Some readers will be tempted to skip this "boring science Section." I urge you to per severe because knowledge of the basic principles of exercise physiology will help you under stand how your body responds to exercise. You'll learn why you can't train at race pace every day, why interval training is necessary, why recovery is an essential part of training, and why the training methods recommended in this guide will lead to improvements in performance. This knowledge will help you understand key concepts throughout this guide.
THE CARDIORESPIRATORY SYSTEM
The cardio respiratory system--the key system in all endurance activities, including cycling--consists of the heart, blood vessels, blood, air passages, and lungs. The cardio respiratory sys tem provides a pathway to extract oxygen from the air and transport it throughout the body to where it is needed, and transports carbon dioxide from the working tissues to the lungs for release into the atmosphere. The cardio respiratory system plays an important role in transporting glycogen (the storage form of blood glucose, a sugar) from the liver to the working muscles to produce energy. And it provides a pathway to move by-products of energy production, such as lactic acid, away from the muscles. Most endurance training is designed to create adaptations that increase the transport and utilization of oxygen, which in turn increases performance.
------------- The heart is a muscle that pumps oxygen-rich blood throughout
the body.
The Heart
The heart is a specialized muscle (myocardium) made up of four chambers: the right atrium, the right ventricle, the left atrium, and the left ventricle. The right half of the heart pumps oxygen-poor blood to the lungs, a process known as pulmonary circulation. The left side of the heart pumps oxygen-rich blood from the heart to the other organs and the muscles; this is known as systemic circulation.
The cycle starts when oxygen-poor blood enters the right atrium. From there, the blood travels to the right ventricle, then to the lungs. At the lungs, carbon dioxide (CO2) is released from the blood into the lungs and exhaled. When you in hale, oxygen (O2) is absorbed from the air through the lungs and into the blood. The blood then travels to the left atrium and from there to the left ventricle. The blood leaves the left ventricle through a huge artery called the aorta, which divides into smaller arteries leading to the rest of the body.
The arteries subdivide into smaller and smaller vessels until they become capillaries, the tiniest blood vessels, which run through all the body's tissues. Capillaries are where gases (particularly O2 and CO2) and nutrients are exchanged between the blood and the tissues. The blood then leaves the tissues as the capillaries form venules (small veins), then into larger and larger veins and back to the left atrium.
The heart is a strong muscle, but it is not strong enough to pump blood throughout the en tire body unassisted. For the blood to return to the heart, it must overcome gravity. This is effected by a mechanism known as the "muscle pump." One-way valves, located at close intervals in all the veins, prevent blood from flowing backward through these vessels. As muscles in the legs con tract, the veins are "squeezed," causing blood in the veins to be pumped toward the heart. It is theorized that because of the muscle pump, pedaling at a cadence of 90 rpm or greater increases blood return to the heart due to an increased number of contractions. This phenomenon also occurs in the thoracic (chest) region due to changes in pressure that occur while breathing.
Auto-regulation of Blood Flow
The human body has the ability to direct blood flow to where it is most needed. This process is known as auto-regulation. Blood flow is directed by means of vasoconstriction (narrowing of the blood vessels) and vasodilatation (widening of the blood vessels). When the body is at rest, the skeletal muscles, kidneys, and liver receive about the same amount of blood, which totals about 65 to 70 percent of all the blood flow in the body. When we do anything that takes the body out of a resting state and increases metabolism in any area, blood flow is redistributed to supply the increased need in that area.
During exercise, metabolism is greatly in creased at the working muscles. As muscles become active, they require more oxygen to work effectively, so blood flow is increased to the muscles doing the work. During vigorous endurance activities, approximately 80 percent of blood flow is redirected to the working muscles. There is also a large increase in blood flow to the myocardium to support the increased workload of the heart.
Blood flow also increases to the skin-to help cool the body-and to the brain. To compensate for the large increase in blood delivery to the working muscles, blood flow to other areas, such as the liver and kidneys, is reduced.
Auto-regulation takes some time to occur. By warming up before training or a race, you redirect blood flow to the muscles before it's needed, and therefore increase performance.
Consuming a meal greatly increases the amount of energy required by the digestive system, so, after eating, blood flow is redirected to the digestive organs. To prevent the digestive system from competing with the working muscles for available blood, it is important for athletes to time their meals in context with training or racing. If your muscles are demanding extra blood at the same time that your digestive system is trying to do its job, neither may get what it needs, and the result can be gastrointestinal distress and suboptimal performance. Athletes vary in the amount of time needed between eating and exercise.
Blood
Blood is composed of plasma (the liquid part of blood), hemoglobin (red blood cells), and white blood cells.
Plasma, which accounts for about 55 percent of the blood, is the mechanism by which the other constituents are delivered to the body's tissues. Being about 90 percent water, plasma is a good heat conductor and plays an important role in cooling the body. Plasma also plays a role in decreasing blood acidity, through the process of bicarbonate buffering, and in transporting CO2 to the lungs. Plasma is responsible for transporting about 2 percent of the body's oxygen needs.
The other 98 percent of the body's oxygen requirements are delivered by the red blood cells. Red blood cells contain hemoglobin that are constructed from a globin protein and a heme ring containing four iron molecules. When oxygen binds with the iron molecules, each heme ring carries four oxygen molecules. Hemoglobin normally has a life span of about three to four months; this is shortened by increased physical activity. The body continually produces hemoglobin to replace what is lost. Hemoglobin is thick and requires plasma for transport through the body.
The percentage of hemoglobin in relation to whole blood is known as the hematocrit. Hematocrit is determined by spinning blood in a centrifuge. The heavier hemoglobin and white blood cells settle to the bottom, and the plasma floats to the top. The average individual's hematocrit is approximately 45 percent.
If you follow cycling, you have probably come across the term hematocrit in relation to blood doping, in which additional hemoglobin is added to the blood to increase oxygen transport. At a hematocrit above 50 percent, however, blood starts to become too viscous to flow properly. This can and often does lead to cardiovascular "incidents." Exercise physiology textbooks often cite cyclists as examples of deaths related to blood doping.
Within the context of exercise physiology, white blood cells, which make up less than 1 per cent of the blood's volume and play a key role in fighting illness, are not of great concern. But three important jobs that blood performs are of great concern in this context, gas exchange, nutrient delivery, and thermoregulation.
Gas Exchange
Oxygen and carbon dioxide move from areas of high concentration to areas of low concentration until equilibrium is established. The greater the difference in concentrations between adjacent areas (such as body tissues), the faster the rate of diffusion.
During exercise the working muscles use oxy gen to produce energy, which causes a decrease in oxygen concentrations in the muscle. Oxygen therefore moves from the oxygen-rich blood in the capillaries to the oxygen-depleted cells in the adjacent muscles. The now-oxygen-poor blood returns to the heart and thence to the lungs. Here, oxygen is in high concentration, so it enters the blood, replenishing its oxygen level.
Carbon dioxide moves in a similar manner. As the muscles work, carbon dioxide builds up, creating a pressure differential between the tissues and the blood. Carbon dioxide therefore diffuses into the blood. When the CO2-rich blood reaches the lungs, the CO2 diffuses into the CO2-poor air in the lungs, to be exhaled from the body.
Blood Glucose
Commonly known as "blood sugar," blood glucose is an important source of energy used by the muscles during endurance activities. Glycogen (a form of glucose) is stored in the muscles for energy production, and in the liver for future use. During exercise, muscles use up the glycogen stored there, so glucose moves from the blood into the muscles to replenish the supply. This in turn lowers blood glucose, so glycogen in the liver is mobilized into the blood to restore blood glucose to normal levels. This process is regulated closely by insulin and glucagon to keep blood glucose fluctuations to a minimum.
ENERGY SYSTEMS
The body requires energy to perform any type of movement. Energy systems may be aerobic (chemical processes requiring oxygen) or anaerobic (chemical processes that don’t require oxygen). Both systems come into use when Cycling. The chemical processes discussed here occur within tissue cells-for our purposes, muscle cells.
Carbohydrates, fats, and proteins are three sources that, once broken down, provide energy in the body. Through digestion, carbohydrates are converted to glucose, which enters the blood and is stored as glycogen in the muscles and liver. Glycogen can provide energy relatively quickly.
Fats, when broken down, provide more energy per gram than glycogen, but they require a longer period of time to provide energy, and they require that more oxygen be present.
The body breaks down protein for use as a main source of energy only when carbohydrates and fats are not available-in other words, in a starvation situation. If your body is using protein for a main energy source, you are in trouble.
The body can’t directly use carbohydrates, fats, or protein for energy. All of them must first be converted to an energy source known as adenosine triphosphate (ATP). The body breaks ATP into adenosine diphosphate (ADP) and a phosphate (P). It is only by breaking that chemical bond that energy is released in a form that muscles and organs can use.
There are four basic "energy systems," or pathways, through which ATP is made available for use. The first is the small amount of ATP that is stored within the muscles. This energy is immediately available and requires no oxygen to use, but stored ATP is good for only about two to three seconds, after which it is depleted and must be re-formed.
The second energy system is known as the ATP-PCr system. In this system, phosphocreatine (PCr) donates a P to ADP to re-form ATP, which can then be broken down again for more energy.
This system does not require oxygen and is good for about three to fifteen seconds. The limiting factor in this process is the minute supply of immediate ATP (which provides the necessary ADP) and the stored PCr.
The third energy system is anaerobic glycolysis, in which glucose and glycogen are broken down to form ATP. This system, which is good for about fifteen seconds to two minutes, provides a lot of energy relatively quickly and does not re quire oxygen. Anaerobic glycolysis ends with the formation of lactic acid. This occurs due to the high speed of glycolysis, lack of sufficient oxygen, and the inability of the body to transport excess hydrogen (a product of glycolysis) at high speeds.
The excess hydrogen combines with pyruvic acid to become lactic acid. The intensity, speed of glycolysis, and presence of oxygen determine lactic acid production. At high intensities the body continues to build up lactic acid in this manner.
Whereas the ATP-PCr system alone is good only for about fifteen seconds of energy production, PCr continues working during glycolysis to assist in ATP production.
These first three energy systems-good for producing short bursts of speed or power-come into play when you accelerate for a breakaway or a sprint to the finish. Because these systems function without oxygen, they can provide energy only for brief periods. For any activity lasting more than two minutes (that is, the majority of your riding), the body must use oxidative processes.
The fourth energy system is oxidative phosphorylation, which requires oxygen and, although it does not supply energy as quickly as the other systems, provides larger amounts of energy over a longer period. Oxidative phosphorylation proceeds by two chemical pathways: aerobic glycolysis and beta-oxidation.
Aerobic glycolysis uses glucose and glycogen as fuel. In this pathway the chemical steps of glycolysis occur in the same manner as in anaerobic glycolysis with two exceptions: glycolysis requires oxygen and requires more steps and time. During aerobic activities, you are working at a much lower intensity level in comparison to anaerobic activities. Due to this, aerobic glycolysis runs more slowly than anaerobic glycolysis, and the hydrogen ions don’t bind with pyruvic acid and are not converted to lactic acid. Instead, hydrogen is transported to the electron transport chain (a chemical process that produces ATP), and pyruvic acid can be converted and transported to the Krebs cycle (citric acid cycle). The Krebs cycle in turn sends more hydrogen to the electron transport chain for a much larger energy gain. Due to the hydrogen being transported to the electron transport chain, there is no excessive buildup of lactic acid. To say it simply, these chemical processes provide energy through oxidative processes by creating ATP. You will get 39 ATP per molecule of glycogen.
Aerobic glycolysis provides a lot of energy relatively quickly, but the body stores only a limited amount of glucose. Trained cyclists have about 2,000 kilocalories (Kcal) of stored glycogen. Once these stores are depleted, you will "bonk," or "hit the wall." If you have been riding any length of time, you have probably experienced this feeling of having no energy and wishing you were home on the couch. This is why it's important to replenish glycogen stores during long rides. Beta-oxidation, the second pathway, oxidizes fat for energy. This process takes longer than aerobic glycolysis but provides about ten times more energy (about 460 ATP per molecule of fat, compared to 39 ATP per molecule of glycogen). Beta-oxidation requires a much larger amount of oxygen to be present to form ATP. The body stores considerably more fat than glycogen, so fat constitutes a virtually unlimited fuel source within the context of a race. Glycogen, however, is required to drive the process of beta-oxidation, and when glycogen stores are completely depleted, the body can’t effectively convert fat to energy.
How does this apply to Cycling? The energy systems work on a continuum. For example, when you begin pedaling on a nice easy recovery ride, your body almost instantly uses up its stored ATP and quickly shifts to ATP-PCr, then to glycolysis.
As the ride continues, your body switches to using fat in order to spare glycogen. For the rest of the ride, oxidative phosphorylation is the main source of energy. Intensity also determines whether the body is using glycogen or fat as a primary energy source. The higher the intensity, the more the body relies on glycogen; the lower the intensity, the more the body relies on fat. This is why the majority of your training should focus on developing oxidative systems for endurance performance.
Anaerobic sources of energy, however, should not be overlooked. Let's say that you're 500 meters from the end of a race when the sprint starts.
You stand out of the saddle and start sprinting.
During the first second or two, your body uses stored ATP, after which it switches to the ATP-PCr system for the next three to five seconds, then to anaerobic glycolysis for up to two minutes. That should see you to the end of the race. But what if you miscalculated the distance to the finish line? After about two minutes of anaerobic glycolysis, your sources of instant energy are depleted, and large amounts of lactic acid have built up in your legs. Your muscles hurt and you have no option but to slow down, hopefully right at the finish line.
Anaerobic energy systems are improved through conducting interval training.
MUSCLE FIBERS
Each muscle is composed of thousands of muscle fibers of three basic types: slow-twitch (ST) fibers (also known as slow oxidative, or type I fibers), intermediate fibers (fast oxidative glycolytic, or type IIA), and fast-twitch (FT) fibers (fast glycolytic, or type IIB). Slow-twitch fibers are more useful for en durance events due to their high oxidative (aerobic) capacity; fast-twitch fibers are better for power due to their high glycolytic (anaerobic) capacity. Inter mediate fibers fall somewhere in between.
Muscle composition is determined genetically and can’t be altered. Most people are born with about 50 percent ST and 50 percent FT, but some people have a higher percentage of one or the other.
(The percentage of FT includes fast-twitch and intermediate muscle fibers. Typically half of the FT percentage consists of intermediate fibers.) Elite en durance athletes, such as pro cyclists, may have up to 90 percent ST fibers, whereas a world-class power lifter may have up to about 70 percent FT fibers. Al though these individuals were born genetically pre disposed to their sports, they had to develop that gift in order to excel. This does not mean that you can’t compete well as a cyclist if you do not have a high percentage of ST fibers, but it does decrease your chance of becoming a professional rider.
Fast-twitch fibers are larger and have a higher glycolytic capacity than ST fibers, enabling them to produce power quickly, and without oxygen. The downside is that they fatigue quickly as well. FT fibers are important for track cyclists, who must generate large amounts of power over short distances. Even for endurance cyclists, though, FT fibers can’t be overlooked because they are critical in sprinting. (You may notice that strong sprinters usually have larger legs than the pure climbers.) Slow-twitch fibers are smaller in size and therefore don’t produce as much power; but they have a high oxidative capacity, so they tire more slowly than FT fibers. ST fibers have a higher capillary density, which allows more oxygen to be delivered to the muscle cells. ST fibers also have more mitochondria, the organelles within the cells where energy is produced using the oxidative sys tem. The more oxygen that can be brought into a muscle and the more mitochondria that are avail able to produce energy, the better the muscle can perform in an endurance event.
Intermediate fibers can be recruited to either end of the spectrum by specificity of training. If an athlete trains for power, the intermediate fibers will lean more toward power production. If an athlete trains for endurance, the intermediate fibers will lean that way. Intermediate fibers will not per form as well as FT or ST fibers and can’t change their characteristics, but they provide valuable assistance to FT or ST fibers.
The most accurate way to determine an individual's muscle fiber composition is through a biopsy, usually in the gastrocnemius (one of the calf muscles). This is performed by inserting a special needle and removing a plug of that muscle. The sample is then sliced, stained, and examined under a microscope. The extraction process, which is painful and usually expensive, is not recommended for the recreational athlete. You might be able to reduce or eliminate the cost, however, if you can find a university that's looking for research volunteers. Universities that have the capability to conduct muscle biopsies are always conducting research of some form or another.
A simpler way to make a general assessment of your muscle fiber composition is by determining where you excel. If you perform better at longer distances, you probably lean more toward ST fibers. If you perform better at sprints and short, steep climbs, you probably have a lower percent age of ST fibers. You can also determine this by lean body size. If you have a tendency to bulk up when training, you may be more FT, due to the fact that FT fibers are larger in diameter than ST fibers. If you can’t increase muscle size to save your life, you are probably ST predominant.
Recruitment of Muscle Fibers
Muscle fibers are grouped in arrangements called motor units. Muscles are bundles of one hundred to six hundred motor units. For a muscle to function, of course, it must receive a signal via the body's nervous system. Nerves begin at the brain and spinal cord (the central nervous system) and branch into smaller and smaller units until they reach special nerve cells called neurons. Each mo tor unit consists of a single motor neuron and all the muscle fibers attached to it. Fast-twitch and intermediate motor units have many more muscle fibers per motor unit than slow-twitch motor units.
The body recruits the type of motor units needed to get the job done. For the majority of a race, you will hold a pace that you can maintain aerobically, which will use primarily slow-twitch motor units. As you approach the finish line and your pace begins to exceed the aerobic threshold (more on this below), the body will use more inter mediate and fast motor units. When sprinting for the finish line, the body will recruit primarily FT motor units to apply maximum power for a brief period.
Your body also recruits only the number of motor units needed to do the job. When a signal is sent through a motor neuron to the motor unit, every muscle fiber within that motor unit contracts completely. There's no dimmer switch here-it's either on or off. But not every motor unit in a muscle receives a signal to contract.
Through experience, your body knows how many motor units to recruit to complete a task.
Lifting a coffee cup to take a sip uses the same muscles as curling a 30-pound dumbbell, but your body has learned to recruit the right number of motor units so you do not slam the cup into your face. Likewise in Cycling, your body automatically and unconsciously recruits the type and number of motor units necessary. As you begin a steep climb, you usually slow your cadence and put more power into each stroke to overcome gravity.
Your legs become fatigued faster than when you're riding on the flat because your body is recruiting more intermediate and FT fibers, and more motor units overall. With training, your body learns to save energy by recruiting the fewest motor units necessary to accomplish the task.
VO2 MAX
Much training is focused on improving the capacity to transport and utilize oxygen, which has a direct relationship to endurance capacity. The most accurate way to measure progress in this area is by testing VO2 max (pronounced vee-oh two max). VO2 represents the volume of oxygen utilized by the body.
VO2 max is the body's maximal ability to de liver oxygen to the working muscles, and the muscles' ability to use that oxygen to produce energy for movement. VO2 max is commonly expressed as milliliters of oxygen consumed per kilogram of body weight per minute (ml/kg/min). A higher VO2 max indicates a greater capacity to transport and utilize oxygen and is considered the single best predictor of endurance performance.
TYPICAL RANGES FOR VO2 MAX IN ADULTS Sedentary Trained Elite Athlete Male 45-50 ml/kg/min 55-65 ml/kg/min =70 ml/kg/min Female 35-40 ml/kg/min 45-55 ml/kg/min =60 ml/kg/min
VO2 max is "trainable"-that is, anyone can increase their VO2 max with training-although the amount and speed of improvement varies from individual to individual. A sedentary individual will have a lower VO2 max than a recreational cyclist, and a recreational cyclist will have a lower VO2 max than a professional cyclist.
Although training increases VO2 max, each individual has a predetermined genetic ceiling, which can’t be broken no matter how hard an individual trains. There is also a gender component: women tend to be about 10 ml/kg/min lower than men at any given level, as shown in the table above.
Determining your VO2 max periodically will provide insight into the success of your training program. Various methods used to estimate VO2 max apply formulas that assume a linear relation ship between heart rate and VO2 max. Although these methods may give you a ballpark figure for your VO2 max, they are not accurate enough for monitoring your training. Most fitness facilities can run these simple estimations.
The more accurate way to determine VO2 max involves the use of a computerized test instrument (known as a metabolic cart) and a graded exercise test. The cyclist wears a mask covering the nose and mouth, with valves that allow breathing in room air and exhaling through a tube leading to the metabolic cart. The instrument measures the amounts of O2 and CO2 in the exhaled air and com pares these measurements to the amounts in the room air, thus determining the volume of O2 being used by the body.
The cyclist undergoes a graded exercise test on a cycle ergometer--similar to a stationary bike with mechanically regulated resistance. (Other test devices are used for other sports.) The test starts off at an easy pace and gets progressively harder as more resistance is added every two to three minutes (depending on protocol) until the cyclist can no longer continue. The highest recorded VO2 figure is considered the VO2 max. The cyclist must give a 100 percent effort and not quit early. If the cyclist doesn't push to the limit, the VO2 max is not considered max, but rather peak VO2.
The problem with this method is that it re quires specialized equipment and trained personnel and is therefore expensive to administer. One of the most cost-effective ways of having this procedure conducted is through a university with an exercise physiology department that is currently conducting research. You may be able to get tested at no cost; some studies even pay for qualified subjects. Some sports training facilities will test for a fee.
----------- Laboratory tests with an automated metabolic cart are the most
accurate way to determine VO2 max.
Let's say that you've participated in a VO2 max test and you learn that your VO2 max is 65 ml/kg/min. According to the table above, you fall into the trained category bordering on elite.
There's a strong possibility that you already know that, based on your race performance. If I had to put together a Cycling team and could know only one thing about the cyclists, however, I would not choose VO2 max as the deciding criterion. Instead, I would choose to know how well the cyclists per formed during the past season. Performance is what it's all about. You don’t train just to see your VO2 max increase; you train to improve your Cycling performance. Several factors besides VO2 max play a role in determining who wins a race, such as the rider's pain threshold, bicycle-handling skills, and use of tactics.
That said, VO2 max remains the best way to measure a cyclist's endurance capacity, and this is certainly one of the keys, if not the most important one, to Cycling success. A gradual increase in VO2 max in the span of a year is a strong indication that your training program is effective. If you're overtraining, you may see a decrease.
VO2 max can also be a good predictor of hid den potential. If you are just beginning to train or have been training only haphazardly or sporadically and still score high on a VO2 max test, it could be an indication of future performance.
ANAEROBIC AND LACTATE THRESHOLDS
Lactic acid is always being produced in the body.
At rest and at low levels of intensity, the body is able to remove lactic acid before it's noticed and causes any adverse effects. At higher intensities of work, the body is unable to supply adequate O2 due to the high speed of glycolysis. This causes the production of more hydrogen than the system can handle; this excess hydrogen bonds to pyruvic acid to become lactic acid. The point at which the body's production of lactic acid exceeds its ability to remove it is called the anaerobic threshold.
At high levels of concentration, lactic acid interferes with muscle contraction and can lead to cramping and a burning sensation in the legs.
This pain can become unbearable, forcing a rider to slow or come to a complete stop until the excess lactic acid is removed. This occurs through various mechanisms in the body: lactate buffering, conversion back to pyruvate, use of the lactate shuttle system, and the Cori Cycle.
---------- Blood lactate can be used to determine a cyclist's anaerobic
threshold for a training prescription.
There are three ways to define anaerobic threshold, all of which occur at the same point but differ in their specific markers. The first is characterized by an increase in blood lactate levels just above those normally found at rest in the individual being tested. This would be an increase of less than 1 milli-mole (mM) per liter of blood; it is known as lactate threshold.
The second, marked by a blood lactate level of 4 mM per liter of blood, is known as onset of blood lactate accumulation. Both of these methods involve a graded exercise test on a cycle ergometer.
Resistance is increased every two to three minutes until the cyclist is exhausted. The cyclist's finger is pricked and blood is taken for analysis of blood lactate at every workload.
The body copes with increased levels of lactic acid by buffering and lowering the acidity through a chemical process called bicarbonate buffering. The process of buffering causes an increasing amount of CO2 to build up in the tissue. The CO2 must be removed from the body, a process that causes ventilation (breathing) to increase exponentially. At this point, known as the ventilator threshold (VT), you are breathing hard enough that you will not be able to say more than one or two words easily.
The VT is usually determined during a graded exercise test on a cycle ergometer. When a metabolic cart is being used and gas exchange is re corded, it is usually easy to plot and determine a corresponding heart rate at VT. The VT is usually expressed as a percentage of VO2 max, but the most useful information is the corresponding heart rate. If you know that your VT occurs at 180 bpm, you can better determine your training zones-the levels of training intensity that will produce the greatest gains in endurance. I consider this the most important measure that can be obtained from a graded exercise protocol-even more important than VO2 max-because this is the precise point beyond which you want to extend your limits.
It's possible to determine VT by completing a graded exercise test without a metabolic cart. As your exercise intensity increases, note the heart rate where your breathing increases exponentially. This is the point at which rate and depth of breathing greatly increase. Conduct this test on more than one occasion to ensure that you're re cording the same heart rate. This method is not as accurate, but it will give you a ballpark figure.
Although the anaerobic threshold, lactate threshold, onset of blood lactate accumulation, and ventilatory threshold are technically different, they are basically interchangeable. To keep things simple below, I use the term anaerobic threshold.
Once you reach the anaerobic threshold- the point at which lactic acid production exceeds removal-it will not be long before you have to slow down. The closer your anaerobic threshold is to your VO2 max, the better you will be able to perform.
Take, for example, two cyclists with VO2 max readings of 65 ml/kg/min and 70 ml/kg/min, respectively. One might initially assume that in a time trial, the second cyclist would win. This may not be the case, though, if the first cyclist's anaerobic threshold occurs at 90 percent of VO2 max and the second cyclist's occurs at 70 percent of VO2max.
In this case, the first cyclist is more likely to win.
Your greatest improvements in performance can come through increasing your anaerobic thresh old. Although there can be a considerable increase in VO2 max through training, there can be an even larger increase in anaerobic threshold. Untrained riders typically have an anaerobic threshold of 50 to 60 percent of VO2 max, whereas elite cyclists' thresholds are about 90 percent of VO2 max. Two ways to increase anaerobic threshold-tempo and interval training--are discussed in Section 10.
Before you attempt that, however, you must have a solid endurance base.
Another important concept is what I call racing threshold, which is most apparent in the con text of a steady-state race such as a time trial.
In a road race, your pace increases and decreases continuously depending on what the riders in the front are doing. But during a time trial, it's you against the clock, and you try to maintain as fast and steady a pace as possible.
For any given distance, your maximum sustainable speed is your race threshold. Although not a scientific concept, race threshold is limited by the buildup of lactic acid and neuromuscular fatigue- feeling extreme tiredness in the working muscles.
Naturally, the longer the course, the slower you will ride; the shorter the course, the faster you can ride. Through experience, you learn those limits, beyond which it's all over if you turn the screws.
Inexperienced cyclists tend to turn the screws a little too much and fade as the race proceeds.
TRAINING ADAPTATIONS
The body has a surprising ability to adapt to the stress of training. Training is catabolic, but with a proper training regimen, the body adapts to this stress to build itself back up stronger than before in many different ways.
Aerobic Adaptations Much of a cyclist's training is designed to create aerobic adaptations-changes that increase the delivery of oxygen to the muscles-and increase the muscles' ability to utilize that oxygen for energy production. These adaptations lead to improvements in VO2 max, which translate into improvements in performance. The following are among the most important specific adaptations that occur with endurance training:
__Increase in total blood volume. Plasma and hemoglobin concentrations increase.
Increases in hemoglobin production usually begin three to four weeks into training.
Augmented hemoglobin concentrations in the blood deliver more oxygen to the muscles, allowing them to do more work. Initially, water loss that occurs due to sweating during training lowers plasma volume, but changes occur within the body that promote water retention in general. These changes in the blood in particular result in an increase of plasma volume, which is essential to prevent the blood from becoming too viscous.
__Increase in capillary density within the muscles. There will be a greater number of capillaries in relation to each individual muscle fiber. Gas and nutrient exchange in the muscle tissue occurs at the capillaries, so the more capillaries that exist, the more oxygen and nutrients can be delivered to the working muscles.
__Increase in myoglobin. Put simply, myoglobin is hemoglobin found in muscle tissue. The more myoglobin there is in a muscle, the greater the rate of oxygen transfer from the blood into the mitochondria of the muscle cells.
__Increase in the size and number of mitochondria.
All oxidative energy production occurs in the mitochondria, so an increase in their number and size within muscle cells leads to an increased capacity for energy production.
__Increase in glycogen stores. Glycogen stores top out at about 2,000 kCal in endurance trained individuals. (Untrained individuals store considerably less glycogen.) This provides more ATP through the use of aerobic glycolysis and beta-oxidation, enabling the body to break down fat for energy for longer periods.
__Increase in intramuscular stores of triglycerides (fats) and a decrease in adipose storage of fat. With training, the body begins to move fat from adipose stores (such as love handles) and converts it to triglycerides to store within the muscles, where it can be more quickly utilized for energy.
__Switching to burning fat sooner. The body stores a limited supply of glycogen but a practically unlimited supply of fat (70,000 kCal or greater). To spare glycogen during periods of long activity, the body learns to switch to burning fat sooner.
Another important aerobic training adaptation is a decrease in resting and sub-maximal heart rate.
The average sedentary individual has a resting heart rate of 70 to 80 bpm, compared to figures in the thirties and forties for elite endurance athletes.
To understand how this comes about, consider the "cardiac equation": cardiac output = stroke volume × heart rate Cardiac output is the volume of blood pumped by the heart per minute; stroke volume is the amount of blood pumped per beat; heart rate is the number of beats per minute.
At rest, cardiac output is low due to the body's low energy requirements. As activity increases, cardiac output increases to supply the blood needed to meet the demand. The body can’t greatly alter stroke volume, so the heart rate increases. But over time with training, three key adaptations occur: the heart chambers undergo healthy enlargement, the heart contracts more forcefully, and the blood volume increases.
The increase in blood volume allows for greater filling of the heart chambers. Larger heart chambers mean that the heart can take in more blood during diastole, the "filling" portion of the heart beat. And a more forceful contraction increases the amount of blood ejected from the heart and into the arteries on each beat. All of this means greater stroke volume. Because only a given car diac output is required by the body for any given sub-maximal workload, an increase in stroke volume allows the heart to beat more slowly.
Anaerobic Adaptations
Although the main focus of training for Cycling is aerobic, anaerobic training can’t be overlooked.
Whenever you sprint for the finish line, power up a steep hill, attack off the front, respond to an attack, or bridge a gap, the anaerobic system is called into play. This occurs off and on frequently throughout a race. To be competitive, you need to be able to respond to these situations.
Interval training and tempo work that is slightly above the anaerobic threshold will improve your body's ability to buffer lactic acid. (These forms of training are described in Section 11.) This can result in an increase in anaerobic thresh old by up to 40 percent, which will greatly increase your race threshold for any given distance. At the same time, training above the anaerobic threshold will generate even greater benefits in your aerobic performance.