Science of Marathon Running
To many people, racing a marathon may appear to be a super-human task. Indeed, pounding the pavement (or trail) for 26.2 miles with minimal nutrition and hydration, all while trying to run the distance as fast as possible takes a lot of strength, preparation and commitment. At the physiological level, running a marathon requires an aerobic base, strong muscles, and an abundance of glycogen.
During a marathon, metabolic rates drastically change, which requires the endocrine, respiratory and neuromuscular systems to perform at elevated levels for longer-than-average amounts of time. To the benefit of marathon runners everywhere, exercise scientists have gained a greater understanding of the distance’s effects on the body since the first-ever marathon was run by Pheidippides in Athens, a feat that resulted in the Greek’s sudden death.
One of the most common physiological changes during a marathon is glycogen depletion, where all the “quick” energy from carbohydrates is recruited from either blood glucose or muscular glycogen stores to sustain forward motion during the race. During prolonged strenuous exercise lasting longer than 90 minutes, glucose in the blood is the first to be depleted, which then signals the liver to begin converting muscular glycogen into blood glucose. Once the liver has depleted the muscular glycogen stores, the body begins to burn fat for fuel, which, combined with dehydration, results in muscle cramping and the feeling of “hitting the wall” late in the race.
Carbo-Loading: Is it necessary?
Prior to race day, runners can decrease their chances of hitting the wall by diligently “carbo-loading” 3 – 4 days before the race. Runners are recommended to consume 10g of carbohydrates per kilogram of body weight for efficient carbohydrate loading. These levels ensure glycogen stores are sufficient enough that the body will not have to resort to recruiting fat for fuel. Additionally, some researchers suggest that the intake of carbohydrates during the race, in the form of energy gels or chews, is just as, if not more, important than carbohydrate loading. Consuming 30 – 60g of carbohydrates per hour of exercise can help maintain a steady level of blood glucose for continual energy.
However, there are a bunch of experiments that have debunked the idea of carbo-loading. Many experts now state that you do not need to eat high amounts of carbs right before the race. Instead, a relatively high-carb diet is recommended throughout the training process.
How does it work? This technique, combined with the tapering off of your training plan in the days leading up to the marathon, will be enough to increase the muscle glycogen levels to the necessary levels for the race. There are extreme opinions as well, with few experts who actually recommend low-carb diets throughout the training period. Why? Because you teach your body to burn fat as fuel, not glycogen.
I personally use the first technique – I eat carbs throughout the training process – as I’m skinny and I’m ok with burning carbohydrates in ultra distances. However, I do long runs without the aid of carbs to enhance my “fuel consumption”. More on this in a minute.
There has not been much research1 on the effects of low-carbohydrate endurance training yet. However, one thing is clear. You do not need to eat tons of pasta the night before the marathon.
The Science of “Bonking” or Hitting the Wall
Hitting the infamous wall during a marathon can be a truly miserable experience. Hitting the wall or “bonking” is a well-known phenomena among ultra runners and occurs when the body runs out of sugar to use for physiological processes.
Now, this is where the carbo-loading research started in the first place. There are experts who suggest training in a glycogen depleted state to enhance the metabolic process and experts who prefer the carbo-loading technique.
Since glucose stored in the muscles and liver is bound into large chains called glycogen, the body uses it as a prime fuel for strenuous physical activities such as distance running. Although fat releases more energy than carbohydrates when it is burned, carbs are easier to burn.
The science behind “the wall” at 20 miles/35 km has much to do with the fact that this is as long as the average runner’s muscle glycogen stores will last.
Running in a Glycogen-Depleted State
Karen Van Proeyen et al. published a research paper2 in 2011 after investigating effects of training in a glycogen-replenished and glycogen-depleted state in 20 male cyclists.
The study shows that there where two test groups, and both had the same training regimens and diets. One group performed the training after carbo-loading in the morning about 90 minutes before the daily cycling session, while the other group fasted the night before.
In six weeks both groups showed similar improvements on a 60-minute time trial, yet there were a few changes that showed how the “fasted” group had adapted to burn fat as fuel more efficiently.
• Levels of main enzymes correlated to fat metabolism elevated significantly in the second group, which trained after the overnight fast. Levels remained the same in the carbo-loading group.
• In addition to this, the fat utilization in the “fast” group highly increased. Thus, the higher the pace, the more they could rely on fat instead of glycogen, enabling them to cycle longer without “bonking”.
“The wall” will be an interesting topic for further research in the next years, as more and more scientists and physicians get involved in sports medicine and sports performance.
Super-humans – our so-called champions – are not just the result of hard training or genetics. They are the result of smart training combined with excellent genetics.
The Muscular and Skeletal Systems
As the number of people who drop out of a marathon with minor to serious injuries indicates, prolonged running can cause damage to the muscular and skeletal systems. During a marathon the body takes a sustained beating that is not replicated in the training programs of most runners. Every step during the course of 26.2 miles (approximately 30,000 – 60,000 steps, depending on stride length) will result in the body absorbing the shock of three to four times the person’s body weight.
This constant pressure can cause bones, muscles or tendons already weakened by the stresses of training to break, tear or strain. The nonstop pounding also causes cellular death and damage that can take the body three to four weeks to fully repair, leading to chronic feelings of muscle stiffness, soreness and general weakness.
In preparation for the stresses of a marathon, runners should condition their bodies by performing long runs every one to two weeks. One of the main benefits of 15 – 20 mile long runs is improved efficiency towards handling the strain of the increased mileage. Over time, the body will be become stronger and better able to handle prolonged time spent moving forward. Additional exercises such as stretching, core strengthening and weight training can also help protect the body from damage sustained during a marathon.
Core Body Temperature during a Marathon
During a marathon, core body temperature can increase by almost 3°F/1°C due to dehydration and increases in metabolic rate, which describes the energy expended during the race. For some people, fifteen times the amount of energy normally expended at rest will be consumed during a marathon. Since the burning of energy is an exothermic process (i.e. heat is produced), the body’s basal temperature rises as a result.
To efficiently cool the body, warm blood is pumped through the body towards the skin, where heat is lost due to evaporation of sweat. The increase in heat production during a marathon makes efficient cooling more difficult. Additionally, dehydration decreases blood volume which inhibits the body’s natural cooling mechanism. Although normal body temperature is 98.6° F/37° C, marathon finishers often are reported to have core temperatures near 105° F/41° C. Temperatures in excess of 107° F/42° C are fatal3.
Runners can improve their cooling efficiency by “heat training”.
Activities such as purposely over-dressing, running indoors without proper ventilation or even visiting the sauna or taking a hot bath after a workout can increase blood plasma volume, which will not only improve VO2 max, but also the ability to shed excess heat.
The Health Risks of the Marathon
Recently, marathon running has been making headlines due to the seemingly increased instances of heart attack and cardiac arrest. As of 2005, one out of every 220,000 finishers suffered from a heart attack, which occurs when blood flow to the heart becomes restricted. Running a marathon has been shown to produce mild damage to cardiac tissue3, as evidenced by elevated levels of troponin, creatine kinase and creatine kinase myglobin in the blood stream. The elevation of these proteins, which are direct results of cardiac tissue death, can last for up to a month post-race.
Dr. Dan Tunstall Pedoe was London Marathon’s Medical Director from 1981 to 2006, and he has recently published an article in the British Journal of Sports Medicine stating that the increase in marathon popularity is one of the major contributors to the apparent increase in long-distance racing deaths. He examined well-documented sudden death reports – 650,000 more precisely, and concluded that such risk was 1 in 80,000 finishers in the London Marathon.
For some marathon runners with a history of disease, there is no way to prevent heart tissue damage during strenuous activity. However, for a runner at no apparent risk of heart attack, proper preparation for completing the marathon distance is required. Cardiac muscles are made stronger by building a proper aerobic base before attempting the marathon distance. Consistent mileage, at least in the 35 – 45 miles per week range, but preferably higher, is recommended in order to arrive at the start with a heart strong enough to go the distance.
Although running a marathon is no longer the dangerous endeavor it was once assumed to be, the distance still must be respected. Without proper preparation and caution, serious injury, disorders and even death can occur. However, when approached with a proper training program, marathon racing is a safe and healthy activity.
1. Timothy Noakes, Jeff S Volek, Stephen D Phinney. “Low-carbohydrate diets for athletes: what evidence?”. Br J Sports Med doi:10.1136/bjsports-2014-093824
2. Van Proeyen, Karen et al. “Beneficial Metabolic Adaptations due to Endurance Exercise Training in the Fasted State.” Journal of Applied Physiology 110.1 (2011): 236–245. PMC. Web. 13 Jan. 2016.
3. Maron BJ, Poliac LC, Roberts WO (1996). “Risk for sudden cardiac death associated with marathon running”. J Am Coll Cardiol 28 (2): 428–31. doi:10.1016/0735-1097(96)00137-4. PMID 8800121
4. Trautner BW, Caviness AC, Gerlacher GR, Demmler G, Macias CG (July 2006). “Prospective evaluation of the risk of serious bacterial infection in children who present to the emergency department with hyperpyrexia (temperature of 106 degrees F or higher)”. Pediatrics 118 (1): 34–40. doi:10.1542/peds.2005-2823. PMC 2077849. PMID 16818546.