The role of nutrition Flashcards
How much can nutrition actually enhance training?
Most supplements only show a 1-3%increase in performance. It cannot mask porr training.
What is the ranking system of nutrients?
A= strong scientific evidence that usage will improve performance e.g. sports drinks, gels, whey proteins, caffeine, creatine. There are some macronutrients that are included in this list but they will only help if there is already an existing deficiency
B=There is emerging evidence or potential evidence that is may enhance performance may include new supplements that are being researched
C= Little or no evidence to support their use
D= Harmful supplements that can decrease performance
What is the difference between cardiac and liver cells?
Cardiac muscle – high energy expenditure • Glycogen in muscle fibres • Stored next to mitochondria • Local delivery of fuel
Liver cells – high energy Storage, low consumption • Glycogen in hepatocytes (liver) • Stored in the cytosol for release • To support blood glucose
What is the difference between liver and muscle glycogen stores function?
Liver and muscle glycogen stores have different roles with liver supporting blood glucose levels at 5 mmoles. The larger store in the muscle (400-500g)that is used to create ATP or is stored as glycogen.
In the muscle glycogen is stored next to the mitochondria for local delivery of fuel. whereas in hepatocytes it is stored in the cytosol without clustering ready for release.
What happens to glycogen stores after exhaustive contractions??
1 h of exhaustive exercise 83% reduction on glycogen content pre-post exercise.
This means there is a link between glycogen conc and time to exhaustion. However this isnt a link between performance.
What does recommendation of glucose change depending on?
Duration of the exercise
What are the recommendations between 0-60mins?
There is no role for carbohydrate supplementations (there is some evidence that mouth washing of carbs may help increase performance)
What are the recommendations between 60mins - 3 hours?
Yu should consume 30-60g per hour but there is no physiological benefit to consuming more than 60g. There is new evidence that we can increase performance further by using a range of carbohydrates
What is the oxidation rate of glucose?
up to 1gmin-1 this is faster than other monosaccharides e.g. fructose and galactose 0.4gmin-1
However peripheral glucose infusion results in oxidation rates up to 2.5gmin-1
How does peripheral glucose infusion hint at the rate limiting step?
- Gastric emptying
- Intestinal absorption
- Liver glycogen synthesis
- Muscle glucose uptake
Which GLUT transporter is insulin sensitive?
GLUT 4
What is Vmax?
Maximum rate at which a transporter can work
What is Km?
The conc at which the transporter reaches 50% of its Vmax
- If glucose conc is at or above Km glucose uptake is rapid
- If glucose conc. is below Km glucose uptake is limited
What does differences in Vmax and Km mean?
It means that some transporters can move glucose quicker than others and some are more sensitive to lower concs of glucose
Why not just exploit a universally very low Km?
- Uptake does not equate to metabolism
- Osmotic potential
- Potential rapid and dangerous decline in blood glucose
What are the characteristics of GLUT 1?
Brain
Erythrocyte
Fetus
Km=5mM
GLUCOSE
What are the characteristics of GLUT 2?
Liver
Kidney
Pancreas
Km=17mM
GLUCOSE
What are the characteristics of GLUT 3?
Brain
Placenta
Testes
Km=1-2mM
GLUCOSE
What are the characteristics of GLUT 4?
Skeletal
Cardiac
Adipose
Km=3-5mM
GLUCOSE
What are the characteristics of GLUT 5?
Small Intestine
Sperm
Liver
Km=6mM
FRUCTOSE ONLY
What changes are seen with mixed CHO of glucose and fructose?
Up to a 65%higher exogenous CHO oxidation rate of multiple transportable CHO during exercise compared with single CHO. Exogenous CHO oxidation rates of 1.75g/min vs 1g/min
The increased CH oxidation with multiple transportable CHOs may also increase gastric emptying, fluid delivery and oxidation efficiency. THis reduces the likelihood of gastrointestinal distress
What is the issue with just one CHO?
The sodium transporters get saturated quickly as it has a low capacity for glucose transportation. It can work at about 1g/min. This is why you initially set low glucose recommendations. However, GLUT 5 is involved in fructose movement meaning you can sill absorb different carbs.
Fructose has one ‘dedicated’ transport
protein, with no competition – so if all
glucose transporters are ‘saturated’ using
fructose gives addition carbohydrate
Is there an association between exogenous CHO oxidation rate and body mass?
no, therefore recommendations should not depend on body mass
How quickly is muscle glycogen restored?
Muscle glycogen stores can be restored
completely within 24 hrs. The highest rates of storage occur during the 2 hours after exercise.
The restoration of muscle glycogen following exercise occurs in biphasic manner. – 30-60 mins post exercise (insulin independent)- increased glycogen synthase activity and permeability of the muscle cell membrane. – +60 mins (insulin dependent)- increased insulin sensitivity
Does increasing GLUT4 change Km?
Increasing GLUT4 does not change the Km of glucose
transport for a tissue – just increases the number of total transporters and
hence ↑ total glucose uptake
How is GLUT 4 number increased?
GLUT 4 is insulin dependent and is usually found on the inside of the cell until insulin triggers it to move to the cell surface
How does glycogen synthase affect glucose uptake?
- During early phase you get an increased activity of glycogen synthase which converts glucose to glycogen
- During the first 30-60 mins after exercise there is an increased rate of glycogen synthase and insulin sensitivity. The cell therefore becomes more permeable to glucose as GLUT 4 moves to the cell surface
What happens to RER during recovery?
It drops so you burn fats as you restore glucose stores
For the rapid restoration of muscle glycogen, it has been recommended that
• 75-90g of CHO (1.2 g/kg) are ingested immediately post exercise.
• Similar amounts of CHO should be consumed every hour, for 4-6hrs
post exercise.
