Carbohydrate Intake and Athletic Performance

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Carbohydrate Intake and Athletic Performance
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How much carbohydrate do athletes need to eat?
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What do you need the CHO for?
At rest, brain/nerve cells use about 7 grams/hr
150g but 50 from gluconeogenesis so need to eat
75g Other use (muscle cells, fat cells, etc.
using glucose after a meal) plus general out and
about 125-150g Total about 200-225
grams Physical activity 30 minutes of easy
walking about 25 grams 45 minutes of moderate
running about 75 grams 60 minutes of hard
running 125 grams 120 minutes of interval
running 200 grams
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How much CHO do we have in our bodies? An average
70 kg male has 1500-1600 kcal of CHO stored in
the liver and muscle glycogen and circulating
blood glucose. Muscle 1200 kcal 30g Liver
320kcal 80g Blood Glucose 20 kcal 5g
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• So, athletes need to consume
• approximately
• 225g (100-300g) 325-625g CHO
• The daily recommended intake for athletes
• is 5-10 g of CHO per kg of body weight.
• Ex 70 kg 350-700g CHO (1400-2800 kcal)
• This is 60 of a 2500 kcal - 5000 kcal diet
• (athlete in training).

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Sources of Carbohydrate
Monosaccharide Glucose, fructose, galactose
Disaccharides Table sugar sucrose Milk sugar
lactose Corn syrup glucose/fructose
Complex Carbohydrates STARCH-plants store extra
CHO in the form of starch.
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High Glycemic Index CHO enters the blood from
the gut quickly. They are easy to digest/ absorb
and enter the circulation within minutes. Ex
Source g/serving Gatorade 8oz14g Cornflakes
3/4cup25g Honey 1tbsp15g
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• Low/Mod GI CHO enter the bloodstream more
• slowly. They must be broken down first by
• digestive enzymes before being absorbed.
• (generally have a higher fiber content).
• MOD
• Rice 1cup45g
• Pasta 1cup40g
• Banana 1med25g
• LOW
• Apple 1med20g
• Choc milk 8oz25g
• Yogurt 1cup50g

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CHO Intake Fuels Exercise

• The average American consumes 45 of their daily
  calories as CHO.
• 60 seems like a lot!

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• CHO intake influences liver and muscle glycogen
  stores.
• Glycogen levels affect endurance performance.
• Decreased glycogen hasnt shown a decrease in
  performance time but does show increases in the
  perception of fatigue.
• Runners consuming 40 of energy from CHO could
  not replenish muscle glycogen on a daily basis
  whereas runners on a 70 CHO diet could. (Costill
  et al.)

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Costill et al.
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CHO Intake Before an Event

• So if CHO is good, is more better?
• Is there any evidence in the literature that
• increasing CHO consumption will increase
• muscle glycogen levels?
• And, if you increase your glycogen stores,
• does this have any impact on performance?

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How do athletes increase their muscle glycogen
stores?

• Supercompensation involves swelling muscle
  glycogen by changing diet and exercise patterns
  several days before a major competitive event.
• 2 techniques
• 1. depletion/repletion
• 2. Modified moderate approach
• 1. Depletion/repletion
• - depleting glycogen reserves as much as
  possible through a combination of an extremely
  long bout of exercise about 7-10 days prior to a
  major competition, followed by a few days on a
  very low-CHO diet. Another bout of exercise on
  the 4th day and then 3 days of a high CHO diet.

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• Muscle glycogen stores can be greatly increased,
  often by as much as 50 over the usual full
  condition (e.g. from 300 ? over 400 grams).
• If it costs 100 kcal to run a mile, and 60 of
  energy comes from muscle glycogen 60 kcal of
  glycogen mile 15 g glycogen needed /mile. If
  you start with 300 grams you can run 20 miles
  before running out.
• If increase to 400g, can extend run to 26.5
  miles.

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• 2. More popular approach is to taper training
  the week before competition while increasing the
  CHO in diet (e.g. from 50-60 up to 70-75).
• Although increases in muscle glycogen are not as
  dramatic as with the depletion/repletion
  approach, increases of perhaps 20 are possible
  (300g ? 350g)
• Benefits from CHO loading
• Increases time to exhaustion
• Reduces the time to complete a task
• (time trial endurance by 2-3)
• May improve performance in team sports that
  involve intermittent exercise and skill
  executions.

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The downside to CHO loading/muscle glycogen
supercompensation Only good for a one-time ultra
distance event (marathon). A cyclist riding over
several days would not see benefits...consecutive
competition days are not improved with this
protocol. Every gram of CHO is stored with 3g of
water. This means that the storage of 500g of CHO
is accompanied by a water weight gain of
approximately 2kg. This would not be good for
sports where an increase in body mass is not
desirable.
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CHO intake before exerciseGoal maxmize exercise
performance

• 3-5 hours this is usually breakfast ?
• Large meal to replenish liver glycogen
• Increase muscle glycogen stores

• Remember that the liver glycogen is used to
• Maintain blood glucose levels (its the brain
  food)
• Its decreased after an overnight fast.
• Its decreased by 50 after an hour of exercise
  at 75 VO2max.

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60-30 minutes before exercise...

• Top off liver glycogen
• Increase blood glucose levels, can be used as a
  substrate during exercise...or if intensity is
  low enough it will be used to synthesize muscle
  glycogen.
• Common belief ingesting High GI CHO right before
  exercise will create rebound hypoglycemia and
  decrease performance.
• Why?

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Rebound Hypoglycemia
Insulin release stimulated by glucose promotes
skeletal muscle glucose uptake. Exercise (muscle
contractions) also stimulate glucose
uptake...both are working...

• Hypoglycemia
• Dizziness, nausea, cold sweat...
• Decreased mental alertness
• Decreased motor skills
• Increased HR
• Hunger
• Disorientation

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• There is little evidence to support this
  hypothesis that performance is decreased...
• However, two strategies are widely used to
  prevent rebound hypoglycemia in athletes.
• Consuming lower GI CHO one hour before exercise
• If high GI CHO is consumed right before or at the
  onset of exercise, then there seems to be a
  benefit to maintaining carbohydrate intake during
  exercise.
• once on gatorade-stay on gatorade

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CHO during Exercise

• CHO consumption during exercise gt45min can
  improve performance.
• How?
• Maintain blood glucose and CHO oxidation rates.
• Spares liver glycogen.
• Synthesizes muscle glycogen during LOW intensity
  exercise
• Increases motor skills in prolonged periods of
  play.
• Feel better later into the exercise bout.

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• How much should I consume?
• 1.2g per minute, 70g/hour during endurance
  exercise...
• What should I drink?
• glucose polymer (gatoradegood)
• galactose,fructose-not so good, must first be
  converted to glucose by the liver to be used as a
  substrate.
• The delivery rate from the gut to the muscle
  tissue is 1.0g/min, as intensity increases blood
  flow to the digestive system decreases and there
  is a greater reliance on muscle glycogen as a
  fuel source.
• Choose drinks ranging from 4-8 CHO. Drinks with
  too much CHO (coke has 11.25 CHO) will not be
  absorbed as efficiently and could cause stomach
  upset.
• Remember that CHO replacement during exercise is
  not generally needed for activities lasting less
  than 90 minutes.

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CHO after exercise...

• GOAL To replenish muscle glycogen
• The rate of glycogen synthesis depends on glucose
  transport to the muscle and the enzymes involved
  in glycogen synthesis.
• Exercise increases
• - GLUT 4 (transporters)
• - glycogen synthase
• There are two phases of muscle glycogen
  replenishment after post-exercise CHO
  consumption
• Rapid (not dependent on insulin-but enhanced)
• Slow (gt3hrs, insulin dependent)

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CHO after exercise...

• Factors affecting glycogen synthesis
• Timing
• When CHO is delayed two hours muscle glycogen is
  45 lower compared to immediate consumption of
  the same amount.
• Rate of ingestion (amount) 0.7-1.0g CHO/kg
  consumed every two hours
• Type (High GI, vs. Low GI) High GI, large
  insulin release, more CHO storage
• Combo with protein

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Glycogen Synthesis
Once CHO needs are met, the effect of protein
supplementation does not enhance muscle glycogen
storage.
300
Glycogen synthesis relative to control
200
100

0.8 g/kg/hr CHO
0.8 g/kg/hr CHOPRO
1.2 g/kg/hr CHO
1.2 g/kg/hr CHOPRO
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What do I do if rode 35 miles and left my 2
drink and 3 bar at home?
The key to optimal recover is to create a
hormonal environment that is anabolic and
provides the necessary raw materials. Eating
foods high in CHO provides glucose and also
stimulates a large insulin response that
facilitates entry of glucose into cells and its
storage as glycogen. Maximizing the amount of
glycogen stored depends on both the quantity of
CHO and the insulin response in the short-term
(first 2-6 hours) there does appear to be an
advantage to consuming simple sugars rather than
complex CHO because the insulin response is
greater.
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Strength and Power Athletes

• We know CHO is great for increasing endurance
  performance but what about strength and power
  athletes, do they need CHO the same way?
• Higher intensity activities use muscle glycogen
  as a fuel source so adequate glycogen is
  necessary for performance.
• Glycogen super-compensation does not appear to
  increase performance once a certain intensity is
  reached.
• Supplementation is most advantageous for athletes
  involved in high intensity training regimes where
  time between sessions is limited lt20hours.