Week 3 - carbohydrates after exercise

Question 1

How does cho ingestion change between short term intervals beteen training/rounds of competition (0-8h) and Long term (8-24h)

Answer 1

Long term – 8-24 hours between training sessions/rounds of competition – adoption of general daily CHO intake (week 2) should ensure repletion on day to day basis. Fuelling to meet energy demands.
Short term – 0-8 hours – more specific strategies needed to ensure rapid glycogen repletion. Wont get a full muscle/liver in that time – but want as much carb in them as possible during short time.

Question 2

How does cho ingestion straight after exercise compare to no cho ingestion straight after exercise on glycogen synthesis?

What athletes should adopt this strategy

Answer 2

0-2hr – carbs given post exercise- high rates of glycogen resynthesis.
-0-2hr – no carbs provided -still some recovery of muscle glycogen - glucose in blood can enter muscle and liver can make own glucose – gluconeogenesis provides blood glucose which is available to the muscle. But still a 3fold difference.

Athletes who have less than 8h between training sessions/rounds of competition should adopt this, more aggressive strategy.

Question 3

How does cho ingestion 2-4h after exercise compare to no cho ingestion 2-4h after exercise on glycogen synthesis?

Answer 3

Rate of glycogen synthesis is very similar whether you ingested carbs or not

2-4hr – blunting on rate of muscle glycogen resynthesis – glycogen resynthesis is not as great when ingesting carbs 2-4 hours after exercise

Question 4

What is GLUT4 translocation and what triggers GLUT4 translocation?

Answer 4

GLUT 4 moves to muscle cell membrane through GLUT 4 translocation to move glucose into the cell as it is needed as a fuel.
GLUT 4 is signalled to move to membrane via various signals such as the start of exercise
Post exercise recovery - when fed, insulin induced effect where transporters move into cell membrane to have the same effect on glucose

Question 5

When glucose enters the muscle, what can happen to it?

Answer 5

When glucose enters the muscle, can be partitioned off into oxidation for glycolysis or can continue and be kept as glycogen through enzymes glycogen synthase and branching enzyme

Question 6

What does glycogen synthase do?

Answer 6

Glycogen synthase adds glucose molecules to form a long string. (rate limiting)

Question 7

What does the structure of branching enzyme allow to happen to it?

Answer 7

Branching enzyme allows branching in structure – allows joints to be formed between strings of glucose molecules - more access points for enzymes to break it down. Important as it would be needed rapidly.

Question 8

What is the difference between a-1,4 glycosidic bonds and a-1,6

Answer 8

1-4 bonds give glycogen its flat structure and 1-6 bonds allow branching

Question 9

What are the 2 phases of muscle glycogen recovery post ex?

Answer 9

Rapid phase – insulin independent – approx. first 1-2 hours after exercise completes – occurs independently of insulin. Glut 4 transporters are remaining on cell membrane during this 1-2hours – window of opportunity.
Slow phase – insulin dependent – 2hours+ - slow phase even with carbohydrate ingestion

Question 10

During ex, what does muscle contraction cause?

Answer 10

Ca2+ release
Production of NO
Activation of AMPK

Question 11

During ex, muscle contraction sends positive and negative signals towards certain enzymes/processes in order to provide ATP. What are these?

Answer 11

Muscle contraction causes GLUT4 translocation, bringing glucose into the cell, also a positive impact on glycolysis, ), an inhibition on glycogen synthase (don’t want any glucose to be portioned towards storage – needed to provide ATP as muscle is contracting – during exercise)

Question 12

When exercise finishes, what happens to these signals that were active during ex?

Answer 12

When exercise finishes, removal of these signals over time – removal of inhibition of GS, and removal of glycolysis signal – any glucose entering cell can be portioned towards storage. Some GLUT 4 remains in membrane for an hour ish. Insulin independent.

Question 13

What is the key cause, post exercise, to get glucose into the cell

Answer 13

Insulin

Question 14

Post ex, when eating, insulin has 2 signals with the aim to store glucose. What are these?

Answer 14

Eating a meal – insulin released into circulation through pancreas sensing. Insulin binds with receptors on cell membrane. Insulin has positive effect on GS to cause glycogen synthesis and a signal to move GLUT 4 to membrane. Now partitioning our available glucose in its storage depot – glycogen. Different signal from insulin moves glut4 to membrane to allow more glucose in.

Question 15

When is the optimum, window of opportunity to maximise rate of glycogen synthesis (for athletes who have short amount of time between training/rounds of comp?

Answer 15

The first hour after exercise completion.

Question 16

Why is fructose absorbed slower than glucose and sucrose

Answer 16

Fructose primarily metabolised in liver, (slower process) where as glucose and sucrose handled by muscle without prior metabolism in liver needed.

Question 17

What do carbohydrate rich foods with a moderate to high glycaemic index provide

And what carbs fit this index and what carbs dont

Answer 17

Carbohydrate rich foods with a moderate to high glycaemic index provide a radily available source of substrate for glycogen synthesis. This may be important when maximum glycogen storage is required in the hours after an exercise bout.
High glyceamic foods – glucose. Sucrose would be moderate (fits within guidelines above) Fructose would be lower on the glycaemic index despite being a monoscahhride.

Question 18

What is the science behind protein co-ingestion with carbs?

Answer 18

Added benefit of protein co ingested with cho only occurs with low cho ingesting rates – anything lower than 1.2 g/kg/h
Mechanism – benefits of protein causes stimulatory/direct effect on insulin. Insulin stimulates glycogen synthase and glut 4 translocation to bring glucose into the cell.

Question 19

What are the perfect guidelines for cho feeding post exercise (over 4 hours post ex)
(for speedy refuelling post ex)

Answer 19

-Early and frequent carbohydrate feeding e.g. within the first hour and at 30min intervals for 4h thereafter, before resuming normal diet.
-1.2g/kg CHO/h for first 4 hours, of mod-to-high glycaemic index CHOs
-addition of protein if cho intake is sub-optimal

Question 20

New studies were done on the muscle and liver glycogen synthesis rates when fructose-glucose was ingested compared to glucose. What was found?

Answer 20

Synthesis rate for muscle glycogen was the same for glucose ingested and fructose-glucose ingested.
Follow up study looked at liver – found that storage rate increased with fructose-glucose ingestion – addition of fructose to glucose doubled rate of resynthesis in the liver than just glucose

Muscle – storage of MG is the same with sucrose (glucose and fructose) and glucose
Liver glycogen replenishment higher with frucrose-glucose (sucrose) – provision of G-F is better than glucose alone.

Question 21

What is sucrose?

Answer 21

Fructose and glucose