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Exercise Nutrition > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

What are simple CHO - monosaccharides

A

Monosaccharides
Basic unit

  • Glucose: muscles use directly
  • Galactose: needs to be converted to glucose
  • Fructose: needs to be converted to glucose
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2
Q

What are simple CHO - disaccharides

A
  • Sucrose (table sugar): glucose & fructose
  • Lactose: glucose & galactose
  • Maltose: two glucose
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3
Q

What are complex CHO

A

Includes oligosaccharides & polysaccharides

  • Starch: storage CHO in plants
  • Glycogen: storage CHO in animals
  • Fibre: plant part which is not broken down
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4
Q

What is the breakdown process of CHO

A

Ingestion -> small intestine (breakdown: amylase, sucrase & lactase) -> absorption -> blood glucose in blood stream -> liver glycogen & muscle glycogen

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5
Q

How does CHO enter the muscle

A
  • The glucose travel into the cell using the GLUT4 transporter
  • Hexokinase converts the glucose into glucose-6-phosphate
  • Glucose6-phosphate cannot reconvert into glucose to exit muscle
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6
Q

How does CHO enter the liver

A
  • Glucose travels into the liver cell using the GLUT4 transporter
  • Hexokinase converts the glucose into glucose-6-phosphate
  • Glucose-6-phosphatase can convert glucose-6-phosphate into glucose to be transported into the bloodstream
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7
Q

What is the normal blood glucose range and what happens when blood glucose is too low or high

A

Glucose range: 4-6 mmol/L

High blood glucose

  • When we ingest carbohydrate our blood glucose range increase
  • Insulin is released to store glucose as glycogen in the liver and muscle
  • Blood glucose will then fall into its appropriate ranges

Low blood glucose
- If our blood glucose level is low, the pancreas will release glucagon to transport glycogen from liver into blood stream as glucose

Other factors of blood glucose regulation

  • Growth hormone
  • Cortisol
  • Catecholamines
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8
Q

What is muscle glycogen

- Fuel source

A
  • Optimal fuel source for high intensity training
  • Preferentially use this fuel source when the energetic demands on the muscle exceed the capacity for energy provision by fat sources
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9
Q

Muscle glycogen and exercise intensity

A
  • Very high intensities - rapid breakdown of muscle glycogen (won’t last for long)
  • As intensity decreased - breakdown of muscle glycogen decreases as other fuel sources are also used
    • Exercise longer at lower intensities
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10
Q

Liver glycogen and exercise intensity

A
  • The higher the intensity the higher the liver glucose output
  • For higher intensities, there is rapid breakdown of muscle glycogen which is why the liver glucose output is higher as a means to maintain glucose levels
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11
Q

CHO intake before exercise

  • Goals
  • Supercompensation
  • CHO loading
  • Supercompensation consideration
A

GOALS - Preparing the muscle
CHO feeding in the DAYS prior to competition
- Replenish muscle glycogen stores
- Maximise muscle glycogen stores

SUPERCOMPENSATION - modified regime (1981 Sherman & colleagues)
Best process
- Mixed diet for first 3 days (50% CHO) then high CHO (70%) – moderate supercompensation
* High muscle glycogen stores
* 204 mmol/kg w.w
(without the negative effects of the classic supercompensation)
Training - Slowly reduced their training over a 6 day period – all the way down to complete rest the day before comp

CHO loading

  • Increase endurance performance by 20%
  • Reduces time to complete a task by 2-3%
  • Exercise duration: > 90mins

Supercompensation consideration

  • For every gram of CHO is stored with approx. 3 g of water
  • Example: storage of 500g of CHO is accompanied by an increase in body mass of approx. 2 kg
  • Needs to be considered in sports in which athletes compete in weight categories
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12
Q

CHO intake 3-5 hrs before exercise

A

GOAL- Preparing the muscle…
CHO feeding in the HOURS prior to competition
- Predominately optimise liver glycogen stores

CHO in the hours prior to exercise
- 3-5 hrs before comp (140 - 330g CHO) – fairly large meal
* Usually breakfast - Important after an overnight fast
+ Liver almost depleted of glycogen
* Increase liver and some muscle glycogen
* Hargreaves and colleagues, 2004:
+ Improves exercise performance

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13
Q

CHO intake 30-60 min before exercise

  • Goals
  • Rebound of reactive hypoglycaemia
  • Strategies to minimize change in plasma glucose and ingested CHO
A

GOALS
- Increased plasma glucose and insulin

Onset of exercise – rapid fall in blood glucose
- Rebound of reactive hypoglycaemia

Rebound of reactive hypoglycaemia

  • When consuming CHO 30-60 mins prior exercise it causes hyperglycaemia which results in hyperinsulinemia
  • Hyperinsulinemia then causes a rapid decrease in blood glucose
  • Once exercise begins contractile activity of muscles stimulate further glucose uptake (causing decrease in blood glucose)
  • Normally with exercise liver will release glucose to bloodstream but in this case exercise induced increase in the normal liver glucose output is inhibited with CHO ingestion
  • Early studies: detrimental to exercise performance
  • Recent studies: Not detrimental
Strategies to minimize change in plasma glucose and ingested CHO
 - Fructose 
- CHO with low GI
- Varying the CHO load 
- Ingestion schedule 
- Addition of fat 
- Warm up 
(these strategies modify the metabolic response to exercise & blunt the pre-exercise glyceamic and insulinemic responses)
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14
Q

Glycaemic Index and factors that determine glycaemic response during exercise

A

Increase in BG and insulin in response to food

Factors that determine the glycaemic response during exercise:

  • Insulin and contractile activity – stimulatory effects
  • Balance of inhibitory and stimulatory effects of insulin and catecholamine
  • Magnitude of ongoing intestinal absorption of glucose from ingested CHO
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15
Q

CHO intake during exercise
- CHO feeding in 45 min or longer

  • Maintaining blood glucose and high rates of CHO oxidation
  • Glycogen sparing in the liver and possibly muscle
  • Promoting glycogen synthesis during exercise
  • Affecting motor skills
  • Affecting the central nervous system
A

CHO feeding in 45 min or longer
- Improved endurance capacity and performance

Maintaining blood glucose and high rates of CHO oxidation

  • Blood glucose: maintain exercise for longer & higher plasma glucose level after exercise
  • CHO oxidation: maintain exercise for longer

Glycogen sparing in the liver and possibly muscle
- When CHO intake causes a rise in blood glucose which gets used and liver and muscle glycogen is “spared” (not used)

Promoting glycogen synthesis during exercise
- Intermediate exercise: increased muscle glycogen

Affecting motor skills
- Some evidence to suggest an improvement in motor skills

Affecting the central nervous system

  • No direct evidence
  • Support for CNS effect
    • Positive effects of CHO during exercise on performance lasting approx. 1 hour
    • Rinsing mouth with CHO
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16
Q

Feeding strategies

- Amount based on oxidation rate

A

When considering the amount the goal should be to achieve maximal oxidation rates without causing GI problems

  • Simple sugars oxidize at a rate of 1g/min
  • Maximal oxidation rate is 1-1.2g/min or 60g/hr
  • Anything above will sit in stomach -> negative performance

During exercise

  • Simple Sugars
  • No more then 60g/hr
17
Q

Types of CHO

  • High
  • Low
A

High oxidation rate: 1 g/min

  • Glucose
  • Sucrose
  • Maltose
  • Maltodextrin (from starch breakdown)
  • Amylopectin (from starch breakdown)

Low: 0.6g/min

  • Fructose (needs to be converted to glucose in the liver)
  • Galactose
  • Isomaltulose (honey and sugarcane)
  • Trehalose
  • Amylose (from starch breakdown)

Combination of glucose and fructose increases oxidation rate

18
Q

Exercise Intensity and the VO2 max that oxidation stops

A
  • Increasing exercise intensity the muscle becomes more dependent on CHO for energy
  • Low CHO oxidation rates have been observed at very low exercise intensities when energy reliance from CHO is at a minimum
  • Above 60% VO max oxidation rates will not increase any further
19
Q

CHO after exercise

  • Goal
  • Glucose uptake & glycogen synthesis (process and the stimulation of Glut4)
  • How does CHO enter the muscle
  • Rate of glycogen synthesis depends on
A

Goal
- Replenish depleted stores of liver and muscle glycogen

Glucose uptake & glycogen synthesis

  • Glucose uptake in the muscle through facilitated diffusion by the glucose transporter GLUT4
  • Transports glucose across the sarcolemma

Stimulation of GLUT 4

  • Muscle contraction
  • Insulin secretion

How does CHO enter the muscle

  • GLUT4 sits in the cytosol of cell until it is stimulated by which it moves to the cell membrane to allow glucose to pass through

The rate of glycogen synthesis depends on:

  • Availability of glucose
  • Transport of glucose into the cell which then depends on
    • Prior exercise
    • Insulin concentration
    • Muscle glycogen content
  • Activity of enzymes
20
Q

2 phases - Rapid & Slow glycogen synthesis after exercise

A

Rapid

Glycogen synthase

  • Active I-form: exercise activates glycogen synthase (80% of glycogen synthase is in active I-form)
  • Inactive D-form

First hr after exercise

  • Increased GLUT 4 at the cell membrane facilitating glucose uptake into the muscle
  • Reduced muscle glycogen (enhanced glucose uptake may last longer)

Slow

  • Reduced exercise induced increase in glucose transport wears off
  • Reduced glycogen synthase activity as muscle glycogen levels increase

Glycogen synthesis depends on:

  • Circulating insulin: increases GLUT4 translocation into the cell membrane
  • Muscle contraction: increases insulin sensitivity
21
Q

Post-exercise feeding

  • Timing
  • Window of opportunity
  • Amount
  • Rate of CHO
  • Type of CHO ingestion
A

Timing

  • 2 hrs post exercise: 3-4 mmol/kg w.w
  • Immediately post: 5-6mmol/kg w.w

Window of opportunity

  • 1-hr after exercise - rapid glycogen synthesis - replenish muscle glycogen stores
  • Simple sugars

Amount

  • Glycogen synthesis is rapid if intake is around 1.2 g/min
  • Immediate recovery (0-4hrs) : 1.0-1.2 g/kg/hr

Rate of CHO

  • when you consume no CHO -> slow synthesis rate: 1-2 mmol/kg w.w
  • CHO first hr after exercise -> 4.5 to 11 mmol/kg w.w./h.

Type of CHO ingestion

  • Simple CHO (glucose or sucrose is best)
  • After 6 hours of recovery, muscle glycogen is best restored with a high-GI meal compared with a low-GI meal
22
Q

Protein and CHO ingestion after exercise

A
  • Protein added to CHO increases muscle glycogen synthesis

- Benefits of protein is higher when CHO intake is low

Exercise Nutrition (9 decks)

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