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Glycemic index and glycogen
Glycemic index and glycogen A. Chandrasekara'*,G. Denyer2, & I. Caterson~ ~HumanNutrition Unit ,School of Molecular& MicrobialBiosciences,UniversityOf Sydney 2Schoolof Molecular& MicrobialBiosciences,Universityof Sydney
INTRODUCTION- Fatigue in sports is often associated with depletion of muscle glycogen storage. Obesity is considered to be a major barrier against physical activity in sports. In order to bring the glycogen storage to a satisfactory level sports persons tend to increase consumption carbohydrates, preferred consumption of high glycemic index (HGI) than low glycemic index (LGI) diets. But HGI foods may promote postprandial carbohydrate oxidation at the expense of fat oxidation and increase body fat gain. LGI diets that produce a low and slow glycemic response may enhance higher glycogen storage instead of fat deposition. METHODOLOGY- To test this hypothesis, 30 male Wistar rats after weaning were given either a high glycemic index (HGI) or low glycemic index (LGI) diet for until their age of 12 weeks. Then the subjects were scarified and their plasma, serum, and muscle samples were collected. RESULTS-The study revealed that HGI diets fed rats had higher plasma cholesterol and Leptin (LGI Leptin 1.34 +/- 0.13ng/ml, HGI Leptin 2.12 +/- .20ng/ml) concentrations. It also found the liver and muscle glycogen storage in LGI diets showed higher level (LGl-liver 108 +/-3.0 mg/100g, LGI-muscle 22.6+/- 2.3g/100g) than that of HGI (HGl-liver 96 +/- 2.0mg/100g, HGI-muscle 18+/- 1.5g/100g) diets. CONCLUSION- the long term feeding of LGI carbohydrate encourages more glycogen storage while HGI increases fat deposition. Consumption of LGI diets has an advantage over HGI diets of higher physical activity while elevating glycogen storage and reducing chances of obesity.
Energy balance during an ultraendurance mountain bike relay race in f e m a l e cyclists C. Shing*, S. Ahem, & W. Knez The UniversityOf Queensland
Successful performance in ultraendurance events is related to the ability to sustain a high level of energy expenditure over an extended period of time. The energy needs of individuals in ultraendurance events have been previously described however, little is known about the energy demands of repeated bouts of high-intensity ultraendurance relay performance. The energy intake of five trained female cyclists (age = 35.4 yr, 24-46 yr; mean, range; mass = 57.02 + 4.10 kg; peak VO2= 51.04 + 4.37 ml.kg-l-min-1, mean _+SD) was recorded during a 24-hr relay ultraendurance mountain bike race (24 MTB). Food and fluid ingestion was analysed for macronutrient intake using Foodworks software (Version2.10.146). In addition, plasma glucose (Glu) and body weight were measured at six hour intervals throughout the 24 MTB while heart rate (HR) was recorded at 15 second' intervals. VO2 values that corresponded to the mean HR during each work and rest period were multiplied by 20.9kJ.L-1 to estimate energy expenditure (EE) for each subject. Average EE was 23,886 _+2504 kJ and energy intake (El) was estimated at 14,869 _+6486 kJ with 69 % from CHO, 19 % from Fat and 12 % from protein. There was an average energy deficit of 8767 + 5482 kJ over the 24 MTB, however no significant decrease in Glu levels was observed. There was a significant decrease in performance at the six and 12 hour mark (p<0.05), however CHO intake was not related to this performance decrement. In the present study there was no significant relationship between total energy intake or CHO intake and average lap times, as has been found with individual ultraendurance athletes. The present recommendations for individual ultraendurance events do not appear to be suitable for high intensity ultraendurance relay events, where CHO intake was found to be unrelated to performance. The contributions of energy from CHO, fat and protein during high intensity ultraendurance relay events requires further investigation. 66
INTRODUCTION- Fatigue in sports is often associated with depletion of muscle glycogen storage. Obesity is considered to be a major barrier against physical activity in sports. In order to bring the glycogen storage to a satisfactory level sports persons tend to increase consumption carbohydrates, preferred consumption of high glycemic index (HGI) than low glycemic index (LGI) diets. But HGI foods may promote postprandial carbohydrate oxidation at the expense of fat oxidation and increase body fat gain. LGI diets that produce a low and slow glycemic response may enhance higher glycogen storage instead of fat deposition. METHODOLOGY- To test this hypothesis, 30 male Wistar rats after weaning were given either a high glycemic index (HGI) or low glycemic index (LGI) diet for until their age of 12 weeks. Then the subjects were scarified and their plasma, serum, and muscle samples were collected. RESULTS-The study revealed that HGI diets fed rats had higher plasma cholesterol and Leptin (LGI Leptin 1.34 +/- 0.13ng/ml, HGI Leptin 2.12 +/- .20ng/ml) concentrations. It also found the liver and muscle glycogen storage in LGI diets showed higher level (LGl-liver 108 +/-3.0 mg/100g, LGI-muscle 22.6+/- 2.3g/100g) than that of HGI (HGl-liver 96 +/- 2.0mg/100g, HGI-muscle 18+/- 1.5g/100g) diets. CONCLUSION- the long term feeding of LGI carbohydrate encourages more glycogen storage while HGI increases fat deposition. Consumption of LGI diets has an advantage over HGI diets of higher physical activity while elevating glycogen storage and reducing chances of obesity.
Energy balance during an ultraendurance mountain bike relay race in f e m a l e cyclists C. Shing*, S. Ahem, & W. Knez The UniversityOf Queensland
Successful performance in ultraendurance events is related to the ability to sustain a high level of energy expenditure over an extended period of time. The energy needs of individuals in ultraendurance events have been previously described however, little is known about the energy demands of repeated bouts of high-intensity ultraendurance relay performance. The energy intake of five trained female cyclists (age = 35.4 yr, 24-46 yr; mean, range; mass = 57.02 + 4.10 kg; peak VO2= 51.04 + 4.37 ml.kg-l-min-1, mean _+SD) was recorded during a 24-hr relay ultraendurance mountain bike race (24 MTB). Food and fluid ingestion was analysed for macronutrient intake using Foodworks software (Version2.10.146). In addition, plasma glucose (Glu) and body weight were measured at six hour intervals throughout the 24 MTB while heart rate (HR) was recorded at 15 second' intervals. VO2 values that corresponded to the mean HR during each work and rest period were multiplied by 20.9kJ.L-1 to estimate energy expenditure (EE) for each subject. Average EE was 23,886 _+2504 kJ and energy intake (El) was estimated at 14,869 _+6486 kJ with 69 % from CHO, 19 % from Fat and 12 % from protein. There was an average energy deficit of 8767 + 5482 kJ over the 24 MTB, however no significant decrease in Glu levels was observed. There was a significant decrease in performance at the six and 12 hour mark (p<0.05), however CHO intake was not related to this performance decrement. In the present study there was no significant relationship between total energy intake or CHO intake and average lap times, as has been found with individual ultraendurance athletes. The present recommendations for individual ultraendurance events do not appear to be suitable for high intensity ultraendurance relay events, where CHO intake was found to be unrelated to performance. The contributions of energy from CHO, fat and protein during high intensity ultraendurance relay events requires further investigation. 66