Carbohydrate feeding during exercise

Question 1

effects of carbohydrate feeding during exercise on performance

Answer 1

• endurance assessed in 61 studies
  
  • 0% reduced
  • 18% no effect
  • 82% improved

Question 2

fast and slow carbohydrates

Answer 2

“fast” and “slow” refers to the speed at which these carbohydrate types are digested, absorbed and made available to the body for energy provision
- fast: glucose, maltose, sucrose, maltodextrins, starches rich in amylopectin
- slow: fructose alone, galactose, isomaltose, starches rich in amylose

Question 3

classical guidelines for carbohydrate feeding during exercise

Answer 3

1.0g/min (60g/h) during exercise (some examples below)
- 1 L/h of a typical sports drink (6-7%
- 2 gels/h (containing 30g each)
- 0.5 litre sports drink plus 1 gel
- 80g of jelly babies (78g carb per 100g)

Question 4

updated carb guidelines

Answer 4

• new guidelines consider the duration (and intensity) of exercise
• they also give direction with respect to the type of carbohydrate to consume
• 30-75 mins - small amounts or mouth rinse - single or multiple transportable carbohydrates
• 1-2 hours - 30g/h - single or multiple transportable carbohydrates
• 2-3 hours - 6-g/h - single or multiple transportable carbohydrates
• > 2.5 hours - 90g/h - only multiple transportable carbohydrates

Question 5

carbohydrate feeding during exercise

Answer 5

• carbohydrate feeding during exercise of about 45 min or longer can improve endurance capacity and performance
• effects of carbohydrate feeding during exercise increase with exercise duration
• carbohydrate feeding may also benefit other aspects of sports performance:
  
  • e.g. motor skills during prolonged sports events

Question 6

metabolic effects (benefits) of carbohydrate feeding during exercise

Answer 6

• maintains plasma glucose concentration and helps to sustain high rates of carbohydrate oxidation
• spares liver glycogen (again, helping to sustain plasma glucose and carbohydrate oxidation)
• may spare muscle glycogen… although not often observed

Question 7

multiple transportable carbohydrates

Answer 7

• multiple transportable carbohydrates refers to sugars that are transported across the intestine by stimulating more than one protein transporter (e.g. glucose [via SGLT1] and fructose [via GLUT5]
• this can increase exogenous carbohydrate oxidation by 20-50% above single transported carbohydrates (and it can improve gut comfort)
• in prolonged, intense exercise (>2.5-3h), this can contribute to further performance enhancement

Question 8

speedy refueling after exercise

Answer 8

• early and frequent carbohydrate feeding (e.g., within the first hour and at 30 min intervals for 4 hours thereafter, before resuming normal diet)
• 1.2 g/kg CHO/h for first 4 hours, of moderate to high glycaemic index CHO’s
  
  • addition of protein if CHO intake is sub optimal (but probably some protein anyway for stimulation of MPS)

Question 9

carbohydrate type and short term exercise recovery

Answer 9

• the replenishment of glycogen stores can be accelerated when fructose is co-ingested alongside glucose-based carbohydrates
• fructose co-ingested with glucose in recovery from exercise can also enhance subsequent time-to-fatigue