Dietary Intervention For Athletes: Part 1.

It is extremely important to maintain adequate glycogen stores for athletes training in multiple sprint events. Below you will find some useful information from studies about carbohydrate consumption for different types of sports.

Problem Statement & Rationale

Athletes are involved in a variety of training situations that require a tremendous amount of work over the course of a week, a day, or even a three hour practice. Because it is generally understood that nutrition is a cornerstone of any sports program, it is vital to ensure proper dietary intakes for female and male collegiate athletes if performance is going to be improved or even sustained (Berning, 2000; Economos, Burtz & Nelson, 1993).

The combination of poor nutrition or too few calories and inadequate rest can lead to a lack of energy, compromised immune system and more frequent injuries (MacKinnon, 2000; Venkatraman, Leddy, & Pendergast, 2000).

Schedule requirements of athletes include practice, conditioning, weight training, film review, and this is all above the daily requirements of life. Many of the physical and psychological pressures that have evolved throughout all facets of society influence health and performance (Venkatraman et al., 2000). Extremely busy lives, along with limited nutrition knowledge or appreciation, can make it be difficult to achieve proper nutrition status in athletes (Economos et al., 1993). But actually consuming an adequate diet extends much further than this.

"Clinical examinations show intense exercise inherently
inhibits maximal immune system"

Athletes also find themselves under pressure to meet certain body shape and weight requirements that are unique to not only their particular sport but also the society (Hausenblas & Carron, 1999). Coupling this with strong societal and cultural pressures to meet anthropometric criteria, athletes can struggle with diet and nutrition. In some cases the struggle can be much more drastic than their non-athlete counterparts.

Disordered and poor eating can be associated with a continuum of negative consequences similar to the positive impact proper nutrition can have upon health and performance. Intense exercise has been clinically shown to suppress the immune system and create a susceptibility to infection, and it should be noted that improper nutrition can compound this affect (Bishop, Blannin, Walsh, Robson, & Gleeson, 1999; MacKinnon, 2000; Venketraman et al. 2000). This point can not and should not be an overlooked piece in the preparation of championship athletes.


Assessing A Nutritional Plan

In order to fully assess the nutritional plan that is required with an athlete or team, you must first determine the answers to a few key questions.

  • Do you or your athletes have adequate knowledge about nutrition and its effects upon health and performance?

  • Do you or your athletes follow a proper diet during training?

  • Do you or your athletes have adequate access to healthy food choices?

Evaluating these questions will help unlock the key to increasing nutritional productivity. But when it comes to implementing actions in order to improve nutritional intake of athletes, as a coach, athletic trainer or a dietician you must choose between four steps of action:

  1. Do nothing.

  2. Improve the knowledge of the athletes regarding food and food choices.

  3. Make better food choices available.

  4. Improve the knowledge of the athletes while showing them through making better food choices available.

In order to fully answer this question, we must first take a step back and examine the knowledge aspect and the proper approach which should be taken to fully reap the benefits from sufficient nutrient consumption for elite athletes.


Nutritional Knowledge
The Background

Nutritional intake, and thus knowledge, can be broken down into four simple categories:

  1. Carbohydrates » Learn More.

  2. Proteins » Learn More.

  3. Lipids

  4. Vitamins & Minerals. » Learn More.

Knowledge and understanding of the role of nutrition in health and performance of athletes has grown considerably over the past couple of decades, at least within the scientific community.

The specific role many food components can have on performance and health has become better understood because of new research techniques. The basic concepts of a healthy diet as put forth by the United States Department of Agriculture (USDA, 1992) should most often be the cornerstone of any sport specific diet. Most of their recommendations are appropriate for athletes.

In most cases, if proportions remain the same as the recommendations and the total caloric intake is increased, the nutritional needs of the athlete will be met. Economos, Bortz and Nelson (1993) stated that "there is no special food that will help elite athletes perform better; the most important aspect of the diet of elite athletes is that it follows the basic guidelines for healthy eating" (p. 382).

Obviously there are special considerations that evolve, but this stands true as a general rule. Manipulating timing and specific nutrient combinations is the next frontier in nutritional augmentation.

The ease of information transfer about various "diets", various manipulations if you will, coupled with the pressure to be successful can drive athletes to try unconventional and often unhealthy dietary habits in an attempt to boost performance. These diets, such as those that leave out entire food types, can lead to impaired nutritional status and poor performance.

Athletes often have heavy training regimens and busy schedules. This combination can result in a struggle between proper nutrition, limited financial resources (for those other than professionals), and meeting schedule requirements of daily living. As we dive further into the background of nutrient intake keep this fact to the front of your thinking.


The Role Of Carbohydrates In Athletic Diets

Carbohydrates and creatine-phosphate (CP) are the primary fuel source used by the body's cells to replenish adenosine triphosphate (ATP) stores during moderate to intense activities (Berning, 2000; Gaitanos, Williams, Boobis, & Brooks, 1993; Hargreaves et al., 1998; Hawley, Schabort, Noakes, & Dennis, 1997).

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Glycogen Utilization In Athletes

    Carbohydrate requirements by athletes can vary depending on the type, intensity, and duration of the exercise event. Berning (2000) stated that:

Sports that use both the anaerobic and aerobic pathways also require a higher glycogen utilization rate and the athlete also runs the risk of running out of fuel before the race or exercise is finished.

Sports like basketball, football, soccer, and swimming are good examples of activities where athletes have a higher glycogen utilization rate due to their intermittent bursts of high-intensity sprints and running drills (p. 537).

    During exercise, stored muscle glycogen is the first choice for glucose. When muscle glycogen stores become depleted, the body must rely upon the liver for glycogenolysis and gluconeogenesis to supply carbohydrates to the exercising muscles and central nervous system (Berning, 2000).

    The total reliance of muscle cells upon glycogen as an immediate fuel source is dependent upon the activity's intensity and duration. Rankin (2000) stated:

Muscle glycogen is depleted more rapidly from Type II (fast) than from Type I (slow) muscle fibers during high-intensity exercise. Thus, even when the total depletion of glycogen sampled from a mixture of muscle fibers may be quite modest, extensive glycogen use in some muscle fibers as well as selective depletion of glycogen from specific cellular compartments may precipitate fatigue when bodily stores of carbohydrate are low (p. 1).

    CP is the first fuel source for anaerobic activity next to stored ATP (Berning, 2000; Gaintanos et al. 1993; Hargreaves et al. 1998; Hawley et al. 1997). Because ATP stores are minimal in comparison to the work outputs required, CP becomes a limiting factor during anaerobic activities.

    Gaitanos et al. (1993) found that when subjects performed 10 six-second maximal cycle ergometer sprints with 30 seconds of passive recovery, the fuel source changed from the first to the tenth trial. During the first sprint, glycolysis accounted for 44.1%, CP 49.6% and ATP 6.3%.

    As we would expect, during the tenth sprint a shift occurred towards CP as the glycogen stores depleted. Anaerobic ATP production during the tenth sprint resulted from 80.1% CP and only 16.1% glycolysis with 3.8% of the energy coming directly from stored ATP.

    The authors also noted a significant drop in total power output from the first to the tenth trial primarily from the inability of the metabolic systems to maintain the standard of performance set during the first trial.

    Biopsies of the vastus lateralis muscle confirmed this fact reporting a dramatic drop in total ATP production during the late sprints. Estimated ATP production during the first sprint was 89.3+/-13.4 mmol/kg dry weight. The energy production during the tenth sprint was only 31.6+/-14.7 mmol/kg dry weight showing a dramatic drop off in energy production.

    In a more recent study, (Hargreaves et al. 1998) tested subjects during three 30-second maximal cycle ergometer sprints separated by 4-min of passive recovery. Their results were similar to Gaintanos et al. (1993) with respect to the decrease in power production and output during the latter trials as compared to the first.

    According to Bangsbo, Graham, and Saltin (1992) and Vandeberghe, Hespel, Eynde, Lysens and Richter (1995), the availability of muscle glycogen prior to the start of exercise does not affect the initial glycogen utilization and lactate production.

    It appears that the muscle will use what glycogen is available until the stores become depleted and that there are not any glycogen rationing reactions if the pre-exercise levels are low.

    CP levels became the limiting factor in the studies performed by Hargreaves et al. and Gaintanos et al. because the testing involved passive recovery and not the active recovery that could reduce glycogen stores and is a great example to the relationship between total work performed/required and the energy systems that must be called upon.

    The more intense resistive training is (the greater the percent of 1RM utilized), the larger the relative amount of glycogen that is depleted. This explains why the practice by bodybuilders of matching their carbohydrate intake to the intensity level which they train at works to help maintain lower bodyfat levels throughout training while maintaining performance standards.

    Gaintanos et al. (1993) also found that by the ninth sprint subjects showed a possible partial reliance upon oxidative metabolism to replenish ATP stores, most likely due to a reduction in pH and an increase in muscle lactic acid content during the ninth and tenth sprints.

    High intensity oxidative metabolism relies mostly upon glucose and therefore carbohydrate stores potentially could have become a limiting factor if the trials were to continue. The relationship between these results and nutritional availability can be summarized in the following way:

    Reduced CP and glycogen availability appears to contribute most heavily to the decline in anaerobic energy production and exercise performance (in longer duration training), especially if the exercise is preceded by moderate-intensity glycogen-depleting exercise (Gaintanos et al. 1993; Hargreaves et al. 1998). According to Hargreaves et al. (1988):

"...pre-exercise levels of muscle glycogen in the present (Hargreaves et al. 1988) study were not limiting at any stage and that a greater degree of glycogen depletion is required before glycogenolysis and performance are affected during high-intensity exercise (p. 1689). In other words, carbohydrate intake is not as critical for minimal amounts of work.

Recreational athletes need not follow the extreme carbohydrate intakes that are typically directed toward competitive intensely training athletes with high relative workloads. In fact, extremely high levels of dietary carbohydrates can in fact be detrimental to recreational athletes by increasing adipose storage rates and ultimately decreasing power/mass ratios."

    Intensely training athletes however can sabotage training by creating low pre-exercise glycogen stores through eating low levels of dietary carbohydrates. Carbohydrate loading is a term often reserved for long endurance sports, but it may impact performance during sports such as soccer, basketball, football and skills training because of the additive effect of multiple sprints.

    Hawley et al. (1997) found that carbohydrate loading did not improve performance during either high-intensity exercise lasting less than 20 minutes or moderate-intensity exercise lasting 60-90 minutes in duration.

    Mitchell, DiLauro, Pizza, and Cavender (1997) found carbohydrate ingestion prior to resistance training to have no impact on performance. During these studies, muscle glycogen stores were not reduced to below normal levels and thus glycogen failed to become the limiting factor.

    Pizza, F., Flynn, M., Duscha, B., Holden, J., and Kubitz, E. (1995) and Tarnopolsky, M., Atkinson, S., Phillips, S., and MacDougall, J. (1995) both concluded that when high-intensity exercise to exhaustion, 75% VO2 max and 85% VO2 max respectively, is preceded by sub-maximal glycogen depleting exercise, a high carbohydrate loading diet did improve performance.

Low & High Carbohydrate Diets

    Most sports involve intermittent sprints dispersed between periods of moderate-intensity exercise that deplete glycogen stores throughout the match. As research has shown, having higher levels of stored glycogen pre-exercise and training or assuring consumption of carbohydrates during the performance period can improve performance when compared to the same activities being performed with lower than normal levels of required glycogen.

    Soccer, a multiple sprint sport with active rest periods, was tested to find the implications of low and high carbohydrate diets on performance by Balsom, Wood, Olsson and Ekblom (1999).


Click To Enlarge.

    They tested six male soccer athletes during four 90-minute four per side soccer games when following either a high 65% carbohydrate diet or a low 30% carbohydrate diet.

    Statistical analysis of the results showed approximately a 33% reduction in high-intensity exercise during game play while following the low carbohydrate diet. A reduction of involvement in the high-intensity action within a game may have implications to the total number of scoring and defending opportunities within the contest.

    Carbohydrate restriction causing low muscle glycogen may not only have negative implications on game and practice performance, strength training can be impaired. Competitive athletes are involved in glycogen depleting practice and conditioning as well as strenuous resistive exercise that additively stress the metabolic machinery.

    Whether from low dietary intake or from activities which deplete the carbohydrate stores, low muscular glycogen has been shown to reduce performance during maximal repetition sets of resistance training.

    Leveritt and Abernethy (1999) tested one female and five male subjects performing 3 sets of maximal squat repetitions at a level 80% of their estimated one repetition maximum.

    Each subject was tested following both a high carbohydrate diet and two days of a low carbohydrate diet preceded by 60-minutes of cycling at 75% peak oxygen consumption while exercising on a cycle ergometer followed by four 1-minute bouts at 100%.

    Results indicated a significant reduction in total squat repetitions performed by the subjects after they participated in the moderate glycogen depleting protocol as compared when squatting with maximal stores of muscular glycogen.

    Performance of this nature, that is requiring metabolic systems to maximally perform with depleted glycogen levels during intense training periods, can limit the strength improvements of basketball players and most likely other multiple sprint sports.

"The more intense resistive training is (the greater the percent of 1RM utilized), the larger the relative amount of glycogen that is depleted. This explains why the practice by bodybuilders of matching their carbohydrate intake to the intensity level which they train at works to help maintain lower bodyfat levels throughout training while maintaining performance standards."

    Robergs, R., Pearson, D., Costill, D., Fink, W., Pascoe, D. and Benedict (1991) found that the rate of glycogenolysis during resistive training is relative to the intensity being performed. Using muscle biopsies of the vastus lateralis muscle, the researchers found that working to exhaustion at 70% one repetition maximum leg extension produced approximately double the rate when than performing at 35% per repetition.

"These findings imply that the total amount of muscle glycogenolysis was dependent on the magnitude of muscle force development and that the rate of glycogenolysis was dependent on exercise intensity" (p. 1703).

    There thus appears to be a metabolic response not only to the amount of work performed, but also the relative intensity of the work. Carbohydrate restriction and low muscular glycogen levels can then impair progress during high intensity weight training by minimizing the available energy stores to replenish immediate energy supplies during the workout.

    During isolated training events low glycogen levels most likely will not inhibit performance to any great extent. But when high levels of cellular regeneration are required during a training period that has multiple sessions over the course of a week, attempting to maintain low glycogen levels through improper carbohydrate consumption will negatively impair training and recovery abilities.


Conclusion

In conclusion, to maintain adequate glycogen stores, intensely training multiple sprint sport athletes should shoot for consume approximately 50-70% of calories from carbohydrates, or 7-10 grams of carbohydrates per kilogram of bodyweight per day (g/kg/day) (Berning, 2000; Rankin, 2000; Williams, 1999).

For less active athletes, such as those involved in golf or the pole vault, a reduced lower level of carbohydrates is in order. For these athletes with lower absolute work levels, intakes of 3-5g/kg/day should be sufficient but with monitoring of the variable discussed earlier to ensure training is not being performed under less than optimal conditions.

A majority of carbohydrates should come in the form of complex carbohydrates such as rice, whole oats, lentils, and whole unprocessed fruits to maintain a more level blood glucose level. In turn, there is a limiting of adipose storage as well as providing a greater level of micronutrients (Berning, 2000; Guezennec, Satabin, Djuforez, Koziet & Antoine, 1993; Walton & Rhodes 1997). There are periods when deviating from these recommendations is required.

If the relative intensity and work output during the exercise period is sufficient to significantly reduce glycogen stores, it is recommended that faster absorbing carbohydrates is consumed immediately post training to replenish glycogen more quickly.

Situations that fall into this category are an intense two hour soccer practice, one hour of repetitive sprints, and exhaustive weight training sessions utilizing intense sets over 80% one repetition and lasting at least one hour in length.

Activities which do not require quick replenishment are tempo sprint training, spending time in the batting cage, or low intensity weight training.

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