Editing Weakness (section)

====Peripheral muscle fatigue====
Peripheral muscle fatigue during physical work is considered{{By whom|date=April 2012}} an inability for the body to supply sufficient energy or other metabolites to the contracting muscles to meet the increased energy demand. This is the most common case of physical fatigue—affecting a national{{Where|date=April 2012}} average of 72% of adults in the work force in 2002. This causes contractile dysfunction that manifests in the eventual reduction or lack of ability of a single muscle or local group of muscles to do work. The insufficiency of energy, i.e. sub-optimal [[cellular respiration|aerobic metabolism]], generally results in the accumulation of [[lactic acid]] and other [[acid]]ic anaerobic metabolic by-products in the muscle, causing the stereotypical burning sensation of local muscle fatigue, though recent studies have indicated otherwise, actually finding that lactic acid is a source of energy.<ref name=robergs>{{cite journal |author1=R. Robergs |author2=F. Ghiasvand |author3=D. Parker | title = Biochemistry of exercise-induced metabolic acidosis | journal = Am J Physiol Regul Integr Comp Physiol | volume = 287 | issue = 3 | pages = R502–16 | year = 2004 | doi = 10.1152/ajpregu.00114.2004 | pmid = 15308499|s2cid=2745168 }}</ref>

The fundamental difference between the peripheral and central theories of muscle fatigue is that the peripheral model of muscle fatigue assumes failure at one or more sites in the chain that initiates muscle contraction. Peripheral regulation  therefore depends on the localized metabolic chemical conditions of the local muscle affected, whereas the central model of muscle fatigue is an integrated mechanism that works to preserve the integrity of the system by initiating muscle fatigue through muscle derecruitment, based on collective feedback from the periphery, before cellular or organ failure occurs. Therefore, the feedback that is read by this central regulator could include chemical and mechanical as well as cognitive cues. The significance of each of these factors will depend on the nature of the fatigue-inducing work that is being performed.{{citation needed|date=August 2021}}

Though not universally used, "metabolic fatigue" is a common alternative term for peripheral muscle weakness, because of the reduction in contractile force due to the direct or indirect effects of the reduction of substrates or accumulation of metabolites within the [[muscle fiber|myocytes]]. This can occur through a simple lack of energy to fuel contraction, or through interference with the ability of Ca<sup>2+</sup> to stimulate [[actin]] and [[myosin]] to contract.