 of Sports Medicine (1996) cites other factors that may reduce body temperature. For example, if the second half of the marathon is run slower than the first half, not enough heat may be generated to maintain body temperature. Also, any sweat that builds up can saturate clothing, which will draw additional heat away from the body. Hypothermia can also occur after the race when heat radiates from a warm body to the cooler air temperature.
The best defense against hypothermia is to dress in layers with an outer layer that protects from wind and water. Layers should be removed as air temperature increases to avoid hyperthermia, and any wet layers should be replaced. While not as common as hyperthermia, the number of hypothermia cases could increase along with the popularity of trail and adventure marathons. Hypothermia can produce more than just cold limbs or noses. Irregular and life-threatening heart rhythms can develop, so it should not be treated any less seriously than hyperthermia.
Carbohydrate-loading dinners have become a staple of the modern marathon prerace events. And why not? When the facts are linked together, carbohydrate loading makes sense. For instance, carbohydrates provide energy to the muscles faster than fats and are required for optimal aerobic performances. Inside the body, carbohydrates are found as glycogen in the muscles and liver and as glucose in the blood. During a marathon, the muscle gains energy from the glycogen within its cells and from blood glucose. As the amount of glucose in the blood is used up, the liver converts its glycogen into glucose and releases it into the bloodstream to maintain a constant supply of glucose to the muscles. During prolonged exercise, glycogen levels become depleted, leaving the muscles with little of the high-performance fuel and forced to operate on slower-burning fats. This shift in fuel sources does not go unnoticed. Marathon runners describe it as like running into a wall or “bonking.” It is also known that a diet high in carbohydrates can increase the amount of glycogen stored inside the muscles and liver. Therefore, if glycogen depletion leads to a decrease in running speed and a high-carbohydrate diet can increase glycogen stores, then carbohydrate loading should prevent or delay hitting The Wall.
When carbohydrate-loading studies from all endurance sports were reviewed, Hawley et al. (1997) found that carbohydrate loading did improve performance in endurance sports lasting longer than 90 minutes. However, none of the studies used a full marathon as the performance distance. The closest are studies that looked at the effects of carbohydrate loading on 30K race times. Karlsson and Saltin (1971) found that carbohydrate loading improved 30K race times by an average of nearly eight minutes (143.0 to 135.3 minutes). The faster times were the result of not having to slow down rather than being able to run faster. Similarly, six men cut an average of 3.6 minutes (131.0 to 127.4 minutes) off their 30K time after increasing carbohydrate consumption by 200 grams the week before the race (Williams et al. 1992).
Other studies looked at whether carbohydrate loading could prolong the time to exhaustion. Overall, subjects were able to run 10 to 66 percent longer at 70 to 75 percent of maximal effort after having carbohydrate loaded (Brewer et al. 1988; Chryssanthopoulos et al. 2002; Galbo et al. 1967; Lamb et al. 1991).
On the other hand, a study by Sherman et al. (1981) found that eating a diet of 70 percent carbohydrate for three days elevated muscle glycogen levels but failed to improve 20.9K times compared with a diet of 50 percent carbohydrate. Also, in a second part of the study by Lamb et al. (1991), the run time to exhaustion was 16 minutes longer but not statistically better than the group that did not carbohydrate load.
While carbohydrate loading does appear to be effective for most runners, it does have its drawbacks. Consuming too many calories in the name of carbohydrate loading can add extra body weight, which will increase the energy demands of running a marathon. Also, for every gram of glycogen stored, almost 3 grams of water are stored with it. This can leave a runner with a bloated or heavy feeling. Besides, it may be that hypoglycemia, not muscle glycogen depletion, is a greater concern. If a runner does not consume carbohydrates during a marathon, liver glycogen depletion can occur around two hours, leading to hypoglycemia. Even though muscle glycogen depletion may take longer to develop, hypoglycemia resulting from liver glycogen depletion can reduce running speed from inadequate neural stimulation (Noakes 2003). The problem is that the brain prefers glucose as its fuel, and hypoglycemia impairs brain functions, one of which is stimulation of the muscles. So despite glycogen remaining inside the muscles, hypoglycemia reduces the strength of stimulation from the brain to the muscles, resulting in weaker muscle contraction and slower running speeds (Nybo 2003).
Some experts feel that consuming carbohydrates during a marathon is just as important, if not more so, as carbohydrate loading (Ivy 1999). In fact, many studies have shown that carbohydrate ingestion during exercise helps prevent hypoglycemia and improves performance (Tsintzas and Williams 1998; Jacobs and Sherman 1999). For example, subjects ran two 30K races with either a high-carbohydrate meal before the race and water during the race or a no-carbohydrate solution before the race and a carbohydrate sports drink during the race. Race times were the same regardless of whether carbohydrates were emphasized before or during the race (Chryssanthopoulos et al. 1994). In a study by the same group of researchers, a prerun carbohydrate meal improved run times to exhaustion by about 10 percent, but combining the carbohydrate meal with a carbohydrate sports drink during the run increased performance an additional 10 percent (Chryssanthopoulos et al. 2002). In the marathon study, subjects ran three 42.2K treadmill time trials consuming only water, or a 5.5 percent carbohydrate sports drink, or a 6.9 percent carbohydrate sports drink. Race times were significantly faster (190 minutes) with the 5.5 percent solution compared with either water (193.9 minutes) or the 6.9 percent solution (192.4 minutes) (Tsintzas et al. 1995).
Collectively, these studies show the importance of carbohydrate as a fuel source during prolonged running, but the issue of when and how much carbohydrate should be consumed seems to be an individual matter. Ivy (1999) suggests that both carbohydrate loading before and carbohydrate consumption during an event are needed for those who run between 60 and 70 percent of their V.O2max. But, for faster runners, carbohydrate consumption during exercise is not beneficial because glucose uptake into the muscles cannot occur fast enough to be useful. More research is needed to determine whether these conclusions pertain to marathon runners, but there is little doubt that increasing carbohydrate intake before and/or consuming carbohydrate during a marathon is critical for optimal performance.
The original version of carbohydrate loading starts with three days of a low- carbohydrate diet followed by intense exercise to deplete glycogen stores. This is followed by three days of a high-carbohydrate diet where glycogen levels are supercompensated from a normal value of 100 millimoles per kilogram to 220 millimoles per kilogram. Sherman et al. (1981) found that a gradual increase in dietary carbohydrate along with tapering training resulted in just slightly less glycogen (205 millimoles per kilogram) but with much less stress to the individual. Sherman et al.’s modified version of carbohydrate loading has since been the recommended technique of carbohydrate loading for most endurance athletes.
Consuming carbohydrates during a marathon should be done at a rate of 30 to 60 grams (120 to 180 calories) per hour and 30 to 40 minutes prior to fatigue. The amount and timing are based on the fact that glucose is absorbed into the bloodstream at a rate of 1.0 to 1.2 grams per minute (Ivy 1999). Various types of carbohydrate (glucose, a glucose polymer, or fructose) seem to be equally effective in maintaining blood glucose levels (Noakes 1988). Therefore, it is up to the individual to determine whether sport drinks, energy gels, bananas, flat cola drinks, or some other type of carbohydrate works best.
As if hitting The Wall wasn’t worry enough, running a marathon can be a musculoskeletal nightmare as well. It takes between 30,000 and 50,000 steps to run a marathon. Every time the foot hits the ground, a stress three to four times body weight is absorbed by the ankles, knees, hips, and lower back. Also, with each stride, some muscles contract to propel the body forward while others control the degree of movement by being lengthened. The lengthening or eccentric contractions are notorious for damaging the muscle’s infrastructure. As a result, muscle damage and inflammation can remain for seven days after having run a marathon (Hikida et al. 1983), while repair of muscle fibers can take three to 12 weeks (Warhol et al. 1985). It’s not surprising then that postmarathon data have found “stiffness or pain” in 65 to 92 percent of marathon runners (Satterthwaite et al. 1996; Kretsch et al. 1984; Nicholl and Williams 1982).
Fortunately, only a relatively few marathon runners have experienced injuries while running a marathon that caused them to seek medical attention. A survey of runners who completed the 1980 Melbourne Marathon found that 3 percent of runners reported serious injuries, with the most common being knee pain, hamstring problems, dehydration, blisters, and quadriceps pain or cramps (Kretsch et al. 1984). Similarly, the injury rate from 12 years of the Twin Cities Marathon was 2.1 percent of all runners (21.15 per 1,000 entrants), with the top five injuries being exercise-associated collapse (59.4 percent), blisters (19.9 percent), muscle strain (14.