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Nutrition and Metabolism > During Exercise Carbohydrate > Flashcards

During Exercise Carbohydrate Flashcards

1
Q

What are the main roles of nutrition during exercise?

A
  • Supplement the body’s limited carbohydrate stores

- Compensate for fluid lost as sweat

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2
Q

How does carbohydrate ingestion during exercise impact running performance? Give evience

A

Tzintzas et al 1993 found carbohydrate solution ingestion during a 30km run. Carb trial completed significantly faster than water trial

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3
Q

How does carbohydrate ingestion during exercise impact cycling power output after prolonged exercise? Give evidence

A

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%

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4
Q

How does carbohydrate ingestion during exercise impact running capacity? Give evidence

A

Tsintzas et al 1996: carb solution ingestion every 20 minutes resulted in significant increase in running TTE compared to water

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5
Q

How does carbohydrate ingestion during exercie impact cycling capacity? Give evidence

A

Bjorkman et al 1984: Carb solution ingestion every 20 minutes led to significantly increased cycling TTE compared to water

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6
Q

How does carbohydrate ingestion during exercise impact intermittent exercise capacity?

A

Nicholas et al 1995: Carbohydrate solution ingestion every 15 minutes led to significantly increased time to fatigue compared to water

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7
Q

Does carbohydrate ingestion during exercise improve motor skills during prolonged exercise? Give evidence in support

A

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

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8
Q

How may carbohydrate ingestion during exercise negatively impact motor skills?

A

Rebound hypoglycemia: Afman et al 2015 found skills significantly worse in carb trial in 1st quarter compared to water

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9
Q

What are the main benefits of carb ingestion during exercise?

A
  • Improved aerobic performance
  • Improved exercise capacity
  • Improved maintenance of motor skills late in exercise
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10
Q

What are the main propoed mechanims for the ergogenic effect of carb ingestion during exercise?

A
  • Sparing of liver glycogen
  • Sparing of muscle glycogen
  • Maintaining euglycaemia and CHO oxidation
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11
Q

What evidence is there to suggest that carb ingestion during exercise spares liver glycogen?

A

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

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12
Q

What evidence is there to suggest that carbohydrate feeding during exercise increased total CHO oxidation?

A

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

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13
Q

Why is the ergogenic benefits of CHO supplementation during exercise greater for prolonged exercise (>2 horus) than short duration?

A

Main fatigue mechanism during prolonged exercise is muscle glycogen depletion and hypoglycemia, so carb ingestion stops that.

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14
Q

How does glycogen sparing improve exercise performance?

A

Glycogen can then be used later in exercise once exogenous glucose runs out

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15
Q

Describe the effect of CHO ingestion during exercise on muscle glycogen with evidence

A

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

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16
Q

Describe the differing effects of CHO ingestion during exercise on muscle glycogen between cycling and running with evidence

A
  • 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
17
Q

Explain a potential reason behind why CHO ingestion during exercise causes glycogen sparing in running but not cycling

A

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.

18
Q

Why is timing (frequency) of CHO ingestion less critical in cycling than running?

A

Large amounts of fluid in one go during running may lead to higher GI discomfort due to bouncing of body/stomach.

19
Q

What is the optimal ingestion rate of glucose during prolonged exercise?

A

~1 g/min

Murray (1991) and Wagenmakers (1993)

20
Q

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

a) 2 g/min
b) 1.2-1.7 g/min
c) 1 g/min

21
Q

How can timing of CHO ingestion during cycling exercise impact performance? Give evidence

A

Coggan et al 1989: Ingesting 50% CHO solution 135 min into a cycling TTE increased TTE significantly.

22
Q

Why may timing of CHO ingestion for running and cycling differ?

A

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.

23
Q

What are the three categories determining optimal feeding strategy?

A

Type
Timing
Amount

24
Q

What is the optimal ingestion rate of multiple transportable CHOs during prolonged exercise?
- reference

A

~1.5 g/min

- Jeukendrup (2014)

25
Q

Why is the optimal ingestion rate for GLU+FRU ~1.5 g/min whereas GLU is only 1 g/min?
- reference

A

Possible that multiple transporters used in intestine and then liver converts fructose to glucose. However, GLU+FRU doesn’t alter glucose appearance in circulation or in muscle.
Therefore, increased exogenous CHO oxidation reflects…
- oxidation of liver CHO sources and/or
- increased production and oxidation of lactate from fructose.
- Jeukendrup et al (2006)

26
Q

What are the benefits of GLU+FRU (SUC) vs GLU only?

A

Higher exogenous CHO oxidation rates (1.5 g/min vs 1 g/min).

Lower gut fullness.

27
Q

Why would FRU on its own be a poorer intra-exercise CHO option than GLU?

A

Lower GI (oxidised slower)

28
Q

Why use maltodextrins over glucose in a sports drink?

A

> neutral tasting
lower osmolality than glucose
can be oxidised as rapidly as glucose.

29
Q

Solid or liquid or gel CHO ingestion during exerise?

- Describe the study and give reference

A

Multiple studies from Pfeiffer have shown solid and gel CHO oxidation rates to be similar to liquid. Doses were 1.55 g/min (Glu+Fru) and no severe GI symptoms were reported in any trial.

30
Q

How may liquid CHO ingestion be better than solid or gel?

A

Liquid CHO ingestion aids in fluid intake which helps to compensate for sweat loss and facilitates gastric emptying.

31
Q

What is a common methodological flaw in studies looking at CHO solid vs liquid and how may this affect correct real-world recommendations?

A

Use fixed intensities. (poor ecological validity as races typically ramp up in intensity at the end).
Increased intensity re-directs blood flow from viscera to muscles and skin, therefore, reducing gastric emptying rates - de Oliveira (2014).
Therefore, CHO ingestion as fluid rather than solid (helps facilitate gastric emptying) may be more vital during high-intensity race portions to avoid GI symptoms.

32
Q

Summarise type/timing/amount for CHO ingestion during exercise

A

Type: Solid or liquid, says research. but maybe liquid cos rehydration, and gastric emptying/splanchnic hypoperfusion.
Timing: frequent and early for running, whenever blood sugar drops for cyclists, even 135 min into exercise
Amount: 1g/min for glucose, 1.5g/min for MTC/Gluc:Fruc/Sucrose

33
Q

Does molecular weight of glucose impact effectivenss for CHO oxidation?

A

-No. Rowlands et al 2005

34
Q

What is the optimal CHO ingestion frequency during exercise for prolonged running?

A

A review of nutritional guidelines for ultraendurance runners by Eden and Abernathy 1994 recommends small and frequent intake of carb evey 15-20 minutes, which is reflected in the practice of most running/carb studies where an effect is shown

Nutrition and Metabolism (5 decks)

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