During Exercise Carbohydrate Flashcards
What are the main roles of nutrition during exercise?
- Supplement the body’s limited carbohydrate stores
- Compensate for fluid lost as sweat
How does carbohydrate ingestion during exercise impact running performance? Give evience
Tzintzas et al 1993 found carbohydrate solution ingestion during a 30km run. Carb trial completed significantly faster than water trial
How does carbohydrate ingestion during exercise impact cycling power output after prolonged exercise? Give evidence
Mitchell et al 1989: limited dose response relationship between carb intake and 15 min power output after 105 min of cycling. 6% carb better than placebo, 12% carb same amount better than 6%
How does carbohydrate ingestion during exercise impact running capacity? Give evidence
Tsintzas et al 1996: carb solution ingestion every 20 minutes resulted in significant increase in running TTE compared to water
How does carbohydrate ingestion during exercie impact cycling capacity? Give evidence
Bjorkman et al 1984: Carb solution ingestion every 20 minutes led to significantly increased cycling TTE compared to water
How does carbohydrate ingestion during exercise impact intermittent exercise capacity?
Nicholas et al 1995: Carbohydrate solution ingestion every 15 minutes led to significantly increased time to fatigue compared to water
Does carbohydrate ingestion during exercise improve motor skills during prolonged exercise? Give evidence in support
Welsh et al 2002: Carb solution ingestion every 15 minutes led to significantly reduced decrease in skill performance from 3rd to 4th quarter of basketball game compared to water
How may carbohydrate ingestion during exercise negatively impact motor skills?
Rebound hypoglycemia: Afman et al 2015 found skills significantly worse in carb trial in 1st quarter compared to water
What are the main benefits of carb ingestion during exercise?
- Improved aerobic performance
- Improved exercise capacity
- Improved maintenance of motor skills late in exercise
What are the main propoed mechanims for the ergogenic effect of carb ingestion during exercise?
- Sparing of liver glycogen
- Sparing of muscle glycogen
- Maintaining euglycaemia and CHO oxidation
What evidence is there to suggest that carb ingestion during exercise spares liver glycogen?
Jeukendrup et al 1999 found that during a cycling protocol where participants ingested either water, 4% carb or 22% carb, 4% considerably reduced the contribution of hepatic glucose output to total glucose appearance, and 22% carb had no hepatic glucose output at all, implying no liver glycogen breakdown
What evidence is there to suggest that carbohydrate feeding during exercise increased total CHO oxidation?
Coyle et al 1986 found that blood glucose was maintained and thus CHO oxidation was much higher in minutes 140 to 180 of a cycling time trial in the carb trial, compared to placebo trial where it crashes after 2 hours
Why is the ergogenic benefits of CHO supplementation during exercise greater for prolonged exercise (>2 horus) than short duration?
Main fatigue mechanism during prolonged exercise is muscle glycogen depletion and hypoglycemia, so carb ingestion stops that.
How does glycogen sparing improve exercise performance?
Glycogen can then be used later in exercise once exogenous glucose runs out
Describe the effect of CHO ingestion during exercise on muscle glycogen with evidence
Higher exogenous CHO causes muscle glycogen to be oxidised at a slower rate during prolonged exercise. Multiple studies from Tsintzas et al (1995 - 2001) show 20-28% less muscle glycogen used during prolonged exercise when CHO ingested during
Describe the differing effects of CHO ingestion during exercise on muscle glycogen between cycling and running with evidence
- Coyle et al 1986: No glycogen spared by 3 hours of exercises (but longer TTE by about an hour)
- Tzintzas et al 1996: muscle glycogen significantly higher than placebo at 3 hours
Explain a potential reason behind why CHO ingestion during exercise causes glycogen sparing in running but not cycling
Cycling is very quad heavy but does not strain other muscles as much, running is more full body. Running would then demand glycogen from all the muscles, which requires sparing, whereas if the quads are depleted in cycling, glycogen can be mobilised from other muscles to fuel them.
Why is timing (frequency) of CHO ingestion less critical in cycling than running?
Large amounts of fluid in one go during running may lead to higher GI discomfort due to bouncing of body/stomach.
What is the optimal ingestion rate of glucose during prolonged exercise?
~1 g/min
Murray (1991) and Wagenmakers (1993)
If 2 g/min of glucose were ingested then how much of this would appear from a) the stomach, b) the GI tract, c) the liver?
a) 2 g/min
b) 1.2-1.7 g/min
c) 1 g/min
How can timing of CHO ingestion during cycling exercise impact performance? Give evidence
Coggan et al 1989: Ingesting 50% CHO solution 135 min into a cycling TTE increased TTE significantly.
Why may timing of CHO ingestion for running and cycling differ?
Impact of CHO ingestion during running is to spare glycogen. Ingest too late and it won’t have a benefit. Impact in cycling is to maintain blood glucose, so it can be ingested whenever blood glucose drops.
Also ingesting a lot at once can be bad for runners due to bouncing, but not for cyclists.
What are the three categories determining optimal feeding strategy?
Type
Timing
Amount
What is the optimal ingestion rate of multiple transportable CHOs during prolonged exercise?
- reference
~1.5 g/min
- Jeukendrup (2014)
