Carbohydrate Needs
Burke, L.M. Fat and carbohydrate for exercise. Current Opinion in Clinical Nutrition and Metabolic Care 9:476-481, 2006.
Burke, L.M., A. B. Loucks, and N. Broad. Energy and carbohydrate for training and recovery. Journal of Sports Sciences 24: 675-685, 2006.
Burke, L.M., C. Wood, D.B. Pyne, R.D. Telford, and P.U. Saunders. Effect of carbohydrate intake on half-marathon performance of well-trained athletes. International Journal of Sports Nutrition and Exercise Metabolism 15: 573.89, 2005.
McInerney, P, S.J. Lessard, L.M. Burke, V.G. Coffey VG, S.L Lo Giudice, R.J. Southgate, and J.A Hawley. Failure to repeatedly supercompensate muscle glycogen stores in highly trained men. Medicine & Science in Sports & Exercise 37: 404-11, 2005.
Arkinstall, M.J., C.R. Bruce, S.A. Clark, C. A Rickards, L.M. Burke, and J.A. Hawley. Regulation of fuel metabolism by preexercise muscle glycogen content and exercise intensity. Journal of Applied Physioloy 97: 2275-83, 2004.
Burke, L.M., B. Kiens, and J.L Ivy. Carbohydrates and fat for training and recovery. Journal of Sports Sciences 22: 15-30, 2004.
Burke L. M., G. R. Cox, N. K. Cummings, and B. Desbrow. Guidelines for daily carbohydrate intake: do athletes achieve them? Sports Medicine 31: 267-99, 2001.
Clark, V. R., W. G. Hopkins, J. A. Hawley, and L. M. Burke. Placebo effect of carbohydrate feedings during a 40-km cycling time trial. Medicine & Science in Sports & Exercise 32: 1642-1647, 2000.
Burke, L. M. Preparation for competition. In: Clinical Sports Nutrition (2nd ed.), edited by L. Burke and V. Deakin. Sydney: McGraw-Hill, 2000, p. 341-368.
Burke, L. M. Nutrition for recovery after competition and training. In: Clinical Sports Nutrition (2nd ed.), edited by L. Burke and V. Deakin. Sydney: McGraw-Hill, 2000, p. 396-427.
Burke, L. M. Dietary carbohydrates. In: The Encyclopaedia of Sports Medicine. Vol VII: Nutrition in Sport, edited by R. J. Maughan. Oxford: Blackwell Science, 2000, p. 73-84.
Burke, L. M., and J. A. Hawley. Carbohydrate and exercise. Current Opinion in Clinical Nutrition and Metabolic Care 2: 515-520, 1999.
Palmer, G. S., M. C. Clancy, J. A. Hawley, I. M. Rodger, L. M. Burke, and T. D. Noakes. Carbohydrate ingestion immediately before exercise does not improve 20 km time trial performance in well trained cyclists. International Journal of Sports Medicine 19: 415-418, 1998.
Burke, L. Carbohydrate intake targets for athletes: grams or percent? Sportscience News Jul-Aug 1998. http://www.sportsci.org/news/compeat/grams.html
Burke, L. Carbohydrate depletion - is it for you? Sportscience News Jan-Feb 1998. http://www.sportsci.org/news/compeat/deplete.html
Hawley, J. A., and L. M. Burke. Effect of meal frequency and timing on physical performance. British Journal of Nutrition 77: S91-S103, 1997.
Burke, L. Should athletes nibble or gorge? Sportscience News Jan-Feb 1997.
http://www.sportsci.org/news/compeat/comp1.html
Burke, L.M. Fat and carbohydrate for exercise. Current Opinion in Clinical Nutrition and Metabolic Care 9:476-481, 2006.
PURPOSE OF REVIEW: To examine the results of new investigations that look at the efficacy of nutrient/training strategies on metabolism and athletic performance. RECENT FINDINGS: 'Dietary periodization' involves the manipulation of macronutrient intake in association with changes in physical training. Such interventions have a major effect on altering patterns of fuel utilization during exercise; however, they often fail to enhance performance capacity. In contrast, the ingestion of a combination of different types of carbohydrate during exercise results in high rates of muscle glucose oxidation (1.5 g/min) and can improve intense, short-duration (approximately 60 min), and prolonged (>90 min) submaximal steady-state exercise, either by metabolic or neural mechanisms. SUMMARY: Further investigation into the responses of specific nutrient/training strategies on metabolic and cellular signaling pathways is warranted to determine the underlying mechanisms by which such interventions exert their effect. Such studies, however, should be coupled with investigations that assess the outcomes of these responses on the 'real life' training adaptations in athletes.
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Burke, L.M., A.B. Loucks, N. Broad. Energy and carbohydrate for training and recovery. Journal of Sports Sciences 24:675-685, 2006.
Soccer players should achieve an energy intake that provides sufficient carbohydrate to fuel the training and competition programme, supplies all nutrient requirements, and allows manipulation of energy or nutrient balance to achieve changes in lean body mass, body fat or growth. Although the traditional culture of soccer has focused on carbohydrate intake for immediate match preparation, top players should adapt their carbohydrate intake on a daily basis to ensure adequate fuel for training and recovery between matches. For players with a mobile playing style, their is sound evidence that dietary programmes that restore and even super-compensate muscle glycogen levels can enhance activity patterns during matches. This will presumably also benefit intensive training, such as twice daily practices. As well as achieving a total intake of carbohydrate commensurate with fuel needs, the everyday diet should promote strategic intake of carbohydrate and protein before and after key training sessions to optimize their adaptations and enhance recovery. The achievement of the ideal physique for soccer is a long-term goal that should be undertaken over successive years, and particularly during the off-season and pre-season. An increase in lean body mass or a decrease in body fat is the product of a targeted training and eating programme. Consultation with a sports nutrition expert can assist soccer players to manipulate energy and nutrient intake to meet such goals. Players should be warned against the accidental or deliberate mismatch of energy intake and energy expenditure, such that energy availability (intake minus the cost of exercise) falls below 125 kJ (30 kcal) per kilogram of fat-free mass per day. Such low energy availability causes disturbances to hormonal, metabolic, and immune function.
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Burke, L.M., C. Wood, D.B. Pyne, R.D. Telford, P.U. Saunders. Effect of carbohydrate intake on half-marathon performance of well-trained athletes. International Journal of Sports Nutrition and Exercise Metabolism 15:573.89, 2005.
Eighteen highly-trained runners ran two half marathons in mild environmental conditions, 3 wk apart, consuming either 426 ± 227 mL of a flavored placebo drink (PLACEBO) or an equivalent volume of water (386 ± 185 mL) and a commercial gel (GEL) supplying 1.1 ± 0.2 g/kg body mass (BM) carbohydrate (CHO). Voluntary consumption of this fluid was associated with a mean BM change of ~ 2.4%. Runners performed better in their second race by 0.9% or 40 s (P = 0.03). Three runners complained of gastrointestinal discomfort in GEL trial, which produced a clear impairment of half-marathon performance by 2.4% or 105 s (P = 0.03). The effect of GEL on performance was trivial: time was improved by 0.3% or 14 s compared with PLACEBO (P = 0.52). Consuming the gel was associated with a 2.4% slower time through the 2 x 200 m feed zone; adding a trivial ~ 2 s to race time. Although benefits to half marathon performance were not detected, the theoretical improvement during 1-h exercise with CHO intake merits further investigation.
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McInerney, P, S.J. Lessard, L.M. Burke, V.G. Coffey VG, S.L Lo Giudice, R.J. Southgate, J.A Hawley. Failure to repeatedly supercompensate muscle glycogen stores in highly trained men. Medicine & Science in Sports & Exercise 37: :404-11, 2005.
PURPOSE: It is not known whether it is possible to repeatedly supercompensate muscle glycogen stores after exhaustive exercise bouts undertaken within several days. METHODS: We evaluated the effect of repeated exercise-diet manipulation on muscle glycogen and triacylglycerol (IMTG) metabolism and exercise capacity in six well-trained subjects who completed an intermittent, exhaustive cycling protocol (EX) on three occasions separated by 48 h (i.e., days 1, 3, and 5) in a 5-d period. Twenty-four hours before day 1, subjects consumed a moderate (6 g.kg)-carbohydrate (CHO) diet, followed by 5 d of a high (12 g.kg.d)-CHO diet. Muscle biopsies were taken at rest, immediately post-EX on days 1, 3, and 5, and after 3 h of recovery on days 1 and 3. RESULTS: Compared with day 1, resting muscle [glycogen] was elevated on day 3 but not day 5 (435+/-57 vs 713+/-60 vs 409+/-40 mmol.kg, P<0.001). [IMTG] was reduced by 28% (P<0.05) after EX on day 1, but post-EX levels on days 3 and 5 were similar to rest. EX was enhanced on days 3 and 5 compared with day 1 (31.9+/-2.5 and 35.4+/-3.8 vs 24.1+/-1.4 kJ.kg, P<0.05). Glycogen synthase activity at rest and immediately post-EX was similar between trials. Additionally, the rates of muscle glycogen accumulation were similar during the 3-h recovery period on days 1 and 3. CONCLUSION: We show that well-trained men cannot repeatedly supercompensate muscle [glycogen] after glycogen-depleting exercise and 2 d of a high-CHO diet, suggesting that the mechanisms responsible for glycogen accumulation are attenuated as a consequence of successive days of glycogen-depleting exercise.
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Arkinstall, M.J., C.R. Bruce, S.A. Clark, C.A. Richards, L.M. Burke, J.A. Hawley . Regulation of fuel metabolism by preexercise muscle glycogen content and exercise intensity. Journal of Applied Physiology 97: 2275-83, 2004.
To date, the results of studies that have examined the effects of altering preexercise muscle glycogen content and exercise intensity on endogenous carbohydrate oxidation are equivocal. Differences in the training status of subjects between investigations may, in part, explain these inconsistent findings. Accordingly, we determined the relative effects of exercise intensity and carbohydrate availability on patterns of fuel utilization in the same subjects who performed a random order of four 60-min rides, two at 45% and two at 70% of peak O(2) uptake (Vo(2 peak)), after exercise-diet intervention to manipulate muscle glycogen content. Preexercise muscle glycogen content was 596 +/- 43 and 202 +/- 21 mmol/kg dry mass (P < 0.001) for high-glycogen (HG) and low-glycogen (LG) conditions, respectively. Respiratory exchange ratio was higher for HG than LG during exercise at both 45% (0.85 +/- 0.01 vs. 0.74 +/- 0.01; P < 0.001) and 70% (0.90 +/- 0.01 vs. 0.79 +/- 0.01; P < 0.001) of Vo(2 peak). The contribution of whole body muscle glycogen oxidation to energy expenditure differed between LG and HG for exercise at both 45% (5 +/- 2 vs. 45 +/- 5%; P < 0.001) and 70% (25 +/- 3 vs. 60 +/- 3%; P < 0.001) of Vo(2 peak). Yet, despite marked differences in preexercise muscle glycogen content and its subsequent utilization, rates of plasma glucose disappearance were similar under all conditions. We conclude that, in moderately trained individuals, muscle glycogen availability (low vs. high) does not influence rates of plasma glucose disposal during either low- or moderate-intensity exercise.
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Burke, L.M., B. Kiens, J.L Ivy. Carbohydrates and fat for training and recovery. Journal of Sports Sciences 22: 15-30, 2004.
An important goal of the athlete's everyday diet is to provide the muscle with substrates to fuel the training programme that will achieve optimal adaptation for performance enhancements. In reviewing the scientific literature on post-exercise glycogen storage since 1991, the following guidelines for the training diet are proposed. Athletes should aim to achieve carbohydrate intakes to meet the fuel requirements of their training programme and to optimize restoration of muscle glycogen stores between workouts. General recommendations can be provided, preferably in terms of grams of carbohydrate per kilogram of the athlete's body mass, but should be fine-tuned with individual consideration of total energy needs, specific training needs and feedback from training performance. It is valuable to choose nutrient-rich carbohydrate foods and to add other foods to recovery meals and snacks to provide a good source of protein and other nutrients. These nutrients may assist in other recovery processes and, in the case of protein, may promote additional glycogen recovery when carbohydrate intake is suboptimal or when frequent snacking is not possible. When the period between exercise sessions is < 8 h, the athlete should begin carbohydrate intake as soon as practical after the first workout to maximize the effective recovery time between sessions. There may be some advantages in meeting carbohydrate intake targets as a series of snacks during the early recovery phase, but during longer recovery periods (24 h) the athlete should organize the pattern and timing of carbohydrate-rich meals and snacks according to what is practical and comfortable for their individual situation. Carbohydrate-rich foods with a moderate to high glycaemic index provide a readily available source of carbohydrate for muscle glycogen synthesis, and should be the major carbohydrate choices in recovery meals. Although there is new interest in the recovery of intramuscular triglyceride stores between training sessions, there is no evidence that diets which are high in fat and restricted in carbohydrate enhance training.
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Burke L. M., G. R. Cox, N. K. Cummings, and B. Desbrow. Guidelines for daily carbohydrate intake: do athletes achieve them?. Sports Medicine 31: 267-99, 2001.
Official dietary guidelines for athletes are unanimous in their recommendation of high carbohydrate (CHO) intakes in routine or training diets. These guidelines have been criticised on the basis of a lack of scientific support for superior training adaptations and performance, and the apparent failure of successful athletes to achieve such dietary practices. Part of the problem rests with the expression of CHO intake guidelines in terms of percentage of dietary energy. It is preferable to provide recommendations for routine CHO intake in grams (relative to the body mass of the athlete) and allow flexibility for the athlete to meet these targets within the context of their energy needs and other dietary goals. CHO intake ranges of 5 to 7 g/kg/day for general training needs and 7 to 10 g/kg/day for the increased needs of endurance athletes are suggested. The limitations of dietary survey techniques should be recognised when assessing the adequacy of the dietary practices of athletes. In particular, the errors caused by under-reporting or undereating during the period of the dietary survey must be taken into account. A review of the current dietary survey literature of athletes shows that a typical male athlete achieves CHO intake within the recommended range (on a g/kg basis). Individual athletes may need nutritional education or dietary counselling to fine-tune their eating habits to meet specific CHO intake targets. Female athletes, particularly endurance athletes, are less likely to achieve these CHO intake guidelines. This is due to chronic or periodic restriction of total energy intake in order to achieve or maintain low levels of body fat. With professional counselling, female athletes may be helped to find a balance between bodyweight control issues and fuel intake goals. Although we look to the top athletes as role models, it is understandable that many do not achieve optimal nutrition practices. The real or apparent failure of these athletes to achieve the daily CHO intakes recommended by sports nutritionists does not necessarily invalidate the benefits of meeting such guidelines. Further longitudinal studies of training adaptation and performance are needed to determine differences in the outcomes of high versus moderate CHO intakes. In the meantime, the recommendations of sports nutritionists are based on plentiful evidence that increased CHO availability enhances endurance and performance during single exercise sessions.
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Clark, V. R., W. G. Hopkins, J. A. Hawley, and L. M. Burke. Placebo effect of carbohydrate feedings during a 40-km cycling time trial. Medicine & Science in Sports & Exercise 32: 1642-1647, 2000.
PURPOSE: The placebo effect, a favorable outcome from belief that one has received a beneficial treatment, may be an important phenomenon in athletic performance. We have therefore investigated the placebo effect of a carbohydrate supplement on endurance performance.
METHODS: Forty-three competitive endurance cyclists (2 female, 41 male) performed two simulated 40-km time trials on an air-braked ergometer. In the first trial they ingested water to establish baseline performance (mean power 265 +/- 46 W for 58 +/- 4 min, mean +/- SD). For the second trial 6-8 d later they were randomized to two groups: one group ingested 16 mL x kg(-1) of a drink containing 7.6 g x 100 mL(-1) carbohydrate; the other ingested an indistinguishable noncaloric placebo drink. Cyclists in each group were further randomized to three subgroups according to whether they were told the drink contained carbohydrate, placebo, or either (not told).
RESULTS: Changes in mean power in the second trial were: told carbohydrate, 4.3 +/- 4.8%; told placebo, 0.5 +/- 5.8%; and not told, -1.1 +/- 8.5%. The difference between the told-carbohydrate and told-placebo groups was 3.8% (95% likely range 7.9 to -0.2%). The change in performance in the not-told group was more variable than that of the told groups by a factor of 1.6 (2.6 to 1.0). The real effect of carbohydrate was a slight reduction in power of 0.3% (4.4 to -3.8%).
CONCLUSIONS: (a) The placebo effect of a potentially ergogenic treatment during unblinded laboratory time trials lasting approximately 1 h is probably a small but worthwhile increase in endurance power. (b) Blinding subjects to the treatment increases individual differences in endurance effort, which may reduce precision of performance outcomes in controlled trials.
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Burke, L. M. Preparation for competition. In: Clinical Sports Nutrition (2nd ed.), edited by L. Burke and V. Deakin. Sydney: McGraw-Hill, 2000, p. 341-368.
The outcomes of pre-event nutrition strategies range from psychological well-being and confidence to optimal fluid and fuel status. The importance of these strategies will depend on the range and severity of physiological challenges that are likely to limit performance in the athlete's individual event. This may be determined by characteristics of the event itself, as well as the degree to which the athlete has been able to recover since their last workout or competition event. Nutrition strategies may include increased CHO intake during the day(s) prior to the event, as well as the extended fuelling-up known as CHO loading, which has been shown to enhance endurance and the performance of prolonged exercise events. The pre-event meal also provides an opportunity to refuel muscle and liver glycogen stores. There is some concern that pre-exercise CHO feedings may increase CHO utilisation during exercise, but the intake of substantial amounts of CHO can offset the increased rate of substrate use. The choice of low-GI CHO-rich foods in the pre-event menu may also sustain the delivery of CHO during exercise, however this does not provide a guaranteed performance advantage, especially when additional CHO is consumed during the event. Pre-event preparation should also consider fluid balance, with strategies to rehydrate from previous dehydration associated with exercise or weight-making activities, as well as the potential for hyperhydration in preparation for events in which a large fluid deficit is unavoidable. A variety of eating practices can be chosen by the athlete to meet their competition preparation goals. These need to consider the practical aspects of nutrition such as gastrointestinal comfort, the athlete's likes and dislikes, and food availability. Above all, the athlete should experiment with their pre-event nutrition practices to find and fine-tune strategies that are successful. These may be individual to the athlete and their specific event. Pre-event nutrition practices should be undertaken as part of an integrated competition nutrition plan. Ideally, an athlete should combat these challenges of competition by undertaking a systematic plan of nutrition strategies before, during and even in the recovery after an event.
Further details on Clinical Sports Nutrition can be found in the Publications section of our site.
Burke, L. M. Nutrition for recovery after competition and training. In: Clinical Sports Nutrition (2nd ed.), edited by L. Burke and V. Deakin. Sydney: McGraw-Hill, 2000, p. 396-427.
Recovery after exercise poses and important challenge to the modern athlete. Important nutrition goals include restoration of liver and muscle glycogen stores, and the replacement of fluid and electrolytes lost in sweat. Rapid resynthesis of muscle glycogen stores is aided by the immediate intake of CHO (1 g/kg BM each two hours), particularly of CHO-rich foods of high GI, towards a total CHO intake over 24 hours of 7-10 g/kg BM. Rapid refuelling may be important for the athlete who has less than eight hours between lengthy exercise sessions. Provided adequate CHO is consumed, it appears that the frequency of intake, the form (liquid versus solid) and the presence of other macronutrients does not appear to affect the rate of glycogen storage. Practical considerations, such as the availability and appetite appeal of foods or drinks, and gastrointestinal comfort may determine ideal CHO choices and intake patterns. Rehydration requires a special fluid intake plan since thirst and voluntary intake will not provide for full restoration of sweat losses in the acute phase (zero to six hours) of recovery. Steps should be taken to ensure that a supply of palatable drinks is available after exercise. Sweetened drinks are generally preferred and can contribute towards achieving CHO intake goals. Replacement of sodium lost in sweat is important in maximising the retention of ingested fluids. A sodium content of 50-90 mmol/L may be necessary for optimal rehydration, however, commercial sports drinks are formulated with a more moderate sodium content (10-25 mmol/L) to allow a greater overall use and palatability. Of course, sodium replacement can occur via salt added or eaten with meals and snacks. Caffeine- and alcohol-containing beverages are not ideal rehydration fluids since they promote an increased rate of diuresis. It may be necessary to consume 150% of fluid losses to allow for complete fluid restoration. Since athletes often compete in a foreign environment, the practical issues of food availability and food preparation facilities must be considered when making recommendations for post-exercise nutrition.
Further details on Clinical Sports Nutrition can be found in the Publications section of our site.
Burke, L. M. Dietary carbohydrates. In: The Encyclopaedia of Sports Medicine. Vol VII: Nutrition in Sport, edited by R. J. Maughan. Oxford: Blackwell Science, 2000, p. 73-84.
Dietary carbohydrates (CHOs) provide the major energy source in the diets of most people and include a range of compounds which share the common basic elements of carbon, hydrogen and oxygen, and an empirical formula of (CH 2 O) n . CHOs occurring naturally in foods, or more recently, manufactured by special chemical techniques and added during food processing, are generally classified according to their chemical structure. However, this system does not account for the variety and overlap of functional, metabolic and nutritional characteristics of 'CHO foods'. This chapter describes briefly the types of CHO-rich foods that may be of interest to athletes and physically active people, justifying the recommendations of many expert nutrition bodies that we should further increase our dietary CHO intake. [introduction]
Dietary CHO is provided by a wide variety of CHO-rich foods and drinks. There is no universal system that can adequately describe the diverse metabolic, functional and nutritional features of these various foods. Dietary guidelines for athletes make recommendations for everyday intake of CHO as well as CHO intake for specific situations pre, during and postexercise sessions. Athletes are encouraged to meet these guidelines by choosing CHO-rich foods and drinks that offer appropriate characteristics such as nutrient-density, desirable glycaemic index, appeal and practicality according to the requirements of the situation. [conclusion]
Burke, L. M., and J. A. Hawley. Carbohydrate and exercise. Current Opinion in Clinical Nutrition and Metabolic Care 2: 515-520, 1999.
Total body carbohydrate stores are limited, and are often less than the carbohydrate requirements of athletic training and competition. However, the availability of carbohydrate as a substrate for muscle metabolism is a critical factor in the performance of both high-intensity intermittent work and prolonged aerobic exercise. The rate of carbohydrate oxidation during exercise is tightly regulated, with glucose availability closely matching the needs of the working muscles. Both the absolute and relative work rate play important roles in the regulation of substrate metabolism: carbohydrate-based fuels predominate at moderate to high power outputs, with muscle glycogen and glucose utilization scaling exponentially to the relative work rate. As such, strategies to maintain or enhance carbohydrate availability, such as the ingestion of carbohydrate before, during and after exercise, are critical to the performance of a variety of sports events, and are a key recommendation in current sports nutrition guidelines.
Palmer, G. S., M. C. Clancy, J. A. Hawley, I. M. Rodger, L. M. Burke, and T. D. Noakes. Carbohydrate ingestion immediately before exercise does not improve 20 km time trial performance in well trained cyclists. International Journal of Sports Medicine 19: 415-418, 1998.
This study examined the effects of carbohydrate ingestion on 20 km cycle time-trial (TT) performance in 14 well-trained cyclists (11 males, 3 females; peak oxygen uptake [VO2peak] 4.52 +/- 0.60 l/min; values are mean +/- SD). All subjects performed two experimental trials on their own bicycles mounted on an air-braked ergometry system (Kingcycle). Subjects were instructed to maintain the same training and dietary regimens before trials, which were conducted in a random order, 3-7 days apart, and at the same time of day for each subject. On the day of a trial, subjects reported to the laboratory and ingested an 8 ml/kg body mass bolus of either a 6.8 g/100 ml commercial carbohydrate-electrolyte (CHO) beverage (39 +/- 4 g of CHO), or a coloured, flavoured placebo. Ten min after finishing the drink, subjects commenced a 5 min warm-up at 150 W, before commencing the 20 km TT. The average power output (312 +/- 40 vs 311 +/- 38 W) and heart-rate (171 +/- 6 vs 171 +/- 5 beats/min for CHO and placebo, respectively) during the two rides did not differ between treatments. Accordingly, the performance times for the two TT's were the same (27:41 +/- 1:39 min:sec, for both CHO and placebo). We conclude that the ingestion of approximately 40 g of carbohydrate does not improve maximal cycling performance lasting approximately 30 min, and that carbohydrate availability, in the form of circulating blood glucose, does not limit high-intensity exercise of this duration.
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Burke, L. Carbohydrate intake targets for athletes: grams or percent? Sportscience News Jul-Aug 1998.
http://www.sportsci.org/news/compeat/grams.html
Using different terminology to educate athletes about their carbohydrate intake goals interferes at times with the interpretation of studies on carbohydrate and sports performance, and may cause athletes to have their diets unfairly criticized. Nutrition guidelines for the community express carbohydrate intake goals in terms of the percentage of energy that should be consumed from carbohydrate. This works because the message is general and the emphasis is on a relative change in fat and carbohydrate consumption. When the muscle fuel needs of an athlete are moderate, adequate carbohydrate intake should be provided by a diet that meets these guidelines for healthy eating. In most Western countries this message is to increase carbohydrate intake to at least 50-55% of energy.
Burke, L. Carbohydrate depletion - is it for you? Sportscience News Jan-Feb 1998.
http://www.sportsci.org/news/compeat/deplete.html
The original carbohydrate loading protocol was probably one of the first modern sports nutrition strategies to receive widespread publicity. It had all the ingredients to make a good story - scientists using special techniques to study a muscle, evidence of performance improvements, and good timing. It hit exercise science journals in the early 70s, then found its way into running magazines during the start of the popular running boom. For both elite and recreational runners, this new carbohydrate loading technique seemed like a perfect prescription to build up muscle glycogen.
Hawley, J. A., and L. M. Burke. Effect of meal frequency and timing on physical performance. British Journal of Nutrition 77: S91-S103, 1997.
Two areas of sports nutrition in which the periodicity of eating has been studied relate to: (1) the habitually high energy intakes of many athletes, and (2) the optimization of carbohydrate (CHO) availability to enhance performance. The present paper examines how the timing and frequency of food and fluid intake can assist the athlete and physically-active person to improve their exercise performance in these areas. Frequent eating occasions provide a practical strategy allowing athletes to increase energy intake while concomitantly reducing the gastric discomfort of infrequent large meals. The optimization of CHO stores is a special challenge for athletes undertaking prolonged training or competition sessions. This is a cyclical process with post-exercise CHO ingestion promoting muscle and liver glycogen re-synthesis; pre-exercise feedings being practised to optimize substrate availability and feedings during exercise providing a readily-available source of exogenous fuel as endogenous stores become depleted. The timing and frequency of CHO intake at these various stages are crucial determinants for optimizing fuel availability to enhance exercise capacity.
Burke, L. Should athletes nibble or gorge? Sportscience News Jan-Feb 1997.
http://www.sportsci.org/news/compeat/comp1.html
This is the question that was pondered recently in Paris as part of a consensus meeting on "Periodicity of Eating and Human Health." The meeting was endorsed by the American Dietetic Association and European Federation of the Associations of Dietitians, and sponsored by Mars Inc. An international panel of nutrition experts considered the effects of the timing and frequency of our eating occasions on things like blood glucose, blood lipids, tooth decay, obesity and energy expenditure, mental performance, and sports performance.
