HLTH2200 Lecture Notes - Lecture 6: Myocyte, Mhc Class Ii, Skeletal Muscle
15 Jun 2018
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HLTH2200
LECTURE 6- 10/04/18
Neuromuscular Adaptations to Training
Outcomes
• Describe the adaptations in skeletal muscle to resistance and endurance training
• Define myoplasticity and describe the process by which it occurs
• Describe the differences in muscle fibre types
• Describe the adaptations that occur in skeletal muscle as a result of concurrent
resistance and endurance training
• Identify and describe the neural components of strength
Adaptations in skeletal muscle to resistance training
• Stimulated by large increase in activation frequency of large muscle fibres and large
increase in load.
o Load is the greater determinant
• Major adaptation is hypertrophy (increased quantity of protein)
o Increased CSA
▪ Not hyperplasia
• High resistance training results in an increase in the cross-sectional area of both type
1 type 2 muscle fibres , but type 2 the greatest probably due to the nature of the
training stimulus and increased responsiveness to the resistance stimulus in type 2
fibres
Adaptations in muscle structure to endurance training
• Stimulated by large increase in activation frequency but only moderate increase in
load
• Minimal increase in CSA
• Results in metabolic adaptations (increased mito and enzymes)
o Increased quality of protein
• Adaption depends on pre training state
o Sedentary individuals have a greater potential of endurance improvement
o The degree of motor unit responsiveness is dependant on the degree of
involvement of the motor unit in the training regime
▪ fibres must be recruited for a change to occur
Myosin Heavy Chain II (MHC II)
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2 o ot 2…
Fibre typing
• Fibre type, determined by
o Histochemical staining of ATPase activity (True fibre type)
o Immunohistochemical staining for Myosin heavy chain (MHC) isoforms
• 2 main types Type 1 and Type 2
o Each type is further divided into subtypes eg. Type 2a and 2b
• But… Tpe 2 does ot eist i huas
• Type 2x is the most glycolytic of the human muscle fibres
• Type 2 is dark, ATPase attaches
What is Myoplasticity?
• Myoplasticity refers specifically to the capacity of skeletal
muscle for adaptive change.
• Skeletal muscle adaptations are characterised by
modifications of morphological, biochemical and
molecular variables that alter the functional attributes of
fibres in specific motor units
• Protein comprises the a large component of skeletal muscle (20%)
o balance is water, ions etc
Myoplasticity - How?
• When gene expression is altered it results in an increase and /or a decrease in the
amount of specific muscle proteins
o +’e adaptatios result i ore effetie exercise
• Altered gene expression is the molecular basis for adaptations that occur as a result
of training or detraining
Myoplasticity
• Chemical messengers (protein complexes, hormones, signaling molecules etc) have
an important role in stimulating adaptations to exercise training
o Chemical messengers respond to physical and mechanical stress, neural
signals, metabolic, bioenergetic, hypoxic and temperature signals resulting
from aerobic or resistance exercise
Regulation of gene expression
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Regulation of gene expression
Human Muscle fibre types
• Neither method actually measures the metabolic nature of the fibre
• Training results in the increased expression of one MHC isoform compared to
another
• Training does not result in a true fibre type change.
• Type 1 can become more like a type 2 fibre but can never specifically become it
Myoplasticity
• Myoplastiity is prediated o the aility of the usle fire’s geeti ahiery to
change either the quantity (amount) or quality (specific type) of protein it expresses
o e.g. a muscle fibre (a fast IIx fibre) may undergo hypertrophy in response to
resistance training by increasing the amount of protein normally comprising
the fibre
o Or, a IIx fibre may not only enlarge in size but also repress the gene encoded
for expression of the fast IIx myosin heavy chain (MHC) while turning on the
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Document Summary
Identify and describe the neural components of strength. Adaptations in skeletal muscle to resistance training: stimulated by large increase in activation frequency of large muscle fibres and large increase in load, load is the greater determinant, major adaptation is hypertrophy (increased quantity of protein) Increased csa: not hyperplasia, high resistance training results in an increase in the cross-sectional area of both type. 1 type 2 muscle fibres , but type 2 the greatest probably due to the nature of the training stimulus and increased responsiveness to the resistance stimulus in type 2 fibres. Adaptations in muscle structure to endurance training: stimulated by large increase in activation frequency but only moderate increase in load, minimal increase in csa, results in metabolic adaptations (increased mito and enzymes) Fibre typing: fibre type, determined by, histochemical staining of atpase activity (true fibre type) Myoplasticity: factors that influence the muscle cell environment are: insufficient energy balance thyroid hormones insulin-like growth factor.
