E ffe ct of W alking S pe e d on Low er E x trem ity Inte rn al and E x tern al Rot ation W hile T urning 90 D e g re e s

In t ro du c t i o n

No one has to run but ev ery on e has t o turn for performing activities of daily living . T urning is cla ssified as one of the un safe

m om ent s durin g ambulation in the elderly (T inetti et al, 1986). It incr ea ses the biom echanical dem an d m or e than str aight w alking (P erry , 1992). How ev er , str aight w alking on lev el surfaces has been the

E ff e c t o f W alk in g S pe e d o n L o w e r E x tre m ity Int e rn al an d E x t e rn al Rot at ion

W h ile T u rn in g 9 0 D e g re e s

Y oon Jan g - w h on , M .A ., R .P .T .

Dept . of Phy sical T her apy , S chool of Education , New York Univ er sity

국 문 요 약

9 0도 회 전 시 보 행 속 도 가 하 지 의 내 외 회 전 에 미 치 는 효 과

윤장원

뉴욕대학교 물리치료학과

회전(turning )은 보행 중 방향을 바꾸는 운동 기술(motor skill)이고, 회전 전략(turning

str ategy )은 회전을 완수하는데 사용되는 일반적 행동 전형(generalized movement

pattern )이다. 회전에 대한 보행속도의 영향은 분명하지 않다. 이 연구의 목적은 보행속도 의 돌기 전략에 대한 영향을 분석하고 보행속도의 하지 내외 회전(internal and external r ot ation )에 대한 영향을 분석하는 것이다. 건강한 젊은 성인 15명이 이 연구에 자발적으 로 참여하였다. 맥리플렉스 측정 장치(MacReflex measurement system )가 동작 분석 (m otion an aly sis)을 위해 사용되었다. 각각의 자원자들은 보행 중 90도 왼쪽으로 회전을 10회씩 완수하였다. 각각의 시도마다 보행속도를 다르게 하기 위해서 세 가지의 다른 요 구들(slow , regular , fast )이 임의적으로 주어졌고 각각의 실제 보행속도가 자원자의 무게 중심 변화에 따라 구해졌고 요구별 평균이 구해졌다. 회전 안쪽 발의 스핀(in side foot spin )은 보행속도가 증가함에 따라 증가했지만, 회전 바깥쪽 발의 스핀(out side foot spin ) 은 보행속도와 상관이 없었다. 하지의 내외 회전은 보행속도와는 상관이 없었지만, 같은 쪽 발의 스핀과는 역관계가 있었다. 회전은 발 스핀이 있는 돌기와 발 스핀이 없는 돌기 로 구분되는 것이 합당한 듯 하다. 제한된 시간과 공간 내에서 스핀은 보행속도가 빨라질 수록 몸의 전방 운동량(forward momentum )에서 몸의 전방 운동량(forward momentum ) 으로의 전환이 스핀이 없는 회전 시보다 효율적이다. 고관절의 내외 회전 근육들은 회전 전략에 상관없이 회전되는 동안 몸의 역학(body mechanics)을 조절하는데 중요한 역할을 맡고 있는 것으로 보인다. 앞으로 회전 시 몸의 생체 역학적 그리고 신경 근육적 기전들 (biom ech anical and neur omu scular mechanism s)을 밝히는 연구들이 필요하다.

핵심단어: 내외 회전; 동작분석; 보행 속도; 회전.

basic t ask u sed in the m ajority of studies on hum an locom otion . Limit ed studies (Andr ew s et al, 1977; Hase and St ein , 1999; Patla et al, 1991) exist on activities other than str aight w alking , such as, turning .

T urnin g is a m ot or skill of changing dir ection while w alking , an d the turning str at egy is the gen er alized m ov ement patt ern u sed t o complet e the turning . T he cour se of turning con sist s of deceler ating the for w ar d m omentum , r ot ating the body , and st epping out t ow ar d the n ew dir ection (Ha se and St ein , 1999). Based on the int er action betw een mu scle t en sion and m echanical dem an d, sev er al deceler ation m echanism s ar e gener ally u sed to decr ease the for ward moment (Hase and St ein , 1999).

An ext en sion syn er gy of the for w ar d low er extr emity and r educed pu sh - off pow er in the other lower extremity are the fun dam ent al deceler ation m echanism s during the same st ep cycle (Hase and St ein , 1999). On ce the w alking speed is deceler at ed, r ot ational m ov em ent s of the locom otor unit , form ed by th e t w o low er limb s and pelvis, occur in the tr an sv er se plane t o turn the body toward a new direction (Perry, 1992). Rot ating the upper body on one hip j oint and spinning of the w hole body on the floor ar e the m ain str at egies t o r ot at e the body ar oun d th e longitu dinal axis in the tr an sv er se plan e.

A dju stm ent of gait is r equir ed t o alt er the dir ection of locom otion (P atla et al, 1991). T urnin g has been defined as a ba sic str at egy t o av oid an ob st acle in the path (Patla et al, 1991). While changing dir ection , the follow ing chang es w er e foun d thr ough

the gr oun d r eaction for ce stu dy : 1) an increase in mediolater al impulse component s ; 2) an in cr ease in the br aking impulse component for ant erior - posterior and v ertical impulse component s ; and 3) a decr ease in both horizontal and vertical push - off impulse component s (P atla et al, 1991). P atla and his a ssociates con cluded that changing dir ection while w alking n orm ally mu st be plann ed in the pr eviou s st ep (P atla et al, 1991). T his plan mu st occur r egar dless of the m agnitude of the chang e in dir ection of locom otion in or der t o r educe th e accele- r ation of the body cent er of ma ss tow ar d the landing foot (Patla et al, 1991).

Chan ging dir ection within th e sam e st ep w as not limit ed by r eaction tim e, but by the inability of the mu scles t o r otate the body t o the new dir ection (P atla et al, 1991).

Ha se and St ein (1999) defined the spin and st ep turning str at egies in their stu dy on turning the body 180 degr ees. In the spin turn , the body spin s on the floor ar oun d the ball of one foot , and in the st ep turn , both feet continue t o st ep and each hip can serv e a s the axis for part of the turn (Hase and St ein , 1999). Andr ew s and his colleagues (1977) described the spin turn as the cr ossov er cut an d the step turn as the sidest ep cut for turning 90 during hum an running . It w as found that the st ep turn is an easier str at egy for subj ect s t o u se when turnin g 180 becau se it h as a br oader base of support an d separ at es the deceler ation and the turn while m aint aining the w alking rhythm (Hase and St ein , 1999).

T he timing of a t actile signal during a gait

cy cle w as believ ed t o be a det erminant for

the selected turning str at egy . It w as found that the st ep turn w a s pr eferr ed if th e cent er of gr avity (CoG) had alr eady passed the supporting foot when the tactile sign al was given. The walking speed was elimin at ed as a possible factor that influen cing the choice of turnin g str at egy by assumin g that all of their subj ect s w alked at similar speeds. How ev er , it is unclear wh eth er the sam e turning str ategy w ould be u sed at v ariou s w alkin g speeds .

Hip is the best ex ample of the ball- and - socket joint s in the body , which pr ovides st ability and mobility (Hollin shead and Jenkin s, 1991). Rot ation of the hip in th e tr an sv er se plane occur s as th e contr alat er al lower extremity swings forward in pr epar ation for the next st ep while str aight w alkin g (Norkin and Lev angie, 1992). An av er ag e of 13 of hip int ernal and ex t ernal r ot ation occur s during a norm al gait cy cle (Nor din and F r ankel, 1989). In str aight w alkin g , ext ernal r otation of the hip occur s durin g the swing phase of the limb , and int ern al r ot ation occur s durin g the st ance phase (Lev en s et al, 1948; Nor din an d F r ankel, 1989; Johnston and Smidt , 1969). The r otation of the hip minimizes the dr op of the cent er of gravity and the energy expenditure during the double support period by len gthening the lower extremities (Norkin and Lev angie, 1992). While turning without spin , the int ernal r otation of the in side hip may be incr eased an d the ext ernal r otation of th e out side hip m ay be incr eased durin g the ipsilat er al single limb support period. If the body is spinning on the floor , the hip int ernal and ext ernal r ot ation m ay differ fr om wh en the body is turning without

spinning . T he hip int ernal an d ext ernal r ot ation w hile turning has n ot been clearly det ermined.

T urnin g 90 is one of m ost function al activities and is m or e fr equ ently r equir ed than turning t o any other angle in activities of daily livin g . How ev er , th er e ha s been little interest in this motor skill and normativ e dat a ar e unav ailable. T his stu dy is the fir st effort t o determin e the gen er alized locom otion patt ern while turnin g 90 at v ariou s w alking speeds an d to assess the am ount of low er ex tr emity int ernal and ext ernal r ot ation in the tr an sv er se plan e.

T he purpose of this stu dy w as to analy ze the effect of w alking speed on the turning str at egies u sed and on th e am ount of lower extremity internal and external r ot ation while turnin g 90 in healthy y oun g adult s.

T he followin g w er e hypothesized:

1) T h e turning str ategies u sed will differ at the v ariou s w alkin g speeds while turnin g 90 .

2) T he amount of lower extremity int ernal and ext ern al r ot ation will be r elat ed to the walking speed while turning 90 . 3) T he amount of lower extr emity int ernal and ext ernal r ot ation an d the turning str at egies u sed will be r elat ed while turnin g 90 .

M e t h o d s

S ubje c t s

S ev en fem ale an d eight m ale v olunt eer

subject s without any history of neur omu scular

or mu sculoskelektal disease, disor der , or

con dition participat ed in this study . T heir

ages r anged fr om 22 t o 32 y ear s. T w o out

of fift een subject s w er e left - han d domin ant (13.3%). T he characteristics of subject s wh o participat ed in this study ar e shown in T able 1.

T he subject s w er e r ecruit ed fr om New York Univ er sity and fr om the adj acent communities on a v olunt ary basis. Prior t o participation , all subject s signed a writt en con sent form , indicating that they had been inform ed about the natur e of this study . A participation qu estionn air e w as complet ed by each subject t o obt ain inform ation regarding the age and any previou s m edical hist ory . If subject s fulfilled the crit eria, they w er e select ed as candidat es for this study . T h ey r eceiv ed a brief phy sical ex amination , which inclu ded m easur em ent of h eight , w eight , activ e r ange of m otion of both hip s, and m anu al mu scle t esting of the hip int ern al an d ext ernal r ot at or s bilat er ally . All subj ect s w er e a sked t o bring their own sn eaker s. Dark - color ed tight short s an d a sleev eless black T - shirt w er e pr ovided t o each subject to incr ea se the visibility of the m arker s and to minimize the artifact s fr om the vibr ation of the m arker s .

E quipm ent

T he MacReflex m easur em ent sy st em ¹⁾

1. Qualisys Inc. Glast onbury , CT

w as u sed in this study t o detect the in st ant location of the m arker s on the subject s body and on the floor . T h e only sy st em that can possibly captur e all the dat a fr om hum an m ov em ent is an im aging m easur em ent sy stem becau se of it s com - plexity (Winter, 1990). Three- dimen sion al m otion an aly sis sh ow s the body s true spatial m otion s an d is closer t o the r eality of the movement (Barlett , 1997). F urtherm or e, the int er segmental angles could be calculat ed accur ately without viewing dist ortion s in thr ee- dim en sional motion analy sis (Barlett , 1997). T he MacReflex m easur ement sy stem w as found t o offer a flexible and easily operat ed solution for recording of mov em ent s with a high r esolution (Josefs son et al, 1996). T he sy stem in cluded fiv e cam er as , fiv e video pr oces sor s, fiv e cam er a - t o- video pr oces sor cables, fiv e video pr oces sor - t o- m onit or cables, t w enty - on e m arker s, a calibr ation frame, and a Macintosh comput er . Cam er a unit s emitt ed invisible infr ar ed light t o det ect the r eflectiv e m arker s in the im age ²⁾ . Video pr ocessor s calculat ed th e cent er of each m arker and sent the coor dinates t o the comput er . In this study , spherical, 3.6- centimeter - diameter ed, passiv e r etr o- r eflectiv e m arker s w er e u sed. T he sampling r at e of 60 ㎐ and the exposur e

2. Qualisys Inc . MacRefelx User Manual.

Version 3.0 Glast onbury , CT . 1995.

T able 1 . Descriptiv e st atist ics of height an d w eight of subj ect s

N Mean St an dar d

Deviation Maximum Minimum Ran ge

Height (inch ) 15 66.74 3.04 74.00 61.80 12.20

W eight (pound) 15 136.01 22.40 185.00 110.00 75.00

time of 0.25 ㎳ w er e select ed. Calibr ation of the MacReflex m easur em ent sy st em w as done at the beginning of each session with the calibration fr ame from the m anufactur er . All settin g pr ocedur es w er e r ecor ded on videotape for r epr oduction . T h e MacReflex software (version 3.0) ³⁾ was used for collectin g and digitizin g the data . T he Cy anLab soft w ar e (v er sion 1.0) ⁴⁾ w as u sed for obt ainin g th e in st ant cent er of gr avity (CoG) of whole body at sampling r at e of 60 ㎐ and for sm oothening r aw data by the butt erworth filt er with cut - off fr equen cy of 10 ㎐. Micr osoft Ex cel (v er sion 2000) ⁵⁾ w as u sed for pr oces sing the dat a. T he SP S S (v er sion 9.0) ⁶⁾ w a s u sed for the st atistical analy sis.

P ro c e dure s

Eight een sph er ical, 3.6- centim et er - d i a - m et er ed , passive retro- reflective markers were att ached by u sing a double- sided adhesiv e t ape. T he m arker s w er e att ached bilater ally on gr eat er tuber cles and lat er al epicondyles of the humeri, styloid pr ocesses of the ulnae, gr eat er tr och ant er s an d lat er al con dyles of the femur s, lat er al m alleoli, heel an d t oe en ds of th e shoes and unilat er ally on the glabella of th e fr ont al bone and m ental pr otuber ance of the m andible bone of the skull (Fig 1). When necessary , the hair ar ound the location of m aker s w as shav ed t o av oid det achm ent of the m arker during the test . Each spot on the skin w as m arked with a w at er - soluble

3. Qualisys Inc. Glast onbury , CT 4. Cy anSoft Inc.

5. Micros oft Inc.

6. SPS S Inc. Chicago, IL

pen t o assur e r eplacem ent of the marker on th e sam e spot if a m arker det ached.

T he cam er as w er e position ed a s shown in F igur e 2. An adhesiv e color t ape w as u sed t o m ark th e ex act location of th e cam er a m ountin g tripod.

Before starting the data collection, subject s perform ed fiv e pr actice trials t o familiarize them with the t est pr ocedur e. A t w o- minut e r est period w as allow ed aft er the pr actice trials. A s soon as the r esear ch er said, r eady , set , g o, the subj ect s w er e asked t o w alk along the 7- m eter path without looking down . String s fr om the ceiling t o the floor indicat ed the point at which the turn w as t o occur (F ig 2).

T urnin g 90 only to the left w a s perform ed based on the r esult s of pr eviou s studies (Andr ew s et al, 1977; Hase an d St ein , 1999; P atla et al, 1991) in which th e char acteristics of th e both side turn s w er e symm etric. Aft er turning 90 , the subject s w er e asked t o continue w alking as fast as they did prior to turning until the r esear cher said, stop. T w o set s of fiv e trials w er e perform ed with differ ent w alking speeds in a r andomized or der to av oid the effect of fatigue. A t w o- minut e r est period w as allow ed bet w een the set s.

T o v ary the w alking speed at each trial,

one of th e thr ee comm ands (slow , r egular ,

fast ) w a s giv en in a r andomized or der . F or

each command, at least thr ee trials w er e

perform ed. Each subj ect perform ed a t ot al

of t en trials. T he cent er of gr avity (CoG)

of the whole body w a s calculat ed based on

the dislocation dat a of all body segm ent s

at a sampling r at e of 60 ㎐. W alking speed

w as calculat ed ba sed on the t empor al dis -

location of th e cent er of gr avity while it w as passin g the pr edet ermined zone, which w as locat ed ju st befor e the turning point (F ig 3). T he zon e, wher e the w alking speed w a s m easur ed, w a s pr edet ermined t o obt ain the v elocity of the cent er of gr avity ju st befor e turnin g . T he w alking speeds w er e av er aged within comm ands for each subject .

T he am ount of foot spinnin g on the floor w as m easur ed by the amount of chang e in angles bet w een the foot line (fr om heel to t oe m arker s) and the r efer ence lin e (fr om m arker 19 t o marker 20) on the floor durin g the ipsilat er al single limb support period (fr om contr alat er al toe off t o contr alater al heel contact ) while turnin g . T he single limb support period w as det er - mined based on the v elocity of the marker s on the contr alat er al heel (m arker 15 and m arker 16) an d the contr alat er al t oe ends (m arker 17 an d marker 18). T he accur acy of mea suring the st ance pha se fr om the kinematic data by a motion analy sis sy st em w as found t o be sufficient in comparison

t o the m easur em ent by a for ce plate sy st em (Peham et al, 1999). T he adv ant age of this m ethod w a s that the t empor al par ameter s of gait could be obtained without u sing an addition al device, such a s, a foot swit ch (P eham et al, 1999).

Lower extremity (LE) rotation was m easur ed by the chan ge in the an gle bet w een the F ig 1 . T he location of m arkers in the

front al and sagittal view s .

F i g 2 . T he location of the cam er a and the w alking pathw ay in the superior view .

F ig 3 . Schem atic diagram of t he cent er

of gravity pathw ay and the zone w here

t he w alking speed w as m easured. T he

univ ersal coordinat e is displayed in the

upper left corner .

hip line (fr om left gr eat er trochanter marker and right greater tr och ant er m arker ) and the foot line (fr om h eel marker t o t oe m arker ) durin g the ipsilat er al single limb support period while turning (F ig 4). While this w as not the dir ect mea sur em ent of hip joint r ot ation in the tr an sv er se plan e, it was con sidered as a representative m easur e of hip r otation in the tr an sv er se plan e becau se the other low er extr emity joint s (kn ee and ankle) allow v ery limited r ang es of r ot ation al m otion in the tr an sv er se plane durin g ip silat er al sin gle limb support . T he r ange of motion of the flex ed hip is 90 in ext ernal r ot ation and 70 in int ernal r ot ation (Nor din an d F r ankel, 1989). A s the hip is ext ended, the r ange of r ot ation al m otion in the tr an sv er se plane decr eases becau se of th e limiting for ce of the adj acent ligam ent s (Nor din an d F r ankel, 1989). T he r ange of r ot ation at the knee joint increases as the knee is flexed, r eaching a m ax imum at 90 of flexion : ex tern al r ot ation r an ges fr om zer o t o appr oxim at ely 45 and int ernal r ot ation r ang es fr om zer o t o appr oxim at ely 30 (Nor din and F r ankel, 1989). With the knee in full ext en sion , r ot ation is alm ost complet ely r estrict ed by the int erlocking of the fem or al an d tibial con dyles (Nor din and F r ankel, 1989). T h e int erlockin g of the knee occur s becau se the m edial fem or al condyle is lon ger than the lat er al condyle (Nor din and Fr ankel, 1989).

Rot ation of th e ankle and foot in th e tr an sv er se plan e is inher ently limit ed by the orientation s of their structur e (Nor din and Frankel, 1989). Lower extremity int ernal and ex t ernal r ot ation in the tr an sv er se plane is pr edominantly pr odu ced by r otation

at the hip joint s . T he low er extr emity r ot ation in cr eased with hip ext ern al r otation and decr eased with hip int ern al r ot ation (F ig 4).

S t ati s tic s

T he pair ed t - t est w a s u sed to det ermine the differ en ce bet w een the am ount s of in side an d out side foot spin while turnin g . T he Pear son pr oduct m om ent corr elation coefficient w as u sed t o determin e the r elation ships : bet w een the am ount of foot spin while turning and the w alking speed ; bet w een the amount of low er extr emity int ernal and ext ernal r ot ation while turning and the w alking speed; and bet w een the am ount of foot spin an d the am ount of lower extremity internal and external r ot ation while turnin g 90 . T he r egr es sion equation w as calculat ed t o det ermine the n atur e of the r elation ship, a s n eeded.

F ig 4 . Schem atic diagram of the low er

extremity (LE ) rot ation angles in the

transv ers e plane.

R e s u lt s

E ff e c t of w alkin g s pe e d on f o ot s pin

T he distribution s of all w alkin g speeds ar e show n in F igur e 5. T he m ean w as 1.69

㎧ with a standard deviation of .20 ㎧ and the distribution w as close t o the norm al curv e. T he m aximum w alking speed w as 2.03 ㎧ and the minimum w as 1.27 ㎧.

T he descriptiv e st atistics for each foot spin while turning ar e displayed in T able 2 and the distribution s ar e shown in F igur es

6, 7 and 8. All spin s w er e positiv ely skew ed becau se of their concentr ation s in the low er r an ges and their long tails in the higher r anges. T he m ean of th e in side foot spin w as 15.64 with a st an dar d deviation of 15.50. T he m ean of the out side foot spin w as 5.33 with a standar d deviation of 6.46.

T he mean of the tot al spin of both feet in a single trial w as 20.97 with a st andar d deviation of 18.08. During the left turn , spinning of the left (in side) foot happen ed m or e fr equ ently than spinning of the right T able 2 . Descript iv e st atistics of foot spin w hile turning

N Minimum Maximum Mean St an dar d Deviation

Skewness

(degr ee) St atistic St andar d

Err or

Left spin 45 .29 59.66 15.64

15.50 1.44 .35

Right spin 45 - 2.95 23.87 5.33

6.46 1.50 .35

Both side

spin 45 - 1.86 73.01 20.97 18.08 1.07 .35

*

p< .001

F ig 5 . Hist ogram s of the w alking speed.

Normal curve is illustrated for com parison .

F i g 6 . Hist ogram s of the in side (left )

foot spin . Norm al curv e is illustrat ed for

comparis on .

(out side) foot . T he number of spin s gr eater than 5, w hich w er e con sider able spin s in this study , w as 31 on the in side foot spin (68.9 %) and 17 on the out side foot spin (37.8 % ). T he m ean of the left (in side) foot spin w a s gr eat er than that of the right (out side) foot spin (t =4.50, p< .001).

T he P ear son corr elation coefficient (R) bet w een w alking speed an d am ount of in side (left ) foot spin w as .44 (p =.002).

W alking speed an d am ount of out side (right ) foot spin w er e not st atistically significantly corr elat ed (R =.12, p =.419). T he P ear son corr elation coefficient (R) bet w een w alking speed an d am ount of both side spin in one trial w as .43 (p =.004). T he corr elation s ar e dem on str ated in Figur e 9.

T he r egr ession equation bet w een the am ount of in side foot spin in a trial and the w alking speed w a s :

Am ount of in side foot spin

= 35.08 (w alking speed) - 42.79

T he r egr ession equation w as st atistically significant (F (1,44)=10.56, p=.002) and w alking F ig 7 . Hist ogram s of the out side (right )

foot spin . Norm al curv e is illustr at ed for comparison .

F ig 8 . Hist ogram s of the both feet spin in a single trial. Normal curve is illust rat ed for comparis on .

F ig 9 . Scatt er plot for t he relat ionship

bet w een the w alking v elocity and each

foot spin . Each line repr esent s the regre-

ssion equation betw een tw o v ariables .

Squared corr elation coefficient s (Rsq) are

displayed t o det ermin e the accuracy of

prediction s based on the regression

equations .

speed account ed for 19.7% of in side foot spin v ariance (Fig 9). T he slope (B - w eight s) (p =.002) and the con st ant (p =.022) of the r egr ession equation w er e st atistically significant . A unit (1 ㎧) incr ease in the w alking speed w as as sociat ed with an incr ease in in side foot spin by 35.08 on aver age. Becau se the standar dized coefficient in a univ ariat ed r egr ession equation with a single pr edict or is equal to th e corr elation coefficient , on e st andar d deviation (.20 ㎧) chan ge in the w alking speed w as r elat ed t o a .44 st andar d deviation (15.50 ) chan ge in the am ount of in side foot spin on av er ag e.

E ff e c t s of w alkin g s pe e d an d f o ot s pin on lo w e r e x t re m ity rot ati on LE r ot ation w as m easur ed in th e tr an sv er se plane during ipsilat er al single support period while turning . T he descriptiv e statistics of each LE rotation while turning are displayed in T able 3 an d the distribution s ar e dem on str at ed in F igur es 10 and 11. T he m ean for in side (left ) LE r ot ation while turning was - 37.25 with a st andard deviation of 14.19 an d th e m ean for out side (right ) LE r ot ation while turning w as 9.07 with a standar d deviation of 10.98 .

F ig 11 . Hist ogr am s of the out side (right ) low er extremity (LE ) rot ation . Norm al curv e is illustrat ed for comparison . T able 3 . Descriptiv e st atistics of the inside (left ) and out side (right ) low er extremity (LE ) rot at ion w hile turning

N Minimum Maximum Mean St an dar d

Deviation (degr ee)

In side LE r ot ation 45 - 58.95 - 7.99 - 37.25 14.19

Out side LE r ot ation 45 - 11.24 28.37 9.07 10.98

F i g 10 . Hist ogr am s of the inside (left )

low er ex tremity (LE ) r ot ation . N orm al

curv e is illustr at ed for comparison .

F i g 12 . Scatt er plot s for the relationship betw een the w alking v elocity an d each side low er ext remity (LE ) rot ation . Each line repres ent s the regression equation betw een tw o variables. Squared correlation coefficients (Rsq) are displayed to det ermine the accuracy of predictions bas ed on t he regres sion equations .

The Pear son correlation coefficient bet w een each LE r ot ation an d w alking speed revealed no statistically significant r elation ship (for right p =.101, for left p =.281). Left (in side) LE r ot ation corr elat ed with the am ount of in side foot spin (R =.59, p< .001).

Right (out side) LE r ot ation corr elat ed with the am ount of out side foot spin (R =- .60, p< .001). T he corr elation s ar e dem on str at ed in F igur e 12 and 13.

D i s c u s s i o n

T he purpose of this study w as t o analy ze the effect of w alking speed on the turning str at egies and on the am ount of low er extr emity int ernal and ex tern al r otation while turning 90 degr ees in healthy y oung

adult s. T he followin g w er e hypothesized:

1) T h e turnin g str ategies u sed w ould differ at th e v ariou s w alkin g speeds while turning 90 .

2) T he amount of lower extr emity int ernal and ext ernal r ot ation w ould be r elated to the walking speed while turning 90 . 3) T h e am ount of low er extr emity int ernal an d ext ernal r ot ation and the turnin g str at egies u sed w ould be r elat ed while turning 90 .

T he st ep str at egy without a foot spin

w as u sed pr edominantly during th e slow

speed trials. T h e fr equ ency an d m agnitude

of in side foot spin in cr eased a s w alking

speed incr eased, but out side foot spin w a s

not corr elated with w alking speed. T he

am ount of low er ex tr emity int ernal and

F ig 13 . Scatt er plot s for the relat ionship

betw een each low er extremity (LE )

rot ation and each foot spin . Each line

represents the regression equation betw een

tw o v ariables . Squared correlation coeffi-

cient s (Rsq) are displayed t o det ermine

the accuracy of pr edict ions based on the

regression equation s .

ext ernal r ot ation while turning 90 w as not corr elat ed with w alkin g speed. T he am ount of low er extr emity intern al and ext ern al r ot ation and th e am ount of spin of both feet were negatively correlated while turning 90 .

S t e p s trat e g y v s s pin s trat e g y

T o complet e turnin g 90 during w alking , a spin and/ or a st ep str ategy of turning m ay be u sed. In th e spin str at egy , the whole body r ot at es on the floor ar ound the ball of one foot . In the st ep str at egy , the upper body (head, neck, both upper extr em - ities, an d trunk ) and contr alat er al low er extr emity r ot at e on on e hip j oint . T he st ep str at egy seem ed t o be m or e dominant than the spin str ategy sin ce only t w elv e out of forty fiv e trials (26.6%) u sed a v ery sm all am ount of spin (less than 5 of both feet spin ). T he trial complet ed by u sing only the spin str at egy without the st ep str at egy w as r ar e (the maximum of both feet spin in one trial w as 75 ). Hase and St ein (1999) foun d the st ep str at egy w as easier than the spin str ategy due t o lar ger base of support and a separ ation of the com - pon ent s of deceler ation an d turn . Ev en in spin turn s, th e am ount of foot spin v aried fr om trial to trial. T he st ep an d spin str ategies wer e supplement ary to each other r ather th an ex clu siv e. Based on r esult s of this stu dy , it seem s to be m or e r ea sonable t o cla ssify turn s int o the turn s w ith a foot spin an d the turn s without a foot spin .

In s ide s pin v s out s i de s pin

In left turn s, spinnin g on th e left (in side) foot happened m or e fr equently and t o a

gr eat er degr ee th an on the right (out side) foot . In the case of in side foot spin , the dir ection of the foot spin w as th e sam e as the dir ection of turning . In the ca se of out side foot spin , the dir ection of the foot spin w a s opposit e t o the dir ection of turning . If a per son turned 90 t o the left , the turning dir ection of the body during in side foot spin w as t o the left and for w ar d, and the turning dir ection of the body during out side foot spin w as t o the right and backw ar d. An ex tr a for ce w as needed t o spin the body in the opposite dir ection of the turn durin g out side foot spin . T his might be th e r eason why in side foot spin s occurr ed m or e fr equently .

E ff e c t of w alkin g s pe e d on f o ot s pin

Ha se an d St ein (1999) elimin at ed th e w alking speed as an influen cing fact or in deciding turning str at egies by assuming all the testing velocities were similar . How ev er , accor ding t o the r esult s of this study , the w alking speed befor e turnin g w as one of the m ajor influ encing fact or s on the am ount of in side (left ) foot spin while turnin g . T his findin g in dicated that the turning str at egy might v ary accor ding t o the walking velocity test ed. T he r elation ship bet w een the w alking speed an d the am ount of out side (right ) foot spin w as not statistically significant . T he positive r elation ship bet w een the w alking speed an d the am ount of the in side foot spin m ay be explain ed with New ton s law s of m otion . Accor ding to the law of acceler ation (second law of m otion ), m om entum (G) is defin ed as

G = m x V

w her e m = ma ss, V = w alkin g speed (Enoka, 1998). Wh en th e w alkin g speed is incr eased, gr eat er for w ar d mom entum of the body occur s. T he st ep str at egy has a limit ed capacity t o tr an sform for w ar d m om entum of the body int o r otational m om entum in a short period of tim e becau se of the position of the cent er of gr avity (anterior to turning foot ) an d limit ed r ange of int ernal r ot ation of hip. If the for w ar d m om entum of the body ex ceeded the capacity of a st ep str at egy (r ot ating the upper body on a hip j oint ) t o transform forward momentum into r ot ation al m om entum , incr eased for w ar d m om entum of th e body could be tr an sform ed int o r ot ation al m om entum by t akin g an other st ep or by spinning on the floor ar ound the longitudinal axis of the in side foot t o complet e th e turn . T aking anoth er st ep while turnin g , how ev er , w ould r equir e m or e time and space to complete the turn . T h e spin str ategy could deceler at e the w alking speed an d turn the body at the sam e tim e, becau se spinning occur s w hile the cent er of gr avity is passing the turning foot fr om post erior t o anterior (Hase an d St ein , 1999). Becau se of this adv ant age with the spin str at egy , spinnin g on the in side foot is m or e effectiv e than t aking another st ep t o tr an sform incr eased for w ar d m om entum int o r ot ational m omentum in a limit ed time and space. Spinning on the out side foot w ould m ake it mor e difficult t o han dle incr eased for w ar d m om entum becau se the dir ection of spinnin g is opposite t o the dir ection of turning and t o the dir ection of w alking . Other possible influen cing fact or s on the am ount of spin during turn m ay be

the angle of turnin g , the am ount of friction bet w een the shoes and th e floor , individual ability t o m aint ain balance durin g spin , and individual pr efer ence.

E ff e c t s of w alkin g s pe e d an d f o ot s pin on lo w e r e x t re m ity rot ati on In the case of w alking str aight , low er extr emity r ot ation in the tr an sv er se plane w as foun d t o hav e a n egativ e v alue becau se the hip r ot at es int ernally during ipsilat er al sin gle support period. In the case of the turn without a foot spin , in side LE r ot ation gener ally decr eased as the upper body r ot at ed intern ally on the in side hip, and out side LE r ot ation g ener ally incr eased as the upper body r ot at ed ext ernally on the out side hip durin g the ipsilat er al foot spin . LE r ot ation w as in depen dent of w alking speed (F ig 12), but it w as affect ed by the am ount of ipsilat er al foot spin (F ig 13).

T her e w as a positiv e linear r elation ship bet w een the am ount of in side (left ) LE r ot ation and the am ount of in side (left ) foot spin . T he am ount of out side (right ) LE r otation w as n egativ ely corr elat ed with the am ount of out side (right ) foot spin . These result s need to be carefully int erpr et ed.

In this study , intern al LE r otation s w er e

defined to have negative values with r espect

t o ext ern al LE r ot ation s (F ig 4). T he

positiv e r elation ship betw een in side LE

r ot ation and in side foot spin m eant that th e

am ount of in side LE int ern al r ot ation w as

decr ea sed or th e in side LE r otation angle

w as maint ained m or e with the gr eat er

am ount of in side foot spin while turning .

T he in side hip w as locked t o deliv er th e

r ot ation al m om ent fr om the body and the

out side LE t o th e in side LE during th e in side foot spin . In the sam e w ay , the negativ e r elation ship betw een out side LE r ot ation and out side foot spin m eant the out side LE r ot at ed les s ext ernally with out side foot spin than without a foot spin by locking the out side hip t o tr an sfer the r ot ation al mom ent t o the out side LE . By locking it s r ot ational m ov ement , the hip joint serv ed as a solid axis t o tr an sfer the r ot ation al m om entum of the body t o th e ipsilat er al LE in the spin str at egy . In this situation , in side hip ext ernal r ot at or s an d out side hip int ern al r ot at or s n eeded t o contr act eccentrically or isometrically again st the r otational mom ent of the body t o lock hip r ot ation for tr an sferrin g the r ot ational m om ent fr om the body t o the appr opriat e LE though the hip j oint . In spin turn s, the whole body could r ot at e on the floor as one solid unit by locking th e turnin g hip joint . In other w or ds, turning 90 w as complet ed by spinning of the foot r ather than by r ot ating th e body on the hip as the amount of LE r ot ation w as decr eased.

T he function of the hip int ern al an d ext ernal r ot at or s has not r eceiv ed the sam e focu sed att ention as h av e the hip abductor s and ext en sor s in activities of daily living . T he hip abdu ct or s pr oduce the m ain for ce t o pr ev ent the cent er of gr avity fr om dr opping during the ipsilater al single support period while w alkin g (Nor din and F r ankel, 1989). T h e hip ext en sor s ar e th e m ajor mu scle gr oup u sed for fast er w alking or to ascen d st air s (John st on and Smidt , 1969).

Accor din g t o th e r esult s of this stu dy , hip int ernal and ext ernal r ot at or s seem ed t o be essential for completing th e turn while

w alking r egar dless of the turning str at egy u sed. In the step str at egy , they r ot at ed the body on the ipsilateral hip as they contr act ed con centrically . In th e spin turn , they locked the hip joint t o tr an sfer th e r ot ational m om entum of the body to the ipsilat er al lower extremity by contracting isom etrically or eccentrically . T hese findin g s suggest ed that the ther apeutic ex er cise for the hip int ernal an d ex tern al r ot at or s should be enhan ced for patient s in hip r ehabilit ation pr ogr am s t o pr epar e for their performance durin g activities of daily living .

P ossible limit ation of this study w er e that : 1) hip r ot ation in the tr an sv er se plane w as designat ed by the angle betw een the pelvis and foot by assuming that am ount of the r ot ation of kn ee and ankle in th e tr an sv er se plane w as n egligible; 2) foot spin during th e double support period w a s not included in the am ount of foot spin ; and 3) a limit ed sample size w as u sed.

F or th e furth er studies, it might be

m eaningful t o analy ze the sequence of

segmental body rotation including eye mov e-

m ent s while turning and t o study the

function of arm m ov em ent s while turning .

Electr omy ogr aphic study of the hip r ot at or s

and par a spinal mu scles w ould also be

import ant t o det ermine their function in

turning. Determining the amount of r ot ation al

m om ent of the low er extr emities in turn s

with or without a foot spin w ould be

beneficial for patient s specially w ith low er

extr emity amput ation . Study with subject s

from different age groups would also v aluable

t o fin d out the r elation ship bet w een the

turning str at egy and aging .

Co n c lu s i o n

In side foot spin in cr eased with incr eased w alking speed, but out side foot spin w as not r elat ed to w alking speed. Spinnin g on the in side foot seem ed m or e effectiv e than t aking an other st ep t o turn the body quickly w ith high speed w alking . Low er extr emity int ernal and ex tern al r otation w as n ot r elat ed t o w alkin g speed, an d it w as n egativ ely r elated t o the am ount of in side and out side foot spin. As the am ount of foot spin incr ea sed, hip r otation in the tr an sv er se plane decr eased t o tr an sfer the r ot ation al m om entum t o the ipsilat er al lower extremity. The hip internal and ext ernal r ot at or s seemed t o hav e an import ant r ole in contr ollin g th e body m ech anism while turning r egar dless of the turning str at egy u sed. Incr eased ther apeutic ex er cise for the hip r ot at or s in hip r eh abilitation pr ogr am s is r ecomm ended. F urther study is needed t o analy ze the biom echanical and neur o- mu scular m echanism s of the body while turning .

R e f e re n c e s

Andr ew s JR, McLeod WD, W ar d T , et al.

T he cutting mechanism . Am J Sport s Med. 1977;51:11- 121.

Barlett R. Introduction t o sport s bio- m echanics. 1st ed. Oxfor d, UK : E &

F N Spon , 1997:174- 201.

En oka RM , Neur om echanical Basis of Kin esiology . 2nd ed. Champaign , IL, Hum an Kinetics. 1998.

Hase K , St ein RB. T urnin g str at egies during hum an w alking . J Neur ophy siol.

1999;81:2914- 2922.

Hollin shead WH , Jenkin s DB. Hollin shead s F unctional An at omy of the Limb s an d Back . 6th ed. Philadelphia, PA , WB S aunder s, 1991.

John ston RC, Smidt GL. Mea sur em ent of hip - joint m otion during w alkin g . J Bon e Joint Sur g . 1969;51(6):1083- 1094.

Josefsson T , Nor dh E , Krik sson P O. A flexible high - pr ecision video sy stem for digit al r ecor ding of m ot or act s thr ou gh lightw eight r eflex m arker s.

Comput Methods Pr ogr am s Biom ed.

1996;49(2):119- 129.

Lev en s A S , Inm an VT , Blosser JA . T r an sv er se r ot ation of the segm ent s of the low er ex tr emity in locom otion . J Bon e Joint Sur g . 1948;30(4):859- 872.

Norkin CC, Lev an gie P K. Joint Structur e and Function : A comprehensive analy sis.

2nd ed. Philadelphia, PA , F A Davis, 1992.

Nor din M , F r ankel VH . Basic Biomechanics of the Mu sculoskelect al Sy st em . 2n d Ed. Philadelphia, PA , Lea and F ebiger , 1989.

P atla AE , Pr entice SD, Robin son C, Neufeld J. Visual control of locomotion: Str at egies for ch angin g dir ection and for going ov er ob st acles. J Exp P sy chol: Hum P er cept P erform . 1991;17(3):603- 634.

P eham C. S cheidl M, Licka T . Limb locom otion - speed distribution an aly sis as a new method for stance phase detection . J Biomech . 1999;32:1119- 1124.

P erry J. Gait An aly sis : Norm al an d Pathological Function. 1st ed. T hor ofar e, NJ , Slack . 1992.

T in etti ME, William s F T , May ew ski R. F all

risk index for elderly patient s based on

number of chr onic disabilities. Am J

Med. 1986;80:429- 434.

Wint er DA . Biom ech anics and Mot or Contr ol of Hum an Mov em ent . 2n d ed.

New York , NY, Wiley - Inter science

Pub ., 1990:18- 48.