Week 2 - Carbohydrate Flashcards
Describe the distribution of carbohydrates in the body
Liver glycogen (80-110g)
Bloodstream (4-6 glucose)
Muscles (300-600g glycogen)
How does exercise impact liver glucose output
Exercise increases liver glucose output in an intensity-dependent manner,
Close matching between muscle glucose uptake and liver glucose output
Define the relationship between carbohydrate utilisation and exercise intensity
Exercise increases carbohydrate oxidation in an intensity-dependent manner, leading to
- Increased liver glucose output and
- Increased muscle glycogen breakdown
What is the effect of diet on muscle glycogen and fatigue
Exercise capacity increases from low carbohydrate diet < mixed diet < high carbohydrate diet.
Significant percentage of muscle fibres being empty after intense physical activity
Describe the correlation between fatigue and carbohydrate depletion during prolonged strenuous exercise
Fatigue is strongly correlated with carbohydrate depletion, including muscle glycogen depletion and hypoglycaemia reflecting liver glycogen depletion
Carbohydrate feeding increases muscle glycogen and maintains blood glucose
How are the daily carbohydrate recommendations for sport typically determine
Daily carbohydrate recommendations are usually based on body weight rather than energy intake, with low carbohydrate diets shown to decrease muscle glycogen after training bouts of exercise.
Light 3-5g/kg/d (>1h)
Moderate 5-7g/kg/d (=1h)
High 6-10g/kg/d (1-3h)
Very High 8-12g/kg/d (4-5h)
Describe General Fuelling, Carb Loading, and Pre-event fuelling procedures
General fuelling (< 90mins): 7-12g/kg/d as per daily fuel needs
Carb Loading (> 90mins): 10-12g/kg/d as per daily fuel needs
On the day (> 60mins): 1-4g/kg/ body mass, consumed 1-4 hours prior
What are the fat recommendations for athletes
Daily fat intake should be 20-35% of total energy intake, with saturated fat limited to less than 10% of energy intake
Describe fat adaptations observed in high fat diets
Increased fat oxidation, decreased carbohydrate oxidation, and spared muscle glycogen.
Impaired high-intensity exercise performance.
What are the key points regarding ketogenic diets and keto-adaptations
Involves <50g carbohydrate intake, 70-80% of energy from fat, 15% protein or 1.5g/kg/d (not >25%), ensure adequate sodium/potassium
Elevated blood levels of ketones and tissue adaptations to enhance their use as fuel
Increase use of fat as muscle fuel
At least 2-3 weeks adaptation
How do keto-adaptations benefit endurance performance
They ensure a stable fuel source for exercising muscle in the face of low carbohydrate availability, shifting to fats and ketones as primary fuels
Inducing ketosis over several weeks
What are the results of the Supernova study regarding ketogenic diets and performance
Adaptation to low carbohydrate, high fat diet increased fat oxidation but impaired performance in elite endurance athletes compared to high carbohydrate availability.
Reduced economy at velocities
How does carbohydrate feeding during exercise affect liver glucose metabolism
Suppresses liver glucose output and spares liver glycogen
What does research show about muscle glycogen stores during football games
42% reduction of muscle glycogen stores during second half
47% fibres empty or almost empty
69% FT fibres and 80% SLT fibres empty or almost empty
What is the recommended carbohydrate intake athletes before exercise
4h before: 4g/kg (toast, bagels, cereal, rice, bananas)
3h before: 3g/kg
2h before: 2g/kg (Low fat in last 2-3h)
1h before: 1g/kg (low fibre if GI problems common)
