History

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History

• Krogh and Lindhardt 1920
• RER change after high fat diet
• Levine, Gordon and Derick 1924
• Boston marathon, blood glucose decline
• Christensen 1932
• Exercise intensity increased, carbohydrate
  utilization increased
• Bergstrom and Hultman 1966-67
• Muscle biopsy technique
• Muscle glycogen
• Costill, Coyle, Sherman 1980s
• High carbohydrate diet vs endurance capacity
• Costill 1973
• Isotope technique

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Role of Carbohydrate

• Glycogen
• Muscle glycogen
• 1216 g/kg
• Liver glycogen 80100g
• Maintain blood glucose level
• Fuel for brain 0.1 g/min
• May down to lt 20 g after overnight fast
• Hepatic glucose output
• liver kidney

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Sources of blood glucose
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Hypoglycemia

• blood glucose lt 3 mM
• During exercise, when liver glycogen depleted
• Glucose production rate insufficient for glucose
  uptake by muscle
• Symptoms
• Rate of glucose uptake by brain insufficient
• Dizziness, nausea, cold sweat, reduced mental
  alertness, loss of motor skill, increased heart
  rate

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Carbohydrate Before Exercise

• Carbohydrate Supercompensation
• Carbohydrate loading ????
• Classic protocols
• Low CHO diet (25) for 3 days, followed by 3 days
  high CHO diet (75)
• Moderate protocols
• Mixed diet 3 days (50 CHO) followed by 3 days
  high CHO diet (70)
• During taper period, gradually decreased
  training 75VO2max for 90 min on 1st day, to
  complete rest on 6th day

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Classical vs moderate protocol
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Stage 1 100 g CHOstage 2 400-625 g CHO
(classical)
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Moderate protocol
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Carbohydrate Supercompensation

• Classic protocols disadvantages
• Hypoglycemia
• Practical problems
• GI problem
• Poor recovery
• Uncomfortable on training
• Mood disturbance

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Benefits

• 20 increases time to exhaustion
• ?2-3 in Time trial
• At least 90 min before the benefits
• Improve performance in team sports involving
  high-intensity intermittent exercise and skills
• Soccer, hockey
• No effect on Sprint performance, or repeated
  bouts of high-intensity ex
• Athletes in high-intensity training still need
  high CHO in diet
• Low CHO diet impaired endurance capacity

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CHO loading improve soccer performance
In second match (3 days after 1st match)
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Supercompensation Strategies in Sport

• Endurance sports
• Consecutive days
• May be difficult for supercompensation
• Marathon and triathlon
• High intensity exercise (95-100 VO2max) not a
  limit factor
• 1g glycogen 3g waterincrease mass

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Carbohydrate Intake 3-5 hour before Exercise

• Can ?muscle and liver glycogen
• CHO within 1 hr before exercise only ?liver
  glycogen
• Overnight fasting liver glycogen depleted
• CHO-rich meal (140-330 g)
• Bread, jam, honey, cereals, bananas, canned
  fruits, juice
• increase muscle glycogen (Coyle et al 1985)
• improved endurance performance (Neufer et al
  1987)
• For practice
• 200-300 g CHO 3-4 hours before exercise
• Especially when CHO is unavailable during exercise

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Carbohydrate Intake 3-5 hour before Exercise

• Transient fall in plasma glucose at onset of
  exercise
• ?CHO oxidation,?glycogenolysis
• Compensated by ?CHO availability
• Blunting FA mobilization and fat oxidation
• NO detrimental effect to exercise performance

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Carbohydrate Intake 30-60 min before Exercise

• Ingestion CHO Within 1 h before exercise
• Largely elevated blood glucose and insulin
• Transient fall in plasma glucose with the onset
  exercise
• Increased CHO oxidation rate
• Blunting of FA mobilization (insulin-mediated
  inhibition of lipolysis), and ?fat oxidation in
  muscle
• Transient fall in plasma glucose with the onset
  exercise
• Hyperinsulinemia
• Muscle contraction stimulate muscle glucose
  uptake
• Exercise-induced normal liver glycogen output
  inhibited by CHO ingestion
• Still improved endurance exercise performance
• Individual variations, try and error

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Carbohydrate Intake 30-60 min before Exercise

• Glycemic Index (GI)
• AUC (X) / AUC (glucose) x 100

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Carbohydrate during Exercise

• Ingestion CHO during exercise (gt45 min) improved
  endurance capacity and performance
• Mechanisms
• Maintaining blood glucose and high level of CHO
  oxidation
• Glycogen Sparing
• Promoting glycogen synthesis during exercise
• ?glycogen breakdown, ?glycogen syn in
  low-intensity ex
• Affecting motor skill
• Especially involving fast running, rapid
  movement, explosive
• Affecting the central nervous system

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Carbohydrate during Exercise

• Feeding schedule bolus vs intervals
• Little effect on exogenous CHO oxidation
• Amount of CHO
• Maximal exogenous CHO oxidation rate 1-1.2 g/min
• 70 g/h 1L sports drink 600 ml cola 3 banana
  1.5 power bar, energy bar
• Type of CHO
• Glucose, maltose, sucrose, maltodextrins up to
  1 g/min
• Fructose, galactose up to 0.6 g/min, usually GI
  discomfort
• Inclusion of 2-3 different CHO result in
  exogenous CHO oxidation rates 1.3 g/min
• Glucose, fructose, sucrose
• Separate transporters across intestinal wall

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Results in time trial and total power output
during the time trial
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Carbohydrate during Exercise

• Exercise intensity
• lt50VO2max, exogenous CHO oxidation rateincrease
  with increasing total CHO oxidation rate
• gt60VO2max, no further increase of CHO oxidation
• Limitation to Exogenous CHO oxidation
• Gastric emptying not a limiting factor
• Limited by rate of digestion, absorption,
  transport of glucose into systemic circulation
• gt 80 VO2max reduce blood flow to gut
• Hepatic glucose output highly regulated, if
  supply from intestine too large, glycogen
  synthesis may be stimulated in liver
• Infusion of glucose (gt 10 mM in blood) can make
  Exogenous CHO oxidation gtgt 1 g/min

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Metabolic effects of CHO intake during exercise

• CHO ingested at onset of exercise
• ? insulin in first minutes of exercise
• ?lipolysis, ? FA, ?fat oxidation rates
• Also ?transport of FA into mitochondria
• CHO ingested later during exercise
• Fat oxidation less affected because insulin
  release is inhibited by epinephrine

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Carbohydrate After Exercise

• Replenishment of muscle glycogen
• Regulation of Glucose uptake and Glycogen
  Synthesis
• Glucose uptake - GLUT-4
• Muscle contraction (Ca)
• Insulin secretion
• Glycogen synthesis depends on
• enzyme activity, especially glycogen synthase
• transport glucose into cell, influenced by muscle
  glycogen concentration and insulin

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Glycogen synthesis

• Rapid phase of glycogen synthesis
• Glycogen synthase Inactive D-form ? active I
  form
• Exercise, low muscle glycogen activate glycogen
  synthase
• GLUT-4 translocation last for only few hours in
  the absence of insulin
• When muscle glycogen level low, enhanced glucose
  uptake may last longer
• Slow phase of glycogen synthesis
• Depends on insulin concentration
• Muscle contraction increases insulin sensitivity,
  lasted for several hours
• Increased GLUT-4 expression

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Carbohydrate After Exercise

• Postexercise feeding and rapid recovery
• Glycogen resynthesis very low without CHO
  ingestion
• Timing of CHO intake
• As soon as possible after exercise
• Rate of CHO ingestion 1.4 g/min
• Type of CHO ingested High GI
• Especially in the first hours after exercise,
  ?glucose availability
• glycogen synthesis rate for fructose 50 of
  glucose
• Protein and CHO ingestion
• Additive effect, certain amino acids stimulate
  insulin secretion
• Some study showed no additional effect when CHO
  ingestion at 1.2 g/kg/h, some study showed
  addition effect even in high CHO intake
• Solid versus Liquid
• Similar results
• High-GI

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Post-exercise recovery
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CHO-PRO 1 g/kg CHO, 0.3 g/kg pro HCHO 1.3
g/kg CHO LCHO 1 g/kg CHO
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Carbohydrate After Exercise

• Muscle glycogen, diet and repeated days of
  training
• Glycogen recovery between exercise bouts
• Amount of CHO
• 10-13 g/kg/d when exercise for gt3 hr on daily
  basis
• Amount of CHO intake important in determining
  total amount of muscle glycogen stored
• High CHO intake during repeated days of training
  can also Reduce symptoms of overreaching
• such as changes in mood states, feelings of
  fatigue
• But can NOT prevent them
• High-GI during 24 hr post-exercise ?muscle
  glycogen by 50 compared to low-GI
• Higher insulin response

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Post-exercise recovery
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Carbohydrate After Exercise

• Recommendation for long-term recovery
• 5-7 g/kg during moderate intensity training
• 7-10 g/kg during prolonged hard training
• 10-13 g/kg during very prolonged very hard
  exercise
• High GI
• Use sports drink to provide convenient source of
  CHO at 1st hour after exercise

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Glycogen level and endurance training adaptation

• At same absolute level of training intensity,
  training with low muscle glycogen ?muscular
  adaptation to endurance exercise
• Higher perceived exertion
• If choose the training intensity by athletes
  themselves, they may train at lower intensity
• Endurance training with low glycogen ?AMPK, ? P38
  MAPK (mitogen-activated protein kinases), ?
  sympathetic nerve system
• ?peroxisome proliferator-activated receptor
  ?coactivator-1a (PGC-1a)
• activation of PGC-1a mediates the initial phase
  of the exercise-induced increase in mitochondria
• Trained hard and long enough in low glycogen?

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Other roles of PGC-1a
Czubryt MP, PNAS 2003
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PGC-1 promotes mitochondrial biogenesis in
cardiac myocytes

• Ad-GFP control Ad-PCG-1 overexpression of
  PCG-1
• Red-orange color mitochondria

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How to produce low glycogen

• 2 training sessions in 1 day, low CHO consumption
  after 1st session
• 2nd session will be in low glycogen state
• Chronically low CHO diet
• Replaced with fat, especially omega-3 PUFA
• Very hard to maintain training intensity

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Glycogen in different endurance training periods
- running

• Base phase (preparatory phase), best time for low
  glycogen strategy
• Trained at moderate intensity, ?aerobic
  adaptation
• Build up phase
• Maintain high glycogen before speed training
• Low glycogen before other types of training
• Consolidation phase
• Maintain high glycogen before speed training
• Incorporate low-glycogen 2nd session 2-3
  times/week
• Competition phase
• Maintain high glycogen at all times

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P38 MAPK pathway
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Glycogen in different endurance training periods
cycling, rowing

• Muscle mass, muscle strength also important
• Base phase (preparatory phase)
• High glycogen to promote muscle gain
• Build up phase
• Endurance training in morning following a low-CHO
  meal, low glycogen
• Strength training later in the day, after
  replenishment of CHO, protein,
• Consolidation phase
• Maintain high glycogen before speed training
• Incorporate low-glycogen 2nd session 2-3
  times/week
• Competition phase
• Maintain high glycogen at all times