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The effects of solid and liquid carbohydrate feedings on high intensity intermittent exercise performance Walton, Peter Trent 1996

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THE EFFECTS OF SOLID AND LIQUID CARBOHYDRATE FEEDINGS ON HIGH INTENSITY INTERMITTENT EXERCISE PERFORMANCE by Peter Trent Walton BPE, Acadia University, 1992 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES School of Human Kinetics We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA January, 1996 © Peter Trent Walton, 1996 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. S c h o o l Department of The University of British Columbia Vancouver, Canada Date DE-6 (2788) 11 ABSTRACT Ten elite female soccer players were studied to determine the effects of pre-exercise solid carbohydrate (SCHO) and liquid carbohydrate ( L C H O ) feedings on high intensity intermittent exercise performance. At 5 min pre-exercise subjects consumed either 50 g of S C H O + 400 ml of H 2 0 , 50 g of L C H O in a 400 ml solution, or 400 ml of artificially sweetened H 2 0 (PL). Exercise consisted of two 19 min periods of high intensity intemittent running separated by a 10 min break. At 5 min post-exercise, subjects completed a performance trial (PT) in which they ran repeated 10 s, 120% V 0 2 max sprints in a 1:1 work to rest ratio until exhaustion. Blood lactate was not different (p>0.05) between feedings. Blood glucose (BG) was greater (p<0.05) for S C H O and L C H O at 10, 20, and 30 min during exercise compared to P L . A t 40 min B G was not significantly different between S C H O and P L and S C H O and L C H O . However, at 40 min B G for L C H O was significantly higher than P L . At 2 min post-exercise B G was similar between interventions. Time to exhaustion in PT was greater in both carbohydrate trials compared to P L ( X ± SE, S C H O = 693 s ± 135, L C H O = 648 ± 113, P L = 436 ± 70; p<0.01). Results indicate that the intake of equal amounts of S C H O and L C H O 5 minutes prior to high intensity intermittent exercise improve performance similarly. Ill TABLE OF CONTENTS ABSTRACT ii T A B L E OF CONTENTS iii LIST OF TABLES v LIST OF FIGURES vi ACKNOWLEDGMENTS vii CHAPTER 1: INTRODUCTION TO THE PROBLEM 1 1.1 Introduction to the Problem 1 1.2 Statement of Problem 2 1.3 Delimitations 2 1.4 Limitations 2 1.5 Primary Hypothesis 2 1.5.1 Secondary Hypotheses 3 1.6 Significance of Study 5 CHAPTER 2: REVIEW OF LITERATURE 6 2.1 Introduction 6 2.2 Carbohydrate Intake Immediately (< 5 min) Prior to Exercise 6 2.3 Carbohydrate Intake 30-60 Mnutes Prior Exercise 7 2.4 Carbohydrate Intake 3-4 Hours Prior to Exercise 11 2.5 Carbohydrate Intake During Exercise 13 2.5.1 Rate of Carbohydrate Ingestion 15 2.5.2 Types of Carbohydrate 16 2.5.3 Forms of Carbohydrate 17 CHAPTER 3: M E T H O D O L O G Y 20 3.1 Experimental Design 20 3.2 Dependent and Independent Variables 20 3.2.1 Other Dependent Variables Measured 20 3.3 Subjects 20 3.4 Methods 21 3.4.1 Maximal Oxygen Uptake (V0 2 max) Test 21 3.4.2^ Intermittent Testing ; 21 3.5 Data Analysis 23 CHAPTER 4: RESULTS AND DISCUSSION 24 4.1 Results 24 4.1.1 Subjects 24 iv 4.1.2 Performance 24 4.1.3 Blood Glucose 26 4.1.4 Blood Lactate 27 4.2. Discussion 29 BIBLIOGRAPHY 35 APPENDIX 'I 40 V LIST OF TABLES 1. Characteristics of subjects. 24 2. Time to fatigue in the performance trial for the solid carbohydrate (SCHO), liquid carbohydrate (LCHO), and placebo (PL) trials. 25 3. Effects of the solid carbohydrate (SCHO), liquid carbohydrate (LCHO), and placebo (PL) on blood glucose levels (mmol/1) during the high intensity intermittent exercise and during the 5 minute rest break preceding the performance trial. 26 4. Effects of solid carbohydrate (SCHO), liquid carbohydrate (LCHO), and placebo (PL) on blood lactate during the high intensity intermittent exercise, during the 5 minute rest break preceding the performance trial (50 minutes) , and at the end of the performance trial (referred to as END in the graph). 28 5. Individual characteristics of subjects. 41 6. Individual subjects time to fatigue (sec) in the performance trial for the solid carbohydrate (SCHO), liquid carbohydrate (LCHO), and the placebo (PL) trial. 42 7. Individual subjects blood glucose levels (mmol/1) for the solid carbohydrate (SCHO), liquid carbohydrate (LCHO), and the placebo (PL) trial. 43 8. Individual subjects blood lactate levels (mmol/1) for the solid carbohydrate (SCHO), liquid carbohydrate (LCHO), and placebo (PL) trial. 44 vi LIST OF FIGURES 1. Overview of exercise protocol. 23 2. Time to fatigue in the performance trial for the solid carbohydrate (SCHO) , liquid carbohydrate (LCHO), and placebo (PL) trials. 25 3. Effects of the solid carbohydrate (SCHO), liquid carbohydrate (LCHO), and placebo (PL) on blood glucose levels (mmol/1) during the high intensity intermittent exercise and during the 5 minute rest break preceding the performance trial (50 minutes). 27 4. Effects of solid carbohydrate (SCHO), liquid carbohydrate (LCHO) , and placebo (PL) on blood lactate during the high intensity intermittent exercise, during the 5 minute rest break preceding the performance trial (50 minutes), and at the end of the performance trial (referred to as E N D in the graph). 28 9 vn A C K N O W L E D G M E N T S I would like to thank my wife Paula for her patience, support, understanding, listening to me complain, and proofreading. I would like to thank my parents and family for their life long support and their support during my thesis even though they were not and still are uncertain what exercise physiology is. I would like to thank my graduate advisor Dr. Rhodes for his wisdom throughout my graduate degree and for the Canucks tickets. I would like to thank my committee members Dr. Coutts, Dr. Crawford, and Dr. Taunton for their input and suggestions in preparing and concluding my thesis. Finally, but not lastly, I would like to thank Dusan Benicky and Moira Petit for their finger pricking, hose hooking up, treadmill running, lactate taking abilities. 1 C H A P T E R 1 1.1 Introduction to Problem Carbohydrates are essential fuels for many types of activities. The depletion of muscle glycogen (Ahlborg et al., 1967; Bergstrom and Hultman, 1967) and/or hypoglycemia (Coggan and Coyle, 1987) are associated with an inability to exercise at a desired intensity. Because of the importance of carbohydrate, numerous studies have investigated the intake of carbohydrate immediately prior to or during exercise and have concluded that carbohydrate ingestion is able to improve performance (Bacharach et al., 1994; Bjorkman et al., 1984; Coggan and Coyle, 1988, Coggan and Coyle, 1989; Coyle et al., 1983; Coyle et al., 1986; Fielding et al., 1985; Hargreaves et al., 1984; Ivy et al., 1979; Mitchell et al., 1988; Mitchell et al., 1989; Murdoch et al., 1993; Neufer et al., 1987). However, the majority of these studies have emphasized endurance exercise, with limited research directed at intemittent exercise. To date, laboratory investigations that have looked at intermittent exercise and carbohydrate intake have utilized long periods of moderate intensity exercise with short rest breaks (Mitchell et al., 1988; Mitchell et al., 1989) or long periods of low intensity exercise interspersed with high intensity sprints and short rest breaks (Fielding et al., 1985, Hargreaves et al., 1984). No intermittent exercise studies have involved intensities above 100% VO2 max or short high intensity and low intensity exercise periods with short rest i" " breaks common to sports such as soccer, hockey, and basketball. Therefore, it is the purpose of the present study to examine how the ingestion of carbohydrate will effect high intensity intermittent exercise performance, specifically, looking at how carbohydrate ingestion immediately prior (5 minutes) to high intensity intermittent exercise will effect performance. A secondary purpose of this study is to examine whether or not differences exist between solid and liquid carbohydrate intakes. Few studies have compared solid and 2 liquid carbohydrate intakes (Mason et al., 1993; Murdoch et al., 1993; Neuter et al., 1987), with no study involving high intensity intermittent exercise. 1.2 Statement of Problem The purpose of this study is to examine the effects of solid versus liquid carbohydrate feedings on high intensity intermittent exercise performance. 1.3 Delimitations 1. Subjects being highly competitive female soccer players. 2. A sample size of 10 subjects. 3. The amount and types of carbohydrates ingested. 4. The design of the intermittent exercise testing. 1.4 Limitations 1. The performance to fatigue trial being representative of performance. 2. The ability of the^ methods and instruments utilized to give accurate values of RER, V0 2 , blood lactate, and blood glucose. 1.5 Primary Hypothesis 1. Solid carbohydrate (SCHO) and liquid carbohydrate (LCHO) intake will increase time to fatigue compared to the placebo (P) intake. Time to fatigue (T) will be the same for both forms of carbohydrate. T SCHO = T LCHO > T P (p < 0.05) Rationale i \ Constable et al. (1984) and Kuipers et al. (1987) have shown that glycogen synthesis can occur in non-active muscle fibers, when blood glucose levels are elevated from exogenous carbohydrate, during low to moderate intensity exercise that is preceded 3 by high intensity exercise. This has led to the deduction that carbohydrate ingestion may allow the body to synthesize muscle glycogen during intermittent exercise that involves low and high intensities (Coyle, 1991). Therefore, it is believed that during the rest breaks and low intensity periods of the intermittent protocol of the present study, muscle glycogen will be synthesized in the non-active muscle fibers from the elevated blood glucose levels made available from the ingested carbohydrate. Higher muscle glycogen levels at the end of the carbohydrate trials will allow for a longer time to fatigue relative to the placebo trial, since the capacity to perform exhaustive sprint activity is dependent on muscle glycogen (Maughan and Poole, 1981), 1.5.1 Secondary Hypotheses 2. The intake of SCHO and LCHO will result in significantly higher blood glucose (BG) levels during the intermittent exercise protocol when compared to the P intake. B G levels will be the same for both forms of carbohydrate. BG SCHO = BG LCHO > BG P (p < 0.05) Rationale It is well documented that when carbohydrate is ingested immediately prior to or during exercise, blood glucose levels are greater than when no carbohydrate is taken (Bjorkman et al., 1984; Coggan and Coyle, 1988; Coyle et al., 1983; Fielding et al., 1985; Hargreaves et al., 1984; Ivy et al., 1979, Mitchell et al., 1989; Neufer et al., 1987). Carbohydrate that is ingested empties from the stomach and is absorbed by the small intestine, increasing blood glucose levels. Therefore, it is hypothesized that carbohydrate feedings will increase blood glucose levels compared to the placebo. No difference will be found between the form of carbohydrate since identical amounts of solid and liquid carbohydrate have been shown to effect blood glucose levels the same during exercise (Mason et al., 1993). 4 3. The intake of SCHO and LCHO will result in blood lactate (BL) levels during the intermittent exercise protocol that are similar to the P intake. However, BL levels will be significantly higher after the performance trial, with the SCHO and LCHO compared to the P. BL levels will be the same for both forms of carbohydrate after the performance trial. During Intermittent Exercise BL SCHO = BL LCHO = P (p < 0.05) After the Performance Trial BL SCHO = BL LCHO > P (p < 0.05) Rationale Blood lactate levels are similar when subjects ingest carbohydrate immediately prior to or during exercise, compared to a placebo intake (Coggan and Coyle, 1988; Coyle et al., 1983; Hargreaves et al., 1984; Neufer et al., 1987). As long as an individual is able to perform at a given intensity, there is no apparent mechanism that would cause carbohydrate availability to increase anaerobic metabolism. Hence, it is hypothesized that blood lactate levels during the intermittent exercise protocol will be the same between the placebo and carbohydrate intakes. High intensity exercise relies heavily on muscle glycogen and anaerobic metabolism, in which lactate is produced. Therefore, blood lactate will be higher following the performance trial after carbohydrate ingestion opposed to the placebo. Greater muscle glycogen levels prior to the performance trials will increase time to exhaustion and increase the amount of lactate produced in the carbohydrate trials. 5 1.6 Significance of Study No study has examined carbohydrate ingestion immediately prior to high intensity intermittent exercise. If carbohydrate intake 5 minutes prior to this type of exercise can be shown to improve performance, the results could be applied to high intensity intermittent sports such as soccer, hockey, and basketball. Also, if it is shown that performance is similar between solid and liquid carbohydrate intake, the athlete who wishes to consume carbohydrates at this time would be able to choose the form that he/she prefers. 6 C H A P T E R 2 2.0 Review of Literature 2.1 Introduction Performance in moderate to high intensity exercise is dependent on the availability of carbohydrate for fuel. A reduction in this substrate to the exercising muscle can be detrimental to an athlete. Low muscle glycogen (Ahlborg et al., 1967, Bergstrom and Hultman, 1967) and/or plasma glucose (Coggan and Coyle, 1987) levels have been shown to impair performance, in prolonged exercise, by causing premature fatigue. To possibly delay or eliminate a reduction in the body's carbohydrates, carbohydrates are ingested prior to and during exercise. This paper will review the investigations that have studied the effects of carbohydrate ingestion before and during exercise and how this may affect performance. 2.2 Carbohydrate Intake Immediately (< 5 min ) Prior to Exercise There has been little research investigating the effects of carbohydrate intake immediately prior to exercise. However, research that has involved carbohydrate feedings immediately prior to exercise has shown that intake at this time may be of benefit to performance. Neufer et al. (1987) demonstrated that either 45g of liquid carbohydrate (8.25% glucose polymer and 3% fructose) or solid carbohydrate (confectionery bar) ingested 5 minutes pre-exercise can similarly improve performance in a 15 minute all out cycling performance!trial, following 45 minutes of exercise at 77% V O 2 max. Neufer et al. (1987) associated the enhanced performance with improved carbohydrate availability and oxidation. There was no difference in muscle glycogen utilization between the two carbohydrate trials and the placebo. In regard to the enhanced oxidation of carbohydrate, it has been reported, that endurance athletes are capable of oxidizing carbohydrate from 7 other sources, besides muscle glycogen, in the latter stages of prolonged exercise to "ward off' fatigue (Coyle et al., 1986). Therefore, it appears that carbohydrate intake 5 minutes prior to exercise may benefit performance'by maintaining plasma glucose and carbohydrate oxidation late in exercise. The importance of this will be discussed later when examining the effects of carbohydrate intake during exercise. The intake of carbohydrate at this time also reduces the risk of hypoglycemia occurring since the intake is very close to the onset of exercise where catecholamines are released and insulin release is suppressed (Brouns et al., 1989; Galbo et al., 1975). The importance of insulin suppression will be made clear in the next few paragraphs. 2.3 Carbohydrate Intake 30-60 Minutes Prior to Exercise Studies that have examined the intake of carbohydrate 30-60 minutes prior to exercise have found varying results. Results have shown that carbohydrate intake at this time may either impair performance (Foster et al., 1979), improve performance (Okano et al., 1988; Sherman et al., 1991, Ventura et al., 1994), or have no effect on performance (Calles-Escadon et al., 1991; Devlin et al, 1986; Hargreaves et al., 1987; Koivisto et al., 1981). Foster et al. (1979) demonstrated that the intake of glucose 30 minutes prior to exercise impaired performance in subjects who exercised at 80% VO2 max on a bicycle ergometer until exhaustion. There was a 19% decline in time to exhaustion when subjects had ingested 75g of glucose compared to a mixed meal or water. The presumption by Foster et al. (1979) was that the early exhaustion was caused by the depletion of glycogen in the exercising muscles. It should be noted, however, that muscle glycogen was not measured and the idea of it causing fatigue was formulated based on the descriptions of fatigue by subjects at the end of exercise and the resultant low blood lactate levels observed at the time of exhaustion. Foster et al. (1979) proposed that the depletion of 8 muscle glycogen occurred due to the pre-exercise hyperglycemia, rapid fall in plasma glucose at the onset of exercise, and the delayed rise in plasma free fatty acids. This reasoning was based on the earlier research of Costill et al. (1977). Costill et al. (1977) found that an increased plasma free fatty acid concentration produced a sparing of muscle glycogen during exercise. However, the opposite was observed when 75g of glucose was taken 45 minutes prior to exercise. It produced an increased utilization of muscle glycogen and carbohydrates compared to a placebo. The intake of glucose produced a 38% increase in plasma glucose, which caused a 3.3 fold increase in plasma insulin. Once exercise began the plasma glucose level fell dramatically and remained below levels of controls during exercise. The extreme fall in plasma glucose is representative of the rapid uptake of glucose that occurs in exercising muscle at the beginning of exercise when high insulin levels are present (Defrenzo et al., 1981). Also, Costill et al. (1977) demonstrated that the increase in plasma insulin was accompanied by a reduction in free fatty acid levels during the exercise period. The negative results of glucose ingestion 30-60 minutes prior to exercise have been shown by others. Hargreaves et al. (1985) demonstrated that the intake of 50g of glucose 45 minutes prior to 30 minutes of cycling at 75 % VO2 max produced the same high pre-exercise plasma glucose levels, elevated insulin levels, and rapid fall in plasma glucose at the onset of exercise. Muscle glycogen was also measured and was found to be lower than the control at the end of the exercise period. Unlike the previously discussed findings, glucose intake 30-60 minutes prior to exercise has been shown in some studies to significantly improve performance. Sherman et al. (1991) demonstrated that glucose solutions containing 1 g/kg or 2 g/kg of body weight, taken 1 hour prior to exercise can have a positive effect on performance. Improvements of 12.5%, compared to the control trials, were observed in a vigorous time trial following 90 minutes of cycling at 70% V 0 2 max. They related the improvements in performance to greater carbohydrate availability during exercise. The rate of carbohydrate 9 utilization was 12% higher compared to the placebo trial. They proposed that the increased carbohydrate availability came from the gastric emptying and intestinal absorption of carbohydrate throughout exercise. Improvements occurred in the Sherman et al. (1991) study even though there were elevated levels of plasma insulin present at the beginning and throughout exercise and an initial drop in plasma glucose at the onset of exercise. This opposes the findings that suggest that increased plasma insulin levels and a sudden drop in blood glucose may be responsible for premature exhaustion in prolonged exercise. Similarly, Ventura et al. (1994) reported that 75g of glucose, taken 30 minutes prior to exercise, could significantly increase time to fatigue, compared to a placebo, in subjects who exercised at 82% V 0 2 max. It is uncertain how the glucose improved performance since the respiratory exchange ratio (RER) was not different between the glucose and placebo trial. Although, the reliability of the RER is questionable because of the intensity of the exercise and the short duration (approximately 10 minutes) of the exercise. Numerous studies have shown that the intake of carbohydrate has no effect on performance when taken 30-60 minutes prior to exercise (Calles-Escadon et al., 1991; Devlin et al., 1986; Hargreaves et al., 1987; Koivisto, et al. 1981). These studies had their subjects exercise to> exhaustion after glucose feedings. Performance was found to be similar between trials when fed carbohydrate or when fed a placebo. In all of the studies, the carbohydrate feedings caused higher plasma glucose and higher plasma insulin levels at the onset of exercise compared to a placebo. These increased levels either resulted in a decrease in blood glucose levels to the placebo trial levels (Calles-Escadon et al., 1991, Devlin et al., 1986), below the placebo trial levels (Hargreaves et al., 1987), or to hypoglycemic levels (Koivisto et al., 1981), within the first few minutes of exercise. Although, as discussed above, these decreases did not affect performance. Also, studies in which muscle glycogen had been measured, found non-significant differences in the 10 amount of muscle glycogen utilized between carbohydrate and placebo feedings (Devlin et al., 1986; Hargreaves et al., 1987). Glucose and fructose have been shown to elicit different responses during exercise, when taken 30-60 minutes prior to exercise. Fructose, compared to glucose, has been found to produce a smaller increase in plasma glucose (Fielding et al., 1987; Hargreaves et al., 1985; Hasson and Barnes, 1987; Koivisto et al., 1981, Ventura et al., 1994), a smaller increase in plasma insulin at the beginning of exercise (Fielding et al., 1987; Hargreaves et al., 1985; Koivosti et al., 1981), a smaller decrease in plasma glucose at the onset of exercise (Fielding et al., 1987; Hargreaves et al., 1985; Hasson and Barnes, 1987; Koivisto et al., 1981), and a sparing of muscle glycogen throughout exercise (Hargreaves et al., 1985; Levine et al., 1983). Unfortunately, many studies have found that the intake of fructose 30-60 minutes pre-exercise is unable to improve performance (Calles-Escadon et al., 1991; Haregreaves et al., 1987; Koivisto et al., 1981; Ventura et al., 1994). Nevertheless, one study has shown performance improvements when fructose was consumed 1 hour pre-exercise. Okano et al. (1988) showed that the intake of 65g or 85g of fructose enhanced performance, by increasing time to exhaustion. However, they were unable to account for the increase in performance that occurred when the fructose was taken. Evaluation of the studies that have examined carbohydrate intake 30-60 minutes prior to exercise makes it uncertain whether carbohydrate ingestion will impair performance by decreasing muscle glycogen, improve performance by enhanced carbohydrate oxidation, or have no effect on performance. Although, negative and neutral outcomes may be avoided and positive results may occur if an athlete consumes a low glyceamicc index food prior to exercise. Thomas et al. (1991) has recently shown that a low glycemic food (lentils) can significantly improve time to exhaustion compared to a placebo, while high glycemic foods (potato or glucose) are unable to influence performance. The reasons why the low glycemic food improved performance may be a 11 result o f less of a glucose response and insulin response prior to exercise (Thomas et al., 1991). A s a result o f these findings, it may be in the best interest o f an athlete who prefers to eat carbohydrates 30-60 minutes prior to exercise, to consume a carbohydrate food with a low glycemic index. Finally, athletes choosing to consume carbohydrates pre-exercise in the hope of receiving ergogenic effects, should experiment with feedings in order to discover whether carbohydrates will be beneficial to performance. 2.4 Carbohydrate Intake 3-4 Hours Prior to Exercise Carbohydrate intake 3-4 hours prior to exercise has been suggested to be non beneficial to performance, even when the intake of carbohydrate at this time can increase muscle glycogen by 42% by the onset of exercise (Coyle et al., 1985). However, despite this early opinion, more recent research has demonstrated that carbohydrate ingestion 3-4 hours pre-exercise has a definite positive effect on performance (Neufer et al., 1987, Sherman et al., 1989; Wright et al., 1991). Sherman et al. (1989) demonstrated a 15% improvement in performance when 312g of carbohydrate (primarily maltodextrin and 50g of sucrose) in liquid meal was taken 4 hours pre-exercise. Subjects cycled intermittently for 95 minutes (between 52% and 70% VC<2 max) followed by the completion of as many revolutions as possible equivalent to 45 minutes of exercise at 70% V O 2 max. Sherman et al. (1989) indicated from the results that the improvement in performance was due to an enhancement of carbohydrate utilization. Respiratory exchange ratio (RER) was greater than the placebo trials and plasma free fatty acid levels were suppressed throughout exercise periods. Blood glucose was maintained during exercise, in spite of higher insulin levels compared to the control trials. Sherman et al (1989) attributed the maintained blood glucose levels to continued gastric emptying and intestinal absorption of the carbohydrate. Also, they found that 45g or 165g o f carbohydrate taken 4 hours prior to exercise did not improve performance, indicating a larger intake such as 312g may be required for enhanced performance. 12 Wright et al. (1991) demonstrated an 18% increase in performance when 333g of carbohydrates in solution (21% glucose polymers and 4% sucrose) were ingested 3 hours prior to exercise. The trials in the experiment were completed at 70% V0 2 max to exhaustion. Wright et al. (1991) attributed the improvements to an enhanced carbohydrate oxidation, as did Sherman et al. (1989). Wright et al. (1991) suggested that the greater carbohydrate oxidation probably arose from the availability and utilization of blood glucose from: the ingested carbohydrate. A significant correlation was found between the amount of carbohydrate consumed and the carbohydrate utilized. The studies just discussed demonstrated that carbohydrate intake 3-4 hours before exercise has a positive effect on performance. However, it has been shown that carbohydrate ingested at this time, combined with the intake of a smaller amount immediately prior to (Neufer et al., 1987) or during (Wright et al., 1991) exercise, has a greater effect on performance. Neufer et al. (1987) demonstrated that a- light carbohydrate meal (200g of i carbohydrate in the form of cereal, bread, milk, and fruit juices) ingested 4 hours prior to exercise accompanied by a lesser carbohydrate intake ( 45g of carbohydrate in a confectionery bar) 5 minutes pre-exercise, can improve performance in a 15 minute performance trial following 45 minutes of exercise at 70% V0 2 max. The fed trials work output during the 15 minutes was greater than the placebo trials or when carbohydrates were ingested 5 minutes before exercise. During the hour of exercise there was an increased rate of carbohydrate oxidation and a reduction in plasma free fatty acids, in the combination intake.j Neufer et al. (1987) found there to be a significant correlation between the amount of work produced and carbohydrate oxidized in the 15 minute all out performance. In the study by Wright et al. (1991), previously discussed, it was shown that carbohydrate intake 3 hours prior to exercise may improve performance. This study also had a trial in which carbohydrate was taken 3 hours pre-exercise, along with during 5 13 exercise. The combination intake had a substantial influence on performance. Time to exhaustion was increased by 44% compared to the placebo trials. This is a 16% improvement over trials where carbohydrates were only taken during exercise and 26% increase in time to exhaustion compared to the trials where carbohydrates were taken 3 hours pre-exercise. Wright et al. (1991) proposed that the increased performance was due to greater carbohydrate oxidation during exercise. Once again, Wright et al. (1991) suggested the combination intake continued to be absorbed during exercise, maintaining blood glucose levels and enhanced carbohydrate oxidation. Overall, the intake of relatively large amounts of carbohydrate 3-4 hours pre-exercise may benefit performance by providing glucose to the blood through continued gastric emptying and intestinal absorption and allow for enhanced carbohydrate oxidation. Also, carbohydrate intake at this time may perhaps increase muscle glycogen stores prior to exercise. To further optimize performance, an athlete may want to combine a carbohydrate meal with a smaller intake 5 minutes prior to exercise or smaller feedings during exercise. 2.5 Carbohydrate Intake Dur ing Exercise Carbohydrate intake during exercise has been shown to improve performance by increasing time to exhaustion (Bjorkman et al., 1984; Coggan and Coyle, 1988; Coggan and Coyle 1989; Coyle et al., 1983; Coyle et al., 1986; Murdoch et al., 1993), by increasing the amount of work that an individual can perform at the end of exercise (Bacharach et al., 1994; Below et al., 1995; Ivy et al., 1979; Mitchell et al., 1988; Mitchell et al., 1989), and by improving sprint performance following prolonged exercise (Fielding et al., 1985; Hargreaves et al., 1984). These positive results have been observed in both continuous and intermittent exercise that range in intensities from 60% to 100% VO2 max. 14 The early consensus for carbohydrate improving performance during exercise was that it caused a sparing of muscle glycogen (Hargreaves et al., 1984; Bjorkman et al., 1984). However, more recent studies have indicated that carbohydrate intake during exercise is ineffective in sparing muscle glycogen (Bosch et al., 1994; Coyle et al., 1986; Fielding et al., 1985; Mitchell et al., 1989). The inability of carbohydrate to spare muscle glycogen even occurs when plasma glucose is maintained at 10 mM (Coyle et al., 1991). Alternatively, it is suggested that carbohydrate feedings maintain relatively high plasma glucose levels and carbohydrate oxidation near the end of exercise when the body's natural carbohydrate reserves are fairly depleted (Coggan and Coyle, 1987; Coggan and Coyle, 1989; Coyle et al., 1986 ). In addition, carbohydrate ingestion during exercise may also be beneficial to performance by sparing the breakdown of liver glycogen , by decreasing the glucagon to insulin ratio (Mitchell et al., 1990) and/or by utilizing exogenous carbohydrate before relying on endogenous stores (Bosch et al., 1994). However, the effectiveness of carbohydrate to improve performance may be dictated by pre-exercise muscle glycogen levels (Widrick et al., 1993). As discussed above, improvements in performance from carbohydrate intake appears to be due to maintained plasma glucose and carbohydrate oxidation, when the body's carbohydrate-.reserves are low, and not from the sparing of muscle glycogen. The majority of the studies that demonstrated a lack of muscle glycogen sparing were studies that used continuous exercise (Bosch et al., 1994; Coyle et al., 1986) or intermittent exercise that was very similar to continuous exercise (Mitchell et al., 1989). Indeed, carbohydrate may have the potential to spare muscle glycogen in certain types of activities. Constable et al. (1984) and Kuiper et al. (1987) showed that muscle glycogen can be synthesized in non-active glycogen depleted muscle fibers, from ingested carbohydrate, during low intensity exercise that was preceded by a high intensity work period (the study by Constable et al., 1984 was performed on rats). This has led to the deduction that carbohydrate ingestion during exercise may result in the synthesize of 15 muscle glycogen in non-active muscle fibres during exercise that includes rest breaks or intermittent activity that involves low and high intensity periods (Coyle, 1991). This might explain the sparing of muscle glycogen observed by Hargreaves et al. (1984) when they fed their subjects a solid carbohydrate during 4 hours of intermittent cycling which consisted of short bouts of high intensity sprinting and prolonged bouts of low intensity exercise. A sparing of muscle glycogen has also been observed in male university hockey players who consumed carbohydrate before and during a hockey game (Simmard et al., 1988) and in elite male soccer players who consumed carbohydrate before and during a soccer match (Leatt and Jacobs, 1989). The potential glycogen sparing effect, in sports such as hockey and soccer could be very beneficial since both rely heavily on muscle glycogen for energy (Green, 1979; Hawley et al., 1994). Because carbohydrate feedings have been shown to spare muscle glycogen during high intensity intermittent activities, it is plausible that exogenous carbohydrate influences performance by a different mechanism during this type of activity compared to continuous exercise. However, more laboratory research is needed comparing high intensity intermittent exercise and continuous exercise in order to approve or disprove this idea. 2.5.1 Rate of Carbohydrate Ingestion The rate at which carbohydrates should be ingested during exercise to enhance performance varies. Studies have shown improvements with intakes as low as 21.5 g/h (Fielding et al., 1985) and as high as 100 g/h (Coggan et al., 1988; Coyle et al., 1986). Although, caution should be taken in regard to very low carbohydrate intakes during exercise, since Fielding et al. (1985) observed significant improvements when 21.5 g/h of carbohydrate had been ingested as 10.25 g feedings every half hour, while no improvement in performance was observed when 21.5 g of carbohydrate was ingested as a single bolus every hour. Low carbohydrate intakes may explain the inability of carbohydrate to improve performance in the studies of Williams et al. (1990) and 16 Nishibata et al. (1993), who had their subjects consume less than 30 g/h of carbohydrate. Also, it may be ill advised to consume very large amounts of carbohydrate during exercise since Mitchell et al. (1989) found that rates of consumption of 111 g/h were non-beneficial to performance. Nonetheless, it appears that it is essential that carbohydrate intake delivers approximately > 1 g/min of carbohydrate to the working muscles in the latter stages of exercise, ifjexercise is to be maintained without fatigue occurring earlier (Coggan and Coyle, 1987). The continuous intake of carbohydrate during exercise may not be required. It may be sufficient to consume a large amount of carbohydrate 30 minutes prior to when fatigue would have occurred without supplementation (Coggan and Coyle, 1989). Coggan and Coyle, (1989) found a large intake to be as effective as the studies that included similar exercise protocols with intermittent feedings throughout exercise. It is crucial that carbohydrate be ingested prior to fatigue since oral carbohydrate beyond this point is ineffective in the reversal of fatigue (Coggan and Coyle, 1987). Carbohydrate taken after fatigue is believed not to empty fast enough from the stomach or is not absorbed by the small intestine rapidly enough to meet the requirements of the exercising muscles (Coggan and Coyle, 1987). 2.5.2 Types of Carbohydrate The type of carbohydrate that can be taken to allow for enhanced performance can vary. Identical concentrations of maltose and glucose have been shown to empty from the stomach at similar rates, are absorbed by the small intestine at similar rates, and are similar in regard to the amount of exogenous carbohydrate that is oxidized during prolonged exercise (Hawley et al., 1992). Rerher et al. (1992) observed similar results when comparing glucose to maltodextrins during exercise. Although, maltodextrins may actually allow for better net water absorption than the monosaccharide glucose (Rerher et al., 1992). Performance and plasma glucose levels have been shown to be alike when 17 either sucrose or glucose are ingested during exercise (Murray et al., 1989). Therefore, from these findings it would appear that sucrose, glucose, maltose, and maltodextrins are equally effective nr maintaining plasma glucose and carbohydrate oxidation during exercise. Fructose was not included with the above mentioned carbohydrates since it is an exception to these carbohydrates and should be avoided because of its inability to improve performance (Bjorkman et al., 1984). Fructose's inability to improve performance may be explained by its glycaemic index. As might be expected, the other types of carbohydrates are considered to have a high glycaemic index while fructose has a low glycaeniic index fc i-(Jenkins et al., 1984). Overall, it may be in the best interest of athletes to avoid fructose, since it may cause gastric distress when taken during exercise (Murray et al., 1989). However, Adopo et al. (1994) reported that the amount of exogenous carbohydrate oxidized during exercise was greater when 50g of fructose was taken in the same solution with 50 g of glucose; during exercise, compared to when lOOg of glucose was taken during exercise. Whether the increase in exogenous carbohydrate oxidation is important to performance is uncertain, given that the combination intake did not alter the amount of endogenous carbohydrate oxidized compared to the l.OOg of glucose. However, Adopo et al. (1994) findings probably indicate that fructose taken in combination with glucose may be as effective as the other carbohydrates in improving performance. 2.5.3 Form of Carbohydrate The form in which carbohydrate should be ingested has received little attention. Few studies have compared the intake of solid and liquid carbohydrate during exercise (Mason et al., 1993; Murdoch et al., 1993; Neufer et al., 1987). Even though Neufer et al. (1987) study had subjects consume carbohydrate 5 minutes pre-exercise, it can be considered as an intake during exercise because it is so close to the onset of exercise. It appears that the intake of either form of carbohydrate during exercise, in the same 18 amounts, cause similar physiological responses (Mason et al., 1993; Murdoch et al., 1993; Neufer et al., 1987) and enhance performance similarly (Murdoch et al., 1993; Neufer et al, 1987). Although, identical amounts of solid and liquid carbohydrate may not be required to cause similar physiological responses during exercise. Rerher et al. (1992) observed that gastric emptying does not limit exogenous carbohydrate oxidation. Higher concentration drinks: emptied slower from the stomach than lower concentration drinks, however, the amount of carbohydrate delivered to the small intestine per volume was greater for the higher concentration drinks. This is of importance to an athlete who may prefer a solid carbohydrate which may be more concentrated in the stomach, than perhaps a lower concentration commercial carbohydrate drink. The form in which carbohydrate should be ingested may rely on an athlete's specific needs. If rehydration is a concern the choice is made easy; liquid. Below et al. (1995) found that a large amount of water (1330 ml)or a small amount of water (200 ml) with carbohydrate (79 g) can improve performance (in a warm environment) by 6%, in a performance ride following 50 minutes of cycling at 80% VO2 max. This is compared to a small amount of water (200 ml), while a large amount of water combined with carbohydrate improved performance by 12% during the same conditions. These findings indicate that it is important for an athlete to pay attention to both hydration and fuel needs while performing in warm conditions. Carbohydrate drinks of concentrations of 6% and perhaps as high as 10% allow fluid to be absorbed by the small intestine as effectively as plain water (Owen et al., 1986). Actually, a 6% carbohydrate solution or a 6% carbohydrate-electrolyte solution may provide better fluid absorption than water itself (Gisolfi et al., 1991). Therefore, to ensure that both hydration and energy needs are met, an athlete should consume a low concentration drink at high rates or volumes during exercise. The increased amounts will increase gastric volume which will increase the rate of gastric emptying (Noakes et al., 1991). However, large volumes of fluids may not be tolerable to most athletes, therefore 19 special care must be taken so that large volumes of carbohydrate drinks do not adversely affect performance by causing an athlete gastric distress. 20 C H A P T E R 3 3.0 Methodology 3.1 Experimental Design This study used a single factor repeated measure design with 3 levels. Factor : Pre-exercise intake Level 1: Solid carbohydrate Level 2: Liquid carbohydrate Level 3: Placebo 3.2 Dependent and Independent Variables Time to fatigue was the main dependent variable with pre-exercise intake being the independent variable. 3.2.1 Other Dependent Variables Measured Blood glucose and blood lactate. 3.3 Subjects Ten highly competitive (8 university players, 1 former university player, and 1 competitive league player) female soccer players participated in this study after giving written, informed consent. The consent form and study was approved by the University of British Columbia Ethics Committee. These subjects were chosen because the exercise protocol used in this study was a high intensity intermittent running protocol, making soccer players an ideal choice since soccer is a high intensity intermittent running sport. 21 3.4 Methods All testing was performed in the Buchanan Exercise Science Laboratory at the University of British Columbia. 3.4.1 Maximal Oxygen Uptake (VO2 max) Test A VO2 max test was performed at least 3 days prior to the first intermittent exercise test. The VO2 max test used a running protocol performed on a treadmill. Treadmill speed began at 5 mph and was increased by 0.5 mph every minute until 2 of the 3 following criteria were met: 1) Leveling off of oxygen uptake (VO2) while workload was still increasing; 2) Heart rate (HR) within 10% of age predicted maximum; 3) RER was greater than 1.1. HR was monitored with a Sports Tester Heart Monitor PE3000 and V 0 2 and RER were measured using a Beckman Metabolic Cart interfaced with a Hewlett Packard Data Acquisition System. The results of this test were used to calculate the work loads that correspond to 50%, 70% and 120% of each subjects V 0 2 max, which were used in subsequent testing. 3.4.2 Intermittent Testing The intermittent testing consisted of three trials. Subjects maintained regular training throughout the duration of the study, except on the day prior to testing. In an attempt to control muscle glycogen levels between trials, subjects were asked to refrain from any vigorous physical activity and to consume a similar diet the day prior to each trial. On the day of testing, subjects consumed a lOOg carbohydrate meal (consisting of fruit, bagels, and fruit juices) 4 hours before exercise. The meal was used to simulate a light pregame meal that an athlete would ingest 4 hours before exercising. After arriving at the lab, subjects performed a 5 minute warm up on the treadmill at 60% VO2 max. The 5 minute warm up took place 10 minutes prior to the beginning of exercise. At 5 minutes 22 prior to exercise in PL TRIAL, subjects consumed 400 ml of an artificially sweetened placebo. At 5 minutes prior to exercise in LCHO TRIAL, subjects consumed 400 ml of liquid containing 50g of carbohydrate. At 5 minutes prior to exercise in SCHO Trial, subjects consumed a\ solid carbohydrate (69g solid bar; 50g carbohydrate, 6g protein, and 3g fibre) plus 400 ml of water. The three trials were counter balanced to eliminate any bias of a learning effect. Since it was impossible to blind subjects to the form of carbohydrate that they were receiving, they were told that the purpose of the study was •i compare three different carbohydrate sources. Each trial consisted of two 19 minute intermittent exercise periods separated by a 10 minute break. The intermitittent exercise periods consisted of the following: treadmill running at 70% VO2 max for 20 seconds followed by a 10 second acceleration to 120% V 0 2 max, where this pace was maintained for 5 seconds, followed by a 15 second deceleration to 50% VO2 max, where this pace was maintained for 15 seconds, followed by a 15 second acceleration to 120% VO2 max and a maintenance of this pace for 5 seconds, and a finald5 second deceleration to 50% V 0 2 max, followed by a 30 second rest break; this set was repeated 9 times in each exercise period. The second exercise period was followed by a 5 minute break and a performance to fatigue trial. Subjects were given 250 ml of water during the 10 and 5 minute rest breaks. Subjects were also cooled with an electric fan during the trials. The performance to fatigue trial started immediately after the second 5 minute break. The performance trial consisted of 10 second 120% VO2 max sprints, which were separated by 10 second rest breaks. Time to fatigue was taken as the last completed sprint that the subject was able to perform. Time to fatigue included both the rest and exercise. No verbal encouragement was given during any of the performance to fatigue trials. Blood samples were taken, using a finger prick, immediately prior to exercise and at 10:20, 20, 30:40, 39:20 minutes during the high intensity intermittent exercise, which consisted of the two 19 minute periods of high intensity exercise and the 10 minute rest 23 break. Another blood sample was taken at 50 minutes (three minutes prior to the performance trial), during the 5 minute rest break that followed the second 19 minute period. Part of the blood sample was immediately analyzed for blood glucose (One Touch II; Johnson & Johnson) and the other part was placed in a hemolyzing agent and refigerated for later analysis of blood lactate (Kontron 640). Samples could not be taken at exactly every tenth minute because blood could only be taken while the subjects were stationary during the 30 second rest breaks (for convenience, the times at which blood samples were taken will be referred to as 10, 20, 30, 40, and 50 minutes during exercise). A final blood sample was taken after the performance trial and was analyzed for blood lactate. Figure 1: Overview of exercise protocol. Pre-Exercise Feeding First Exercise Period it. 10 min Rest Break Second Exercise Period 5 min Rest Break Performance Trial -5 min 0 10 19 min min min 20 29 min min 30 40 48 min min min 50 53 min min To Fatigue A A / |\ / j \ / |\ / j \ A Blood 1 2 Samples 3.5 Data Analysis Time to fatigue for the performance trial was analyzed using a one-way ANOVA for repeated measures. Blood glucose and blood lactate were analyzed using a two-way ANOVA for repeated measures on both factors (trial x time). Significant differences between means were determined using a Tukey post-hoc test. Significance was chosen to be p < 0.05. Data are reported as mean + standard error. 24 C H A P T E R 4 4.0 Results and Discussion 4.1 Results 4.1.1 Subjects Ten elite female soccer players participated and completed this study. Subjects characteristics are presented in Table 1. TABLE 1: Characteristics of subjects. Characteristics X ± SE Age(yrs) 2 1 . 9 ± 0 . 9 5 Height (cm) 1 6 5 . 6 ± 1 . 6 Mass (kg) 6 2 . 3 ± 1 . 3 V 0 2 max (ml/kg/min) 45.8 ± 1.3 4.1.2 Performance Time to fatigue in the performance trial was significantly (p < 0 . 0 1 ) greater for both the SCHO ( 6 9 3 ; ± 135 .1 sec) and LCHO ( 6 4 8 ± 1 1 3 . 2 sec) trials compared to the PL trial ( 4 3 6 ± 7 0 . 5 sec) (TABLE 2 and FIGURE 2 ) . The ANOVA and post-hoc tests revealed no differences in time to fatigue between the two forms of carbohydrate. 25 TABLE 2: Time to fatigue in the performance trial for the solid carbohydrate (SCHO), liquid carbohydrate (LCHO), and placebo (PL) trials. Trial Time to Fatigue (sec) SCHO 693 ±135.1* LCHO *' 648 ±113.2* PL 436 ± 70.5 * Indicates that the values are significantly (p < 0.01) different from the placebo. FIGURE 2: Time to fatigue in the performance trial for the solid carbohydrate (SCHO), liquid carbohydrate (LCHO), and placebo (PL) trials. SCHO LCHO Carbohydrate Trial PL 26 4.1.3 Blood Glucose Blood glucose levels were similar among the three trials immediately prior to the onset of exercise (TABLE 3 and Figure 3). During exercise, blood glucose levels were significantly higher (p < 0.05) at 10, 20, and 30 minutes when either form of carbohydrate was consumed compared to the PL trial (TABLE 3 and FIGURE 3). At 40 minutes, blood glucose was significantly (p < 0.05) higher for the LCHO trial (5.07 ± 0.30 mmol/1) compared to the PL trial (3.89 ± 0.19 mmol/1), however, glucose levels were non-significant (p > 0.05) between the SCHO (4.59 ± 0.22 mmol/1) and the PL trial, and the SCHO and LCHO trial. Three minutes prior to the performance trial blood glucose levels were non-significant (p > 0.05) between any of the interventions (TABLE 3 and FIGURE 3). TABLE 3: Effects of the solid carbohydrate (SCHO), liquid carbohydrate (LCHO), and placebo (PL) on blood glucose levels (mmol/1) during the high intensity intermittent exercise and during the 5 minute rest break preceding the performance trial. Trial Time (min) 0 10 20 30 40 50* SCHO 4.28 5.18A 6.03A 6.41A 4.59 4.90 ±0.15 ±0.17 ±0.21 ±0.26 ±0.22 ±0.22 LCHO 4.20, 5.52A 6.28A 6.61A 5.07A 5.21 ±0.16 ±0.27 ±0.30 ±0.25 ±0.30 ±0.19 PL 4.17 4.22 4.87 4.36 3.89 4.70 ±0.12 ±0.17 ±0.23 ±0.17 ±0.19 ±0.18 * Time 50 is two minutes into the 5 minute rest break. A Indicates that values are significantly (p < 0.05) different from the placebo. 27 FIGURE 3: Effects of the solid carbohydrate (SCHO), liquid carbohydrate (LCHO), and placebo (PL) on blood glucose levels (mmol/1) during the high intensity intermittent exercise and the 5 minute rest break preceding the performance trial (50 minutes). « 1.00 QOO-j 1 1 1 1 1 0 10 20 30 40 50 Tirre(rrin) 4.1.4 Blood Lactate Blood lactate levels were not significantly (p > 0.05) different between the three trials pior to or during the high intensity intermittent exercise or three minutes prior to the performance trial (TABLE 4 and FIGURE 4). Also, differences in blood lacate at the end of the performance trial were non-significant between the SCHO (9.24 + 0.97 mmol/1), LCHO (9.26 ± 0.74 mmol/1), and PL (9.00 ± 0.67 mmol/1) trials (Table 4 and FIGURE 4). 7.00 SCHO L C H O PL 28 T A B L E 4: Effects of the solid carbohydrate (SCHO), liquid carbohydrate ( L C H O ) , and placebo (PL) on blood lactate (mmol/1) during the high intensity intermittent exercise, during the 5 minute rest break preceding the performance trial (50 minutes), and at the end of the performance trial (referred to as E N D in the table). Trial Time (min) 0 10 20 30 40 50 E N D S C H O 3.37 5.72 6.04 6.43 6.62 5.49 9.24 ±0.37 ±0.53 ±0.43 ±0.68 ±0 .79 ±0.82 ±0.97 L C H O 4.10 6.28 7.02 5.98 6.48 6.40 9.26 ±0 .50 ±0.60 ±0.86 ±0.57 ±0.72 ±0.70 ±0 .74 P L 3.80 5.73 6.13 5.85 5.35 5.38 9.00 ±0.52 ±0.57 ±0.56 ±0.54 ±0.57 ±0 .55 ±0.67 F I G U R E 4: Effects of the solid carbohydrate (SCHO), liquid carbohydrate ( L C H O ) , and placebo (PL) on blood lactate during the high intensity intermittent exercise, during the 5 minute rest break preceding the performance trial (50 minutes), and at the end of the performance trial (referred to as E N D in the graph). Time (min) 2 9 Discussion 4.2 The majority of the research, over the past two decades, investigating carbohydrate feedings and exercise has concentrated on continuous moderate intensity exercise. It is widely accepted that carbohydrate feedings immediately before or during exercise can improve performance for prolonged work (Coyle, 1991). However, there is a paucity of information on how carbohydrate feedings influence high intensity intermittent exercise and whether a solid or liquid carbohydrate feeding is more advantageous. The major finding of this study, suggests performance is improved with the intake of carbohydrate 5 minutes prior to high intensity intermittent exercise. Findings also indicate that the form in which the carbohydrate is consumed is not critical to performance. It would appear that the improved performance is due to the elevated blood glucose levels (compared to the PL) during the intermittent exercise. However, it can only be speculated to how the elevated glucose levels led to an increased time to fatigue in the performance trial. Researchers have demonstrated that ingested carbohydrate is able to enhance performance by maintaining blood glucose levels and carbohydrate oxidation, when stores are depleted (Coggan and Coyle, 1987; Coggan and Coyle, 1989; Coyle et al., 1986) and not from the sparing of muscle glycogen (Coyle et al., 1986; Hargreaves and Briggs, 1988). However in the present study, blood glucose levels were only higher than the PL trial during the first 30 minutes of exercise for the SCHO and only up to 40 minutes of exercise for the LCHO trial. At three minutes prior to the performance trial, blood glucose levels werernot significantly different between the three trials. Therefore, it is unlikely that the improvements seen in the performance trial, when carbohydrate was consumed, is due to the maintenance of blood glucose levels and enhanced carbohydrate oxidation. However, it is proposed that the elevated glucose levels allowed for the resynthesis or the sparing of muscle glycogen during the intermittent exercise. This would allow for an increased time to fatigue in the performance trial. 30 High intensity exercise, of the type performed in this study, greatly depletes muscle glycogen stores in the exercising musculature (Gollnick et al., 1974; MacDougal et al., 1977). Maughan and Poole (1981) found that high intensity exercise (105% VO2 max) is significantly reduced when muscle glycogen stores are low. Subjects were able to exercise at 105% of their VO2 max for 6.65 minutes when muscle glycogen levels were elevated. This is compared to 3.32 minutes when glycogen levels were low (Maughan and Poole, 1981). The intensity of the performance trial in the present study was higher than the exercise intensity in the Maughan and Poole (1981) study. This infers that muscle glycogen was an important substrate in increasing time to fatigue in the performance trial. The findings of Katz et al. (1987) further support the idea that muscle glycogen must have been higher prior to the performance trial. They reported that blood glucose is not a major fuel in high intensity exercise (97% V 0 2 max). Cells of the active muscles take up glucose, however, the glucose accumulates in the cell and is not metabolized to any extent at high intensities. Katz et al. (1987) stated the following, " In fact this makes sense that one glucosyl unit from glycogen provides more ATP then an extracellular glucose molecule since the phosphorylation of glucose by hexokinase requires ATP". This would explain why extracellular glucose is not metabolized at such a high intensity as 97% VO2 max. Therefore, even if blood glucose had risen during the performance trial (from either exogenous carbohydrate or glucose from the liver) it is unlikely that elevated levels would have contributed to energy production and performance. Rather, it is likely that performance gains were a result of increased muscle glycogen levels. Kuipers et at; (1987) reported that muscle glycogen can be resynthesized in non-active muscle fibres during low intensity exercise. In their study, cyclists depleted muscle glycogen stores through exhaustive exercise, after which they exercised for an additional 3 hours at 40% Wmax. During the 3 hours of light exercise the subjects consumed carbohydrate drinks.' At the end of the 3 hours significant increases in muscle glycogen were found in the both Type II muscle fibres. In addition to these findings, Constable et 31 al. (1984) found that glycogen depleted muscles of rats can resynthesize glycogen, during moderate intensity exercise, when sufficient blood glucose is present. These findings have led to the deduction that carbohydrate ingestion may result in the resynthesis of muscle glycogen in non-active muscle fibres during exercise (Coyle, 1991). This would include both rest breaks or intermittent exercise that involves low and high intensities (Coyle, 1991). It is possible that the elevated levels of blood glucose in the SCHO and LCHO trials led to a resynthesis of muscle glycogen. The exercise protocol required subjects to exercise at intensities Of 50% VO2 max, to decelerate slowly, and to rest 30 seconds between each bout of running. During the slow downs and stoppages, resynthesis may have occurred in the type II fibres. Resynthesis in the fast twitch fibres being important, since the 120% VO2 max sprinting in the performance trial would rely heavily on muscle glycogen from these fibres (Gollnick et al., 1974). Also, blood glucose levels were elevated during the .10 minute break that separated the two 19 minute exercise periods. Muscle glycogen may have been resynthesized in this 10 miinutes, which occurs post-exercise when sufficient blood glucose is available. However, it should also be acknowledged that the exogenous carbohydrate may have been utilized during exercise instead of muscle glycogen leading to a sparing of muscle glycogen. Field studies have evaluated carbohydrate and muscle glycogen sparing and have demonstrated that carbohydrate can significantly spare muscle glycogen (Jacobs and Leatt, 1989; Simmard et al., 1988). Jacobs and Leatt (1989) fed five elite male soccer players 0.5 L of 7% glucose polymer 10 minutes prior to a match and again at half time. Another five players matched for position and skill level received a liquid placebo at these times. At the end of the match, muscle glycogen was 31% higher in the players who received carbohydrate compared to those who did not (both ^ groups had similar muscle glycogen levels prior to the match). Simmard et al. (1988) reported similar results when they fed university hockey players lOOg of carbohydrate 75-210 minutes prior to a game along with 32 20g between periods. Players had a greater sparing of muscle glycogen per distance skated in the game that they received carbohydrate compared to the game in which they received no carbohydrate. Both Jacobs and Leatt (1989) and Simmard et al. (1988) studies involved sports that are considered high intensity and intermittent making their results relevant to the present study. Also relevant, was that in the present study the subjects were (female) soccer players and the protocol was set up to mimic running intensities familiar to soccer. Decreased muscle glycogen utilization in intermittent exercise has also been reported in a laboratory study. Hargreaves et al. (1984) discovered that less muscle glycogen was used during 4 hours of intermittent exercise. They demonstrated that time to fatigue in a 100% V 0 2 max sprint ride (following the 4 hours of exercise) could be significantly increased when subjects consumed 43 g/h of carbohydrate during the 4 hours of exercise. The exercise consisted of repeated bouts of 20 minutes of cycling at 50% V 0 2 max and 10 minutes of 30 second 100% V0 2 j max sprints, separated by 2 minute breaks. These findings support the contention that elevated muscle glycogen levels were responsible for the enhanced performance in the present study. Both the present study and Hargreaves et al. (1984) study involved intermittent exercise with intensities at 120% V 0 2 max and 100% V 0 2 max respectively. As discussed previously, at these intensities exercise relies heavily on muscle glycogen and fatigue is delayed when there are elevated levels of muscle glycogen. However, another investigation performed byiFielding et al. (1985), using the same exercise protocol as Hargreaves et al. (1984), found that the intake of carbohydrate during exercise was unable to spare muscle glycogen. Despite any sparing of glycogen, performance in the sprint ride was greater when 10.75g of carbohydrate was ingested every 30 minutes compared to a placebo trial. The lack of muscle glycogen sparing may be due to the limited glucose feedings of 21.5 g/h of carbohydrate. In the present study along with Hargreaves et al., (1984) subjects received 50 g/h and 43 g/h of carbohydrate 33 respectively. The small amount of carbohydrate given by Fielding et al. (1985) may not have been sufficient {to evoke a sparing of muscle glycogen. However, it is not explained how the 100% VO2 max sprint ride was improved (in Fielding et al. (1985) study) when glycogen utilization during exercise was the same between trials. It does not seem possible for improvements to occur at such high intensities without the advantage of elevated glycogen levels. Mitchell et al. (1989) investigated whether carbohydrate feedings during intermittent exercise could spare muscle glycogen. Exercise consisted of seven 15 minute cycling rides at 70% VO2 max which were separated by 3 minute rest breaks. Following the last ride a 15 minute all-out ride was performed. The ingestion of 12g of carbohydrate every 15 minutes (48 g/h) elevated glucose throughout exercise and prior to the performance ride. Performance was improved in the ride when subjects received the carbohydrate, however, there was no sparing of muscle glycogen. This opposes the concept that muscle glycogen may be resynthesized during intermittent exercise. However, the exercise in this study resembles continuous exercise more than intermittent, making their findings more closely related to Coyle et al. (1986) and Hargreaves and Briggs (1988). This*relationship is suggested because the performance trial in Mitchell et al. (1989) study only elicited an average intensity of 84% VO2 max and carbohydrate oxidation during the performance ride was greater for the carbohydrate trial than the placebo trial. Therefore, it is plausible, that exogenous carbohydrate influences performance by a different mechanism in high intensity intermittent exercise than during moderate continuous exercise. It may be that the active muscles in continuous moderate exercise, never have the opportunity to resynthesis muscle glycogen. Unlike intermittent exercise, there are no slow downs or stoppages that would allow the previously active muscle to resynthesize glycogen. As stated, SCHO and LCHO improve performance similarly. Mason et al. (1993) demonstrated that 25 g of liquid carbohydrate and 25 g of solid carbohydrate elicit the 34 same physiological responses during 2 hours of exercising at 65% VO2 max. There were no differences in blood glucose or insulin levels during the 2 hours. Neufer et al. (1987) demonstrated that 45 g of liquid carbohydrate and solid carbohydrate ingested 5 minutes prior to 45 minutes of exercise at 77% VO2 max can similarly improve performance. Performance was measured in a 15 minute performance ride proceeding the exercise. Also, the ingestion of slurried or solid bananas can similarly improve performance and elevate blood glucose levels (Murdoch et al., 1993). In the present study blood glucose levels were not significantly different between the two forms of carbohydrate during exercise. These findings are in accordance with the results of Mason et al. (1993). Also, it should be noted that subjects did not complain of any gastric distress during exercise, with either the solid or liquid carbohydrate. They were asked if they felt any distress, during exercise, in the 10 and 5 minute breaks. In summary,.the present study demonstrated that the pre-exercise feeding of solid and liquid carbohydrate can similarly improve performance in high intensity intermittent exercise. The improvements appear to be a result of the elevated blood glucose levels during the first 30 to 40 minutes of exercise. It is possible that the elevated glucose levels may have led to the;resynthesis or sparing muscle glycogen. This may have allowed for the increased times to fatigue when subjects consumed the SCHO and LCHO. 35 BIBLIOGRAPHY Ahlborg, B., Bergstrom, J., Ekelund, L.G., and Hultman, E. Muscle glycogen and muscle electrolytes during prolonged physical exercise. Acta Physiologica Scandanavia 70:129-142, 1967. 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Journal of Applied Physiology 71: 1082-1088, 1991. 40 APPENDIX 41 TABLE 5: Individual characteristics of subjects. Subject Age (yrs) Height (cm) Mass (kg) V 0 2 max (ml/kg/min) 1 20 166.0 62.0 49.00 2 21 164.7 67.7 40.07 3 18 172.6 66.6 53.80 4 23 169.4 66.8 40.66 5 26 158.9 54.1 45.14 6 24 169.9 63.8 45.18 7 27 162.0 60.0 42.44 8 19 165.4 63.0 47.50 9 20 157.4 59.9 49.09 10 21 170.0 62.0 44.33 42 TABLE 6: Individual subjects time to fatigue (sec) in the performance trial for the solid carbohydrate (SCHO), liquid carbohydrate (LCHO), and placebo trial. Subject Trial SCHO LCHO PL 1 490 770 430 2 270 230 210 3 1130 870 510 4 370 290 390 5 430 510 230 6 1350 1230 670 7 650 530 410 8 1290 1070 850 9 750 770 550 10 190 190 110 43 TABLE 7: Individual subjects blood glucose levels (mmol/1) for the solid carbohydrate (SCHO), liquid carbohydrate (LCHO), and placebo (PL) trial. Subject Trial Time (min) 0 10 20 30 40 50 SCHO 3.7 5.2 5.1 5.1 3.4 3.9 1 LCHO 4.4 5.9 5.8 6.1 4.4 4.7 PL 3.8 3.6 3.7 3.7 3.4 3.8 SCHO 5.0 4.9 5.4 6.1 4.1 5.3 2 LCHO 4.12 4.6 5.1 6.3 5.7 5.5 PL 4.0 4.4 5.2 5.0 2.8 4.7 SCHO 4.2 5.2 6.2 6.3 4.9 4.6 3 LCHO 3.4 5.5 5.2 6.1 4.6 4.9 PL 4.1 4.2 4.5 4.2 4.1 4.7 SCHO 4.1 5.4 5.9 6.1 3.9 4.1 4 LCHO 4.9 6.0 6.9 6.7 4.4 5.2 PL 4.0 4.8 4.4 3.7 3.6 4.4 SCHO 3.6 4.6 5.7 5.8 5.3 6.3 5 LCHO 3.5 5.1 6.2 5.8 4.9 4.7 PL 4.2 4.0 5.4 4.6 4.5 5.3 SCHO ; 4.4 6.0 7.2 7.4 5.1 4.8 6 LCHO 4.8 6.6 8.3 8.2 6.7 6.4 PL 4.4 4.7 5.0 4.5 4.5 4.9 SCHO 4.4 5.9 6.7 7.2 4.5 4.6 7 LCHO 4.4 7.0 6.8 7.7 6.6 5.3 PL 4.7 4.7 5.6 4.6 3.9 4.6 SCHO 4.7 5.5 6.7 7.8 5.6 5.4 8 LCHO 4.4 5.1 6.2 6.5 4.6 5.5 PL 4.7 4.8 5.4 4.9 4.4 5.2 SCHO 3.8 4.7 5.8 6.1 4.5 4.7 9 LCHO 3.8 4.8 5.7 5.6 3.9 4.3 PL 3.5 3.3 3.8 3.6 3.3 3.9 SCHO 4.9 4.4 5.6 6.2 4.6 5.3 10 LCHO 4.3 4.6 6.6 6.4 4.9 5.6 PL 4.3 3.7 5.7 4.8 4.4 5.5 44 TABLE 8: Individual subjects blood lactate levels (mmol/1) for the solid carbohydrate (SCHO), liquid carbohydrate (LCHO), and placebo (PL) trial. Subject Trial Time (sec) 0 10 20 30 40 50 END SCHO 1.76 3.24 4.96 5.36 2.92 2.96 9.96 1 LCHO . 5.76 4.60 2.64 3.88 6.20 2.60 10.16 PL 3.08 3.40 5.36 4.96 3.28 2.60 8.20 SCHO 4.82 6.26 7.42 9.70 7.60 9.70 11.82 2 LCHO 6.88 8.92 8.20 9.04 11.40 8.36 13.08 PL • \ 6.04 7.70 8.20 ,8.18 7.10 7.06 9.68 SCHO 3.32 4.30 3.94 4.24 4.40 3.82 8.76 3 LCHO 2.36 3.80 4.12 3.96 3.16 3.68 5.86 PL 2.80 4.28 4.98 3.66 3.24 3.64 9.08 SCHO 2.30 3.84 7.30 4.18 5.34 4.00 7.96 4 LCHO 3.84 4.80 5.74 4.92 6.24 5.84 8.98 PL • 2.20 4.16 4.22 5.02 4.24 5.38 8.12 SCHO 3.00 4.70 5.76 4.50 6.10 5.98 11.84 5 LCHO 4.42 5.92 6.82 5.00 6.10 7.66 12.26 PL 3.14 6.38 7.50 5.68 6.50 7.28 12.62 SCHO : 1.96 5.84 4.12 ,6.00 4.52 2.00 3.60 6 LCHO 1.20 4.52 6.88 4.92 3.80 5.56 7.76 PL 2.02 2.98 3.00 3.92 3.34 2.90 7.84 SCHO 3.60 8.28 6.02 6.62 7.78 4.16 6.24 7 LCHO 3.78 7.04 9.94 7.34 7.42 10.08 6.54 PL , 3.74 6.92 5.96 4.54 5.64 6.24 7.10 SCHO 5.32 7.00 6.44 8.02 9.26 5.58 7.00 8 LCHO 4.28 7.84 8.16 5.36 5.92 6.84 8.00 PL 4.62 7.58 6.08 7.92 6.22 5.34 6.44 SCHO . 3.48 5.80 6.60 5.76 6.92 8.00 12.88 9 LCHO 4.28 6.30 5.74 7.38 6.34 5.74 9.12 PL 7.06 6.96 8.14 6.78 5.42 6.69 12.68 SCHO 4.10 7.94 7.82 9.96 11.32 8.74 12.30 10 LCHO 4.24 9.06 11.92 8.02 7.94 7.62 10.84 PL 3.32 6.94 7.86 7.58 8.50 6.40 8.24 

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