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The Latest on Carbohydrate Loading: A Practical Approach Darlene A. Sedlock Wastl Human Performance Laboratory, Purdue University, Department of Health and Kinesiology, W. Lafayette, Indiana

SEDLOCK, D.A. The latest on carbohydrate loading: a practical approach. Curr. Sports Med. Rep., Vol. 7, No. 4, pp. 209Y213, 2008. High dietary carbohydrate (CHO) intake for several days before competition (CHO loading) is known to increase muscle glycogen stores, with subsequent ergogenic performance benefits often seen in events longer than 90 min in duration. CHO-loading strategies vary in characteristics such as type and duration of dietary manipulation and the accompanying exercise/training activities. Additionally, glycogen concentration may remain elevated for up to 5 d. This versatility in CHO-loading strategies allows the athlete greater flexibility in tailoring pre-event preparation. Women who attempt to CHO load should be particularly attentive to both total energy intake and relative CHO intake; dietary CHO should exceed 8 gIkg body massj1 Idj1 or 10 gIkg lean body massj1 Idj1. As long as the amount ingested is adequate for loading, the type of CHO is less important, with the exception of 1-d loading protocols where the glycemic index may be an important consideration.

INTRODUCTION will translate to improved performance. The degree to which muscle glycogen stores can be supercompensated Carbohydrate (CHO) loading, also known as glycogen varies considerably, with increases ranging from less than loading or glycogen supercompensation, is a performance- 25% (5Y8) to a doubling or near-doubling (2,3,9,10) of the enhancement strategy often used by endurance athletes preloaded value. Moreover, the relationship between post- before competition. Increased carbohydrate intake through loading increases in muscle glycogen and subsequent dietary manipulation increases muscle glycogen stores (1Y5) improvements in performance is inconsistent (2,3,5,6,8). and improves performance (1,2,4,5), presumably by delaying For example, performance was increased coincident with a the onset of fatigue. Pioneering work by Scandinavian 13% increase in muscle glycogen (5), but not with other researchers in the late 1960s and early 1970s (1,2) relatively small but significant increases of 18% (6) and demonstrated this relationship among dietary CHO intake, 23% (8). Similarly, large increases in muscle glycogen muscle glycogen content, and subsequent exercise perform- (~100%) were reported to increase (2) or have no effect ance. Since that time, the ergogenic value of CHO for upon (3) performance. prolonged exercise, as well as the associated physiologic Because CHO loading can be an effective performance- mechanisms, has been studied perhaps more extensively enhancing strategy for some endurance athletes but perhaps than any other singular performance-enhancing strategy. not others, it is important to be aware of factors that can There is little doubt as to the importance of CHO as a modify the outcome. These include, but are not limited to, fuel for endurance performance. However, athletes must be loading strategy, type of CHO ingested, characteristics of the cautious when assuming that CHO loading will greatly ensuing exercise performance, the presence or absence of a increase glycogen stores, and that this increase in glycogen high fat diet/adaptation period before loading, the presence or absence of preloading glycogen-depleting exercise, timing of supercompensation relative to the performance event, and Address for correspondence: Darlene A. Sedlock, Ph.D., FACSM, Wastl Human gender. Few studies regarding CHO loading were published in Performance Laboratory, Purdue University, Department of Health and Kinesiology, the last year (9,11). To incorporate this new information, 800 W. Stadium Ave., W. Lafayette, IN 47907-2046 (E-mail: [email protected]). this article will focus on loading strategies, preloading glycogen depleting exercise, timing of CHO loading, and 1537-890X/0704/209Y213 CHO loading in women, with a brief mention of some issues Current Sports Medicine Reports Copyright * 2008 by the American College of Sports Medicine regarding the other previously mentioned factors.

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Copyright @ 2008 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. CHO-LOADING STRATEGIES PRELOADING GLYCOGEN DEPLETION

The classic CHO-loading procedures were first reported by Findings from some (7,15) but not all (3) research Scandinavian researchers (1,2) in the late 1960s and suggest that a greater amount of glycogen storage occurs involved either a 3- or 6-d exercise and diet manipulation. when performing GD exercise rather than lighter exercise The protocol involved performing prolonged (i.e., glycogen- bouts (e.g., exercise tapering) before ingesting a high-CHO depleting [GD]) exercise followed by 3 d of a high- diet. Although the modified loading protocol of Sherman CHO diet with minimal to no training (3 d), or the same et al. (3) produced muscle glycogen concentrations similar procedure preceded by GD exercise and subsequent 3-d low to the classic protocol, other studies yielded equivocal CHO diet (6 d). Although these classic exercise/dietary findings regarding the ability to maximize muscle glycogen regimens induce increases in muscle glycogen, they may not concentration without initially depleting those stores. represent the optimal way to prepare for competition. The Roedde et al. (15) reported muscle glycogen concentrations exercise/diet manipulation is difficult to execute, especially of 174 mmolIkgj1 following a 6-d classic loading regimen the 6-d protocol, and may result in untoward physical and compared to 115 mmolIkgj1 following a modified proce- mental consequences. A GD workout just a few days before, dure. Goforth et al. (7) used 13C magnetic resonance as well as 3 consecutive days of inactivity immediately spectroscopy to measure the pattern of muscle glycogen before a prolonged endurance event, may be disruptive to concentration after CHO loading with or without a the usual regimen of the athlete. Moreover, the low dietary preceding GD exercise. After a GD exercise or non-GD CHO phase may increase the risk for injury (12), make it (20 min of moderate-intensity cycling) exercise, subjects difficult to adhere to an optimal training/tapering regimen, consumed a high-CHO (80%) diet for 3 d and then a and result in manifestations of hypoglycemia such as normal mixed diet (56% CHO) for an additional three ˙ listlessness, irritability, and diminished mental acuity. days with 20 min of moderate intensity (65% VO2peak) Bloating, gastrointestinal (GI) distress, and weight gain cycling performed daily. Muscle glycogen increased during the high CHO phase also are of concern (13). significantly in both the GD (38%) and non-GD In 1981, Sherman et al. (3) reported a more ‘‘user- (24%) groups after the high-CHO diet phase. During friendly’’ strategy for increasing muscle glycogen stores. the mixed diet phase, glycogen concentration contin- Briefly, they showed that muscle glycogen content could ued to increase in the GD group, whereas glycogen almost double by undergoing a 3-d exercise taper starting peaked after the first day and then decreased gradually approximately 1 wk before the event while consuming a back to the baseline value over the next 3 d in the normal mixed diet (~50% of energy as CHO), then non-GD group (Figure). ingesting a high (70%) CHO diet for the remaining 3 d The larger increases in muscle glycogen observed after with approximately 20 min of low-intensity exercise during preloading GD exercise are suggested to result from the first 2 d and resting on the last day. This modified factors such as a faster rate of glycogen resynthesis (16), regimen effectively supercompensated the muscle, yet greater glycogen synthase activity (17,18), and enhanced eliminated the need to perform an exhausting exercise bout glucose transport (19). This enhanced muscle sensitivity to within a few days of a competitive event, allowed for a reasonable exercise taper, and relative to the classic 6-day loading protocol, avoided several days of low dietary CHO intake while simultaneously decreasing the duration of exaggerated dietary manipulation. More recently, researchers have shown increases in muscle glycogen stores with a single day of high CHO consumption (10,14). Bussau et al. (10) found that physical inactivity coupled with ingestion of a high CHO diet (10 gIdj1Ikgj1 high CHO and high glycemic index food and beverage) increased muscle glycogen stores by 90% after only 1 d, with no additional significant increase after 2 more days of the diet and inactivity intervention. Subjects in this study performed a normal training workout on the day preceding the intervention. In a related study (14), endurance-trained men increased muscle glycogen content by an average of 82% after performing a short-term, high- intensity cycling exercise (150 s at 130% V˙ O followed 2max Figure. Profile of muscle glycogen during depletion and nondepletion by an all-out 30-s sprint) with a subsequent day of inactivity exercise regimens. Measurements were made daily between 8:00 A.M. j1 and ingestion of a similarly high-CHO diet (12 gIkg lean and 12:00 noon for depletion group (N = 15) and nondepletion group body mass or ~10 gIkgj1 body mass). (N =10).*P G 0.01 versus baseline;†P G 0.001 versus nondepletion group. Each of the previously mentioned CHO-loading protocols (Reprinted from Goforth, H.W., D. Laurent, W.K. Prusaczyk, et al. Effects of depletion exercise and light training on muscle glycogen super- can increase muscle glycogen to some extent. However, other compensation in men. Am J Physiol Endocrinol Metab 285:E1304Y1311, factors must be considered if maximal levels of intramuscular 2003. Copyright * 2003 The American Physiological Society. Used with glycogen are to be attained, some of which are discussed below. permission.)

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Copyright @ 2008 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. CHO after GD exercise may be analogous to muscle CHO LOADING IN WOMEN adaptations that occur from training. For example, Hansen et al. (20) examined muscle glycogen content in response to Relative to the preponderance of research in men, little knee extensor training 5 dIwkj1 for 10 wk in untrained information exists on CHO loading in women. For example, young men. Subjects trained one leg for 1 hIdj1 (high the link between CHO loading and performance has been glycogen) and trained the other leg every other day for two well documented in men (1,2,13,22,24), but this relation- 1-h sessions separated by a 2-h recovery (low glycogen). ship in women is tenuous at best (4,5,25,26). Tarnopolsky This protocol equated workload and training volume for et al. (4) reported no significant increase in muscle glycogen both legs throughout the training program; however, the leg or performance in trained women after CHO loading (75% in the high glycogen condition always began training with CHO for 4 d), whereas similarly trained men exhibited a relatively high glycogen stores, whereas the second hour of 41% increase in glycogen and a 45% improvement in training for the leg in the low glycogen condition always cycling time trial performance. In contrast, women in a began with significantly reduced glycogen. Muscle glycogen study by Walker et al. (5) were able to increase significantly increased in both legs in response to training, but the both glycogen (13%) and performance (~8%) in response to increase was significant only for the leg that trained using CHO loading (75%Y80% CHO for the final 3Y4 d of a 7-d the low glycogen protocol. diet/exercise taper). Others reported significant increases in Preloading GD exercise is not a prerequisite for super- muscle glycogen from CHO loading but no subsequent compensating the muscle with glycogen (3,5,21,22). How- increase in performance (11,27). Factors that seem to ever, evidence regarding the importance of a preloading GD determine the efficacy of CHO loading in women are total exercise (or at least significantly reducing in muscle energy intake, amount of CHO ingested, and menstrual glycogen content) (12) for maximizing increases in glycogen cycle phase. Tarnopolsky et al. (28) suggested that energy storage is sufficient to warrant further study. intake influences the ability of women to glycogen super- compensate. Increasing fractional CHO intake from 58% to 75% significantly increased muscle glycogen in men but not TIMING OF CHO LOADING in women. However, by increasing energy intake of women by approximately 34% (the difference in habitual energy Regardless of the type and duration of CHO-loading intake between the men and women) while keeping protocols used, research examining the relationship fractional CHO intake at 75% did result in increased between CHO loading, muscle glycogen content, and glycogen stores. Other research suggests that the important exercise performance includes consumption of a high- factor governing the ability of muscle to store additional CHO diet up until the day of the performance event. glycogen is CHO intake relative to body mass (BM) or lean This is because the length of time muscle glycogen body mass (LBM). Significant increases in muscle glycogen concentration remained elevated was largely unknown, in women were reported when CHO intake was 8.4 gIkg unlike supercompensated liver glycogen, which is relatively BMj1Idj1 (11), 8.2 gIkg BMj1Idj1 (10.1 gIkg LBMj1Idj1) short-lived (23). Researchers have since shown that muscle (5), 11.2 gIkg LBMj1Idj1 (27), and 12.3 gIkg LBMj1Idj1 glycogen stores can remain elevated for several days after (29). In the previously mentioned study by Tarnopolsky being supercompensated (7,18,23). In one study (23), et al. (28), CHO intake was 8.8 gIkg BMj1Idj1 during the endurance-trained men underwent a classic 6-d loading increased energy trial in which glycogen increased, but only regimen, followed by a 3-day postloading phase consisting of 6.4 gIkg BMj1Idj1 with the isocaloric high-CHO diet. moderate CHO intake (~60% total energy) and limited Thus it seems that women have the capacity to increase physical activity. Muscle glycogen remained significantly muscle glycogen stores provided CHO intake exceeds elevated above baseline throughout the postloading phase. approximately 8 gIkg BMj1Idj1 or approximately 10 gIkg In the previously mentioned study by Goforth et al. (7), LBMj1Idj1. Although this recommendation seems scientifi- muscle glycogen significantly increased after 3 d of high cally reasonable, the practical aspect is more daunting CHO intake (~9.0 gIkgj1; 80% total energy) and remained because this dose amounts to ingesting more than 93% of elevated for an additional 3 d when CHO ingestion was total energy as CHO for a 60-kg woman with a caloric more moderate (~6.5 gIkgj1; 56% total energy) and coupled intake of 2000 kcalIdj1 (28). Hence, women who attempt with 20 min of moderate intensity cycling each day. More to CHO load should be particularly attentive to both total recently, Arnall et al. (9) found that, after GD exercise energy intake and relative CHO intake. with subsequent CHO loading, muscle glycogen remained Menstrualcyclephasealsomayplayaroleinthe significantly elevated for 5 d with a CHO intake of effectiveness of CHO loading. Women have higher uncom- approximately 60% total energy and limited physical pensated glycogen levels (11,30) and a greater capacity for activity. storing glycogen (11,26) during the luteal phase than the A variety of CHO-loading regimens can produce super- follicular phase. The natural fluctuations of female repro- compensated muscle glycogen, and the elevated glycogen ductive hormones throughout the menstrual cycle may be a content may persist for up to 5 d. Thus athletes have a critical factor for the difference in CHO sensitivity between variety of strategies to explore regarding the type and timing cycle phases. Without these hormonal fluctuations, James of the loading protocol that would result in minimal et al. (29) were unable to detect a difference in glycogen disruption to their personal training/tapering schedules and content during the follicular versus luteal phase in pre-event preparation. response to CHO loading in women who were taking oral

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Copyright @ 2008 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. contraceptives that resulted in similar values for progester- Any CHO-loading strategy used by an athlete should be one, estradiol, luteinizing hormone, and follicle-stimulating one that is well tolerated by the individual. Ingesting CHO hormone at the time glycogen was measured. in amounts adequate to elevate muscle glycogen, which is not as difficult a task for men as it may be for women, as well as tolerating side effects such as bloating and general OTHER FACTORS GI discomfort that often accompany high-CHO intake, are important considerations. Glycogen is stored with water in a Y Type of CHO ratio of approximately 1:3 5 (22), so the extra weight and feelings of ‘‘fullness’’ and ‘‘heaviness’’ experienced with Combinations of simple, complex, solid, and liquid CHO CHO loading also must be considered, especially if the are most often used by athletes who CHO load. It is events are weight-bearing (e.g., running or cross-country accepted widely that the type of CHO ingested is not as skiing) as opposed to weight-supported (e.g., cycling or important for supercompensating muscle if the amount is swimming). adequate. The quantity of food that must be ingested to attain the proper dose of CHO depends on its CHO content, with a smaller amount required if the food has a CONCLUSION relatively high CHO content (e.g., pasta or rice) rather than a relatively low CHO content. High-CHO beverages can The ergogenic benefit of CHO loading for endurance provide at once much of the additional CHO needed for performance is a widely accepted tenet. Several strategies loading without adding extra ‘‘bulk’’ to the diet. However, can be used to supercompensate muscle glycogen, many of the glycemic index (GI) of ingested CHO may play a role in which vary in duration, extent of dietary manipulation, and some loading protocols. High-GI food was reported to result the amount and intensity of any accompanying exercise. in a greater restoration of glycogen than low-GI food in the Reports of successful single-day loading protocols as well as first 24 h after a GD exercise (31). Additionally, both the duration that glycogen remains elevated allow athletes Bussau et al. (10) and Fairchild et al. (14) used high-GI food many permutations of loading strategies with which to and beverages for their 1-d loading protocols. Thus GI may experiment. The greatest challenge for women to success- be an important consideration when using short duration fully elevate muscle glycogen seems to be the ability to (i.e., 1-d) CHO loading protocols or when relatively rapid ingest an appropriate amount of CHO without incurring a glycogen restoration is needed. large disruption to daily energy requirements. Because CHO loading is most likely to provide ergogenic effects in Preloading Fat Adaptation competitive events exceeding approximately 90 min in The ability to enhance lipid oxidation may be beneficial duration, athletes who have a low tolerance for fluid or for prolonged endurance events during which fat utilization CHO consumption during competition are likely to derive would spare CHO oxidation. Several days or weeks of the greatest benefits. ingesting a high-fat diet produces metabolic alterations during exercise that favor increased fat oxidation (32,33). References Subsequent restoration of muscle glycogen with a day of rest and high-CHO intake does not abolish this adaptation 1. Bergstro¨m, J.L., L. Hermansen, E. Hultman, and B. Saltin. Diet, muscle glycogen, and physical performance. Acta Physiol. Scand. 71:140Y150, (34,35). In theory, this CHO-sparing effect should manifest 1967. in improved endurance performance. However, research is 2. Karlsson, J., and B. Saltin. 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Copyright @ 2008 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.