THE EFFECTS OF FEEDING SCHEDULE ON MARATHON SWIMMING

Introduction

This report documents two separate attempts to swim the Catalina Channel. We will specifically address the feeding patterns used during the swims and the probable effects of those patterns on the outcome.

The first attempt began at approximately 11:00 PM on August 19, 1992. The athlete involved was a 40 year old male with extensive long distance open water experience. The attempt culminated in a New World record for swimming from the mainland to Catalina.

The second attempt began at approximately 1:30 AM on August 22, 1992. The athlete involved was a 32 year old male with extensive athletic experience. His experience included numerous endurance events including the Ironman triathlon, and a 25 KM swim in training for his Catalina Channel attempt. The attempt ended less than one mile from the finish in a near fatality due to hypothermia, exhaustion, and water aspiration.

Background

During prolonged exercise, the body's fuel deposits are used to provide energy for the muscular contractions. The primary fuel sources for the body are fat and carbohydrate. During a swim the magnitude of a Catalina Channel crossing large quantities of fuel will be burned to sustain the effort.

In 1991 the International Center for Aquatic Research (ICAR) conducted a study with several open water swimmers to evaluate consumption of a carbohydrate supplement during a controlled swim. The swims were done in ICAR's swimming treadmill, or "flume." Each swim was four hours in duration. Some of the swims were done with the athletes being "fed" 8oz of Gatorade every 15 minutes. The Gatorade was mixed to a concentration of approximately 45g carbohydrate per quart. The remainder of the swims were done "unfed" where the athletes were given 8 oz of water every 15 minutes. Some of the swimmers did both fed and unfed swims. In this case both swims were at the same flume speed for any given swimmer.

During the swims capillary blood samples were taken every half-hour; venous blood samples were taken every hour; oxygen consumption was measured every hour; and muscle biopsies were taken before the swim, after three hours, and after four hours. The intent of the study (and rather intrusive testing) was to evaluate the physiological responses of the swimmers during strenuous four-hour swims in both the fed and unfed condition.

The ICAR report on this study stated that no difference in performance was observed between the fed and unfed swims. This is, at best, misleading. Actual performance differences could be observed only for the swimmers who did both a fed and an unfed swim. A subjective indicator would be the swimmers perceived level of effort during the swims. Since the tests were performed in the flume at a controlled speed, objective performance differences could be observable if the swimmer was unable to maintain the same speed during one of the four-hour swims. If significant physiological differences between a swimmers fed and unfed swim occurred this would also be an objective indication of a performance difference. Indications of the performance differences observed were:

The primary conclusion of the ICAR report was that the body's stored glycogen was used at an approximately 75% higher rate for the unfed swimmers than those who were fed. The implication of this is that the fed swimmers should be able to maintain the high level of energy expenditure much longer than the unfed swimmers before suffering effects of exhaustion. The conclusion of this study was, "Swimmers who work out, train or compete for more that 60 minutes should be consuming a 6% (45g per quart) carbohydrate beverage to spare glycogen and maintain hydration. The beverage should be consumed ideally at 15 minute intervals or at least in 30 minute intervals to have its greatest effect."

August 19, 1992 Attempt

During this attempt the athlete stopped every 15 minutes and consumed 8 oz of fluid. The fluid used was Shaklee's Performance Sports Drink. Two different concentrations were used and alternated between each feeding. One concentration was 60g carbohydrate per quart and the other was 120g carbohydrate per quart (for a total carbohydrate intake of 90g per hour). This feeding pattern and these concentrations were selected by the athlete based on experience during training and racing. Previous feeding patterns involved feeding intervals from 10 to 30 minutes and carbohydrate concentrations from 45g to 150g per quart. The feeding stops averaged under 10 seconds. At the end of the swim the athlete reported being pleasantly warm during the entire swim and, with the exception of extreme pain in the left shoulder, capable of swimming back to the mainland.

Ten-second feeding stops may seem extremely short when compared to feeding patterns of just a few years ago. However, they are actually a little long when compared to normal feeding stops for the current US National open water team. It should be noted that the athlete was one of the subjects of the ICAR study and trained with the US National team. He felt that this experience was crucial to the success of his swim.

August 22, 1992 Attempt

During this attempt the athlete stopped every 20 minutes and consumed 6-8 oz of fluid. The fluid used was Exceed. In addition the athlete ate 1/4 of a Power Bar and had some water at each stop. The total carbohydrate intake was approximately 55g per hour. The feeding pattern was selected by the athlete based on his training and other endurance experience. While the quantity of fluids consumed was less than recommended by the ICAR study the athlete noted no symptoms of dehydration. The feeding stops took as long as 4 minutes. The swim ended less than one mile from the finish with the exhausted athlete being taken to the hospital where he remained in intensive care for several days.

Of particular significance are the long feeding stops. These were driven by the consumption of solid food, particularly solid food which required a significant amount of time to chew and swallow. The primary problem with long feedings is related to hypothermia. During exposure to cold the body shunts blood away from muscles which are not being used to help maintain the body's core temperature. During a long feeding stop the swimmer will have to tread water which uses different muscles than swimming does. While trying to use muscles which are cold and have been receiving very little blood flow may cause cramps, it can definitely contribute to hypothermia. To stop swimming and tread water takes muscles, which are cold and significantly increases the blood flow to allow them to exert the necessary effort. This blood is then cooled by those cold muscles and returned to the heart to reduce the core temperature. In addition, while treading water the muscles used for swimming are allowed to cool and will then contribute to reducing the core temperature when swimming resumes.

Conclusions

Both athletes consumed carbohydrates in excess of the amounts recommended by the ICAR report. Whether or not the difference between 90g and 55g of carbohydrate per hour was significant is not known, it is simply noted. The ICAR study only extended to four hours but noted that a significant physiological shift occurred between three and four hours. To extrapolate the ICAR data to a Catalina Channel swim (times ranging from 7 to 33 hours) is risky at best. Perhaps higher carbohydrate intake is needed for longer swims. Only further study and experience can answer that question.

What can be concluded is that feeding stops which change the swimmers muscle usage for significant periods of time should be avoided. Hypothermia is a very real problem in marathon swimming, with potentially fatal results. Every effort should be made to avoid treading water for more than just a few seconds. This essentially requires the elimination of solid food from the swimmers diet during a swim.

While many factors contribute to the success or failure of a swim, the feeding pattern used can be significant. Certainly a world class marathon swimmer will not be forced into an unsuccessful attempt simply because of a poor feeding pattern. However, the August 19 attempt would not have been a world record swim if a poor feeding pattern had been used. In the same vein, a less proficient swimmer will not break a world record simply by using a proper feeding pattern. However, the August 20 attempt might well have been a successful crossing if the athlete had used a better feeding pattern.