Final answer:
Peripheral muscle fatigue is caused by a combination of ATP depletion, H+ ion accumulation, changes in Ca2+ ion levels, and ion balance disturbances. This process involves ATP consumption for muscle contraction and active transport of Ca2+ ions, as well as the build-up of acidity from anaerobic metabolism, all contributing to the decreased capacity for muscle contraction.
Step-by-step explanation:
Peripheral muscle fatigue is a complex phenomenon where muscles can no longer contract efficiently. This mainly happens due to a series of biochemical events that occur within the muscle fibers during physical activity. The most relevant factors that may lead to muscle fatigue include depletion of ATP (adenosine triphosphate), which is critical for muscle contraction, accumulation of H+ ions (protons) that contribute to the acidic environment lowering the pH (a result of anaerobic metabolism and lactic acid production), changes in the levels of Ca2+ ions impacting the contraction-relaxation cycle, and alterations in sodium (Na+) and potassium (K+) ion balance affecting membrane potential.
The general order of events that leads to peripheral muscle fatigue starts with the hydrolysis of ATP by myosin's ATPase which is essential for cross-bridge cycling and muscle contraction. If ATP levels decrease significantly due to prolonged muscle activity and insufficient resynthesis, energy supply for these processes drops, leading to reduced muscle function. Concurrently, anaerobic glycolysis is favored during high-intensity, low-oxygen conditions, resulting in an increase in H+ ions which contribute to acidosis within muscle cells. This acidosis can interfere with enzymatic activities necessary for energy production and muscle contraction. Additionally, for muscle relaxation to occur, Ca2+ ions need to be actively pumped back into the sarcoplasmic reticulum (SR), a process that also requires ATP. If this function is impaired due to ATP deficit or damage to the SR or sarcolemma (as might occur with sustained exercise), Ca2+ regulation within the muscle fiber is disrupted, thus contributing further to muscle fatigue.