Biochemical Strategies for Ultrarunning—Draft Version
|Written by Bruce R. Copeland, PhD|
|Wednesday, 14 May 2008 15:49|
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Aerobic Exercise—Keep Those Carbohydrates Coming
The human body burns about 100 calories per mile while running. A typical runner stores enough glycogen for perhaps three hours at race pace. This is why many runners can last for an entire marathon—maybe even a 50K—with little or no additional carbohydrate besides a pre-race meal of 300-600 calories. The body can obtain some of its energy from fat metabolism, but the rate of fat metabolism is too slow to sustain race pace for most runners. For longer distances, therefore, a runner has two choices: slow down, or consume carbohydrate during the event.
Most of us understand that we need to eat predominantly complex (low glycemic) carbohydrates in everyday life. High (or even moderate) intensity exercise is an exception to this rule. The process of digestion actually requires significant energy in its own right. Under exercise stress, the rate and quality of digestion therefore decline considerably. To increase the likelihood that nutrients will actually reach the bloodstream rapidly (and reduce the amount of energy expended for digestion itself), we need to consume predominantly simple (high glycemic) carbohydrates. There are additional considerations. A typical 150 lb. runner can only take up (transport from the digestive tract to the bloodstream) 300-500 calories per hour during exercise, and optimal carbohydrate and water uptake from the stomach occurs when the stomach contains 60-100 grams of carbohydrate per quart of liquid (300-450 calories per quart) [Am J Physiol Endocrinol Metab. 2002 Sep;283(3):E573-7. Plasma glucose kinetics during prolonged exercise in trained humans when fed carbohydrate. Angus DJ, Febbraio MA, Hargreaves M.; Sports Med. 2000 Jun;29(6):407-24. Oxidation of carbohydrate feedings during prolonged exercise: current thoughts, guidelines and directions for future research. Jeukendrup AE, Jentjens R.]. Above 110 grams/quart, uptake decreases rapidly, and gastrointestinal distress is highly likely [Eur J Appl Physiol. 2003 Jan;88(4-5):431-7. Epub 2002 Nov 19. Metabolic profile of 4 h cycling in the field with varying amounts of carbohydrate supply. Meyer T, Gabriel HH, Auracher M, Scharhag J, Kindermann W.]. (The optimum of 60-100 grams of carbohydrate per quart of water applies to runners of all sizes, but the total needs for calories and water scale with body size. Runners lighter or heavier than 150 lb. should scale their intake of carbohydrate and water down or up but maintain the appropriate ratio of carbohydrate to water.)
The highest levels of carbohydrate uptake appear to only occur only when multiple sugars (e.g. glucose, fructose) are consumed that can be metabolized through different biochemical pathways [Adopo E et al (Appl Physiol 1994 Mar;76(3):1014-9)]. Thus honey (a roughly equal mixture of glucose and fructose), sucrose (which is digested to equal parts glucose and fructose in the upper GI tract), and even high fructose corn syrup (typically 55% fructose and 45% glucose) are useful carbohydrate sources for endurance running. Fructose leaves the stomach more slowly than glucose and is metabolized (in both liver and skeletal muscle) mostly through biochemical pathways that are insensitive to insulin and glucagon. Therefore under exertional stress, consumption of fructose in addition to glucose has the extra benefit that it levels out some of the blood sugar swings that can occur with glucose or dextran (glucose polymer) alone. Maltodextran (a simple starch) is sometimes used with or as an alternative to glucose because it has very little sweet taste but is metabolized nearly as quickly (and through the same pathway) as glucose.
A little arithmetic shows that ultrarunning competition actually takes place at or near the limits of human aerobic energy metabolism. Top average paces in longer ultra races are in the range 5 to 6 miles per hour, which translates into a need for 500 to 600 calories per hour. Fat metabolism can be estimated to provide as much as 200 to 300 calories per hour (the higher number probably only for women). Thus a top competitor needs to be able to consume something like 300 to 400 calories of carbohydrate per hour. This is near the limit of what a human can take up. A winning ultrarunner must either have greater biomechanical efficiency (therefore requiring slightly fewer calories), or be able to take up and use calories at maximum rate, or both! It is possible that the very fastest ultrarunners may have a genetic predisposition for a higher fat metabolism rate, which allows them to sustain faster paces without having to consume more carbohydrate.
One convenient way to consume carbohydrate while running is in the form of a sports drink. These are formulated to provide electrolytes and carbohydrate at optimal concentrations for uptake from the stomach. However, different athletes will have different electrolyte needs, so it is important to choose a sports drink that contains an electrolyte mix appropriate for you. Sports drinks also differ widely in the type of carbohydrates they provide, and quite a few contain no fructose, so choose wisely. Sports drinks free the athlete of the need to separately monitor carbohydrate, electrolyte, and water intake during an event. At the same time, the fixed carbohydrate/electrolyte/water ratio in a sports drink is a potential drawback. Carbohydrate needs do not tend to vary much under different race conditions, but electrolyte and hydration needs can vary a lot. You may therefore need to have different sports drink formulations for different temperatures and stages of an event.
A more flexible approach is to consume carbohydrate gel. Two to three gels (30 grams carbohydrate or 110 calories per gel) consumed with 24-32 ounces of water over the course of an hour works effectively. You can vary the amount of water you drink, depending on temperature. You can and should also use electrolyte supplements. Make sure to consume enough water, and do not try to mix gels with sports drink unless you are absolutely certain you know what you are doing. Consuming more than 110 grams of carbohydrate per quart of fluid or more than 100 grams of carbohydrate per hour (for a 150 pound runner) greatly increases the chances your stomach may shut down. It can take more than an hour and a half for your stomach to recover. During that time you will be traveling slower, and/or starving your mitochondria of carbohydrate and electrolytes—a situation from which they will not recover during your event.
Some ultrarunners believe it is better to consume "real food" than simple carbohydrate (gel or sport drink). Certainly ultrarunners DO need some amount of protein (or at least certain amino acids) in addition to carbohydrate. It is also likely true that some runners can settle an upset stomach with food that contains soluble fiber and protein. It is important to understand, however, that soluble fiber works mainly by slowing the rate of digestion. Under such conditions, ultrarunners are probably reduced to traveling at a pace that is limited by their rate of fat metabolism. So some real food is probably a good thing; just don't overdo it, or you are likely to feel better and better because you are traveling slower and slower.
Finally, some of you may be in a position to estimate your maximal contribution to pace from fat burning alone. If you have ever done a long race in which you had to slow down late in the race because of the inability to consume food, that pace is a good measure of your maximum speed when metabolizing fat. If you want to race at a faster pace, you need to consume 0.67 calories (about 0.2 g) of carbohydrate per hour per pound of body weight for each mile per hour that you want to go faster.
Aerobic Exercise—Maintain Electrolyte Balance
Most distance runners know about the need to maintain electrolytes. There are four main electrolytes of importance to endurance athletes—sodium, potassium, calcium, and magnesium. Sodium tends to receive the most attention. It is the primary electrolyte in sweat and is therefore the electrolyte most likely to be depleted during warm temperatures or from heavy exertion over the course of a few hours. Potassium, calcium, and magnesium play important roles in mitochondria and are extremely important for muscle and nerve function during aerobic exercise. Like sodium, these can also be depleted in sweat and in the kidneys, but it typically takes longer. A runner suffering from muscle cramps at distances less than 40 miles probably has a sodium deficiency. Whereas a runner suffering from cramps after 40 miles (or especially in cool temperatures) may well be deficient in potassium, calcium, and/or magnesium.
Do not fall into the trap of believing that all runners have identical electrolyte needs. Humans may have overwhelming genetic similarity, but we all still differ in significant (and obvious) ways. Some of our most pronounced individual differences show up in ion transport systems and in the relative balance of Type I versus Type II muscle. Different muscle types utilize oxidative metabolism to different extents and are optimized to contract with different levels of force and for different durations. These different conditions require different amounts of the various electrolytes. Thus different runners show significant variation in their need for and response to different electrolytes. Because of this variation, it is extremely important to experiment with different electrolytes and their amounts and ratios during training.
Aerobic Exercise—Supplement with CoQ10 to Prevent Fatigue
Coenzyme Q10 (CoQ10 ) is a non-essential quinone vitamin found primarily in mitochondrial membranes. It plays a necessary role in mitochondrial energy conversion [Littarru, Gian Paolo, et al. Clinical aspects of coenzyme Q: Improvement of cellular bioenergetics or antioxidant protection? In Handbook of Antioxidants, eds. Enrique Cadenas and Lester Packer, NY, Marcel Dekker, Inc., 1996, pp. 203-39; Vanfraechem, J.H.P. and Folkers, K. Coenzyme Q10 and physical performance. In Biomedical and Clinical Aspects of Coenzyme Q, Vol. 3, eds. Folkers, K. and Yamamura, Y., Amsterdam, Elsevier, 1981, pp. 235-41]. It is considered non-essential because the body can synthesize it. However, levels of naturally produced CoQ10 drop about 10% every decade after age 20. CoQ10 is one of the most effective anti-oxidants in the human body. It is re-used (regenerated) under normal mitochondrial energy conversion, but is destroyed under oxidative stress conditions. CoQ10 depletion is the most likely cause of mitochondrial destruction besides carbohydrate and electrolyte deficiency. The mitochondrial membrane can store large quantities of CoQ10 . This improves the efficiency and fidelity of energy conversion. More importantly it serves as a CoQ10 reservoir, thereby permitting CoQ10 to be preloaded and stored for extended aerobic exercise.
CoQ10 supplementation is recommended for all adults over 50 and for anyone taking a statin drug to treat elevated cholesterol. It appears to be highly beneficial for anyone exercising (even hiking or backpacking) at altitude. It is likely to be beneficial for any endurance athlete over 40. In my experience, supplementation with 50 to 100 mg of CoQ10 per day for seven to ten days prior to an ultra race eliminates the fatigue often experienced at distances near or greater than 50 miles. It also substantially decreases muscle soreness and cramping during and after an event. These benefits presumably result because fewer mitochondria are destroyed due to quinone depletion and because the anti-oxidant effects of CoQ10 mitigate much of the oxidative stress associated with endurance exercise.