutes of the workout. This suggests that an ample carbohydrate intake is necessary for recovery between workouts that occur on consecutive days, but that the glycogen-depleting nature of sprint sessions may nonetheless deplete the glycogen stores of athletes following a high-carbohydrate diet and slow performance during the latter stages of workouts. Prior to extended sprint workouts, it appears to be very important to load leg muscles maximally with glycogen.
Overall, scientific evidence suggests that sprinters should avoid the high-protein, carbohydrate-restricted diets that are fairly popular today and should include an ample amount of carbohydrate in their daily eating.24 For sprinters and endurance runners engaged in high-quality training sessions, adequate carbohydrate intake appears to help performance during extended sprint workouts and enhance recovery between demanding sprint sessions.24
Protein Needs
Considerable research has focused on how much protein sprinters actually need in their diets in order to improve training adaptations and maximize performances. A popular theory is that sprinters require more daily protein than endurance athletes in order to optimize gains in strength and power. Many sprinters engage in strength training along with their high-intensity running training and attempt to increase muscle mass in their legs and upper bodies, believing this will enhance maximal speed. Thus, it is logical to think that added protein might be beneficial for sprinters.
Scientists and coaches from Eastern Europe have recommended that sprinters and other power athletes who are engaged in weight training should ingest as much as 3 grams of protein per kilogram (2.2 lb) of body weight per day. This is a huge intake given that normal, recommended protein intake rates are often set at 0.8 grams per kilogram of body weight per day.25 There is little published research that supports such recommendations.
Current recommendations call for sprinters to consume from 1.2 to 1.7 grams of protein per kilogram of body weight per day especially during early phases of training when increases in muscle mass and muscle-repair processes may be operating at their highest levels.26 Such provisos have emerged from nitrogen-balance studies seeming to show that protein requirements increase during periods of chronic, intense exercise. A key flaw in this research is the fact that athletes become more efficient with their protein usage over extended periods of time, and most nitrogen-balance studies have rather short durations. Another problem is that a high protein intake by itself tends to increase protein use.27 Thus, nitrogen-balance studies might overestimate protein requirements in sprinters.
Research regarding the effects of elevated protein intakes on performance, strength, and power has generally been carried out with strength trainers rather than sprinters and has produced contradictory results. One inquiry found that a daily protein intake of 2.1 grams per kilogram of body weight per day produced a significant gain in muscle mass over a 6-week period, but a normal intake of 1.2 grams of protein per kilogram of body weight failed to do so.28 In contrast, a broad survey of high-quality, published studies concerning the effects of high protein intake on muscle strength suggested that supplemental protein ingestion has little impact on strength and body mass.29
The debate over whether sprinters should ingest 1.2 grams, 1.7 grams, or some higher number of grams of protein per day is softened by studies that reveal that most power athletes, including sprinters, take in well over 2 grams of protein each day during training. The exception to this rule is the case of female sprinters who are reducing their daily energy intake in hopes of controlling weight and body fat. Such athletes may indeed be consuming too little protein and could usually benefit from an increase in overall daily energy intake, which almost automatically increases protein consumption.
Conclusion
During periods of strenuous or prolonged training, a high-carbohydrate diet that focuses on the consumption of 4 grams of carbohydrate per pound (0.45 kg) of body weight per day is optimal for glycogen storage and therefore endurance performance. The classic repletion stage of carbohydrate loading is not necessary and in many cases is counterproductive from a psychological standpoint. The protein requirement for endurance runners is about 1.5 grams per kilogram of body weight per day, which is easily met with a standard Western diet. Even sprinters should follow a high-carbohydrate eating plan in order to optimize tough training sessions. The best endurance athletes in the world—the Kenyan runners—follow a diet that is extremely rich in carbohydrate, moderate in protein, and low in fat.
Chapter 45
Fueling Strategies During a Run
Many runners are still stuck in the dark ages when it comes to sport drink use. Ingesting a sport drink during workouts and competitions lasting longer than an hour, and during some very intense running sessions, can enhance carbohydrate oxidation in the muscles and thus advance both endurance and speed. Research has established not only the overall effectiveness of sport drinks but has also shown runners how much to consume, how to time their sport drink intakes, and how to combine carbs within a sport drink in order to maximize carbohydrate absorption.
Usefulness of Sport Drinks
Ingesting a carbohydrate-containing sport drink just before and during running sessions lasting longer than an hour can increase average running speed and delay exhaustion. This simple fact has been known for over 30 years, and yet many endurance runners today fail to use sport drinks properly during their long runs.
Interest in using a sport drink to enhance performance originated in the early 1970s after exercise physiologist David L. Costill of Ball State University traveled to Sweden to study the highly successful Swedish National Ski Team. The main purpose of Costill’s Scandinavian journey was to measure the sky-high O2max readings of the amazing Swedish cross-country skiers, but what startled Costill the most was the Swedes’ strange drinking habits. Prior to their 180-minute training sessions, the skiers prepared prodigious quantities of tea and then completely saturated the tea with honey. The athletes were mixing up 36 percent carbohydrate solutions with 360 grams (13 oz) of carbohydrate (from honey) in each liter (1.06 qt) of tea.1 At the time, 2.5 percent sport drinks were considered to be highly concentrated, and the majority of exercise physiologists were advocating the ingestion of plain water during prolonged running rather than a carbohydrate-containing beverage. There was a belief that carb ingestion during running could disturb blood insulin levels or upset the digestive system.
During their workouts, the Swedish skiers drank about one liter (1.06 qt) per hour of their hyperconcentrated brew, an intake rate of approximately 8 ounces (.2 L) every 15 minutes. When Costill pumped out the Swedes’ stomachs after their workouts (a remarkably inhospitable act by a foreign guest), he found them to be almost empty! Nearly all of the ingested tea had moved into the skiers’ small intestines during their training sessions, presumably supplying rich lodes of easily absorbed carbohydrate to sustain their activities.
Costill was shocked by such findings because one of his early sport drink inquiries had revealed that water drained from the stomach into the small intestine more quickly than a 2.5 percent sport drink, which in turned emptied more rapidly than a 5 percent sport beverage. Because of such slow emptying rates, it had appeared doubtful that the carbohydrate contained in sport drinks could ever be absorbed quickly enough to make a significant energy contribution during sustained running.
But those first investigations by Costill were carried out with individuals at rest, and as the exercise physiologist soon learned, running changed everything. The mechanical jostling associated with running helps to force fluids of varying carbohydrate concentrations down and
out of the stomach and into the small intestine (where actual absorption occurs) at similar rates. As a result, most carbohydrate-containing sport drinks can exit the stomach during running as quickly as pure water.
In follow-up research, Costill demonstrated that taking in carbohydrate during sustained exercise could boost performance significantly.2 In the subsequent inquiry, 10 subjects consumed either an artificially sweetened beverage or a combination of 43 grams (1.5 oz) of table sugar (sucrose) and 400 milliliters (13.5 oz) of water. The latter created a 10.75 percent sport drink once the sugar and water mixed together. The subjects swallowed one of these two alternatives immediately before and after 1, 2, and 3 hours of continuous exercise at a mild intensity of 50 percent of O2max (i.e., about 65 percent of maximal heart rate). During the prolonged effort, exercisers who ingested the sucrose-water combination depleted glycogen stores in their quadriceps muscles at a slower rate and had higher blood glucose concentrations than participants who ingested the artificially sweetened drink.
After 4 hours of exercise, each of the 10 individuals exercised at 100 percent of O2max and 100 percent of maximal heart rate until unable to continue. The exercisers who had consumed the sucrose and water kept going for 45 percent longer at O2max. Costill concluded that the ingested sucrose was used effectively by the leg muscles for energy during exercise, saving intramuscular glycogen. The increased glycogen levels present in the leg muscles for the final, intensive exercise period then boosted performance during the highly demanding effort.
Since Costill’s groundbreaking research was published in 1984, follow-up scientific investigations have indicated that imbibing a carbohydrate-containing sport drink during prolonged running has four positive effects:
It raises blood glucose levels and increases the rate at which carbohydrate supplies the energy needed for running, especially during late stages of a workout or competition.3, 4
It preserves glycogen stores in the liver; this is beneficial because the liver can then release more glucose into the blood during a prolonged exertion.5
It increases glucose uptake by the muscles.6
It slows the rate at which muscle glycogen is broken down, leaving greater supplies of glycogen available to sustain desired paces over long distances.7, 8
It is also possible that the heightened carbohydrate availability associated with sport drink ingestion may upgrade the functioning of the central nervous system during extended running.9 This may be especially important since current theories concerning the cause of fatigue during running pinpoint the nervous system as the originating source of tiredness.
For some runners, consuming a sport drink can be a problem when they attempt to swallow fluid on the run. If this is a problem, runners may tuck a straw into the waistband of their running shorts and use it to suck 1-ounce (29.6 mL) portions of the sport drink out of a cup or container without risk of aspiration or slowing of pace.
Fueling High-Intensity Workouts
Although sport drink consumption has classically been linked with exertions lasting longer than an hour, there is increasing evidence that it can be beneficial in shorter high-intensity efforts as well. Several studies have connected sport drink ingestion with improved performance in high-quality interval workouts lasting 60 minutes or less.10-13 Carbohydrate intake seems to upgrade carbohydrate oxidation during such efforts, promoting faster running. The simple rule of ingesting some sport drink 10 minutes before an intense workout begins (see the following section) and then downing six regular swallows of sport drink every 15 minutes or so should help promote superior-quality training sessions.
When and How Much to Drink
Research suggests that sport drink use is especially beneficial during a glycogen-depleting running event like the marathon. In a study carried out by Robert Cade, the inventor of Gatorade, and his colleagues at the University of Florida, 21 experienced marathon runners (18 men and three women) from the Florida Track Club were divided into three groups of roughly equivalent running ability.14 Members of one group drank plain water while running a marathon; those in a second group consumed a glucose-electrolyte solution of 5 percent glucose with sodium, chloride, and phosphate; and subjects in a third group ingested a mixture that was half water and half glucose-electrolyte solution, yielding a 2.5 percent concoction. To ensure maximal muscle glycogen levels at the start of the race, all 21 runners carb loaded during the days prior to the marathon, relying on diets that were rich in carbohydrate.
Ten of the runners experienced difficulties during the last third of the race that caused them to drastically reduce pace from 6 to 9 or 10 minutes per mile (1.6 km) or to adopt a walk-run strategy for finishing. This drop-off in speed took place in 67 percent of the runners who drank only water during the competition. Fifty percent of the athletes who consumed the half-strength beverage hit the wall in this way. Only 29 percent of the glucose-electrolyte drinkers suffered from such precipitous falls in pacing. Overall, use of the sport drink reduced the risk of bonking.
Ingesting a sport drink during a run lasting longer than an hour can preserve speed and promote endurance.
Richard Wareham/age fotostock
Science has also addressed the important question of exactly how much carbohydrate should be ingested during prolonged running. If a runner takes in too little carbohydrate during prolonged running, the effect on muscle glycogen use will be minimal. If too much carbohydrate is ingested, significant amounts of water will be pulled osmotically into the stomach from surrounding tissues to dilute the carbs, and gastric upset and diarrhea will follow.
Traditionally, the highest rate at which ingested carbohydrate can be broken down for energy during running has been thought to be about 1 gram per minute in the average runner.15
It is easy for runners to adjust their drinking on the run in order to take in 1 gram of carbohydrate per minute (60 grams per hour). By definition, an 8 percent sport drink is a beverage with 8 grams of carbohydrate per 100 milliliters (3.4 oz). To hit the 60-gram mark, a runner needs to swallow 750 milliliters (25.4 oz) per hour (or 60/8 = 7.5 100-mL portions of the drink). A regular swallow of fluid approximates 1 ounce, so the desired intake amount could be achieved with a 6- to 7-ounce intake every 15 minutes, producing an ingestion rate of 24 to 28 ounces per hour. Thus, a simple rule is established: During running workouts or competitions that last longer than an hour, a runner should ingest six or seven regular swallows of an 8 percent sport drink every 15 minutes. A slightly smaller intake rate would be needed with a stronger sport drink, and a higher rate would be required with a weaker sport drink.
When using sport drinks in this way, it is important to avoid the intake of plain water throughout the prolonged effort; ingested water dilutes the sport drink in the stomach and thus decreases the rate of carbohydrate absorption. It is important and reassuring to know that sport drinks are just as effective as water for the prevention of dehydration during running.
Training Effect on Rate of Carbohydrate Oxidation
Exercise scientists have wondered whether it is possible to increase the rate of carbohydrate oxidation during running by employing specific kinds of training; such an upgrade would provide muscles with fuel at a more rapid rate and thus foster faster running. The leg muscles of well-trained runners normally do a remarkable job of removing carbohydrate from the blood and oxidizing it during exercise, especially when blood glucose and insulin concentrations are high.16, 17
Training-induced changes provide mechanisms for this upgraded carbohydrate oxidation capacity. Capillary densities expand in response to endurance training, and higher capillary densities promote a faster delivery rate of glucose to muscle fibers. GLUT4, a glucose transporter protein that facilitates the passage of glucose into muscle cells, also responds to endurance workouts. Finally, the enzymes responsible for breaking down glucose inside muscle cells increase their activity in response to running workouts.
The exact form of training that is best for optimizing these three factors is
not precisely known; it would seem, though, that high-intensity training would have a larger impact on carbohydrate oxidation rate than would lower-intensity, higher-volume work. The reason for this is that higher-intensity running would seem to be a more powerful promoter of capillary growth and would rely more heavily on carbohydrate use than would more moderate running. Moderate running depends on fat oxidation to a greater extent, and this would be unlikely to optimize GLUT4 activity.
Carbohydrate Concentration
Research indicates that the optimal carbohydrate concentration for sport drinks is about 6 to 10 percent.18 Drinks with less than a 6 percent carbohydrate content probably do not provide enough exogenous energy to make a significant difference during endurance running. Some runners are tempted to follow the strategy of Costill’s Swedish skiers and ingest drinks with a carbohydrate concentration greater than 10 percent, but there are risks involved.
Highly concentrated drinks tend to drag water into the stomach via osmosis, creating sensations of bloating and feeling overfull. More concentrated sport drinks also increase the risk of nausea during prolonged runs. In one study, 70 percent of the athletes who ingested 12 percent sport beverages became nauseated during 2 hours of exercise while just 20 percent felt unwell when using 6 percent sport drinks.18 Table 45.1 provides a list of popular sport drinks and their nutrient composition, including carbohydrate concentrations. Note that Shaklee Performance Pure Hydration provides the greatest amount of carbohydrate to the muscles per minute.
Running Science Page 62