The central nervous system (CNS)
During endurance training the CNS adapts to the specifics of the training demand. Thus, as a result of training the CNS increases its working capacity and improves the nervous connections required for a well and co-ordinated function of the organs arid systems. Fatigue, which often impairs training, occurs at the CNS level Thus decrease in the CNS working capacity is a major cause of fatigue. The struggle against fatigue is a battle engaged by the nervous centres in order to maintain their working capacity.
The increment of the CNS endurance and its optimal status ought to be one of the main concerns in training. The coach may facilitate this by selecting adequate and optimal means of training. Uniform work with moderate intensity improves and strengthens the entire activity of the CNS; namely, its neuro-muscular co-ordination specific for endurance activities. Similarly, long duration endurance activity performed under increasing levels of fatigue increases nervous cell resistance to stressful work (Ozoltn, 1971).
Willpower is a paramount ingredient in endurance training. It is mostly required when work has to be performed in a state of fatigue, or when the level of fatigue increases as a result of prolonged activity. This is even more obvious when intensity is an important component of training. The required level of intensity cannot be maintained unless the athlete's desire and will order the nervous centres to continue the work or even increase it (i.e., at the finish). Human beings do hold a great ileal of endurance reserves. Such reserves may be maximized only by appealing to the athlete's will to defeat his/her weaknesses which may often result from fatigue. Thus, an important training objective is to increase pain tolerance so that the athletes can psychologically tolerate the hurt, pain, and agony of training and competitions.
During endurance training the organs and especially the system which supplies the oxygen (respiratory system) become well developed. In fact certain organs are devel-oped in accordance to the training method employed. Thus, interval training strengthens the heart, while high altitude or long duration training increases the O2 utilization capabilities (Ozolin, 1971). However, the aerobic capacity relics on the development of the respiratory system and correct breathing.
As far as breathing is concerned, it plays an important role in endurance training. It has to be performed deeply and rhythmically, where an active exhalation is critical for an adequate performance. Most athletes have to learn how to exhale, to evacuate from the lungs as much air as possible from which the O2 had already been ex-tracted. Otherwise the concentration of O2 in the freshly inhaled air will be diluted and performance will be adversely affected. A forceful exhalation is even more impor-tant during the critical phase of a race/game, when an adequate supply of O2 enables one to overcome the difficulty.
A high aerobic capacity positively transfers to the anaerobic capacity. If an athlete improves his/her aerobic capacity the anaerobic capacity will also improve since he/she will be able to function longer before reaching an 62 debt, and will recover more quickly after building up an O2 debt (Howald, 1977). This finding is of significant importance for most sports where the anaerobic capacity is an important component. By improving aerobic capacity most team sports would maximize their technical and tactical knowledge. Therefore the improvement of aerobic endurance must be a permanent goal for the vast majority of athletes.
A strong aerobic capacity also stabilizes speed. During the competitive pliase of many sports anaerobic capacity is emphasized. But very often the consistency of anaerobic performance is affected by exaggerated stressful, intense work. Thus, in order to prolong a successful performance when anaerobic capacity is an important component of training, aerobic types of activities have to be introduced in training. In such cases training lessons stressing aerobic, long duration endurance, pray the role of alternating activities of various intensities. Under this new circumstance the body can regenerate and thus increase the durability of anaerobic power. The same concept is also valid for the unloading (tapering) phase. Prior to important competitions when the athletes reduce their training demands, training lessons of aerobic activity ought to be introduced to replace stressful intensive activities. As a result, the body will regenerate since the. load is lighter while the degree of training is not affected. Howald (1977) implies that there is a definite trend showing that athletes using long duration sub-maximum training do have higher anaerobic thresholds (the blood level of lactic acid rises above the resting level) than those using a higher percentage of high intensity endurance and interval types of training. Consequently, on the basis of the above realities coaches should revise their training concept and introduce into their training programs a much higher percentage of aerobic activities.
For sports which demand maximum exertion, and during the initial stages of those requiring sub-maximum exertion, energy is produced in the absence of O2 by the anaerobic system. Energy contributed by the anaerobic system is directly related to the intensity of the performance. For example, if an athlete runs a 400 m race and a velocity of 7.41 m/s the ergogenesis (the production of energy) is 14% aerobic and 86% anaerobic while running the same distance with a velocity of 8.89 m/s the ratio is 7.7% aerobic and 92.3 anaerobic (Razumovski, 1968). Therefore, it appears that the utilization of the two energy systems is dependent not only on the distance of the race but also on the classification or the level of performance of an athlete. From the above example, it is also obvious that the two systems can provide energy in various proportions. The proportion of the aerobic component increases as the distance increases and the intensity decreases. Ozolin (1971) claims that the body's anaerobic capacity is affected by the CNS processes which facilitate an athlete to continue intensive work, or work under exhausting conditions. It is also suggested that the anaerobic capacity is affected by hyperventilation, or the provision of extra O2 prior to the start by inhaling additional O2 through increasing the rate of respiration.
Specific training in the respective sport is the best method of improving the anaerobic capacity. However, as explained above, anaerobic training has to be often alternated with aerobic training. For sports which endure longer than 60 seconds, aerobic training should predominate. The anaerobic type of training, like the overemphasized interval training in North America, will not necessarily make an athlete (competing in sports of a duration longer than 2 minutes) faster, that is helpful for the first part of the face only
The speed reserve
One of the factors which affects endurance, especially specific endurance, is the speed reserve. Its importance in cyclic sports may often be determinant, although many coaches are still unaware of it, or disregard it. However, speed reserve is considered to be the difference between the fastest time achieved on a distance much shorter than the racing distance (i.e., 100 m) and the time achieved over the same short distance during a longer race (i.e., 800 m) . In Older to have any validity the lest has to be performed during the same period of time. If an.athlete is capable of covering a short distance very fast; he/she will be able to travel longer distances at a lower speed more easily. Under audi circumstances, an athlete with a higher speed reserve would spend less energy to maintain a given speed as compared to others with a lower reserve.
A speed reserve test may be performed as follows: At first the coach should determine the distance to be tested. For mid distance running events, a standard speed distance (100 m dash); for swimming, either 25 or 50 m (or one length of the pool); while for rowing 500 m and canoeing 250 m. Then the athletes should be tested to determine the maximum speed with which they can cover the standard distance. The following step should be to test the athlete's speed over the standard distance (i.e., 100 m) while he/she competes or is tested over the distance in which he/she is specialized.
Let 11 seconds be the maximum speed over 100 m and 12.4 seconds the time achieved over 100 m while ninnmg 400 m. The difference (1.4 seconds) is considered to be the speed reserve index. The larger the difference, the higher the speed reserve. A good speed reserve and a systematic specific endurance training will lead to high performance in the chosen event. Similarly, provided that the athlete has a good speed, the smaller the index the better the specific endurance. Therefore, although this aspect of training is inadequately researched, it is obvious that there is a strong interdependence between speed reserve and the athlete's abilities to reach a high performance. An athlete running 100 m in 10.6 seconds even without too much specific training would cover 400 m in 50 seconds (a speed reserve of probably 1.8 seconds and a mean speed of 12.5 seconds). However, an athlete with a speed of 12 seconds/100 m would have a hard time, or may even be unable to perform a similar time over 400 m. Therefore, speed in general, and a speed reserve in particular may be a limiting factor in an athletic progress.