Lecture 3 - Carbohydrates

Question 1

are high carb vs low carb diets more suitable for athletes

Answer 1

• high carbs are more suitable
• the aviailibility of carbs as a substrate for skeletal muscle contraction and the central nervous system is importance for endurance exercise performance

Question 2

relate glycogen storage to fluid storage

Answer 2

• greater glycogen storage is associated with greater fluid storage, with a ratio of 1 gram of glycogen resulting in 3 grams of additional water storage

Question 3

why are carbs and glycogen so important in exercise

Answer 3

• blood glucose and level of carbs (i.e. glycogen) stored in the muscles can delay fatigue
• serves as an energy source both at rest and during exercise
• becomes sole source of energy during very intense exercise

Question 4

describe muscle glycogen at low/moderate vs high levels of intensity

Answer 4

Low/Moderate
- most of the energy can be obtained from oxidative phosphorylation of Acetyle coA derived from both carbs and fat
High levels
- muscle glycogen becomes the most important substate because anaerobic energy delivery (ATP resynthesis from glycolysis) is mstly derived from muscle glycogen

Question 5

role of glycogen in the liver

Answer 5

MAINTAIN A CONSTANT BLOOD GLUCOSE LEVEL
- glycogen is broken down in the liver to glucose and then released into the circulatory system
- glycogen in muscle does not support blood glucose

Question 6

how does liver glucose output change during exercise

Answer 6

• liver glycogen is decreased by about 50% after 1hr of exericse at 75% of VO2max and its importance (in absolute terms) increases when exercise intensity increases
• during exercise, the liver glucose output increases dramatically. during high-intensity exercise, liver glucose output increases to about 1g/min, and the majority of this glucose is derived from the breakdown of liver glycogen

Question 7

liver vs muscle glycogen

Answer 7

the liver glycogen is primarily responsible for stabilizing blood glucose, whereas the muscle glycogen is mainly responsible for providing an energy source to working muscles that can be metabolized both anaerobically an aerobically

Question 8

blood glucose concentration

Answer 8

4-5 mmol/L

Question 9

how is blood glucose regulated by insulin

Answer 9

insulin increases the uptake of glucose into various tissue
- after a meal, plasma insulin conc increases and as a result glucose uptake by muscle, liver and other tissues increases
insulin promotes not only the uptake, but also the storage of glucose. Glycogen synthase activity increases, and glycogen phosphorylase (enzyme responsible for the breakdown of glycogen) decreases

Question 10

how is blood sugar regulated by glucagon

Answer 10

• the most important counteractive hormone
• secretion of glucagon causes the breakdown of glycogen and the release of glucose into circulation

Question 11

how can hypoglycemia occur in very prolonged exercise

Answer 11

if blood glucose concentrations drop below 3mmol/L due to insufficient stores, the rate of glucose uptake by the brain is insufficient to meet its demands/needs
- hypoglycemia symtoms will occur
* dizziness, nausea, cold sweats, reduced mental alertness and concentration, increased HR, hunger, disorientation and loss of motor skills

Question 12

list some possible strategies to provide adequate carbohydrates

Answer 12

• high carb diets in the the days before comps
• carb feeing before exercise to top up muscle glycogen and liver glycogen stores
• carb feeding during exercise to keep high rates of glucose oxidation derived from plasma
• carb feeding post exercise to replenish stores

Question 13

carb intake recommendations for gen pop vs athletes

Answer 13

The institute of Medicine recomends 140gs (520Kcal) of carbs per day, which is the average minimal usage of glucose by the brain
- the desirable range of carb intake is 45-65 percent of caloric intake (AMDR)
- the typical rec. for athletes is 55-65% of total calories being carbs, assuming an adequate total caloric intake

Question 14

what should an athlete eat in the days leading u to competition

Answer 14

• well balanced diet with familiar, lower fibre, carb rich foods
• the primary role of carbs in the days leading up to competition is to fully replenish muscle glycogen stores
• carb loading, increases time to exhaustion on average 20% and reduces time to complete a set task by 2-3%
• supercompensation protocols

Question 15

Supercompensation

Answer 15

• not always applicable and may not be possible given the time frame and rules of the sport

Question 16

what should an athlete eat in the hours before exercise

Answer 16

4-24hrs before exercise
- balanced high carb meals/snacks
- familiar foods
- carbs = ~ 60-70% of total calories
1-4hrs prior to sport
- 1-4g of carbs/kg of BW
- easily digestible, low fiber
- complex carbs

Question 17

types of carbohydrates

Answer 17

• glycose
• glucose plymers
• fructose
• starches

Question 18

how much and when should you consume carbs DURING exercise

Answer 18

Amounts
- 30-70g per hr (up to 90g for ultra endurance events)
- individual tolerance will vary
Timing
- begin soon after onset
- continue at regular intervals
the mechanisms may be maintaining blodd glucose levels and high carb oxidation rates

Question 19

Low-glycemic index (GI) carbohydrates

Answer 19

• slow release carbo that is slowly absorbed and doesn’t cause a spike in blood insulin
• such producs have not been showed to have any performance benefits compared with high GI carbohydrate meals consumed before exercise

Question 20

high-glycemic index (GI) carbs during exercise

Answer 20

high GI carbs are rapidly digested and absorbed, these are preferred for exercise
- such products help to maintain blood glucose and high rates of carb oxidation

Question 21

carb mouth rinse

Answer 21

• before and during exercise, a 10 second mouth rinse with a carb solution may have performance enhancing effects through the CNS
• both sweet and nonsweek carbohydrates activates regions in the brain associated with reward and motor control

Question 22

what should an athlete eat AFTER exercise

Answer 22

carb consumption after exercise is important for glycogen replenishment
- carbs should be consumed as soon as possible after exeercise
- solid or liquid forms are acceptable

Question 23

how much should an athlete eat after exercise

Answer 23

1-2g of carbs/ kg every hour for 4 hrs
THIS IS CRAZY