The table featured last time shows a simple concept on hormone reactions during exercise. As seen in the table glucose and glycogen breakdown during exercise is mainly the role of the catecholamines- the epinephrine and the norepinephrine. They ensure that these energy sources are available in the blood during activities. However one of the catecholamines, the norepinephrine also contributes to lipolysis or fat metabolism, transforming it to another consumable energy. Free fatty acid (FFA) mobilization that leads to lipolysis is being triggered by the GH. Protein synthesis on the other hand, has been shown to be stimulated again by the GH and others like testosterone, cortisol, and IGF-1. These hormones create and break down protein to provide growth and energy as well (gluconeogenesis).
It is also notable from the table above that each hormone has its own stimulant for release. As mentioned earlier, hormone response depends on the type of activities an individual is performing. As with this discourse, we focus on the reactions of the hormones to the different forms of exercise. And we shall see that the catecholamines are stimulated by performance of moderate to intense exercise. But later on we shall see that the release of these hormones is more sensitive when the body does an intense type of activity (anaerobic). On the other hand, prolonged exercise triggers cortisol release while light to moderate exercises stimulate estrogen release (aerobic). In addition, GH, testosterone, and IGF-1 are activated with any type of exercise but more of the aerobic (Marks and Kravitz, 2000).
What should be understood from the above concepts? We have to understand that upon anaerobic activities, when the body gets its energy from glucose and glycogen (needless of oxidative process), the catecholamines mainly come into play. But for aerobic activities, catecholamines partially affect energy production, and other hormones more dominantly act into the scene. These hormones include cortisol, GH, IGF-1, estrogen and testosterone. The reason for this is that aerobic activities require more complex sources of energy other than glucose and glycogen, namely fats and proteins. And fat-protein utilization is being handled by the hormones previously discussed.
Catecholamine and Glucose Response to Intense/ Anaerobic Exercise
During an intense exercise, when there is a huge demand for glycogen and glucose, rapid muscular and hepatic glycogenolysis takes place. This induces a seven- to eight-fold increase in glucose production as manifested by its concentration in the blood (Figure 1). The reason for this tremendous glucose production is the marked 14- to 18-fold increase in both epinephrine and norepinephrine (Figure 2; A and B). And from the figures below (1 and 2), we can observe the direct relationship between glucose and catecholamine production.
To further emphasize the major role that glucose and catecholamine play in anaerobic activities, we can refer to the works of Marliss and Vranic (2002). In their discourse, they discussed the huge difference between plasma catecholamine concentration during aerobic exercise and plasma catecholamine concentration during anaerobic exercise (Figure 2). If in anaerobic activities, catecholamines respond largely as stated above, in aerobic the plasma concentration of these hormones only increases by two- to four-fold.
What can we infer from these findings? Two points can be conceptualized from the above facts: (1) that though aerobic exercise is more of a fat and protein burner, we cannot elude from the idea that small percentage of energy used also comes from glucose as manifested by increase in glucose production and catecholamine level; but (2) since anaerobic exercise is more of a glycogen/glucose burner, more catecholamines are utilized by such exercise than aerobic to produce a greater amount of plasma glucose.
Dominating Hormones during Aerobic Exercise
First, let us discuss another possible reason why the catecholamine plasma concentration also increases up to a certain extent in aerobic exercise. Aside from the reason stated earlier, we also have to remember that catecholamines, especially the norepinephrine (Figure 2 showing norepinephrine level is greater than epinephrine level during aerobic activity), play an important role in lipolysis. And in aerobic exertion, lipolysis is one of the important processes needed to utilize fat as one of the energy sources. And so it would be justifiable for the body to somehow increase its catecholamine production in anticipation for lipid/ fatty acid use.
But again as discussed in the previous parts, this catecholamine production during aerobic exercise is no match to the catecholamine production during anaerobic exercise. This is because during aerobic exercise, the body shifts from usage of glucose as energy source to utilization of fats and proteins with aid of oxidation.
How does the body carry out this utilization shift? The body is able to manage such shift with the aid of the following hormones: cortisol, GH, estrogen, testosterone, and IGF-1. As the endocrine system senses that the body is into aerobic activity, it all the more stimulates GH, estrogen, and cortisol to be secreted to decrease glucose uptake. This mechanism would then possibly decrease glycogenolysis and so glucose level in the blood will not increase as much as in anaerobic exercise. And as glucose uptake is decreased, GH, estrogen, and cortisol continue their roles as they promote fatty acid mobilization and protein utilization (gluconeogenesis). These hormones are being supported by other hormones like testosterone, and IGF-1.
But does this mean that during anaerobic exercise cortisol, GH, estrogen, testosterone, and IGF-1 are not being activated? No. In fact both aerobic and anaerobic exercises are shown to stimulate these hormones (Table 2). And what we have to understand now is that if in anaerobic exertion, the more dominant hormones are the catecholamines, in aerobic they are cortisol, GH, estrogen, testosterone, and IGF-1 (Marks and Kravitz, 2000; Robergs and Roberts, 1997).
Figure 3 shows cortisol and GH behavior during prolonged/ aerobic exercise. And as we shall see, the group under the exercise condition was noted to have an increased plasma cortisol and GH concentration within the exercise, compared to the group under resting condition. These increases again mean that the body anticipates cortisol and GH usage by the cells.
Unfortunately we failed to gain clear sample graphs that compare plasma concentration of cortisol and GH in aerobic and anaerobic exercise. We are also unable to search graphs that examine testosterone, estrogen, and IGF-1 behavior during exercise. But despite of these, most researchers agree to the fact that these hormones do really increase their activities especially during aerobic exertion.
TO BE CONTINUED...
It is also notable from the table above that each hormone has its own stimulant for release. As mentioned earlier, hormone response depends on the type of activities an individual is performing. As with this discourse, we focus on the reactions of the hormones to the different forms of exercise. And we shall see that the catecholamines are stimulated by performance of moderate to intense exercise. But later on we shall see that the release of these hormones is more sensitive when the body does an intense type of activity (anaerobic). On the other hand, prolonged exercise triggers cortisol release while light to moderate exercises stimulate estrogen release (aerobic). In addition, GH, testosterone, and IGF-1 are activated with any type of exercise but more of the aerobic (Marks and Kravitz, 2000).
What should be understood from the above concepts? We have to understand that upon anaerobic activities, when the body gets its energy from glucose and glycogen (needless of oxidative process), the catecholamines mainly come into play. But for aerobic activities, catecholamines partially affect energy production, and other hormones more dominantly act into the scene. These hormones include cortisol, GH, IGF-1, estrogen and testosterone. The reason for this is that aerobic activities require more complex sources of energy other than glucose and glycogen, namely fats and proteins. And fat-protein utilization is being handled by the hormones previously discussed.
Catecholamine and Glucose Response to Intense/ Anaerobic Exercise
During an intense exercise, when there is a huge demand for glycogen and glucose, rapid muscular and hepatic glycogenolysis takes place. This induces a seven- to eight-fold increase in glucose production as manifested by its concentration in the blood (Figure 1). The reason for this tremendous glucose production is the marked 14- to 18-fold increase in both epinephrine and norepinephrine (Figure 2; A and B). And from the figures below (1 and 2), we can observe the direct relationship between glucose and catecholamine production.
To further emphasize the major role that glucose and catecholamine play in anaerobic activities, we can refer to the works of Marliss and Vranic (2002). In their discourse, they discussed the huge difference between plasma catecholamine concentration during aerobic exercise and plasma catecholamine concentration during anaerobic exercise (Figure 2). If in anaerobic activities, catecholamines respond largely as stated above, in aerobic the plasma concentration of these hormones only increases by two- to four-fold.
What can we infer from these findings? Two points can be conceptualized from the above facts: (1) that though aerobic exercise is more of a fat and protein burner, we cannot elude from the idea that small percentage of energy used also comes from glucose as manifested by increase in glucose production and catecholamine level; but (2) since anaerobic exercise is more of a glycogen/glucose burner, more catecholamines are utilized by such exercise than aerobic to produce a greater amount of plasma glucose.
Figure1. Comparison of responses during 40 minutes of moderate intensity exercise (aerobic/boxes) and 15 minutes of intense exercise in normal young male subjects (anaerobic/circles); Y-axis- GP for glucose production; X-axis- min for minutes of exercise.
Figure2. Comparison of responses during 40 minutes of moderate intensity exercise (aerobic/boxes) and 15 minutes of intense exercise in normal young male subjects (anaerobic/circles); Y-axis- catecholamines (A-Norepinephrine; B-Epinephrine); X-axis- min for minutes of exercise.
Dominating Hormones during Aerobic Exercise
First, let us discuss another possible reason why the catecholamine plasma concentration also increases up to a certain extent in aerobic exercise. Aside from the reason stated earlier, we also have to remember that catecholamines, especially the norepinephrine (Figure 2 showing norepinephrine level is greater than epinephrine level during aerobic activity), play an important role in lipolysis. And in aerobic exertion, lipolysis is one of the important processes needed to utilize fat as one of the energy sources. And so it would be justifiable for the body to somehow increase its catecholamine production in anticipation for lipid/ fatty acid use.
But again as discussed in the previous parts, this catecholamine production during aerobic exercise is no match to the catecholamine production during anaerobic exercise. This is because during aerobic exercise, the body shifts from usage of glucose as energy source to utilization of fats and proteins with aid of oxidation.
How does the body carry out this utilization shift? The body is able to manage such shift with the aid of the following hormones: cortisol, GH, estrogen, testosterone, and IGF-1. As the endocrine system senses that the body is into aerobic activity, it all the more stimulates GH, estrogen, and cortisol to be secreted to decrease glucose uptake. This mechanism would then possibly decrease glycogenolysis and so glucose level in the blood will not increase as much as in anaerobic exercise. And as glucose uptake is decreased, GH, estrogen, and cortisol continue their roles as they promote fatty acid mobilization and protein utilization (gluconeogenesis). These hormones are being supported by other hormones like testosterone, and IGF-1.
But does this mean that during anaerobic exercise cortisol, GH, estrogen, testosterone, and IGF-1 are not being activated? No. In fact both aerobic and anaerobic exercises are shown to stimulate these hormones (Table 2). And what we have to understand now is that if in anaerobic exertion, the more dominant hormones are the catecholamines, in aerobic they are cortisol, GH, estrogen, testosterone, and IGF-1 (Marks and Kravitz, 2000; Robergs and Roberts, 1997).
Figure 3 shows cortisol and GH behavior during prolonged/ aerobic exercise. And as we shall see, the group under the exercise condition was noted to have an increased plasma cortisol and GH concentration within the exercise, compared to the group under resting condition. These increases again mean that the body anticipates cortisol and GH usage by the cells.
Figure 3. Mean profiles of plasma cortisol and GH secretory rates in the resting position (unshaded) and in the exercise (shaded).
Unfortunately we failed to gain clear sample graphs that compare plasma concentration of cortisol and GH in aerobic and anaerobic exercise. We are also unable to search graphs that examine testosterone, estrogen, and IGF-1 behavior during exercise. But despite of these, most researchers agree to the fact that these hormones do really increase their activities especially during aerobic exertion.
TO BE CONTINUED...
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