(a) (b) S t i ffn ess o f t h e l u m bo p e l v i c reg i o n fo r l o a d tran sfe r 85 � :TS ��I I I I I I A � £��I I I I I I I I I 1 8 A Fi g u re 5 . 7 U l t r a so u n d i m a g e s of t h e l u m b a r m u l t i fi d u s i n l o n g i t u d i n a l se ct i o n : (a) re l a x ed sta t e ; ( b) a ft e r i s o m e t r i c c o n t ra c t i o n . T h e l i n e AB re p rese n ts t h e d e p t h o f t h e m u s c l e fro m i t s s u p e r i o r a s pect t o t h e su pe rior a s pect o f t h e L4- L5 zyg a p o p h ys e a l j o i n t . In t h e r e l axe d state (a l . t h i s i s 2 . 3 7 cm ; o n c o n t ra c t i o n ( bl . t h i s d e pt h i n c re a s e s to 2 . 7 3 c m . S, sk i n ; ST, s u b c u ta n e o u s t i s s u e ; H, t h e d i rect i o n of t h e fi b re s i n t h e m u l t i fi d u s . copy ( F i g . S . l l a , b ) . A t t h i s p o in t, i t is rel ev a n t to emp hasize, as explai ned ea rli er in th i s chap ter, tha t the concept of a shorten i n g con tra cti on of tra n sver sus a bd om i n i s d u ring th e d raw in ma noe u v re is c u r rentl y bei n g v a l i d a ted i n o ur fu nc tion a l M RI s tu d i e s . T h e s u bj e c ts w e r e a l so req u i red to d o a ' b ra cing' con tra c t io n, invo l v i n g a l l o f the abdom i n a l m u scles, so tha t t h e effect of two d i fferen t muscle rec r u itment p a tterns on pelvic s upport c o u l d be com p a red . Thi s second a b d o m in a l muscle pa ttern was a lso assessed visua l l y then rec ord ed using real t i me ul trasound (Fig. S . l l a ,c ) . I n ad d ition , surface EMe on t h e a b d om i n a l m u sc l es a l l owed the gl oba l response of these muscles, as a res u l t of manoe u v res, to be q u a n tified . Sa cro-il i a c j o i n t la xity w a s m e a s u red u s i n g Doppler i m a gi ng of v ib ra t i ons. T h i s is a n e w m e a s u re m e n t tech n i qu e from Eras m u s U n iversi ty in w h ic h la x i ty is assessed in the p rone, non vv eightbea ring posi t i o n . By a d d ing a known vibra tion to the pelv is from below ( v i a the region o f th e a n te r i o r superior iJ i clC spine), th e di ffere nce in the resultan t frequency of v ibration between the sac r u m a n d i l i um is m e a su red u s i n g Doppler i m a g i ng . As t h e s e two bones are c o n n e c ted via the sac ro-i l i a c joi nt, the larger the d i fference i n res u l tant frequ ency a s it passes th rough each bone, the greil ter the lax i ty in the j o i n t . The results demonstrilted tha t a spec i fic con trac tion of the tra nsversus abd ominis and m u l tifid u s (con firmed u sing real-time ul tra sound) w i th 8 6 T H E JOI N T PROTECTION MECHA N IS MS F i g u re 5 . 8 T h e m u sc l e c o n t ra c t i o n of ' d ra w i n g i n ' o f t h e a b d o m i n a l w a l l w i t h a n i so m e t r i c c o n t ra c t i o n o f t h e l u m b a r m u l t i fi d u s . T h e i n t e r re l a t i o n s h i p a n d t h e i n te r a c t i o n betwe e n t h e se two m u sc l es a n d t h e fa sc i a l sys t e m ca n b e a p p r e c i a t e d , a n d t h e d i a g ra m i l l u s t r a tes how t h ey c a n w o r k tog e t h e r to g i ve s p i n a l s u p p o r t . .... F i g u re 5 . 9 C o n ce p t t h a t co m p ress i o n of j o i n t s u rfa ces by m u s c l e fo rce h e l ps to p reve n t s h e a r i n g . ( R e p rod u ce d w i t h p e r m issi o n fro m S n ij d e rs e t a l 1 9 9 5 , p . 420.) minimal c o n t r a c t i o n of t h e superfi c i a l a b d o m i n a l m u sc les ( co n firmed w i th EMG) increased sti ffn ess (or d ecrei1sed l 1 . 5 e- x ro --J 0 . 5 0 2 trial I . Rest 0 D raw-in 0 Balance I Fi g u re 5. 1 2 S a c r o - i l i a c j o i n t l a x i ty reco r d e d d u r i n g rest , d ra w - i n exercise a n d b ra c e exerc i s e . A l o w e r t h res h o l d u n i t re p rese nts a s t i ffe r sa c r o - i l i a c j o i n t . T h e d ra w - i n a n d t h e b ra c e resu l t i n a red u c t i o n o f j o i n t l a x i ty, b u t t h e d ra w - i n test w i t h i n d e p e n d e n t t ra n sversus a bd o m i n i s contracti o n i s m o re e ffe c t i v e . Ave ra g e va l u e s of a l l s u bj e cts m e a s u re d i n t w o r e p e a t e d t ri a l s. ( R e p ro d u ce d w i t h p e r m i s s i o n o f R i c h a rd s o n e t a l 2002, p . 404.) These two con d i tions a p p l y to a c t i v a te the local m u s c l es a nd s u p por t the l u mbope l v ic reg i on fo r w eigh tbearin g . 1 . Ma i n ta i n a n e u t r a l l u m b a r spine (ma i n ta i n a l l s p i n al cu rves) 2 . Dra w in the lower abdo minal wall, w i tho u t spina l movement. Check tha t the corset is a c ti vated, i . e . tra ns versus a b d o m i n i s i s fo r m i ng a shortening ( c orset) contra c t ion with the ma n oe u v re, a n d the lumbar erec tor s p i n a e a re co-co n tra c ting isometrica l l y. C h J p ters 1 2 a n d 15 w i l l expl ain h o w the a b i li ty to hold ne u t rJ I spinal c u rves can be assessed an d w i ll d iscuss reseJ rc h find i ngs th a t pJ tie n ts with I mv ba ck pJ i n C J n no t h o l d ne utral spinal c u rves in u p r i gh t w o r k ing pos tu res . In J d d i t i o n , C h a p ter 1 5 e x p l a i n s how to chec k i f t ra n sv erses a b d o m i n i s i s form i n g a sh ortening (corset) con tra c ti on a u to m a t iCJlly i n res ponse to the i n s truction ' d rJ \'" in the l ow e r a b d o m i n a l w a l l ' and in this way a lso Jssess when the corset c a nn o t be formed , for eXJmple, in pa t ie nts w i th low b a c k pai n . C L I N I CA L E V I D E N C E O F E F F E CT I V E N E S S O F R ET R A I N I N G T H E C O R S E T A C T I O N The d ee p m u s c u lo-fa sc i J I c orse t h J S b ee n i mp l i c a ted i n p rov id i n g t h e s ti ffn ess of t h e j o i n ts o f the lumbopelvic region for both movement a n d wcigh t bearing fu nc ti on. Howev er, t h e most sign i f i c a n t ev idence fo r importance o f t h e corset i n re l a ti o n t o l u mbopelv ic s tabi l i ty has b e e n in cl i nica l tr i a l s where train ing of th is a c t i o n has res u l ted in the reli ef of low back p a in symptoms and preven tion of recurrence ( H ides e t al 1 996b, 200 1 , O'Su l l i v a n et a l 1 997, Golby e t a l 200 1 ) . I n these s t u d ies, th e e xerc ise that is e ffec tive in the m a n a g e me n t o f low back p a i n i nvolves tea c h. i ng patients to form a dyn amic m uscle 'corset' i nv o l ving con tra c t i o n o f transverses abd omini s a nd m ul t i fi d u s . Our current MRJ research is a l so demo nstra ting that dysfu. nction in. thi s m u s c u l o - fasc i a l sys te m i s c l ose l y rel a ted to the presence o f low back p a i n ( C h . 1 2) . However, c li n i ca l evidence o f the effec tiveness o f re tra i n ing the co rse t a c tion i n chronic low back pa i n h a s demonstra ted tha t stren gth tra in i n g (w i th the addition o f load ) i s a lso req u i red to obta i n sign i fi cant improvement i n m u scle func tion o f m u l tifid us, a s a ssessed b y its c ross-section a l a rea (Danneels et al 2000 ) . Thi s can also be in ferred from a s t u d y where speci fic stabi l izing exerci ses ( tea ch i ng the deep corset a c tion) g i ven for 4 weeks did not ch a n ge the c ross-sec ti o n a l area o f m u l ti fi d u s i n subjects with ch ro n ic low b a c k pa i n w h o h a d u n de rgone s u rgery ( S . Kelley e t a l 2003, u n p u b l i shed d a ta) . B o th these s t u d i es lend support for our conte nt i on th a t stab i l ization and prote c t i on of the low ba ck in pa ti e n ts w i th c h roni c Imv back pai n a ls o involves h i gher l eve l s treng thening exer c ise . Our resea rch would seem to sugges t t h J t th is strengthen ing exe rci se sh o u l d foc u s o n the J n t i gra v i ty s y s t e m , which con tro l s h ig h - l o a d w c i g h t bea ri n g function ( C h s 6 a n d 13) . However, ,l lthou gh h i gh-load \veightbea r in g fun c ti on i s important, the ini tia l stagl::' of reh a b i l i ta tion and preven tion (i.e. a c t i v a tion of tlw d l'l'p muscle c o rs e t) is recognized a s the essen t i a l co m ponen t o f d evelo p i n g the j o i n t-p ro tection Illl' c h ani s ms o f the lu m bope l v i c region a n d for m i n g t h e ' m otor con tro l ' b u i l d i n g b l ocks f o r weightbea r i n g . F o r th is reason, tra i n i n g o f t h e d el'!.1 co r s e t s h o u l d remain t h e i n i t i a l foc u s o f prev e n tion a n d reha b i l i ta tion progra m ml::'s (Ch . 1 4 ) . O nce tht' a u toma t i c corset ac tion h a s b e e n tra i ned, p ro g ress t o t h e Junc tiona l in tegra tion o f the deep corset w i th the globa l m u sc l e system fo r l o a d e d , a n ti g ra v i ty w e i g h tbca r i n g c a n b e b eg u n . A P P E N D I X : THE U S E O F R E A L - T I M E U LT R A S O U N D IMA G I N G I N PHYS I OTHE R A PY Rea l - t i m e u l traso u n d imagi n g has been exten sively used in medicine since the 1 960s. It a llows ra pid eva l ua tion o f the morphology and pa tho morphology of n u mt' rous o rgans and tiss ues. Its most common a pp l ica tion h a s been in the field o f obstetrics, where i t h a s been o f speci a l benefi t because it docs not i nvolve exposure of the fetus to ioni zing rad ia tion . Other a reas of u se in m edicine i n clude gynaecol ogy, in tern a l med icine, surgery, orthopaedics, sp orts medici ne, n eu rology and p a ed i a tr i c s . U ltra soun d has p roven to be very useful in spo rts mE:'dicine, allmving i maging of m u scles, tendons, joi n ts, l igam en ts and b ur sa e . Rea l - t i m e u l tra sou n d has p roven t o b e o f spec ific ben e f i t in resea rch a nd reha b i l ita tion of pa tien ts w i th l u mbope l v ic p a i n . Bas i c p r i n ci p l es a n d i n st r u m e n tation U l traso u n d tech no logy i s not new and d a tes back to World War 1 , w h e re u l traso u nd was used to detect s ubma r ines . It i nvolves send ing short p u lses of ul t ra so u nd into the bod y a n d us i ng reflections recei ved from tissue in terfaces to prod uce images o f in terna I structu re s . P u lsed u l trasou nd is described by frequency, propaga tion speed , i n ten sity, a tten u a tion imd p u l se length (Krem kau 1983) . For m u sc u loskeleta l i maging, frequencies from 3 . 5 t o l O MHz are usu a l ly used . S i m i lar t o the princi pl es ta ugh t for the rapeu tic ultrasowld, h igh er fre quenc ies p rovid e less penetra tion into the tissues, a nd lower frequencies a re used for penetra tion into deeper tissues. For i m ag i n g, h igh er frequencies p rovid e less penetra tion b u t b e t ter image resolu t i o n . Lower frequencies provide images of deeper s t ructures, b u t the trad e-off is decreased im a ge res o l u tion . The veloci ty, or speed, of sOLmd wa ves in soft tiss u e i s an a v e r a ge of 1540 m / s, and in bone is a b o u t 4000 m / s . The so wl d waves a tten ua te as they progress through the ti ss ues a s a result of reflection, re fracti on, sca tter ing, abso rp tion and d i vergence of the beam . At d iagnostic frequenc ies, u l t rasOlmd obeys the laws of l igh t in tha t it is reflected a t in terfa ces, refra c ts a t i n terfaces and can be foc used . Sti ffn ess of t h e l u m bopelvic reg i o n fo r l oa d t r a n sfe r 8 9 Imaging systems con sist o f a p u l ser, transdu cer, receiver, me mory and d isplay. An example of ul tra sound equipment is shown in Figure 5 . 13 . Si milar to thera peutic u l tra s o u n d , d iagnostic ul traso u nd is genera ted by the piezo-electric effect. Thi s i nvolves conversion of electrical vol ta ge s into u l traso u n d , w h i c h is sen t i n to the body, re flec ted b a c k a n d reconverted into elec tri ca l v o l tages . F o r ult rasou nd ima ging, the same transduce r is u sed to send p u lses and receive echoes reflected back to it. Various types of t ransd u ce r a re avai lable: multielement tran s d ucers of both s tra igh t linear and c u rvi l inear arrays. For imaging the m ultifidus, we h a v e used a 5 M Hz c u rv i l i near tra nsducer ( Fig. 5.14). It pro d uces a well-defi ned i m age of the comp le x fa sc i a l p l a nes o f this m uscle . This transd ucer c a n a lso b e used for the tra nsverses abdominis and gen era l l y wo uld be the m ost useful transd uce r for this area . For larger pa tients, a 3 . 5 MHz tra nsd u cer m a y be required . The d ista nce from the transducer to the tissues is determined by travel time. This form of Figure 5 . 1 3 Exa m p l e of rea l - t i m e u l t r a s o u n d i m a g i n g e q u i p m e n t . Figure 5 . 1 4 A 5 M H z c u rv i l i n e a r t ra n sd u c e r u s e d t o i m a g e t h e m u l t i fi d u s m u sc l e . 9 0 T H E J OINT PROTECT I O N M E C HAN I SMS i m a g i n g i s kno wn as B-mode ( brigh tness m o d e ) . G rey sca l e i m a g i n g i s a B - m o d e scan n i ng tec h n i q u e tha t permits t h e brightness o f th e B-mode d ots to be d i splayed in various shades o f grey to rep resent d i ffere n t echo a mp l i hl des (Van Holsbeeck a n d ln trocaso 1992 ) . On an u l trasound image, fl u i d a p pears black, w herea s reflection from a bone h a s i n c reased echogenic i ty a n d a p pea rs w h i te . M u s c l e o ften a p pea rs b l ac k on u l tra sou nd i mag ing a s it is fu l l of fl u i d ( b lood ) . The a d v a n ta ges o f ultrasou nd i m a gi ng a re tha t i t i s re l a tively i n e x p e n s i v e a n d d oes n o t involve ex posure to ionizing ra d i a t i on. I ts d isadvan tages a re tha t it i s opera tor d e pendent, has a l i m i ted field of v i e w a nd i ts res o lu t i o n i s i n fe r i o r to MRJ a nd com puted tomog ra p h y scann ing . U s e of u l traso u n d im a g i n g i n rehab i l i tation T h e t w o main uses of rea l-t ime u l trasou nd im agi ng in reh a b i l i til tion a re for resea rch a n d fo r feed back of muscle ac t i v a tion p a t ter n s . Research R e a l - t i m e u l traso u n d i maging h a s been used to g u i d e fi ne- w i re e l ec trode placement i.nto the trans versus abd o m inis, i nt e rn a l o b lique and ex ternal oblique mu scl es (Cresswell e t a1 1992a, Hodges and Ric h a rdson 1 997c) . U l t r a s o und ima g i n g a l l ows v is u a l i za tion o f the muscle tissue an d the fasc i a s w h i l e t h e need l e is bein g inse rted, en s u r i n g il ccur a te pl acement o f the electrodes . A n other research a p p l ic a t i o n of re il l - ti m e u l tra sOLL n d i m aging i s meilsuremen t o f m uscle size. Th i s is p oss ible a s ultwsoun d imaging a l l ow s m e a s u re m en ts in cross-sec tion, th u s d i rectly a ssessing m u scle a t rophy a nd hypertrophy. Va riou s m u scles h a ve been measure d in this w a y, includ ing q u a d ri ceps, a n terior tibia l muscles an d the l u m b a r m u l t i fid us ( Stokes and Yo u n g ] 9 8 6 , L o o a n d Sto kes 1 990, M a rti nson a n d Stokes 1 99 1 , Hides e t a l 1 992, 1 994, 1 995, 1 996b, Sipila and Su ominen ] 993, S. Kel ley et al 2003, unp ub l ished d a ta , T. Wa l hvork e t al u n p u b l ished d a ta ) . For the m u l t i fidus, ini t i a l tria l s w e re cond ucted to ascerta in i f measurement b y u l trasou n d i m a g i n g was re peatable ( H i d es e t a l 1 992) . Forty-eig h t s u bj ec ts w i tho u t a h i s to ry o f low b a c k p a i n w e re stud ied , a n d m u l t i f i d u s cross sechonzd a rea measurements were performed bi l a ter il l ly. Res u l ts sh owed good d u p l ic a t i o n of the mea s u re m e n ts a n d th a t the m u l t i fi d u s is s y m metrica l i. n subjects who have never su ffered low b a c k p a i n . The sha pe o f t h e mu scl e v a r ied between ma l e and female s u bj ec ts . Va l i d i ty of the measure h a s a lso been e x a m i ned by c o m p a rison w i th MRI (H i d e s e t aI 1 99 5 ) . Ten s u bj ects w i th o u t a h i s tory o f l ow back pa i n were measured using both ultrasound i m a g i n g a nd M R ! by bl i n d ed assessors. Desp i te tl'1l' d i ffer ence in posi tion of the su bjects ( p rone for u l tra so u n d and s u p i ne for MRI), ev 'ry a ttemp t W il S made to s tand a rd ize subj ect pos i ti o n, as j oi n t posi tion and muscle length m a y infl uence cross-sectional a rea . Figu re 5.15 shows a s u bject i n the stud y u nd er going assessmen t. M u l t i fi d u s w a s measu red b i l a t erally a t five ve rtebra l l e v e l s . Res u l ts showed a s i gn i fica nt d iffe re nce in m u l t i fi d u s c ross-sec t i on a l a rea between v e r te b ra l l e v eb, b u t n o s i gn i fi c a n t d iffe rence between t h e t w o moda l i ties u sed. This measure was then used in a longihld i n a l randomized Fi g u re 5 . 1 5 S u bj e c t u n d e rg o i n g u l t r a s o n i c i n ve s ti g a t i o n of m u l t i fi d u s cross-sect i o n a l a re a . To re p l i ca te t h e p o s i t i o n o f t h e h i ps i n t h e m a g n et i c reso n a n ce sca n n e r. w h i c h w e re f l e x e d , t h e h i p s w e re f l e x e d to t h e sa m e a n g l e i n t h e p r o n e p o s i t i o n b y t i l ti n g t h e b o t t o m h a l f o f t h e b e d fo r u l t r a s o u n d ex a m i n a t i o n . c l inica l tr i a l i n v o l v i n g s u bj e c ts w i th acu te low back pa i n . One gro u p u n d e r w e n t spec i fi c m u l ti fi d u s reha b i l i ta t ion a nd the re w a s a con trol gro u p ( H i d e s et a l 1 996b, 2001 ) . I t had been essen t i a l to esta b l i s h repeatab i l i ty, re l i a b i li ty an d v a l i d i ty of the m�a s u re prior to its a d option as the study depended upon repea ted meas u res. I f measurement error was l a rge, i t would have masked the e ffects of the in terv e n t i o n . Exa m. i n a tion of the m u lti fid u s i n parasagi tta l sec tion rev ea led i ts u n usua l m orphol ogy. Because o f d ep th d i ffere n ces o v e r the cou rse of one ve rtebra l l ev e l , l a nd marks had to be used to e n s ure th a t m e a s u reme nts were a cc u ra te . The ver teb ra l a m i n a p rov ided s u c h a l a n d m a r k . The mea s u re m e n t o f m u l ti f i d u s is a d i ffic u l t parameter a n d 'hould only be a d o p ted a fter repe a t a b i l i ty a n d re l i a b i l i ty s t u d ies have been esta b l ished . U l traso u n d i ma g i n g has a l so been used to a ssess the s ti ffness of the sacro- i J iac j oi n t ( D a m e n et a 1 2002, R i c h a rdson et a l 2002 ) . S u bjects were positi oned in prone l y ing, and v i bra tions from a mech a n i ca l v ibra tor were a p p l ied u n i l a terally to the an te r i o r s u perior i l i a c spin e . T h e vertical v i brations p ro pa ga ted fro m the i l i u m to the sacru m , d epend i n g o n t h e l a x i ty of the i n terven i n g s a c ro- i l i a c j o i n t . T h e v i b r a t i o n s o f t h e i l i u m a n d t h e s a c r u m w ere de tected by a colour Doppler i ma g i n g tra nsd ucer ( Dop p l e r i m a g i n g o f v i b r a t i o n s ) . The m e a s u re has been v,l l id a tcd on mea s u remen ts m a de on a m o d e l p e l v i s a n d 011 e m b a l med huma n pel v ises ( Da men et a l 2002 ) . Rd i,l bi l i ty has also been demonstrated ( l),lll1l'n et a I 20(2 ) . Feedback o f m uscle activa tion One of the m a i n ,1 dvantages of rea l - t ime u l tra sowld i m a g i n g i s tha t muscle contra c t i on can be i m il ged a s it actua l l y occ u rs . Th is i s very useful in re h a b i l i tation ,1 S i t c a n prov i d e d i rect feed b a c k to the sub ject and e n h a nces l e a rni n g . The li se o f u l t r a so u n d i m a g i n g t o pro v i d e fee d b a c k o f m u l t i fi d u s m u scle a c tiva ti on w a s reported by Hides d al ( 1 9%b ) . The m u l tifi d u s w a s i maged in lonh>i tu d i n a l (pa ra sagitta l sec tion) an d p a t i ents were a skc'd to ' sw e l l ' the m u l ti f i d us gen tl y, wh i c h vv a s a gentle i s o m e t r i c con t r a c t ion. On t h e u l trasou n d i mage, the m u s c l e was seen t o increase i n d ep th a s t h e m u s c l e con tra c fL' d , p rov i d i ng immed i a te v i s u a l feedback of muscle a c t i v a tion t o the s u bjects a s they Stiffness of the l u m bo p e l v i c reg i o n for l o a d tra n sfe r 9 1 co n t ra c ted the m u s c l e . The e ffec t o f u l traso und a s a for m o f feedb a c k o n m o to r l e a rn i n g of t h e m u lti fi d u s isometric con tra c t i o n has been L n vestiga ted (K. Van e t a 1 2003, unp u b lished d a ta; Fig. 5. 16) . Two groups of s u bjects witho u t a h i s tory of l o w b a c k p a in were ta ught h o w t o con tract t h e m u l ti fi d u s iso metrica l ly bu t on l y one group rece i v d v i s u a l feed b a c k of the c o n tra c t i o n . The group who rec e i v e d the fee d b a c k o f m u l ti fi d u s a c t i v a ti o n v i a t h e ultra sound m a i n ta ined the skill s i gn i ficantly better th a n the s u bjec ts of the con trol group. This m e a s u rem e n t of t h e increase i n m u scle d e p th of the m u l tifidus on isomet ric c o n trac tion has been shown to be repea t a b le a n d reliable (K. Va n e t al 2003, u n p u b l ished d a ta , T Wa l l w or k et a I , u n p u b l i shed d il ta ) . The tra nsversus abdom.inis, i n te r n a l ob l i q u e and ex tern a l o b l i q u e m u sc l es can be i m aged q u i te easily using u l traso u n d i maging. The transdu cer is pla ced l a te r a l to the u mb i l ic u s, on the a n te ro l a te ra l a s pec t of th e ilbd omi n a l 'N a i L The in ti ma te rela tion s h i p be tvveen abdominal musc les a n d t h e i r fasci a l a ttach ments can be clea r l y w i tnessed u s i n g u l trasou nd imagin g . The corset a c ti o n of the tra nsversus a bdo mi n i s i s easily observed . W h e n the m u scl e contracts a n d shortens, i t is seen to p u l l i ts a n terior fa sc i a l a t tachmen ts i n a l a tera I d i rection . Th. i s sh ould occ u r evenly b i l a tera lly, a n d i f i t d oes, i t w i l l p u ll the a n te r i o r a b d o m inal w a ll in a p o s teri o r d i recti o n . T h e fea tures w e l o o k for i n a good activation pa t tern a re (a) th a t tra nsvers us a b d om in i s ten s i ons i ts fasc i a l a t tach ment a n d p u l l s i t l a te r a l l y ; ( b ) tha t tra nsv er sus a b d o m i n i s w ril p s a round the wa is t l i n e ( c o rset a c t i o n ) ; (c) tha t tra n s v e rses a b d om inis thickens s l ightly; a nd ( d ) th a t in tern a l o b l i que a n d e x t e rn a l o b l iq u e remil i n rela tivdy i nil c tive. W e a r c c u r re n t l y va lidating the u l tra sowld assessment o f abdom i n a l a c tiv a tion p a t terns b y compari son w i th M R I i n sub jects w i th and w i th o u t a h i s to ry of low b a c k p a i n . Th e a d v "m t a ge o f the M RI i s th a t the w h o l e corset can be i maged at once, a s it has a m u ch w i d e r field of view t h a n the u l t r a so u n d i m a g i n g . We b e l i e v e thM a symmetrica l concentric con traction of th e transversus a b d o m i ni s is the i d e a l p a ttern o f a c t i v a t i o n . This s t u d y i s providing fil sc i n a ting i n s igh ts in to the corset m echan ism a n d sho u l d h e l p to gL' n erate s i mple meas uremen ts o f c o rset e fficiency The re lation s h i p b e tween the i n c rease in m u s c l e thick ness observed d u r i n g con t r a c ti o n on u l trasound i m a g i ng and EMG il c t iv i ty has bt'cn 9 2 T H E J OINT PROTECT I O N MECHANISMS exa m ined for the trans versus a b d o m in i s (Hod ges et al 2003d ) . Res u l ts showed tha t the relationship w a s g o o d fo r t h e t r a n sversus abdom i n is a n d t h e i n tern a l ob l i q u e m u s c l e a t l o w levels o f maxi m u m v o l un t a ry contraction. T h e rela tionship w a s n o t a s close f o r t h e e x ternal oblique, p robably rel a ted to the a rc h i tec t u re of the musc l e a n d orien ta tion of i ts fibre s . S u rface EMC sho u l d , there fore, be used F i g u re 5 . 1 6 S u bj e c t p e rfo r m i n g i s o m e t r i c c o n t ra c t i o n of t h e m u l t i fi d u s w i t h v i s u a l fe e d b a c k provi d e d by u l t r a so u n d i m a g i n g . T h e s u bj e c t i s v i e w i n g t h e c o n t ra c t i o n t h r o u g h a h o l e i n t h e b e d , a n d t h e u l t ra s o u n d i m a g e i s b e i n g d i s p l a yed o n a TV m o n i to r a n d refl e c t e d by a m i rror, to a l l o w t h e s u bj e c t t o v i e w t h e s c re e n w i t h t h e h e a d p l a ced i n t h e m i d l i n e . in a d d i tion t o u l trasound i ma g i n g o f t h e interna l obl iqu e a n d transv ers u s abdom i n i s to give a n a d equa te i n d i ca tion of acti v a tion o f the th ree m u s cles o f the an tero la tera l abdom ina l w a l l . We Ll sed this comb in a tion of measures to v e r i fy the p a t t e rn s of abdom in a l a c t i v a t i o n i n o u r rece n t study of the e ffec ts o f m u scle a c t i v a tion o n th e s t i ffness of the sacro- i l i a c jOi n t (r� i c h a rd son e t al 2002 ) .