Skeletal Muscle
Principles of Skeletal Muscle Adaptations
Skeletal muscle fibre repair
• Mature adult skeletal muscle cells:
o Highly specialised
o Terminally differentiated
o Multinucleated
o Post-mitotic
o Cannot replicate but able to regenerate
(repair) and adapt
Adaptations to training and detraining
• The structure and function of skeletal muscle
adapts in response to repetitive use and disuse
o Use = physical activity
o Disuse = detraining, physical inactivity, zero gravity
• Changes dependent on:
o Type
o Intensity
o Duration of physical activity
• Neuromuscular system, musculoskeletal system and other biological systems also experience
adaptations
Adaptations to injury and ageing
• Injury = consequence of physical activity
• Injured muscles can repair or regenerate
• Skeletal muscles respond to spinal cord injuries and nerve damage
• Ageing also results in sarcopenia = adaptation to skeletal muscle
• Inter-individual variation in responses to training, detraining, regeneration, ageing
• Adaptation window – determined genetically
• Adaptation takes place within unique limits
Skeletal muscle adaptations – SUMMARY
Hypertrophy Increase in muscle size
Atrophy Decrease in muscle size
Sarcopenia Loss of muscle mass associated with the ageing process
Necrosis Tissue death of body tissue
Fibrosis Development of fibrous connective tissue as a reparative response
to injury/ damage
• Thickening/ scarring of the tissue
,Types of exercise
1. Endurance
• Type I muscle fibre
• Slow contraction speed, small contraction force, high resistance to fatigue
2. Strength
• Type IIx muscle fibre
• Fast contraction speed, large contraction force, low resistance to fatigue
3. Intermediate combinations
Myoplasticity
• Plasticity – the ability of tissues to adapt
• Myoplasticity – specifically refers to skeletal muscle
• Training, de-training and inactivity alter gene expression in skeletal muscle
o Protein turnover is also affected
o Amount (quality) and type of proteins in muscles can be alters ® adaptation
Maintaining homeostasis
• Maintain stable internal environment of the body
• Regulatory mechanisms maintain homeostasis during rest and exercise
• Adaptation = less disruptions in internal environment = improvements in the body’s ability to
maintain homeostasis
o Blood glucose o Core body temperature
o Blood oxygen content o Volume of body water
o pH o [electrolyte]
o arterial blood pressure
a. Molecular responses to exercise
• Exercise stimulates a range of molecular responses in skeletal muscle
• Adaptations = size, force, endurance, contractile velocity (structure and function)
• Activation or repression of molecular pathways by different stimuli:
o Neuronal, mechanical, metabolic, hormonal stimuli
• Regulation of:
o Pre- and post-transcriptional processes
o Protein translation and degradation processes
, b. Adaptation to exercise – cellular level
• Biogenesis of organelles e.g. mitochondria and ribosomes
• Changes in abundance, regulation or maximal activity of key proteins
• Proteins involved in:
o Energy provision
o Remodelling of cellular components e.g. contractile proteins
o Extracellular matrix
c. Adaptation to exercise training – tissue level
• Cellular changes ® alterations at tissue level
• Angiogenesis, muscle hypertrophy, altered substrate metabolism, fibre type distribution,
remodelling of extracellular matrix
d. Adaptation of skeletal muscle to exercise training
• Coordinated changes in skeletal muscle structure and function = minimise pertubations to cellular
homeostasis
• Contributed to improved fatigue resistance and improved performance
SUMMARY
Exercise ® biological signal ® signalling transduction networks ® mRNA synthesis + turnover and
protein synthesis + degradation ® cellular adaptations ® tissue adaptations ® improvement in
maintaining homeostasis ® resistance to fatigue/ reduced risk of disease
Broad range of adaptations
• Muscles also adapt to: (1) nutritional factors and (2) endocrine factors
• Adaptations range from a:
o Decrease capacity to generate/ maintain power because of reduced activity
o Increased capacity to maintain power for longer periods of time (endurance training)
o Increased capacity to develop max strength and power (resistance training)
Note: adaptations are reversible when the stimulus is removed or decreased
Principles of Skeletal Muscle Adaptations
Skeletal muscle fibre repair
• Mature adult skeletal muscle cells:
o Highly specialised
o Terminally differentiated
o Multinucleated
o Post-mitotic
o Cannot replicate but able to regenerate
(repair) and adapt
Adaptations to training and detraining
• The structure and function of skeletal muscle
adapts in response to repetitive use and disuse
o Use = physical activity
o Disuse = detraining, physical inactivity, zero gravity
• Changes dependent on:
o Type
o Intensity
o Duration of physical activity
• Neuromuscular system, musculoskeletal system and other biological systems also experience
adaptations
Adaptations to injury and ageing
• Injury = consequence of physical activity
• Injured muscles can repair or regenerate
• Skeletal muscles respond to spinal cord injuries and nerve damage
• Ageing also results in sarcopenia = adaptation to skeletal muscle
• Inter-individual variation in responses to training, detraining, regeneration, ageing
• Adaptation window – determined genetically
• Adaptation takes place within unique limits
Skeletal muscle adaptations – SUMMARY
Hypertrophy Increase in muscle size
Atrophy Decrease in muscle size
Sarcopenia Loss of muscle mass associated with the ageing process
Necrosis Tissue death of body tissue
Fibrosis Development of fibrous connective tissue as a reparative response
to injury/ damage
• Thickening/ scarring of the tissue
,Types of exercise
1. Endurance
• Type I muscle fibre
• Slow contraction speed, small contraction force, high resistance to fatigue
2. Strength
• Type IIx muscle fibre
• Fast contraction speed, large contraction force, low resistance to fatigue
3. Intermediate combinations
Myoplasticity
• Plasticity – the ability of tissues to adapt
• Myoplasticity – specifically refers to skeletal muscle
• Training, de-training and inactivity alter gene expression in skeletal muscle
o Protein turnover is also affected
o Amount (quality) and type of proteins in muscles can be alters ® adaptation
Maintaining homeostasis
• Maintain stable internal environment of the body
• Regulatory mechanisms maintain homeostasis during rest and exercise
• Adaptation = less disruptions in internal environment = improvements in the body’s ability to
maintain homeostasis
o Blood glucose o Core body temperature
o Blood oxygen content o Volume of body water
o pH o [electrolyte]
o arterial blood pressure
a. Molecular responses to exercise
• Exercise stimulates a range of molecular responses in skeletal muscle
• Adaptations = size, force, endurance, contractile velocity (structure and function)
• Activation or repression of molecular pathways by different stimuli:
o Neuronal, mechanical, metabolic, hormonal stimuli
• Regulation of:
o Pre- and post-transcriptional processes
o Protein translation and degradation processes
, b. Adaptation to exercise – cellular level
• Biogenesis of organelles e.g. mitochondria and ribosomes
• Changes in abundance, regulation or maximal activity of key proteins
• Proteins involved in:
o Energy provision
o Remodelling of cellular components e.g. contractile proteins
o Extracellular matrix
c. Adaptation to exercise training – tissue level
• Cellular changes ® alterations at tissue level
• Angiogenesis, muscle hypertrophy, altered substrate metabolism, fibre type distribution,
remodelling of extracellular matrix
d. Adaptation of skeletal muscle to exercise training
• Coordinated changes in skeletal muscle structure and function = minimise pertubations to cellular
homeostasis
• Contributed to improved fatigue resistance and improved performance
SUMMARY
Exercise ® biological signal ® signalling transduction networks ® mRNA synthesis + turnover and
protein synthesis + degradation ® cellular adaptations ® tissue adaptations ® improvement in
maintaining homeostasis ® resistance to fatigue/ reduced risk of disease
Broad range of adaptations
• Muscles also adapt to: (1) nutritional factors and (2) endocrine factors
• Adaptations range from a:
o Decrease capacity to generate/ maintain power because of reduced activity
o Increased capacity to maintain power for longer periods of time (endurance training)
o Increased capacity to develop max strength and power (resistance training)
Note: adaptations are reversible when the stimulus is removed or decreased
