Transcript Muscles

Muscle Responses to Training
Objectives:
 Define key terms hyperplasia,
hypertrophy.
 Explain how training increases
muscle strength
Homework:
Long Answer Question:
A tennis player needs to use their muscles to exert
different amounts of force throughout a match.
Use your knowledge of muscle contraction to explain
how this is possible.
(12 marks)
A tennis player needs to use their muscles to exert
different amounts of force throughout a match.
Use your knowledge of muscle contraction to explain how
this is possible.
(12 marks)
What should be included in a good answer?
• mechanism of muscle contraction – sliding filament
theory
• different fibre types
•explanation of motor unit
• methods of changing amount of force:
• number of units recruited
• type of units recruited
• frequency of stimulation
Mechanism of muscle contraction
• Action potential arrives at neuromuscular junction
• ACH released
• Binds to receptors on sarcolemma
• wave of depolarisation in muscle
• t-tubules
• Sarcoplasmic reticulum releases Ca2+
• Ca2+ binds to troponin
• moves tropomyosin
• this leaves the binding sites on the actin free
• Myosin heads attach to actin binding site to form cross bridges
• ATP required to form cross bridge.
• Myosin head moves towards the centre/power stroke occurs
• Actin slides over the myosin/actin moves towards the centre of
the sarcomere
• Cross bridge then broken but can be recreated if calcium ions are
still present
• ATP is also required to allow the myosin to break the cross bridge
• Muscle shortens and movement generates force
•Max 7
Different fibre types:
• Type I / slow twitch fibres are aerobic
• contract slowly
• do not fatigue
• produce low force
• Type II b / Fast Glycolytic fibres are anaerobic
• contract quickly
• produce high / highest force
• fatigue quickly
• Type IIa / Fast Oxidative fibres are anaerobic
• Contract quickly
• Have some resistance to fatigue
•Max 5
Explanation of motor unit
• Each nerve innervates a number of muscle fibres /
definition of motor unit
• Same type of fibre in each motor unit
• All or None / Nothing law
Methods of changing amount of force:
• more units recruited means more force
• larger units recruited means more force
• ST units produce lowest force / FT units produce highest
force
• All units recruited for maximum force.
•Max 5
Frequency of stimulation:
• Single nerve impulse produces twitch
• Wave summation – several impulses in quick succession
increases strength of contraction
• Tetanic contraction – sustained stimulation reaches
maximum force of contraction but fatigues quickly
• Spatial summation – different motor units contracted at
different times to maintain level of force without fatigue.
Max 6
What happens in / to your
muscles when you train?
It depends…
What does it depend on?
Type of training
Type of muscle fibre
Nature vs Nurture
Aerobic Training of Type I fibres
• Muscle fibre hypertrophy (fibres get larger)
•
in mitochondrial size and density
•
in activity of oxidative (aerobic) enzymes
•
in muscle myoglobin
•
triglyceride and glycogen stores
•
capillarisation
Resistance training of Type II fibres
• Hypertrophy of Type II fibres
• Hyperplasia (splitting and production of new) of Type
II fibres
•
activity of glycolytic (anaerobic) enzymes
•
muscle ATP and PC stores
• Improved buffering capacity (tolerance of lactic acid)
Aerobic Training of Type II Fibres
• Conversion of Type IIb fibres to Type IIa fibres
through:
•
mitochondrial density
•
capillarisation
•
triglyceride stores
•
myoglobin
CELLULAR ADAPTATION PRODUCED BY AEROBIC
TRAINING
BEFORE
TRAINING
glycogen
fats
oxygen uptake
AFTER SEVERAL WEEKS
OF AEROBIC TRAINING
glycogen
fats
oxygen uptake
= SLOW TWITCH MUSCLE FIBRE (type I)
= FAST TWITCH MUSCLE FIBRE (type II) (do not increase in size)
CELLULAR ADAPTATIONS PRODUCED BY STRENGTH
TRAINING
MUSCLE CELL
BEFORE TRAINING
ATP
PC
glycogen
glycolytic
enzymes
lactic acid
AFTER SEVERAL WEEKS OF
STRENGTH (ANAEROBIC)
TRAINING
ATP
PC
glycogen
glycolytic
enzymes
lactic acid
= SLOW TWITCH MUSCLE FIBRE (type I) (starts small gets smaller)
= FAST TWITCH MUSCLE FIBRE (type II) (starts big gets bigger)
Read the review article on the evidence
for hyperplasia
Pick out what you think are the 5 most
important/interesting/relevant pieces
of evidence supporting the occurrence
of muscle hyperplasia.
A2 revision guide