Isokinetic muscle training has all the advantages of isometrics and isotonics while minimizing their deficiencies. By holding the speed of movement constant throughout the full range of motion, isokinetic training devices respond with increased resistance rather than acceleration when the power output of the muscle is increased. Isokinetic training is superior to isometric and isotonic training with respect to increases in strength, specificity of training, desirable changes in motor performance tasks, lack of muscle soreness, and decreases in relative body fat

Corbin, B.

Olree, H. D.

Smith, C.

English

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FINAL REPORT
Contract dumber NAS 9-15596
Isokinetic Fxer-cise - A Review of the Literature
Harry Olree, Bob Corbin, Carroll Smith
Harding College, Searcy, Arkansas
Principal Investigator:	 Barry D. Olree, Ed. D.
Sponsoring Institution	 Harding College, Searcy, Arkansas
Period Covered by the Report:	 May 1, 1978 - October 31,	 1978
( N ASA-CI -151841) ISOKIN F ?'IC ER F RCISE :
	A N71?-12695I °VIEW OF THE LITERATURE
	 Final Report,
	
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Isokinetic Exercise - A Review of the Literature
Introduction
In contrast to the studies of isotonic and isometric exercises,
research investigating isokinetic training have been few in number.
Most of these have also been limited in scope.
Isometric exercise occurs when a muscular contraction, though
maximum, results in no motion because the resistance is greater thc.n
the force applied due to muscle tension. No work is performed since
the joint is locked and the muscle length remains constant. All force
is applied at a few points of joint bearing surface.
The only advantage of isometric exercise is that it can be per-
formed anywhere at any time with little or no equipment. Isometrics
have several disadvantages. one is the difficul.Ly of motivating since
there is no movement and therefore no positive feedback to the subject.
People usually evaluate their efforts by the weight of the object moved
or by the distance and speed of motion.
The strength which is developed by isometrics tends to be static,
not dynamic. The increased strength is only effective in a narrow range
close to the joint angle at which it was developed. It has been found
that isometrics have little influence on desirable changes in motor
performance tasks so important in athletics.
A final disadvantage is the danger to older people with athero-
sclerosis. During an isometric contraction the glottis is closed which
creates very high pressure in the thoracic cavity. This in turn reduces
the flow of blood from the lower extremities to the heart and brain.
Isotonic exercise involves dynamic muscular contractions against
a constant load, therefore the resistance is constant throughout the
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entire ranee of motion. The ma g nitude of the resistance is limited to
the maximum load wh ich can be moved at the woak es t angle. 'I'hc, woai , es t.
angle will Fo at the extremes of the ran g e of motion. Only at this
angle 0111 a maxirnml contraction I , o elicited. At all other anciles the
muscle tension which develops, will. he much less t han max iwum. Since
the lond is con::tant and t1w torcluo varios, with the angle, the s:poed of
motion will likewise vary with the angle. The most common exa1'.1plo of
isotomic exercise is. weight lifting.
IsotoIlic exerci.--o has these diCill'vantages. o trongth is increased
most for the weakest anglo an.i much less for all other angles throu•11)
out tho range of motion. Also, the joint is traine '_o han.11e only a
fraction of the Iraxivmm torque which the muscle is capable of develop-
inn. rinally, at the Ieginnin,< . of training there is an initial loss of
strength kIIw to mus.c.10 s:olviless
Isokinet ic imiscul ar tra ining, a relat."voly now coIlcept, was, intro -
duced in 1967 (?, 13) . This training method has all t ht , a dvant ag es of
isometrics and is:otoni.cs while miniwi:. ing their deficiencies. Isok iI ot-
1CS illVi-I IVeu (1^ 'IlaI11iC exerci.,t y in which the ros:istance varies throughout
the full  ranee of motion
	 i n direct proportion to th e '. o r ce exerted by
the	 111 uSCIO.	 T)IL'	 11111 S Cte	 is+ loadCCi 1ftaXimall)'	 at
	
c-V(-! - }'	 angIt' of	 tlIL'	 joint-
without overloading at any point. The joint therefore is also loaded
optimal 1 y at every an<_r 1 e so that its: strength i ncrez s.es i n harmony w i th
that of the n111s-Cle.
in isometrics tho dist ance in controlled. in isot-onics the rosis-
t:.AIICO 1S 00I1tr011Oki.
	 I n laokinet.ic tho -speed of t he movoI1ent i S cen-
trolled.	 wit h the' speed of the 1110%'0111011t 1101LI CI)II.Stant t h roughout the`
full  range of motion, the is,okinctic training device ro.--ponds, with in-
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creased resistance rather than acceleration when the power output of
the muscle is increased. In isotonic exercise limb speed rarely exceeds
600 per second, while in athletics limb speed is usually greater than
g 0°P er second. There are isokinetic devices in which the limb speed
or a movement can be varied from 0 0 per second (isometric) to 200° per
second.	 ; I^
Research has shown that there is a high degree of specificity in
	
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training. Development of power, force or rndur.ance at one angle has
a minimal effect at other angels in the range of motion. This is the
reason that isometrics has fallen into disfavor. Only isokinetics
permits optimal strength development throughout a full range of motion.
	 i
Isokinetics has other advantages. This method of training produces
very little or no muscular sorc:less (8,15). Another plus is that iso-
kinetic training devices will automatically adjust (1.) with increased
resistance as the strength of the muscle increases, (2.) with decreased
resistance to tiring muscles, and (3.) to the strength of any individual
i
who uses it. Some isokinetic equipment can also be used to measure the
power, force, and endurance of a muscle at every angle in the full ranee
of motion. Maximum work is obtained with the isokinetic method and can
be integrated over the full range of motion.
I
Equipment
Exer-Genie
The Exer-Cenie is one of the simplest isokinetic devices. The
speed of the movement can be varied and is controlled by the friction
r
of a nylon rope which is wrapp`d internally around a cylinder. The
greater the number of wraps, the greater the friction and the slower
the movcn :lent. Slight tension on the rope feeding.into the cylinder
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great-1.1, increli.ses	 friction.	 The speed of tho movement call also I)c
controlled in this 111111111C.17.	 1 ho devict, can be atta ched 	 to tho	 floor,
1,'.111
	 or coilizi(I
	
that.	 a great
	 uuv+t , r of	 different lintovoments art. , pos-
sible.
Tho	 Mini-(Iym	 -is	 an	 isok inotic devico	 th,it .	II..;('s a	 I-ope and a
	 evil-
trifigal	 clutch	 to maintain	 t...oils, t -lilt	 spot , t!.	 This	 clutch	 is	 similar	 to,
t-lie tjovernor usod on atitomotivo. ongines.
	 On sonic modols, 	 tile :--poed	 is
\, ,I r i n	 swino niodelts	 have	 I	 i-ca,i-o il t	 of	 t1 io	 t*0l'CC	 ( I X01"tt. 1 d 	 by	 tho musclo.
Tn	 somo models	 this.	 is	 a	 graph;	 in	 other....
	 it	 comsi.st . s of	 11	 cilck"I ' ll .
	 ;C.Ilv
and	 poi ntor.
	 11,0
	 not	 ack-111-Mol ' y Calit'ratod	 ill any
	 :,pek- ific units.
Like	 tho	 rxor-Cc% nio,	 tho mini-C.ym, 1111i is	 C.111	 1 1 0 a(tichod	 to ally
to	 obtain	 virtually	 any	 kiml	 of	 I1.,ovk ­11'.('nt..	 ullits	 11.1vo	 ,11 so	 booll	 1,11ilt
bicyolvs.
Nalit i Ills
The	 Nautilus	 ijl poars	 to	 ially
	 althou'll	 th"
(Ioniet .,	 t1ii.s.	 "Nie	 ro.,;istarco	 i.-z	 v,ivied	 throuclhout
	 tilt`	 011 11
range 01",	 rot ioll
	 by	 1	 CCIM.	 This	 allows,	 th"	 t"	 1 , c	 near ma"i -
111ally
	 Ioadod
	 at	 overy
	 'll"(11e
	 of	 tile	 joint.
	 okil1ip.."1011t.
	 is
I- Ilctured
	 ill	 ordor	 to	 ol)taizi	 I	 11111 . +Or	 of	 k1i!'t't'I't 1 IIt	 V.k,Vov,,Vllts.
al'o.x	 (01-thotron)
The	 Cj+ox
	 is	 tho	 jijont	 isokinot ic	 dk'ViCt'	 tll,lt	 is
I t	 vnipl o y , ;	 vither	 an	 oloctroinxincLic	 dL'ViCV	 01'
	 a	 Jj\•(1r;jjIjiC
%:y1il1-101 .	 to	 111.1ititaill	 con.".t.ant.
	 "tt"."'d
	 Hiroughout
	
tilt`
	 111ovell"vilt
	 VOWCVOT',
.11'004	 Of	 Ijj0\•k'Ijjt1Ijt	 V,11-ied	 1 , 1'	 altering	 tilt`	 r0to	 at	 whicii	 f lui(i	 f jowt;
t llivli,)ll	 tho
	 Cy I in ' tor.
	 Tho	 anquIal , 	 .1 *.j 1 0t 1 k1 	 0,*Ill	 I't , 	\ . ,% I it'd	 fi-om
	 0 t'	 1 1 01 ,	 ­.0001ld
()to	 200l`Illt
	 to	 obtaill	 kliff-
=one a
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erent movements. The Cybex II is adjustable so that the axis of rota-
tion can be aligned to match the atomical axis of rotation. The Cybex
II also has strip chart recording capabilities. This allows the accu-
rate measurement of the force exerted by the muscle at every joint angle.
Research Results
A number of the papers in the list of References do not report ori-
ginal research. They merely explain the concept of isokinetics, compare
and contrast isokinetics with isometrics and i.sotonics, or give basic know-
ledge concerning isokinetic training equipment and techniques. Most of
the research that is reported is limited in scope.
Three papers have reported electromyographic st lies. Hin •_;on and
Rosentsweig (3) in comparing mean muscle action potentials of isometric,
isotonic and isokinetic contractions concluded that (1.) no single type
of contraction will eelicit the greatest action potentials for all sub-
jects, (2.) isometrics appear to produce the greatest action potentials,
and (3.) the isokinetic method prodvzceL^ greater action potential than the
isotonic method for the largest number of subjects.
Rosentsweig and Ilinson (10) examined action potentials at four angles
during isometric, isotonic and isokinetic work, their conclusions were
that (1.) the action F,otential of a muscle will significantly vary with
the angle during isotonic work, (?.) there were no significant differ-
ences in muscle action putentia-1 (MAP) at the four angles during iso-
metric or isokinetic work, (3.) isokinetic contractions elicited signifi-
cantly greater mean MrI
 than isometric or isotonic contractions,_ and (4.)
the difforences in :strength at different :angles is a function of Lhe lever
and not due to muscle activity.
	 Ii	 -
Rosentweig, Vinson. and Ridgway (11) examined MAP during is:,okinet.ic 
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contractions at three different speeds. It has been generally believed
that slower contractions develop strength and faster contractions develop
endurance. They found no significant differences in MAP at different
speeds. They interpreted this to mean that muscles, regardless of the
speed of contraction accemodate so that they are maximally loaded at all
speeds.
Wilson (16) worked high school athletes can a 12 station Mini-Gym
circuit. Good increases in strength were obtained. There was no con-
trol group and no comparisons were made with other types of work.
Van Oteghen (14) examined the increases in strength and vertical
jLmip height in female intercollociatc volleyball players who trained at
fast and slow speeds on a Mini-Gynr Leer Press machine. Ile found that only
those who trained at a slow speed had a significant ilv..provement in strength
as compared to controls. Roth the fast and slow groups iigllifiCL tl
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creased their proformances in the vertical jump when compared with controls.
The increase in peak muscular farce with isokinetic, isotonic and
isometric trai.ninq was examined by Thistle, Iiislop and Moffroid (13).
Their results are presented in the table below.
Group	 Tnerease in Poa k Force of heft ()undriceps Femoris
Isoki.nctic
	 42.2%
TsotoTlj.c-	 28.6%
Isometric
	 13.18
Using the Cybex, Moffroid, Whipple, Ilofkosh, Lo%,'rran and Thistle (6)
establi.,,hed norms of different muscle groups for measurements of torque,
cork, r.iru3e of motion, and power. They also compared isokinetic with
isotonic and isometric exercise. They found that (1.) isokinetic exercise
increases the work a naisc.le can do more rapidly than isometric or isotonic
training, and (2.) muscl y
 response to training tends to be specific; that
w
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is, a muscle which is overloaded in a partial range of motion will increase	 1
in strength significantly more in this range than at other less exercised
joint angles.
i
Pipes and wilmore (8,9) have reported the most extensive .investigation
of isokinetics. They compared isotonic, isokinetic low speed, isokinetic
high speed and control groups with respect to relative body fat, motor per-
formance tasks, specificity of training, muscular soreness, and strength.
Isometric procedures were not investigated because of previous extens-ve
study and the fact that it has been shown that isometrics has little in-
fluence on motor performance tasks. They measured static strength by
cable tensiometer., isotonic str.enth with weights and isokinetic strength
at slow and fast speeds using a Cybex.
They found that the isokinetic high speed group had a significantly
greater decrease in relative body fat than the isotonic or isokinetic low
speed groups. Poth isokinetic training groups had significant desireable
changes in motor performance. None of five motor performance tasks i•:ere
altered by isotonic training. The isotonic group experienced initial
muscle soreness ^:,hich was not observed in either isokinetically trained
group.
Strength measurer;ents slowed that both isokinetic low speed and iso-
kinetic hi g h speed training increased static: strength to a sigr;ificancly
greater degree than isotonic training. I •,hile the isotonic g roup had no
significant changes in strength when measured on the Cybex al: high and low
speeds, both of the isokinetic groups had significant increases in strength
at both speeds. The isokinetic groups had the greatest gains in strength
regardless of the manner in %•,hich strength was expressed, u hether isometri-
call.y, isotonically, or iso_kinetically. The isoki.netic high speed group
had the greatest overall strenth increases.
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Conclusions
Isokinetic training is superior to isometric and isotonic training
with respect to increases in strenth however expressed, specificity of
training, desireable changes in motor performance tasks such as those	 f'
occurring in athletics, lack of muscle soreness, and decreases in rela-
tive body fat. Isometric training has the advantage of requiring little
or no equipment. Isotonic training provides more motivation for many
people who are accustomed to lifting weights.
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•	 List of References
1. Coplin, T.11. "Isokinetic I' rcise: Clinical Usacje", J. N,-itional Train.
Assoc. C:110-14 (Fall 1971)
2. Counsilman, J. "Isokinetic Exercise", Athletic ,?. 52:58 (February 197?)
3. Hinson, M. and Rosentsweig, J., "Comparative El ectromyographic Values
of Isomctr.ic, Isotonic and Isokinetic Contraction",Rose.-3rc.h Cuart.
44:71.-8 (1073)
4. Iiislop, H.J. and Pcrrine, J.J., "The Isokinetic Concept nf 1'xcrcise,"
"LLys. Thcrai . 47:114-17 (1967)
5. t•lillor, C., "Tsokinotics-Another Fad or Isere +-o Stay?", Athletic_ J.
55:20 (November 1974)	 r
6. Moffroi d, M., Whipplo, R., Iiofkosh, J., Lowman, E. and Thistle, 1-I,
"A Study of Isokinetic Exercise", Phis. Thor-a . 49:735-46 (1969).
7. Pcrrine, J..7. , "Isokinetic Fxercise anti - the P•'echanic;:1 Fnor.gy Potentials
O f Muscle", J. 1-'ea 1t1l Phvs. Fduc. Rec. 39:40-4 (May, 1968)
B. Pipes, T.V. and Wilmoro, 0.1-1., "Isokinetic vs Isotonic Strength Train-
in(; in 71,dult Men", MeO. Sci. Set s 7:262-74 (1975)
9. Pipes, T.V. and Wilmorc_, J. 1i., "Muscular Strength Throuch Isotonic.
anti Isokinetic Resistance Training", Athlet ic J. 56:42 (June 197(,)
10. Rosentswei,,, J. and 1linson, t".At, "C^mpari_son of Isometric, Isotonic
and Tsok.inetic E%L-rcises L)y F.lectron:yoyraphy", Ar.ch. Phys. Merl. P.(.11,11).
53:249-253 (1972)
11. Rosentsweig, J., Hinson, M. and Ridgway, M., "An Electr.or-yographi.c
Comparison of an Tsokinetic Pench Press Performed at Three Speccis",
Resear ch
 Oucirt. 46:471-5 (1975)
12. Stone, W. J. and Kroll, W.A., "Strength Development for Sport::",
Sports C ondi t ioni no and Weicaht T rai ninc_r, Allyn and Bacon, Inc.
Boston, 1978, pp 33-101.
13. Thistle, 11.G., Iiisl.op, H.J. and Moffroid, M., "Isokinetic Contraction:
A Nov Contort. of Resistive 1:xercise", Ai ch. Phv:,. 1*cd. Reba))., 48:
279-82 (19+7) .
14. Van nte g hen, S.L., "Two Speeds of Isokinetic exercise as Related to
tho Vertical Jump Performance of Women", Research mart., 46:78-24,(1975) .
15. Irilmore, J. Ii.," Funclamenta.ls of Physical Training", Athleti c Trciini n^c
and Phys.ical Fitne'e., Allyn and Bacon, Inc.: Roston, Mass., (1977)
pl). 68- 86.
16. Wilson, J., "Isokinetics for Maxi	 -:m.:", Athletic J. 53:39 (April)
1973) .
QKII;INAI, 1':^l;h% lb
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Isokinetic exercise: A review of the literature

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