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Hoe werk isometriese kontraksie?

Hoe werk isometriese kontraksie?



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  1. Wat gebeur presies met myosien tydens isometriese kontraksie? Ek vermoed dat myosienkoppe in die middel van die dwarsbrug -siklus net "vries", of dat hulle herhaaldelik deur die volledige dwarsbrug -siklusse gaan, sodat die verlengingstempo gelyk is aan die inkrimpingstempo (basies is 'n spier nie stil nie, maar strek herhaaldelik met <1 mm, en dan trek myosien onmiddellik saam om te kompenseer vir hierdie uitbreiding om spiere op 'n statiese lengte te hou - en dit gaan terug).

  2. Waarom bestee isometriese kontraksies energie, as die fisika dit duidelik maak dat energie slegs bestee word as ons die snelheid van iets verander? As my tweede hipotese waar is en die spier is nie in werklikheid stil nie, dan word energie natuurlik bestee. Maar as myosienkoppe vries in die middel van die siklus vasgeplak aan aktien, is daar geen rede waarom energie bestee moet word nie.

  3. Sê, 'n persoon probeer 'n rots van 10 ton lig met al die krag wat hulle gekry het. Dit is ook 'n isometriese sametrekking, maar in hierdie geval behoort die tweede hipotese nie te werk nie, want as myosien 'n dwarsbrug -siklus onder so 'n weerstand kon voltooi, sou dit beteken dat die spier sterk genoeg is om die rots op te lig. Dus, in hierdie geval moet dit in die middel van die siklus vasval, terwyl die massa van die gesteentes nie die vormingsverandering kan laat voltooi nie. Indien wel, hoekom spandeer spiere dan energie? Myosin sit letterlik vas, en totdat 'n siklus voltooi is, bind dit nie 'n ander ATP nie.


5 isometriese oefeninge vir mense om te probeer

Isometriese oefeninge is oefeninge wat die sametrekking van spiere behels sonder enige beweging in die omliggende gewrigte. Die konstante spanning op die spiere kan help om spieruithouvermoë te verbeter en dinamiese oefeninge te ondersteun.

Die meeste spierversterkingsoefeninge behels die beweging van die gewrigte, die gebruik van die spiere om teen weerstand te stoot of te trek. Isometriese oefeninge behels egter die hou van statiese posisies vir lang tydperke.

Hierdie artikel sal bespreek wat isometriese oefeninge is en 'n paar voorbeelde verskaf.

Deel op Pinterest Beeldkrediet: Andrey_Popov / Shutterstock.

Isometriese oefeninge plaas spanning op spesifieke spiere sonder om die omliggende gewrigte te beweeg. Deur konstante spanning op die spiere toe te pas, kan isometriese oefeninge nuttig wees om fisiese uithouvermoë en postuur te verbeter deur die spiere te versterk en te stabiliseer.

Daar is twee tipes spiersametrekking: isotonies en isometries. Isotoniese kontraksies vind plaas wanneer spiere korter of langer word teen weerstand, en spanning bly dieselfde. Isometriese sametrekkings vind plaas wanneer spanning toeneem maar die spier op 'n konstante lengte bly.

Baie kragbou-oefeninge behels konsentriese of eksentrieke bewegings, wat albei isotoniese kontraksies is. Konsentriese bewegings veroorsaak dat die spier verkort word, en eksentriese bewegings verleng die spier.

Isometriese oefeninge behels nie dat die spiere verkort of verleng word nie. Tydens isometriese oefeninge is die gewrigte stil, en die spiere verander nie van vorm of grootte nie. Mense hou gewoonlik 'n paar sekondes of minute die isometriese sametrekking.

Sommige isometriese oefeninge ontwikkel spanning deur die liggaam in 'n sekere posisie te hou, terwyl ander gewigte kan hou. Deur die spiersametrekking vas te hou, kan die spierweefsel met bloed vul en metaboliese spanning op die spier veroorsaak. Dit kan help om krag en uithouvermoë te verbeter.

'n Voordeel van isometriese oefeninge is dat dit redelik maklik is om uit te voer, gewoonlik geen toerusting benodig nie, en maklik in baie gewigopteloefeninge opgeneem kan word.


Wat is skeletspierkontraksie? (met foto's)

'n Skeletspiersametrekking is die meganisme waardeur spiere van die beweegbare gewrigte van die liggaam beweging by daardie gewrigte produseer. Skeletspiere word onderskei van hartspiere, wat die hart pomp, en gladde spiere, wat 'n komponent van verskeie interne organe is en bewegings produseer, soos om voedsel langs die spysverteringskanaal te stoot, deurdat dit aan albei sy ente met been verbind. As sodanig trek dit aan die twee bene as dit saamtrek - dit wil sê wanneer die vesels verkort en verleng, en dit veroorsaak beweging by die gewrig wat dit kruis. Skeletspiersametrekking, wat 'n chemiese reaksie op die vlak van proteïenkomponente in elke spiersel behels, is wat beweging van die skelet moontlik maak.

Daar is 'n paar verskillende tipes sametrekkings wat skeletspiere kan produseer. 'N Sametrekking waarin die spiervesels verkort word, soos gesien wanneer die ribbekas tydens 'n abdominale knars nader aan die bekken getrek word, staan ​​bekend as 'n konsentriese sametrekking. As die spiervesels langer word, soos in die verlaagde fase van 'n knars, vind 'n eksentrieke inkrimping plaas. 'N Skeletspierkontraksie wat beide die konsentriese en eksentrieke fase van 'n beweging behels, staan ​​bekend as 'n isotoniese sametrekking. 'N Isometriese kontraksie, aan die ander kant, is die spier waarin die spier nie in lengte verander tydens kontraksie nie, soos om 'n hurkposisie te hou sonder om te beweeg.

Skeletspiere bestaan ​​uit bondels spiervesels, wat weer bondels spierselle is. Spierselle is lank, smal en silindries van vorm, en bestaan ​​uit eenhede genoem sarkomere wat verantwoordelik is vir skeletspiersametrekking. Die model wat verduidelik wat in die sarkomeer voorkom as 'n spier saamtrek, staan ​​bekend as die glidende filamentteorie. Dit kan gebruik word om alle vorme van spiersametrekking te verduidelik, wat slegs verskil as gevolg van die vraag of die krag wat op die spier toegedien word, kleiner as, groter as of gelyk is aan die krag wat deur die spierselle geproduseer word.

Binne elke sarkomeer, 'n eenheid wat in die honderde duisende in elke spiersel voorkom, is proteïene wat in lang filamente georganiseer word genaamd aktien en miosien. Die aktienproteïene is passief, wat beteken dat dit kettings vorm wat die aktiewe myosienproteïene ontvang. Gerangskik in afwisselende lyne, gly die miosien heen en weer verby die aktien, en in die proses straal dit kalsiumione uit wat veroorsaak dat elke miosienproteïen aan 'n ooreenstemmende plek op elke aktienproteïen bind.

Tydens die sametrekking van skeletspiere gryp die myosien filamente na die aktien en trek verby dit. Dit gebeur gelyktydig in die sel se vele sarcomere, wat in bande gerangskik is. Hierdie 'beroerte', soos dit algemeen bekend is, veroorsaak 'n kollektiewe verkorting van die spier, wat dan terugkeer tot sy ruslengte terwyl die myosien homself van die aktien vrystel.


Wat is isometriese oefening? Wetenskap en voordele

’n Isometriese oefening is ’n oefentegniek waarin jou gewrigte en spiere nie eerder beweeg nie, hulle trek saam in ’n statiese posisie.

Isometriese oefeninge, ook bekend as isometrie, is een van die oudstes in die geskrewe geskiedenis en verkry gewoonlik 'n geestelike waarde in joga en oosterse vechtkunsten, veral Tai Chi.

Het u geweet dat Bruce Lee self isometrie gebruik het om sy spierbeheer en uithouvermoë te bou wat hom wêreldberoemd gemaak het?

Isometrie is 'n goeie keuse as jy aan beenfrakture of gewrigspyn ly sonder om doeltreffendheid in te boet, alhoewel jy aandag moet gee aan jou bloeddruk as jy 'n soort kardiovaskulêre siekte het, soos hipertensie.

Behoorlike asemhaling is uiters belangrik, aangesien asem ophou terwyl u isometrie doen, u bloeddruk tot gevaarlike vlakke kan verhoog.

Hier is 'n paar van die voordele van isometriese oefeninge:

  • Krag en spierversterking sonder soveel slytasie op die gewrigte
  • Verhoogde melksuurverdraagsaamheid
  • Verdieping van die verstand-spier-konneksie
  • Verhoogde liggaamsbeheer
  • Tyddoeltreffende oefensessies

In die 1950's het navorsers Hettinger en Muller gevind dat 'n enkele daaglikse poging van 2/3de van 'n persoon se maksimum inspanning wat vir ses sekondes op 'n slag vir tien weke aangewend word, krag met ongeveer 5% per week verhoog het, terwyl Clark en medewerkers getoon het dat statiese krag voortduur om groei selfs na die afsluiting van 'n vyf weke lange program van isometriese oefeninge.

Die beginsel van isometriese oefening is eenvoudig: hou 'n gewig of 'n posisie waarmee jy gemaklik is vir 'n vasgestelde tydperk. Verhoog geleidelik die weerstand of die tyd wat onder spanning gehou word, en jou krag en uithouvermoë sal dienooreenkomstig groei.

Die intense isometriese sametrekking in u spiere is die sleutel hier!

As jy voel dat sommige van jou spiergroepe agter die res van jou liggaam bly, kan isometrie die faktor wees wat jou sal help om deur jou biseps of kuitplato's te druk.


Isometrie: Statiese houe en statiese kontraksie opleiding

Die term isometrie verwys na oefenprotokolle waartydens geen verkorting of verlenging van die spier plaasvind nie. Tradisionele isometriese protokolle behels gewoonlik die skielike toepassing van 'n maksimum kontraksie van 10 tot 15 sekondes, gewoonlik uitgevoer teen 'n onroerende voorwerp of 'n ander spiergroep. Sommige protokolle behels dat u 'n liggaamshouding vir 'n langer tydperk moet hou deur die liggaam se eie gewig as weerstand te gebruik (muurhurk, planke, verskillende joga -houdings).

Oor die afgelope paar dekades is verskillende isometriese protokolle met hoë intensiteit ontwikkel. Hierdie wissel aansienlik in duur, van minder as 6 sekondes in John Little’s Max Contraction opleiding, tot 90 sekondes in Ken Hutchins’ Tyd Static Contraction protokol. Sommige gewilde hoë-intensiteit oefenmetodes, soos wyle Mike Mentzer se Static Holds en John Little se Omega Sets, inkorporeer beide 'n isometriese en dinamiese of “isotoniese” komponent, wat gewoonlik 'n isometriese sametrekking behels, gevolg deur 'n gedeeltelike of volle reeks negatief.

Basiese beskrywings van gewilde hoëintensiteitsopleiding isometriese protokolle

Mike Mentzer & # 8217s statiese houvas behels 'n isometriese sametrekking in die “volledig-gekontrakteerde” posisie van 'n enkelgewrig of saamgestelde trekoefening of die middelafstandposisie van 'n saamgestelde stootoefening, deur 'n gewig te gebruik wat die proefpersoon tussen 8 en 12 sekondes kan hou vir die bolyf, of 15 tot 30 sekondes vir die onderlyf. As die onderwerp die gewig nie meer onbeweeglik kan hou nie, voer hulle 'n stadige negatief uit.

John Little’s Maksimum sametrekking protokol is soortgelyk aan Mike Mentzer’s statiese houvas, maar behels 'n baie korter (0,25 tot 6 sekondes) isometriese sametrekking, en word slegs gebruik in die ten volle gekontrakteerde posisie van 'n enkel-gewrig of roterende oefening. Wanneer dit uitgevoer word as deel van 'n Omega -stel, kan die maksimum sametrekking herhaal word vir verskeie herhalings.

Ken Hutchins’ tydige statiese kontraksieprotokol behels 'n 90-sekonde isometriese sametrekking teen 'n vaste of onbeweeglike bron van weerstand, bestaande uit drie 30-sekonde segmente van geleidelik toenemende inspanning. Onderwerpe word opdrag gegee om gedurende die eerste 30 sekondes 'n matige ” -poging aan te wend, amper so hard soos hulle waag gedurende die tweede 30 sekondes, en om so hard soos hulle te kontrakteer waag vir die laaste 30 sekondes, dan om moeite na die volle 90 sekondes geleidelik te verminder.

Die proefpersoon word opdrag gegee om so hard soos hulle saam te trek waag eerder as so hard soos hulle kan om hulle te herinner om versigtig te wees, aangesien dit moontlik is om te produseer baie hoë vlakke van krag.

As 'n proefpersoon nie in staat is om 'n oefening dinamies uit te voer as gevolg van 'n besering of gewrigsmisvorming nie of as hulle pyn of irritasie in sekere gedeeltes van die bewegingsreeks ervaar, is 'n isometriese sametrekking wat uitgevoer word in 'n posisie waar die proefpersoon nie pyn of irritasie ervaar nie. 'n effektiewe alternatief.

Vakke wat ly aan nekprobleme wat vererger word deur verskeie dinamiese oefeninge vir die bolyf, kan dikwels daardie oefeninge uitvoer deur tydige statiese sametrekking te gebruik met min of geen irritasie aan die nek.

Aangesien baie min vaardigheid of motoriese beheer nodig is, kan vakke met 'n te swak motoriese vermoë om dinamiese oefening op 'n gekontroleerde manier uit te voer, isometrie veilig uitvoer.

Baie tydige statiese kontraksie -oefeninge benodig geen spesiale toerusting nie en kan uitgevoer word met behulp van 'n eie liggaam, 'n muur of gewone items soos stoele, balle en gordels. Sulke oefeninge maak dit vir diegene sonder toegang tot oefentoerusting moontlik om sekere spierstrukture direk aan te spreek wat slegs indirek aangespreek word deur gebruik te maak van tradisionele liggaamsgewigoefeninge, moontlik as 'n vooruitput vir die oefeninge. Een voorbeeld hiervan sou wees om 'n tydige statiese sametrekking van die borsvlieg uit te voer, wat saamtrek teen 'n bal wat tussen die elmboë gehou word om die bors aan te spreek, wat as 'n vooruitlaat vir opstote gedoen kan word.

Isometriese protokolle kan dikwels effektief uitgevoer word op toerusting wat te veel wrywing of onbehoorlike weerstandskrommes het vir gebruik met dinamiese protokolle.

Nadele

Isometriese protokolle bied geen rek nie en doen min om die buigsaamheid van die gewerkte spiere te verbeter. Hierdie probleem word maklik opgelos deur afsonderlike strekoefeninge vir daardie spiere uit te voer indien nodig (slegs 'n paar spiere kan eintlik gestrek word).

As gevolg van die verhoogde bloeddruk (BP) wat moontlik is met isometriese oefening en veral tydens oefeninge wat aangryp, is ekstra versigtigheid nodig vir persone met hoë bloeddruk of toestande wat kan vererger deur aansienlike BP -verhoging. Behoorlike asemhaling is absoluut noodsaaklik om die BP -verhoging tot 'n minimum te beperk, en veral nie die maneuver van Val Salva nie.

Isometriese oefenprotokolle mag produseer kragtoenames spesifiek vir die posisie of gewrigshoek wat opgelei is, en nie oor die volle omvang van beweging (ROM). Dit hang af van verskeie faktore, wat in meer besonderhede onder die afdeling oor Saamgestelde Bewegings hieronder bespreek sal word.

Nog 'n nadeel is die behoefte aan sterk oefenmaats om die gewig in posisie vir die vak te lig wanneer statiese houe uitgevoer word. Die meeste mense kan aansienlik meer gewig gebruik vir statiese houe vir die duur wat aanbeveel word as vir normale dinamiese opleiding, so dit kan vinnig baie veeleisend word vir die oefenmaats of afrigter, asook 'n groter risiko van besering inhou indien interpersoonlike oordrag nie korrek uitgevoer word nie. Sterker onderwerpe sal ook vinnig die mees algemene gekeurde masjiene uitkom. As gevolg van hierdie nadele is tydige statiese kontraksies 'n veiliger en meer praktiese alternatief.

Tydige statiese sametrekking

Tydens tydige statiese sametrekking trek die proefpersoon saam teen 'n effektief onbeweeglike bron van weerstand soos 'n bewegingsarm wat in 'n vaste posisie gesluit is of roerloos gehou word deur 'n instrukteur of oefenmaat. Dit is anders as 'n statiese hou waar die onderwerp hou en probeer om die negatiewe beweging van 'n barbell of masjien’s beweging arm weerstaan.

Tydige statiese sametrekking word die beste uitgevoer op oefenmasjiene waarvan die bewegingsarms op enige punt oor die ROM of met 'n kragrek in posisie gesluit kan word. Dit is ook moontlik om gekeurde masjiene met konvensionele gewigstapels te gebruik waarmee 'n voldoende mate van weerstand vasgemaak kan word met die bewegingsarm in die gewenste posisie, wat verdere positiewe beweging voorkom. Sommige opleidingsfasiliteite bevat verstelbare kettinglengtes in hul toerusting wat gebruik kan word om die bewegingsbereik te beperk vir die uitvoering van tydige statiese kontraksie. As u masjiene gebruik wat nie die bewegingsarm in posisie kan sluit nie, kan dit deur 'n instrukteur of opleidingsvennoot onbeweeglik gehou word as hulle voldoende hefboomfinansiering het. Dit kan ook uitgevoer word met behulp van handmatige weerstand vir baie oefeninge. Tydige statiese inkrimping kan vir sommige vakke veiliger wees as statiese houvas, aangesien die gebruik van 'n vaste eerder as beweegbare weerstand geen tussen- of intra -persoonlike oordrag van 'n bewegingsarm of staaf nodig is nie.

Begin met 'n minimale poging, die onderwerp verhoog geleidelik die hoeveelheid krag wat hulle toepas totdat hulle’re oefen 'n benaderde 50% poging, en gaan voort om te kontrakteer teen die weerstand op hierdie vlak van inspanning vir ongeveer 30 sekondes. Na 30 sekondes verhoog hulle hul poging geleidelik tot 75%. Na nog 30 sekondes verhoog hulle geleidelik hul poging tot “naby maksimum”. Uiteindelik, na 30 sekondes van “byna maksimum” poging, oefen die proefpersoon vir nog 30 sekondes 'n maksimum poging uit. Hierna moet die onderwerp baie geleidelik die intensiteit van sametrekking oor 'n tydperk van 'n paar sekondes verminder, eerder as om skielik te los. Dit is net so belangrik om die intensiteit van sametrekking geleidelik te verminder as om dit op 'n geleidelike en beheerde manier toe te pas.

Ken Hutchins se protokol vir tydige statiese sametrekking is soos volg:

    Geleidelike toename van inkrimping van 0% tot vermeende inspanning van 50%:

Alhoewel dit kan klank maklik, as dit behoorlik uitgevoer word, is dit ongelooflik intens en in staat om 'n baie diep spiervlak te produseer.

’n Nadeel van tydige statiese sametrekking is dat, tensy dit op toerusting met ’n kragmeter uitgevoer word, daar geen objektiewe of akkurate manier is om oefenprestasie of vordering te meet nie. Aangesien die onderwerp saamtrek teen 'n vaste voorwerp eerder as om die swaartekrag op 'n staaf of die tegendruk van 'n masjien se bewegingsarm te weerstaan, is daar geen manier om weerstand te kwantifiseer nie.

Statiese houvas

Tydens 'n statiese houvas word 'n barbel of die bewegingsarm van 'n masjien van die instrukteur of oefenmaat na die proefpersoon oorgedra in óf die ten volle gekontrakteerde posisie óf eindpunt van 'n eenvoudige oefening, of in die middel van 'n saamgestelde beweging. Die subjek trek dan teen die weerstand saam en probeer dit so lank as moontlik onbeweeglik hou. Nadat die spiere ingedraai is tot die punt waar dit onmoontlik is om die afwaartse beweging van die weerstand te voorkom, gaan die onderwerp voort om teen die weerstand saam te trek en die negatiewe so stadig as moontlik uit te voer.

Die meeste proefpersone benodig ongeveer 20% meer weerstand vir statiese houvas as wat hulle vir 'n stel dinamiese oefeninge van soortgelyke duur sou gebruik. Dit sal ietwat verskil tussen individue en spiergroepe, en wanneer barbells of toerusting met verkeerde weerstandskurwes gebruik word, hang die toename in weerstand wat nodig is af van die posisie of gewrigshoek waarteen die oefening uitgevoer word.

Mike Mentzer se protokol vir 'n statiese houvas is soos volg:

  1. Die instrukteur of oefenmaat help om die weerstand tot die verlangde posisie te verhoog, of in die geval van liggaamsgewigoefeninge soos ken of dips, met behulp van 'n stap wat die proefpersoon homself in die beginposisie lig met sy bene.
  2. Die weerstand word oorgedra van die afrigter na die onderwerp, of die onderwerp dra die weerstand van die bene na die bolyf oor.
  3. Die weerstand word roerloos gehou totdat statiese spierversaking plaasvind - die punt waarop die spiere nie meer voldoende krag het om negatiewe beweging van die weerstand te voorkom nie.
  4. Die weerstand word dan verlaag stadig onder streng beheer.

Statiese houvas verg aansienlik meer omsigtigheid as tydige statiese inkrimping, as gevolg van die vereiste vir 'n relatief hoë weerstand en die behoefte aan inter- of intra -persoonlike oordrag van weerstand in baie oefeninge. statiese vashouvermoë is dalk nie geskik vir sommige vakke wat nie dinamiese oefening kan duld nie as gevolg van beserings of gewrigsmisvormings, in welke geval tydige statiese sametrekking gebruik moet word.

Die enigste voordeel van statiese houe oor tydige statiese sametrekking is dat dit voorsiening maak vir meting van oefenprestasie en vordering in terme van weerstand x vasgestelde duur. As 'n proefpersoon 'n statiese houvas vir die voorgeskrewe duur uitvoer voordat spierversaking plaasvind, moet die weerstand die volgende oefensessie verhoog word.

Interpersoonlike Weerstandoordrag

dit is uiters belangrik dat interpersoonlike oordrag van weerstand behoorlik uitgevoer word. By die oorhandiging van die staaf of bewegingsarm aan die onderwerp, is dit belangrik om nie skielik los te laat nie en die onderwerp skielik te laai, aangesien dit letsel kan veroorsaak. Wanneer die staaf of bewegingsarm in die verlangde posisie is en die proefpersoon aandui dat hy gereed is, moet die instrukteur of oefenmaat die proefpersoon inlig dat hy gaan begin om die weerstand oor te dra. Terwyl die proefpersoon die staaf of bewegingsarm roerloos hou, moet die oefenmaat die hoeveelheid krag wat hy toepas baie geleidelik verminder, aangesien die proefpersoon die hoeveelheid krag wat hy toepas geleidelik verhoog totdat die proefpersoon al die las ondersteun. Op die punt waar die oefenmaat die gewig heeltemal na die onderwerp oorgedra het, moet hy aandui dat hy dit gedoen het, en begin om die stel te bepaal.

Oefeninge wat interpersoonlike oordrag vereis, moet uitgevoer word met masjiene met gesmelte arme eerder as onafhanklike bewegingswapens, en haakstange eerder as halters, aangesien dit die onderwerp en die oefenmaat beter toelaat om die gewig tydens die oordrag te beheer en dus baie veiliger is.

Intrapersoonlike Weerstandoordrag

Tydens intrapersoonlike oordrag, eerder as dat die weerstandsoordrag tussen die instrukteur of opleidingsvennoot en die onderwerp plaasvind, dra die onderwerp die weerstand oor van een van sy spiergroepe na 'n ander. Byvoorbeeld, wanneer die uitvoering van statiese of negatiewe slegs ken op die Nautilus Multi Oefening, sou die onderwerp die masjien’s wa so stel dat terwyl staan ​​op die boonste trap die chinning bar is gelyk met die bokant van sy bors. Hy sal dan geleidelik sy voete van die trap af lig en sy liggaamsgewig van sy bene na sy arms en bolyf oordra. Dit kan ook uitgevoer word met 'n gewone chinning-staaf met 'n trapleer of lang stoel.

Posisiespesifieke vs. Volreeks-sterkteverhogings

Isometriese oefeninge moet naby die middel van die bewegingsreeks uitgevoer word vir die meeste oefeninge waar die oorvleueling van miofibrille optimale kragproduksie en groter spanning in die geteikende spiere moontlik maak. Posisies by of naby die eindpunt kan meer effektief wees in sommige oefeninge solank aktiewe ontoereikendheid van die geteikende spiere vermy word. Isometrie moet nie uitgevoer word by of naby die eindpunt van saamgestelde stootoefeninge waar die doelspiere min betekenisvolle weerstand ondervind nie, terwyl die gewrigte onderhewig is aan groot drukkragte as gevolg van die hefboomvoordeel.

Arthur Jones, die stigter van Nautilus, het dikwels gesê dat die enigste posisie waarin 'n mens in staat is om al die vesels in 'n spesifieke spier te kontrakteer, die volle spiersametrekking is. Dit is verkeerd. Terwyl posisies of bewegingsgebiede wat 'n mindere mate van verkorting behels dalk nie so ideaal is nie, vereis motoriese eenheidwerwing (sametrekking) en dus die moontlikheid van stimulasie, nie om na die “volledig-gekontrakteerde” posisie te beweeg nie. Werwing van motoreenhede hang af van die kragvereistes van die oefening. As die kragvereistes hoog genoeg is, word alle motoreenhede gewerf, ongeag waar in die ROM die oefening uitgevoer word.

Gebaseer hierop wil dit voorkom asof isometriese oefenprotokolle soos tydige statiese sametrekking en statiese vashouvermoë moet lei tot volle-reeks eerder as posisie- of reeksspesifieke sterkteverhogings. Die feit dat baie oefeninge veelvuldige spiere of groepe spiere behels waarvan die relatiewe betrokkenheid aansienlik oor die volledige ROM kan wissel, bemoeilik die probleem ietwat.

Saamgestelde (meervoudige of lineêre) bewegings

Isometriese oefenprotokolle sal dalk nie volle sterktetoename in sommige saamgestelde bewegings lewer nie. Anders as baie eenvoudige of enkelgewrigsoefeninge, is aansienlik meer spiere tydens saamgestelde oefeninge betrokke en die relatiewe betrokkenheid van daardie spiere verander voortdurend van posisie tot posisie deur die hele bewegingsreeks. Afhangende van die mate van verandering in spierbetrokkenheid van posisie tot posisie, kan isometriese oefening in sommige posisies van 'n saamgestelde beweging onvoldoende belading en stimulasie bied vir spiere wat nie in 'n minimale mate by die posisie betrokke is nie, maar kan tot 'n groter mate in ander dele van die ROM. As gevolg hiervan sou daar 'n onproportioneel lae sterkte toename in die dele van die ROM wees.

Byvoorbeeld, tydens die aftrek van die voorste greep, is die bors betrokke by die skouerverlenging tydens die eerste 30 tot 45 grade beweging. As 'n persoon tydige statiese sametrekking of statiese hou op die voorste greep aftrek in 'n posisie verby daardie gedeelte van die ROM wat die borskas behels, sal die gevolglike kragtoenames nie eweredig wees oor die volle omvang van die oefening nie. Hulle sal laer wees as die ROM met die bors.

Besef dat in so 'n situasie alhoewel kragtoenames dalk nie eweredig is oor die volle ROM nie, dit ook nie beperk sal wees tot die spesifieke posisie wat opgelei is nie.

In oefeninge waar dit 'n probleem is, moet 'n mens die oefening óf uitvoer in 'n posisie waarin al die spierstrukture betrokke by die dinamiese weergawe van die oefening sinvol gelaai is óf die onvoldoende gelaaide spiere met 'n ander oefening aanspreek.

Gewig vs. Weerstand

Tydens saamgestelde stootbewegings soos hurke, borsdruk en oorhoofse druk, word geen van die spiere wat by die oefening betrokke is, betekenisvol gelaai naby die posisie van volle verlenging as gevolg van veranderinge in hefboomwerking nie. In posisies by of naby volle verlenging ondersteun die bene die grootste deel van die las en kry die spiere aansienlik minder weerstand. Hierdie hefboomvoordeel is die rede waarom 'n persoon gedeeltelike herhalings in hierdie oefeninge oor die gedeelte van die ROM naby verlenging kan doen met baie meer gewig as wat hulle kan gebruik om die oefening oor die volle ROM uit te voer.

Gewig en weerstand is nie dieselfde nie. Gewig is 'n skalêre hoeveelheid, 'n maatstaf van 'n voorwerp’ se massa. Weerstand is 'n vektorhoeveelheid, 'n tipe krag wat in die geval van oefening 'n produk is van gewig en hefboom. Afhangende van die hefboomwerking, kan 'n mens baie gewig hê met baie min weerstand in sommige posisies, soos in die bogenoemde saamgestelde oefeninge, of 'n geweldige hoeveelheid weerstand met baie min gewig. Dit is die weerstand wat die spier tydens oefening ondervind wat belangrik is.

By gebruik met saamgestelde stootbewegings moet statiese houe uitgevoer word in die posisie waar die teikenspiere die grootste weerstand ondervind, nie waar die meeste gewig hanteer kan word nie. Hierdie posisie sal wissel na gelang van die toerusting wat gebruik word. 'N Uitsondering hierop is gevalle waar hierdie tegnieke gebruik word om 'n besering of 'n fisiese toestand te voorkom wat dinamiese oefensessies voorkom, in welke geval die posisie afhang van die fisiese beperkings van die vakke.

Sterkte toets

Vergelykings van die relatiewe doeltreffendheid van verskillende oefenprotokolle deur 'n dinamiese toets te gebruik om veranderinge in sterkte te meet, is grootliks onakkuraat as gevolg van verskeie faktore. Dit sluit in die gevolge van vaardigheid, wrywing van toestelle, wisseling van wringkrag van liggaam en apparaat, momentum en probleme met posisionele verwysing, ens. Deur statiese toetse uit te voer, los die meeste van hierdie probleme op en verminder ander. Statiese toetsing behels geen beduidende wrywing, geen momentum, geen wringkragverandering nie, en verminder die invloed van vaardigheid deur dinamiese oefenprotokolle. MedX mediese masjiene maak dit ook moontlik om die liggaam se wringkrag en faktor vir wringkrag wat deur gestoor energie tydens isometriese toetsing geproduseer word, akkuraat te balanseer.


Hoe werk isometriese kontraksie? - Biologie

Eenheid ses. Diere Lewe

22. Die diereliggaam en hoe dit beweeg

Drie soorte spiere vorm saam die gewerwelde spiersisteem. Soos ons bespreek het, kan die gewerwelde liggaam beweeg omdat skeletspiere die bene met groot krag trek. Die hart pomp as gevolg van die inkrimping van die hartspier. Voedsel beweeg deur die ingewande as gevolg van die ritmiese sametrekkings van gladde spiere.

Aksies van skeletspier

Skeletspiere beweeg die bene van die skelet. Sommige van die belangrikste menslike spiere is regs aangedui in figuur 22.12. Spiere word aan bene geheg deur bande van digte bindweefsel wat senings genoem word. Bene draai om buigsame verbindings wat gewrigte genoem word, heen en weer getrek deur die spiere wat daaraan geheg is. Elke spier trek aan 'n spesifieke been. Die een punt van die spier, die oorsprong, word deur 'n sening aan 'n been geheg wat stil bly tydens 'n sametrekking. Dit verskaf 'n voorwerp waarteen die spier kan trek. Die ander kant van die spier, die invoeging, is vasgemaak aan 'n been wat beweeg as die spier saamtrek. Byvoorbeeld, oorsprong en invoeging vir die sartoriusspier is aan die linkerkant in figuur 22.12 gemerk. Hierdie spier help om die been by die heup te buig en die knie na die bors te bring. Die oorsprong van die spier is by die heup en bly stil. Die invoeging is by die knie, sodat wanneer die spier saamtrek (korter word) die knie na die bors opgetrek word.

Figuur 22.12. Die spierstelsel.

Sommige van die belangrikste spiere in die menslike liggaam is gemerk.

Spiere kan net trek, nie stoot nie, omdat myofibrille eerder saamtrek as uitbrei. Om hierdie rede word die spiere in die beweegbare gewrigte van gewerwelde diere in teenoorgestelde pare vasgemaak, flexors en extensors, wat die bene in verskillende rigtings beweeg wanneer hulle saamtrek. Soos u in figuur 22.13 kan sien, word die onderbeen nader aan die dy beweeg wanneer die buigspier aan die agterkant van u bobeen saamtrek. As die ekstensorspier aan die voorkant van u bobeen saamtrek, word die onderbeen in die teenoorgestelde rigting beweeg, weg van die dy.

Figuur 22.13. Flexor en extensor spiere.

Beweging van die ledemate is altyd die gevolg van spiersametrekking, nooit spierverlenging nie. Spiere wat ledemate intrek, word fleksors genoem. Spiere wat ledemate verleng, word ekstensors genoem.

Alle spiere trek saam, maar daar is twee tipes spiersametrekkings, isotonies en isometries. By isotoniese kontraksies word die spier korter en beweeg die bene soos pas beskryf. By isometriese kontraksies word 'n krag deur die spier uitgeoefen, maar die spier word nie verkort nie. Dit gebeur as u iets baie swaar probeer lig. Uiteindelik, as jou spiere genoeg krag genereer en jy in staat is om die voorwerp op te lig, word die isometriese sametrekking isotonies.

Niemand wat die vetring sien wat my middel versier nie, sou my as 'n hardloper neem. Slegs in my geheue staan ​​ek op met die robins, trek my drafskoene aan, wip by die voordeur uit en hardloop die strate om Washington Universiteit voor ek werk toe gaan. Nou is my 5-K-lopies 30-jarige herinneringe.

Elke melding wat ek maak van my hardloop in 'n wedloop, roep net skree van die lag van my dogters op en 'n boog van my vrou. Geheue is die wreedste as dit akkuraat is.

Ek onthou duidelik die dag toe ek opgehou hardloop het. Dit was 'n koel herfsoggend in 1978, en ek was deel van 'n gepeupel wat 'n 5-K (dit is 5 kilometer vir die oningewyde) wedren hardloop, wat om die heuwels naby die universiteit gedraai het. Ek het pynflitse in my bene onder die knieë begin kry—soos shin splints, maar baie erger. Stel jou voor dat daar vuur op jou bene stort. Het ek opgehou hardloop? Nee. Soos 'n beenkop het ek aangehou en deur die pyn gewerk, "en die wedloop voltooi. Ek het sedertdien nog nooit 'n wedloop gehardloop nie.

Ek het 'n spier in my bobeen getrek, wat 'n deel van die pyn veroorsaak het. Maar dit was nie al nie. The pain in my lower legs wasn't shin splints, and didn't go away. A trip to the doctor revealed multiple stress fractures in both legs. The X rays of my legs looked like tiny threads had been wrapped around the shaft of each bone, like the red stripe on a barber's pole. It was summer before I could walk without pain.

Wat het verkeerd gegaan? Isn't running supposed to be GOOD for you? Not if you run improperly. In my enthusiasm to be healthy, I ignored some simple rules and paid the price. The biology lesson I ignored had to do with how bones grow. The long bones of your legs are not made of stone, solid and permanent. They are dynamic structures, constantly being re-formed and strengthened in response to the stresses to which you subject them.

To understand how bone grows, we first need to recall a bit about what bone is like. Bone, as you have learned in this chapter, is made of fibers of a flexible protein called collagen stuck together to form cartilage. While an embryo, all your bones are made of cartilage. As your adult body develops, the collagen fibers become impregnated with tiny, needle-shaped crystals of calcium phosphate, turning the cartilage into bone. The crystals are brittle but rigid, giving bone great strength. Collagen is flexible but weak, but like the epoxy of fiberglass, it acts to spread any stress over many crystals, making bone resistant to fracture. As a result, bone is both strong and flexible.

When you subject a bone in your body to stress—say, by running—the bone grows so as to withstand the greater workload. How does the bone "know” just where to add more material? When stress deforms the collagen fibers of a leg bone, the interior of the collagen fibers becomes exposed, like opening your jacket and exposing your shirt. The fiber interior produces a minute electrical charge. Cells called fibroblasts are attracted to the electricity like bugs to night lights, and secrete more collagen there. As a result, new collagen fibers are laid down on a bone along the lines of stress. Slowly, over months, calcium phosphate crystals convert the new collagen to new bone. In your legs, the new bone forms along the long stress lines that curve down along the shank of the bone.

Now go back 30 years, and visualize me pounding happily down the concrete pavement each morning. I had only recently begun to run on the sidewalk, and for an hour or more at a stretch. Every stride I took those mornings was a blow to my shinbones, a stress to which my bones no doubt began to respond by forming collagen along the spiral lines of stress. Had I run on a softer surface, the daily stress would have been far less severe. Had I gradually increased my running, new bone would have had time to form properly in response to the added stress. I gave my leg bones a lot of stress, and no time to respond to it. I pushed them too hard, too fast, and they gave way.

Nor was my improper running limited to overstressed leg bones. Remember that pulled thigh muscle? In my excessive enthusiasm, I never warmed up before I ran. I was having too much fun to worry about such details. Wiser now, I am sure the pulled thigh muscle was a direct result of failing to properly stretch before running.

I was reminded of that pulled muscle recently, listening to a good friend of my wife's describe how she sets out early each morning for a long run without stretching or warming up. I can see her in my mind's eye, bundled up warmly on the cooler mornings, an enthusiastic gazelle pounding down the pavement in search of good health. Unless she uses more sense than I did, she may fail to find it.

Recall from figure 22.6 that myofibrils are composed of bundles of myofilaments. Far too fine to see with the naked eye, the individual myofilaments of vertebrate muscles are only 8 to 12 nanometers thick. Each is a long, threadlike filament of the pro- terns actin or myosin. An actin filament consists of two strings of actin molecules wrapped around one another, like two strands of pearls loosely wound together. A myosin filament is also composed of two strings of protein wound about each other, but a myosin filament is about twice as long as an actin filament, and the myosin strings have a very unusual shape. One end of a myosin filament consists of a very long rod, while the other end consists of a double-headed globular region, or “head.” Overall, a myosin filament looks a bit like a two-headed snake. This odd structure is the key to how muscles work.

How Myofilaments Contract

The sliding filament model of muscle contraction, seen in the Key Biological Process illustration below, describes how actin and myosin cause muscles to contract. Focus on the knobshaped myosin head in panel 1. When a muscle contraction begins, the heads of the myosin filaments move first. Like flexing your hand downward at the wrist, the heads bend backward and inward as in panel 2. This moves them closer to their rodlike backbones and several nanometers in the direction of the flex. In itself, this myosin head-flex accomplishes nothing—but the myosin head is attached to the actin filament! As a result, the actin filament is pulled along with the myosin head as it flexes, causing the actin filament to slide by the myosin filament in the direction of the flex (the dotted circles in panel 2 indicate the movement of the actin filament). As one after another myosin head flexes, the myosin in effect “walks” step by step along the actin. Each step uses a molecule of ATP to recock the myosin head (in panel 3) before it attaches to the actin again (panel 4), ready for the next flex.

How does this sliding of actin past myosin lead to myofibril contraction and muscle cell movement? The actin filament is anchored at one end, at a position in striated muscle called the Z line, indicated by the lavender-colored bars toward the edges in the Key Biological Process illustration on the facing page. Two Z lines with the actin and myosin filaments in between make up a contractile unit called a sarcomere. Because it is tethered like this, the actin cannot simply move off. Instead, the actin pulls the anchor with it! As actin moves past myosin, it drags the Z line toward the myosin. The secret of muscle contraction is that each myosin is interposed between two pairs of actin filaments, which are anchored at both ends to Z lines, as shown in panel 1. One moving to the left and the other to the right, the two pairs of actin molecules drag the Z lines toward each other as they slide past the myosin core, shown progressively in panel 2 and panel 3. As the Z lines are pulled closer together, the plasma membranes to which they are attached move toward one another, and the cell contracts.

When a muscle is relaxed, its myosin heads are “cocked” and ready, but are unable to bind to actin. This is because the attachment sites for the myosin heads on the actin are physically blocked by another protein, known as tropomyosin. Myosin heads therefore cannot bind to actin in the relaxed muscle, and the filaments cannot slide.

For a muscle to contract, the tropomyosin must first be moved out of the way so that the myosin heads can bind to actin. This requires calcium ions (Ca++). When the Ca++ concentration of the muscle cell cytoplasm increases, Ca++, acting through another protein, causes the tropomyosin to move out of the way. When this repositioning has occurred, the myosin heads attach to actin and, using ATP energy, move along the actin in a stepwise fashion to shorten the myofibril.

Muscle fibers store Ca++ in a modified endoplasmic reticulum called the sarcoplasmic reticulum. When a muscle fiber is stimulated to contract, Ca++ is released from the sarcoplasmic reticulum and diffuses into the myofibrils, where it initiates contraction. When a muscle works too hard, the Ca++ channels become leaky, releasing small amounts of Ca++ that act to weaken muscle contractions and result in muscle fatigue.

Key Learning Outcome 22.8. Muscles are made of many tiny threadlike filaments of actin and myosin called myofilaments. Muscles work by using ATP to power the sliding of myosin along actin, causing the myofibrils to contract.

Running, flying, and swimming require more energy than sitting still, but how do they compare? The greatest differences between moving on land, in the air, and in water result from the differences in support and resistance to movement provided by water and air. The weight of swimming animals is fully supported by the surrounding water, and no effort goes into supporting the body, while running and flying animals must support the full weight of their bodies. On the other hand, water presents considerable resistance to movement, air much less, so that flying and running require less energy to push the medium out of the way.

A simple way to compare the costs of moving for different animals is to determine how much energy it takes to move. The energy cost to run, fly, or swim is in each case the energy required to move one unit of body mass over one unit of distance with that mode of locomotion. (Energy is measured in the metric system as a kilocalorie [kcal] or, technically, 4.184 kilojoules [note that the Calorie measured in food diets and written with a capital C is equivalent to 1 kcal] body mass is measured in kilograms, where 1 kilogram [kg] is 2.2 pounds distance is measured in kilometers, where 1 kilometer [km] is 0.62 miles). The graph to the right displays three such "cost-of-motion” studies. The blue squares represent running the red circles, flying and the green triangles, swimming. In each study, the line is drawn as the statistical "best-fit” for the points. Some animals like humans have data in two lines, as they both run (well) and swim (poorly). Ducks have data in all three lines, as they not only fly (very well), but also run and swim (poorly).

a. Variables. In the graph, what is the dependent variable?

b. Comparing Continuous Variables. Do the three modes of locomotion have the same or different costs?

a. For any given mode of locomotion, what is the impact of body size on cost of moving?

b. Is the impact of body mass the same for all three modes of locomotion? If not, which mode's cost is least affected by body mass? Why do you think this is so?

a. Comparing the energy costs of running versus flying for animals of the same body size, which mode of locomotion is the most expensive? Why would you expect this to be so?

b. Comparing the energy costs of swimming to flying, which uses the least energy? Why would you expect this to be so?

4. Drawing Conclusions In general, which mode of locomotion is the most efficient? The least efficient? Why do you think this is so?

a. How would you expect the slithering of a snake to compare to the three modes of locomotion examined here? Hoekom?

b. Do you think the costs of running by an athlete decrease with training? Hoekom? How might you go about testing this?

1. One of the innovations in animal body design, segmentation, allowed for

a. development of efficient internal organ systems.

b. more flexible movement as individual segments can move independently of each other.

c. locating organs in different areas of the body.

d. early determination of embryonic cells.

2. Which of the following is the correct organization sequence from smallest to largest in animals?

a. cells, tissues, organs, organ systems, organism

b. organism, organ systems, organs, tissues, cells

c. tissues, organs, cells, organ systems, organism

d. organs, tissues, cells, organism, organ systems

3. Which of the following is not a function of the epithelial tissue?

b. provide sensory surfaces

d. protect underlying tissue from damage and dehydration

4. An example of connective tissue is

a. nerve cells in your fingers.

5. When a person has osteoporosis, the work of _____ falls behind the work of _____.

a. osteoclasts osteoblasts

c. osteoblasts osteoclasts

6. Nerve impulses pass from one nerve cell to another through the use of

7. The type of muscle used to move the leg when walking is

d. All of the these are correct.

8. The vertebral column is part of the

9. Movement of a limb in two directions requires a pair of muscles because

a. a single muscle can only pull and not push.

b. a single muscle can only push and not pull.

c. moving a limb requires more force than one muscle can generate.

10. The role of calcium in the process of muscle contraction is to

a. gather ATP for the myosin to use.

b. cause the myosin head to shift position, contracting the myofibril.

c. cause the myosin head to detach from the actin, causing the muscle to relax.

d. expose myosin attachment sites on actin.

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What is an Isometric Contraction? (met foto's)

An isometric contraction is a specific type of muscle contraction used in some forms of training. Neither the joint angle or the length of the muscle changes during this type of muscle contraction. It takes place while the body is in a static pose, without any range of motion.

Beginners may not understand isometric exercise because it's not as easy to see the muscle contracting while it is immobile. This type of contraction is a specific training tool that only works on a muscle in its static position. By contrast, lots of sports related training requires isotonic contraction that happens through a range of motion.

Some experts believe that isometric contractions are helpful for specific kinds of training. Some examples of common isometric exercise drills include wall sitting, where the individual maintains an unsupported sitting position against the wall for a specific period of time. Others might include holding free weights at static angles from the body, or pushing against a wall or other unmovable barrier.

Some bodybuilders in various training programs use this type of exercise. The renowned strongman Charles Atlas included some similar kinds of activities in his “Dynamic Training” program, although fitness guides point out that most of these were not truly isometric because, while there was resistance balanced against a muscle group, the muscles still moved during the contractions.

Any activity where the body pushes against a static resistance is an isometric activity, and all kinds of muscle groups can get stronger as a result. The core, the central muscle area that supports the body, can especially benefit from this type of exercise. Trainers can get their limbs stronger and more capable with isometric training, though many experts still recommend mixing it with the more common isotonic training, such as free weights, to allow for development through a range of motion.

Beginners who want to include isometric contraction in a routine can take a look at public materials from a gym or health club that show a range of upper and lower body activities for promoting strength and body response. Trainers can analyze a person’s condition and fitness history, and recommend a personalized program that contains both isometric and isotonic exercises. With a diversity of exercise types, muscle groups can develop fuller capabilities for sports, recreation, or functional use.


Muscle produces force by forming cross-bridges, using energy released from ATP. While the magnitude and duration of force production primarily determine the energy requirement, nearly a century ago Fenn observed that muscle shortening or lengthening influenced energetic cost of contraction. When work is done by the muscle, the energy cost is increased and when work is done on the muscle the energy cost is reduced. However, the magnitude of the ‘Fenn effect’ and its mirror (‘negative Fenn effect’) have not been quantitatively resolved. We describe a new technique coupling magnetic resonance spectroscopy with an in vivo force clamp that can directly quantify the Fenn effect [E=Ek+W, energy liberated (E) equals the energy cost of isometric force production (Ek) plus the work done (W)] and the negative Fenn effect (E=EkW) for one muscle, the first dorsal interosseous (FDI). ATP cost was measured during a series of contractions, each of which occurred at a constant force and for a constant duration, thus constant force–time integral (FTI). In all subjects, as the FTI increased with load, there was a proportional linear increase in energy cost. In addition, the cost of producing force greatly increased when the muscle shortened, and was slightly reduced during lengthening contraction. These results, though limited to a single muscle, contraction velocity and muscle length change, do quantitatively support the Fenn effect. We speculate that they also suggest that an elastic element within the FDI muscle functions to preserve the force generated within the cross-bridges.

All muscles produce force during contraction. The mechanisms, costs and consequences have been the fodder for studies for at least the past century. Prominent among these studies are the pioneering experiments of A. V. Hill and his remarkable students (for review, see Bassett, 2002). One of those students, Wallace Fenn, is credited with the observation that if a muscle does work (in a shortening contraction), the energy it requires is increased by an amount roughly equal to the work done (Fenn, 1923). In an outstanding paper, Rall (1982) summarized the ‘Fenn effect’ quantitatively with the simple equation E=Ek+W [energy liberated (E) equals the energy cost of isometric force production (Ek) plus the work done (W)] but cautioned that the Fenn effect has not been quantitatively demonstrated.

A second observation also emerged from the same early experiments of Fenn. Namely, if muscles are stretched when they actively ‘contract’, the energy cost of force production is reduced compared with an isometric contraction of the same magnitude and duration. Fenn's second and less familiar conclusion was that ‘lengthening during contraction decreases the energy liberated’. Specifically he stated, ‘When the work done by the muscle is negative, the excess energy is also negative’ (Fenn, 1924). This observation caused considerable intrigue and, in retrospect, a somewhat puzzling search led by none other than Fenn's mentor A. V. Hill. Hill led an effort to demonstrate that the identical chemical reactions that consume ATP in muscle during shortening could be reversed when muscles are subjected to mechanical stretch (‘negative work’) during lengthening (eccentric) contractions (Abbott and Aubert, 1952 Abbott et al., 1952 Hill, 1960 Hill and Howarth, 1959). In other words, the operational hypothesis was that during lengthening (eccentric) contractions, muscles synthesize ATP, minimizing the energy cost relative to an isometric contraction (E=EkW?). For an outstanding review of this topic and its history, see Loiselle et al. (2008).

Although the notion of a muscle behaving like a generator when used ‘in reverse’ has been rejected and forgotten, the reduced cost of muscle force production during a lengthening contraction remains a poorly explained reality. Lengthening contractions are common in all animal movements, and it is apparent that these occur at a reduced energetic cost for the equivalent amount (magnitude and duration) of force produced relative to a shortening contraction (Bigland-Ritchie and Woods, 1976). Despite the general acceptance of this idea, there is no clear consensus of the magnitude of energy savings, let alone its cause. For example, when lengthening contractions are compared with isometric contractions, Beltman et al. (2004), like Bigland-Ritchie and Woods (1976), reported a reduction in the cost of lengthening contractions while paradoxically Ryschon et al. (1997) found a slight increase in cost, although neither result was statistically significant. One study on isolated single fibers examined energetics via inorganic phosphate release in shortening and isometric contractions (Homsher et al., 1997). They confirmed that shortening was more energetically costly than the equivalent force produced isometrically. Interestingly, this same study also included four fibers that were stretched while activated. Energy costs in these fibers were among the lowest measured in their study but an inadequate sample size prevented a statistical analysis.

Thus, rather than ‘settling’ the debate initiated by Fenn, many questions linger after nearly a century of research. Significant gaps remain in our understanding, in particular of the in vivo relationship between force production, energy cost and the magnitude and nature of the muscle load. While both the mechanics and cost of cross-bridge formation are well understood, the substantial movement-dependent variation in the energy cost of the force–time integral (FTI – the product of force production and its duration) of skeletal muscle is not. What is the nature of the Fenn effect in vivo? Is there a ‘negative Fenn effect’ such that lengthening (eccentric) contractions occur at a reduced cost compared with isometric force production?


Benefits of Isometric Exercises

There are many benefits to using isometric exercise after injury or surgery. These may include:

  • You can safely contract a muscle while protecting a surgical incision or scar tissue.
  • Your muscle can be strengthened in a very specific range of motion around a joint.
  • No special equipment is necessary to perform isometric exercises.

Your physical therapist can help you determine if isometric exercise will benefit you for your specific condition.


Isometric Exercises That Work!

Maximum hypertrophy of most muscle groups is best accomplished with a combination of three different approaches to training:

  1. You should train heavy with loads that are around 85% of your one-rep max for 8-10 sets. You can’t go wrong with 10 sets of 3 reps.
  2. During a different workout, you should rip off the maximum number of reps in 10 seconds with a load that’s 60-70% of 1RM for 8-10 sets.
  3. Trigger muscle growth is with isometrics.

You might’ve experimented with isometrics in the past and if you’re like most lifters, that experimentation was limited to holding the last rep of a set for as long as possible. And it probably didn’t help much. Isometrics are something I didn’t experiment with nearly enough in my early training days. Like most of you, I considered it nothing more than an afterthought – just hold the last rep for as long as possible and hope that something magical happens. But magical stuff never did happen, so I tried to figure out why.

My approach for troubleshooting muscle growth doesn’t consist of experimenting with dozens of different training parameters for months on end with all of my clients. That takes too long and it doesn’t guarantee success. Instead, I troubleshoot by looking at athletes that have extraordinary development in a specific muscle group. Then I try to figure out what they’re doing that the rest of us aren’t doing.

What I Learned From Ballet and Gymnasts

If you were born with genetically inferior calves or biceps, you know how tough it is to get those damn things to grow. We all know that biceps-building articles get the most hits on the Internet and there’s an endless discussion of theories on how to trigger growth in the calves. Indeed, if you haven’t figured out how to make your biceps or calves bigger, you’re definitely not alone.

A while ago I happened to watch a documentary on ballet dancers, and what really caught my attention was their calf development. It didn’t matter if the dancer was young, old, male or female, they all had calves that were well above the norm. That’s quite an accomplishment considering that most of them spend their training days completely malnourished, consuming nothing more than glasses of distilled water and a bowls of tofu-scented oxygen. Likewise, we’ve all seen the mind-blowing arms and shoulders on those Olympic dudes who master the rings. You won’t find a better pair of proportionally large biceps on any athlete, including professional bodybuilders.

So what are ballet dancers and rings gymnasts doing to their calves and biceps that you probably aren’t doing? A whole lot of isometrics, that’s what. Ballet dancers spend considerable time during their routines with their heels elevated in the peak-contraction calf raise position. And the routines that gymnasts do from the rings consist of moving from one isometric hold to the next as opposed to busting out endless reps.

Why Are Isometrics So Powerful?

An intense isometric contraction is terrific for muscle growth for two reasons. First, it quickly recruits the largest motor units because it’s a maximum voluntary contraction. Second, isometrics increase the neural drive between the motor cortex in your brain and the trained muscle. When you perform a regular, full range of motion rep, the tension in the working muscle will vacillate due to biomechanical changes throughout the movement. This makes it more difficult to really feel the muscle working. It’s no surprise that most guys who can’t get their biceps or calves to grow also have a tough time squeezing the muscle to the highest possible level of tension.

If you experienced subpar results from isometrics in the past, it’s probably because you did them when you were already fatigued, such as at the end of a set. This is the least effective time to use an isometric because your descending neural drive and largest motor units are already fatigued from the reps that preceded it.

How to Add Isometrics Into Your Plan

There are three rules to follow in order to get the best muscle-building results from isometrics:

  1. Do Them Separately From Your Main Workouts. Fatigue is a complex animal that consists of peripheral and central nervous system components, and it’s most accurately defined as “an inability to reach your highest level of performance.” In order to trigger the most growth with isometrics it’s important to do them when your neural drive and largest motor units are free from any fatigue. Therefore, do them at least six hours away from your primary workouts, or on a different day.
  2. Perform 5 Sets of an Intense 10-Second Squeeze. Virtually all of my training parameters for concomitant gains in size and strength stemmed from Bill Starr’s 5࡫ program. I’ve found that when you’re training with an intense contraction, or a relatively heavy load, five work sets hits the sweet spot for almost everyone. And a 10-second continuous contraction is the top end for keeping the largest motor units recruited. Rest 2-3 minutes before repeating the isometric hold, but feel free to perform another isometric for a different muscle group during that time.
  3. Progress by Increasing the Training Frequency. A higher training frequency is the common key element among athletes that have developed proportionally large muscle groups. A gymnast hangs from the rings every day, and a ballet dancer is constantly up on the toes throughout the week. When you have a stubborn body part, the best solution is to increase the number of times you train it each week. Isometrics are an ideal supplement to your regular training program because they represent a unique training stimulus that doesn’t require an extended recovery time. Start training your most underdeveloped muscle group twice per week with isometrics, in byvoeging to your current training program. Every other week add another session until you reach 4-6 sessions per week, depending on your recovery capacity.

The Best Exercises

Biceps/Forearms/Upper Back:&emspSingle-Arm Hang

Want to know how those rings gymnasts built such incredible biceps? One word: maltese. That exercise is, without a doubt, the most effective strength exercise to add biceps mass.

It’s also the most gevaarlik biceps exercise. In fact, training your way up to a maltese is so risky that I’ve hesitated for years to even mention the correlation between it and massive biceps. The likelihood of tearing your biceps, jacking up your elbows, or screwing up your shoulders is enormous. You should only embark on that journey with an Olympic-level gymnastics coach.

Alternately, the isometric exercise I recommend for biceps development is the single-arm hang.

How to do it: Hang from a pull-up bar with an underhand (palms up) grip with the pinky fingers touching each other. Pull yourself up so the elbows are at 90 degrees. Next, quickly grab your left wrist with your right hand so the left hand is the only one gripping the bar. Maintain the 90-degree left elbow angle as your forearms, biceps, and upper-back fire to maintain your body position. Switch sides and repeat with the right hand gripping the bar.

Calves:&emspSingle-Leg Standing Calf Raise Peak Contraction

How to do it: Let’s say you’re training the right calf first. Stand barefoot on your right foot, spread the toes as wide as possible, and then perform one calf raise to the peak contraction, keeping your right leg locked straight. Squeeze the peak contraction as intensely as possible by pushing through the big toe. Limit the amount of assistance you give your balance and challenge yourself to be able to perform the calf raise and hold without any balance support. That’s much harder than it sounds. Repeat with the left calf.

Hamstrings:&emspNordic Hamstring

How to do it: Place a firm foam roller on the floor, rest your upper shins on it, hook your heels under a padded, secure structure, then shift your body as far forward as your strength allows. There should be no hip hinge in the forward position – your body should be in a straight line from the neck to the knees. Most guys only need to shift their body forward around 10-15 degrees before the hamstrings start firing intensely.

The Nordic hamstring is excellent for adding muscle to the hamstrings, but it’s also an exception to the frequency guidelines mentioned earlier. This intense exercise shouldn’t be performed more than three times per week, and you should work up to that frequency very slowly.

Glutes:&emspHip Hinge With Abduction/External Rotation

How to do it: Place a strong mini-band around your thighs, just above the knees. The feet are slightly wider than shoulder width and pointed straight ahead. From a standing position, place the palm of your hands against the front of the thighs, then push your hips back and let the knees bend slightly while sliding your fingertips forward. When your fingertips reach your knees, you’re at the correct knee, hip and torso position. Maintain this body position as you push your knees out to the side, against the resistance of the band, without rolling the feet outward. Hold your arms straight out in front during the exercise.

The purpose of this drill is to maximally engage the glute fibers that abduct and externally rotate the hip since those are the fibers that are most underdeveloped on almost everyone.

Chest:&emspPush-Up Peak Contraction

How to do it: Get in the top position of a push-up, hands wider than shoulder width and elbows just short of lockout. Brace your abs, squeeze the glutes, and then attempt to pull the hands together as intensely as possible. Your hands won’t move, but your pectorals will be firing like hell. You can also do this drill with your feet elevated on a bench or Swiss ball.

Triceps:&emspDip Peak Contraction

How to do it: Get in the top position of a dip on rings or parallel bars. Push your palms down to remove any shoulder shrug and then maximally squeeze the triceps to lock out the elbow joints at the end range of motion. There should be some slight hyperextension in your elbow joint at full lockout. Strong guys can do this drill with extra weight added to a chin/dip belt, but most people should start with just body weight.

Importantly, your elbows must slightly hyperextend at the end range lockout to take full advantage of this drill. If your elbow(s) can’t slightly hyperextend naturally (without load), get soft tissue work around the elbow to free up the restriction because it will eventually lead to problems with all upper body exercises.

Deltoids:&emspCrucifix

How to do it: Stand with a weight in each hand, lift your arms up and out to the sides until they’re parallel with the ground. Maintain this arm position while keeping the palms facing down and without shrugging the shoulders. Keep the shoulder blades pulled down throughout the hold.

What About the Quads?

You probably noticed that I didn’t mention an isometric exercise for the quadriceps.

I’m not a fan of the leg extension machine, even though it’s popular for isometrics. Furthermore, I haven’t been satisfied with the times I’ve experimented with free weight or body weight isometric exercises to challenge the quads because most of them irritate the knee joint.

While isometric holds are intended to increase hypertrophy, the best way to grow the quads with extra workouts is to pedal on an exercise bike with the highest resistance you can handle for 3-5 minutes straight. The quads thrive on long duration sets. Just ask any cyclist, speed skater, or downhill skier.


Kyk die video: Я строитель 45 лет. но я никогда не видел такой техники раньше - гениальные работники.5 (September 2022).