Week 2

Question 1

Main functions of carbohydrates

Answer 1

-provide energy for physical activity and muscle contraction
-provide energy for the central nervous system and the brain to carry out cell signalling

Question 2

Link between glucose metabolism and the brain

Answer 2

Brain has preference for glucose metabolism (comes from breakdown of carbs). Body places high priority on maintaining glucose levels to a narrow range due to its link with the brain.

Question 3

What challenges the ability to maintain blood glucose?

Answer 3

PA and muscle contraction places a high demand on cho metabolism – trade off between maintenance of blood glucose for brain and muscle increasing turnover of fuel – challenging ability to maintain blood glucose.

Question 4

How much cho stores do we have compared to fat stores?
And why are cho stores preferred as ex intensity increases?

Answer 4

CHO stores are extremely limited compared to the vast amounts of fat that we have available in the body
Increasing ex intensity leads to greater cho oxidation as it generates atp faster than is possible through fat ox.

Question 5

Key sources of carbohydrates in the body

Answer 5

Blood glucose – must be maintained to a narrow range (3-5g)
Liver glycogen – gluconeogenesis keeps this liver glycogen sufficient, also topped up via feeding. This trickles into the blood glucose store to keep it maintained.
Muscle glycogen

Question 6

What happens to the contribution of blood glucose and muscle glycogen as exercise intensity increases/

Answer 6

During exercise intensites of over 70% vo2 max, increase in cho’s ability to provide atp, and decline in fat – increase in contribution of blood glucose and muscle glycogen.

Question 7

How does the muscle affect blood glucose from deviating from its narrow range?

Answer 7

Muscle contracting, extracting glucose from blood to provide energy it needs. This means blood glucose may fall.

Question 8

Due to the muscle contraction extracting blood glucose, what other mechanism ensures the narrow range of blood glucose is maintained?

Answer 8

Liver pumps out more glucose. Exercise increases liver glucose output in an intensity dependent manner. Close matching between muscle glucose uptake and liver glucose output

Question 9

How does blood glucose change in response to liver glucose output and muscle uptake?

Answer 9

Blood glucose tries to stay the same – however, sometimes goes up slightly due to adrenalin. (more glucose pumped by liver than muscle uptake)

However, this is only possible for as long as the liver has glycogen. Therefore, longer periods of ex, cause glycogen to run out, meaning blood glucose might fall.

Question 10

How are fatigue and muscle glycogen related

Answer 10

Exhaustion was associated with depletion in muscle glycogen.

Question 11

What analogy is used to describe muscle glycogen during exercise

Answer 11

Muscle glycogen can be seen as a petrol tank
Lots of fuel = lots of muscle glycogen, but how long the journey is determined by the fuel. How long you exercise for = how long it takes for MG to run out.

Question 12

How is blood glucose related to cho oxidation
What happens as a result?

Answer 12

Decline in blood glucose during placebo trial coincides with low rates of cho oxidation. This makes fat the primary source, meaning we start to feel fatigued, as atp production doesn’t meet atp demand.

Question 13

What does supplementation of cho during exercise (e.g. sugary drinks) do to muscle glycogen depletion?

Answer 13

Supplementation of cho during ex (e.g. sugary drinks) does not slow muscle glycogen depletion. Rate of muscle glycogen depletion is the same regardless of consumption of cho or not. It slows liver glycogen depletion, not MG depletion.

Question 14

Last page

Question 15

What are daily carbohydrate recommendations based on?

Answer 15

They are based on body weight, not % of energy intake
e.g. 5 g/kg/d NOT 50% of energy intake

Question 16

What are the daily recommendations for cho for athletes?

reference the different intensities

Answer 16

Light ex (skill based activities) - 3-5 g/kg/d
Moderate (jogging, 1hr/day) - 5-7 g/kg/d
High (high level athletes, 1-3hr/day) - 6-10 g/kg/d
Very high (extreme scenerios - ironman training) - 8-12g/kg/d

Question 17

what happens to muscle glycogen levels between a low and high cho diet when doing training bouts each day

Answer 17

Low cho diet – depletes muscle glycogen rapidly – MG levels rise very slowly and do not recover to pre exercise levels.

High cho diet – start each training session with much higher MG levels – athlete can meet their training demands and keep up quality of training for much longer than athlete with low cho diet

Question 18

How should cho ingestion change for an athlete?

Answer 18

CHO intake can be flexible, depending on training and competition needs.
For example, coming up to competition, high volume of training, means high cho diet. Lower volume of training week – lower cho diet. After comps, rest period, low cho diet.

Fuel for the work required.

Question 19

On the day/on the days leading up to the event, how should cho targets change based on either generally fuelling up or carbo loading

Answer 19

General fuelling up - prep for events lasting less than 90mins of exercise - 7-12 g/kg/d

Carbo-loading - prep for events lasting <90mins in sustained, intermittent ex - 10-12 g/kg/d for 36-48h pre event

Question 20

What are some of the issues with these methods of fuelling?

Answer 20

Practicality – can you digest the food required. If 100kg following 10g/kg/day – 1kg of cho – large volume of food

Potential side effects for eating large volumes of food

Sustainability – may be able to eat these large volumes of food for 1-2 days, but not sustainable in long term. So only choosing specific events to carb load for before coming down to a more moderate carb intake.

Question 21

On the day of an event, what is the main goal of pre event fuelling

How much should be consumed on the day?

Answer 21

Main goal here is around ensuring liver glycogen stores are high ready for performance.
Liver store – 100g, may fall overnight to 60g – as contributing to maintainace of blood gucose overnight in absence of food intake. So food in morning tops up liver glycogen.

for exercise lasting less than 60min, 1-4kg/body mass consumed 1-4hr before ex
SEE DIAGRAM.
As you get closer to the event, focus less on carbs

Question 22

Why should you eat a low fat diet before exercise

Answer 22

Eating low fat in the last 2-3hr before exercise is beneficial as fats last in blood for 8 hours so the post prandial lipaemia is very long. And you don’t want fatty meal sitting in you during competition.

Question 23

Why should you eat a low fibre diet before exercise

Answer 23

bulky aspect causes GI problems – discomfort during event

Question 24

How long is the window post exercise to maximise glycogen resynthesis rates?

Answer 24

4 hours

Question 25

Post exercise, how is cho ingestion and rate of glycogen resynthesis related?

What is the optimal rate of cho ingestion for the first 4h after ex

Answer 25

More you eat (higher rate of cho ingestion) the greater the rate of glycogen resynthesis until a plateau.

1.2-1.4 g/kg/h for first 4hr after ex.

Question 26

Is there any evidence for any benefits for coingestion of cho and protein post ex?

Answer 26

Co-ingestion of cho and protein to maximise muscle glycogen resynthesis – greater insulin spike – insulin activates glycogen synthase (responsible for building glycogen pool.)

However only beneficial when eating low amounts of cho intake. Providing consuming enough cho in the first place, added protein has no benefit.

Question 27

In the leanest of individuals, what is the fat availability like?

Answer 27

Fat availability for energy production not limited even in leanest of athletes

Question 28

When is fat a fuel source?

Answer 28

Fat is a fuel source during low to mod intensity aerobic ex.

Question 29

What are the fat recommendations for sport inc fat intake for those looking to lose weight

Answer 29

Fats have many important functions in the body and should not be excluded from the diet so:
Daily fat intake – 20-35% of total energy intake.
Proportion of saturated fat limited to less than 10% of energy intake
*For weight loss/body comp changes, chronic fat intakes <20% of energy intake discouraged

Question 30

For weight loss/body comp changes, chronic fat intakes <20% of energy intake discouraged. Why?

Answer 30

One of the key functions of fat (seen in week 1) was the consumption of essential fatty acids and at soluble vitamins, so a very low fat diet means these essential fatty acids will not be consumed.

Question 31

What does a fat adaptation, carbohydrate restoration study mean

Answer 31

A high fat diet for a period of days then a high carb diet for a day to create the best of both world

There is evidence to suggest that a high fat diet makes people better fat burners

Question 32

What were the results for the fat adapttion, carbohydrate restoration study

Answer 32

Increased fat ox, decreased cho ox, spared muscle glycogen
However, in terms of performance, not effect on cycle time trial performance.

Question 33

A study was done to see the affects of a high fat diet on high intensity sprints during a 100km cycling. what were the results

Answer 33

Shows that with a high fat diet, the power from cyclists was reduced by lots more than high cho diet. Means that not only are no better at endurance ex with high fat diet, you get worse with a high intensity ex.

Question 34

What is a ketogenic diet
What does it lead to

Answer 34

-<50g cho/day, fat intakes >70-80% energy, 15% or 1.5g/kg/d protein (not >25%)
At least 2-3 weeks adaptation
Leads to blood levels of ketones and tissue adaptations to enhance their use as fuel
Increase use of fat as muscle fuel

Question 35

What is the reason for the protein levels of a ketogenic diet not being above 25%

Answer 35

we have a powerful insulin response to protein ingestion. Insulin inhibits fat metabolism with would be counter intuitive for a high fat diet)

Question 36

What are the benefits for a ketogenic diet

Answer 36

Lowering cho intake and increasing fat intake will induce ketosis (>0.5mmol/L) over several weeks
Keto-adaptation ensures stable fuel sources for exercising muscle (and brain) in the face of low cho availability
Shift to fats and ketones as primary fuels could benefit endurance performance

Question 37

However, what has been the research found when analysing a ketogenic diet in comparison to a high cho diet

Answer 37

results only found subjects were able to match performance of cho diet. Sparked discussion. No evidence to suggest it was better.
Does not recommend this diet to athletes due to a high fat diets ability to impaire high intensity exercise (e.g. during a sprint in cycling)

Question 38

What did the supernova study find

Answer 38

Adaptation to a ketogenic low cho, high fat diet markedly increased rates of fat ox during ex in race walkers over a range of ex intensities
However alongside that increase rates of fat ox,
*increased rates of fat ox in reduced economy (increased ox demand for a given speed) at velocities that translate to real life race performance in elete race walkers. Costing them more oxygen to perform at this work rate.
Results: ex performance: in contrast to training with diets providing chronic or periodised high cho availability, adaptation to an Low carb, high fat diet impaired P in elite endurance ex.

Question 39

Is there any evidence for a performance advantage from ketogenic diets?

Answer 39

No