Download Slow twitch or Fast twitch?

Sports Physiology
• Exercise Physiology
• Improvements through training
Muscle Fiber Type
• Slow Twitch
(Endurance)
• Fast Twitch a
(Intermediate)
• Fast Twitch b
(Sprints)
Make-up of calf muscle…a comparison
Marathon runner - 90% Slow Twitch
Sprinter
- 25% Slow Twitch
Slow Twitch, Fast Twitcha, Fast Twitchb
comparison
ST
FT a
FT b
Oxydative Capacity
High
Moderately High
Low
Glycolytic Capacity
Low
High
Highest
Contraction Speed
Slow
Fast
Fast
Fatigue Resistance
High
Moderate
Low
Muscle Fiber
Low
High
High
Strength
Let’s Play the Muscle Fiber Game!
Slow twitch or Fast twitch?
I – Slow-twitch
II – Fast-Twitch
Energy Systems
(source of ATP for cross bridge formation)
• Phosphagen System (10 seconds)
– Stored ATP – 3 secs
– Phosphocreatine – 7 secs
4 moles ATP/min
• Glycolytic System (1-2 minutes)
– Glycolysis
2 moles ATP/min
– Inefficient but fast
– Buildup of Lactic acid – must be buffered
• Oxydative (aerobic) (indefinite)
– Very efficient
1 mole ATP/min
Capacity of Energy System vs. Exercise Duration
Fiber Type Recruitment Order
(As you increase the effort you recruit more numbers of fibers but
what about fiber type?)
• Low intensity (walk; slow jog)
slow twitch
• Medium intensity (fast jog; run)
slow twitchfast twitch a
• High intensity (run; sprint)
slow twitch & fast twitch a  fast twitch b
Oxygen and Fuel
• Oxygen
• From blood
• Stored bound to myoglobin
• Fuel
– Glucose
• From blood (liver make it from glycogen)
• Stored in muscle (glycogen)
• Fast delivery rate
– Fat
• Very abundant energy source!
• Slow delivery rate
– Protein
• Abundant but not ideal source
• Slow delivery rate
Oxygen Debt
Tchotchke,
Tchotcholate
Tchallenge!
Assuming no change in physical activity,
what would happen to the partial pressure of
oxygen in veins of the systemic circulatory
system if cardiac output were increased by a
factor of 2?
Fatique
• Energy Depletion
– Phosphocreatine (short, hard efforts)
– Glycogen Depletion (longer efforts)
• Buildup of Metabolic Byproducts
– Lactic acid
• Inhibits glycolytic enzymes
• Inhibits crossbridge formation (H+ interferes)
• Nervous System
– Mostly Psychological***
Can I Keep Going?
Endurance Training
•
•
•
•
•
Increased Vascularization – more capillaries
Increased Myoglobin
More Mitochondria
More Oxydative Enzymes
Psychological factors
– Become comfortable with/embrace pain &
discomfort
Anaerobic Training
(increase Anaerobic Threshold and increase
Anaerobic Capacity)
• More Glycolytic Enzymes
• Increased Capacity for Lactic Acid
– More blood
– More bicarbonate
– Increased ability of liver to metabolize lactic
acid
• Psychological Factors
– Deal with Pain
A common nonsense polymorphism (R577X) in the ACTN3 gene results in
complete deficiency of the fast skeletal muscle fiber protein a-actinin-3 in an
estimated one billion humans worldwide. The XX null genotype is underrepresented in elite sprint athletes, associated with reduced muscle strength
and sprint performance in non-athletes, and is over-represented in endurance
athletes, suggesting that a-actinin-3 deficiency increases muscle endurance at
the cost of power generation. Here we report that muscle from Actn3 knockout
mice displays reduced force generation, consistent with results from human
association studies. Detailed analysis of knockout mouse muscle reveals
reduced fast fiber diameter, increased activity of multiple enzymes in the
aerobic metabolic pathway, altered contractile properties, and enhanced
recovery from fatigue, suggesting a shift in the properties of fast fibers towards
those characteristic of slow fibers. These findings provide the first mechanistic
explanation for the reported associations between R577X and human athletic
performance and muscle function.
A common nonsense polymorphism (R577X) in the ACTN3 gene results in
complete deficiency of the fast skeletal muscle fiber protein a-actinin-3 in an
estimated one billion humans worldwide. The XX null genotype is underrepresented in elite sprint athletes, associated with reduced muscle strength
and sprint performance in non-athletes, and is over-represented in endurance
athletes, suggesting that a-actinin-3 deficiency increases muscle endurance at
the cost of power generation. Here we report that muscle from Actn3 knockout
mice displays reduced force generation, consistent with results from human
association studies. Detailed analysis of knockout mouse muscle reveals
reduced fast fiber diameter, increased activity of multiple enzymes in the
aerobic metabolic pathway, altered contractile properties, and enhanced
recovery from fatigue, suggesting a shift in the properties of fast fibers
towards those characteristic of slow fibers. These findings provide the first
mechanistic explanation for the reported associations between R577X and
human athletic performance and muscle function.
Cost of
Transport
1 m/sec = 2.24 miles/hr
Human
Nature 432, 345-352 (18
November 2004) |
doi:10.1038/nature03052;
Received 25 July 2004;
Accepted 23 September
2004
Endurance running and
the evolution of Homo
H. erectus
Dennis M. Bramble1 and
Daniel E. Lieberman2
Chimp
A.afarensis