The Marathon: Implications for Endurance Physiology
By William Misner, Ph.D.
The Marathon running event of 26.2 miles duration may have endurance physiological implications for all endurance events. This event has been widely studied because it's better competitors have both 5000 meter speed and ultra marathon endurance. The maximal human capacity for storing and "efficiently burning" muscle glycogen has been estimated to peak at 90 minutes for very fit individuals. After 90 minutes intense duration the body must begin to resolve its energy from body fat stores and lean muscle mass. This 26.2 mile event lasts for a few minutes more than 2 hours consuming the best of competitors like a great white shark finding prey in open waters. The mile run, a 4 minute event, takes 7 days recovery before efficient performance levels are resumed, the 10,000 meter run, lasting 30 minutes takes 10-14 days, but the marathon run may take between 6-10 weeks before efficient racing and training levels return.
This makes the marathon event an ideal model for studying what the mechanics are that limit endurance performance. Physically speaking, then, what are the factors that contribute to optimal Marathon running performance?
The ideal physiology for the Marathon Event is one we have few individual physiological measurements for comparison. Frank Shorter is the exception. Shorter was 70.07 inches tall weighing in at a little over 134 lbs. These figures give him a BMI (Body Mass Index) of 19.2, similar to Marco Pantani, one of cycling's greatest climbers. His VO2 Max value in 1976 was found to be 71.3 ml/kg/min. Derek Clayton, who held the World Best Record in the Marathon for 12 years had one of the lowest VO2 Max values of elite marathon runners at 69.7 ml/kg/min, while Alberto Salazar recorded VO2 Max values of 76.0 ml/kg/min respectively. Steve Prefontaine recorded an 84.4 ml/kg/min, and Dave Bedford had a 85.0 ml/kg/min as the two highest men, and Grete Waitz recorded the highest women's mark that I know of to date at 73.0 ml/kg/min.
Shorter's gastrocnemius calf muscle biopsy revealed that he had an 80% composition of slow-twitch fibers (with a record low 2.2% body fat percentage!) Salazar's registered 92% slow-twitch muscle fiber content. How do the specific demands of each sport influence muscle fiber makeup? Two points to consider is that those with a certain muscle fiber makeup may select or are selected by their success in a sport because of their genetic gift of muscle fiber composition. It is generally accepted that their are 5 sets or types of muscle fibers, Fast Twitch for speed, Slow Twitch for endurance, and 3 types of Fast-Oxidative-Glycolytic fibers which may adapt to imposed demands. It is well accepted that great sprinters and great endurance athletes are born with the composite muscle fiber types that allow them to achieve great performances if they totally give themselves to develop the talent they've been born with. Below follows is what slow-twitch muscle fiber contents is typically found in a variety of sports.
|Cross Country Skiers||72-79%|
|Elite Distance Runners||79-88%|
VO2 Max is an indicator of how much oxygen is consumed during exercise. As exercise intensity increases there is a correlative linear increase in oxygen demand. When an athlete reaches his or her peak level of oxygen use, a plateau is reached called the maximum volume of oxygen consumption, or VO2 Max. The athlete can go a little farther and/or faster but their body is not able to extract more oxygen. While VO2 Max is a strong indicator of endurance performance, studies show that maximum achieved work load such as top running or cycling speed are superior indicators for predicting performance in endurance events during all sporting events. Endurance work torque output has not been studied to the degree of VO2 Max applications.
Since VO2 Max has been studied at length, let us briefly review the data from this research. Training influences VO2 Max from increases of 5 to 15%, regardless of what age the athlete or gender initiated training. Got good genetics?...You can add up to +15% volume oxygen, or did you come from a couple of "turtles"?...You can still improve on what you got by a whopping +15%!
Females tend to have lower VO2 Max than males as a group, which is probably due to smaller muscle mass, greater body fat percents, and lower muscle torque output values.
Healthy inactive subjects experience gradual losses of VO2 Max of -9% every 10 years after age 25. A couple of researchers (Heath 1981 & Pollock 1987) have suggested that continual training may reduce VO2 Max loss related to aging from -9% to -5% every 10 years! Several other notable sportscientists argue that the cause for these losses in volume of maximal oxygen capacity are a decrease in the maximal cardiac output and/or a decrease in muscle contractility, or muscle mass loss with aging. It is an interesting correlation to note that researchers have found that moderate endurance training also plays a prominent role in optimal cognitive thinking during the aging process. This means that we may conclude that endurance activities practiced through the years may, in fact, slow the aging process more dramatically than once thought by modern scholars.
So as not to cause further "eyestrain", or boredom let me end this treatise early, but not before mentioning that we have failed to discuss several other factors of influential for endurance fitness such as: lung capacity, vascular mechanics, muscle contractility, superior myosin-ATPase activity, calcium carrier mechanics, blood serum hemoglobin content, microergogenics, training mechanics-methodology, and the "heart" and "mind" set of a competitor. Perhaps we can discuss these another day when time permits.