the isoinertial technology (1)

8/17/2019 The Isoinertial Technology (1)

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THE ISOINERTIAL TECHNOLOGY

Julio Tous Fajardo1 and Marco Pozzo

INEFC Barcelona. Laboratorio de Biomecánica.Karolinska Institute. Department of Phsiolo! and Pharmacolo!.

1! INTRO"#CTION

Durin! the late "#$%s t&o researchers from Karolinska Institutet '(tockholm) had a brilliant idea

that later became a bi! inno*ation in the stren!th trainin! field. +ans Ber! ,a doctoral student, and Per

-esch ,his mentor, had one of their usual meetin!s at a popular restaurant in the beautiful (&edish

capital to share some beers and then eno a dinner. Ber! &as an/ious to sho& his mentor an idea that

&as around his brain durin! the past das and that could be the solution to the problem of stren!th

trainin! in a micro!ra*it en*ironment. 0sin! a paper napkin he started to dra& the basic scheme of a

!ra*it,independent er!ometer to pro*ide an inertial accommodated resistance. -he solution &as

simple but !enial1 b means of a special setup2 a fl&heel is set into rotational motion *ia concentric

muscle action and decelerated b a subse3uent eccentric muscle action. B performin! the brakin!

eccentric action o*er a smaller an!ular displacement and hence &ith a !reater muscle tor3ue than that

for concentric action2 an eccentric o*erload is accomplished.

-he first presentation of the de*ice &as performed at a space conference at -riestre #. No&adas2

more than 4% scientific publications 'includin! some doctoral thesis dissertations) ha*e *alidated this

so,called isoinertial technolo!. 5mon! all studies a special mention is deemed to the 6 90-day bed rest

study72 performed at the (pace Clinic in -oulouse &hich has produced se*eral publications includin!

the thesis of Born 5lkner 82 one of former -esch9s PhD students. In this proect2 the lon!,term effects of

musculoskeletal unloadin! due to simulated micro!ra*it2 and the possible benefits of this resistance

e/ercise paradi!m &ere e*aluated. It &as demonstrated that such inter*ention pre*ented loss in muscle

si:e2 ma/imal stren!th as &ell as impairment in rate of force de*elopment and increased susceptibilit

to muscle fati!ue;2


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-he purpose of this communication is to briefl re*ie& the literature o*er the iso,inertial

technolo! as source of resistance. Publications that reported mere descripti*e information &ere not

included.

=. ECCENTRIC M#SCLE ACTIONS$ %&' (') *or i+,r'ssi-' ada,%a%ions!

It is &ell kno&n that eccentric muscle actions !enerate !reater force at a lo&er acti*ation le*el8>2

2 re3uires less metabolic cost"% and e/pose muscles to more se*ere dama!e than concentric actions

do>%2 8=2 8;. -hus2 it is accepted that muscle inuries often occur &hile the contracted muscle is suddenl

o*erstretched beond its limits=#. 0nfamiliar eccentric e/ercise fre3uentl results in muscle dama!e2

&hose smptoms include stren!th loss2 pain2 and muscle tenderness4%. ?ecent data supports that fast

*elocit eccentric e/ercise causes !reater muscle dama!e than slo& *elocit e/ercise in untrained

subects"4. 5fter the first eccentric e/ercise bout and follo&in! complete reco*er2 a repeated bout of

the same e/ercise results in minimal smptoms of muscle dama!e and has been referred to as the

6repeated bout effect78$. -he e/act mechanism of this adaptation is not &ell defined but it seems to

in*ol*e neural2 mechanical and cellular adaptations4#2 8%. It appears2 ho&e*er2 that if the muscle9s

threshold for failure increases and the attenuation of loads is enhanced2 a protecti*e effect can occur "$2

=;2 >$. Interestin!l2 this repeated bout effect ma last for se*eral months8#. -hose are the main reasons

&h no&adas eccentric trainin! is accepted as the preferred model to pre*ent muscle inuries4;.

(e*eral studies ha*e demonstrated the effects of eccentric trainin! to impro*e contractile

characteristics and muscle si:e in humans"#2 ="2 >=2 >82 >;2 >$2


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An the other hand2 eccentric trainin! has been sho&n to be successful in chronic tendinosis

rehabilitation. (e*eral randomi:ed studies ha*e found *er !ood short,term clinical results after

performin! eccentric trainin! in both achilles4$2 ;$2 2 4=2 $=tendinopathies. In addition2 non,

randomised studies also ha*e found similar results in both achilles>2 42 =>2 482 ;%2


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.! THE YOYOTM FLYWHEEL TECHNOLOGY

-he use of inertia &heels to pro*ide resistance is not ne&. 5s earl as "#==2 Nobel Laureate

5rchibald . +ill emploed a hea* fl&heel to anal:e muscle &ork and its mechanical efficienc >4.

In this classical stud2 the *ariation of the e3ui*alent load of the sstem &as obtained b &indin! astrin! around one of the ei!ht different si:es pulles. +o&e*er2 this de*ice &as desi!ned onl to

pro*ide resistance durin! the concentric phase.

-he &orkin! principle of the oo- Fl&heel -echnolo! de*ice is based on a fl&heel &ith its

a/le fi/ed to a frame. 5 strap is &inded onto its shaft2 and its other end is connected to le! pads2

handles or a harness tied to the trainee. -he strap is pulled for its entire len!th durin! a concentric

muscle action2 settin! a fl&heel into rotation. 5t the end of the concentric action2 the fl&heel

continues to spin b *irtue of its inertia and recoils the strap2 pullin! the trainee9s limb back. 5fter

initiall lettin! the strap re&ind2 the trainee then resists2 thus deceleratin! the fl&heel until all the

kinetic ener! pre*iousl accumulated has been dissipated and the fl&heel has come to a complete

stop.

(ince such eccentric action is e/erted o*er a smaller an!ular displacement than in the concentric

action &hile the ener! is the same for both actions2 the eccentric tor3ue is hi!her than the concentric2

therefore producin! eccentric o*erload8

. 5n e/ample of a repetition &hile e/ercisin! on a ooG le!,

e/tension confi!uration is sho&n in fi!ure =.

5n ad*anta!e of fl&heel de*ices is that the resistance is *irtuall unlimited and self adustin!2

since the fl&heel adapts b opposin! its inertia to &hate*er force is e/erted. -his also implies that all

the repetitions in an e/ercise are actuall ma/imal2 and that the athlete can train until e/haustion2

despite force production decreases &ith fati!ue. For the same reason2 the fl&heel can also

accommodate *ariations in force o*er the ran!e of motion 'e.!.2 due to different biomechanic efficienc

at different oint an!les). -hese do not happen on con*entional &ei!ht,based trainin! de*ices2 &hich

oppose instead a constant resistance &hich e3uals to the load.


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Fi/ur' . From bottom to top1 muscle tor3ue2 knee an!le and multichannel electromo!raphic 'EH) acti*it on kneee/tensor muscles durin! one bout of e/ercise on a le! e/tension ooG de*ice 'from Po::o et al ;>2 &ith permission)

>.". -he 5-weeks unilateral lower limb unloading study

5 *er particular model &as used in this research proect to unload the left lo&er limb of ="

subects durin! 8 &eeks. For an upri!ht or ambulator acti*it subects used short,len!th crutches2

aided b hand!rip and forearm support distal to the elbo&. -he ri!ht foot &as e3uipped &ith a shoe

ha*in! a "%,cm,thick sole. -his remo*ed &ei!ht bearin! from the left unloaded limb2 &hich could

adopt a strai!ht position and et mo*e passi*el about the hip oint 'see fi!. >)


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5fter the 8 &eeks of unloadin! the inertial resistance e/ercise did not onl offset muscle

atroph2 but in fact &as capable of promotin! marked hpertroph of the chronicall unloaded muscle.

Con*ersel2 the control !roup sho&ed a si!nificant decrease in knee e/tensor *olume


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>.>. -he hamstrings’ studies.

-he hamstrin! muscle comple/ are important hip e/tensors and fle/ors of the knee durin! !ait

ccle but also act as brakes of this oint &hen the foot strikes the !round in a runnin! ccle. +amstrin!

strains continue to be a challen!in! and often frustratin! problem for coaches of hi!h caliber athletes.(e*eral studies ha*e reported this inur as the most pre*alent in track and field2 professional soccer2

5merican and 5ustralian Football. 5lso2 the re,inur rate has been found to be bet&een "= and >"@ >>2

;". an authors su!!est the use of dnamic eccentric e/ercise to pre*ent andor rehabilitate hamstrin!s

inuries"2 ""2 "=2 "%J of knee e/ion. -his de*ice fulfils this recommendation2 albeit

a certain amount of coordination and familiari:ation is needed to appl brakin! forces such as to elicit

the desired eccentric o*erload. Furthermore2 the biceps femoris 'BF) muscle sho&ed hi!her

eccentricconcentric ratio of EH acti*it than the semitendinosus '(-). -his findin! mi!ht su!!est

that the BF muscle plas a more critical brakin! role than the (-


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differences in force2 po&er and *elocit profiles could be obtained. Emploin! !reater moment inertia

't&o fl&heels) is preferable to emphasi:e eccentric,force production and o*erload and then associated

trainin! adaptations. Con*ersel2 muscle,po&er and speed impro*ements &ould benefit more from

trainin! usin! reduced moment inertia 'one fl&heel)


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Fi/ur' . -= contrast shift of 3uadriceps at rest and post the fl&heel s3uat and the barbell s3uat e/ercise2 respecti*el.

alues are meanM(D. denotes si!nificant chan!e from rest to post e/ercise 'pO%.%8). denotes !reater increase &ith the

fl&heel s3uat compared to the barbell s3uat e/ercise 'pO%.%8)8


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3! T&' 4'rsaPull')TM

(imilar in concept to ooG technolo! de*ices2 the ersaPulleG 'P) features a cone instead

of a fl&heel. 5 cord is &inded on a conic shaft2 therefore offerin! a supposel *ariable inertia o*er the

ran!e of motion2 &ith a hi!her resistance offered at the narro&er part of the cone.

-hanks to its construction2 the pullin! direction of the cord can be arran!ed freel in the three

dimensions2 therefore offerin! the possibilit to train on more comple/ and specific mo*ements.

+o&e*er2 the main difference bet&een these machines is that the P pro*ides hi!h eccentric *elocities

at moderate to lo& forces2 &hile the ooG pro*ides hi!h forces at moderate to lo& eccentric

*elocities 'personal unpublished obser*ations). Both trainin! paradi!ms are needed to co*er the entire

force,*elocit spectrum. -he possibilities of e/ercises &hich can be performed &ith the P are almost

unlimited as in an other kind of pulle2 &hile its ke difference is in the eccentric o*erload that can be

achie*ed &ith a proper coordination.

-he P presents the option to chan!e the speedforce ratio b modifin! the position of the closer

round pulle &ith respect to the cone. 0sin! a similar principle than a biccle !ear2 it is e/pected to

obtain hi!her force le*els in upper positions &here the rope &inds around the narro& part of the cone in

contrast &ith hi!her *elocities obtained in lo&er positions &here a &ider area of the cone is used.

?ecentl2 &e ha*e confirmed these statements in our lab.

Chiu and (alem"8 ha*e compared for the first time the oint kinetics durin! three different

e/ercises performed usin! free &ei!hts &ith a load e3ui*alent to 8? *s. P set at onl the upper

position 'le*el 8 or 4 dependin! of the e/ercise). In that report2 the impulse 'i.e. the area under the

cur*e of net oint tor3ue *s time) &as anal:ed to determine the contribution of the main three oints of

the lo&er e/tremit. Front s3uats performed &ith fl&heel resistance re3uired !reater contribution of

the hip and ankle2 and less contribution of the knee2 compared to free &ei!ht. Push presses performed

&ith fl&heel resistance had similar impulse re3uirements at the knee compared to free &ei!ht2 but

!reater impulse re3uirement at the hip and ankle. E/ercises in*ol*in! dnamic lo&er and upper

e/tremit actions2 such as the push press2 ma benefit from fl&heel inertial resistance2 due to the

increased mechanical demand on the knee e/tensors.


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Further studies are needed in order to anal:e the effects of this e/ercise paradi!m on functional

abilities such as umpin!2 sprint,speed2 a!ilit2 etc...

3! CONCL#SIONS

-he isoinertial technolo! is a real accommodated inertial resistance able to pro*ide2 &hen proper

used2 an eccentric o*erload and all its associated trainin! effects.

(e*eral studies ha*e reported the efficac and feasibilit of these de*ices to pro*ide a &ide ran!e

of adaptations 'muscle *olume2 force and po&er2 runnin! speed2 etc...)

5! PRACTICAL APPLICATIONS

-rainin! situations &hen *er short time is a*ailable to include comprehensi*e stren!th trainin!

sessions 'i.e. team sports &ith &eekl competitions) &ill speciall benefit from this e/ercise paradi!m.

(ubects &ith &eak trunk unable to support hea* loads o*er the upper bod can also benefit from

these de*ices and perform lo&er bod e/ercises at a ma/imum intensit. -hese machines could also be

easil used as testin! de*ices offerin! real time feedback to monitor the trainin! load.

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>41";#,"#8,>#$1=;>,=


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$%. oods2 C.2 ?. +a&kins2 . +ulse2 5. +odson2 -. E. 5ndersen2 and ?. Bahr. -he Football

5ssociation edical ?esearch Pro!ramme1 an audit of inuries in professional football,,analsis

of preseason inuries 2r # Sports Med . >;14>;,44"2 =%%=.

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patellar tendinopath in *olleball plaers. 2r # Sports Med . >#1"%=,"%82 =%%8.

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