Liver and Muscle Glycogen Use During Exercise. Clinical Trial
Carbohydrate is stored in the body as glycogen, which is mainly found in the liver and
muscle. During endurance exercise, muscle glycogen is used as fuel for the working muscles
and liver glycogen is broken down to provide glucose to maintain blood glucose (sugar)
levels. Both liver and muscle glycogen are important for the ability to perform
intense/prolonged endurance exercise. Therefore, nutritional strategies which can maximise
the availability of glycogen in muscle and liver can benefit endurance exercise capacity.
The carbohydrates typically found in sports drinks are glucose and sometimes fructose. If
glucose only is ingested during exercise, then the maximum rate at which can be absorbed
from the intestine into the blood stream is ~1 g/min. However, if different sources of
carbohydrate (fructose) are used, which are absorbed through a different pathway, absorption
of carbohydrate can be up to ~1.8 g/min. With more carbohydrate available as a fuel, this
translates into an improvement in performance.
Sucrose is a naturally occurring sugar that is made up of a single glucose and single
fructose molecule. Therefore, theoretically, this can use the two different pathways of
absorption and also maximise carbohydrate delivery. It is not yet known however, what impact
this has on our liver and muscle glycogen stores during exercise. Therefore the aim of this
study is to assess whether sucrose ingestion influences liver and muscle glycogen depletion
during endurance exercise.
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Allocation: Randomized, Intervention Model: Crossover Assignment, Masking: Double Blind (Subject, Investigator, Outcomes Assessor), Primary Purpose: Basic Science