Lec 3: Carbohydrates Flashcards
(20 cards)
What is glycogen and where is it stored?
-Stored form of glucose, located in the liver and muscle
-Liver= ~100-200g, skeletal muscle= ~350-750g
How does glycogen get broken down and used?
- Liver glycogen -> glycogenolysis -> glucose -> systemic circulation and delivery to brain or -> muscle
- Intramuscular glycogen -> glycogenolysis -> glucose
Glucose -> glycolysis -> pyruvate + ATP -> acetyl CoA in mitochondria -> TCA cycle -> ETC -> ATP
Is glycogen a primary source of fuel during high-intensity exercise?
-yes, increase intensity= increase muscle glycogen use, at 75% WR max fat utilization decreases and muscle glycogen increases
Carbohydrate intake increases (3)
- Muscle glycogen stores
- Work capacity
- Performance (less time to fatigue with high CHO)
Scenario: we are responsible for the nutritional support for a 60kg elite level male cyclist competing in the Tour de France. The cyclist will be competing in a stage that will last from 12-5pm and will begin another stage the next day starting at 12pm. What is our optimal fueling strategy?
Pre-fueling time 8-12, exercise 12-5, recovery 5-10, sleep 10-8, pre-fueling 8-12…
Liver glycogen during sleep
-Liver glucose output supports blood glucose homeostasis overnight
-When you first wake up there is a 50% drop in liver glycogen
Pre-exercise fueling: Existing ACSM guidelines for pre-exercise carbohydrate intake
-1-4g/kg carbohydrate, 1-4 hours before the event
-For a 60kg athlete that is 60-240g of carbohydrate (not specific)
-Liver ~100-200g of glycogen
-50% reduction= loss of 50-100g
-So let’s make sure they ingest 120g every 1-4 hours, or 473mL Gatorade every 1-4 hours
During exercise
-of the 61 published studies, 82% showed a statistically significant performance benefit from carbohydrate supplementation
-consuming glucose exogenously/carbohydrate feeding during exercise can causes muscle glycogen sparing (more sparing in slow-twitch fibres)
-carbohydrate feeding during exercise improves time to fatigue
During exercise required amount of carbs*
-During exercise that lasts no longer than 75 mins (~20-30km) carbohydrate not needed
-During exercise that lasts no longer than 2.5 hours (~50 km) carbohydrate should be consumed at a rate of 30-60g per hour
-During exercise that lasts ~3 hours (>75 km) carbohydrate should be consumed at a rate of up to 90g per hour
*there is a dose-response relationship between carbohydrate intake and performance
*higher amounts of carbohydrates are associated with better performance, and products providing multiple transportable carbohydrates achieve high rates of oxidation
Different types of carbs (3)
- Glucose- chain length=1, intestinal membrane transporters= GLUT2; SGLT1…
- Fructose- chain length= 1, intestinal membrane transporters= GLUT 2; GLUT5…
- Sucrose- chain length= 2, monomers= glucose + fructose, intestinal membrane transporters= GLUT2; SGLT1…
Best type carbs for performance
-sucrose (combination of carbs), more carbs= better performance
-110g/h of a glucose/fructose ingestion at a 2:1 ratio improves time-trial performance
-However, more carbs= more calories, therefore not good for weight loss
-Glucose and sucrose spare liver glycogen during exercise
-Sucrose reduces symptoms of GI discomfort during exercise compared to glucose
Recap (4)
1) Carbohydrate is an important source of fuel during exercise
2) We store this fuel as glycogen in skeletal muscle and liver, but stores are limited
3) Ingesting carbohydrate during exercise helps prolong exercise capacity and improve performance
4) Multiple transportable carbohydrates (glucose + fructose) confer the most benefit
Problem with carb supplementation during exercise
-110g per hour for 5 hours= 550g of carbohydrate
-One 473 mL bottle of Gatorade = 30g carbs
-need 8.67L = 8.67 kg, therefore you would gain that in weight and decrease performance based on power to weight ratio
Gels vs. Drinks
-No difference in carbohydrate utilization between a drink and a gel (same breakdown by acids)
-Difference is gels require less amount= less weight gain= better performance
-1 gel= 60mL= 25g carbs, therefore 1.32L required (1.32kg weight)
-1 drink= 473mL= 30g carbs, therefore 8.67L required (8.67kg weight)
-But, drinks= less body mass loss from sweating/fluid loss (electrolytes replenish), some gels don’t have fluid or electrolytes to help replenish
Drinks/gels: CHO type and rate depending on duration of exercise (+endogenous vs exogenous sources) *diagram
1 hour= glucose, 30g (endogenous stores)
2 hours= glucose, 60g (mostly endogenous)
Every hour after= sucrose, 110g each hour (4 hours= half endogenous, half exogenous, 5+ mostly exogenous, 8+ all exogenous)
Ex. 2 hours duration= 90g glucose required
Ex. 6 hours duration= 90g glucose + 440g sucrose = 530g carbs required
Post-exercise: Recommendations
-1–1.2 g/kg/h for first 4 h then resume daily fuel needs
-No mention of carbohydrate source/type or the liver
-Don’t delay !!!
-Carbohydrate intake is key for post-exercise muscle glycogen re-synthesis (does not matter what type)
-Protein ingestion repairs damaged muscle tissue, co-ingestion of protein and carbohydrate enhances glycogen re-synthesis and use of insulin
-Milk= good source of protein and carbohydrate
Caffeine effect
-8mg/kg (0.8g/kg) of caffeine co-ingested with carbohydrate enhances muscle glycogen re-synthesis
Recap #2 (3)
- Important to consume 1.0-1.2g/kg of multiple carbohydrates to maximise glycogen resynthesis
- Adding protein to our recovery will enhance tissue repair and potentiate muscle glycogen resynthesis
- Co-ingesting caffeine may also confer some benefit towards glycogen resynthesis
Pre-fueling, during exercise and recovery amounts of carbs/recommendations
Pre-fueling: 2g/kg CHO or 0.5g/kg/h
During exercise: 110g/h CHO for 2+ hours, multiple types, drinks/gels
Recovery: 1.2g/kg/h CHO, 0.24g/kg protein, 8mg/kg caffeine?
Carbohydrate mouth rinsing
-spitting out Gatorade shown to improve performance “carbohydrate sensing in mouth”
-tricks brain by stimulating CNS, but avoids GI/intake issues
-very inter-individual
