Muscle Cells and Contraction mitochondria contractile filaments sarcoplasmic reticulum.
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Transcript of Muscle Cells and Contraction mitochondria contractile filaments sarcoplasmic reticulum.
Muscle Cells and Contraction
mitochondria
contractile filaments
sarcoplasmic reticulum
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
glucose
BLOOD MUSCLE
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
FAT
fatty acids
GLYCOGEN
glucose
fatty acidsglucose
WATLIVER
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
acetyl CoA
CO2
pyruvate
fatty acids
GLYCOLYSIS
FATTY ACID OXIDATION
Fatty Acid Oxidation inhibits Glucose Oxidation
glucose
acetyl CoA
CO2
pyruvate
fatty acids
GLYCOLYSIS
FATTY ACID OXIDATION
lactate
to liver
inhibits
WAT
LIVER
Summary of Gentle Exercise
– Initially, glucose is used
– Then fatty acids take over and glucose is recycled
FAT
fatty acids fatty acids CO2
GLYCOGEN
glucose
glucoselactate
lactate
CO2
MUSCLE
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
WAT
LIVER
FAT
fatty acids fatty acids CO2
GLYCOGEN
glucose
glucoselactate
lactate MUSCLE
Strenuous Exercise–As the intensity of the exercise increases
further, muscle glycogen is broken down.
WAT
LIVER
FAT
fatty acids fatty acids CO2
GLYCOGEN
glucose
glucose
lactate MUSCLE
GLYCOGEN
Glycogen Depletion during a Marathon Race
0
25
50
75
100
0.0 0.5 1.0 1.5 2.0 2.5
Time (hours)
Gly
cog
en
(m
g/g
)
slower
faster
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.
0
25
50
75
100
0 1 2 3 4 5
Time (days)
pre-exercise level
Glycogen Loading - Classical
0
25
50
75
100
0 1 2 3 4 5
Time (days)
HiFAT HiCHO
– Interrupts training!
–Potentially dangerous
–Uncomfortable
–Character building!
Glycogen Loading - Tapered
0
25
50
75
100
0 1 2 3 4 5
Time (days)
• Fits well into normal training
• No dangerous full glycogen depletion.
always High Carbohydrate
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
• Inefficient and incomplete
• High turnover
• Accumulation of lactate
• Takes time to stimulate glycogen breakdown
GLYCOGEN
pyruvate
lactateacetyl CoA
GLYCOLYSISADP
ATP
to blood stream
Buying time with Creatine Phosphate
• Less than 5 seconds supply of creatine phosphate–Enough to get glycogen mobilisation going
• Adrenaline stimulates massive glycogen breakdown.
creatine phosphate + ADP ATP + creatine
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?
• Have to ensure adequate glycogen resynthesis between races
• Rapidly absorbed carbohydrate
0
25
50
75
100
0 1 2 3 4 5
Time (hours)
depleted
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 ChangesLIGHT INTENSE
MODERATE
Fatty acids CO2
Fatty acids CO2
Fatty acids CO2
Glucose CO2
Fatty acids CO2
Glucose CO2
Fatty acids CO2
Glucose CO2
Glycogen CO2
SPRINTING
Glycogen lactate
Glycogen lactate
Creatine P creatine
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