Sports Fitness Training

Exercise Intensity

Several early studies indicated that at least with aerobic ­type exercise, the contribution of amino acids to exercise energy production was linearly related to exercise intensity. The branched-chain amino acids (leucine, isoleucine, and valine) are the major ones oxidized and the mechanism responsible is thought to be an exercise intensity-dependent activation of the limiting enzyme (branched-chain oxoacid dehydrogenase activity) in their oxidation pathway.

Exercise Type

Apparently any increased protein need for strength exercise does not involve this exercise intensity mechanism because, despite the intense nature of this type of exercise, amino acid oxidation remains unchanged . Likely, this is a result of the large anaerobic component of strength exercise. Consequently, if body­builders need large amounts of protein it is not to provide auxiliary exercise fuel (carbohydrate provides that) but rather because sufficient amino acids must be available to maximize any increase in muscle synthetic rate produced by the exercise stimulus. Several studies indicate that there may be some truth to this commonly held beliet However, the optimal intake would appear to be 1.5-2.0 g/kg/day. This is an amount far less than what many strength athletes consume on a regular basis. Several possibilities might explain this apparent contradiction. Obviously, the athletes could be incorrect, i.e., they may have been influenced by a powerful placebo effect.

Alternatively, some other constituent in high-protein foods might, in combination with the surplus supply of amino acids, be responsible for a muscle-building effect. Several candidates are possible including creatine, a nitrogen compound found in meat and fish that has been studied recently, Although not all studies report positive effects with creatine supplementation, many demonstrate significant ergogenic effects (10% or more), especially during intense brief efforts. Such exercise-enhancing effects combined with a training program might accelerate further the normal gains observed with strength training indirectly via a super training effect. Moreover, some data exist indicating that creatine has anabolic effects on muscle, which could also playa role. Finally, although associated with a variety of adverse health effects, some compounds (i.e., anabolic steroids) are known to be anabolic 46 and it is possible that the high-protein intakes consumed by some strength athletes are only advantageous when combined with these agents.

Exercise Duration

With exercise duration, energy use from amino acids increases likely due to the decreased availability of carbohydrate as the body’s stores of this important fuel can be depleted in a single exercise bout. A similar response occurs with starvation, i.e., protein can be used for energy once the limited carbohydrate stores are exhausted. This may play some role for strength athletes if training sessions are prolonged.

Training History

In endurance exercise training, it appears that amino acid oxidation both at rest and during exercise increases perhaps due to training-induced changes in branched ­chain oxoacid dehydrogenase activity. Yet, this possibility remains controversial as the data from one study disagree and no obvious explanation to explain the discrepancy is available. The data with strength training are also somewhat unclear. It has been suggested that protein needs of novice bodybuilders might exceed those of more experienced strength trainers. Although this is consistent with the well-known observation of greater gains in muscle growth of novice strength trainers, several other studies indicate protein needs remain at similar levels for more experienced strength athletes. A recent study with acute eccentric exercise demonstrated similar increases in protein synthesis between resistance-trained and untrained subjects but that protein breakdown was greater in the latter This observation may explain why prior eccentric exercise reduces subsequent muscle damage and pain, and because eccentric exercise is part of most training programs this may indicate that the magnitude of increased protein needs induced by strength training could be reduced as one becomes more experienced. However, at this point in time, this question cannot be answered conclusively. More study of the protein needs of novice versus experienced strength trainers is definitely needed.

Tags:endurance training, exercise, exercise duration, exercise intensity, exercise training, exercise type, placebo effects strength training

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Carbohydrate, which carries kilocalories per gram, is the macronutrient needed in greatest amounts during training and competition. The primary function of carbohydrates is to fuel the body’s energy to power muscular contractions and numerous physiological functions. This is accomplished via the breakdown of ingested carbohydrate and stored glycogen to its active energy form, glucose.However, relative to fat, the stored glycogen present in liver and muscle is relatively small. This becomes apparent during endurance exercise in particular, where a lack of available energy can be detrimental to performance.

However, endurance exercise is not the only form of training and competition in which carbohydrate depletion can compromise performance; it can also occur during high-intensity exercise as well especially during activities that involve high quantities of repeated anaerobic bouts. This depletion can then trigger a phenomenon known as gluconeogenesis, a process by which additional energy is formed by the synthesis of glucose from protein and fats. Unfortunately, a prevailing disadvantage of this compensatory energy-producing mechanism is the potentialloss of muscle tissue. This, of course, flags the significance of adequate carbohydrate intake and its role in the maintenance of the body’s protein stores.

Furthermore, a dangerous side effect of inadequate carbohydrate intake is impaired central nervous system (CNS) function, considering that the brain uses glucose almost exclusively as its primary fuel. This is apparent during starvation and prolonged endurance exercise, when depleted glycogen stores can induce feelings of dizziness and general malaise. In the case of low-carbohydrate diets, prevalent side effects are symptoms of fatigue, weakness, and hunger Conversely, excess carbohydrate intake can lead to undesired weight gain. Because ingested carbohydrates are converted to muscle and liver glycogen, once their carrying capacity is achieved, the rest is converted to fat. Obviously, this is an unwanted result for those who want to lose weight and improve body composition. It is also critically disadvantageous for those athletes engaged in events in which weight gain can diminish performance (i.e., distance running). Therefore, this signifies the extreme importance of a dietary regimen that strikes a balance between adequate energy production and physique maintenance or improvement.

Tags:Benefits of Carbohydrates, carbohydrate depletion, carbohydrate intake, cns function, endurance exercise, function of carbohydrates, glycogen stores protein

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Compared with prolonged endurance activity, much less has been researched and written regarding the influence of carbohydrate intake on high-intensity sporting events. The authors define high-intensity events, also termed strength/power sports, as exercise requiring high power or force output. This includes events in which power output leads to muscular fatigue in a few minutes of activity or less, and exercise that requires repetitive, high-force production from specific muscles. High-intensity exercise, therefore, cannot be sustained for extended periods of time, and frequent or prolonged rest periods are required. Fortunately for strength/power athletes, rest periods are usually included in such sports, owing to the depletion of energy substrates (i.e., phosphocreatine, glycogen) and accumulation of metabolic products (i.e., lactate, ammonia).Although the performance benefits of carbohydrate ingestion are well documented in endurance athletes, strength and power athletes must also be aware of this macronutrient’s potential ergogenic effects. Whereas glycogen use is insignificant during brief anaerobic events (i.e., Olympic weightlifting), in situations that call on athletes to perform repeated anaerobic exercise bouts (i.e., repetitive sprints, basketball, football), proper carbohydrate ingestion becomes increasingly significant. Too often, adequate carbohydrate intake is overlooked and the resulting glycogen debt becomes the culprit when premature fatigue surfaces in strength/power sports. In contrast, the energy attained via glycogen use in many prolonged low-intensity endurance sports (i.e., marathon running) is aided by the oxidation of fats. However, in the case of such anaerobic sports as basketball and ice hockey, the repetitive nature (and correspondingly high-glycogen use) does not physiologically allow for surplus energy production from fats. Thus, the ample glycogen availability demanded by these sports necessitates an augmented carbohydrate intake. Certainly, the carbohydrate requirements for high­intensity sports are not as great as those for endurance events, although some studies have noted the ability to maintain higher training intensities when greater than normal intakes were consumed. However, as the intensity of the event increases (and thus the duration decreases), higher than normal glycogen concentrations do not appear to offer any additional benefits. Therefore, a supplemental carbohydrate intake is most advantageous for those athletes involved in repetitive high-intensity events or training regimens of a similar nature. As an example, ice-hockey players who consumed a carbohydrate supplement (360 g/day for 3 days) in addition to their normal diet before a competition possessed muscle glycogen levels that were twice as high as those in players who were not given the supplement. It may also be important for similar athletes to ingest a high­carbohydrate diet during periods of intense training. events or training regimens of a similar nature. As an example, ice-hockey players who consumed a carbohydrate supplement (360 g/day for 3 days) in addition to their normal diet before a competition possessed muscle glycogen levels that were twice as high as those in players who were not given the supplement. It may also be important for similar athletes to ingest a high­carbohydrate diet during periods of intense training. events or training regimens of a similar nature. As an example, ice-hockey players who consumed a carbohydrate supplement (360 g/day for 3 days) in addition to their normal diet before a competition possessed muscle glycogen levels that were twice as high as those in players who were not given the supplement. It may also be important for similar athletes to ingest a high­carbohydrate diet during periods of intense training.

Tags:anaerobic exercise, carbohydrate intake, Diet and Training, ergogenic effects, glycogen, muscular fatigue, oxidation of fats, phosphocreatine, power athletes power sports

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Pre-Exercise Carbohydrate Intake

Adequate carbohydrate intake is especially important before endurance training or competition. Given that many endurance events last 2 hours or longer, and that glycogen stores are sufficient for approximately 2 hours of intensive exercise, pre-exercise carbohydrate feedings carry utmost significance. When properly ingested before exercise, carbohydrates have been shown to improve performance especially when combined with during ­exercise feedings. Additionally, ingesting carbohydrates during these two critical time periods also induces a glycogen-sparing effect which prolongs intensive exercise.

The goals of pre-training nutrition are to maximize glycogen stores, avoid a significant increase in plasma insulin concentrations (resulting in a hypoglycemic state), and avoid gastrointestinal upset during exercise. The pre-exercise period can be defined as the 4- hour period before an activity and can be further delineated into two distinct phases: 2 to 4 hours before and 30 to 60 minutes prior to exercise.

The 2- to 4-hour period preceding exercise takes on special significance in cases in which glycogen concentrations may be depleted as a result of intense exercise or insufficient carbohydrate ingestion in the days before an event. In these instances, the intake of a sizable amount of carbohydrates, approximately 300 g, 4 hours before exercise has been shown to increase work output and performance. Similar findings, along the same lines of enhanced endurance and work output, have also been reported when greater than 200 g CHO were consumed 3 to 4 hours before endurance-type exercise Therefore, research indicates that athletes should ingest 200 to 300 g CHO in the 2 to 4 hours preceding exercise. The case can even be made for a greater intake in special circumstances (before significantly long endurance events, following a fasted state, and following successive days of intense endurance exercise).

To promote sustained carbohydrate availability throughout an exercise session, the 30 to 60 minutes before an event is significant not only in that a sufficient intake must be achieved, but the proper type of carbohydrate must also be consumed. In light of this importance, properly manipulating the glycemic index of this meal may optimize carbohydrate availability for ensuing exercise. Because a potential disadvantage of pre-exercise carbohydrate intake is an exaggerated insulin response, which suppresses fat metabolism and curtails available glucose for subsequent exercise, the glycemic index becomes an indispensable tool. For example, Foster et al. reported that feeding 75 g of glucose (a high-glycemic carbohydrate) 30 minutes before exercise impaired the resulting cycle time to exhaustion.

In contrast, Thomas and colleagues noted that consuming 1 g CHO/kg body weight of a low-GI food (lentils) 1 hour before endurance exercise prolonged work capacity when compared with the ingestion of an equal amount of a high-glycemic food (potatoes). The authors suggested that this performance increase was attributable to glycogen sparing following the consumption of low-glycemic carbohydrates. Thus, according to this study, low-GI meals appear to elicit a sustained source of energy throughout exercise and recovery However, other studies have expressed no differences in performance following ingestion of low- or high-glycemic foods, although the investigators did find that high-GI meals caused a decline in blood glucose concentration before exercise. Perhaps these differences in glucose concentration during the early phases of exercise are short-lived and do not negatively affect the performance of most athletes. Further research is needed in this area, but it is clear that low-GI foods definitely promote a more favorable metabolic environment for exercise.

Regardless of glycemic index, it is evident that adequate glycogen stores before exercise is the predominant nutritional factor in subsequent performance. In the 30­to 60-minute window preceding exercise, most studies suggest that 60 to 75 g of carbohydrates consumed in this period are sufficient to top off glycogen stores and improve performance One should make sure that these feedings do not cause excessive fullness or gastrointestinal upset, however, which can actually impair exercise performance.

Carbohydrate Intake During Exercise

The primary goals of carbohydrate fee dings during exercise are to maintain glucose levels to sustain energy and work output, and spare liver glycogen. When ingested in sufficient quantity, elevated carbohydrate availability during endurance exercise can improve work capacity in events lasting more than 1 hour Also, the manner in which carbohydrates are ingested during exercise, specifically in terms of feeding schedule and composition (solid or liquid), is an important performance-related variable.

With regard to quantity, research indicates that the maximal oxidation rate for exogenous carbohydrate is approximately 60 g/hr It is this finding that gives rise to the common belief that carbohydrates ingested at a rate of 45 to 75 g/hr are sufficient to improve exercise performance. Accordingly, various types of carbohydrates, including glucose, sucrose, and maltodextrins, are all effective choices to make to enhance training and competition. In fact, the glycemic index does not appear to elicit any physiologically important differences. Ingesting fructose, however, because it is slowly absorbed, is not advised during exercise because of the increased risk of gastrointestinal distress.

Although the effect of feeding frequency does not seem to influence subsequent carbohydrate oxidation during endurance exercise, withholding carbohydrates until late in an exercise bout will impair performance Similarly, this points to the necessity of ingesting carbohydrates throughout exercise not only to sustain energy, but to avoid possible gastrointestinal disturbance. Correspondingly, consuming carbohydrates in liquid or solid form elicits similar effects, although liquid solutions provide the added benefit of maintaining hydration. To coincide with the 45 to 75 g/hr recommendation, this would typically involve ingesting approximately 1 liter of sports drink (carbohydrate-electrolyte solution) per hour. Fortunately, these solutions playa dual role of providing both adequate energy and hydration without causing excessive fullness.

Post-Exercise Carbohydrate Intake

The primary objective of ingesting carbohydrates following exercise is to replenish glycogen stores for subsequent exercise bouts. In doing so, overtraining is prevented and adequate energy is again available for forthcoming exercise. It was previously thought that full restoration of muscle glycogen stores takes approximately 48 hours. If performed properly, however, research now indicates that this process can be accomplished in approximately 20 hours.

Research also confirms that glycogen restoration occurs most rapidly when carbohydrates are consumed immediately post-exercise In fact, when carbohydrate feedings ensue immediately following exercise, the rate of muscle glycogen storage is almost twice that of when they are consumed after a 2-hour delay, However, because full glycogen restoration can still be achieved via adequate intake (regardless of timing), these results indicate the importance of immediate feedings only when further exercise is imminent. Therefore, this strategy is most important when only 4 to 8 hours of recovery pass between exercise sessions. As the time for recovery increases (longer than 24 hours), the importance of carbohydrate quantity takes precedence over feeding frequency or timing. Interestingly, the frequency of feedings does not significantly alter muscle glycogen restoration rates as long as the daily carbohydrate needs of endurance athletes (7-10 g/kg body weight) are met.

The optimal rate of glycogen storage appears to be achieved when at least 0.7-1.0 g CHOlkg body weight is consumed every 2 hours in the early stages of recovery, leading to a daily total of 7 to 10 g/kg body weight. Although this can be achieved with solid or liquid forms of carbohydrate, particular glycemic types seem to have differing effects on subsequent glycogen restoration. Glucose and sucrose fee dings have been shown to induce similar rates of glycogen recovery, whereas fructose produces a tower rate of storage. These findings have sparked suggestions that post-exercise carbohydrate intake should consist mainly of moderate- to high-glycemic foods. Given their more rapid introduction to the bloodstream, it appears that these types of carbohydrates are more beneficial in achieving swift glycogen restoration. Indeed, studies have indicated that high-glycemic carbohydrate foods consumed post-exercise promote greater glycogen storage than do an equal amount of low-GI foods. Specifically, it has been suggested that foods with a low glycemic index should not make up more than cine-third of recovery meals.

Tags:Benefits of Carbohydrates, carbohydrates intake, exercise, gastrointestinal distress, glycemic index, maltodextrins, nutrition sports supplements

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It is well understood by the athletic community that increased carbohydrate intake (loading) can significantly enhance exercise performance in situations in which muscle glycogen stores are limiting. Less well known, but of critical importance is that there is a brief window of opportunity perhaps 60 minutes or so following exercise in which the muscle glycogen synthetic rate is significantly greater than at any other time during the day. Similarly, it is becoming clear that strength exercise causes disruptions in both muscle protein synthesis and degradation, resulting over time in substantial muscle growth. Perhaps, nutrient supplementation post­exercise might optimize muscle growth. For example, this overall growth response could be limited by energy and/or amino acid availability. If so, providing either or both could enhance muscle growth/repair via increasing protein synthesis or decreasing protein degradation. Some evidence Combining carbohydrate and amino acids may be the best approach because the insulin released in response to the carbohydrate stimulates amino acid uptake by muscle, leading, at least potentially, to enhanced protein synthetic rates . As mentioned above, some amino acids are also powerful stimulators of insulin release. Moreover, other hormones important for positive training adaptations could be involved. It appears that the essential amino acids are the most crit­ical and that only small amounts may be necessary. As further study clarifies the details of the effects of strength training on net protein balance in muscle it should become possible to prescribe precise recommendations regarding type, amounts, and timing of nutrient supplementation to maximize the anabolic stimulus following strength training. If so, this information would be of considerable benefit not only to the athletic community but also to any group of individuals who have lost muscle function due to disease or disuse (i.e., post-surgery, injuries, elderly, zero-gravity environment, etc.).

Tags:carbohydrate, Diet and Training, essential amino acids, exercise causes, exercise performance, insulin release, muscle glycogen, muscle growth, muscle protein synthesis, nutrient supplementation, protein degradation strength exercise

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