The quality of endurance performance is limited by a number of factors out of which the most important are those which are related primarily to oxygen transport, energy utilization (cardiorespiratory system, blood volume, total mass of haemoglobin, oxidative enzymes, fat utilization etc.) and to neuromuscular function and economy of movement (quality of CNS and peripheral nerves, strength, speed, endurance, coordination, technique, performance) and quality of this factors can be called a physiological profile of an athlete.

For training needs, endurance can be divided into four groups according to dominant metabolism which supplies energy to muscles:

1. Speed endurance – duration 20-30 seconds, alactate anaerobic metabolism is the basic energy system ensuring motor activity at the start of movement (phosphagen system).
2. Short-time endurance – between 30 seconds and 2 (3) minutes, motor activity of high intensity is primarily supplied with energy by anaerobic lactate system (fast glycolysis).
3. Middle-time endurance – between 2 (3) minutes and 8-10 minutes, from this period on, aerobic system is dominant but the portion of anaerobic lactate metabolism can still be big (fast and slow glycolysis).
4. Long-time endurance– from approx. 10 minutes till several hours. Motor activity is ensured by aerobic energy system from more than 90 % (oxidative system).

Aerobic and anaerobic threshold

As we proceed from walking to jogging and further to running and sprinting, we gradually employ slow and then fast muscle fibres. The start of the exercise involves mostly aerobic energy system, than slowly anaerobic system is activated until it finally becomes dominant, the fibers create lactit acid (LA) the increase in which causes an unpleasant feeling in the muscles and we are forced to slow down or stop. Aerobic threshold (AT) and anaerobic threshold (ANT) represent for us a transition zone which means increasing share of anaerobic energy metabolism.

AT defines the top of easy training load and is defined as the point where LA begins to rise, usually around the level of 2-3 mmol/L. ANT is the point beyond which LA levels rise steeply. Such a range is called maximal lactate steady state (MLSS) and can vary between 3-8 mmol/L depending on every individual. An athlete can move for several hours at AT, but beyond ANT fatique appear quickly. It is the upper limit for utilizing lactate from the muscle and transition zone in which fibers of the II type (fast fibers) get involved more and more. With proper training system, it is possible to increase the intensity or velocity at the level of both thresholds. The level of ANT is highly related to success in events lasting for 15 minutes or more, such as longer running, swimming, cross country-skiing, rowing or cycling and is important for all endurance sports.

Energy System of Endurance Performance

Endurance performance is a process of long-time static or dynamic contractions of various muscles, which requires a perfect transfer of neural signals from the motor cortex (CNS) to the muscles, which have to be supplied with great amount of energy. During endurance activities, both aerobic and anaerobic energy systems (depending on the type of sport) are made use of. The closer to two minutes the duration of loading is, the lower the aerobic metabolism share in overall performance is; and the longer the duration is, the more dominant the aerobic system becomes.

Proportion of the share of anaerobic and aerobic metabolism during time at maximal movement intensity.

Anaerobic energy system

This system is the dominant contributor in exercises of high intensity lasting from 20-30s to 100 – 120s. However, with intensive activity in duration of about 2 minutes, both energy systems are balanced and with increasing time, the portion of anaerobic system decreases and for example during high intensity exercises lasting for 4-6 minutes its portion is still high, of 20-30%. Anaerobic energy system (fast glycolysis) is the term for non-oxidative decomposition of glycogen, which is not very effective. This way restores a small amount of ATP (3 units for each molecule of glucose) while producing a by-product, lactic acid (LA). Accumulating LA reduces muscle force, makes muscle contraction more difficult and leads to fatigue.

Optimizing efficiency of anaerobic metabolism is required for sports such as mid-distance events in track and field for 800 and 1,500 meters, 200 meter swimming, 200 and 500 meter canoeing, 500-1,500 meter speed skating, most events in gymnastics, alpine skiing etc.

Aerobic energy system

Aerobic energy system (oxidative system) is the primary energy source for events ranging from two-three minutes to over several hours (typical endurance sports and activities). Aerobic metabolism starts working slower and it takes 60-80 second to start producing sufficient amount of energy for ATP resynthesis because at this time interval, cardiorespiratory system starts to develop slowly into higher efficiency the and muscles start to be better supplied with oxygen which makes efficient ATP creation possible through oxidation of carbohydrates, fats and proteins. Maximal output of these systems is reached after several minutes of maximal effort with regard to given intensit.

Adaptation to Aerobic Load

The system of endurance training is a complex process which has to respect the basic natural relations and biological adaptation (training stimuli, stress) with the help of training load to reach a higher level of fitness. The strategy for endurance development draws on from basic adaptation cycle, training or performance development or such stages which form the contents on training process during whole-year training macrocycle.

Thanks to systematic aerobic load, the athlete is able to work at higher intensity of load, prolongs the duration of exercise and works more efficiently. Body adaptations which are in progress with the help of endurance training can be either acute or long-term in nature.

Acute reaction to aerobic load brings about adaptations which influence the process of energy transfer and reserves and working capability of a muscle. The time of the first reaction with the help of periodic stimuli lasts from several days to weeks. This stage includes the optimization of ATP resynthesis connected with respective homeostatic responses, activation of oxygen transfer, use of energy reserves and better coordination of working muscles, and basic morpho-functional changes in muscles. During load of lower intensity, an athlete is able to resist fatigue, train, practise or exercise for a longer time; his or her coordination gets better, recovery improves, energy stores increase and movement effectiveness grows. Adaptation to training stimuli of the same load is manifested mainly by lower heart rate (HR), blood pressure and respiratory rate.

Structural and functional changes which appear during prolonged time intervals in ordinary training are related to long-term adaptation. The result of endurance or aerobic training is for instance increased concentrations of myoglobin and haemoglobin, activity of mitochondrial enzymes, increased respiratory volume and oxygen transfer (bigger aerobic volume and performance) or increased heart performance. Main cellular and morpho-functional adaptations are for example visible in bigger size and number of mitochondria, capillar density and heart muscle adaptation. Thanks to aerobic endurance training, the volume of blood increases by 10-15 %, which means the average volume of blood increases from 5 liters to 5.5-6 liters. The quality of heart performance improves, which means that blood volume per minute pumped into circulation by the hear increases; this is related to better aerobic capacity and performance. Respiratory system performance improves, which ensures more air in smaller number of inflations, mainly thanks to bigger volume of a single inflation. A long-term type of reaction is mainly adaptation to specific performance, which lasts from several months to several years. After frequently repeated training stimuli, changes in the athlete’s body appear (the athlete’s body contains less hypodermic fat, body posture improves), muscles get stronger, during load of high intensity less lactic acid is accumulated, resting heart rate decreases, resting blood pressure decreases and both overall fitness and psychic reaction to load improve.

Training endurance abilities

The achievement of personal maximal performance in endurance sports is a long-term process. The most of top endurance athletes are aged over 25. The development of endurance involves a long training process of big volume with gradually increasing quality.

Systematic and regular endurance training usually starts around the age of 13-15 years and the individual top performance can be reached after 12–15 years of a very demanding training process. Aerobic endurance is normally developed before 13-15 years of age but it should be mainly with the help of non-specific means, exercises and non-intensive methods as a part of general fitness development and training of a young athlete.

Therefore, the main aims of endurance aerobic training are the improvement of personal limiting factors, which means mainly improving personal physiological profile and motor abilities. Simultaneously with these important goals of aerobic training, race technique and tactics experience must be improved and psychic qualities must be fixed. These goals of training are achieved with the help of the right type of training, proper training system, and methods and means of training.

Every biological improvement caused by training stimuli is carried out in cycles. The most benefits of a specific training process come together with load that matches the orginial condition with duration around six weeks. After six weeks, it is necessary to increase volume, intensity and frequency of training load, because a training program which is exceeds six weeks becomes less effective after this period. Without increasing load and variability of training, this process cannot effectively continue and the development of training and performance is slow. This six-week period is divided to four stages.

During first stage (up to about 10 days), the improvement of movement coordination is prevalent. During the second stage, energy store inreases, the performance of energy system improves and changes in the muscle structure begins (up to about 20 days). After rebuilding muscle structure, it is necessary to renew neural control of motor ability on a higher level. This is the aim of the third stage, which is finished till about 30 days. During the last stage, many systems get coordinated on a higher level such as cardiorespiratory system, vegetative neural system, hormonal system, centre of thermoregulacy, or immunity system. The fourth stage completes the whole cycle of optimal benefit of the respective training load and brings this six-week period to an end.

Zones of Training Intensity in Sports Training

Every coach should know zones for anaerobic or aerobic training. Organizing the system of loading into specific zones of training intensity is usual interest of coaches. They use several zones of load intensity to stress the importance of training in the whole range of energy systems. The number and range of training zones have been recommended in coaching literature and a standardized scale consists of up to six different intensity zones. To develop training and performance of endurance athletes, it is recommended to make use of four intensity zones, which cover entire training needs. It is important to use a single system of intensity zones following the specifics of a given sport.

Intensity Zone 1

Within this zone, load intensity is under anaerobic threshold (ANT) and it should help to improve athlete´s aerobic metabolism, which vital in most sports, especially those in which oxygen consumption represents a limiting factor of performance. Among these sports, there are for example medium- and long-track running, swimming, sculling, cross-country skiing, cycling events etc., but it is important also for other sports such as a games.

Many coaches and authors call it aerobic threshold training (AT), which develops basic functional efficiency of the cardiorespiratory system and the economy of metabolic system and increases the capacity to resist stress during effort which lasts for a longer time. The purpose of aerobic threshold training is to increase aerobic energy capacity through using a high volume of work without interruption at a constant or alternating pace. Average LA concentration is 2-3 mmol/l; a typical range is between50 – 70 % of VO_2max or 70 – 75 % HR_max. The low intensity load makes up the vast majority of a training process volume (about 70-75 % HR). It is important for achieving desirable functional improvements that form basis for training of higher intensity. Appropriate training methods of developing basic endurance within intensity zone 1 are both uninterrupted or long, slow distance methods and fartlek.

An optimum period to improve aerobic performance is the preseason period, however, evens during pre-competition and race seasons, we need regular load of lower stimuli to keep aerobic metabolism on a required level.

Aerobic compensatory training is also part of intensity zone 1. This intensity makes easier athlete´s recovery after competitions and high-intensity training which are typical of intensity zones 2 and 3. It means loading with very low intensity (about 50% of HR_max) and it can be planned for all stages of a macrocycle in order to eliminate metabolites from the system and to speed up the process of recovery and regeneration. It is training of active recovery and we can use cycling, running or swimming of low intensity for 20-40 min, which helps to speed up recovery.

Training Intensity Zone 2

This zone consists of training load which is equivalent to higher intensity of exercise but the rate of the diffusion of LA into blood is constant in relation to the rate of its removal. It is training with intensity in the area of anaerobic threshold. The main aim of the training is to improve the athlete’s ability to utilize higher LA production during long-term load, keep high intensity of load without accumulation of LA (for a period longer than 5 minutes). The ability to remove LA from blood circulation and transfer it to muscles to further use it as a source of energy is an adaptive reaction which postpones the start of fatique and improves performance. Intensity is around ANT or slightly below of above it, which means between 3 mmol/l LA and personal level of ANT. The range of load intensity is between 75-85 % VO_2max or 80-93 % HR_max. This load helps to shift ANT curve towards higher speed of cyclic movement. Training within this zone can be further divided into two types: uninterrupted continuous or long, slow distance training and interval training, whereas both of them are of the same relative intensity. Load at the level of ANT through uninterrupted continuous or long, slow distance training and interval training are very much useful if we begin with specific endurence. This type of training together with more repetitions (between five and seven repetitions) can stimulate anaerobic metabolism without any significant accumulation of LA. This intensity is followed by hard training which is unpleasant and painful.

Intensity zone 3

The training of this intensity stimulates the increase of maximal oxygen consumption through increased need of oxygen transfer and the efectiveness of its utilization. During both training and competition, cardiorespiratory system, nervous and locomotive systems are very much stressed with load of such intensity. Better transfer of oxygen to muscle cells and especially better efficiency of oxygen utilization are important factors for better performance in sports in which the aerobic system is dominant or at least very important. The rate of LA diffusion into the blood starts to exceed the rate of utilization and the main physiological aim of training intensity zone 3 is to increase resistance to LA accumulation, the adaption to the increased creation of LA, better utilization of LA from working muscles and increasing physiological and psychological resistance to pain or spasm during training and demanding competitions. This type of load is often used towards the end of preseason and in first transition period to build the athlete’s maximum functional capacity and during competition period to maintain high level of performance.

Load intensity within this zone should be between 85 % to VO_peak or 90 (93) - 100% of HR_max. The number of repetitions performed during one training session depends on the duration of the training: the longer the duration, the smaller number of repetitions. The main training method for developing this intensity zone is mainly the intermittent method.

Training Intensity Zone 4

Phosphagen energy system (ATP-CP) is dominant in all sports which require to exercise speed and explosiveness. Trainig of this intensity can improve and maintain short-time speed-time endurance. However, this intensity has its justification also in endurance training, primarily for developing movement economy, technical and tactic skills which make use of ATP-CP system as the source of energy. Athletes have to make use of very short intervals (not exceeding 20 seconds) of short and explosive exercises of intensity over 100 % effort with resting period long enough to fully recover the source of energy. The main training method is the intermittent method with sufficient resting period.

Practical application of all intensity zones must be planned according to the athlete’s potential and performance, his or her resistance to load and according to the specific stage of the training process. The application of intensity zones to an athlete´s training is more familiar of individual sport coaches but it is validfor all sports.

Frequency of training stimuli

The frequency of training stimuli is an important part of the training process and it very much affects the improvement of training and performance. The training stimulus which follows can be applied only in the period when the athlete’s body has been fully recovered from the preceeding intensive training unit. The variability of the types of load and active recovery during the whole macrocycle is therefore very important.

The frequency of training stimuli is a variable in the training process which affects the improvement of aerobic performance, mainly during the first stage of systematic training of children, untrained individuals and young athletes. The basic frequency of training sessions at the beginning of a regular training process should be three times per wekk for children, less fit athletes or to maintain health. Performance endurance athletes need 5-7 training sessions per week and top athletes from 7 to 20 training sets.

Basic Relationships between the Variables of Training Load

Optimum results of the training process can be achieved through systematic alternation of the training contents, the size of load (volume, intensity), training means, methods, frequency of stimuli, organisational forms etc. To make the development of performance gradual and systematic, it is necessary first to increase the frequency of stimuli, then we can slowly increase the volume of intensity and the last parameter which much be increased is load intensity. Training intensity is of lower significance at the beginning of regular training but training of higher intensity usually leads to improved specific performance, faster reaching better performance, for a short time though, if required training volume has not been mastered.

Methods of Aerobic Endurance Training

System of endurance training includes a number of methods which are suitable for developing different kinds of endurance. Every method has its own characteristic effect for development of specific preconditions. Some methods can have similar impact on the athlete’s adaptation provided we use it under similar conditions. The training methods for aerobic or anaerobic endurance development can be divided to several groups:

• Uninterrupted methods
• Intermittent methods
• Fartlek

Uninterrupted Methods

These methods include continous method and method of alternating intensity.

Continuous method means load with constant level of intensity or speed. The load lasts usually for longer than 30 minutes (up to several hours). This method is used to develop basic (general) endurance, mixed aerobic-anaerobic metabolism, or to maintain the level of reached endurance adaptation. Load of lower intenisty (below 80-85 % HR _max) is suitable to develop energy resources, improving the ability to supply working muscles with energy substrate for a long time and developing movement economy. Medium or submaximal intensity is used to increase speed at ANT level. High or submaximal intensity is used in testing, in check race or in testing the ability to maintain racing speed. The possibility to incrase VO_2max is lower than when using different methods (e.g. interval training) but within training process for novices or children, even this method is able to help to improve this parameter, mainly during the initial months of regular training.

Uninterrupted method of alternating intensity

During uninterrupted load of alternating intensity, the athlete alternates, regularly or irregularly, different intensity and length of sections. Load intensity can vary from low to very high. The number, length and intensity of sections is usually planned.

Intermittent Methods

This group includes interval methods and repetition methods. The main difference between these methods is the condition of the athlete before starting the next unit. During interval training, another repetition starts with insufficient recovery of the athlete. During repetition training, another unit starts only with relative recovery after a longer pause between units.

Interval method

Interval training contains several load units of high intensity (from submaximal to maximal). As a rule, we distinguish between short, medium and long interval methods according to the time-period of load. Short intervals last between 45 and 60 seconds, medium from 1 to 3 minutes and long 3-5 minutes. Time for rest is relatively short. Resting period for short and medium interval lasts 60-90 seconds and for long interval it is approximately half of the time for which lasts one unit, or until HR decreases down to 120-130 beats per minute. It is recommended to spend the resting period with active acitve rest (walking, jogging etc.), which improves removal of LA from stressed muscles. Interval training has a great influence on cardiorespiratory system and it is the best way to increase the value of maximal oxygen consumption (aerobic perfromance and capacity). The main aim of interval training is preparation for specific competition load.

The interval method is not suitable for children and it can be applied to the youth training only with great care. Children are not ready for anaerobic load of longer duration and the youth are only developing this ability. The incorporation of intervals into youth training can lead to very steep rise in performance development in relatively short time, which is followed by stagnation or decrease in performance, or can lead to the ovetraining.

Examples of interval training:

During natural interval, load lasts for 90 seconds and rest for 60-90 seconds or until HR is as low as 120 – 130 b.p.m.

Extensive interval method recommends the load of submaximal load for 3-5 minutes followed by 3-5 minute rest. The impact of this type of interval training concerns mainly respiratory system and ANT level.

Repetition method

This type of training involves repetitions of several legs. The intensity of a repeated leg is most often at the competition pace lavel but it can also be submaximal speed or also slightly faster for a given distance. This training is not directly connected to development of VO_2max, it is related to improving or maintaining race pace which is different for milers and 10-kilometer runners. These legs are usually longer than 5 minutes. Resting period fasts from 5 to 15 (or 20) minutes.

Fartlek

This method has originated in Swedish training system and it means the play with speed.

Changes of load (intensity and length of legs) are included in training according to personal feelings of every athlete, natural conditions, profile of terrain etc. The content of fartlek is not usually given in advance. During training, the intensity or the length of legs changes irregularly. Minimum duration of fartlek training is 30 minutes.

Another kind of fartlek has originated in Polish training school. Coach determines what training means, intensity and legs are to be included in training units. The place and time of being carried out during training is on the athlete’s decision.

System of Endurance Training

Endurance training is a process which can be divided into several parts. Each part covers certain specifics of endurance development. Performance of endurance athletes is based mainly on fitness factors and during training process, general fitness and general endurance are being developed first, followed by specific endurance.

General endurance and general fitness

It is started with general ability to resist fatique during physical activity but without any significant influence on sports performance. It is very useful for leisure sport activities, for non-elite athletes to maintain basic fitness or functional and energy systems. General endurance and general fitness on a good level is the basis for athletes to achieve better recovery, increase volume and intensity of training process or higher frequency of traning stimuli etc. This type of general fitness and general endurance can be improved with various cyclic movements such as walking, running, cycling, canoing, sculling or working out on specific fitness machines.

Specific endurance

It is an ability to resist fatique during specific sports movement for a longer time period; both with low intensity of load and during competitions with hight intensity of load. Training specific endurance is closely connected to maximum personal performance in a specific sport and training system must contain large-scale proportion of specific training means, methods and intensities.

Stages of endurance training

Within the training process of endurance development, periods or stages are usually planned during which the foundations for further improvements are established. The stages must focus on specific needs of each sport. With long-term endurance development (years), we have to apply step by step improving physical and physiological preconditions in time intervals of different duration (stages) during annual training process. The length of every stage depends on the specifics of each sport. General principles of endurance development in all sports are: successiveness, adequacy, suitable volume and intensity, and gradual impelementation of specific training procedures and methods. There are several models suitable for developing aerobic performance. During simple competition model (monocycle), the athletes develop endurance in three stages – general endurance, introductin to specific endurance and specific endurance. During a two peaks model (bi-cycle) with shorter periods, two stages with two periods are usually applied – development of basic endurance and development of specific endurance.

Stages of general endurance

During this stage, the athlete creates or maintains basic level of endurance which is necessary for further development. Athletes improve general or basic specific endurance and they are able to postpone the the start of fatique during long-time load of low intensity. This stage lasts from 6 weeks to 3 months, depending on the required level of adaptation and the kind of sport and it is in progress during transitory period and preseason of annual cycle.

During this stage, any development or adjustment of training load must be carried out by increasing volume with low intensity load. This training regime does not expose the athlete to high level of effort of muscle or physiological system and the athlete trains mainly below individual ANT. This load induces glycogen depletion in the muscle, increase lipid metabolism and force the body to maintain or enhance the acquired functional adaptations within the cardiorespiratory or muscle system. The most suitable training methods in this stage are both uninterrupted methods and fartlek. Load should be mainly below 85 % of HR_max. This represents intensity zone 1 and partly also intensity zone 2. General and specific training means are usually balanced. The best training means is bipedal or quadrupedal movement such as cycling, running, walking, cross-country skiing, nordic walking, canoing, sculling or long-time working out on fitness machines.

Stages of introduction to specific endurance

The aim of this stage is to improve physiological adaptation of the athlete and focus on motor activities which are specific for a given sport. Aerobic endurance is still the main element of training although anaerobic activities start to be part of training program as well. Depending on the difficulty of motor structures and the rate of the athlete’s adaptation, this stage lasts from 6 weeks to 4 months depending on the kind of sport.

At the beginning of this stage, higher volume of load remains and intensity starts to increase slowly. When required level of basic endurance is achieved, it is necessary to include a higher number of specific traning means and intensive methods of endurance development into training process in order to further improvement of training and performance. Now, the duration of stimuli (volume) gradually shortens until it finally reaches medium levels while load intensity can move within the area of individual ANT whereas some training units can exceed ANT. This should be applied with increasing frequency towards the end of this stage. All methods, both uninterrupted and fatlek and intermittent, are suitable. All intensity zones take part in this stage; within the initial part, the volume in zones 3 and 4 is small, but in the other part, the volume is increasing so that is possible to reach higher level of training and performance. During this stage, specific training means of the given sport become prevalent in training process.

Stages of specific endurance

In this stage, maximum potential of endurance performance of the athlete must be achieved. Intensity reaches the highest level possible. To further increase the volume of high-intensity training, we must decrease volume. Duration of training units or load must respect the specifics of the sport and training is focused on the dominant energy system. This stage can last approximately for 3-5 months, during preseason and competition season in annual training cycle. During this stage, high rate of specific and race training means are involved in the training process.

The main recommended method for development and maintaining high level of aerobic performance is intermittent method. However, we never must forget to maintain good level of basic endurance through training units with load of lower intensity with the help of uninterrupted methods and fartlek.