Transcript L23_Exercise

Muscle Cells and Contraction
mitochondria
sarcoplasmic
reticulum
contractile filaments
Muscle Types
• Type I - “Red”, “Slow”
– Contracts relatively slowly
– Many mitochondria
– Good blood supply
• Type IIb - “White”, Fast”
– Contracts relatively rapidly
– Few mitochondria
– Poor blood supply
– Packed full of contractile filaments
Gentle exercise
• Type I muscles recruited
– good blood supply, heaps of mitochondria
• Most readily available fuel is glucose
– Glucose transporters move to cell surface
BLOOD
MUSCLE
glucose
glucose
glucose
Transporters
Consequences of Glucose
Usage
• Muscle glucose uptake leads to a
decrease in blood glucose
concentration
• Need to keep blood glucose
constant!
– Small change in blood glucose causes...
insulin
glucagon
Effects of Low Insulin and High
Glucagon
– Stimulation of glycogen breakdown in liver
– Stimulation of fat breakdown in white adipose
tissue
LIVER
WAT
GLYCOGEN
FAT
glucose
fatty acids
fatty acids
glucose
Glucose Recycling
• Glucose stores (glycogen) are
limited
– Cannot convert fatty acids into glucose
• GLUCOSE CONSERVATION AND
RECYCLING
– Fatty acids substitute for glucose as a fuel
– Fatty acids prevent glucose from being
wastefully oxidised
Fatty Acid and Glucose Oxidation
glucose
GLYCOLYSIS
pyruvate
fatty acids
FATTY ACID
OXIDATION
acetyl CoA
CO
2
Fatty Acid Oxidation inhibits
Glucose Oxidation
glucose
to liver
GLYCOLYSIS
pyruvate
inhibits
fatty acids
FATTY ACID
OXIDATION
acetyl CoA
CO
2
lactate
Summary of Gentle Exercise
– Initially, glucose is used
– Then fatty acids take over and glucose is recycled
LIVER
GLYCOGEN
lactate
MUSCLE
glucose
WAT
lactate
FAT
glucose
CO2
fatty acids
fatty acids
CO2
Moderate Exercise
• As the pace increases, the rate of
fatty acid utilisation increases, but....
– The enzymes that catalyse fatty acid oxidation
soon reach their maximum capacity
– During running, fatty acid oxidation alone is
not sufficient to maintain ATP production
– Inhibition on glucose oxidation is removed
• Glucose oxidation occurs!
• Less glucose recycling
• Liver glycogen stores depleted faster
Summary of Moderate Exercise
LIVER
GLYCOGEN
lactate
MUSCLE
glucose
WAT
lactate
FAT
glucose
fatty acids
fatty acids
CO2
Strenuous Exercise
– As the intensity of the exercise increases
further, muscle glycogen is broken down.
LIVER
GLYCOGEN
lactate
glucose
WAT
MUSCLE
GLYCOGEN
FAT
glucose
fatty acids
fatty acids
CO2
Glycogen Depletion during a
Marathon Race
Glycogen (mg/g)
100
75
slower
50
25
faster
0
0.0
0.5
1.0
1.5
2.0
Time (hours)
2.5
Why Glycogen is Important
• When glycogen has run out, only
fatty acid oxidation can be used for
ATP generation
• Power output is lower when using
only fatty acids
• “Hitting the Wall”
• Cannot sprint if there’s no glycogen
Strategies
• Start the event with more
glycogen than your competitors
• Spare the glycogen by making
more use of fatty acids
• Use fatty acids sooner so less
glycogen is used in the early
stages
Glycogen Supercompensation
– After extensive
depletion,
glycogen
resynthesis
overshoots.
100
75
50
pre-exercise
level
25
0
0
1
2
3
Time (days)
4
5
Glycogen Loading - Classical
100
– Interrupts training!
– Potentially
dangerous
– Uncomfortable
– Character building!
75
50
HiFAT
HiCHO
25
0
0
1
2
3
Time (days)
4
5
Glycogen Loading - Tapered
• Fits well into
normal training
• No dangerous full
glycogen
depletion.
100
75
50
always High Carbohydrate
25
0
0
1
2
3
Time (days)
4
5
Glycogen Sparing
• Increase the use of fatty acids
– Carnitine helps fatty acids enter
mitochondria
– Training increases the activity of fatty acid
oxidation enzymes
• Start fatty acid release from White
Adipose Tissue early
– Strong cup of coffee!
– NOT glucose drinks BEFORE an event
insulin
glucagon
= inhibition of fatty acid release
Fitness
• Better cardiovascular system
• Increased vascularisation of
muscles
– better oxygen supply
– better fuel supply (especially fatty acids)
• More mitochondria
– Higher capacity to burn fatty acids
• Conversion of Type IIb to Type I?
Sprinting
• Uses Type IIb muscles
– Poor blood supply
– Packed full of contractile filaments
– Few mitochondria
– VERY rapid consumption of ATP
• Fuel selection problem
– Fatty acids?
» oxygen supply, mitochondria
– Blood Glucose?
» transporter recruitment, blood supply
Anaerobic Glycogen Utilisation
GLYCOGEN
GLYCOLYSIS
ADP
ATP
pyruvate
acetyl CoA
lactate
to blood stream
• Inefficient and
incomplete
• High turnover
• Accumulation of
lactate
• Takes time to
stimulate
glycogen
breakdown
Buying time with Creatine
Phosphate
creatine phosphate + ADP  ATP + creatine
• Less than 5 seconds supply of
creatine phosphate
– Enough to get glycogen mobilisation going
• Adrenaline stimulates massive
glycogen breakdown.
Fatigue
• Role of lactate??
• Acidity interferes with many processes
– Enzymes involved in glycolysis
– Contractile process
– Calcium movements
• All very controversial!
– But one things for sure: very low pH and running
out of glycogen are definitely bad news
– OK, so that was TWO things…
Fatigue 2
• Use pH buffers?
– Bicarbonate widely used
– Certainly works but check with doctor first!
• Does glycogen ever run out in a
sprint?
– Not in short events (100 m)
– Important in longer events and multi-heat
competitions
Does Glycogen run out during
Sprinting?
100
• Have to ensure
adequate glycogen
resynthesis between
races
• Rapidly absorbed
carbohydrate
75
50
25
depleted
0
0
1
2
3
Time (hours)
4
5
Sprint Training
• Increased power output
– Increased cell size
– More contractile filaments
– STEROIDS!
• Co-ordination
• Conversion of Type I to Type IIb?
• Adequate glycogen stores
Lessons
• Muscle Contraction
– Muscle Types
• Getting energy from fat and
carbohydrate
– No work, no energy consumption!
– Increase work, increased oxidation of fuel
• Fuel mix during....
– Walking, Jogging, Running and Sprinting
• Training effects
How the Fuel Mix Changes
LIGHT
INTENSE
Fatty acids
CO2
Fatty acids
CO2
Fatty acids
CO2
Glucose
CO2
Glycogen
CO2
Glycogen
lactate
MODERATE
Fatty acids
CO2
Glucose
CO2
Fatty acids
CO2
Glucose
CO2
SPRINTING
Creatine P
creatine
Glycogen
lactate
Take Home Message!
• Glycogen is an important fuel to
all athletes
– Using fatty acids quickly and copiously
reduces the use of valuable glycogen
• Carbohydrate intake has to be
high to allow adequate glycogen
synthesis