Muscle Bio Week 5.docx

***Week 5, Module 5: Homeostasis and Skeletal Muscle Adaptation to Exercise*** - Homeostasis: to maintain a constant internal environment - When exercise occurs, it disturbs homeostasis and our energy systems have to rapidly respond to replenish ATP stores. - When homeostasis is disrupt...

***Week 5, Module 5: Homeostasis and Skeletal Muscle Adaptation to Exercise*** - Homeostasis: to maintain a constant internal environment - When exercise occurs, it disturbs homeostasis and our energy systems have to rapidly respond to replenish ATP stores. - When homeostasis is disrupted, it creates a negative feedback loop that signals to the body to initiate a response. If no response happens, it can lead to long term damage.   *Homeostasis in Skeletal Muscle* - Skeletal muscle cells, like everything else, have an internal environment which is comprised of the contractile proteins, organelles, enzymes and energy sources. At rest, all the biological processes occurring within this environment happens at a steady pace, however, at the onset of muscle contraction, this rapidly changes. - ATP demands increase rapidly during exercise, up to 100 times as much. The balance between energy supply and demand during exercise is thrown out of whack and the cell has to quickly adjust to meet the requirement. - The increase demand for ATP leads to increased build up of metabolic by products which causes stress on our system known as metabolic stress. - Mechanical stress: tension and stretch which occurs when we lift heavy loads. Exercise can be thought of as physiological stress. - Our body\'s have different cells/receptors to sense change in the body and initiate appropriate reactions to help restore homeostasis. Eg: ATP become ADP + Pi + Energy. Then another ADP becomes AMP + Pi + energy to restore ATP. - Exercise stimulates an increase in AMP and ADP concentrations. - This perturbation in homeostasis is 'sensed' by an enzyme residing within the cytosol of the muscle cell, known as ***AMP-activated protein kinase*** (or AMPK).  - As its name suggests, this enzyme is sensitive to changes in cellular AMP concentrations, or ***rises in the AMP:ATP ratio***. When stimulated, this enzyme acts to switch on cellular pathways that generate energy, and switch off cellular pathways that consume energy. It also acts to activate various genes that promote an increase in the number of mitochondria within the muscle cell. Because the cell has now a greater capacity for aerobic ATP production (within the mitochondria), it is somewhat protected against future disturbances in the AMP:ATP ratio.   *Hormesis* - Hormesis describes the idea that low doses of a given stress cause adaptations in cells or organisms that enhance their capacity to withstand future stress. - Because the physiological stress in muscle cells caused by exercise is not sufficient to fatally damage the cell, the muscle cell is able to respond and adapts in a manner that protects it from future stress   *FITT Principle and Homeostasis* - Exercise of a particular FITT will disrupt homeostasis - When the physiological stress is constantly applied, the body is forced to adapt and will respond better over time. - For example, the mechanical stress caused by resistance training is sensed by receptors located in the muscle fibre membrane (sarcolemma). The sending of this mechanical stress then signals the muscle cell to start making more contractile proteins (actin and myosin, along with other proteins involved in force transmission in the muscle fibre). This then leads to growth (hypertrophy) and improved strength of the muscle fibre membrane, which helps the muscle cope with mechanical stress encountered in future.  - Correct manipulation of the FITT principle variables is therefore required when designing an exercise training program aimed at causing physiological adaptation in our bodies. It is these adaptations that will lead to improvements in our health, function, or athletic performance that encompass the benefits of exercise. Each of the FITT variables may be manipulated to modify the amount of stress caused by exercise on our physiological systems, and also to induce particular types of stress. *Exercise Induced Hormesis and the Principle of Progressive Overload* - Our bodies will only adapt when there is sufficient stress placed on them or lack there of. - Exercise needs to induce a certain level of stress for progressive overload to occur.