Carbohydrate ingestion during exercise

Question 1

Name the 6 possible sources of energy during exercise

Answer 1

liver glycogen 
muscle glycogen 
blood glucose 
free fatty acids 
IMTG
triglycerides from adipose tissue

Question 2

how can training and diet increase the amount of muscle glycogen, and what is roughly the maximum amount of muscle glycogen which can be stored

Answer 2

increases the activity of glycogen synthase

can increase stores up to 1kg

Question 3

how does muscle glycogen utalisation change as exercise intensity increases

Answer 3

increases to meet demands

utalisation of other fuels stays relatively constant

glycogen stores will only depleat quickly if exercising at very high intensities

Question 4

what benefits have been show to occur from ingestion of carbohydrates during exercise

Answer 4

better maintainance of plasma glucose levels

increased time to exhaustion

Question 5

what effect does carbohydrate feeding during exercise have on the rate of glycogen utalisation during exercise

what is a possible explanation for this finding

Answer 5

no difference in utalisation vs placebo

rate of glycogen synthesis is much slower than its rate of utalisation
therefore depletion still occurs at the same rate

instead, glucose feeding spares liver glucose, which can then be used later in exercise when blood glucose levels fall

Question 6

describe evidence which shows that the consumption of glucose during exercise leads to improved performance

Answer 6

1 minute improvement in time for a 40km TT

for electrolyte vs placebo drink

Question 7

explain how the relationship between the amount of glucose ingested, emptied from the stomach and oxidised changes as the total amount of glucose consumed increases

Answer 7

more glucose ingested = smaller proportion of it emptied from stomach
(but overall amount emptied increases)

there is also no change in the total amount oxidised when compared to smaller amounts of glucose

Question 8

why is there no benefit to increasing the amount of glucose consumed above a certain level

Answer 8

increases the amount of glucose remaining in the stomach and intestines

(bc smaller proportion emptied and oxidised)

so increases risk of vomiting or defecation

Question 9

what is considered to limit exogenous CHO oxidisation and be the reason why not all ingested carbohydrate gets oxidised

Answer 9

intestinal CHO absorption

Question 10

through which transporter are glucose and galactose abosorbed

Answer 10

SGLT 1 and then GLUT 2

Question 11

through which transporter is fructose absorbed

Answer 11

GLUT 5

Question 12

How does combining fructose and glucose in drinks increase the total amount of CHO absrobed

Answer 12

fructose absorbed via a different pathway so can still be absorbed when the absorption of glucose is occuring at a maximal rate

this maintains a high ratio between the amount ingested and the amount oxidised

Question 13

how much CHO should athletes be consuming during exercise

Answer 13

1-1.2g/min

Question 14

has the consumption of drinks containing glucose and fructose combinations been shown the be beneficial

Answer 14

yes

had an 8% performance improvement vs glucose only

Question 15

Is there any benefit to combining caffine with glucose drinks

Answer 15

didn’t cause an increase in the utalisation of exogenous glucose which was consumed

but did cause an improvement in TT performance and cause a better power output during the time trial