Week 3 - cho ingestion during ex Flashcards
What did jeukendrup’s 1997 study find on the effect of carbohydrate during exercise on performance?
40k cycling time trial – cho electrolyte vs placebo
CHO-electrolyte drink improved performance compared to a placebo substance – 2% improvement in performance
Wouldn’t decrease liver and muscle glycogen over this time period – would need longer duration to do this – performance benefit here would be smaller than what it would be for a longer duration exercise
Throughout research, what is the main conclusion about carbohydrate feeding during ex on performance?
That it improves performance
The longer you exercise, are the benefits of carbohydrate feeding greater?
Yes
Benefit of carbohydrates are greater the longer you exercise – if you have cycled/ran for long enough that you have depleted liver/muscle glycogen stores a lot, then you will be relying on whatever you have eaten/drunk during the event
Effects of carbohydrate feeding during exercise increases with exercise duration – more we run out of our endogenous stores of carbs (inside the body), more depend we are on the carbs we consume or drink
What are the different types of dietary carbohydrates?
And some examples
Simple sugars – monosaccharides – galactose, glucose, fructose
Disaccharides – lactose (galactose and glucose) maltose (2 x glucose) sucrose (glucose and fructose)
More complex carbs – amylose starch, amylopectin starch (found in breads, plant based products).
What are fast and slow carbohydrates?
How are they measured?
Refers to the speed at which these carbohydrate types are digested, absorbed and made available to the body for energy provision – how quickly they are used by the contracting muscle and how readily their energy is available.
Meausred by exogenous oxidation rates – rate of oxidation – fuelling muscle contraction
Give some examples of fast and slow carbohydrates
Fast - glucose, maltose, sucrose, starches rich in amylopectin
Slow - fructose alone, starches rich in amylose
Why is amylopectin a fast carb and amylose a slow carb?
Amylopectin is a fast carb as it is a brached molecule meaning it can be attacked quickly by enzymes to be broken down
Starches rich in amylose is a slow carb due to its long string nature – enzyme cant access much of starch at any given time
Why is fructose a slow carb?
Fructose is a slow carb – even though it’s a monosaccharide. Absorbed at half the rate of glucose. This is partly due to the differences in the absorption process between the 2 monosaccharides. Glucose is absorbed from the intestine into the plasma via more than one active glucose co-transporter protein.
What are the recommended guidelines for carbohydrate feeding during exercise?
1.1g/min
as research found that ingesting >1.1g/min of carbs has no more benefit to performance – dosent increase exogenous carbohydrate oxidation (g/min)
If you ingest more carbs than required, sat in stomach instead of intestine – bloated, lower gastrointestinal tract distress – impedes performance.
Why doesn’t all of the ingested carbohydrates transfer into exogenous carbohydrate oxidation?
Never 100% efficiency as some may be sat in stomachor intestine, or been stored in liver, and not transferred into the muscle.
How do the guidelines change for different durations
i.e. how much should be ingested for different intensities and what types of carbohydrates should be ingested?
No performance benefit for ingesting carbs below 60mins exercise - wouldn’t run out of carb stores
45-60 mins - Small quantity of carbs, <30g/h, benefits performance
1-2hr, 30-60 g/h, forms of CHO that are rapidly oxidised e.g. glucose, sucrose (fast carbohydrates)
180mins+, multiple transportable carbs, e.g. glucose-fructose sources, up to 90g/h.
What intensity should we work at to predominantly oxidise carbohydrates?
work in excess of 70% vo2
If on long walk – not 70% vo2 max – use predominately fat ox.
What is the difference between performance and exercise capacity
capacity is time to fatigue, performance outcome is measured in time or distance, performance is a race or a test
Has carbohydrate feeding been seen to benefit other aspects of sports performance?
Yes, for example motor skills during prolonged sports performance
Like taking a penalty
Coyle et 1986 analysed cycling performance during 2 trials - placebo trial and a cho fed trial. How did blood glucose levels compare?
CHO ingestion maintained plasma glucose. Compared to placebo trial, which blood glucose steadily dropped to low enough levels that sensations of fatigue would have stopped athlete from exercising – drifiting in and out of consciousness. Able to exercise for an extra hour with carbohydrate ingestion.
Coyle et 1986 analysed cycling performance during 2 trials - placebo trial and a cho fed trial. How did cho oxidation, and muscle glycogen levels compare
Cho fed trial maintained high rates of cho ox - seen as the primary reason for the performance benefit
Steep decline in muscle glycogen in both trials – cho ingestion isnt enough to stop the decline in muscle glycogen – but with low muscle glycogen – cho trial – cyclists peformed for further hour – powered by whatever they ingested and whatever is in the blood.
What evidence to suggest that there is liver glycogen sparing?
Small glucose from feeding (LO-GLU) - increased total glucose in circulation, but reduced contribution from glucose from liver (liver glycogen sparing)
High glucose from feeding (HI-GLU) - large glucose in circulation, no contribution from liver
= Glucose in stomach has to go via the liver to reach muscle. Goes via liver via the hepatic portal vein. Liver decides whether to retain glucose from stomach and intestine (contributing towards its own resynthesis of glycogen) or lets it out into circulation
In summary, what are the metabolic benefits of cho feeding during exercise
Maintains plasma glucose conc and helps to sustain high rates of cho oxidation that are necessary for muscle contraction.
Spares liver glycogen, helping to sustain plasma glucose and cho ox. More glycogen available later in exercise.
May spare muscle glycogen but not often observed
Are there any non metabolic effects of cho feeding during ex?
Rinsing mouth with non sweet cho – brain detects that energy will be coming in soon – rewarding signal – reduced fatigue signal – allows you to maintain higher exercise intensity for longer
What happens when a low amount of carbs are ingested compared to a high amount at the same ex intensity?
Low cho ingested – most is emptied from stomach to intestine, about half is oxidised
High cho ingested – some is emptied into intestine, meaning some is sat in stomach, causing bloating, still a very similar amount oxidised . suggests limitation between what is leaving stomach and getting to intestine and getting to muscle.
What are the reasons for lots of carbs not leaving the stomach?
What can we do to make sure more carbs are fully digested and used during oxidation?
When low quantities of carbs are ingested, such as glucose and galactose, they use SGLT1 transporter. Fructose uses GLUT5. These transporters are limited. Small quantity of glucose and galactose – transporter can deal with it. Large glucose quantity, ) transporter cannot deal – becomes stuck in intestine
.
Replacing cho load with a second sugar that uses a separate mechanism e.g. fructose – move more across intestinal epithelium to get more sugar into circulation to reach higher exogenous ox rates
What have studies found when comparing, for example, glucose-fructose ingestion, compared to just glucose ingestion.
Why?
Wallis et al 2005 found – maltodextrin-fructose ingestion improved exogenous carbohydrate oxidation rate compared to just maltodextrin.
Fructose uses a different transporter mechanism - different transporter mechanisms are used, more ingested energy available - muscle oxidises carbs at higher rates - performance improves
Multiple transportable carbs
These are sugars that are transported across the intestine by stimulating more than one protein transporter.
Make use of different sugar transporters in intestine e.g. glucose (via SGLT1) and fructose (via GLUT5).
The saturation of which transporter is rate limiting?
Saturation of SGLT1 is rate limiting. Trying to reduce competition for SGLT1 by activating another transporter (glut5) (ingest fructose)
By ingesting GLUT5 aswell as SGLT1, how much can this increase exogenous carbohydrate oxidation by?
This can increase exogenous carbohydrate oxidation by 20-50% above single transported carbohydrates (and it can improve gut comfort)
If performing >2.5h of exercise, (90g CHO/h) what must be ingested?
Multiple transportable carbs e.g. glucose-fructose
Why cant we recommend 90 g/h CHO for a single carbohydrate e.g. glucose?
Would cause GI distress as just would sit in stomach, wouldnt be absorbed by intestine - need to defecate - reduced performance
