CHO intake before & during exercise

Question 1

What are the recommendations of CHO ingestion before exercise?

Answer 1

Before Exercise> 60mins
1-4 g.kg-1 BM consumed
1-4h before exercise
- Very varied recommendations for grams of CHO
- Varied time period before exercise, depends on the amount and type of exercise

Question 2

What limits exogenous CHO oxidation?

Answer 2

• Gastric emptying does not limit exogenous CHO oxidation (Rehrer et al., 1992)
  
  • CHO oxidation did not change even when gastric emptying did
• Muscle glucose uptake does not limit exogenous CHO oxidation (Hawley et al., 1994)
  
  • Much increased CHO oxidation rates
• Intestinal CHO absorption appears to be the rate limiting step

Question 2

How effective is pre-exercise feeding?

Answer 2

• 10 males, 2 x 30km runs
• Trial 1 – 4h before CHO meal, water during exercise
  Trial 2 – 4h before placebo drink, CHO-E drink every 5km
• Blood glucose in fed, there is an increase, but then levels out
• During run feeding blood glucose is exogenous

Question 2

What are the aims of taking exogenous CHO?

Answer 2

• To provide an additional source of fuel
• To maximise oxidation rates
• To prevent gastrointestinal distress
• To maximise performance

Question 3

How is glucose absorbed?

Answer 3

Sodium glucose link transporter 1 - transports glucose
- Gets saturated at 1g per min
- Fructose uses different transporter, allowing CHO to still go through the system
- Glucose to fructose in 1:0.8 ratio transportation

Question 4

What is the effect of CHO mouth rinse?

Answer 4

• CHO or PLA rinse every 12.5%
• ~1 hr/~40km TT performance with or without CHO-E (7.6%)
• CHO Mouth rinse increased performance more than water due to the sensing in the brain
  As it detects that CHO is coming
• 30g of CHO in 500mL of a CHO drink

Question 5

What are the aims for CHO intake after exercise?

Answer 5

Recovery
* Ensure muscle and liver glycogen stores are restored
* The timing of this depends on when resynthesis is required
* Short v long recovery
* Immediate post-exercise meal/snack/drink
* 1-2 hours post-exercise
* Within 8 hours
* 24 hours
* General diet

Question 6

Describe the recovery of muscle glycogen: (timeframe)

Answer 6

Glycogen depletion during exercise
- Ingestion straight after exercise is much quicker
- In the first 10hrs there is the most muscle glycogen resynthesis

Question 7

Why is the timing of CHO important?

Answer 7

Delaying feeding by 2hrs after exercise - not much of an increase, no affinity to uptake glucose into the muscle
Immediately after exercise - there is a lot more replenishment of muscle glycogen

Question 8

What is the optimum intake of CHO for glycogen resynthesis?

Answer 8

1-1.2g/kg BM/h 2-4hrs

Question 9

How can ingesting CHO with protein further improve muscle glycogen resynthesis?

Answer 9

After 5hrs of exercise - insulin is much higher in CHO + protein trials
Addition of protein, due to leucine in protein helps to increase insulin