FOCUS
07-12-2007, 12:58
aining our energy systems
By: Kelly Mackenzie, MSC, BPE, AFLCA trainer
Regardless of what mode of exercise we are using, we can train all three of our energy systems. There are physiological adaptations that can occur within the muscle cells when using training techniques specific to each of the energy systems. Understanding the sources of energy for each of the systems, how energy can be restored as well as how the three systems interact are essential in putting together sound training programs. Further, an appreciation of what training does to the muscle cell’s ability to use energy, both acutely as well as chronically, will strengthen a trainer’s ability to ensure ideal training for results.
Energy!
Adenosine triphosphate (ATP) is the stored form of energy within the body. ATP is an adenine nucleotide bound to three phosphates. ATP will convert to ADP (adenosine diphosphate) and a free circulating phosphate (Figure 1). This conversion breaks the bond of the third phosphate, releasing the stored energy. This energy is what is used for all life functions of a cell. Similarly, energy can be restored for future use by reattaching a phosphate to the ADP.
As an overview, there are three energy systems: the Anaerobic Alactic system (AnA), the Anaerobic Lactic system (AnL) and the Aerobic system (AER). Each creates ATP, which can then be converted into energy for muscle activity. The sources of ATP as well as where within the cell the ATP is created is what differentiates each of the systems.
The Anaerobic Alactic System
There is a limited amount of stored energy (ATP) within the muscle cells. This is the energy of the AnA system, also known as the ATP-CP system. Typically, there is sufficient ATP stored within the muscle to last several seconds. As ATP is converted to release energy, creatine phosphate (CP) which is also present in the muscle cells, will split so as to reform new ATP (Figure 2). So long as CP is present, new ATP continues to fuel the muscle cells with energy. However, there is also a limit of CP stored in the muscle, and typically this system will be tapped out within 10 - 15 seconds of intense activity.
Because the ATP is in a "ready to go" form, it provides instant energy to the working muscles. As the name suggests, this system requires no oxygen (anaerobic) and also has no by-products such as lactic acid (alactic). Time is needed in order to regenerate ATP and CP stores within muscle cells, however the recovery may be little to no activity. Although stored ATP and CP are used up quickly, they will recycle themselves within a very short time. There is some indication that training this system may increase ATP stores within the muscle as well as increase creatine phosphate stores, thus enhancing the ability to create more immediate energy.
The Anaerobic Lactic System
Muscle glycogen is also stored in limited amounts within the muscle. When energy beyond what can be provided from the AnA system is needed, glycogen, a carbohydrate, breaks down into glucose and can then produce ATP within the muscle cell. Due to the multiple steps to create energy, the AnL is a slower process than the
AnA system. This system will continue to provide energy for working muscles so long as there is muscle glycogen present. These stores will typically provide energy for bouts of intense exercise lasting ~ 60 up to ~ 90 seconds.
The conversion of muscle glycogen to ATP happens outside of the mitochondria in the muscle cells, therefore the presence of oxygen is not needed (anaerobic). Without oxygen, however, lactic acid is formed. Lactic acid can produce discomfort in the working muscles as well as limit performance. Ideally, recovery should be a low intensity activity. This allows for better circulation, thus removing the lactic acid and normalizing the pH level of the cells as well as delivering the byproducts (lactate) to the heart and then the liver, where it can be recycled to new potential energy.
As with the AnA system, muscle glycogen stores can be replenished within the working cells with appropriate rest. Training the AnL system can prove beneficial in improving the buffering capacity of the cell (to combat lactic acid). Further, training can lend to an increase in muscle glycogen stores as well as an improved efficiency to convert glycogen to glucose.
The Aerobic System
The AER system is unique from the others in that it can convert any of the three macronutrients into energy. With this energy system, ATP is created within the mitochondria (power house) of the working muscle cells therefore presence of oxygen is required. The breakdown process is much slower than either the AnA or the AnL, however there is a seemingly endless supply of energy for the cells. Thus, the AER system provides continuous supply of energy, however it cannot tolerate higher intensities as the energy is not produced fast enough for such activity.
Similar to the AnA, there are no metabolic wastes produced during the AER conversion of energy, therefore recovery from efforts does not have to be active. Training the aerobic energy system has many known benefits. Ones related to energy stores include an increased ability of the muscle cells to utilize more oxygen due to increased size and numbers of mitochondria as well as an increase in heart stroke volume, resulting in more delivery of substrates to the working muscles.
Interaction of the three systems
Using a 5 km running race, it is possible to better comprehend how the energy systems interact. As an activity is begun, the AnA system kicks in as it has energy "ready to go" when the start gun sounds. As these immediate stores quickly deplete, the AnL takes over. In that it is somewhat slower in producing energy, it cannot provide for the same intensity. Therefore the runner cannot keep the "start" speed and will slow down a bit. The AnL is limited by muscle glycogen stores, therefore it is the AER system that will take over for longer durations in that it can use limitless sources of fuel for energy. The runner would be able to hold a pace for which the aerobic system could provide energy – a pace slower than either of the anaerobic systems. This illustrates the continuum between the three systems.
However, it is important to realize that it is not as simple as switching gears. Rather, there is always a predominant system which is contributing more energy than the others. In other words, the runner would be using some energy from all three systems for most of the 5 km, even though the aerobic system would be the dominant contributor. Further, what happens when the runner gets to a steep hill? If she is working aerobically, that system may not provide for the extra energy needed to get up the hill. In this case, the two anaerobic systems, that have restored themselves during the race, will kick in and get the racer up the hill. Similarly, a sprint finish would require
extra energy above what the aerobic system could provide. Training all three systems allows for the best adaptations specific to each system.
By: Kelly Mackenzie, MSC, BPE, AFLCA trainer
Regardless of what mode of exercise we are using, we can train all three of our energy systems. There are physiological adaptations that can occur within the muscle cells when using training techniques specific to each of the energy systems. Understanding the sources of energy for each of the systems, how energy can be restored as well as how the three systems interact are essential in putting together sound training programs. Further, an appreciation of what training does to the muscle cell’s ability to use energy, both acutely as well as chronically, will strengthen a trainer’s ability to ensure ideal training for results.
Energy!
Adenosine triphosphate (ATP) is the stored form of energy within the body. ATP is an adenine nucleotide bound to three phosphates. ATP will convert to ADP (adenosine diphosphate) and a free circulating phosphate (Figure 1). This conversion breaks the bond of the third phosphate, releasing the stored energy. This energy is what is used for all life functions of a cell. Similarly, energy can be restored for future use by reattaching a phosphate to the ADP.
As an overview, there are three energy systems: the Anaerobic Alactic system (AnA), the Anaerobic Lactic system (AnL) and the Aerobic system (AER). Each creates ATP, which can then be converted into energy for muscle activity. The sources of ATP as well as where within the cell the ATP is created is what differentiates each of the systems.
The Anaerobic Alactic System
There is a limited amount of stored energy (ATP) within the muscle cells. This is the energy of the AnA system, also known as the ATP-CP system. Typically, there is sufficient ATP stored within the muscle to last several seconds. As ATP is converted to release energy, creatine phosphate (CP) which is also present in the muscle cells, will split so as to reform new ATP (Figure 2). So long as CP is present, new ATP continues to fuel the muscle cells with energy. However, there is also a limit of CP stored in the muscle, and typically this system will be tapped out within 10 - 15 seconds of intense activity.
Because the ATP is in a "ready to go" form, it provides instant energy to the working muscles. As the name suggests, this system requires no oxygen (anaerobic) and also has no by-products such as lactic acid (alactic). Time is needed in order to regenerate ATP and CP stores within muscle cells, however the recovery may be little to no activity. Although stored ATP and CP are used up quickly, they will recycle themselves within a very short time. There is some indication that training this system may increase ATP stores within the muscle as well as increase creatine phosphate stores, thus enhancing the ability to create more immediate energy.
The Anaerobic Lactic System
Muscle glycogen is also stored in limited amounts within the muscle. When energy beyond what can be provided from the AnA system is needed, glycogen, a carbohydrate, breaks down into glucose and can then produce ATP within the muscle cell. Due to the multiple steps to create energy, the AnL is a slower process than the
AnA system. This system will continue to provide energy for working muscles so long as there is muscle glycogen present. These stores will typically provide energy for bouts of intense exercise lasting ~ 60 up to ~ 90 seconds.
The conversion of muscle glycogen to ATP happens outside of the mitochondria in the muscle cells, therefore the presence of oxygen is not needed (anaerobic). Without oxygen, however, lactic acid is formed. Lactic acid can produce discomfort in the working muscles as well as limit performance. Ideally, recovery should be a low intensity activity. This allows for better circulation, thus removing the lactic acid and normalizing the pH level of the cells as well as delivering the byproducts (lactate) to the heart and then the liver, where it can be recycled to new potential energy.
As with the AnA system, muscle glycogen stores can be replenished within the working cells with appropriate rest. Training the AnL system can prove beneficial in improving the buffering capacity of the cell (to combat lactic acid). Further, training can lend to an increase in muscle glycogen stores as well as an improved efficiency to convert glycogen to glucose.
The Aerobic System
The AER system is unique from the others in that it can convert any of the three macronutrients into energy. With this energy system, ATP is created within the mitochondria (power house) of the working muscle cells therefore presence of oxygen is required. The breakdown process is much slower than either the AnA or the AnL, however there is a seemingly endless supply of energy for the cells. Thus, the AER system provides continuous supply of energy, however it cannot tolerate higher intensities as the energy is not produced fast enough for such activity.
Similar to the AnA, there are no metabolic wastes produced during the AER conversion of energy, therefore recovery from efforts does not have to be active. Training the aerobic energy system has many known benefits. Ones related to energy stores include an increased ability of the muscle cells to utilize more oxygen due to increased size and numbers of mitochondria as well as an increase in heart stroke volume, resulting in more delivery of substrates to the working muscles.
Interaction of the three systems
Using a 5 km running race, it is possible to better comprehend how the energy systems interact. As an activity is begun, the AnA system kicks in as it has energy "ready to go" when the start gun sounds. As these immediate stores quickly deplete, the AnL takes over. In that it is somewhat slower in producing energy, it cannot provide for the same intensity. Therefore the runner cannot keep the "start" speed and will slow down a bit. The AnL is limited by muscle glycogen stores, therefore it is the AER system that will take over for longer durations in that it can use limitless sources of fuel for energy. The runner would be able to hold a pace for which the aerobic system could provide energy – a pace slower than either of the anaerobic systems. This illustrates the continuum between the three systems.
However, it is important to realize that it is not as simple as switching gears. Rather, there is always a predominant system which is contributing more energy than the others. In other words, the runner would be using some energy from all three systems for most of the 5 km, even though the aerobic system would be the dominant contributor. Further, what happens when the runner gets to a steep hill? If she is working aerobically, that system may not provide for the extra energy needed to get up the hill. In this case, the two anaerobic systems, that have restored themselves during the race, will kick in and get the racer up the hill. Similarly, a sprint finish would require
extra energy above what the aerobic system could provide. Training all three systems allows for the best adaptations specific to each system.