Table of Contents
The robust nature of the human body is always in a state of flux adaptation in order to maintain homeostatic environment. Strenuous exercise, whether aerobic, such as swimming or running, or anaerobic, such as weightlifting, require what are known as “rest and recovery” periods in between workout sessions in order to utilize biological repair and maintenance mechanisms to prepare particular muscles for the next session. Individual athletes, such as swimmers, cyclists, weightlifters and footballers, who engage in successive sessions of strenuous training, require a 2 to 3 day rest period in order to maximize energy stores within the skeletal muscles (muscle glycogen), repair damaged tissue, fluid loss and adapt to the physical stress of the training program. Over the last few years, dietary supplements have emerged to be the basis for boosting performance (Wu, 2009). One common supplement is glutamine; advertized as a muscle strengthening and recovery boosting supplement.
Glutamine, a non-essential five-carbon amino acid, is found in abundance in the human’s body (Roth, 2008). It is quite abundant in human plasma with normal plasma concentration ranging from 500 to 750 μmol/l (Bonetto et al., 2010). There are two main enzymes used in glutamine metabolism: glutamine synthetase and glutaminase. Glutamine synthetase catalyses the production of glutamine from glutamate and ammonia; whereas, glutamine catalyses the hydrosis of glutamine to ammonia and glutamate (Vance et al., 2001). Excess glutamine can be broken down into glutamate and ammonia by ammonia and enzyme glutaminase and converted into other amino acids, used in other reactions, and becomes a part of the body’s other regulatory proteins (Vance et al., 2001).
Although most organs use glutamine as fuel, the gastrointestinal tract and the immune system use it primarily. Glutamine accounts for more than 60% of the overall muscular free amino acids and given that skeletal muscle is a huge accumulation of tissues, it is the most critical location for synthesis of glutamine in spite of the fact that the activity of glutamine synthetase is considerably lower for every unit mass in skeletal muscles (Welbourne, 1987). The body has the ability to make adequate glutamine for its regular daily stresses, however, when the body, manipulated by extraneous stress, requires more than it can produce and prompts consumption of common supplements. Glutamine is one of the most critical components in forming the proteins that maintain cellular health and tissue repair. Physical exercises affect glutamine creation and regulate its uptake.
Strenuous training is often linked with less glutamine levels and immune incompetence (Ivy, 2007). Strenuous training programs and physical exercises lead to the depletion of glutamine because of reduced production and improved absorption by the immune system and liver cells. Thus, glutamine is indispensable and high-performance athletes have to ingest supplements to increase muscular strength to boost the recovery process. During and after a prolonged and strenuous training session, the body has increased levels of glucocorticoid, which are catabolic substances that increase proteins and muscle breakdown (Salehian et al. 2006). Glutamine has muscle protein-sparing effects and counteracts the actions of glucocorticoid to some degree (Salehian et al 2006). It increases the amount of amino acids released from skeletal muscles, reducing protein degradation and increases the rate of muscle glycogen resynthesis. Glutamine assists body recovery from intense exercise at a faster rate by replenating muscle glycogen stores more rapidly. During training, glutamine helps in delaying fatigue by buffering skeletal muscle from metabolic acidosis (Welbourne, 1987). It does this through its conversion to ketoglutarate and an ammonium ion. This serves to buffer the pH of the skeletal muscle; decreasing pH leads to metabolic acidosis and reduces the body's ability to perform (Welbourne, 1987).
During intense training, catabolism of skeletal muscles occurs in order to supplement the use the amino acids in other parts of the body. During this process, preserving muscle mass, a desired goal pertaining to physical training, is not a particularly critical option for the body in regards to necessitating nutrients for critical physiological functions. Administering glutamine to athletes decreases this rate of skeletal muscle degradation (Parry Billings et al 1990). Glutamine also increases absorption of water and maintenance of a normal acid balance as well as preventing the breakdown of muscle protein. A study conducted by Welbourne et al. (1996), analyzed participants who took only two grams of glutamine had increased the amount of plasma bicarbonate in their body. Increase in the plasma bicarbonate levels improves a person’s ability to safeguard against lactic acid build up, thus increasing performance.
Glutamine considerably improves the functions of the immune system of healthy people and athletes whom train at high-stress intensities that usually prompt an immune system breakdown (Perriello et al., 1997).Glutamine regulation is especially important while exercising, both to help fight off infections and to prevent breakdown of muscle (Perriello et al., 1997). The upshots of glutamine on the immune system has also been shown by numerous studies, which have examined records on hospital patients taking glutamine, to drive away complications related to hospital stays and surgeries. In a study by Oquz et al. (2007), half of the patients going through colorectal surgery for cancer ingested glutamine treatment in their dietary regime during their time in the hospital whereas the other half did not receive. The group that received glutamine supplements has fewer problems after surgery and a shorter hospital stay that the group that did not take glutamine supplements. Other studies also show the significance of glutamine on the immune system function. For instance, Fuentes et al. (2004) found that glutamine supplements improve hospitalized patients morbidity by boosting immune system responses and host defenses. Li et al. (2007) found that intravenous glutamine supplementation helps premature infants to spend lesser time in the hospital and decreased the number of hospital related infections.
Most of these studies on glutamine supplementation, as well as immune responses, are not held on people performing aerobic and anaerobic exercises; however, the findings are of great importance to them. Physical exercise is a type of intense stress that causes distress on a human body and this profoundly taxes the immune system. Endurance exercises reduce plasma glutamine levels, which are an essential fuel for immune system cells. People who undergo extreme training often discover that glutamine has positive effects on the performance of their immune system. Castell et al. (1997) examined the effects of consuming glutamine after strenuous exercise in elite rowers and runners; they discovered that there was a considerable less illnesses and infections after strenuous training in athletes who ingested glutamine supplements than those who did not.
When it comes to the correct and useful dosage of glutamine supplements, investigations are very diverse. Different research has shown that success can occur with varied amounts of glutamine. Van Gammeren et al. (2002) argued that people should take as low as two grams of glutamine every day. In Welbourne et al. (1996), only two grams of glutamine boosted the amount of plasma bicarbonate in their body. Other researchers, for example, Candow et al. (2001) provided considerably larger amount of glutamine (45 grams) to their research participants every day. Most of the studies suggest that people taking from four to ten grams everyday is adequate for optimum physiological benefits from glutamine supplements.
Glutamine supplements are usually more effective when taken for longer periods rather than shorter ones. Generally the most important benefits include, supporting immune system, lesser wasting of body and muscle, lower myostatin levels, enhanced levels of human growth hormonal, reduced skeletal muscle catabolic upshots, increased protein synthesis, increased anabolic outcomes as well enhanced capacity to maintain high intensity exercise because of increased capability to safeguard against lactic acid build. Every aspect can potentially cause increased muscle strength, power, and mass. It is evident that glutamine should be in the dietary regimen of athletes because it plays a major role in sustaining health through benefits offered to the immune system.
Objectives of the Study
Numerous studies have shown the importance of glutamine supplementation in athletes. However, there are limited studies examining the recovery process as well as the muscle endurance in athletes who supplement with glutamine versus the ones who do not supplement. The objective of the study is
- To examine the muscle endurance as well as recovery process in two groups of athletes- those who supplement with glutamine versus the ones who do not supplement
- To conduct a Literature Analysis of glutamine's effects when combined with anaerobic and aerobic exercise as the performance of individual athletes is limited by slow recovery and repair of muscle, especially after strenuous exercise.
Though there are many factors that contribute to the recovery process, nutrition is the most important; however it is often misunderstood, neglected and surrounded by many misconceptions. To optimize the performance of muscles, it is important that appropriate nutrients be taken in after exercises (Castell & Newsholme, 1997). Most of the adaptation for increased muscle recovery and endurance occurs between training sessions. The muscle cells go through substantial trauma during exercise. The trauma causes discomfort in the form of muscle soreness and, in turn, triggers muscle repair mechanisms. Taking supplements, like glutamine, during and after exercise bridges the gap between the potential for injuries associated with over-training and outstanding athletic performance.
Studies have shown that there is increase of free radicals during exercise, which is also referred to as oxidative stress; free radicals are mainly responsible for causing damages to the muscle cell membranes. Glutamine stimulates synthesis of muscle protein and preserves the mass of skeletal muscles. Aerobic and anaerobic exercises have different effects on the amount of glutamine needed because aerobic exercises deplete glutamine to lesser extents than anaerobic exercise. Thus, glutamine is necessary for athletics.
This study will adopt a descriptive research design that aims at explaining the nature and the extent of the relationship between the research problem and various variables. This research attempts to obtain a complete and accurate description of the benefits of glutamine and will source information from already published research on the benefit of glutamine. There are considerable studies supporting the thesis of glutamine supplementation in reducing muscle loss as well as assisting in the recovery process of athletes who undertake strenuous and prolonged exercises. In recent years, researchers have conducted numerous studies on glutamine supplementation in athletes and they offer a solid rationale for effectiveness of glutamine supplementation in people who perform various athletics.
Results and Discussion
Glutamine is an essential building block in muscles, beneficial for its ergogenic effects, it comprises over 61% of skeletal muscles and accounts for 19% of the nitrogen within the skeletal muscle (Salehian et al 2006). Glutamine is the main transporter of nitrogen within muscle cells, which is essential to muscle growth and development. Anabolic states, otherwise understood as optimal muscle growth states, demonstrate a greater nitrogen input than the nitrogen output. The reverse, muscle catabolic states, occurs when the nitrogen output is higher than the nitrogen input, leading to muscle degradation. Glutamine is a non-essential amino acid (not required in the diet) since the human body can create it as a derivative of the breakdown of other amino acids. Skeletal muscles use amino acids from protein catabolism to synthesize glutamine and release it for use elsewhere in the body. Under conditions of trauma, stress, and infection, glutamine is a conditional fundamental amino acid, which supports recovery when consumed in supplemental form. Glutamine benefits are numerous for athletes, playing a key function in anti-catabolism, protein metabolism, and volumizing cells (Hills et al. 2003).
Glutamine in Skeletal Muscle
The skeletal muscle produce, store and transport most of the body's glutamine (Parry-Billings et al., 1990).The human skeletal muscles have an approximate net weight of 20 mmol/kg of glutamine (Parry-Billings et al. 1990). The rate of glutamine synthesis is relatively high compared to that of the other amino acids; generally created at 50 mmol/h. This high synthetic rate is important in maintaining glutamine store in the muscles and plasma glutamine homeostasis (Parry-Billings et al 1990). Glucocorticoid influences on the synthesis as well as the transport of glutamine. For instance, muscle glutamine synthetase activity is increased after treatment by glucocorticoid. This increased activity mostly occurs during catabolic states (Parry-Billings et al 1990).
Glucocorticoid boosts the production of glutamine from the skeletal muscles (Parry- Billings et al., 1990); it reduces intracellular glutamine accumulation and changes transportation kinetics, enabling maximum glutamine at reduced intracellular glutamine rates. These effects make certain that there is enhanced availability of glutamine from the muscles when catabolism occurs (Rowbottom et al., 1996). During exhaustive exercises, there is reduction of muscle glutamine levels. This forces the muscles to enter in the catabolic state in which muscle proteins degradation occurs to offer free glutamine to the other body tissues and organs. Salehian et al. (2006) conducted a research on a special muscle regulator known as myostatin, which produces glucocorticoid. In healthy persons, moderate to high myostatin levels cause glucocorticoid muscle wasting. Salehian et al (2006) discovered that glutamine prevents induced muscle wasting; administering glutamine offers a possible method for preventing muscle wasting stimulated by myostatin and glucocorticoid. The subjects who orally ingested glutamine had considerably less wasting on muscles and body weights as well as lesser myostatin expression compared to the control group. This is particularly important because over-training and prolonged exercises create the environment of extreme stress in the body and can lead to increase in injuries and muscle breakdown. By supplementing with external glutamine, athletes aid their body in the healing process.
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Given that skeletal muscles are the key resource for glutamine, prolonged and strenuous exercises lead to glutamine deficiencies, which in turn lead to a considerable loss of skeletal muscle mass and proteins (Salehian et al 2006). Researchers have also put forward the fact that skeletal muscles play a major role in proper immune functions (Parry-Billings et al., 1990) and, therefore, a failure of the muscle to offer adequate glutamine results in the impairment of immune system functions (Parry-Billings et al., 1990). Muscular activity affects the rate of glutamine release therefore, exercise has a direct influence of the immune system.
Glutamine and the Immune System
Glutamine is very abundant in human plasma and muscles. Human beings have a normal glutamine plasma level of 500-to750 µmol/L, which relies on the net stability between its synthesis and absorption by tissues and organs. Rowbottom et al (1996) outline the numerous benefits associated with glutamine such as, transport of nitrogen amongst organs and ammonia detoxification, preservation of acid-base balance when acidosis occurs, serving as a nitrogen precursor during nucleotides production, regulating protein synthesis and degradation, and fueling the immune system and mucosal cells. Regarding the last role, it is widely known that macrophages and lymphocytes use glutamines at very high rates. Glutamine provides energy via its fractional oxidation in glutaminolysis process and offers nitrogen and carbon as precursors of DNA, RNA, and protein synthesis (Wallace & Keast, 1992). Glutamine availability controls critical aspects of the immune function, especially through regulating the biosynthesis of purine and pyrimidine nucleotides. The function of glutamine in acting as a precursor of pyrimidine as well as purine is important for lymphocytes and other cells of the immune system (Wallace & Keast, 1992). The importance of glutamine in providing energy and synthesis of nucleotide, which led Parry Billings et al (1990) to hypothesize that decline in plasma glutamine levels lower than 600 µmol/L, has deadly consequences on the immune system functions. Low glutamine level leads to low synthesis of RNA, low IL-2 production and immunoglobulin synthesis, as well as low proliferative responses to lymphocytes mitogens and reduced rate of macrophages phagocytosis. Glutamine exerts its immunological effects through direct action on immune system cells or indirectly through maintaining gut barrier function or preserving antioxidant glutathione (O'Riordain, 1996).
Evidence suggests that immune depression results from post-exercise glutamine depletion (Castell, 2003). Glutamine plays a major role in assisting the immune system function and affects lymphocyte performance. Lymphocytes, are dependent on glutamine from skeletal muscle for much of their functioning, and therefore, depletion from strenuous exercise hinder the foundation of the immune system (Castell, 2003). Macrophages and monocytes are also a type of cells critical to the immune system that require glutamine to function normally. The behavior of monocytes and lymphocytes in response to certain levels of glutamine shows that glutamine has many actions in the cells that allow them to function properly (Castell, 2003).
Furthermore, exhaustive exercises or training has adverse effects on the immune function. These effects consist of reduced natural killer cells cytolytic activity, reduced circulating amount of T-lymphocytes for three to four hours after intense training, reduced proportion of CD4 to CD8 cells, and reduced proliferation capacity of lymphocytes and neutrophil activity, weakened antibody synthesis and reduced immunoglobulin levels in saliva and blood (O'Riordain, 1996). In most athletes, the responses are usually reasonably temporary and last only for a short period although exhaustive and prolonged exercise affects various parameters for a day or two. This means that undertaking strenuous exercise or training sessions within 2 days, such as running a marathon, offers inadequate time for various factors of the immune system to recuperate adequately to function in a normal manner. Various researchers have observed this after prolonged high intensity exercises (Rowbottom et al., 1996) and after a short period of exhaustive training carried out after eight weeks of endurance runners training who were preparing for a major competition (Castell et al., 2000). Exhaustive and prolonged training boosts the amount of white blood cells (leucocytosis). There is also a slow increase in the number of lymphocytes in the circulation when the rest period begins. Nonetheless, their amount is usually decreased afterward to less than pre-exercise levels in 15-30 minutes following exhaustive training. The white blood cells become dehydrated after an exhaustive exercise.
Relationship between Exercise and Plasma Glutamine Concentrations
Intense bout of exercises cause decrease in plasma glutamine levels and disparities depending on duration, intensity, and type of exercise. Various researchers have discovered that plasma glutamine is increased after a brief period of less than one hour after high intensity exercise (Babij et al., 1983, Erikson et al., 1985). On the other hand, other researchers have observed that after strenuous and prolonged exercises, for instance, full marathon or exhaustive training sessions, there is a considerable reduction in plasma glutamine during and after exercise: Castell (2002), plasma glutamine of athletes’ performing prolonged and extensive exercises like marathons is decreased. The plasma glutamine concentration of athletes who trained on a treadmill at 50% maximum oxygen consumption (VO2max) for 3.75 h was increased during the early stage, however, it was decreased while the exercise came to the end; it declined below pre-exercise amounts. The reduction of plasma glutamine was relatively short for those running a marathon and it lasted for from 6 to 9 hours. Hiscock et al. (1998) found that the resting fasting plasma glutamine concentration in athletes undertaking diverse sports varies significantly. Cyclists had more distinctly elevated resting plasma glutamine levels than all the other athletes being studied whereas power lifters had the least. Parry-Billings et al (1990) observed that athletes who suffered from over-training syndrome have considerably reduced levels of plasma glutamine that stayed relatively low even after resting for a few weeks. This study was supported by Row Bottom et al (1996).
Athletes are usually susceptible to various infections for a few hours, especially after extensive and prolonged training and this is attributed to decreased availability of plasma glutamine in the plasma, which causes immune cells to be challenged. On the contrary, low intensity training is beneficial for the immune system because plasma glutamine levels remain unchanged at the level of exercise.
In case of prolonged exercises, the skeletal muscles fail to provide adequate glutamine because of exercise stress and this is result in hindered state of recovery and performance. Skeletal muscles provide most of the glutamine because it synthesizes and stores it. The amount of glutamine in skeletal muscles is particularly higher compared to that of other amino acids. According to Parry-Billing et al (1990), the high synthetic rate is important for maintaining glutamine homeostasis because skeletal muscles offer most of the glutamine needed by other tissues in the human body.
Plasma glutamine levels fall significantly after strenuous exercises-post exercise/training. Rennie et al. (1994) observed closely the levels of plasma glutamine for 4 hours and 50 minutes after cycling at 50% VO2max for 3.75 hours. They registered reduction from 557 µmol/L while resting to 470 µmol/L immediately after the exercises; this was followed by a further fall to 391 µmol/L. The plasma glutamine levels did not return to the resting rate even after 4 hours and 50 minutes of rest; it was at 482 µmol/L, while normal rates vary between 500-750 µmol/L. Parry-Billings et al. (1992) recorded a considerable fall in glutamine levels after a marathon event to 495 µmol/L (after race) from 592 µmol/L (before the race). This shows that similar to the changes that take place during exercise, the return of plasma glutamine levels to pre-exercise values depend on the duration and intensity of the exercises. In Decombaz et al (1979) study, the plasma glutamine level has not returned to pre-exercise rates even after 24 hours recovery period. As a result, researchers have suggested that there is need for significant recovery periods between training, especially the high-intensity exercise to enable complete recovery of plasma glutamine levels. The decrease in plasma glutamine results from an increased absorption by the kidneys to safeguard against metabolic acidosis. Acidosis comes about from increased production of lactic acid coupled with strenuous exercises as well as accumulation of various organic acids such as acetoacetate and free fatty acids. It also results from production of ammonia in the kidneys and its discharge into the distal tubes and secretion of surplus proton in the urine; this safeguards against acidosis.
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Therefore, it is important that plasma glutamine levels show stability between synthesis and usage by different body tissues and organs. After prolonged physical strain, the reduction in plasma glutamine level results from increased absorption and demand of glutamine by the body. Decrease in plasma glutamine may also result from two factors: increased absorption of glutamine and reduced synthesis and changed transportation kinetics (Rowbottom et al., 1996). As noted, long and strenuous exercises are also a source of increase in plasma cortisol levels, which fuels both catabolism of proteins and release of glutamine and hepatic, gastrointestinal, as well as renal gluconeogenesis. When depletion of liver glycogen and the concentration of blood sugar occur, there is an increased rate of gluconeogenesis in the liver from glutamine, glycerol, and alanine, which places a considerable drain on the availability of plasma glutamine (Nurjhan et al., 1995). The plasma levels of cortisol, glucagon, and growth hormone increase during intense and prolonged exercises. Cortisol and glucagon lead to increased usage of glutamine along with other amino acids by the liver and it allows enlarged usage of glutamine in gluconeogenesis as well as acute-period synthesis of proteins (Nurjhan et al., 1995). On the other hand, growth hormone fuels the absorption of glutamine by the kidneys as well as the gut (Nurjhan et al., 1995).
Benefits of glutamine to athletes
Glutamine is particularly important in the muscle growth process. It preserves the already built muscle tissues rather than directly promoting the growth of new muscle tissues. Muscle breakdown occurs frequently during strenuous training and in case when the body does not receive adequate protein and while resting. The process of muscle breakdown is very natural. Glutamine assists by reducing the rate of muscle breakdown and this result in increased overall net gains in muscle mass.
During prolonged or strenuous exercise, plasma glutamine levels are decreased by as much as 34-50% (Don Santos et al., 2009). Don Santos et al used rats to determine the effects of exhaustive exercises on glutamine production and transportation in skeletal muscles after a 24-hour exercise. They discovered that 24 hours after exercise, lower glutamine synthetase contributed to the decrease in muscle glutamine concentration. This is comparable to Borgenvik et al., (2012) which evaluated alterations in muscle and plasma intensities of free amino acids, particularly in endurance of exercises and after recovery. Nine athletes took part in one-day standard endurance trial together with controlled energy consumption and they took part in twelve sessions of kayaking, cycling, and running. The researchers took blood samples prior, during, after the exercise, and after twenty-eight hours of rest. They also took muscle biopsies before, after the exercises, and after the recovery period. They discovered that ultra-endurance exercises cause considerable increases in muscle and plasma amount of phenylalanine and tyrosine; implying an increase in net muscle protein breakdown at the time of the exercise. During the exercise, there were reduced plasma concentrations and glutamine levels whereas after the exercise, there were no changes in the muscle concentration.
Various immune system cells such as white blood cells, macrophages, and lymphocytes rely on glutamine as their main source of fuel. These cells usually attempt to draw their glutamine from muscle tissue but the supply is normally poorer than the demand. This leads to a temporary suppression of the immune system (Rowbottom et al., 1996). Most athletes experience an increased rate of infections, especially those related to the upper respiratory tracts like flu and common cold. In case that an athlete does not replenish enough glutamine after the workout, it leads to the suppression of the immune system function for a longer period and this leads to more incidences of infections as well as wound healing(Rowbottom et al., 1996).
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During intense exercises, muscle tissues require a lot of glutamine to prevent muscle breakdown. For this reason, the skeletal muscle activities control the immune system directly (Hill et al. 2008). In case of overtraining, for example, when the intensity and frequency of training is disproportionately increased and not balanced with enough recover periods, there is extreme glutamine depletion together with weakening of the immune system. Athletes who over-train do not replenish the glutamine levels to the pre-training levels and further exercises lower glutamine levels in the body leading to muscle loss as well as a weakened immune system (Hill et al. 2008). Moreover, increases in the catabolic cortisol hormone (or stress hormone), fatigue, poor performance, depression, nausea and prolonged illnesses are characterized symptoms of over-training syndrome (Hill et al. 2008). Thus, this warrants glutamine supplementation for athletes who take part in prolonged and intense activities. This allows them to maintain and improve performance and health, increase fitness and train intensely without down periods of sickness.
Glutamine has a powerful anti-catabolic effect which prevents muscle breakdown; the effect powerfully reduces muscle breakdown, it exerts this in various ways: Primarily by neutralizing and attenuating catabolic effects of cortisol (Hill et al2008). The levels of cortisol hormones are increased considerably during stressful periods. Cortisol levels are increased greatly as the workout progresses, which councourently increases the stress on the working muscles; they are particularly high in the end of the strenuous workout (Hill et al (2008). Hill et al (2008) discovered that high intensity exercises provoke increase in circulating cortisol levels. Cortisol increases muscle breakdown for acquiring glutamine as well as other amino acids for energy use evidenced by increase in the glutamine synthetase enzyme needed for glutamine synthesis (Hill et al., 2008). Glutamine supplement increases glutamine concentration in the muscle cells inhibiting the glutamine synthetase enzyme and efficiently neutralizing or reducing muscle breakdown induced by cortisol (Hill et al., 2008).
Glutamine also spares muscle breakdown. Its supplements do this in two ways: maintaining glutamine concentration in the skeletal muscles, thus, inhibiting production of glutamine synthetase and preventing muscle breakdown for glutamine. The second way entails increasing the levels of glutamine in the blood, which helps to meet the demand for glutamine by other cells and tissue such as immune system and small intestine, and again prevents muscle breakdown for releasing glutamine (Bonetto et al 2010). Studies show that glutamine supplements minimize the breakdown of muscles and improve metabolism of proteins. In their research, Bonetto et al (2010) demonstrated that glutamine supplementation efficiently stops induced loss of proteins and reinstates the normal myostatin amounts. In addition, the supplements exert a protective effect that represents a possible strategy for improving muscle mass. Enhanced protein breakdown from activation of proteolytic systems causes depletion of skeletal muscle protein (Bonetto et al., 2010).
Glutamine also acts as an anti-catabolic by preventing down-regulation of synthesis of the myosin heavy chain, one of the muscle contractile proteins and sparing them from breakdown preventing muscle atrophy and muscle wasting (Izaki et al., 2008). The anabolic effect allows enhanced protein synthesis by cell hydration. Glutamine supplements contribute to an anabolic effect. It acts as a cell hydrating/cell volumizing agent through drawing water into the muscle cells and increasing their cell capacity (Bonetto et al. 2010). This serves as a metabolic signal for cellular anabolism, promoting increase in protein and glycogen synthesis. Alternatively, loss of water from the muscle calls causes cell shrinkage, which signals cellular catabolism (Bonetto et al. 2010). This shows the importance of maintaining good hydration status for greater catabolism.
Depletion of glutamine levels during intense training decreases stamina, strength, and recovery. It takes days for glutamine levels to normalize in cases where athletes do not take any supplements (Izaki et al., 2008). The supplements help in glucose regulation and glycogen formation. They serve as an antecedent of glucose because its carbon skeleton synthesizes glucose. Normally, the insulin hormone serves to decrease blood glucose while the glucagon hormone increases blood glucose. Thus, the body requires a balance of the two hormones to maintain normal blood glucose levels. Nonetheless, glutamine helps to maintain blood glucose levels by glucose synthesis (gluconeogenesis) irrespective of the insulin-glucagon ratio (Izaki et al., 2008). Studies have shown that glucogenesis usually increases seven times after glutamine supplementation and there is an increase in muscle glycogen after consuming glutamine after the exercise (Izaki et al., 2008). Studies have also shown that it assists in production and storage of glycogen, which is of great significance to most endurance athletes and a large amount of endurance oriented anaerobic athletes (Castell et al 2003). It is also well known for its anabolic effect of improving muscle mass and strength; it is highly anabolic and considerably reduces protein degradation and catabolism (Roth 2008). It also promotes glycogen synthesis in the skeletal muscle partly because of its cell hydrating effect. Therefore, the general role of glutamine in glucose formation and regulation is increasing glycogen breakdown in the liver independent of any signal from glucagon, increasing blood glucose because of the glycogen breakdown and glucose synthesis and increasing stores of muscle glycogen even in situations where there are low insulin levels (Roth 2008). According to Roth (2008), administering glutamine has a positive effect on glucose metabolism when it comes to insulin resistance. As result, it assists athletes recover quickly between workouts and prevents them from getting sick.
Glutamine also increases the levels of growth hormone, which in turn, increases the growth of muscles. Most studies propose that it plays an imperative role in enhancing a valuable environment for improved growth hormones levels during strenuous exercise levels (Lacey & Wilmore, 1990). Lacey and Wilmore (1990) found that temporary ingestion of glutamine does not have any effect on muscle strength, but that continuing supplementation is more efficient application of glutamine when it comes to gaining strength. Glutamine has beneficial effects on an athlete's performance because of a number of physiological incidents that comprise high levels of growth hormones, reduced skeletal muscle catabolic outcomes, enhanced anabolic effects and improved protein production and more capacity to maintain soaring intensity exercises because of the high capacity of safeguarding lactic acid. It also increases glutathione (GSH), a strong antioxidant in the body (Lacey & Wilmore, 1990). Glutathione is a strong antioxidant defense in the body and comprises three amino acids: glutamate, glycine and cysteine (Izaki et al., 2008). Glutamine increases the synthesis of glutathione, which protects tissues from free radical attachment and further contributed to reducing catabolism. Glutathione also assists in enhancing the immune function (Izaki et al., 2008).
Glutamine also has an active part in healing and recovery. It not only acts in accelerating recovery of muscles after a strenuous training but also plays an active role in recovery from trauma and healing of wounds, it also increases the athlete's capacity to produce human growth hormones, which assist in metabolizing body fat and supporting growth of new muscles (Smith & Norris 2000). Athletes with improper diets and/or who over-train and, thusly, undergo muscle wasting are at times incapable of creating their own glutamine supplies and, thus, benefit from glutamine supplementation (Smith & Norris 2000). Glutamine is versatile and has a range of associated functions making it one of the most vital amino acids in a human body. Ensuring enough glutamine stores in the body is crucial for athlete for muscle gain results. Thus, supplementation is essential.
Since exercise is a form of increased metabolic stress, it depleted glutamine from an athlete’s body. The depletion rate is dependent on the intensity and length of exercise. Low glutamine levels cause damaging effects on the body, however, supplementation wards of the effects in numerous ways as discussed above. In addition, glutamine has an anti-inflammatory effect, which reduces muscle tissue inflammation after strenuous exercise. This assists in reducing swelling and delaying onset muscle soreness after a workout and helps in proper recovery.
Over-training refers to the condition whereby there is stress of the adaptive mechanisms of athletes, which diminishes their capacity to retain a balance between exercise and recovery (Smith & Norris 2000). Excessive stress coupled with inadequate recovery period are the main causes of over-training. It usually occurs from sudden increase in training volume overlapping with shorter recovery time between training session. High-performance athletes, train tirelessly to attain better performance, however, many do so without knowing that glutamine levels go back to normal while resting after strenuous training, which leads to a failure to maintain a proper and healthy balance between training and recovery. The role of glutamine in over-training has received much attention from practitioners and researchers over the last twenty years because of its serious threat to athletic performance and health. Numerous researchers have noted considerable reductions in plasma glutamine after strenuous or prolonged training and exercises. Over-training syndrome causes under performance and prolonged fatigue in athletes, especially after periods of strenuous training. Kingsbury et al (1998) observed that the plasma glutamine levels are lower in over trained athlete than sedentary individuals and well-trained athletes. Smith & Norris (2000) hypothesized that glutamine concentrations go down when an athlete’s amount of work go beyond his or her ability to tolerate physical stress. Researchers have put forward numerous reasons for reduction of glutamine concentration over time, among them are: Increased glucocorticoids levels, reduced nutritional absorption of proteins, mitochondrial lesions in the skeletal muscles, as well as increase rate of use of glutamine by other tissues.
On the other hand, restrained training leads to increased availability of glutamine because of a good stability between peripheral clearance and muscle synthesis (Kingsbury et al 1998). Lack of physical activity leads to lesser glutamine synthesis and uptake, whereas after exercise there is a reduced glutamine availability, which marks over-training. Increased availability of glutamine contributes to lesser inflammation, as well as health benefits allied to optimal training (Castell et al 2003). This indicates that glutamine supplementation may improve immune competence after strenuous training.
In recent years, researchers have carried out various researches on glutamine supplementation in athletes. A strong rationale exists for supporting the effectiveness of glutamine supplementation in athletes. For instance, research has shown that glutamine function in immune system support prevents infection after exhaustive sessions of physical exercises, which tends to decrease the amount glutamine in the plasma (Smith & Norris, 2000: Castell & Newsholme, 1997). Glutamine supplements also have a major part in working against stress hormones like cortisol, which causes muscle wasting, degradation, or catabolism. Glutamine supplements help reduce protein or muscle tissue breakdown, enhance lymphocyte function, and reduced infections (Newsholme, 2001).
The role of glutamine in fueling glycogen synthase, the enzyme that manages the production and storing of glycogen fuel storage in the liver and muscles, offers a means via which glutamine supplementation promotes increased fuel storage (Castell & Newsholme, 1997). Glutamine also increases cells volume and stimulates enzyme activities, which take part in glycogen storage and those concerned in anabolic activities like protein synthesis in the liver and muscles (Castell & Newsholme, 1997). Researchers have also hypothesized that glutamine supplementation increases the amount of growth hormones, which stimulates synthesis of proteins and encourages growth in strength and mass (Castell & Newsholme, 1997).
Glutamine supplementation has a beneficial effect for individuals engaged in intense and chronic exercises. Exercise training boosts the requirement for glutamine necessitating external self-administration for ultimate performance and recovery (Antonio & Street, 1999). Glutamine plays an imperative part in the immune system functioning and its cells, the supplements, thus lessen or prevent the severity of infection or illness after an intense bout of exercise; this enables athletes to carry on intense training. In addition, as stated above, the supplements also offset catabolic effects of increased glucocorticoid levels generated during intense training/ exercise. Furthermore, supplementation fuels other organs and cells such as the kidneys, liver and immune cells, and this spares the potential loss of glutamine because of insufficient dietary intake; most critically, this spares muscle proteins from degradation (Antonio & Street, 1999).
Supplementation also influences the acid-base balance in the body through generating a safeguarding effect (Antonio & Street, 1999). Glutamine changes the acid-base balance through increasing the retention of plasma bicarbonate (HCO3) in the kidneys. This process takes place through deamination, when glutamine enters the kidneys epithelial cells (Antonio & Street, 1999). The ammonium formed from glutamine deamination then binds with H ions to form an ammonium ion.
Antonio et al. (2002) carried out an investigation to determine whether ingesting glutamine affects weight lifting performance. They used a placebo-controlled, double blind cross over study whereby six resistance trained men completed weightlifting exercises after ingesting glutamine supplements together with placebo- a fruit juice that was calorie free. The research subjects performed four full exercise sets to temporary failure one hour after ingestion. The study findings showed that short-term consumption of glutamine did not improve the resistance-trained men weightlifting performance. This study is comparable to Haub et al (1998) study, which investigated the possibility of glutamine supplements to change the blood acid-base balance and as result boost the time to exhaustion when undertaking strenuous exercises. This research had the basis on the theory that glutamine changes the acid-base through boosting retention of plasma bicarbonate in the kidneys. The research subjects performed five sessions of exercises on a cycle ergometer at 100% VO2peak. The first four sessions lasted one minute whereas the last session continued to fatigue. The exercise sessions started one and a half hours after taking 0.03-g.kg body mass of either placebo or glutamine. There were not any considerable variation in plasma bicarbonate, PH, and lactate concentration between pre-exercise, pre-ingestion, bout five and bout four. The time to fatigue was also not considerably different between conditions.
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Generally, the data being obtained showed that acute glutamine ingestion did not improve either exercise performance or buffering potential in the research subjects. Nonetheless, researchers have suggested that an environment should be acidic to set off glutaminase and eventually utilize glutamine to boost plasma bicarbonate. Piatolly et al (2004) researched the effects of glutamine supplement on recovery from intense exercises among elite cyclists. They discovered that the cyclists in the glutamine group took long before they got exhausted after ingesting the supplements for six days and they recovered from exhaustive exercise before the placebo group-cyclists who did not take glutamine. Castell et al. (1996) examined a likely prophylactic effect or oral glutamine supplements on infection occurrence. They found out that providing two-glutamine drink in the first two hours after the race reduced infection incidences in the week that following the event. Similarly, Rohde et al (1998) discovered that a glutamine solution given at particular time intervals (i.e. 0, 30, 60, and 90 min) after the marathon race prevents reduction in plasma glutamine concentration.
In summary, glutamine is the amino acid that is critical for numerous homeostatic roles and for the operation of various tissues in the human body. Various catabolic states such as infection and acidosis affect glutamine homeostasis, resulting in glutamine depletion. Strenuous and prolonged exercises result in decrease the levels of plasma glutamine during and after exercise. Based on the previous research studies performed on glutamine supplements, some researchers believe that glutamine has a possible effectiveness as a dietary supplement for athlete's performing prolonged and high intensity exercises. This arises from the fact that glutamine has numerous benefits primarily due to its positive influence on the acid-base balance in the body. The aim of this literary analysis was to establish the outcomes of glutamine supplements on an athlete's maximum performance, as well as their recovery from prolonged and high intensity training. The supplements help in preserving muscle mass, reducing catabolism after exercise, and hastening recovery from exhaustive training. High strenuous training leads to a well-described reduction in plasma glutamine levels. Some studies reviewed implicate persistently low levels of glutamine contribute to transient immune suppression and greatly increase the risk of illnesses, which usually affect athletes during intensive competitions and training. Under metabolic stress conditions, the body requirement for glutamine becomes conditionally important as the body cannot create adequate levels to supply all its daily requirement, hence, dietary supplements are essential in preventing skeletal muscle catabolism, which is the main port of glutamine storage and transportation. For athletes who have increased stress levels, glutamine supplementation is a vital way to promote tissue repair, reduce muscle catabolism, as well as boosting immune function to prevent infections. The scientific literature reviewed supports the valuable outcomes of glutamine supplementation in preserving muscle mass and assisting the recovery process of the athletes who are engaged in prolonged and strenuous exercises.
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