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Lifting bility and Leg StrengthMary Ann Wilmarth, MS, PTRagini Herekar, MS, PT

o w b a c k i n j u r i e s a r e t h emost prevalent of al lmanual materials-hand-ling injuries (19). Exten-sive studies have b eenundertaken to determine d i fferentfactors involved in lifting injuries.Result s of Snook s s tudy show thatdesigning a jo b to f i t the w orker canreduc e up t o one-th i rd of indust ria lback in juries (1 9) . Th is seems to bemo re effective than selecting aworke r fo r t he j ob o r t ra in ing thewor ker t o lift properly. Chaffin et al(3) suggested that s t rength tes tingshould be pe r fo rmed d u r ing em-ployee selection and placemen t pr o-grams. Th ey a lso suggested thatg ross a rm a nd l eg s t reng th may bepredic tors of l i ft ing abil ity but a renot necessari ly pr edictors for push-ing an d p ulling activities.Stre ngt h test ing has been imple-mented as part of medical examina-t ions in experime ntal medical proce-du res o f a n umbe r o f l a rge indus-tries. According to th e NationalInsti tute of Occupational Safety andHea lth (NIO S H) , however , fu r the rs tudies ar e neede d t o val idate andrefine t he necessary proce dures (2 1).Various s tudies have been per-form ed to m easure i sokinet ic t runkmuscle streng th a nd isokinetic legmuscle streng th ( 5,9,11,1 8). Isoniet-ric back strength has been stu died inrelation to lifting ability (7,15,17). Inaddit ion , l i fting abil ity has been com-pared in normal and low back dys-function patients (2,lO). Recent ad-vances in eq uipm ent design have en-abled isokinetic lift ing t o bemeasured (16).

The purpose of this study was to de termine the relationship between peak torques of lowerextremity muscle groups and lifting ability wi th a floor-to-knuckle leg lift in a healthy person.Twenty-four healthy, young subjects between the ages of 20 and 40 participated in the study. Eachsubject was tested for I ) sokinetic peak torque of the knee extensors and flexors and hip extensorsand flexors on a Cybex 11 dynamometer, 2 isometric lifting ability using a strain gaugedynamometer, and 3) maximum lifting ability using a box and free weights. The subjects used asquat technique and maintained a neutral spine position wi th a lordotic curve during the lifts. Nosignificant correlations were found w ith the data analysis for the entire group. For 15 male subjects,the regression equations revealed a statistically significant correlation between isokinetic kneeextensor peak torque (18Oo/sec) nd isokinetic hip extensor peak torque (3O0/sec)with bothmaximum lifting ability and isometric lifting ability. The regression equations were MAXIMUM LIFT

46.1 0.92Q 0. OH (F 4.07, p < 0.05) and ISOMETRIC llFT 16.6 23Q 1.OSH (F6.32, p < 0.025) (Q: sokinetic knee extensor peak torque at 18O sec; H: isokinetic hip extensorpeak torque at 3O0/sec).No statistically signilicant correlations were found for the nine females.These results indicate that in a healthy, young population, isokinetic knee extensor and hip extensorpeak torque may be predictors of floor-to-knuckle leg lifting ability in males, but not in females.

Owners, Shoreline Physical Therapy and Sports Rehabilitation Center, 278 Hope St., Suite E Mountain View,CA 9404 1 Both were employees oi Richard P. Carr Physical Therapy, Inc. at the time the research wascompleted.ey Words Strength, Lifting, Kneelhip

Although the variables of legstreng th an d l ifting abil ity have beenstudied independent ly , the authorswere unable to f ind any comparat ivestudies between l ift ing abil i ty an d legs t re ng th mea su red i sok ine t ica ll y .There fo re , t he pu rpose o f t h i s s t udywas to de ter m ine if a statistically sig-nificant co rrelat ion exists betweenlifting abil i ty an d leg strength meas-ured isokineticallv with both an iso-metr ic dynam ome ter l if t an d wi th afloor- to-knu ckle leg lift.METHODSRationale

T h e autho rs chose to use i soki -net ic equipmen t to tes t lower ex-tremity s tren gth since i t is often

available to physical therapists, an dprotocols have been previously estab-lished 5). Lifting ability was testedwith a floor-to-knuck le leg lift be-cause it is easily set up , it doe s notrequi re e laborate equipment , an d i tmost closely simulates fu nction (Fig-ur e 1). Although isometric lift ingability has been used widely in thepast d ue t o ease of application, Mar-ras et al su ggested t hat isometric l ift-ing tests mav be misleading (1 3).How ever, a cl inical study has re-vealed that an isometric lift may be aweak predic tor o f a floor-to-knuckleleg l if t (1). Because of i ts ease of a pplication, th e isom etric lift was in-cluded in this study to verify th eclinical study. T h e value obtainedwith th e isometric lift was also usedto de t e rmine a n app rox ima te s t a r t -

Volume 4 Number *Julv 99 *JOSPT

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R E S E A R C H S T U D Y

FIGURE 1: Lrtt~ny: qurpmcn ting weight for the floor-to-knuckleleg lift in this study.

Selection of SubjectsTwenty-four subjects, 15 males

and nine females between the agesof 20 and 40 (males 29.3, fe-males 26..3), participated in thestudy. Th e subjects were volunteersfrom a healthv, young populationwithin the communitv.

All subjects were active individ-uals who did some form of exerciseat least twice a week. One male inthe gro up was a weight lifter. Th er ewere six health professionals, two en-gineers, and on e student in the fe-male population and five hei~lthprofessionals, six engineers. two stu-dents, one teacher, and one physicistin the male population. None of thesubjects had anv history of signifi-cant injuries or pathology of thehack o r lower extremities. Tw o vol-unteers were excluded from thestudy since they reported pain in thelower extremity or back during ac-tivities similar to the ones beingtested in the study.

A screening evaluation W;IS per-fornied on each volunteer. This in-clutled ;I questionnaire and ;I hasici~ssessnientof range of motion andflexibility of the spine and lower ex-trernities. Leg doniinance was deter-mined froni the questionnaire. Fachsubject gave informed consent toparticipate in the study.PRO EDURE

The suhjects were tested for iso-kinetic peak torque of tlie knee ex-tensors, knee flexors, hip extensors,and hip flexors of tlie doniinant es-trenlity. Testing was perfornied us-ing established protocol o n tlie