Carbohydrate during exercise (Lecture nine)

Question 1

Where is glycogen stored in the body?

Answer 1

Liver and muscles

Question 2

What is the purpose of glycogen stores in the liver?

Answer 2

To maintain blood glucose

Question 3

What organ uses blood glucose?

Answer 3

Mostly the brain (30%)

Question 4

What is the purpose of CHO consumption 3-5 hrs before the race?

Answer 4

This is known as breakfast. Its purpose is to increase CHO availability to muscles.

Question 5

What happens to CHO consumed 3-5hrs before the race?

Answer 5

Some remains in the blood, some in muscles, most in the liver.

Question 6

Why should athletes eat on race day?

Answer 6

As muscle glycogen stores are often depleted overnight.

Question 7

What should be eaten for breakfast on the race day?

Answer 7

CHO rich meals. High fat consumption can lead to GI problems, the same as suddenly changing diet on race day.

Question 8

Measuring plasma, what constituents change upon CHo consumption?

Answer 8

There is a spike in insulin and glucose plasma levels

Question 9

insulin that causes glucose storage spikes when CHO is consumed 30-60mins before the race, this is counter effective, what else is done in this time?

Answer 9

Warm up - muscle contraction that causes the muscles to uptake glucose.

Question 10

Having high blood glucose, results in the liver doing what?

Answer 10

Sensing that there is no need to produce glucose, so stopping this - rebound hypoglycemia (can make the athelete feel rubbish, as no glucose production and blodd glucose is stored.

Question 11

What can happen to blood glucose when a meal is consumed 30-60mins before exercise?

Answer 11

Blood glucose can beak sharply and decline to below its start point withint twenty minutes of consumption

Question 12

What else other than storage of blood glucose does insulin do?

Answer 12

Inhibits lipolysis therefore attenuating the FA needed for exercise.

Question 13

So is CHO ingestion 30-60mins before exercise good or bad?

Answer 13

It can be good, but requires thought about GI (glycemic index of the food) - no thought for food leads to metaolic disturbance (increased insulin, decreased lipolysis and thus decreased performance)

Question 14

Do all CHO have the same affect on metabolic response?

Answer 14

No, each one is different based on GI

Question 15

What type of food has the smallest affect on metabolism?

Answer 15

Low GI foods (30-60 mins ingested before) have the smallest affect on transient metabolic disturbance

Question 16

What sort of GI CHO is good for performance?

Answer 16

Low GI CHO is good for performance as glucose is released over time and doesnt influence insulin. It simply provided more fuel for muslces

Question 17

What advice would you give to an athelete who wants to know if they can consume CHO 30-60mins before exercise?

Answer 17

• Try to eat/include low GI foods.
• Experiment to find the best timing for pre-exercise meal
• Small amounts of CHO may be more tolerable.
e.g less than 50g. (as food in stomach can upset the gastrointestinal tract = being ill)
• Include high-intensity exercise in warm-up (muscles take up glucose)
• Consume CHO during exercise.

Question 18

Should CHO be ingested during exercise?

Answer 18

Exercise that extends longer than 45mins has shown to have increased performance when CHO is consumed during the activity.

Question 19

What is the mechanism of increased performance from CHO ingestion during exercise?

Answer 19

• Maintains blood glucose and high levels of CHO oxidation
• Spares glycogen
• Increases motor skills
• Has central effects which tells the body it is well nourished and can continue exercise

Question 20

What can CHO ingestion during exercise do?

Answer 20

• Can improve performance (time trials)
• Can delay the onset of fatigue (improve exercise capacity)
• Can maintain skilled performance late in exercise.

Question 21

What does exercise do to endogenous glucose stores?

Answer 21

• Muscles glycogen stores utilized 250-500g to perform mechanical movement
• Blood glucose used
• Liver glycogen 80-110g used.

Question 22

What is the effect of glucose ingestion during exercise on the other fuel stores?

Answer 22

Muscle glycogen stores spared
liver glycogen stores spared
blood glucose increased

Question 23

Is the limit to the CHO consumed during exercise that the quantity can no longer increase to provide benefit?

Answer 23

Yes beyond 16% CHO provides no benefit as transporters are saturated and so is CHO oxidation is limited to 1 g CHO per minute

Question 24

What is the rate limiting steps of glucose entering the blood during exercise?

Answer 24

Ingestion of more than 2g per min results in 1.7-1.8g min transported from the GI tract to the liver. The liver releases at about 1 g min.

Question 25

How should CHO be ingested for optimal benefit?

Answer 25

Different CHO as different ones use different transporters

i.e Glucose & galactose uses SLGT1 while fructose used GLUT5

Question 26

What simple sugars are oxidized fast?

Answer 26

Glucose
Maltose
Sucrose
Matlidextrin

All oxidized at around 1gmin

Question 27

What simple sugars are oxidized slowly?

Answer 27

Fructose
Galactose

Oxidized at 0.6g min

These have to be converted into glucose in the liver which slows down their oxidation

Question 28

How do cells of the GI tract transport glucose from within to the capillary?

Answer 28

GLUT 2

Question 29

During exercise which sugars should be avoided?

Answer 29

Pure:

Glucose - too sweet
Galactose and fructose oxidize too slowly
Fructose and lactose cause GI problems
Sucrose is good?

Question 30

What are multidextrins?

Answer 30

Used to increase CHO in drinks

CHO polymers (short)
Oxidized as rapidly as glucose
Lower osmalility than glucose
Neutral tasting