I recently had a client turn up to a session waving a piece of paper and telling me, "I want to do this!" I found out "this" is something called the Marathon des Sables. Can you give me any ideas on how to train for it?
The Marathon des Sables is a 144-mile ultramarathon adventure run over six days in the Sahara Desert in Morocco. Competitors are accompanied by a support crew, creating a virtual nomadic village that moves from one bivouac to another. Running an ultramarathon is a unique accomplishment that epitomizes humans’ compelling interest with endurance. However, it represents a number of challenges. Primary among those is metabolism.
Ultramarathons require the largest glycogen storage capacity possible, a very efficient capacity to make new glucose and a very effective system of fat use. Therefore, one of the goals of ultramarathon training is to teach your client’s muscles to rely on fat as fuel. While muscles’ store of carbohydrate is limiting, humans’ store of fat is virtually unlimited, with enough to fuel about five days of marathon running or about 1,000 miles of walking. While women are at a definite cardiovascular disadvantage to men since they have a smaller cardiac output and less hemoglobin in their blood to transport oxygen, making their race performances slower than those of men for every race shorter than a marathon, research has shown that women have a greater capacity to metabolize fat and conserve glycogen, which may give them an advantage for ultramarathons. Indeed, in 2002 and 2003, Pam Reed beat all the men at the 135-mile Badwater Ultramarathon. Here’s what your client can do to train for an ultramarathon.
Running/walking lots of miles is very important for ultramarathons to maximize aerobic capacity. This sometimes requires running twice per day to spread out the stress and maximize recovery. In addition, research has shown that runners who perform high volumes of endurance training tend to be more economical, which has led to the suggestion that running high mileage (greater than 70 miles per week) improves running economy, the volume of oxygen used to maintain a given speed. Economy is improved largely from increases to capillary and mitochondrial density, the former increasing the speed that oxygen can diffuse into the muscles and the latter increasing the muscles’ capacity to use oxygen. It is also possible that the countless repetitions of the movements of running results in optimized biomechanics and muscle fiber recruitment. Additionally, economy may be improved by the weight loss that usually accompanies high mileage, which leads to 1) a lower oxygen cost; 2) the enlargement of slow-twitch skeletal muscle fibers, which are more suited for aerobic metabolism; and 3) a greater ability for tendons to store and utilize elastic energy with each step.
Since our bodies have a much better concept of time than of distance, the amount of time your client spends on his feet is more important than the number of miles covered. Repeatedly running for long periods of time (longer than two hours) presents a threat to the muscles’ survival by depleting their preferred fuel (i.e., carbohydrate). However, the human body responds rather elegantly to situations that threaten or deplete its supply of fuel. When muscle glycogen is depleted by running long, a strong signal is sent to synthesize and store more than what was previously present, thus increasing endurance for future efforts.
While it’s important to create as large a store of glycogen as possible, it’s not enough to get through an ultramarathon. There are two ways to make your client’s muscles more effective at using fat for energy: 1) run/walk for very long periods of time (4-6 hours) and 2) begin the runs with low muscle glycogen by consuming a low carbohydrate diet for a couple of days before each long run. These strategies heighten the threat described above—when you have no more glycogen or blood glucose to use, the muscles learn to use fat more effectively. The downsides to training with little glycogen, however, are that 1) it doesn’t feel good and 2) it compromises any intensity in your client’s program since high intensity running depends on carbohydrate for fuel. If your client is going to try training with low muscle glycogen, make sure he consumes lots of carbohydrates before the ultramarathon, so he “trains low, races high.” Given its duration, the ultramarathon also requires the consumption of calories during the race. This is yet another challenge because, if your client has ever eaten during a long endurance event, he knows the mess it can make of his digestive system. Your client should carry a backpack or fuel belt during long training runs and must practice eating different foods and different nutrients to see what his stomach can handle. The more he practices refueling strategies, the better off he will be on race day.
Other issues your client should be prepared for in the Marathon des Sables are dehydration, hyperthermia, psychological fatigue and the logistics that accompany traversing the desert.
What makes the Marathon des Sables unique is that it’s run through a desert. The very hot conditions make it easy to become dehydrated as your client will sweat a lot in an effort to increase evaporative cooling. Dehydration causes a decrease in the plasma volume of the blood, decreasing the heart’s stroke volume and cardiac output. Oxygen flow to the muscles is then compromised, and the pace slows. Since our sweat rates exceed our ability to ingest fluid while running, dehydration is difficult to prevent. However, since endurance performance declines with only a two to three percent loss of body weight due to fluid loss, it’s important to minimize its effects by drinking fluids with sodium. Since water goes wherever sodium goes, more water is conserved by the kidneys when you ingest sodium with the water. Since rehydrating while running necessitates carrying fluids with you, your client should practice carrying a Camelbak or similar hydration system during long runs.
Since muscles produce heat when they contract, running for long periods of time increases body temperature, and the resulting hyperthermia decreases blood flow to the active muscles since more blood is directed to the skin to increase convective cooling. Hyperthermia is a big issue for the Marathon des Sables since its run through a desert, where temperatures can rise above 100 degrees. If your client doesn’t take the necessary precautions, hyperthermia can lead to heat exhaustion and heat stroke. Tell your client to drink often to keep body temperature low, wear loose fitting, moisture wicking, light colored clothes and acclimatize to the desert conditions beforehand. (While cardiovascular adaptations to running in the heat are nearly complete within one week, the sweating response takes about two weeks.)
Running an ultramarathon can also cause psychological or neural fatigue, the latter of which is due to changes in the levels of brain neurotransmitters, which may increase the perception of effort and feelings of tiredness and lethargy. The act of repeatedly running for very long periods of time will help prepare your client for what he will experience on race day.
Since your client will be out in the desert for a week, make sure he brings sunscreen, hat, protective eyewear (deserts have sandstorms!), sleeping bag, flashlight, compass, warm clothes to sleep in, a heating stove for cooking, a second pair of shoes, survival kit, pocket knife and enough food to last two weeks, accounting for the large caloric expenditure. For more information on the Marathon des Sables, go to http://www.darbaroud.com/index_uk.php.
- Coyle, E.F. (2000). Physical activity as a metabolic stressor. American Journal of Clinical Nutrition. 72 (Suppl.).512S-520S.
- Davis, J.M. and Bailey, S.P. (1997). Possible mechanisms of central nervous system fatigue during exercise. Medicine and Science in Sports and Exercise. 29(1):45-57.
- Jones, A.M. and Carter, H. (2000). The effect of endurance training on parameters of aerobic fitness. Sports Medicine. 29(6):373-386.
- Meeusen, R., Watson, P., Hasegawa, H., Roelands, B., and Piacentini, M.F. (2006). Central fatigue: the serotonin hypothesis and beyond. Sports Medicine. 36(10):881-909.
- Newsholme, E.A. (1981). The glucose/fatty acid cycle and physical exhaustion. Ciba Foundation Symposium. 82:89-101.
- Scrimgeour, A.G., Noakes, T.D., Adams, B., and Myburgh, K. (1986). The influence of weekly training distance on fractional utilization of maximum aerobic capacity in marathon and ultramarathon runners. European Journal of Applied Physiology and Occupational Physiology. 55(2):202-209.
- Sjodin, B. and Svedenhag, J. (1985). Applied physiology of marathon running. Sports Medicine. 2(2):83-99.
- Tarnopolsky, M.A. (1998). Gender differences in lipid metabolism during exercise and at rest. In M.A. Tarnopolsky (Ed.), Gender Differences in Metabolism: Practical and Nutritional Implications. Boca Raton, FL: CRC Press, pp. 179-199.