Week 2 Flashcards
(39 cards)
Main functions of carbohydrates
-provide energy for physical activity and muscle contraction
-provide energy for the central nervous system and the brain to carry out cell signalling
Link between glucose metabolism and the brain
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.
What challenges the ability to maintain blood glucose?
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.
How much cho stores do we have compared to fat stores?
And why are cho stores preferred as ex intensity increases?
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.
Key sources of carbohydrates in the body
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
What happens to the contribution of blood glucose and muscle glycogen as exercise intensity increases/
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.
How does the muscle affect blood glucose from deviating from its narrow range?
Muscle contracting, extracting glucose from blood to provide energy it needs. This means blood glucose may fall.
Due to the muscle contraction extracting blood glucose, what other mechanism ensures the narrow range of blood glucose is maintained?
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
How does blood glucose change in response to liver glucose output and muscle uptake?
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.
How are fatigue and muscle glycogen related
Exhaustion was associated with depletion in muscle glycogen.
What analogy is used to describe muscle glycogen during exercise
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.
How is blood glucose related to cho oxidation
What happens as a result?
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.
What does supplementation of cho during exercise (e.g. sugary drinks) do to muscle glycogen depletion?
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.
Last page
What are daily carbohydrate recommendations based on?
They are based on body weight, not % of energy intake
e.g. 5 g/kg/d NOT 50% of energy intake
What are the daily recommendations for cho for athletes?
reference the different intensities
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
what happens to muscle glycogen levels between a low and high cho diet when doing training bouts each day
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
How should cho ingestion change for an athlete?
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.
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
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
What are some of the issues with these methods of fuelling?
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.
On the day of an event, what is the main goal of pre event fuelling
How much should be consumed on the day?
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
Why should you eat a low fat diet before exercise
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.
Why should you eat a low fibre diet before exercise
bulky aspect causes GI problems – discomfort during event
How long is the window post exercise to maximise glycogen resynthesis rates?
4 hours
