List the factors that control muscle mass?
Protein synthesis and degradation
What are the three fibre types present in muscle?
Describe the difference in twitch responses between FF, FR and S muscle fibres?
FF: fast twitch
FR: fast twitch
S: slow twitch
Describe the difference in fatiguability between FF, FR and S muscle fibres?
FF: fatigue rapidly
FR: fatigue slowly
S: do not fatigue
Describe the concept of muscle fibre malleability?
Fibres exist as either pure (one type of MHC) or hybrids (multiple forms of MHC)
What determines the composition of MHC in a muscle fibre?
Varies according to stimuli
Composition reflects function
What are the goals of intervention to attenuate muscle wasting?
Attenuate muscle atrophy
Promote muscle strength
NOT: increase muscle fatigue
Give an example of a genetic influence on muscle mass?
Myostatin: negative regulator of muscle mass
Knockout > increase muscle mass
Describe the situtations which may lead to disuse muscle atrophy?
Prolonged bed rest
Describe the effect of denervation on muscle mass?
Describe cancer cachexia?
Severe wasting and weakness in many cancer patients
Disruption of muscle architecture
Affects up to 80% lung, pancreatic and GIT cancer patients
Impairs response to chemo and radiotherapy
Loss of how much muscle mass is fatal?
Describe why muscle wasting is thought to occur so rapidly in the ICU?
How is this being combatted?
Inflammatory environment > cascade of signalling pathways > favour protein degradation
Occurs over days
Treatment with electrical stimulation and exercise in the ICU
Describe the outcome of loss of muscle mass in disease states and old age?
Compromises QoL and survival
Age-associated loss of skeletal muscle mass and function
Describe the cause of sarcopenia?
Multifactorial: disuse, endocrine changes, chronic diseases, inflammation, insulin resistance, nutritional deficiencies
In which patients should a diagnosis of sarcopenia be considered?
All older patients with observed declines in physical function, strength or overall health
Bedridden, cannot rise from a chair or measured gait speed <1 m/s
Describe the functional effects of sarcopenia?
Descreased running performance
Descreased performace in explosive events
Eventually impacts upon personal care, feeding and domestic duties
Describe the changes that occur in muscle during sarcopenia?
Decreased muscle mass
Increased connectove tissue and fat
Inability to develop an initial force appropriate for the circumstances
At what age does loss of muscle strength usually onset?
Which muscle types are most affected by sarcopenia?
Fast muscles more affected than slow
Describe the effect muscle fibre denervation and reinnervation with a new fibre type?
Muscle fibre changes to match new innervation
Describe the chnages in speed of contraction that occur with ageing?
When do these changes occur?
Changes in Ca handling (impaired release and reuptake) > speed of contraction affected
Occurs before severe muscle wasting
Describe how motoneuron losses in ageing are handled?
Type IIB fibres most susceptible > may be renervated by axonal sprouting from slow fibres, or may cease functioning
Describe the changes that are thought to occur in motoneurons with ageing?
Remodelling of motor end plates
Increased connective tissue
Smaller diameter axons
Are the changes that occur in sarcopenia reversilbe?
Can they be attenuated?
Generally not reversible
Can be attenuated with strength training
Describe the effects of strength training in the elderly?
Significant increase in muscle strength
Increase lean total body mass
Increase in muscle fibre area
What are the adaptations that occur in strength training in the elderly thought to be an effect of?
Combination of neural adaptations and muscle hypertrophy
Describe the hormonal changes that occur with ageing that may have an effect on muscle mass and strength?
Decreased circulating levels of anabolic hormones: GH, IGF-1, testosterone
Compromises efficiency of muscle regeneration and repair