Distance Running

Distance running is commonly thought of as any distance 10,000 meters (6.2 miles) or longer. To go these distances, runners place a premium on relying primarily on aerobic metabolic pathways during the majority of the run. Runners who are capable of doing this rely mainly on fat for the majority of fuel, enabling them to limit the usage of carbohydrate. Carbohydrate storage is finite, but fat storage is, from a practical standpoint, limitless. The higher reliance on fat enables long-distance runners to run very long distances. It also enables them to preserve carbohydrate for moments during the race when they require fast acceleration (e.g., at the end of the race or while passing another runner). According to one study, only 2 to 7 percent of the total energy burned in aerobic activity is derived anaerobically.²⁴ A small amount of carbohydrate is used even when maintaining aerobic activity, so distance runners must develop strategies for delivering carbohydrate during the run. A failure to do so will result in either low blood sugar or low muscle glycogen, both of which impair endurance by leading to premature muscle fatigue.

Keeping this in mind, distance runners must consider the following nutritionally relevant factors for their sport.

Long-distance runners are at risk of amenorrhea, low bone density, and stress fractures. The distances that these athletes run weekly to train may predispose them to stress fractures, despite the potential stimulating impact of running on skeletal mass.²⁵ Although stress fractures occur more frequently in women runners than in men, all runners should ensure that their calcium intake is adequate to reduce the risk of fracture. Female runners are at higher risk of stress fractures because hard endurance training is often associated with cessation of the menstrual cycle. The reduced estrogen associated with amenorrhea is linked to lower bone density. Therefore, runners who experience either primary or secondary amenorrhea should seek appropriate medical advice to determine if rea son able steps can be taken to return to normal menstrual status.²⁶

Female runners should take the following steps to reduce the risk of osteoporosis:

• Consume calcium (1,500 milligrams per day) from food or a combination of food and supplements.
• Avoid overconsumption of protein because excess protein is associated with higher urinary calcium losses.
• Control the production of stress hormones (particularly cortisol) by maintaining hydration and blood sugar during exercise.
• Avoid overtraining, which is associated with amenorrhea.

Inadequate energy intake is a red flag that the intake of vitamins and minerals may also be low. A study comparing the nutrient intakes of trained female runners who were amenorrheic, oligomenorrheic, or menstruating normally found clear nutrition differences between these groups, despite being matched on height, weight, training distance, and body fat percentage.²⁷ The runners who were not menstruating had zinc intakes well below the recommended level of intake and lower than those found in the runners who had normal menses. In addition, the runners who had normal menses had higher intakes of fat and a more adequate total energy consumption. This suggests that high-carbohydrate diets, which are preferred for optimal performance, make it more difficult to consume the needed level of energy because carbohydrates have a lower caloric density than high-fat foods. Therefore, athletes should concentrate on consuming more food when carbohydrates constitute the main energy source. A failure to menstruate normally is a strong risk factor in the development of weaker bones and resulting stress fractures. Female runners have good cause to be fully aware of the adequacy of their energy and nutrient intakes because almost no injury is more frustrating or potentially career ending than the development of frequent stress fractures. Endurance runs require enormous amounts of energy (a marathon requires about 2,900 calories); they cannot be adequately trained for or run without an adequate total energy consumption. Food intake strategies, including eating snacks between meals and consuming snacks or sports beverages before, during, and after exercise, are important for ensuring that fuel consumption matches need.

Elite runners depend heavily on both fat and carbohydrate for fuel to accelerate and vary speed over the course of a long-distance race.

Surveys of distance runners confirm that total energy and carbohydrate intakes are below the recommended levels, suggesting that runners must make a concerted effort to consume the recommended amounts before, during, and after exercise.^28,29 In a case study assessing the nutrient intake of an ultraendurance runner during a race, it was found that if the pre-event and during-event guidelines for food and beverage are followed, then athletes will have sufficient energy and fluids to successfully complete the event.³⁰

Tapering activity before a competition improves competition performance.³¹ It does so by increasing glycogen stores, but it also makes the runner calmer, which gives the athlete an improved economy of running motion that enhances endurance. The importance of tapering exercise and of carbohydrate loading before an important event cannot be overemphasized.

Fluids are crucial. Fluid consumption should be on a fixed time schedule (every 10 to 15 minutes) to avoid underhydration and thirst. Perhaps no single factor is more important for ensuring a long-distance runner's success than maintaining an optimal hydration state. Athletes should drink now, drink again in 10 to 15 minutes, and when they believe they've had enough, they should drink more. Of course, the type of beverage consumed is also important.

A great deal of body heat is generated over the course of an endurance run, and this heat is liberated through sweat evaporation. Studies strongly suggest that a 6 to 7 percent carbohydrate solution with electrolytes is most effective in maintaining exercise endurance.³¹ It has been firmly concluded that acute heat exposure is detrimental to muscular endurance.³² Therefore, long-distance runners should develop the habit of frequent fluid consumption to maintain body water status, whether they are thirsty or not. A fluid intake of .5 to 1 liter per hour is sufficient to prevent significant dehydration in most athletes in mild environmental conditions, but a greater intake of fluids is needed for athletes running at higher intensities or in more severe environmental conditions in order to avoid heat stress.³³

Distance runners typically have relatively low body fat levels. Successful long-distance runners are commonly thin, and this body profile may be advantageous to them in dissipating heat during long runs.³⁴ However, since very low body fat levels are associated with amenorrhea, female athletes should seek a balance between low body fat levels and normal hormone function.

A critical factor in the performance of all endurance athletes is iron status, and evidence exists that endurance runners have reduced hemoglobin, hematocrit, and red blood cell counts when compared with strength and mixed-trained athletes.³⁵ Iron status is sufficiently important that one of the more common illegal ergogenic aids used by endurance runners is erythropoietin (EPO),³⁶ which stimulates the production of red blood cells, thereby enhancing oxygen-carrying capacity.³⁷ Iron is an essential oxygen-carrying component of hemoglobin (red blood cell iron), myoglobin (muscle cell iron), and ferrochromes (oxygen-carrying enzymes essential for making ATP) in the mitochondria. It appears that hemoglobin status is of highest priority, so iron from other cells is cannibalized to support a normal hemoglobin production when iron stores (ferritin) and intake are inadequate. Therefore, a standard blood test measuring hemoglobin may appear normal while other iron-containing cells are depleted. For this reason, it is important that blood tests in endurance athletes always include a measure of ferritin, which should be at the level of a minimum of 20 nanograms per deciliter. Besides having an inadequate dietary intake, which is most common in runners who do not eat red meat or who are vegetarian, there are several other common causes of low iron status in runners:^38-40

• Excess iron loss in sweat
• Excess loss of blood through the GI tract
• Excess loss of blood in the urine (hematuria)
• Excess menstrual blood loss in female runners
• Poor absorption of iron
• Intravascular hemolysis

The issue of blood donations should also be considered because iron is so crucial to running success. According to Noakes (1991), runners wishing to donate blood should first assess iron status. Normal hemoglobins and ferritins above 60 nanograms per milliliter after 5 days of hard training are the margin point for safely donating blood.⁴¹In addition, runners who do donate blood should not exercise with normal intensity for 3 to 6 weeks after the donation to allow for sufficient time to return blood volumes and iron status back to normal levels.