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Cho Loading and the Female Cyclist

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CHO Loading and Female Cyclists 1


The Effectiveness of CHO Loading in Female Cyclists
PRF 810 Thesis Paper Christopher S. Burt

CHO Loading and Female Cyclists 2 The Effectiveness of CHO Loading in Female Cyclists Carbohydrate [CHO] loading is the intentional ingestion of above normal amounts of carbohydrate to increase muscle glycogen stores prior to physical activity. This method is often used by elite athletes to improve their performance. With respect to cyclists, the increase in performance is measured experimentally as a decrease in time to complete a race or time trial, an increase time to fatigue, and by decreased power output. There is no singular method for CHO loading. The “first” standard protocol for CHO loading was developed by Bergstrom and Hultman (1), in which the athlete exercised to deplete glycogen from the muscle, then consumed excess CHO over 3 days, without exercising. More recently an exercise tapering protocol has been developed, in which the athlete reduces the amount of exercise being done over 3 days, and does no exercise on day 3 (2). This reduction in exercise is followed by 3, or up to 6, days of loading. However in both versions, and the many modifications thereof, the athlete’s regular training protocol is interrupted. Two recent articles reported the success of consuming 12g/kg of lean body mass high CHO, high glycemic index foods, for 24 hours (3, 4). Both studies showed an increase in muscle glycogen levels at levels equal to or higher than those of a 2-6 day regimen. However an increase in performance was not examined in either study. Thus the athlete must consider which protocol to use, and what specific CHO [low or high glycemic index carbohydrates] to consume. In cyclists, the benefit of CHO loading is unclear. Several articles report that cyclists who consumed CHO rich diets had improved performance (5, 6). However these studies did not compare the experimental group to one consuming a placebo; the comparison was made to groups who knew they were not obtaining additional CHO. Thus there is the possibility that the

CHO Loading and Female Cyclists 3 improvement in performance was a result of psychological effect, and not of increased muscle glycogen content. In studies using a placebo, no increase in performance was seen (7, 8). Thus it would be easy to conclude that CHO loading in cyclists is not effective for increasing performance. However, these studies were done using male subjects only. This leaves the question of what is the effect of CHO loading in female cyclists? Studies on dietary practices in female cyclists have indicated that female athletes in general do not meet the CHO intake guidelines, and that they consume insufficient amounts of nutrients as to reduce their overall body fat percentage (9). There are only a few studies on the diets of female cyclists specifically, and they all reach this same conclusion (10, 11). Thus CHO loading may have a different result in female athletes because of their improper diet. Several reports on CHO loading in female cyclists have been done, but they do not come to the same conclusions (12, 13).

Research Question: Is carbohydrate loading effective in female cyclists?

CHO Loading and Female Cyclists 4

Annotated Bibliography


Ahlborg B, Bergstrom J, Brohult J, Ekelund LG, Hultman E, Maschio G. Human muscle glycogen content and capacity for prolonged exercise after different diets. Foersvarsmedicin. 1967; 3:85–99. This work was one of the first reports to present a methodology for carbohydrate loading, and it is frequently cited. It indicated that an athlete should deplete muscle glycogen via exercise, and then ingest high levels of carbohydrate for each of three days. During the time, the athlete was to remain inactive, so as to maintain stored muscle glycogen. This has become known as the 3-day classical carbohydrate loading regimen.


Sherman WM, Costill DL, Fink WJ, Miller JM. Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. Int J Sports Med. 1981; 2(2):114-8. This report introduced the “tapering down” protocol for carbohydrate loading. In this protocol, an athlete consumes a high carbohydrate diet, while reducing the amount of physical activity over 3-6 days, with no physical activity on the day prior to the athletic event. The study showed that muscle glycogen levels could be increased without ceasing physical activity.


Fairchild TJ, Fletcher S, Steele P, Goodman C, Dawson B, Fournier PA. Rapid carbohydrate loading after a short bout of near maximal-intensity exercise. Med. Sci. Sports Exerc. 2002; 34(6):980–986. The goal of this work was to determine if carbohydrate loading could be accomplished in 24 hours, following a short workout to deplete muscle glycogen levels. If true, then an

CHO Loading and Female Cyclists 5 athlete would not have to discontinue his/her training regimen form more than 24 hours before the event. Seven male endurance athletes were asked to deplete their muscles of glycogen with a 3- minute “bout of high intensity exercise”, then to ingest 12 g of high glycemic index carbohydrates/day x kg body mass. Muscle biopsies on days 1 and 3 showed that muscle glycogen content increased significantly from preloading levels by 82%, within 24 hours. This finding was corroborated by histochemical analysis of muscle biopsies, which showed muscle glycogen content reaching similar levels in all muscle fibers, as determined by optical density measurements [OD] of tissue stained with Periodic acid-Schiff stain [PAS], which is a standard method for identifying glycogen in tissues. The authors claim that the levels of muscle glycogen content after 24 hours of loading was similar to that obtained by methods lasting 3-6 days. As the results were reported in terms of wet weight, while other studies reported in terms of dry weight, comparison of muscle glycogen levels could not be made in this paper. 4. Bussau VA, Fairchild TJ, Rao A, Steele P, Fournier PA. Carbohydrate loading in human muscle: an improved 1 day protocol. Eur J Appl Physiol. 2002; 87:290–295. This study is a follow-up to the previous report by Fairchild et al. The goal of this work was to determine if supercompensated muscle glycogen levels could be accomplished in 1 day, without muscle glycogen depletion via exercise. If true, then an athlete would not have to discontinue his/her training regimen prior to the event. Eight male endurance athletes did NOT deplete muscle glycogen via exercise, and were asked to ingest 10 g of high glycemic index carbohydrates/day x kg body mass over three days, and to be inactive during these days. Muscle biopsies on days 1 and 3 showed that muscle glycogen content increased significantly from preloading levels (P < 0.05), within 24 hours, and that there was no significant difference in muscle glycogen content on days 1

CHO Loading and Female Cyclists 6 and 3 (P < 0.05), with glycogen content reaching similar levels in all muscle fibers, as determined by OD of tissue stained with PAS. The authors conclude that even without a glycogen-depleting period of exercise, trained athletes can achieve maximal levels of glycogen content in all muscle fibers within 24 hours, with no added benefit if high levels of carbohydrate intake are extended for more days. Thus, that which is “carbohydrate loading” need only take 24 hours. However it was not examined in this or the previous study, if the 24 hour carbohydrate loading protocols resulted in improved performance, as performance, not increased muscle glycogen levels, is the main goal of carbohydrate loading. And, as only male subjects were used, there was no information as to how a female athlete would respond to these 24 hour carbohydrate loading regimens. 5. Rauch LH, Rodger I, Wilson GR, Belonje JD, Dennis SC, Noakes TD, Hawley JA. The effects of carbohydrate loading on muscle glycogen content and cycling performance. Int J Sport Nutr. 1995; 5(1):25-36. This study was conducted by a group that includes John Hawley and Timothy Noakes, who have published extensively in the area of exercise metabolism. They have published several papers in the area of sports nutrition and performance, and sometimes collaborate with Louise Burke. In this report, the normal diets of cyclists were supplemented with carbohydrate for a total of 10.5 g/kg body mass x day, for 3 days. This yielded an increase of carbohydrate intake of 72%, which resulted in increased muscle glycogen. This study used a riding trial [2 hour ride at 75% VO2 peak, followed by five 60 second sprints at 100% VO2 peak, then a 1 hour performance ride], that was longer than most in the literature [30-90 minutes]. The results showed that carbohydrate supplementation resulted in improved power output and farther distance covered. In addition, muscle glycogen levels of supplemented and control subjects were not significantly different at

CHO Loading and Female Cyclists 7 the end of the exercise trial, indicating that those subjects who were carbohydrate loaded had greater glycogen utilization. Thus carbohydrate loading may actually be effective for exercise lasting extended periods of time. 6. Maughan RJ, Poole DC. The effects of a glycogen-loading regimen on the capacity to perform anaerobic exercise. European Journal of Applied Physiology. 1981; 46(3):211-9. This study compared the effects of diets with various amounts of carbohydrate on the ability of cyclists to perform anaerobic exercise. All subjects were male, and had either the subject’s habitual diet, which served as control, a carbohydrate free diet [begun after muscle glycogen depletion], or a high carbohydrate diet [also begun after muscle glycogen depletion]. Subjects then worked to exhaustion, which was not done in several carbohydrate loading studies examined. Mean work times of the experimental groups were lower for the carbohydrate-free subjects, and higher for the high carbohydrate subjects. Also while the rate of lactate accumulation was not significantly different between the three groups, resting and post-exercise blood lactate levels were lower than normal for the carbohydrate-free group, and higher than normal for the high carbohydrate group. This indicates that the differences in endurance capacity of the groups are due to the “capacity of the system”. While it is possible that a psychological effect accounts for the improved performance of the high carbohydrate group, it cannot account for the differences in blood lactate levels. Thus the data in this study indicates that carbohydrate loading is effective in increasing the time to exhaustion, a measure of improved performance. 7. Hawley JA, Palmer GS, Noakes TD. Effects of 3 days of carbohydrate supplementation on muscle glycogen content and utilisation during a 1-h cycling performance. Eur J Appl Physiol Occup Physiol. 1997; 75(5):407-12.

CHO Loading and Female Cyclists 8 This is another report by the Hawley and Noakes group. The goal of this work was to investigate if an athlete’s normal diet is supplemented with additional carbohydrate resulted in improved cycling performance during a 1-hour time trial. In this study 6 male endurance cyclists were evaluated in two trials. In one, they were given a carbohydrate supplement to increase their intake to 9.3 g/kg body mass x day, for 3 days, while in the other they were given colored and flavored water, so that it “replicated” a commercial drink, thus acting as a placebo, also for 3 days. The result was that there was no difference in time trials for the group after undergoing carbohydrate supplementation, when compared to their performance after consuming the placebo. Thus this study indicates a placebo effect regarding carbohydrate loading. However, exercise was only for one hour, which may not have been long enough for supercompensation of carbohydrate to be a factor on performance. And, carbohydrate intake was below 10 g/kg body mass x day, and thus may not have accomplished supercompensated muscle glycogen levels. To determine if such levels were attained, the authors would have had to obtain and examine muscle biopsies. As no female athletes were evaluated, it could not be determined if carbohydrate loading has any true effect on females, versus males. 8. Burke LM, Hawley JA, Schabort EJ, Gibson AS, Mujika I, Noakes TD. Carbohydrate loading failed to improve 100-km cycling performance in a placebo-controlled trial. J Appl Physiol. 2000; 88:1284–1290. Dr. Louise Burke is one of the leading researchers in nutrition and athlete performance. This work addresses a potential flaw in the design of many studies asking if carbohydrate loading improves performance. Several studies have indicated that carbohydrate loading does result in increased performance, but they did not include a placebo against which to evaluate the results. Instead, exercise performance of subjects without carbohydrate

CHO Loading and Female Cyclists 9 loading and with carbohydrate loading were compared. Thus the possibility exist that the increase in athlete performance was due to a psychological effect, as it is accepted in the literature and athletic communities that carbohydrate loading results in increased performance. This potential psychological effect was examined by Burke and her group. In this study seven well-trained male cyclists performed time trials on separate occasions, 3 days after consuming either a carbohydrate-loading (9g CHO/kg body mass x day) or a placebo-controlled moderate-carbohydrate diet (6g CHO/kg body mass x day). It should be noted that 9 g/kg BM x day is not considered a high carbohydrate diet by current standards [see 9]. It is possible that there is no significant difference between the amounts of carbohydrate given in the two diets. Several other studies used 10-15g CHO/kg body mass x day for their carbohydrate loading diets. Also, a carbohydrate drink (1g CHO/kg body mass x hr) was consumed during the time trials to optimized carbohydrate availability, which may have offset the results. Carbohydrate consumption during a time trial is a common practice by cyclists, but its effect on performance has not been fully documented, and this calls the validity of the conclusions into question. 9. Burke LM, Cox GR, Cummings NK, Desbrow B. Guidelines for Daily Carbohydrate Intake: Do Athletes Achieve Them? Sports Med. 2001; 31(4):267-299 This literature review aims to re-evaluate guidelines for routine carbohydrate intake of athletes undertaking heavy training loads, and to examine the actual carbohydrate intakes of athletes. The review reports that the recommended amounts of carbohydrate for daily needs/recover are 7-10 g/kg body mass for endurance athletes, while 10-12 g/kg body mass for high intensity exercise, such as the Tour De France. Published surveys showed that male athletes tend to meet their daily requirements for carbohydrate intake, with endurance athletes self reporting that they consume ~7.5 g/kg body mass, which is close to

CHO Loading and Female Cyclists 10 the minimum requirement. The authors point out that subjects often underestimate these values, and suggest that the true amount is likely 10-20% higher, thus in the range of 8-9 g/kg body mass. Female endurance athletes, however, reported daily carbohydrate intake of 5.5 g/kg body mass, and with a 10-20% increase, would mean 6-6.5g/kg body mass of daily carbohydrate intake, far below suggested levels. The review points out that the literature reports that when completing dietary surveys, female athletes are “conscious of their dietary patterns or body composition goals ” [reduction in body fat], and as a result either eat less than, or underreport, their true intake values. And while this is likely true, it is also likely that female athletes do not consume enough daily carbohydrate to meet their performance needs. The review suggests that this can be overcome by properly educating female athletes. 10. van Erp-Baart AM, Saris WH, Binkhorst RA, Vos JA, Elvers JW. Nationwide survey on nutritional habits in elite athletes. Part I. Energy, carbohydrate, protein, and fat intake. Int J Sports Med. 1989;10 Suppl 1:S3-10. There are very few reports on the nutritional habits of female cyclists. In this athlete dietary survey, female cyclists were found to take in less that optimal carbohydrate, according to Dutch recommendations. Dutch national female cyclists consumed, on average, 5.3 g/kg body mass, while guidelines call for 7-10 g/kg for most athletes. As this was a self-reporting survey, it is possible that athletes under-reported their carbohydrate intake. However, even allowing for this, and considering the higher energy needs of endurance cyclists, it is safe to conclude that in this group of athletes carbohydrate intake is insufficient. This work correlates that the habitual diet of female athletes does not provide for adequate energy. 11. Burke LM. Nutritional Practices of Male and Female Endurance Cyclists. Sports Med. 2001; 31(7):521-532

CHO Loading and Female Cyclists 11 In this literature review, the dietary habits of male and female cyclists are discussed. The review points to data that indicates that female cyclists restrict their carbohydrate and caloric intake to reduce body fat. However, in doing so they also are taking in too few carbohydrates to match their energy expenditures for regular training and racing. To compensate for the deficit, cyclists rely on race day supplementation with high carbohydrate bars and drinks. This data is in contrast to that for male cyclists, who do tend to consume a sufficient amount of dietary carbohydrate to meet energy expenditures. Thus female cyclists do not consume sufficient amounts of carbohydrate, which may affect data regarding the effectiveness of carbohydrate loading in female cyclists. 12. Tarnopolsky MA, Atkinson SA, Phillips SM, MacDougall JD. Carbohydrate loading and metabolism during exercise in men and women. J Appl Physiol. 1995; 78(4):1360-1368 This work was led by Mark Tarnopolsky, of McMaster University, who has published extensively in the area of neuromuscular and neurometabolic disorders, and the effects of nutrition and exercise on them. Previous work by his group showed that women oxidize more lipids than men during endurance exercise, and therefore decrease their oxidation of carbohydrate. In this work the ability to increase muscle glycogen after dietary carbohydrate was increased from 55-60% to 75% of the energy intake, for 4 days [their carbohydrate loading regimen], was evaluated. The subjects were similarly trained male and female endurance cyclists, who cycled at 75% VO2 peak for 60 minutes. In addition, a placebo was used. The results were that males increased muscle glycogen concentrations and improved performance, while females did not increase muscle glycogen concentrations, nor improve performance. In addition, females were again found to oxidize more lipid and less carbohydrate than the males. The study did not consider the likely under-consumption of carbohydrates by female athletes.

CHO Loading and Female Cyclists 12 13. Walker JL, Heigenhauser GJF, Hultman E, Spriet LL. Dietary carbohydrate, muscle glycogen content, and endurance performance in well-trained women. J Appl Physiol. 2000; 88:2151–2158. The goal of this study was to evaluate the ability of female endurance athletes to attain supercompensated muscle glycogen levels after being given a high carbohydrate diet. In addition, the female subjects were examined in the luteal phase of their menstrual cycles, as the elevated reproductive hormones have been shown to result in increased muscle and glycogen synthesis, events which do not occur during the follicular phase. Six female subjects were used, and evaluated after completing diet and exercise tapering regimens that included either a high carbohydrate diet [78% CHO], or a moderate diet [48%]. Subjects then cycled to voluntary exhaustion, at ~80% VO2 max. Both diets resulted in increased muscle glycogen prior to exercise, with the high carbohydrate diet having a 13% higher muscle glycogen level than the moderate diet. Also, net glycogen utilization during exercise was greater after the high carbohydrate diet. Finally, the subjects cycled longer at 80% VO2 max after the high carbohydrate diet, versus the moderate diet. Thus the authors conclude that while the amount of carbohydrate supercompensation was lower in females than that seen in males, females could successfully increase muscle glycogen levels during the luteal phase, which resulted in increased performance. It should be noted that no placebo was given, so a psychological effect could account for the improved performance, but not the measured muscle glycogen content. 14. Devries, MC, Hamadeh MJ, Phillips SM, Tarnopolsky MA. Menstrual cycle phase and sex influence muscle glycogen utilization and glucose turnover during moderateintensity endurance exercise. Am J Physiol Regul Integr Comp Physiol. 2006; 291: R1120–R1128. The data on the effects of female sex hormones on carbohydrate utilization is not conclusive. Animal studies indicate that estrogen increases muscle glycogen storage at

CHO Loading and Female Cyclists 13 rest and result in the reduction of glycogen utilization during prolonged submaximal exercise. This reduction may be a result of increased oxidation of free-fatty acids. Studies in humans have not been as conclusive. Some reports, as recent as 2000, indicate that menstrual phase, and thus estrogen levels, have no effect on the ability of muscle to store glycogen, on RER, or other markers of carbohydrate metabolism. While other studies, including this report, indicate that sex hormones do have an effect, but there is no agreement about what the effect is. In this 2006 report by Tarnopolsky’s group, the data indicate that in luteal phase, and thus under high estrogen levels, female athletes have lower glucose rate of appearance, rate of disappearance, and metabolic clearance rate, than women in follicular phase. Measurements were taken after 90 minutes of cycling at submaximal levels. Thus hormone levels likely affect female athlete carbohydrate metabolism, and needs to be considered when evaluating the effectiveness of carbohydrate loading in female cyclists. 15. Tarnopolsky MA, Zawada C, Richmond LB, Carter S, Shearer J, Graham T, Phillips SM. Gender differences in carbohydrate loading are related to energy intake. J Appl Physiol. 2001; 91:225–230. This work asked if female athletes were given enough carbohydrate [to meet guideline levels], would they increase muscle glycogen levels to that similar to males. The authors put forward three hypotheses as to why women don’t carbohydrate load: first is the reported lower carbohydrate intake in women, which means lower amount of CHO/kg fat free mass [FFM]. Second is a gender differences in the muscle enzymatic and/or transport capacity for glycogen storage. This is refuted by 2 pieces of evidence- lack of effect of estradiol on glucose transporter 4, and the equal rates of glycogen re-synthesis in men and women, during the first 4 hours after exercise. The third hypothesis is that there are gender differences in the proportion of proglycogen to macroglcogen. Proglycogen is smaller in

CHO Loading and Female Cyclists 14 mass, while macroglycogen is “the main portion that increases in response to the consumption of a high carbohydrate intake”. This study sought to address all three of these hypotheses. They found that there were no gender differences in hexokinase activity [which would indicate a gender difference in glucose transport], nor in pro- and macroglycogen levels. They did find that women were able to increase their muscle glycogen stores by a magnitude that was similar to that seen for men in response to a higher energy and carbohydrate intake. When female carbohydrate intake is 8-10 g/kg body mass x day, on par with that for males, it would mean that this amount of carbohydrate would equal 93-120% of the caloric intake [2000 kcal/day for a 60 kg athlete]. Thus the authors increased the daily energy intake of female subjects so the 8-10 g of CHO/kg body mass x day could be achieved. The result was that the female athletes did increase muscle glycogen levels similar to those seen in males, a result different from an earlier study by this same group [12]. And, while this study addressed the ability of females to carbohydrate load, it did not examine the effect of supercompensation on performance. 16. Carter SL, Rennie CD, Hamilton SJ, Tarnopolsky MA. Changes in skeletal muscle in males and females following endurance training. Can. J. Physiol. Pharmacol. 2001; 79:386–392. There is the possibility that males and females use different muscle fibers, and that this plays a role in the effectiveness of carbohydrate loading. This study is the first to examine muscle enzyme adaptation in endurance trained males and females, considering each group separately. Thus, if given identical endurance training stimuli, would the muscle enzyme adaptations be similar or different in males and females. Previous work by this group and others has shown that female endurance athletes have a lower respiratory exchange ratio [RER] than males, during endurance exercise, and this is an indication that female athletes oxidize more lipid and less carbohydrate during

CHO Loading and Female Cyclists 15 submaximal endurance exercise. This may be due in part to utilization of different muscle fiber types. This study showed that females had a higher type I muscle fiber area than males, while males had larger type II fibers. Type I fibers have a “3-fold higher intra-muscular triglyceride content”, versus type II fibers, which the authors claim could explain the higher lipid oxidation seen in females. Type I fibers would have a higher number of mitochondria. But the authors do not report if or how the muscle composition differs between males and females. Clinical Implications Athletic performance, such as cycling, is affected by several factors, including nutrition and thus glycogen availability. To give one a competitive edge, many cyclists increase their muscle glycogen levels prior to an event, a popular practice that research has not definitively shown is effective (5-8). For cycling events that are longer than 90 minutes or that require short bouts of high intensity effort, it is likely that CHO loading is effective in improving performance. But for female athletes, CHO loading alone is insufficient. The data show that females must have CHO intake levels exceeding 7-10 g/kg body mass for CHO loading to occur (15). While elite female athletes need to reduce body fat, they must also consume enough carbohydrate to attain their energy needs. And although educating the athletes about nutrition may help (9), it may be useful to educate the coaches as well, so that the message for proper nutrition is reinforced. As a restriction of CHO intake to lower body fat likely affects performance, improving an athlete’s diet, especially that of a female athlete, may be a realistic and safe way to give an athlete a competitive edge.

CHO Loading and Female Cyclists 16 Conclusions Despite the number of studies on CHO loading, its effect on cycling performance is still not clear. Most of the studies cited in this review were done with fewer than 10 subjects, and such small population sizes make it difficult to draw significant conclusions. Also there is no standardized value for a high CHO diet (1-8). With regard to female cyclists, CHO loading only occurred when CHO intake levels exceeded the minimal recommended level of 7-10 g/kg body mass x day (15). In addition, as estrogen levels may affect CHO metabolism in muscles (13, 14), consideration as to stage of menstrual cycle is an important factor as well. Another gender difference is muscle fiber type and metabolic enzymes is unclear, as the study was done in females who had not consumed enough CHO for CHO loading to occur (16). Also, the psychological effect of CHO loading has not been properly evaluated, as the amount of CHO for high CHO diets, used in studies, are below 10 g/kg body mass (7, 8). Finally, the type and duration of exercise have to be considered, as cycling for less than 90 minutes at submaximal levels did not result in a positive performance response to CHO loading (7, 8). Thus CHO loading is more than just short term increase of dietary CHO, and the above factors need to be considered when evaluating CHO loading reports. Future Research There is still much to understand about CHO loading, and repeating some of the studies cited in this review, using standardized CHO intake values, could address these concerns. Such consistent reevaluation of the data would be beneficial for both male and female cyclists. With specific focus on CHO loading in female cyclists, a likely first step is a repeat of the 2001 Tarnopolsky (15) study, with the addition of evaluating performance in female cyclists post CHO

CHO Loading and Female Cyclists 17 loading. Also, analysis of muscle fiber enzymatic adaptations in female cyclists in which CHO loading has occurred would be useful in determining if females truly do oxidize more lipids, and less CHO, in response to endurance training. All of these experiments should be done with placebo, to rule out a psychological effect for performance improvement. And even if the improvement is not statistically significant, for elite athletes, improvement on the scale of milliseconds can mean the difference in winning.

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