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Sport Biomechanics
How can biomechanics help the marathoner? Most of us who have run a marathon have used a simple biomechanical strategy. When running into the wind, we have drafted off another runner or, better yet, a group of runners. In doing so, we have reduced the adverse effects of air resistance, or drag. When we draft, the oxygen cost of running is reduced dramatically, improving running efficiency and saving energy for the latter part of the race.
The goal of the sport biomechanist is to improve movement efficiency, mainly by maximizing propulsive forces and minimizing resistive forces, and thus provide the athlete with a mechanical edge. Using high-speed cinematography, the biomechanist can analyze a runner’s form and detect problems in running form that may be inefficient, such as overstriding, and that may waste energy. Although most elite and experienced marathoners have developed efficient running styles, even a small improvement in running efficiency may make a significant difference over the duration of a marathon.
There are several biomechanical strategies you can use to improve your marathon time. One involves selecting the right sportswear, and the other is optimizing your body weight and composition.
Running Sportswear
A uniform and shoes are the only sportswear equipment the marathon runner normally uses. Well-fitting uniforms should be selected to minimize wind resistance without retarding sweat evaporation. Most uniforms (shorts, singlets, socks) in use today are very lightweight and of such composition as not to interfere with proper body temperature regulation. The shoe is the most significant piece of sportswear worn by the marathoner, particularly its weight. The oxygen cost of accelerating each foot an average 90 times per minute over the course of a marathon may influence energy efficiency. Ed Frederick, a biomechanist at the Nike Sports Research Laboratory in the early 1980s, calculated that use of a racing flat weighing approximately 4 ounces less per shoe than a regular training shoe can save approximately 2.5 to 3.0 minutes over the course of a marathon.
Body Weight
Sport scientists have calculated the energy cost of running, a weight-bearing sport activity. If we disregard the normal resting oxygen consumption, according to a formula developed by the American College of Sports Medicine, the energy cost of horizontal running is 0.2 milliliter of oxygen per kilogram of body weight per meter per minute (ml O2/kg/m/min). The more you weigh, the more oxygen, or energy, it takes to run at a given speed.
Optimizing your body weight may be a very effective means to improve your marathon performance. V.O2max may be expressed in several ways, including total V.O2max in liters per minute (L O2 /min), or based on body mass (ml O2/kg/min). If your total V.O2max is 4.0 liters/min (4,000 ml/min) and if you weigh 80 kg, then your V.O2max is 50 ml O2/kg/min (4,000 ml O2 /80 kg). If you lose 5 kg (11 pounds; 1 kg = 2.2 lbs) to 75 kg and maintain your V.O2max at 4,000 ml/min, then your V.O2max increases to 53.3 ml O2/kg/min, a 6.6 percent increase.
Let’s apply this body-weight change to marathon running. To run a marathon in four hours, you would need to maintain a pace approximating 176 meters per minute (42,200 m/240 min). Again, disregarding the resting O2 in the ACSM formula, the oxygen cost to run a four-hour marathon approximates 35.2 ml O2/kg/min (0.2 ml O2 3 176 m/min). For an 80-kg runner, this totals about 2,816 ml O2/min (which is running at about 70 percent of V.O2max). If this runner would lose 5 kg of body fat (about a 6 percent loss), the oxygen cost would drop to 2,640 ml O2/min, a savings of about 176 ml O2/min (over 6 percent). Since the cost of running each meter for our 75-kg runner is 15 ml O2 (0.2 ml O2 3 75 kg), the speed of running would increase approximately 11.7 m/min (176 ml O2/15 ml O2) to a speed of 187.7 m/min. This would improve the marathon running time to 3:44:50, or an improvement of about 15 minutes (about 6 percent faster).
In general, for every 1 percent loss of body mass, primarily as body fat, there will be an approximate 1 percent increase in running speed. Most elite marathon-ers are most likely at an optimal body weight and composition. However, other marathoners who are carrying excess body weight, primarily body fat but also excess upper-body muscle, may enhance performance by losing the excess weight. If you decide to undertake a weight-loss program, a general guide is to lose no more than a pound a week. If you have difficulty losing weight, see a sports health professional, such as a sports dietitian with an R.D. (registered dietitian) degree.
Excessive weight loss, however, may impair the health and performance of marathon runners. There is a fine line between optimal body weight for marathoning and excessive loss of body mass. Excessive weight loss may adversely affect performance if muscle tissue function and energy stores are impaired. Health may also be impaired. For example, the female athlete triad involves disordered eating patterns and weight loss affecting hormonal disturbances that may predispose the athlete to premature osteoporosis.
Caffeine
Caffeine is a drug, a stimulant whose use is restricted by the IOC but not completely prohibited because it is found naturally in a variety of beverages, particularly coffee, that are consumed by athletes. Numerous studies using various doses of caffeine have evaluated its effect on a wide variety of running events but particularly on distance running.
Caffeine may enhance marathon performance in several ways. First, caffeine may stimulate the central nervous system and help prevent mental fatigue. Second, caffeine stimulates the release of epinephrine (adrenalin) from the adrenal gland, which may enhance cardiovascular functions and fuel utilization. In particular, caffeine may help spare the use of muscle glycogen by increasing the use of free fatty acids for energy during the early stages of the marathon, leaving more of the muscle glycogen for the latter part of the marathon to help you maintain an optimal pace. Terry Graham and Lawrence Spriet, from Guelph University in Canada, are two of the principal sport scientists who have evaluated the performance-enhancing effect of caffeine. In several recent reviews of the available scientific laboratory research, they concluded that caffeine could enhance aerobic endurance performance in elite as well as amateur runners, even when taken in legal doses approximating 5 milligrams of caffeine per kilogram of body weight. They noted that although the underlying mechanism has not been clearly identified, it could involve muscle glycogen sparing. However, they also noted that the beneficial effects of caffeine have been documented mainly under laboratory conditions and not during competition. Thus, although one would theorize that the beneficial laboratory findings would be applicable to field competition, it is possible that the natural excitement of competition may provide a stimulation effect to override that associated with caffeine.
Nevertheless, in a recent issue of Sports Medicine, an international review journal of sport science research, several reviewers calculated that caffeine could enhance performance in a 40K cycle time trial by 55 to 84 seconds. If extrapolated to marathon run performance, the enhancement would approximate 135 to 210 seconds, a savings of several minutes.
If you want to experiment with caffeine, take about 5 milligrams of caffeine per kilogram of body weight, or about 300 to 400 milligrams of caffeine. Most over-the-counter stimulants such as Vivarin contain about 200 milligrams per tablet, so two tablets should suffice. Taking more than this amount has not provided additional benefits. Although caffeine is a relatively safe drug, some individuals may experience adverse reactions such as nervousness, trembling, anxiety, and even heart palpitations, especially when taking larger doses.
Carbohydrate
Carbohydrate is the primary dietary energy source for high-intensity aerobic endurance exercise (> 65 to 70 percent V.O2max), but endogenous supplies of muscle and liver glycogen are limited and may become suboptimal within 90 minutes of intense aerobic endurance exercise. John Hawley, a renowned sport nutrition scientist, has noted that carbohydrate loading (consuming 400 to 600 grams of carbohydrate several days before a marathon) may elevate endogenous muscle and liver glycogen stores, postponing fatigue and improving performance in which a set distance is covered as quickly as possible (such as a marathon) by 2 to 3 percent. For a four-hour marathon, carbohydrate loading could improve performance by about five to seven minutes if it helps prevent premature depletion of muscle glycogen.
Sports Drinks and Water
Various factors may contribute to fatigue during prolonged aerobic exercise, but dehydration and depleted carbohydrate stores are most common, particularly when exercising in warm or hot environmental conditions. Sports drinks are designed to delay the onset of fatigue by providing both fluids and carbohydrate. Sports drinks were developed in the early 1960s and were modeled after medicinal oral rehydration solutions. Although water is the main ingredient, carbohydrate content approximates 5 to 10 percent; the type of carbohydrate also varies, including glucose, sucrose, fructose, and glucose polymers, depending on the brand. Caloric content ranges from about six to 12 kilocalories per ounce. Most sports drinks include electrolytes, mainly sodium, chloride, and potassium. Some sports drinks contain other substances as well, such as miscellaneous vitamins and minerals, protein, herbals, and caffeine. However, the key ingredients for the marathoner are water and carbohydrate.
Water ingestion is essential to help optimize body water balance and body temperature regulation during exercise under warm environmental conditions. Rehydration, about 6 to 8 ounces every 10 to 15 minutes, during exercise in the heat, has been shown to decrease physiological stress as evidenced by a decreased heart rate response, lesser rise in the core temperature, and increased endurance performance. Hyperhydration, such as consuming a pint of fluid before exercise, may also be helpful, but it has not been shown to be as effective as rehydration. When compared to consuming only water, numerous studies have shown that consuming carbohydrate, approximately 60 grams per hour, significantly increased performance in prolonged aerobic endurance exercise tasks.
In a recent Sports Medicine review, several sport scientists concluded that sports drinks with carbohydrate concentrations less than 10 percent are among the few nutritional food products that may enhance sport performance in exercise tasks where performance may be impaired by dehydration and depleted endogenous carbohydrate reserves. Other sport scientists concluded that sports drinks may decrease the time to complete a 40K cycle time trial by 32 to 42 seconds, which would approximate 80 to 105 seconds if extrapolated to running a marathon.
Palju aega Teie kokku saite, palju uus PR maratonis tuleb :D???
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