Week 6

Question 1

Amylose structure

Amylopectin structure

Answer 1

Amylose-starch= long glucose chains connected
Amylopectin-starch= branched structure and is a bit like glycogen

Question 2

Mono/di/polysaccharides

Answer 2

single sugar unit, 2 , many

Question 3

Dietary monosaccharides?

Answer 3

Glucose, galactose and fructose- May find fructose in fruit though will not often find the other types. Instead they are often delivered as part of a monosaccharide where two disaccharides are joined together by a special bond. e.g. glucose bound to galactose to form lactose which is the sugar found in milk.
e.g. two glucose units combine to form maltose - is uncommonly found but can be found in beer.
Glucose bound to fructose forms sucrose

Question 4

What is starch?

Answer 4

What is the storage form of carbs in plants and can be found in bread, potatoes , pasta etc.

Question 5

Carb feeding products generally contain?

Answer 5

Carb feeding products normally contain monosaccharides or disaccharides like sucrose or a glucose polymer like multidextrins.

Question 6

Examples of fast and slow carbs

Answer 6

Fast carbs - Glucose, sucrose, maltose, starches rich in amylopectin, maltidextrins
Slow carbs- Fructose alone (as needs to be converted into glucose in the liver) , galactose, isalomaltulose, and starches rich in amylose.
Carb feeding generally found to improve performance..

Question 7

At what intensity or duration are carbohydrate feeding techniques not really necessary?
How much carb intake do they recommend for 45 mins to an hour of exercise?

Answer 7

Low intensity exercise and and duration of less than 45 mins

Recommend a small amount of carbohydrate somewhere between 0 and 30 grams of carbohydrate- can include mouth rinsing.

Question 8

How much carbs should be consumed for an hour to 2 and a half hour exercise?
How much carbs should be consumed in 2.5-3 hour exercise?

Answer 8

30-60 grams of carbohydrate per hour- not regulated to weight but should be absolute values- fast carbs should be used.
Around 90 grams of carb should be consumed an hour in 2.5 - 3 hour exercise and should come from multiple transportable sources e.g. glucose and fructose sources.

Question 9

Carb feeding effects?

Answer 9

Carb feeding improves endurance capacity and performance in exercise over 45 mins. Effects of carb feeding get greater with increased performance duration and carb feeding can improve other parts of performance.

Question 10

Where can glycogen be found?

Answer 10

Glycogen can be found in the liver and there is a circulating pool of glucose.

Question 11

Effect of carbs in endurance cycling at 70% of V02 max

Answer 11

On average were able to cycle an hour longer with carbs. Carb group helped better maintain blood glucose levels than control group- means more blood glucose to the brain so better functioning and provides a continued fuel source to the working muscles to keep them functioning. Carb group hit fatigue later as were better able to maintain muscle glycogen- fatigues as cannot provide energy from fats fast enough. There was no difference in carb utilisation between the carbs group and the control group despite the increased endurance displayed. Blood conc maintenance may play a role in the increased endurance performance.

Half the studies suggests carb feeding helps with sparing of muscle glycogen versus half dont.
In control group liver glycogen decreases but not as much in the carb group.

Question 12

Effects of carb feeding during exercise?

Answer 12

Maintains plasma glucose levels-which helps to sustain carbohydrate oxidation, can help spare muscle glycogen.
Also helps spare liver glycogen which helps maintain plasma glucose and carbohydrate oxidation.

Question 13

Concept of mouth rinsing

How does it work?

Answer 13

Do so in exercise of duration of around 45 mins- 1 hour where carbohydrate consumption would have little effect. Rinsing is found to improve exercise performance even in 1 hour long exercise. Rinsing might have central effects on the brain.

Rinsing may have a central effect to the brain and there is feedback processes to the brain e.g. about regulating body temp, metabolic status, physical signals about contraction etc- all negative feedback systems. The brain controls motor unit recruitment and how much power you can produce and ultimately your exercise performance. Presence of carbs in the mouth may positively affect neural pathways to the brain that affect motor unit recruitment- perhaps by alerting brain energy so it can keep pushing.

Carb rinsing also seems to improve short term, high intensity exercise performance. More consistently when athletes compete in overnight, fasted state.
Might be associated with central fatigue mechanisms linking oral carbohydrate sensing to motor output

Question 14

What is exogenous carbohydrate?

Answer 14

Exogenous carbohydrate is carbs not already stored within the body.
If you intake around 36g of carbohydrate an hour you get an oxidation rate of around 0.5 g a min.
If you double this intake you get an oxidation rate you get an increased oxidation rate of around 0.8 g a min. Oxidation rate will keep increasing until ingest around 108 grams of carbs an hour and then a plateau will start to be experienced and increasing carbohydrate further then does not further increase oxidation rate.

Question 15

Carb absorption into the intestine

Answer 15

To get into the intestinal cell uses SLGt transporter and on other side to get into the bloodstream so can be used by the cell uses GLUT 2 transporter.
This SGLt1 transporter gets saturated somewhere in-between 1 and 1.2 grams. So if you are ingesting 60-70 grams of glucose an hour so if you are ingesting more it does not result in getting more into the system.
Glut 5 - another transporter for sugars in the small intestine.- fructose uses Glut 5 to get across the first part of the intestinal wall and Glut 2 is on the other side.

Idea thought of in early 2000’s is that you could increase total carb availability by ingesting large amounts of glucose to saturate SGLT 1 but also to recruit fructose to find an alternative carb transporter.- helps get more carbohydrate into the intestine and into the wall.

Question 16

Maltodextrin feeding

Answer 16

When we feed maltodextrin oxidation rate seems limited to around 1 gram per minute oxidation rate- so there is definitely a sealing (think means max) to glucose oxidation when feed glucose in exercise. Combining glucose and maltodextrin get an increased carbohydrate oxidation of around 1.4-1.5grams a minute. Including fructose with glucose when exercising leads to a higher oxidation rate. Multiple transportable carbs can lead to increased carb availability during exercise. - can improve endurance performance.

Question 17

What are multiple transportable carbs

Answer 17

They are sugars transported across the intestine by stimulating more than 1 protein transporter (e.g. glucose and fructose sources.) This can help increase gut comfort and increase exogenous carbohydrate oxidation by 20-50% above single, transported carbohydrate types. In prolonged, intense endurance exercise can lead to improved performance.

Question 18

What happens if you do not replenish carbs.

Answer 18

If you do not replenish carbs glycogen will not recover though if you replenish with a high carb meal then glycogen can recover within 24 hours post exercise.

Question 19

Strategies for 0-8 hours after exercise and 8-24 hours after exercise.

Answer 19

0-8 hours develop strategies to ensure rapid glycogen repletion.
8-24 hours should lead to repletion of carbs on a day to day basis.

Question 20

General daily carb intake for athletes

Answer 20

Light- 3-5 g/kg/d
Moderate- moderate exercise program 5-7 g/kg/d
High e.g. endurance training 1-3 hours a day- 6-10 g/kg/d
Very high- extreme commitment- more than 4-5 hours a day- 8-12 g/kg/d

Question 21

How is glucose uptaken into the muscle and forms glycogen?

Answer 21

Glucose is uptaken into the muscle by GLUT 4 transporter and converted into glycogen by glycogen synthase. Glucose uptake by the muscle is largely regulated by the delivery of glucose to the muscle coming from the circulation-if you feed carbs you would increase delivery of carbs into circulation and also uptake into the muscle- regulated by GLUT 4 (usually found within the muscle though can be activated and translocated within the membrane in special circumstances and help glucose get in).
So increased amount of feed carbohydrate increases the amount of glucose in circulation and GLUT 4 uptake.

Question 22

2 main stimuli for GLUT4 translocation?

Answer 22

Muscle contraction– calcium ions released during muscle contraction stimulate GLUT 4 for translocation

Also insulin stimulated contraction- so hormone insulin binds to insulin receptors on the cell membrane and triggers cascade signals which result in translocation.

Known as contraction mediated processes and insulin stimulated process.

Question 23

Exhaustive exercise bout effect on muscle glycogen?

Glycogen synthesis 2 phases?

Answer 23

Causes low muscle glycogen.

Rapid phase - within first 1-2 hours- insulin independent phase as does not rely on insulin for insulin stimulated GLUT 4 translocation.

Slow phase- still quick but not as quick and is the insulin dependant phase

Question 24

Muscle cells response to exercise and cessation of exercise?

Answer 24

Muscle contract and switch off glycogen synthase activity as do not want to produce glycogen. Contraction signals also stimulate glycolysis and GLUT 4 translocation into the cell so glucose can be used as a fuel in the muscle.

Opposite happens at the cessation of exercise- glycogen synthase inhibition stops as want glycolysis production again and glycolysis stops. Glut 4 remains in membrane for a period after cessation of exercise.- this glucose coming in is then is likely to be channeled into glycogen synthesis. Eventually Glut 4 molecules wane away from the membrane.

Question 25

Insulin effects-

Answer 25

When feed carb and glucose released into the bloodstream- insulin is released from the pancreas and binds to receptors on the muscle causing 2 things:

• Glut 4 translocation
• Stimulation of glycogen synthase

Question 26

Summarize glycogen synthesis

Answer 26

Exercise induced glycogen synthesis
Increased blood glucose conc when consume carb will cause increased blood glucose uptake by mass action.
Insulin maintains glut 4 in the cell membrane after exercising increasing glucose transport.
The insulin stimulates glycogen synthase.

Question 27

Why is important to feed immediately after exercise rather than 2 hours later?

Answer 27

Glycogen synthesis rates are higher immediately after exercise as contraction induced Glut 4 translocation means GLUT4 remains in the membrane which aids glucose uptake and is combine with the sustained stimulation of glucose uptake via glycogen synthesis through insulin mediated mechanisms.
If you delay feeding you miss the insulin independent phase and you get slower glycogen synthesis

Question 28

Dose response to carbs-

Answer 28

Feed more carbs get increased glycogen synthesis. Above 1.2 value though there is no additional benefit

Question 29

Are fast or slow carbs better at increasing glycogen synthesis?
What does glycemic index mean?

Answer 29

Fast carbs are better at increasing glycogen synthesis
Glycemic index- the degree / rate that blood glucose increases in response to carbohydrate feeding. Evidence suggests sources with higher carbohydrate get into your system quicker.
Some sources suggest protein can be a useful substance to co-ingest with carbs.
For values 0.6-1.2 protein addition helps increase muscle glycogen synthesis.- but this is only if you are ingesting carbs at a sub optimal rate. This can be useful as consuming large amounts of carbs can be impractical and protein generally is beneficial to recovery. Pretein can cause greater increases in blood insulin responses driving glycogen synthesis and glucose uptake.

Question 30

MRI’s link to glycogen?

Liver glycogen stores when broken down where are they used by?

Answer 30

Gives us an insight into how to optimize liver glycogen recovery.
Used by the brain and the muscle.

Question 31

What happens when combing glucose and fructose uptake?

Answer 31

It almost doubles glycogen synthesis rate versus just glucose on it’s own. So if you combine one source that optimizes glycogen synthesis in the muscle and one source that optimizes it in the liver you can optimise whole body carb storage.
Fructose needs to be metabolised in the liver before it can be used for anything else and can be converted to glucose or lactate.