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                   Endurance 耐力

Endurance is a wide concept, which represents the ability to maintain a certain intensity over a period of time. An individual's endurance is relative to such factors as intensity (speed, force, load, tension, etc.), technical efficiency, the muscles adaptation to the movement, psychological state during execution of the work, etc…. The different types of endurance are determined by intensity and duration of the effort.
From a duration point of view we can divide them into:

• short duration (up to 2 minutes )
• medium duration (approximately 2-8 minutes )
• long duration (above 10 minutes )
• ultra duration (more than two hours )

Based on physiological criteria and intensity level endurance is influence by both: aerobic and anaerobic capacity. Both of them can be related to general and muscle specific endurance and are share interrelated factors in most sports.

Aerobic capacity

Aerobic capacity is ability to produce work by utilizing fuel in presence of oxygen. Aerobic capacity is a function of maximal oxygen uptake (VO2MAX). VO2MAX represents the body's maximum total aerobic metabolic rate. It can be measured using gas analyzer during a maximal stress test. The difference between the oxygen content of the inhaled and exhaled air is measured to find out how much oxygen (O2) was consumed per minute. This value is expressed as liters per minute of oxygen and can vary from 2 to 7.5 liters/minute. However, it is more common to express the V02 max of an individual in relation to their body weight in kilograms to see their aerobic efficiency. These values range from 20 to over 90 milliliters per kilogram of body weight per minute. The highest values of VO2MAX per kilogram of body weight are found in cross country skiers, where these levels are directly related to performance. On the other hand, the highest absolute V02max values are found in rowers, where weight is relatively unimportant.

In terms of training for improvement of aerobic capacity, one must remember, that training above V02 max is not very effective, because rapid fatigue will reduce the volume of work an athlete can do. On the other hand, the minimum intensity required to force changes in adaptation is about 50% of V02 max or 75% of maximum heart rate. Although the rate of improvement may be higher with continuous methods (running for 60 minutes, cycling for 2 hours), high intensity intervals (running 10 x 800 meters, cycling 3 x 30 minutes) allow greater volumes at desired intensity loads and better control over the training process. Improvement of aerobic capacity can be achieved at lower effective intensity levels with higher duration. One must remember that effective changes, especially on the muscle level, are produced at lower intensities. This is very important since reducing intensity is desirable for many young, recreational and recovering from injury athletes trying to reduce the risk of overtraining and injury. From my experience and observation increasing duration of work beyond 40 minutes per session at lower intensity (of 70-80% of VO2MAX), can produce as much benefit as a shorter duration at higher intensity work.

The two main factors determining performance in endurance events are:

1.maximal oxygen capacity(VO2 MAX) and
2.Muscle adaptation

An athlete's VO2 MAX, and the percentage of VO2 MAX they can use for an extended period of time, will determine average speed of their race. The amount of time this speed can be sustained depends on muscle adaptation. Muscle adaptation encompasses structural changes, which allow the muscles to become more efficient through adaptation to specific types of work related to specific sports.

Although changes in VO2 MAX and muscle adaptation occur simultaneously, the rate of change is significantly different. The separation between VO2 MAX and muscle adaptation can be illustrated by the following examples. A long distance runner, after taking two weeks off, loses on average 2-3% of VO2 MAX but overall performance (measured as the time to exhaustion at a given speed) can be reduced as much as 24%. If you would take a group of professional cyclists preparing for a big event like the Tour de France and test them in February and later in July. Most likely in July, through training, they can expect approximately 5% improvement in VO2MAX. In the same period of time, enzymes responsible for aerobic metabolism would be doubled, resulting in four fold higher mitochondrial enzyme levels. As you can see, in both cases, changes in muscle adaptation are more rapid, than those of V02max. In the eyes of most educated coaches, improving muscle adaptation is the main target in the training process.

The main factors determining an athlete's speed in an endurance race are:

1. V02max and
2. Economy of motion or technique.

The time this speed can be maintained is a function of glycogen storage in the muscles and efficiency in fuel utilization. VO2 max is used to improve the ability to keep high average race pace. However, the amount and quality of work that can be done to improve VO2 Max is determined by the amount of work done to improve anaerobic threshold (AT).

The anaerobic threshold refers to the maximum workload, where it can be met by aerobic metabolism. Increase of workload at this point leads to involvement of anaerobic metabolism, which is reflected in accumulation of by product of this process-lactic acid. Up to that point the balance between lactic acid production and removal can be maintained. AT provides the most accurate starting point for monitoring training in endurance sports. Training near AT level seems to improve aerobic capacity most, while reducing the risk and occurrence of overtraining. There is also proof that training above AT level too frequently will cause a loss of aerobic capacity. As a matter of fact, athletes from sports like long distance running, swimming, cycling, rowing and cross country skiing spend annually approximately 80-95% of their time training at or below AT level.

Since VO2 Max is, in great degree determined by genetics, the focus of the endurance athlete should be directed toward better use of their given potential through raising their AT. Individuals may have similar VO2 max values but differing AT levels and, therefore, performance times may differ substantially at a given intensity of exercise. As was mentioned earlier, a high anaerobic threshold, relative to VO2 max, will benefit the endurance athlete. However, it should be noted that the possible benefits to performance of a high relative AT decreases as the intensity of exercise approaches or exceeds VO2 max.

Anaerobic Capacity

The influence of anaerobic capacity on the final outcome of maximum performance is greater as the duration of performance gets shorter. Utilization of energy without oxygen is relatively short lasting. However, it is under these conditions that humans can achieve the highest possible performance. In sports, which require maximal effort (sprints, jumps, throws weight lifting, etc.), energy is produce with little or no presence of oxygen. During longer events, anaerobic metabolism can be utilized in the beginning of the event, at the finish and, in some sports, during the middle of the event, for the tactical purposes or responding to an opponents attack. For example, in cycling, without a well developed anaerobic capacity, you will not be able to escape or respond to sudden attacks by your opponents. It worth mentioning that during the start of the race or in events like jumps, throws, and weight lifting of under 15 seconds duration, energy is derived from a chemical compound (creatine phosphate), without any by products. However, if the event lasts longer than 20 seconds, later in the race, when aerobic capacity is not sufficient to cover the level of intensity or speed needed, the energy comes from anaerobic breakdown of fuel (glycogen). An athlete's ability to maintain or dramatically raise intensity or speed of performance comes with the price of a waste product (lactic acid) which, due to its acidic character, disturbs body biochemical balance and leads to fatigue, thus reducing the ability of the muscles to contract.

Training to improve anaerobic capacity should be focused on improvement of anaerobic metabolism rate, which will produce more of the lactic acid. Well organized anaerobic training will, as well, improve the athlete's ability to reduce the negative effect of the lactic acid by developing buffering abilities, which convert lactic acid to a weaker acid, which does not offset the body's chemical balance, allowing longer duration of high intensity. Lastly, anaerobic training helps by elevating athlete's pain tolerance. The level of strength and speed development has a great influence on anaerobic capacity and their improvement should be treated as prerequisite to anaerobic endurance development.

The frame of annual periodization of endurance, as well as periodization of multi year development, is consistent with other abilities. It always starts with general development, focused on aerobic endurance accompanied with other general functions like speed and strength. In the next stage, which focuses on building bases for specialized training, the focus is shifted to higher intensity work to develop Vo2 max and anaerobic metabolism. The last phase, of course, is strictly focused on sport specific endurance training. However, a small amount of work is devoted to maintenance of level basic functions developed in pervious phases.

Endurance is related directly to the ability to tolerate high levels of fatigue and all the discomforts that come with it. For this reason, it is worth mentioning the importance of psychological preparation to deal with monotony, pain and motivation. Coaches must remember that, when it comes to endurance sports, one of the most over looked abilities which, in fact, determines an athlete's future success, is the ability to carry great amounts of work over long periods of time as needed to develop all aspects of endurance.

                                                                                                                                                         Sport is Life 1999

     In life not the fastest win, but those with most endurance.