Exercise physiology is the study of how systems of the human body integrate to perform work. For the purposes of this chapter, the focus is on understanding the physiology of training based on the energy systems and then applying it to the muscular and cardiorespiratory systems of the human body. In addition, this chapter covers how to monitor, evaluate, and manipulate training and describes physiological adaptations to different environments.
The ability of any athlete to sustain prolonged bouts of training or competition depends on the body’s ability to generate energy. The human body can be trained so it can generate hours of muscular contraction through the energy stored within the body. Energy within the human body comes in the form of adenosine triphosphate (ATP), which is considered the universal currency of the body. Three key energy sources are available and utilized to power the production of ATP. These are creatine phosphate (CP), carbohydrate, and fat.
ATP for muscle contraction is produced by three energy systems: the immediate energy system (ATP–CP), anaerobic glycolysis (nonoxidative), and the aerobic energy system (oxidative). The first two energy systems are frequently known together as the anaerobic energy system and are able to function without the presence of oxygen (O2). This energy system predominates in exercise bouts lasting up to 4 minutes. The anaerobic energy system can generate large amounts of energy very quickly; however, it is limited and provides energy for only a short period of activity. Conversely, the aerobic energy system is slower at generating energy, but it can do so for hours so that work can be sustained.
The energy systems work on a continuum, as depicted in figure 9.1. Although one energy system may be predominating, all three will work together to provide the energy needed during exercise. Energy production by each of the three systems is dependent on exercise intensity and duration. In table 9.1, the energy systems are divided based on a time continuum, and the source of energy is also provided.
The muscular system consists of the elements in a muscle cell that allow the skeletal muscle to contract and exert force. The human body requires a continuous supply of oxygen and nutrients to maintain the production of energy for its many complex functions and to sustain work during exercise. This process is facilitated by the cardio-respiratory system of the body, which consists of the heart and lungs. Together, these organs work to ensure that blood is carrying oxygen and other nutrients to active tissues (muscle, liver, and so on). This becomes especially important during exercise because oxygen and fuel are needed so the muscles of the body can continue to perform work.
Aerobic and anaerobic training lead to general adaptations of the muscular system that stimulate the cardiorespiratory system. This means the muscles provide signals for the heart and lungs. Running, swimming, and cycling provide both general and specific training adaptations. For example, all these sports give you general adaptations such as an improved heart muscle contraction rate, but it is discipline specific, meaning that swimming at a heart rate of 160 beats per minute does not prepare you to run at a heart rate of 160 beats per minute, but it did help improve general fitness. Improvements in the capacity of the muscle fibers are specific to the sport and event being participated in. This is primarily because muscle fibers learn to repeat the movements used in training. An example is the difference in muscular training that is received for the legs from running versus that of swimming. Both forms of training help develop muscle characteristics that can be utilized to train for any sport; however, running requires the right amount of ligament strength and an adaptation to the muscular and cardiorespiratory strain of bearing body weight that swimming does not. In these next sections, you will learn how muscles work, come to understand the different types of muscle, and find out how the heart and lungs adapt to training.
Skeletal muscle contraction is controlled by the brain through the central nervous system (CNS). The motor cortex is the area of the CNS that memorizes muscular contractions and commits them to memory. Muscles contract when messages from the CNS submit impulses to the nerves that connect to motor neurons, which directly innervate and control the muscles. The force produced from a muscular contraction is a function of the number and size of the motor neurons that are recruited and the frequency with which they are stimulated.
Force production is dependent on the type of muscle fibers recruited to perform the work. There are three primary types of muscle fibers: slow oxidative (SO), or Type I; fast oxidative glycolytic (FOG), or Type IIa; and fast glycolytic (FG), or Type IIb. Muscles are made up of all muscle fiber types. The distribution of muscle fiber type is dependent on training, genetics, and the function a muscle serves. Slow oxidative muscle fibers are associated with endurance performance and promote the production of energy through the aerobic energy system. Fast oxidative glycolytic and fast glycolytic muscle fibers are associated with strength and power performance and produce energy that is generated through glycogen and ATP–CP stored within the muscle cell. The sport of triathlon requires a significantly higher proportion of SO muscle fibers; however, it is still critical to develop the capacity of both the FOG and FG muscle fibers so that a full spectrum of energy capacity can be utilized.
Muscle fibers operate on a concept known as the sliding filament theory and are made up of many proteins. The two key proteins needed for contraction are actin and myosin. Myosin has a head-like structure, and when a muscle fiber is stimulated to contract, it binds to actin to create what is known as a muscle crossbridge. When multiple myosin heads are bound to actin, they pull one protein past another in an oar-like fashion, causing the muscle to contract. As the amount of force required by the muscle increases, more and more muscle crossbridges must be formed.
Several factors influence the number of muscle crossbridges formed and sustained during a bout of exercise. These include muscle temperature, oxygen delivery, acidity and electrical charge of the muscle, and fuel supply. Increases in muscle and whole-body temperature inhibit the ability of actin and myosin to bind and contract. In addition, the ability of the body to off-load oxygen to the muscle decreases as body temperature increases, and as a result muscle fatigue occurs. Oxygen delivery is a function of not only temperature but also the acidity of the blood and muscle.
Acidity (pH) of the blood is defined in physiology by the accumulation of hydrogen ions and lactate. The pH that can be handled during training and competition is dependent on the buffering capacity of the muscle, which is the body’s ability to “soak up” and tolerate hydrogen that is produced from energy metabolism. Buffering capacity is limited by the amount of bicarbonate in the muscle. The accumulation of hydrogen is detrimental because it interferes with the ability of actin and myosin to bind. The hydrogen that is produced can be “picked up” by bicarbonate (hydrogen + bicarbonate) and converted to carbonic acid, which is immediately broken down by the body into water and carbon dioxide. Water is then recirculated into the body’s system, and carbon dioxide is off-loaded at the lungs. Lactate that is produced remains in the blood and either accumulates or is used as a fuel source by the other tissues of the body. As pH continues to decline, less oxygen can be off-loaded to the muscle, more muscle fibers must be recruited to complete any exercise bout, and the amount of oxygen needed for exercise continues to increase; together, these factors will result in fatigue.
The electrical charge of a muscle is primarily maintained by two key electrolytes, sodium and potassium. Every time a muscle contracts, it is a function of the muscle’s sodium and potassium levels moving through its gates and manipulating its electrical charge. A positive charge relaxes the muscle, and a negative charge contracts the muscle. The ability of a muscle to continue this process is highly dependent on the concentration of electrolytes available to it. Sodium and potassium can be significantly lost in sweat during exercise; this is why it is important that an athlete maintain fluid and electrolyte balance while in training and competition (see chapter 27 on hydration for more information). Sodium depletion through decreasing the consumption of sodium-containing foods, drinking only water, or not properly replacing electrolytes lost in sweat can lead to significant issues during prolonged exercise, including muscle cramps and thus fatigue, especially in the heat. These electrolytes are also key in assisting with muscle recovery.
The last factor in determining the number of muscle crossbridges needed to sustain work is fuel supply. Muscles require energy in the form of ATP to be available from creatine phosphate, carbohydrate, and fat sources. In the sport of triathlon, it is important that an athlete’s muscles learn to predominantly derive energy from fat as a fuel source as well as from glycogen (carbohydrate) stores. As glycogen reserves become depleted, the ability to sustain muscle contraction begins to diminish, and an increased number of muscle crossbridges must be formed to continue producing the same amount of work. During competition, athletes will progressively fatigue if they lack sufficient energy supply in the form of carbohydrate, showing the importance of developing a training and competition nutrition plan that will sustain the amount of carbohydrate needed. You’ll learn more about this process in chapter 26 on nutrition.
The heart, lungs, and many blood vessels of the body form a continuous circuit that transports blood throughout the body and makes up the cardiorespiratory system. Blood consists of plasma (approximately 55 to 65 percent), leukocytes and platelets (approximately 1 percent), and red blood cells (approximately 38 to 45 percent). Red blood cells (RBCs) are the key component responsible for transporting oxygen throughout the body to working tissues. There are many RBCs in the human body, and within each RBC are approximately 250 million molecules of hemoglobin. Hemoglobin (Hb) is the protein that transports oxygen; thus it is key in providing oxygen-enriched blood to the body’s tissues. An increase in blood volume through increased water, electrolyte, RBC, and hemoglobin production is a key adaptation an athlete receives from endurance training.
The lungs and other organs involved in breathing are responsible for providing oxygen-rich air and removing carbon dioxide through gas exchange. For each breath a person takes, oxygen is supplied and carbon dioxide is removed. With training, athletes adapt the muscles associated with the lungs so that breathing rate becomes more efficient. A larger amount of air is exchanged with each breath.
The response of the cardiorespiratory system to exercise training is characterized by the measures of cardiac output (CO), maximal oxygen-carrying capacity (
O2max), and the fractional percentage of maximal oxygen consumption (% O2max) needed to perform a set workload. Cardiac output is the amount of blood pumped by the heart over a 1-minute period. It can be defined as heart rate (HR) multiplied by stroke volume (SV), where HR refers to the frequency the heart contracts and SV is the volume of blood ejected from the heart with each contraction. O2max is the maximal amount of oxygen the body can consume. It is found by multiplying CO by the (a-
)O2 difference, which is the average difference between the oxygen content of the arterial and mixed venous blood. Oxygenated blood is supplied to the working muscles via the arterial blood vessels, and oxygen remaining in the blood once it has passed through the body is returned to the lungs via venous blood vessels.
Adaptations to training require a repeated stimulus for approximately 2 to 4 weeks before the body fully takes on the stress that has been applied to the muscular and cardiorespiratory systems. Training adaptations for triathlon involve both local muscular endurance and whole-body cardiorespiratory endurance; however, it is the training performed by the muscular system that stimulates and drives adaptations of the heart and lungs. As a result, it is important that the effects of training be understood first and foremost in regard to the muscular system.
Training can be classified based on the aerobic and anaerobic energy systems. Aerobic endurance training encompasses those adaptations that result from training at intensities at or below the anaerobic threshold (defined as the highest intensity a steady state of exercise can be maintained without significant rises in blood lactate). The intensity of training is intended to be only so high as to ensure it can be sustained for a period similar to or greater than the actual competition duration. The goal of aerobic endurance training is to help the muscles perform more efficiently through increasing and improving structural adaptations that promote the use of oxygen. This is accomplished by increasing the capacity of SO muscle fibers and potentially by converting FG fibers to FOG fibers, which improves their use of oxygen.
Four key structural adaptations can occur as a result of aerobic endurance training: (1) an increase in the number of capillaries supplying the muscle fibers, (2) an increase in muscle myoglobin content, (3) an increase in the number and size of the mitochondria in skeletal muscle, and (4) an increase in concentrations of oxidative enzymes. Capillaries are the very small blood vessels that are embedded deep within the skeletal muscle. They serve as the direct transporter of oxygen and nutrients (e.g., carbohydrate, electrolytes) and also remove carbon dioxide and metabolic by-products such as lactate and hydrogen ions. An increase in the number of capillaries that surround the muscle promotes oxygen delivery. Myoglobin is the muscle’s equivalent of hemoglobin. The increase in myoglobin that occurs as a result of aerobic training improves the ability of the muscle to utilize oxygen. Myoglobin accepts the oxygen from hemoglobin and transports it to areas of the muscle that need it most. This primarily entails the oxidative pathways that exist in the mitochondria. Mitochondria are considered the powerhouse of the muscle cell. They utilize the oxygen that is delivered to create ATP through the oxidative metabolic pathways. These pathways are further enhanced by the increase in oxidative enzymes, and as a result the body is able to increase the utilization of fat as a fuel source during exercise. This boosts the amount of energy derived through aerobic metabolism and also spares muscle glycogen, both of which are critical for sustaining performance in endurance events.
Anaerobic interval training for endurance events increases the amount of energy that can be efficiently produced through anaerobic glycolysis and the ATP–CP energy systems. Interval training improves the buffering capacity of skeletal muscle and, if designed properly, improves maximal power, strength, and anaerobic capacity. This type of training, frequently referred to as high-intensity interval (HIT) training, involves repeated exercise bouts of short to moderate duration (30 seconds to 5 minutes). The training intensities associated with HIT are above the anaerobic threshold and are predominantly based on critical power outputs and paces at and above what is sustained during competition. After a period of HIT, athletes can perform the same workload with lower levels of lactate and a decreased rating of perceived exertion. In addition, higher work intensities can be sustained for longer, and the athlete also tolerates greater levels of lactate while removing lactate from the muscles at a faster rate.
The improvements in work capacity reported with HIT are a result of three key adaptations. The first key adaptation is an increase in the enzymes associated with the production of ATP through anaerobic glycolysis and the ATP–CP energy system. This allows for an improved utilization and oxidation (generating energy through oxygen-based metabolism) of carbohydrate as a fuel source. High-intensity interval training increases use of the oxidative energy pathways and decreases the amount of lactate that is spilled into the blood at a specific workload; this is a result of carbohydrate continuing through what is known as the Krebs cycle of the mitochondria to further generate ATP.
In addition to improving the oxidation of carbohydrate, the body is also capable of utilizing more carbohydrate as a result of HIT. High-intensity interval training increases the number of muscle fibers that can be recruited to do work and thus increases work capacity. As a result, higher levels of carbohydrate are utilized, and a greater amount of lactate is produced at the end of a maximal effort, thus indicating an increase in the capacity of the anaerobic energy system. The ability to tolerate high lactate levels also stimulates the development of bicarbonate. As discussed previously, bicarbonate soaks up hydrogen ions that are produced during the breakdown of carbohydrate through nonoxidative energy production. When bicarbonate levels are higher, more hydrogen ions can be removed, thereby allowing for continuous formation of a greater number of muscle crossbridges and sustainment of more forceful muscle contractions, resulting in improved performance.
Another significant benefit that comes from HIT is a decrease in the core body temperature reached during exercise. As core body temperature—the amount of heat stored by the body—increases over time, work output will begin to decrease. At a set workload, the energy cost of submaximal exercise is substantially decreased after HIT where maximal power has been improved. As a result of the improved exercise economy, the body does not accumulate heat as rapidly and muscle function is not impaired as quickly, thus resulting in a higher sustainable work output.
The development of neuromuscular patterns has also been suggested as one of the benefits of HIT. High-intensity interval training facilitates adaptations in the neuromuscular patterns that are recruited during race-pace activity. As was mentioned earlier, the brain has a region known as the motor cortex. Within this region of the brain, muscular patterns are stored along with the number of motor units required to perform them. During competition, these patterns are called upon to facilitate performance, and those muscular patterns that have been utilized the most will predominate during this time of physical stress.
Resistance training is another means of improving performance through adaptations in the muscular system. There are three key goals with this type of training. The first is to improve muscular strength as defined by the maximum force that can be generated by a muscle or group of muscles. A second goal is to improve muscular power, which is the explosive aspect of strength, by performing a specific movement at a given speed. The third goal of resistance training for endurance athletes is to improve muscular endurance. This is defined as the ability to sustain repeated muscular contractions at a fixed workload for an extended period of time. Increasing the amount of force that can be produced at a given speed, and improving the ability to sustain that force over a distance, will enhance performance because the muscles will not be as susceptible to fatigue.
Adaptations in the cardiorespiratory system are a direct result of adaptations of the skeletal muscles to the work they are performing, and in turn this stimulates the heart and lungs to adapt. The effects of training on the cardiorespiratory system are seen as increases in O2max and cardiac output. Because of genetic factors both will eventually plateau; however, training adaptations and the economy of the cardiorespiratory system can still be significantly improved. Improvements in O2max and cardiac output are a function of three key adaptations occurring in the body: (1) Total blood volume is increased; (2) the heart becomes stronger as a result of the work it is doing; and (3) oxygen delivery to the muscles of the body is enhanced. As a result of these adaptations, the heart is capable of more efficiently pumping larger amounts of blood to the working muscles with every contraction, and in turn oxygen is delivered and carbon dioxide, along with other by-products of metabolism, is removed more efficiently. These adaptations are described further in the following paragraphs.
The increase in total blood volume that occurs with endurance training is the result of a two-phase process. In the first, hormones stimulate an increase in total body water retention over a 10-day period, and the second is an increased production of red blood cells over an approximate 4-week period. The improvement in total blood volume benefits athletes through three different mechanisms: (1) an improved ability to regulate body temperature, as the increased water content allows for improved heat dissipation and thus an increase in sweat rate; (2) an improved efficiency and functionality of the heart muscle; and (3) an increased oxygen-carrying capacity as a result of the increased number of red blood cells.
The heart is a muscle that responds to training much like skeletal muscle. A load can be imposed on the heart by increasing the number of times it must contract or the strength with which it contracts. With repeated contraction, the heart muscle becomes stronger and more efficient, and as a result, the heart does not have to contract as frequently to perform the same amount of work. In addition, prolonged engagement in aerobic long-distance training enhances stroke volume, with a resultant reduction in resting and exercising heart rate at a specific workload. Using the formula for cardiac output (stroke volume × heart rate), it can be understood how heart rate is reduced at submaximal exercise intensities as a result of an increase in stroke volume. During maximal exercise, the increase in blood volume causes an increase in maximal cardiac output, and as a result an increase in O2max is seen. Another benefit of a stronger heart and a larger stroke volume is a faster recovery after a hard or near-maximal bout of exercise.
The improvement in total blood volume and heart efficiency also results in an improved delivery of oxygen to the working muscles. In addition, because there is an increase in red blood cell volume, the concentration of hemoglobin is increased. This raises the oxygen-carrying capacity of the blood, and the increase in blood volume improves the transit time for supplying oxygen to working muscles. Together, these lead to improved endurance performance.
Adaptations in the lungs also facilitate the improvements in O2max and cardiac output. With training, the lungs become more efficient and can increase the amount of oxygen supplied with each breath; as a result, ventilation is decreased. Ventilation is a function of tidal volume and the frequency of breathing (tidal volume × frequency). Tidal volume is the volume of air that is inspired or expired with each breath. The primary means for a decrease in ventilation is the increase in tidal volume, which allows for a lower frequency of breathing. The improved capacity of the lungs during exercise is an important factor in improving endurance performance.
Monitoring training provides a coach and athlete with a physiological snapshot of what is occurring in an athlete’s body as a result of the training stimulus. The monitoring system utilized should objectively evaluate an athlete’s training status and include assessment of the training load, identify the effects of a training intervention, and further serve to refine training design. Measures of adaptation to training should be taken daily and summed to provide an overall picture of the physiological changes occurring throughout the training cycle.
The key physiological predictors of triathlon performance are submaximal exercise economy and maximal velocity and power output. These predictive measures can be objectively evaluated for a triathlete through physiological measures of blood lactate, heart rate, rating of perceived exertion (RPE; see figure 9.2), and submaximal oxygen uptake. Monitoring can be accomplished through field- or laboratory-based measures depending on what an athlete and coach prefer and have access to in regard to physiological testing equipment. Regardless of whether the measures are performed in a laboratory or field setting, it is most beneficial to understand submaximal levels of work output in relation to maximal exercise capacity; thus submaximal efforts can be viewed as a relative percentage of maximal effort.
Monitoring the training load helps coaches understand how an athlete’s body is tolerating the physical training being performed. Training load tells us how much work an athlete performed and how hard it was to do it. It is defined as duration multiplied by intensity (as perceived by the level of exertion). Research has shown that people can have different tolerances to the same training load. There are three potential levels or perspectives of monitoring: the athlete’s, the coach’s, and the sport scientist’s or sports physician’s view. Each has a degree of responsibility for monitoring how well an athlete is adapting to training; however, each has a different perspective on what is monitored and how it is done. The most important level is that of the athlete because she can monitor herself intrinsically on a daily basis and provide feedback and data that may inform the coach, scientist, or physician.
One of the most effective ways to monitor the training load and the athlete’s responses and adaptation (positive or negative) is through the regular use of athlete-focused training journals. Both quantitative physical data and more qualitative data (feelings, moods, and emotions) should be recorded on a daily basis and reviewed regularly with coaches and assisting support staff. If introduced and monitored effectively, training journals can become a very valuable tool for raising athlete and coach awareness as well as supporting long-term athlete development and preventing overtraining.
The quantitative physiological data needed for calculating the training load can be easily assessed by monitoring either heart rate (HR) or the rating of perceived exertion (RPE) in relation to training velocity or power output. The training load can thus be defined as RPE or HR × duration (in minutes). The addition of a score from the satisfaction scale (see figure 9.3) adds a subjective psychobiological measure that includes the athlete’s mental perspective on how well he believed the training session went. This is important because psychological state can significantly alter the training load. When using a satisfaction scale, the satisfaction component is added to the formula to look like this: RPE or HR × duration × satisfaction score. You can then see how your mental view played into how hard a training session seemed to be, which is very valuable to a coach or an athlete trying to understand why something just doesn’t work on certain days or why it works extremely well on other days. For example, let’s assume an athlete doesn’t sleep well the night before a 6-hour bike session and gives it a satisfaction score of 9 because she got her butt kicked by her training partners. The next week she completes the same session but sleeps well the night before and performs well in practice; she gives this session a satisfaction score of 2. As you can see, the training load was significantly reduced from the week before, showing you how an athlete’s satisfaction plays into how much she is loaded by a training session.
An example of a calculated training load utilizing RPE and a score from the satisfaction scale can be seen in table 9.2; an additional example utilizing HR is provided in table 9.3.
Another key aspect of monitoring training is recovery. The primary measures that can be monitored to examine adaptation to training are the number of hours an athlete sleeps, the quality of the sleep, and a total quality recovery score (TQR; figure 9.4). The amount and quality of sleep an athlete achieves are two of the greatest predictors of recovery and how well he can handle the training load. TQR was developed around the RPE scale to emphasize the relationship that must exist between recovery and the difficulty of a training session. The goal is to understand the athlete’s ability to recover from different types of training sessions. If he recovers very well from a 1-mile repeat session where the RPE is 9 out of 10 but not from a 200-meter repeat session with the same RPE, it tells us he will require more recovery after those training days, and so usually a coach or athlete training himself will allow more time in between hard training sessions. TQR also indicates the type of training sessions where the athlete has to be more proactive at recovery and make it a priority. According to the principle of supercompensation, the greater a training stimulus, the more recovery will be needed. When recovery is monitored closely along with the training load, the negative effects of a high training stimulus can be prevented. Athletes who recover adequately are able to tolerate the training load, whereas athletes who have limited or no recovery cannot tolerate a high training load. If an athlete recovers from training, the body can adapt, and he can then move forward with training.
Monitoring the training load along with an athlete’s satisfaction with training and ability to recover can be a valuable process, but it often takes patience and reflection to understand what it all means. The training load should be examined in relation to the performance gains obtained from training underneath the total load and the loads tolerated at various intensities, with the goal of understanding how much of a load is necessary for subsequent training cycles to produce similar improvements. When examining the training load and the types of training used to achieve the load, a coach or athlete must consider how this form of training was tolerated psychologically and how well an athlete recovered in appropriate amounts of time considering the way training was designed and delivered. Over time, the goal is to find patterns of loading that result in the best physiological and psychological rewards and to avoid training styles that result in poor training tolerance and adaptation.
Criterion workouts and training courses are two of the best and simplest ways to monitor adaptations to training. Measures of blood lactate, HR, and RPE can be monitored during these training sessions to provide objective and subjective feedback regarding training. Criterion workouts and training courses typically involve completing (or attempting to complete) a set number of repetitions or covering a distance in a given amount of time. This may include choosing to perform a long-course swim session at race pace (e.g., 4 × 1K at pace identified) or finding a 10-mile (16 km) loop to run and evaluating how well training is going based on how quickly you run it. Recovery times between repetitions are usually manipulated, either shortened or lengthened, based on how fit you are. As you get fitter, you should be able to shorten recovery times, and if you are away from training for a long period, more recovery is given so you can complete the work.
Physiological Adaptations to Training in Extreme TemperaturesTriathletes attempting to train at altitude or in very hot or cold temperatures should be aware of important changes in the cardiorespiratory and muscular systems that occur in these environments. A hot environment will increase the strain of work by raising core body and muscle temperature and the heart rate associated with a given work intensity. The sweat rate is higher, and the potential for dehydration increases as the body attempts to dissipate heat.
Successfully competing in the heat requires acclimatization, or the physiological adaptations that improve work tolerance after a chronic change in environment. When first arriving in a hot environment, it is best to train in the cooler parts of the day and to slowly increase the amount of training volume done in the heat of the day that best mimics competition. Once the body has adapted to low-intensity training volumes, acclimatization can be furthered by introducing sessions that require intensity. Acclimatization to a hot environment is first marked by decreases in HR and RPE during a training bout, then by an increase in sweat rate to help maintain a lower core body temperature. The timeline for these adaptations can be seen in figure 9.5
Athletes who train and compete in cold environments must focus on maintaining core body temperature. This requires dressing appropriately (and not removing too much clothing during training or competition) and ensuring adequate fuel and fluid intake. The loss of too much body heat can result in hypothermia, which alters the physiological systems of the body. When hypothermia begins, the ability to produce muscular contractions is significantly reduced, and work output will begin to decline. As hypothermia continues, core body temperature will decline to dangerous levels, with a further decrease in the quality of work output. Indicators of hypothermia include a rapidly declining HR and increased shivering as the body attempts to maintain its temperature through muscular contractions. Adaptations to the cold can be seen in figure 9.6.
Designing training is never an easy task. Each athlete is a unique person and requires an individualized plan that will optimize training stress. The key to manipulating the training load is variation of the three key stressors (frequency, intensity, and volume) and periodization of the energy systems while following basic yet important principles of training.
Any training program should progressively increase the training load in a manner that promotes a high quality of work. For most athletes, the most effective way to increase the training load is by using the step method. This method increases the training load through the manipulation of one variable every week for a period of 2 or 3 weeks. A week of regeneration in which the training load is significantly reduced should then follow before any further increases in training load occur.
Increasing the training load is first accomplished by establishing the frequency at which training will take place. Once this has been established, the volume of training is increased to the point desired, and then increases in training intensity should follow. Volume and intensity of training should not be increased simultaneously. Training volume is the total duration of time spent in training or the number of miles or kilometers run, bike, or swum over a period of time (usually a week; however, most athletes calculate total volume for a training period as well). Training intensity is how hard the athlete works. It typically is expressed as a percentage out of 100 percent. For example, an athlete completes a session at 80 percent of maximal effort. The other way to describe intensity is based on pace. For example, an athlete completes a 50-mile (80 km) bike training session at a pace she is targeting for the 112 (180 km) miles of an Ironman bike. Volume should be increased by no more than 10 percent at a time and can be manipulated by increasing the duration of a training session, the number of repetitions performed, or the distance or duration of a repetition. The intensity of training can be manipulated by increasing velocity, power output, and the number of repetitions and decreasing the rest interval between repetitions.
Periodization is the key to ensuring training load is manipulated appropriately. Periodization can be defined as the structuring of a training program to produce optimal performance at a given time. It is critical that the energy systems be structured appropriately to ensure that an athlete has a solid aerobic foundation and does not increase fitness too rapidly or train too intensely for a prolonged time, which can lead to overtraining. Periodization of training is traditionally divided into three phases that may be repeated several times throughout the year depending on the number of identified competitions:
Preparatory
Competitive
Transition
The preparatory phase is further divided into general and sport-specific speed and power development. The energy system components of these phases are divided into the following eight elements during a training cycle: active recovery, general endurance, aerobic endurance, lactate threshold, aerobic interval, anaerobic power, anaerobic tolerance, and maintenance. An example of a single training cycle based on a traditional plan for periodization of the energy systems is provided in figure 9.7. Although it is important to always be tapping into some aspect of each energy system, the focus of training should always predominate.
Successful periodization of the energy systems requires that specific principles of training be applied to each athlete. There are four key principles that should be incorporated into periodization: progressive overload, individualization, specificity, and reversibility. The proper integration of these principles should lead to higher levels of performance for athletes of all capabilities.
Progressive overload is an intentional increase in training volume or intensity to create a training adaptation that will improve performance. For short periods, athletes can handle an increase in stress that taxes their maximal work capacity. For a muscle to build strength, it must be gradually stressed by working against a load greater than what it is used to, and in order to increase endurance, muscles must work for a longer time or at a higher intensity than what they are accustomed to performing. Various methods have been examined in regard to imposing an increase in training load. The three primary methods that have been documented include a linear and continuous method, a step method, and a method known as flat loading.
The linear and continuous method involves athletes continuously training at workloads that are higher than those normally encountered. There is not an intentional unloading until after the season is completed. The step approach, which was described earlier, allows for a progressive increased loading, with a phase of unloading that also allows the athlete to adapt and regenerate. Flat loading places the highest volume and intensity an athlete can tolerate in the first 3 weeks of a training cycle and is followed by a week of unloading for regeneration and relaxation. It is intended only for experienced national and international athletes and should be used only after the general endurance phase of the preparatory cycle. Regardless of the loading method utilized, the key to successfully adapting the body to any training demand is recovery that in turn allows for regeneration. Incorporating the regeneration period into the training cycle is important to remove both the physiological and psychological fatigue that has accumulated during the period of overload.
The principle of individualization refers to designing training based on each athlete’s physical capabilities, utilizing his strengths and improving his weaknesses in a progressive manner so he does not ever limit his strengths. This aspect of training should integrate the objective use of physiological assessment measures as well as the subjective understanding a coach has from working with an athlete. In the sport of triathlon, it must also take into account the differences in an athlete’s physical build and the sport discipline he is most suited for and has a background competing in. For example, an athlete who enters triathlon and is built with broad shoulders and a significant amount of upper body musculature from swimming and competing in flat-water kayaking will need to train at a different run volume and intensity than an athlete who comes from a running background. In the same sense, because of a lack of upper body strength and musculature, the amount of swim training a runner will be capable of performing will determine how much swim volume and intensity he can handle. Placing both of these athletes on the same training program will push them past their tolerance level in a nonprogressive manner and will only result in injury and a poor quality of training.
The principle of specificity refers to training athletes toward the relevant elements of what will be necessary for successful performance. This includes designing training to match the volume and intensity of competition as well as preparing an athlete for things such as the strategy she will need to use in racing each of the sport disciplines and the environment she may have to compete in. For example, if an athlete must learn to take repeated attacks during the cycling component of the race and then come off the bike to run above her lactate threshold for the first part of the run, this should be progressively incorporated into the training cycle to mimic the specificity of the race.
Reversibility is the training principle that refers to the gradual loss of work capacity as a result of decreases in training frequency, intensity, or volume. Periodization should be designed to provide an athlete with regeneration periods where there is little or no physical activity; although rest and recovery are important, these time periods should never be so long that there is a significant loss in physical fitness. The loss of physical work capacity is known as detraining. Significant decreases in physiological work capacity occur after approximately 2 weeks of inactivity; thus it is recommended that no more than a 2-week regeneration period be incorporated into the training plan.
Physiological Adaptations to Training at AltitudeAir pressure is reduced at altitude, which means less oxygen is taken in with every breath of air. This results in hypoxia (the rate of oxygen supply cannot meet the oxygen used by the body). The initial reaction of the body is depicted in figure 9.8. Endurance athletes intentionally travel or live at altitude to improve oxidative capacity and increase the RBCs and Hb available to transport oxygen to the exercising muscles. Training at altitude can also improve the body’s ability to utilize fat as a fuel source and the muscles’ ability to buffer lactic acid.
There are several different approaches to altitude training; the two most promising are living high, training low and living high, training high and low. These allow an athlete to successfully maintain training quality, which is key for optimal performance. Aerobic work capacity begins to significantly decrease at 4,900 feet (1,500 m), and despite acclimatization, an athlete’s maximal work capacity will not be the same as at sea level; thus the quality of HIT and aerobic training sessions is compromised at altitude.
Using the live high, train low approach, athletes live for the majority of the day at altitude (above 4,900 feet and no higher than 9,800 feet, or 3,000 meters). The athlete trains at or below 4,000 feet (1,200 m) and ideally as close to sea level as possible. Utilizing the live high, train high and low approach, athletes complete low-intensity training sessions at altitude and train low for any sessions that are of a high intensity or prolonged aerobic effort at a critical race intensity (i.e., long threshold training sessions that are relative to race intensity).
Another option is simulated altitude systems, which allow an athlete to live at altitude without leaving the comforts of home. Most athletes prefer to stay close to family and friends, and many cannot afford the time away from work to train at altitude. Simulated altitude training systems also allow an athlete to perform low-intensity training in a hypoxic environment by breathing reduced-oxygen air through a mask.
Physiology provides an explanation for how the body’s muscular and cardiorespiratory systems adapt to training. As a result, it is the basis for every aspect of training, whether it be strength training, tapering for competition, or even choosing tactics for an-open water race. Physiology is also critical in understanding the response to training in different environments. Monitoring the body’s response to a training plan is a key component for refining training design regardless of the level an athlete competes at. Periodization and the implementation of key training principles will provide a structured plan for long-term development in the sport of triathlon.
