Factors That Affect The Activity Of Contractile Activity

839 Words Aug 25th, 2016 4 Pages
During prolonged activity, muscles show a decline in ability to respond to stimulation with optimal levels of contractile activity; this is a phenomena denoted as muscle fatigue (MF) (1). The causes of MF are not yet understood, however there are many observations of associations between metabolic and biochemical factors with MF. In order for force to be generated by muscles, calcium ions which are released from the sarcoplasmic reticulum bind to troponin. The new troponin-Ca2+ complex cause’s tropomyosin to change shape, exposing the binding site on actin. Myosin then binds to actin, causing cross bridge tilting, and generating contraction (1).
Lactic acid is commonly perceived as a primary cause of MF to due to its intracellular muscle acidosis effects. Acidosis lowers the sensitivity of the contractile apparatus to calcium ions, because the H+ ions competes against Ca2+ for binding to certain binding sites on troponin. (2).This leads to decreased force development. However, low pH has many effects which do not favour development of MF, such as its ability to help maintain excitability, and decreased rate of fatigue. Overall, there is little evidence suggesting that the net effect of lactic acid results in MF.
Potassium ions is a metabolite which decreases calcium ion release from the SR. Shifts in levels of potassium and calcium ions in and around skeletal muscle fibres will alter the membrane potential of the muscle cell, making it more or less prone to stimulation.…
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