1. Brief history of marathon running

2. Energy pathways during exercise
     Phosphogenic    Anaerobic    Aerobic (Oxidative)  

3. Physiological characteristics of marathon runners
     Aerobic capacity (VO_2Max)    Components of aerobic capacity    Limitations to aerobic capacity (VO_2Max)    Cardiac    Oxygen carrying capacity    Secondary limitations    Running economy    Lactate threshold  

4. Alternative factors contributing to marathon performance
     Fuel    Thermoregulation and body fluid loss    Environmental  

5. References

The physiology of marathons are typically associated with high demands on a marathon runner's the cardiovascular system and their locomotor system. The Marathon was conceived centuries ago and as of recent has been gaining popularity among many populations around the world. The, now, 26.6 mile (42.195 km) distance is a physical challenge that entails distinct features of an individual's energy metabolism. In order to understand why marathon runners finish at different times, it is important to understand what physiological characteristics of marathon runners consistently present themselves.

The interaction between different energy systems captures the essence of why certain physiological characteristics of marathon runners exist. The differing efficiency of certain physiological features in marathon runners evidence the variety of finishing times among elite marathon runners that share similarities in many physiological characteristics. Aside from large aerobic capacities and other biochemical mechanisms, external factors such as the environment and proper nourishment of a marathon runner can further the insight as to why marathon performance is variable despite ideal physiological characteristics obtained by a runner.

Brief history of marathon running

The first marathon ever run was an unintentional 25 mile trek performed by Pheidippides. Pheidippides was a Greek soldier who ran to Athens from the town of Marathon, Greece in order to announce a battle victory over the Persians in 490 B.C. Shortly upon arrival, he had dropped dead due to this exhaustive journey from Marathon to Athens.^[1] Thousands of years later, marathon running began to be part of world sports starting at the inaugural Marathon featuring in the 1896 Modern Olympic Games. After variations for about 40 or so years, the established distance of the 42.195 kilometer or 26.2 mile trek has popularized over the last half century. The number of marathons in the United States has grown just over 45 times in this period.^[2] With an increase in popularity, the scientific field has a large basis to analyze some of the physiological characteristics and the factors influencing these traits that led to Pheidippes' death. The high physical and biochemical demands of marathon running and variation across finishing times make for an intricate field of study that entangles multiple facets of human capacities.

Energy pathways during exercise

Humans metabolize food to synthesize energy in the form of Adenosine triphosphate (ATP). This is the human body's instant accessible form of energy for all functions of cells within the body.^[3] For exercise the human body places high demand for ATP to supply its self with enough energy to support all the corresponding changes in the body at work. The 3 energy systems involved in exercise are the Phosphogenic, Anaerobic and Aerobic energy pathways.^[4] The simultaneous action of these three energy pathways prioritizes one specific pathway over the others depending on the type of exercise an individual is partaking in. This differential prioritization is based on the duration and intensity of the particular exercise being performed. The variable usage of these energy pathways is central to the mechanisms that allow for long, sustained exercise, such as a marathon running, to be maintained.

Phosphogenic

The Phosphogenic (ATP-PC) anaerobic energy pathway restores ATP after its breakdown via Creatine Phosphate stored in skeletal muscle. This pathway is anaerobic because it does not require oxygen to synthesize or utilize ATP. ATP restoration only lasts for approximately the first 30 seconds of exercise.^[3] This rapid rate of ATP production is essential at the onset of exercise. The amount of creatine phosphate and ATP stored in the muscle is small, readily available, and is utilized quickly due these two factors. An example of exercise that would primarily use this energy pathway could be weight lifting or performing sprints.

Anaerobic

The Anaerobic Glycolytic Energy Pathway is the source of human energy after the first 30 seconds of an exercise until 3 minutes into that exercise. The first 30 seconds of exercise are most heavily reliant on the Phosphogenic Pathway for energy production. Through Glycolysis, the breakdown of carbohydrates from blood glucose or muscle glycogen stores yields ATP for the body without the need for oxygen.^[4] This energy pathway is often thought of as the transitional pathway between the Phosphogenic Energy Pathway and the Aerobic Energy Pathway due to the point in exercise this pathway onsets and terminates. An example of exercise most heavily using this pathway would be a 300-800 meter run as these are typically higher intensity than endurance exercise and are only sustained for 30–180 seconds depending on one's level of training.

Aerobic (Oxidative)

The Aerobic Energy Pathway is the third and slowest ATP producing pathway that is oxygen dependent. This energy pathway typically supplies the bulk of the body's energy during exercise after 3 minutes from the onset of exercise until the end of the exercise or when the individual experiences fatigue. This energy pathway is used for lower intensity exercise that lasts longer than 3 minutes, which corresponds to the rate at which ATP is produced using oxygen.^[3] This energy system is essential to endurance athletes such as marathon runners, triathletes, cross-country skiers, etc. The Aerobic Energy Pathway is able to produce the largest amount of ATP out of these three systems. This is largely in part to this energy system's ability to use fats, carbohydrates, and protein in conjunction with its capacity for converting these macro-nutrients into a state capable of entering the mitochondria, the site of aerobic ATP production.^[5]

Physiological characteristics of marathon runners

Aerobic capacity (VO_2Max)

Marathon runners obtain above average aerobic capacities, oftentimes up to 50% larger than normally active individuals.^[6] One's aerobic capacity or VO_2Max is an individual's ability to maximally take up and consume oxygen in all bodily tissue during exhaustive exercise.^[7] Aerobic capacity serves as a good measure of exercise intensity as it is the upper limit of one's physical performance. An individual cannot perform any exercise at 100% VO_2Max for extended periods of time.^[7] The marathon is generally ran at about 70-90% of VO_2Max and the fractional utilization of one's aerobic capacity serves as a key component of marathon performance.^[6] The physiological mechanisms that aerobic capacity or VO_2Max consist of are blood transportation/distribution and the utilization of this oxygen within muscle cells.^[7] It is said that VO_2Max is one of the most salient indicators of endurance exercise performance. The VO_2Max of an elite runner at maximal exercise is almost 2 times the value of a fit or trained adult at maximal exercise.^[8] Marathon runners demonstrate physiological characteristics that enable them to deal with the high demands of a 26.2 mile (42.195 km) run.

Components of aerobic capacity

The primary components of an individual's VO_2Max are the properties of aerobic capacity that influence the fractional utilization (%VO_2Max) of this ability to take up and consume oxygen during exhaustive exercise. The transportation of large amounts of blood to and from the lungs to reach all bodily tissues is dependent on having a high cardiac output along with sufficient levels of total body hemoglobin. Hemoglobin is the oxygen carrying protein within blood cells that allows for the proper transportation of oxygen from the lungs to other bodily tissues via the circulatory system.^[9] In order for the transportation of oxygen in blood to be effective during a marathon, the distribution of blood needs to be equally efficient in order for a marathoner's oxygen demands to be met during a race. The mechanism that allows for this distribution of oxygen to the muscle cells is muscle blood flow.^[10] A 20 fold increase of local blood flow within skeletal muscle is necessary for endurance athletes, like marathon runners, to meet their muscles' oxygen demands at maximal exercise that are up to 50 times greater than at rest.^[10] Upon successful transportation and distribution of oxygen in the blood, the extraction and utilization of the blood within skeletal muscle are what give effect to a marathoner's increased aerobic capacity and the overall improvement of an individual's marathon performance. The extraction of oxygen from the blood is performed by myoglobin within the skeletal muscle cells that accept and store oxygen for utilization.^[9] These components of aerobic capacity help to define the maximal uptake and consumption of oxygen in bodily tissues during exhaustive exercise.

Limitations to aerobic capacity (VO_2Max)

During the course of the marathon and endurance exercise in general limitations to one's aerobic capacity are what yield these athletes' aerobic capacity and therefore, their performance in running a marathon.

Cardiac

Marathon runners often present enlarged dimensions of the heart and decreased resting heart rates that enable them to achieve greater aerobic capacities.^[7][11] Although these morphological and functional changes in a marathon runner's heart aid in maximizing their aerobic capacity, these factors are also what set the limit for an individual to maximally take up and consume oxygen in their bodily tissues during endurance exercise. Increased dimensions of the heart enable an individual to achieve a greater stroke volume . A concomitant decrease in stroke volume occurs with the initial increase in heart rate at the onset of exercise.^[6] The highest heart rate an individual can achieve is limited and decreases with age (Estimated Maximum Heart Rate = 220 - age in years).^[22] Despite an increase in cardiac dimensions, a marathoner's aerobic capacity is confined to this capped and ever decreasing heart rate. An athlete's aerobic capacity is prevented from continuously increasing due to the designation estimated for one's maximum hear rate that would only allow an enlarged stroke volume to pump a specific number of times per unit of time.^[12][7]

Oxygen carrying capacity

An individual running a marathon experiences appropriation of blood to the skeletal muscles. This distribution of blood serves to maximize oxygen extraction by the skeletal muscles in order to aerobically produce as much ATP needed to meet the demands of the race. In order to achieve this blood volume increases.^[7] The initial increase in blood volume during marathon running can later lead to decreased blood volume as a result of increased core body temperature, pH changes in skeletal muscles, and the increased dehydration associated with cooling during such exercise. Oxygen affinity of the blood depends on blood plasma volume and an overall decrease in blood volume. Dehydration, temperature and pH differences between the lungs and the muscle capillaries can limit ones ability to fractionally utilize their aerobic capacity (%VO_2Max).^[7][13]

Secondary limitations

Other limitations affecting a marathon runner's VO_2Max include pulmonary diffusion, mitochondria enzyme activity, and capillary density. These features of a marathon runner can be enlarged compared to that of an untrained individual but have upper limits determined by the body. It is thought that improved mitochondria enzyme activity and increased capillary density allow for more aerobically produced ATP. These increases can only occur to a certain point and help to determine one's peak aerobic capacity.^[7] Especially in fit individuals, the pulmonary diffusion of these individuals correlates strongly wit VO_2Max and can limit these individuals in an inability to efficiently saturate hemoglobin with oxygen due to large cardiac output.^[7][14] The shorter transit time of larger amounts of blood being pumped per unit time can be attributed to this insufficient oxygen saturation often seen in well trained athletes such as marathoner's. Not all inspired air and its components make it into the pulmonary system due to the human body's anatomical dead space, which, in terms of exercise, is a source of oxygen wasted.^[15]

Running economy

Despite being one of the most salient predictors of marathon performance, a large VO_2Max is only one of the factors that may effect performance in a marathon. A marathoner's running economy is their sub maximal requirement for oxygen at specific speeds. This concept of running economy helps to explain different marathon time's for runners with very similar aerobic capacities.^[11] The [https://www.sciencedirect.com/science/article/pii/S1569904817301581?via%3Dihub steady state] oxygen consumption used to define running economy demonstrates the energy cost of running at sub maximal speeds. This is often measured by the volume of oxygen consumed, either in liters or milliliters, per kilogram of body weight per minute (L/kg/min or mL/kg/min).^[6] Discrepancies in time of winning performances of various marathon runners with almost identical VO_2Max and %VO_2Max values can be explained by different levels of oxygen consumption per minute at the same speeds. For this reason it can be seen that Jim McDonagh has run the marathon faster than Ted Corbitt in his winning performances compared to that of Corbitt. This greater requirement for sub maximal oxygen consumption (3.3L of oxygen per minute for Corbitt vs. 3.0L of oxygen per minute for McDonagh) is positively correlated with a greater level of energy expenditure while running the same speed.^[6]

Running economy (efficiency) can be credited with being an important factor in elite marathon performance as energy expenditure is weakly correlated with a runner's mean velocity increase.^[6] A disparity in running economy determined differences in marathon performance and the efficiency of these runners exemplifies the marginal differences in total energy expenditure when running at greater velocities than recreational athletes.

Lactate threshold

A marathon runner's velocity at lactate threshold is strongly correlated to their performance. Lactate threshold or anaerobic threshold is considered a good indicator of the body's ability to efficiently process and transfer chemical energy into mechanical energy.^[7] Although the marathon is considered an aerobic dominant exercise, higher intensities associated with elite performance uses a larger percentage of anaerobic energy. The lactate threshold is the cross over point between predominantly aerobic energy usage and anaerobic energy usage. This cross over is associated with the anaerobic energy system's inability to efficiently produce energy leading to the buildup of blood lactate often associated with muscle fatigue.^[16] In endurance trained athletes, the increase in blood lactate concentration appears at about 75%-90%VO_2Max, which directly corresponds to the VO_2Max marathoner's run at. With this high of an intensity endured for over 2 hours, a marathon runner's performance requires more energy production than that solely supplied by mitochondrial activity. This is the reason for a higher anaerobic to aerobic energy ratio during the marathon.^[7][16] The higher the velocity and fractional utilization of aerobic capacity an individual can have at their lactic threshold the better their overall marathon performance will be.

Uncertainty exists in regards to how lactate threshold effects endurance performance. The contribution of one's blood lactate levels accumulating is attributed to potential skeletal muscle hypoxemia but also to the production of more glucose that can be used as energy.^[11][7] The inability to establish a singular set of physiological contributions to blood lactate accumulation's effect on the exercising individual creates a correlative role for lactate threshold in marathon performance as opposed to a causal role.^[17]

Alternative factors contributing to marathon performance

Fuel

In order to sustain high intensity running, a marathon runner must obtain sufficient glycogen stores. Glycogen can be found in the skeletal muscles or liver. With low levels of glycogen stores at the onset of the marathon, premature depletion of these stores can reduce performance or even prevent completion of the race.^[6][7] ATP production via aerobic pathways can further be limited by glycogen depletion. Free Fatty Acids serve as a sparing mechanism for glycogen stores. The artificial elevation of these fatty acids along with endurance training demonstrate a marathon runner's ability to sustain higher intensities for longer periods of time. The prolonged sustenance of running intensity is attributed to a high turnover rate of fatty acids that allows the runner to preserve glycogen stores later into the race.^[11]

It is suggested that ingestion of monosaccharides at low concentrations during the race could delay glycogen depletion. This lower concentration, as opposed to a high concentration of monosaccharides, is proposed as a means to maintain a more efficient gastric emptying and faster intestinal uptake of this energy source.^[11] It is thought that carbohydrates are the most efficient source of energy for ATP. Pasta parties and the consumption of carbohydrates in the days leading up to a marathon are common practice of marathon runners at all levels.^[6][18]

Thermoregulation and body fluid loss

The maintenance of one's internal core body temperature is crucial to a marathon runner's performance and health. An inability to reduce rising core body temperature can lead to hyperthermia. In order to reduce bodily heat, the metabolically produced heat needs to be removed from the body via sweating (also known as evaporative cooling). The dissipation of heat by sweat evaporation can lead to significant losses of water from the body.^[11] A marathon runner can lose enough body fluid to lose about 8% of their total body weight.^[6] Replacement of fluid is limited but can help keep the body's internal temperatures cooler. Fluid replacement is physiologically challenging during exercise of this intensity due to the inefficient emptying of the stomach. Partial fluid replacement can serve to avoid a marathon runner's body over heating but not enough to keep pace with the loss of fluid via sweat evaporation.

Environmental

Environmental factors such as air resistance, rain, terrain, and heat all contribute to a marathon runner's ability to perform at the full potential of their physiological characteristics. Air resistance or wind and the physical terrain of the marathon course (hilly or flat) were often associated with increased insensities in order to maintain pace.^[11][7] The rain can affect a marathon runner's performance by adding weight to the attire of the marathon runner causing their overall load to carry to be slightly heavier. Temperature, in particular the heat, is the strongest contributor of environmental factors leading to poorer marathon performance.^[19] An increase in air temperature affects all the runners the same. This negative correlation of increased temperature and decreased race time is affiliated with marathon runners' hospitalizations and exercise induced hyperthermia. There are other environmental factors less directly associated with marathon performance such as the pollutants in the air and even prize money associated with a specific marathon itself.^[19]

References

• Anton Hecht
• Anton Hegarty
• Anton Heida
• Anton Heiden
• Anton Heiller
• Anton Hekking
• Anton Herman Gerard Fokker
• Anton Holavaty
• Anton Holban
• Anton Holovaty
• Anton Hubert Fischer
• Anton Hulman, Jr.
• Antoni
• Antonia and alexander
• Antonia Aranda
• Antonia Barber
• Antonia Bembo
• Antonia Bennett
• Antonia Bertucci-Pinelli
• Antonia Bird
• Antonia Brickell
• Antonia Brico
• Antonia Caenis
• Antonia campbell hughes
• Antonia Campbell-Hughes