Muscle Bio Week 7.docx

***Week 7, Module 7: Maladaptation\'s in Skeletal Muscle to Inactivity*** - The opposite to adaptation is maladaptation. During periods of inactive or disuse, maladaptation\'s can occur within skeletal muscle. These negative effects can change muscle function and metabolism - Due t...

***Week 7, Module 7: Maladaptation\'s in Skeletal Muscle to Inactivity*** - The opposite to adaptation is maladaptation. During periods of inactive or disuse, maladaptation\'s can occur within skeletal muscle. These negative effects can change muscle function and metabolism - Due to skeletal muscle being highly malleable, it is prone to maladaptation after a prolonged period of inactivity. - Physical inactivity can be the result of physical injury or illness or decreased activity due to age or lifestyle choices. - Spaceflight can also lead to negative maladaptation for skeletal muscle. When in space, skeletal muscle experiences a significant amount of unloading of mechanical stress due to lack of gravity. This results in loss of muscle and bone mass and muscle function. - Those in space have to work out for 2.5hrs per day to combat the effects of unloading.   *Maladaptation\'s to unloading and inactivity* - Muscle atrophy commonly occurs in many situations associated with muscle disuse - Muscle wasting is associated with many different diseases. - Reduction in muscle mass worsens health outcomes by compromising metabolic and endocrine function - Bed and immobilisation are forms of unloading and can be studied. Spaceflight is another major form of unloading but isn\'t as easily studied. - Unilateral lower limb suspension is also another form of unloading. Was designed to mimic inactivity during space flight. Participants can still use crutches, stance leg is elevated so that the free leg can swing and be unloaded. Physiological maladaptation\'s found with this muscle: 1. Decreased max force 2. Decreased rate of force development. 3. Reduced tendon stiffness and contractile components 4. Impaired force steadiness. The ability to maintain constant levels of force, and is important for performance in tasks where fine motor skills are required. After inactivity, reductions in force steadiness of \~22 and 12% in the knee extensors and plantar flexors has been reported, respectively. 5. Reduced muscular endurance: reported to be reduced by \~13% and \~24% after 21 and 30 days of inactivity, respectively. This is likely due to a combination of factors, including a shift in metabolism towards oxidation of CHO as opposed to fat. 6. Decreased VO2peak and ventilatory threshold levels. 7. Decreased whole muscle size, occurring at 2.5% per week for knee extensors and greater for plantar flexors. 8. Shift towards fast twitch fibres to help maintain explosive qualities but makes the muscles more fatigable 9. Muscle composition changes: increase intramuscular fat content, reduced activity of enzymes in energy pathways involved in oxidative phosphorylation (aerobic metabolism), such as citrate synthase, as well as reduces the expression of mitochondrial and oxidative phosphorylation-related genes. To compensate, skeletal muscle **increases its reliance on anaerobic glycolysis**, as evidenced by an increase in the glycolytic enzyme phosphofructokinase (PFK). Unfortunately this leads to **increased fatigue susceptibility** 10. Loss of bone density. Exercise doesn\'t offset this. 11. Decrease neural conduction velocity 12. Increase pre synaptic inhibition: reduction in the neural signal caused by an inhibitory neuron 13. Decreased muscle activation. Reduced electrical activity in the muscles. \`   *Mechanisms for Maladaptation\'s with Inactivity/Unloading* Changes in the Nervous System - The CNS has a key role in the transmission of the signal needed for muscle contraction. - Impairments play a key role in reduction of muscle function with inactivity. - Indeed, evidence indicates that although motor unit activation does not seem to be influenced by inactivity, the speed at which neural signals travel to muscles (termed nerve conduction velocity) can be reduced, as well as increased presynaptic inhibition (a reduction in the neural signal caused by an inhibitory neuron).  - The electrical activity measured in muscles (via surface electromyography or EMG) is also reduced with inactivity, which may somewhat reflect a reduced capacity to activate muscles, or muscle atrophy. Changes in Muscle Protein Synthesis and Breakdown Rates - Muscle loss or gain is a result of altered protein metabolism, leading to a net loss or gain in contractile muscle protein. - Inactivity is associated with a reduction in the rate at which muscle proteins are synthesised and a simultaneous increase in the rate at which muscle proteins are degraded. - The imbalance between synthesis and breakdown of contractile muscle proteins leads to atrophy and decreased muscle size.