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.
