A large percentage of athletic training has the objective of producing adaptations in the body's energy systems both, anaerobic and aerobic. Athletes train so they can perform for a longer period of time and at higher intensities. The production and control of lactate is essential for both of these objectives. The sprinter and marathoner both need to produce and control lactate to be successful in their races though they will do it differently. Producing and controlling lactate is only a part of athletic success; however, it is an important part.
While most coaches and athletes associate lactate with both the production of high intensity energy needed to win races and the deterioration of athletic performance, many don't realize the importance of lactate as an energy source. Lactate is one of the most important fuels for exercise and is involved in two of the three major energy systems we use for exercise and athletic performance. An athlete would have a hard time finishing a race or a game if lactate produced in one muscle wasn't being used as a source of energy in other muscles. Because lactate is being used by other muscles as fuel, it moves out of the muscles where it is produced, thus easing the problem of acid build-up in the producing muscles. Controlling lactate is not only one of the keys to good performance, but also essential for the long practices where good performance originates.
There are three important energy systems for athletic performance. These are the creatine phosphate, glycolytic (this is the system we are usually referring to when we use the term anaerobic energy), and aerobic systems. The first two are called anaerobic systems in the sense that oxygen is not needed to produce energy in these systems. It is important to realize that there may be plenty of oxygen available when the anaerobic systems are used. These processes just don't use oxygen. The aerobic system requires oxygen but may be limited by other factors even if there is plenty of oxygen in the system. As mentioned in Lactate Physiology and Sports Training- Part 3,enzymes and mitochondria are important factors in aerobic energy and if they are limited then the amount of aerobic energy is limited. The aerobic system can use more than one type of fuel. Fats and carbohydrates are the two main sources of aerobic energy.
Lactate is a by-product of the anaerobic glycolytic system and a fuel for the aerobic system. Even though lactate is not involved in the creatine phosphate system, the presence of large amounts of lactate while training this system is an indication that the creatine phosphate system is reaching its limits. Also increases in lactate during aerobic training means that less fat and more carbohydrates are being used as fuel. It is important for the coach to understand just what the presence of lactate means if he/she is to design workouts to train all three systems.
The following is a brief discussion of each energy system:
Weightlifting, jumping, throwing, and short sprints depend almost entirely on the creatine phosphate system. Frequently, coaches will have their athletes conduct sets of very short sprints to develop this system. In competition, creatine phosphate lasts only a few seconds. So for most sports activity it provides only limited energy. Creatine supplemation has been the focus of much discussion and research in recent years. It is speculated that creatine supplemation will increase the length of time this system can be used and also reduce the amount of time it takes to restore resting creatine levels.
Even though the creatine phosphate system does not use or produce lactate, lactate measurements can be used to evaluate it. When energy from this system is exhausted, the body will shift to the other anaerobic system and start to produce large amounts of lactate. So lower lactate levels after a series of sprints are an indication of a well trained creatine phosphate system. Tracking this over time will tell the coach how well this system is responding to training.
Both the creatine phosphate and aerobic systems (using fats as fuel) are important for athletic activity but neither will produce sustained bouts of intense exercise needed for most athletic success. The body must use a third source of energy, carbohydrates or more precisely glycogen, to fuel the extended high intensity exercise that is crucial for good most athletic events. Carbohydrates are used both by the aerobic system to produce energy and by the third system, glycolysis or the anaerobic lactate system
Glycolysis. Glycolysis may be an unfamiliar term for many coaches, but it is extremely important for most athletic competitions. Glycolysis means the breakdown of sugars. When a coach, athlete or sports physiologist use the term anaerobic, they are most likely referring to this energy system. This process breaks down glycogen (a large carbohydrate molecule) to produce energy. It is very fast, producing quick energy for exercise. One of the end products of this process is a metabolite called pyruvate. When the right conditions exist, pyruvate will break down further to provide a lot more energy (See aerobic process using carbohydrates below).
When conditions aren't right and pyruvate doesn't break down, it turns into lactate. If the lactate is not removed from the muscle in some way, there will eventually be a problem with muscle contraction because of acidosis and the athlete will have to slow down.
There could be several reasons why all the pyruvate doesn't break down. The necessary amount of oxygen may not be getting to the cell; there may not be enough enzymes to enable the cell to process all the pyruvate; or the part of the cell that breaks down pyruvate (the mitochondria) may not be big enough to handle the sudden influx of pyruvate. Also, some of the cells (one type of fast twitch muscle cell) have hardly any mitochondria or appropriate enzymes and will process very little pyruvate, so nearly all of it turns into lactate7. These fast twitch cells are used more frequently as exercise intensity increases.
One of the interesting things about this process is that the pyruvate used by a muscle fiber to produce aerobic energy may not come from that fiber. As we mentioned above, pyruvate and lactate turn into each other very readily. If lactate is available from a nearby fiber or the blood stream, it will often enter a muscle fiber and be converted to pyruvate for use as fuel for aerobic energy. This is one of the important characteristics of lactate, the ability to move quickly around the body to places that can use it.
Two important points to remember from all of this are:
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Atualizado 17 de fevereiro 2011. Conteúdo © Sports Resource Group, Inc.
7. We have tended to simplify the discussion of fast twitch fibers by not mentioning that there is more than one type. One type of fast twitch fibers has a much higher ability than the others to produce aerobic energy.