Open main menu
Home
Random
Recent changes
Special pages
Community portal
Preferences
About Wikipedia
Disclaimers
Incubator escapee wiki
Search
User menu
Talk
Dark mode
Contributions
Create account
Log in
Editing
Weakness
(section)
Warning:
You are not logged in. Your IP address will be publicly visible if you make any edits. If you
log in
or
create an account
, your edits will be attributed to your username, along with other benefits.
Anti-spam check. Do
not
fill this in!
===Types=== Muscle fatigue can be central, neuromuscular, or peripheral muscular. Central muscle fatigue manifests as an overall sense of energy deprivation, and peripheral muscle weakness manifests as a local, muscle-specific inability to do work.<ref>{{cite book |vauthors=Gandevia SC, Enoka RM, McComas AJ, Stuart DG, Thomas CK |title=Fatigue |chapter=Neurobiology of Muscle Fatigue |volume=384 |pages=515β25 |year=1995 |pmid=8585476 | doi = 10.1007/978-1-4899-1016-5_39|series=Advances in Experimental Medicine and Biology |isbn=978-1-4899-1018-9 }}</ref><ref>{{cite journal |author=Kent-Braun JA |title=Central and peripheral contributions to muscle fatigue in humans during sustained maximal effort |journal=European Journal of Applied Physiology and Occupational Physiology |volume=80 |issue=1 |pages=57β63 |year=1999 |pmid=10367724 |doi=10.1007/s004210050558|s2cid=22515865 }}</ref> Neuromuscular fatigue can be either central or peripheral.{{citation needed|date=August 2021}} ====Central fatigue==== The central fatigue is generally described in terms of a reduction in the [[nervous system|neural]] drive or nerve-based motor command to working muscles that results in a decline in the force output.<ref>{{cite journal |author=Gandevia SC |title=Spinal and supraspinal factors in human muscle fatigue |journal=Physiol. Rev. |volume=81 |issue=4 |pages=1725β89 |year=2001 |pmid=11581501 |doi=10.1152/physrev.2001.81.4.1725 }}</ref><ref>{{cite journal |vauthors=Kay D, Marino FE, Cannon J, St Clair Gibson A, Lambert MI, Noakes TD |title=Evidence for neuromuscular fatigue during high-intensity cycling in warm, humid conditions |journal=Eur. J. Appl. Physiol. |volume=84 |issue=1β2 |pages=115β21 |year=2001 |pmid=11394239 |doi=10.1007/s004210000340|s2cid=25906759 }}</ref><ref>{{cite journal |doi=10.3109/13813459109145909 |vauthors=Vandewalle H, Maton B, Le Bozec S, Guerenbourg G |title=An electromyographic study of an all-out exercise on a cycle ergometer |journal=Archives Internationales de Physiologie, de Biochimie et de Biophysique |volume=99 |issue=1 |pages=89β93 |year=1991 |pmid=1713492 }}</ref> It has been suggested that the reduced neural drive during exercise may be a protective mechanism to prevent organ failure if the work was continued at the same intensity.<ref>{{cite journal |vauthors=Bigland-Ritchie B, Woods JJ |title=Changes in muscle contractile properties and neural control during human muscular fatigue |journal=Muscle Nerve |volume=7 |issue=9 |pages=691β9 |year=1984 |pmid=6100456 |doi=10.1002/mus.880070902|s2cid=13606531 }}</ref><ref>{{cite journal |author=Noakes TD |title=Physiological models to understand exercise fatigue and the adaptations that predict or enhance athletic performance |journal=Scandinavian Journal of Medicine & Science in Sports |volume=10 |issue=3 |pages=123β45 |year=2000 |pmid=10843507 |doi=10.1034/j.1600-0838.2000.010003123.x|s2cid=23103331 }}</ref> The exact mechanisms of central fatigue are unknown, though there has been considerable interest in the role of [[serotonin|serotonergic]] pathways.<ref>{{cite journal |author=Davis JM |title=Carbohydrates, branched-chain amino acids, and endurance: the central fatigue hypothesis |journal=International Journal of Sport Nutrition |volume=5 |issue=Suppl |pages=S29β38 |year=1995 |pmid=7550256 |doi=10.1123/ijsn.5.s1.s29 }}</ref><ref>Newsholme, E. A., Acworth, I. N., & Blomstrand, E. 1987, 'Amino acids, brain neurotransmitters and a functional link between muscle and brain that is important in sustained exercise', in G Benzi (ed.), Advances in Myochemistry, Libbey Eurotext, London, pp. 127-133.</ref><ref>{{cite book |vauthors=Newsholme EA, Blomstrand E |chapter=Tryptophan, 5-Hydroxytryptamine and a Possible Explanation for Central Fatigue |title=Fatigue |volume=384 |pages=315β20 |year=1995 |pmid=8585461 |doi=10.1007/978-1-4899-1016-5_25|series=Advances in Experimental Medicine and Biology |isbn=978-1-4899-1018-9 }}</ref> ====Neuromuscular fatigue==== [[Nerve]]s control the contraction of muscles by determining the number, sequence, and force of muscular contraction. When a nerve experiences [[synaptic fatigue]] it becomes unable to stimulate the muscle that it innervates. Most movements require a force far below what a muscle could potentially generate, and barring [[pathology]], neuromuscular fatigue is seldom an issue.{{citation needed|date=August 2021}} For extremely powerful contractions that are close to the upper limit of a muscle's ability to generate force, neuromuscular fatigue can become a limiting factor in untrained individuals. In novice [[strength training|strength trainers]], the muscle's ability to generate force is most strongly limited by nerve's ability to sustain a [[rate coding|high-frequency signal]]. After an extended period of maximum contraction, the nerve's signal reduces in frequency and the force generated by the contraction diminishes. There is no sensation of pain or discomfort, the muscle appears to simply 'stop listening' and gradually cease to move, often [[Muscle contraction#Eccentric contraction|lengthening]]. As there is insufficient stress on the muscles and tendons, there will often be no [[delayed onset muscle soreness]] following the workout. Part of the process of strength training is increasing the nerve's ability to generate sustained, high frequency signals which allow a muscle to contract with their greatest force. It is this "neural training" that causes several weeks worth of rapid gains in strength, which level off once the nerve is generating maximum contractions and the muscle reaches its physiological limit. Past this point, training effects increase muscular strength through myofibrillar or sarcoplasmic [[Muscle hypertrophy#Strength training|hypertrophy]] and metabolic fatigue becomes the factor limiting contractile force. ====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 fatigueβaffecting 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 = R502β16 | 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.
Edit summary
(Briefly describe your changes)
By publishing changes, you agree to the
Terms of Use
, and you irrevocably agree to release your contribution under the
CC BY-SA 4.0 License
and the
GFDL
. You agree that a hyperlink or URL is sufficient attribution under the Creative Commons license.
Cancel
Editing help
(opens in new window)