The importance of muscle glycogen as a fuel source during exercise has been well documented. Maintaining a high glycogen level before and during activity is a major determinant of performance. Elevation of glycogen levels during recovery from both aerobic and anaerobic bouts of exercise is critical. The purpose of this investigation was to determine the effect of a solid carbohydrate feeding on glycogen resynthesis following aerobic and anaerobic exercise. Eight male cyclists were recruited for this investigation. One hour ride trial, 70 % VO2max followed with feeding (HRY), one sprint trial followed with feeding (SPY), and one sprint trial followed with no feeding (SPN) were randomly performed and separated by ten days. Feeding trials consisted of a solid CHO source (1g CHO per kg bw per hr) fed for four hours of recovery following one hour of passive recovery with no food. Muscle biopsies were obtained immediate post and at six hours of recovery. Bloods were collected at 1, 4, and 30 minutes of recovery for lactate determination. Muscle specimens were analyzed for glycogen and lactate. Muscle glycogen (mmol • kg protein') levels post exercise for HRY, SPN, and SPY trial were 336.9±48.1, 481.0±47.0, and 417.5±26.4, respectively with HRY significantly lower than SPN. The increase in muscle glycogen six hours post-exercise for HRY, SPN, and SPY trials were 117.9±24.8, 29.5 ±22.2, and 207.2 ±20.4, respectively, which were all significantly different (P < 0.05). Blood lactate at + 1 minute for HRY, SPN, and SPY trials were 3.4±.5, 20.6±1.2, and 19.9±1.3 mM, respectively. These data suggest that an athlete training twice during the day with both anaerobic and aerobic components will have greater muscle glycogen available later in the day if anaerobic training is completed first in the day, providing adequate carbohydrate is consumed between bouts. / School of Physical Education

Leung Ling Yan. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 218-259). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Not available / text

No description available.

This study examined and compared the effects of ingesting four different, isocaloric carbohydrate meals (460 kcals), two hour prior to a 60 minute bout of endurance cycling. The meals were chosen to represent a variety of types, forms and modes of delivery of carbohydrate: i) Banana Nut Bread®: semi-liquid, oat based carbohydrate-fat-protein combination, ii) Oatmeal: semi-liquid, oat based carbohydrate, iii) Cream of Wheat®: semiliquid, wheat based carbohydrate, iv) Power BarsTM: dense solid, fructose based carbohydrate-protein-vitamin combination. A standardized exercise and dietary regimen was followed prior to each performance trial. The purpose of the pre-trial preparation was to standardize each subjects endogenous carbohydrate stores thereby placing greater emphasis on the ability of each experimental meal to maintain blood glucose. Dependent variables were assessed at 15 minutes intervals during each performance trial to determine if any of the meals could elicit a different physiological response. No significant differences (treatment x trial) in blood glucose concentration, distance traveled, heart rate, V02, RER or RPE were observed (p > 0.05). It was concluded that none of the experimental meals conferred any particular advantage over the rest and due to this fact, issues such as personal preference, convenience and cost should be considered. / School of Physical Education

In an effort to determine the relative amount of carbohydrates and free fatty acids (FFA) utilized by trained and untrained men at a submaximal workload and the relationship of selected mitochondrial and glycolytic enzyme activities, six trained and six untrained males were exercised for one hour at 50o of their maximal oxygen uptake (V02 max).Muscle samples were taken from the vastus lateralis in three cyclists and from the gastrocmemius in three runners from each group before and after exercise, and later assayed for succinic acid dehydrogenese, malic acid dehydrogenase, lactic acid dehydrogenase, phosphorylane, and carnitine paLmityltransf erase activities, and glycogen levels. Th e post exercise sample was assayed for glycogen, another was sectioned and stained for glycogen and fiber composition (PAS and-glycerolphosphate dehydrogenase) and from a third coupled mitochondria were isolated to determine 14'CO2 production from oxidation of varied levels of 14C-palmityl-CoA. Blood drawn before, immediately after, and thirty minutes after the exercise was assayed for FFA, glycerol, triglycerides, and glucose levels. Activities of oxidative enzymes (SDH, MDH, and CPT) were significantly higher (2-3 times greater) in the trained individuals than in the untrained group. Glycolytic enzyme activities were higher in the untrained group, probably due to higher fast twitch fiber populations. During exercise, FFA levels rose to the same degree in both groups; however, glycerol levels increased almost five times greater during the exercise in the trained subjects indicating the FFA turnover was much larger in the trained subjects. Blood glucose levels increased by an average of 11 mg% during the exercise in the trained subjects but fell by 8 mg% in the others, suggesting a greater selective uptake by the untrained subjects. Muscle glycogen depletion was 66% greater in the untrained group. These catabolic processes were independent of muscle fiber type, indicating that aerobic training increases those enzyme activities associated with FFA oxidation. Trained individuals are thus able to shift to fatty acids as the primary carbon source for the citric acid cycle, sparing glycogen during submaximal work.

Maintenance of adequate muscle glycogen stores has been shown to be essential for endurance performance. For athletes who train on successive days or twice in the same day it is especially important that feeding strategies result in optimal glycogen resynthesis between workouts. The purpose of this investigation was to determine if prior carbohydrate feedings and the form of the carbohydrate consumed affected subsequent endurance performance. Seven endurance trained male cyclists agreed to participate in this study. Each day of testing consisted of two exercise bouts. The first workout was an anaerobic workout consisting of five one minute efforts at 115% VO2max followed by a sprint ride to exhaustion. Each of the sprints was separated from the next by a four minute rest period. For the final ride, the subjects rode at 115% of VO2max. One hour following the completion of the first workout, the subjects began a feeding regimen in which one of four carbohydrate sources were ingested in an amount calculated to provide 1.5g carbohydrate/kg bodyweight/hr for the next four hours. The trials were grouped by carbohydrate forms, dense chewy solid (Powerbars) (DCS), liquid carbohydrate (Gatorlode) (LCHO), and semi-moist solid (Nabisco Snackwells and Fruit Newtons) (SMS). In addition, a water trial (W) was conducted to serve as a control The second workout occurred six hours after the completion of the anaerobic workout and consisted of a one-hour self-paced performance ride on a cycle ergometer. Performance was measured as work (U) performed during the ride. All carbohydrate forms (824.7±109.6 U) improved performance over water (782.0±121.7 U) (p<0.05). In addition, among the various carbohydrate forms, SMS (843.2±94.4 U) significantly improved performance over LCHO (807.3±141 U) and DCS (805.3±115 U) (p<0.05). Carbohydrate feedings between anaerobic and aerobic workouts in the same day improve performance. Also, the physical form of the carbohydrate influences performance. / School of Physical Education

The present study was designed to evaluate the influence of carbohydrate structure on muscle glycogen resynthesis. Eight college-aged male cyclists performed a depletion exercise protocol to decrease vastus lateralis glycogen concentration. This protocol consisted of 60 min of cycling at 75% V O2max, followed by 6 - one min sprints at 125 % V O2max, with a 1 min rest between each sprint. Following the depletion exercise, the subjects consumed - 3000 kcal over a 12 hour period, which was calculated to meet each subject's estimated daily energy expenditure. The carbohydrate (CHO), fat and protein content represented 65:20:15% of the calories consumed, respectively, and totaled 450 - 550 g of CHO. All of the CHO was derived from 1 of 4 solutions: 1) glucose, 2) maltodextrin (glucose polymer), 3) waxy starch (100% amylopectin), or 4) resistant starch (100% amylose). Muscle biopsies were taken after the depletion exercise protocol and 24 hours after the depletion protocol to determine glycogen concentrations. The postdepletion exercise glycogen concentration was similar in all 4 trials, and averaged 234.7 mmol/kg dry weight (d.w.) muscle. Twenty-four hours after exercise, the increase in muscle glycogen concentration was less in the resistant starch trial (90.8 f 12.8 mmol/kg d.w.) than in the glucose, maltodextrin and waxy starch trials, in which glycogen concentration increased 168.7 mmol/kg d.w. Following the 24 h post-depletion exercise biopsy, each subject performed a 30 min cycling time trial, so that the relationship between muscle glycogen concentration and performance could be examined. There were no differences in work output during the time trial or blood lactate concentration immediately following the time trial in any of the trials. In summary, glycogen resynthesis is attenuated following ingestion of carbohydrate with a high amylose content, relative to amylopectin or glucose; however, short duration performance at intensities < 75% VO2max is unaffected. / School of Physical Education

Six runners (V02 max=68.2 ± 3.4 ml/kg/min) were studied on three separate occasions during a 30 min treadmill run at 70% V02 max. On each occasion, the subjects ingested either 75g of glucose (trial G), fructose (trial F) or a sweetened placebo (trial C). No differences were observed between any of the trials for oxygen uptake, heart rate or perceived exertion. Serum glucose levels were elevated as a result of the glucose feeding (P<0.05) reaching peak levels at 30 min post-feeding. With the onset of exercise, glucose levels dropped to a low of 5.89 ± 0.99 mmol/l at 15 min of exercise in trial G. Serum glucose concentrations in trials F and C averaged 6.21 ± 0.31 mmol/l and 5.95 ± 0.23 mmol/l over all the time points, respectively, and were not different (p>0.05). Muscle glycogen utilization in the first 15 min of exercise was similar in trial C (18.8 ± 1.9 mmol/kg), trial F (16.3 ± 4.1 mmol/kg) and trial G (18.8 ± 9.1 mmol/kg), and total glycogen use was also similar in trial C (20.7 ± 5.3 mmol/kg), trial F (35.4 ±6.3 mmol/kg) and trial G (25.6 ± mmol/kg). These data suggest that pre-exercise feedings of fructose or glucose do not affect the rate of muscle glycogen utilization during 30 min of treadmill running in well-trained runners.

This study compared the exercise responses of a waxy starch (WS), resistant starch (RS), glucose (GL) and an artificially-sweetened placebo (PL) ingested prior to exercise. Ten college-age, male competitive cyclists completed four experimental protocols consisting of a 30 min isokinetic, self-paced performance ride preceded by 90 min of constant load cycling at 66% VO2max. Thirty min prior to exercise, they ingested 1 g•kg-1 body weight of GL, WS, RS, or PL. A familiarization trial was first conducted to eliminate a potential order effect. An order effect was evidenced by lower (p<0.05) work rates during the performance ride of the first trial (390 ± 26.1 kJ) than the other four trials. No order effect was observed for the remainder of the experimental treatments which were performed in a single-blind, randomized fashion. At rest, GL elicited greater (P<0.05) serum glucose and insulin responses than all other trials. During exercise, however, serum glucose and insulin responses were similar among trials. Blood C-peptide and glucagon responses were also similar among trials. The mean total carbohydrate oxidation rates (CHOox) were higher (p<0.05) during the GL, WS, and RS trials (2.59 ± 0.13, 2.49 ± 0.10, and 2.71 ± 0.15 g•min-1, respectively) compared to PL (2.35 ± 0.12 g•min-1). Subjects were able to complete more work (p<0.05) during the performance ride when they ingested GL (434 ± 25.2 kJ) or WS (428 ± 22.5 kJ) compared to PL (403 ± 35.1 kJ). They also tended to produce more work with RS ingestion (418 ± 31.4 kJ), although this did not reach statistical significance (p<0.09). These results indicate that pre-exercise CHO ingestion in the form of starch or glucose maintained higher rates of total carbohydrate oxidation during exercise and provided an ergogenic benefit during self-paced cycling. / Human Performance Laboratory