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CHAPTER 1
the runner's body
John Brewer
The structure of our bodies, including bones, muscles, tendons, and ligaments, is our anatomy, whereas physiology is the manner in which the body functions to create a living organism. The human body is a complex organism that constantly adapts and regulates itself to support life, with many systems interacting to ensure that it functions effectively. While human beings have evolved in a manner that means all of us have a similar generic structure, each individual differs as a result of their inherited genes. Science, however, has shown that we can make changes to our bodies, particularly through exercise. The body can adapt to the stimulus of running through positive changes to many of the anatomical structures and physiological processes that support life, and these changes can not only improve running performance, but could also create long-lasting health benefits.
What is running economy?
Why do I get out of breath so easily?
In order to run, the body has to produce energy. This occurs as a result of the breakdown of either carbohydrate or fat within the muscles, and for low- and moderate-intensity running this process always uses oxygen. Approximately one-fifth of the air that we breathe into our lungs consists of oxygen — the rest is mainly nitrogen, along with small amounts of other gases such as carbon dioxide. Oxygen is transported across the membranes of the lungs to attach to hemoglobin in the blood. With each beat of the heart, oxygen-rich blood from the lungs is pumped to the exercising muscles, where it combines with fat or carbohydrate to produce energy. At the same time, blood that is low in oxygen is pumped away from the muscles and back to the lungs.
The amount of energy needed to run at any given speed will vary from one person to another, and this in turn determines how much oxygen the exercising muscles require. Someone who uses a lot of energy — perhaps as a result of poor technique or a high body fat percentage — will need more oxygen, and be less efficient, or economical, than a runner with good technique and low energy expenditure. This is known as "running economy" and it has a real impact on performance.
Efficient runners have good running economy. They use less oxygen, save energy, and suffer less fatigue. On the other hand, runners with poor economy have to use more oxygen at each speed, resulting in an increase in breathing frequency, heart rate, and fatigue.
A simple analogy is to think of two automobiles — if one requires more fuel than another while traveling at the same speed, the one with the highest fuel consumption will stop first. Runners are no different. A runner with poor economy will stop before a runner with good economy when running at the same speed.
Common areas for improvement
1 Weight Carrying extra weight — particularly body fat — requires more energy. Consequently, runners with a high body fat percentage need more oxygen and have poor running economy.
2 Extension of leading knee A straight knee will produce resistance when the foot lands on the ground, which needs to be overcome with extra energy before forward momentum is generated.
3 Foot strike Feet landing too far ahead of the body cause a braking motion that must be overcome before moving forwards. Avoid over-striding by planting the foot slightly ahead of the body.
4 Height of trailing foot Efficient runners with good running economy tend to keep their feet close to the ground, and avoid wasting energy with a high follow-through of their trailing leg.
5 Rotation Over-rotation wastes energy and makes it hard to run efficiently in a straight line. Rotation has to be stabilized with counter movements, requiring more energy and poor running economy.
6 Rear foot action Swinging the rear foot outward while bringing it forward for the next step is a common problem. This creates instability and a loss of forward momentum, which requires additional energy and oxygen.
7 Angle of body Relaxing and leaning slightly forward creates the optimum trunk angle and displacement of the body's center of gravity, making forward momentum easier and minimizing braking forces.
8 Bounding Vertical displacement does not help forward motion, so raising the body vertically should be avoided. Too much vertical displacement uses extra energy and results in poor running economy.
How can a runner's maximum potential be measured?
Will I ever win the Olympic Marathon?
The faster you run, the more oxygen that is needed to sustain the supply of energy to the muscles — a process known as aerobic metabolism. As running speed increases, the body responds by increasing both ventilation rate (the volume of air entering the lungs per minute) and heart rate to pump blood and oxygen around the body more quickly. This results in an increase in the rate of oxygen uptake, known as VO — the amount of oxygen extracted from the air in the lungs each minute — which is measured in milliliters of oxygen, per kilogram of body weight per minute (ml/kg/min).
In an ideal world, runners would be able to increase their oxygen uptake to match the rate at which energy is required. But unfortunately this is not the case, because there comes a point when it is impossible to supply any extra oxygen to the muscles. At this stage, the body has to obtain energy without using oxygen — this process, known as anaerobic metabolism, causes fatigue. When a runner has reached the limit of their oxygen uptake capacity, they have achieved their "maximum oxygen uptake" value, or VO2 max. The higher that a person's VO2 max is, the faster they should be able to run before experiencing fatigue. Scientists around the world use an athlete's VO2 max value as the definitive way of assessing their capacity for endurance exercise.
Scientists have shown that VO2 max can be improved by training, resulting in physiological adaptations that include the utilization of more alveoli in the lungs (small air sacs where oxygen diffuses into the bloodstream), enhanced cardiac output (the volume of blood pumped by the heart each minute), and a greater density of capillaries surrounding the muscles. However, even with training, there is a limit to how much VO2 max can be improved, because it is largely determined by genetic factors. So, if you want to be an Olympic marathon champion, you need to choose your parents carefully.
Need to know
VO2 can be calculated using the Fick Equation:
VO22 = Q × (CaO2 – CvO2)
(CaCO2 - CvCO2) is also known as the arteriovenous difference, where:
Q = cardiac output
CaCO2 = arterial oxygen content (traveling from the lungs to the muscles)
CaCO2 = venous oxygen content (traveling from the muscles to the lungs)
What affects recovery rate after intensive exercise?
Why can't I catch my breath after I stop running?
At slow speeds, the body's demand for energy is low, so the rate at which oxygen is supplied to the muscles to help break down carbohydrate or fat for energy is also low, and can easily be met from oxygen in the air that is breathed into the lungs. The equal matching of energy demand with oxygen supply, resulting in the release of energy, occurs during aerobic respiration. This process produces energy at a sufficient rate for low- and moderate-intensity exercise, with minimal fatigue, meaning that it can be sustained for prolonged periods of time. However, as running speed increases, so, too, does the body's demand for oxygen. When the rate at which oxygen can be supplied to the muscles to produce energy no longer meets the rate at which energy is required, an additional means of providing energy needs to be found.
When faster running and high-intensity exercise cause this situation to arise, the breakdown of carbohydrate occurs without oxygen being present — a process known as anaerobic respiration. Unlike aerobic respiration, anaerobic respiration does not involve the breakdown of fat — this fuel can only provide energy through aerobic respiration.
It is simply not possible for anyone to supply oxygen at the rate required for very high-intensity exercise. The higher a person's maximum oxygen uptake (VO2 max), the more likely they are to be capable of meeting their energy needs through aerobic respiration, whereas individuals with a low VO2 max quickly have to resort to fatigue-inducing anaerobic respiration when running speed increases. One of the main factors that differentiates elite from non-elite endurance runners is that those at elite level can run at higher speeds and exercise intensities using aerobic respiration alone to support energy provision.
At the cessation of high-intensity exercise, the body will have produced an amount of energy without the presence of oxygen, thus incurring an "oxygen debt" — the difference between the amount of oxygen that the body required, and the amount it was able to take in. This debt needs to be repaid when exercise stops, and is the reason why people breathe rapidly and deeply after intensive exercise. Carbon dioxide is also exhaled during the rapid breathing. Elite runners can increase their oxygen uptake rapidly in response to an increase in work rate, so they develop less oxygen debt and their recovery time afterwards is shorter.
What is lactic acid, and why does it build up during exercise?
At the end of a sprint, why do my legs feel like jelly?
While anaerobic respiration results in the rapid provision of energy for high-intensity exercise, it also produces a fatiguing by-product called lactic acid. If running speed remains high, and anaerobic respiration and the consequent production of lactic acid continues, the muscle cells become acidic, which inhibits the metabolic pathways that break down glucose to produce energy. This is actually a safety mechanism, since it helps to prevent the body from harming itself during extreme exercise, and causing injury or permanent damage. As a result, the rate of energy production is forced to slow due to the build-up of lactic acid.
Elite athletes are known to be able to tolerate higher levels of lactic acid than non-elite athletes during exercise, and are also able to clear lactic acid from their blood and muscles more efficiently when exercise has stopped. Their welldeveloped respiratory and cardiovascular systems mean that they can quickly supply high volumes of blood to the muscles to deliver oxygen and remove the lactic acid and carbon dioxide. The length of time that breathing rate remains elevated after exercise will depend on the intensity of the exercise and the fitness of the individual, and an active recovery, consisting of light jogging and stretching, has been shown to result in a more rapid recovery than stopping all movement completely.
Contrary to popular belief, there is little scientific evidence to suggest that lactic acid causes the muscle soreness that is often experienced one or two days after rigorous exercise. However, it does cause a painful "burning" in the muscles during high-intensity exercise, making rapid, coordinated movement difficult and forcing runners to slow down, and sometimes even causing an unsteady, "jelly-like" feeling. One of the reasons why sprinters cannot sustain their pace over longer distances is due to the build-up of lactic acid in their muscles and blood.
What are the main physiological changes that occur with aging?
Am I getting too old for this?
As with any organism, the human body deteriorates with age, a process that normally starts after adulthood is reached in the early or mid-20s. The underlying mechanisms are unclear, but it would seem likely that this is due to a combination of "wear and tear" and lifestyle. While aging is inevitable, the rate at which it occurs can be slowed through a combination of exercise and nutrition.
One of the principle organs of the body that becomes less efficient with age is the heart. Older cardiac muscle contracts more slowly, resulting in a smaller volume of blood being pumped around the bloodstream with each beat. By the age of 90, scientists have shown that the output
of the heart is only 50% of that in someone in their mid-20s. This reduces the capacity to deliver oxygen to the muscles. Concurrently, there is an age-related reduction in the muscles' ability to use the oxygen that they receive, mainly due to a drop in the density of mitochondria in the muscle cells — the "powerhouse" structures where energy is produced.
Strength peaks at around 25 years of age, but can decrease by 25% or more by the age of 65. This is due to a loss of protein from the muscle fibers, and a consequent decrease in their size and strength. As a result, powerful movements and speed decline with age. There is also a decrease in bone strength, resulting from a loss of calcium and reduction in bone density, an issue that is more prevalent in women than men.
Studies have shown that the age-related decline in physiological capacity can be reduced with exercise, resulting in aging that successfully maintains lifestyle and physical capabilities. For many, this will improve quality of life and longevity. Even in older people who have not exercised, targeted exercise programs have resulted in significant improvements in aerobic capacity and strength. While peak performance over shorter running distances where speed, strength, and power are critical tends to occur in the mid-20s, endurance runners often find they can sustain better performance and peak capacity much later in life.
Is running performance dictated by nature or nurture?
Am I going to be a winner over 100 m or the marathon?
While training and coaching are fundamental to successful running performance, our genetic characteristics have a major impact on the events that we are good at. One factor that plays a large part in dictating whether a person is predisposed to either sprinting or endurance running is the composition of the muscles. Each muscle consists of many millions of fibers, which contract when they receive an electrical signal from the nerves. This contraction is fueled by the breakdown of molecules such as glycogen (the body's storage carbohydrate), and while some fibers are able to do this in the absence of oxygen, others are more readily able to contract when oxygen is present. Those fibers that can contract rapidly without oxygen are known as fast-twitch or type 2 fibers — they contract rapidly, but fatigue quickly. Those fibers that utilize oxygen to breakdown fuel, on the other hand, contract more slowly, but take much longer to fatigue. Consequently, they are known as slow-twitch or type 1 fibers. Not surprisingly, individuals with a high proportion of fast-twitch fibers are better endowed for sprinting, while those with a high proportion of slow-twitch fibers are better able to perform endurance running. The proportion of each muscle fiber type varies from muscle to muscle and is largely genetically determined, so the chances of being an elite runner will largely depend on genetic characteristics. Having said that, training and coaching can improve performance over any distance — indeed, although muscle fibers are either predominantly slow or fast twitch, there is evidence to suggest that endurance training can promote changes within fast-twitch fibers, and convert them into fibers that are more predisposed to endurance running.
Other characteristics that determine whether a runner will be good at sprinting include reaction time, strength, and flexibility. Endurance runners require a well-developed cardiovascular system and a high oxygen uptake capacity (VO2 max). All of these can be developed through training, but the extent to which improvements can be achieved will still be dependent, to a degree, on genetic characteristics.
(Continues…)
Excerpted from "Running Science"
by .
Copyright © 2017 Quarto Publishing plc.
Excerpted by permission of The University of Chicago Press.
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