PHYSICAL PROPERTIES OF SOME MECHANICAL VIBRATORS AND THEIR CLINICAL RELEVANCE K . E. B R I N K W O R T H , B.Sc. (P h y s io th e ra p y ) (W itw a te rs ra n d ) SEPTEMBER 1978 P H Y S I O T H E R A P Y 11 D ie k o r r e k le tip e v ib r a to r v ir s k e le ts p ie rs a m e tr e k k in g word bespreek. D is b e la n g rik d a t d ie v ib r a sie fre k w e n s Icorrek is vir terapie. D ie fr e k w e n s van drie vib ra to rs yjat d ik w e ls in die p r a k ty k g e b ru ik w ord, w o r d bepaal. Die g e g ew e n s w o rd v e r g e ly k m e t die wat reeds in die literatuur b e s k r y f is. T h e success o f th e u se o f m e c h a n ic a l v ib r a tio n in o rd e r to e lic it a c o n tra c tio n in sk e le ta l m u sc le is d ep en d e n t on a few m a jo r fa c to rs : 1. A n in ta c t n e rv e s u p p ly to th e m uscle. (B ishop, 1974). 2. T h e site o f s tim u la tio n . (S tillm a n , 1970). I 3. T h e d u ra tio n o f s tim u la tio n . (M a rsd e n e t al. 1969). 4. T h e a m p litu d e o f v ib r a to r y stim u lu s. (M a tth e w s 1967). 5. T h e fre q u e n c y o f v ib ra to ry stim u lu s. (B ishop, 1975). R e c e n t w o rk in th is field d e als w ith a ll these facto rs (1-5), b u t in p ro c u rin g a v ib r a to r f o r th e r a ­ p e utic u se o n e is c o n c e rn e d sp e c ifica lly w ith th e f r e ­ quency a n d a m p litu d e o f v ib r a tio n p ro d u c e d by th e in stru m e n t. T h e re fo re th e fo llo w in g d a ta is e sse n tia l: 1. T h e r a p e u tic fre q u e n c ie s m u st ra n g e f r o m 100H z to 200H z. (B ish o p , 1975). 2. T h e a m p litu d e r e q u ir e d f o r th e r a p e u tic effect v a rie s w ith th e d e p th o f th e m uscle, p re s s u re of a p p lic a tio n a n d th e size o f th e lim b . T h e lite r a ­ tu r e so f a r h a s n o t spe c ifica lly sta te d o r r e c o m ­ m e n d e d d e fin ite a m p litu d e s , b u t a m p litu d e s o f a p p r o x im a te ly 1 to 4 m illim e tre s a p p e a r to be u se d e x p e rim e n ta lly . (M a tth e w s, 1967; B rin k w o rth , 1975). T h re e v ib r a to r s w h ic h w e re c o m m e rc ia lly a v a ila b le a nd m o st c o m m o n ly u sed b y th e ra p is ts in th is c o u n try w ere e x a m in e d u sin g a s tro b o s c o p e (m a tc h in g th e ra te \o f flash in g lig h t w ith fre q u e n c y o f v ib r a tio n ) a n d Readings w e re c h ec k ed o n a n o sc illo sc o p e (T y p e 541 A). 'T h e in v e s tig a tio n re v e a le d th e fo llo w in g : 1. T h e b a tte ry o p e ra te d v ib r a to r , sold as th e “ S tim u ­ la n t ” a n d u se d by P ro fe s s o r R o o d w h e n le c tu rin g h e re in 1969, e m its a la rg e ra n g e o f fre q u e n c ie s. T h e s e fre q u e n c ie s w e re n o t c le a r o n o sc illo sc o p e (as m a n y w e re p ro d u c e d ), b u t b a s ic a lly tw o c o m ­ p o n e n ts o f 330H z a n d 6 6 0 H z em e rg ed . 2. O f th e v ib r a to r s w h ic h o p e r a te off th e m a in s c u r re n t (th o se w h ic h a re p lu g g e d in), th e W a h l a n d th e P ifc o a re th e tw o m o st re a d ily a v a ila b le c o m m e rc ia lly . (a) T h e W a h l e m its a v ib r a t o r y fre q u e n c y o f 100H z a n d th e a m p litu d e o f v i b r a tio n w as e stim a te d as b e in g m o re th a n 3 m m . (b) T h e P ifc o also p ro d u c e s a v ib r a to r y fre q u e n c y o f 100H z a n d th e a m p litu d e w as e s tim a te d at 2 to 3 m m . N O T E : T h e f re q u e n c y o f v i b r a ti o n o f th e in s tru m e n t v a rie s slig h tly w ith th e fre q u e n c y o f th e e x c itin g fo rce . (T his is re p o rte d by E .S .C O M . to b e m in im a l). T h e fig u re 50 c yc le s o r 5 0 H z o n the v ib r a to r m ea n s th at th e y s h o u ld b e o p e ra te d off a c u rre n t a lte rn a tin g a t 50 cycles p e r second. T h is is th e ‘e x c itin g f o r c e ’ o f th e v ib r a t o r y m e c h a n is m w h ic h is trig g e re d b y a n e le c tro m a g n e t. In d u c tio n o f th e m a g n e t o c c u rs w ith the c h a n g e in d ir e c tio n o f th e c u rre n t. T h is h a p p e n s tw ice in e ac h cycle. T h e r e f o r e w ith in th e tim e p e rio d o f o n e se c o n d c o n ta in in g 50 cycles, th e re w ill 'ie a n in d u c tio n r a te o f 100/sec a n d h e n c e v ib r a ti o n o f 100Hz. T a b le I c la rifie s th ese findings: T A B L E I V ib r a to r F re q u e n c y A m p litu d e S tim u la n t 330 - 660 H z n o t a sse ssed W a h l 100 H z > 3 m m s P ifc o 100 H z ' 2 - 3 m m s C o n c lu s io n C o n s id e rin g th e re c o m m e n d e d fre q u e n c y ra n g e o f 100 to 2 0 0 H z in e x p e rim e n ta l s itu a tio n s , a n d w ith the in f o r m a tio n su b m itte d a b o v e , it is u n d e rs ta n d a b le th a t p h y s io th e ra p is ts h a v e o b ta in e d d is a p p o in tin g re sp o n se s w ith th e b a tte ry o p e ra te d v ib r a to r , w h e re a s m o re e n ­ c o u ra g in g re p o rts te n d to be re c e iv e d f r o m th e ra p is ts u sin g th e o th e r v ib r a to r s d e sc rib e d . A c k n o w le d g e m e n ts I w o u ld lik e to th a n k M r J. L. C ra w fo rd (D e p t, o f P h y sic s, U n iv e rs ity o f th e W itw a te rs ra n d ) a n d D r D . G . S c h u ste r (D e p t, o f P h y sic s, U n iv e rs ity o f N a ta l) fo r th e ir a ssista n c e in in v e s tig a tin g v ib r a to r y fre q u e n c ie s. R e fe re n c e s 1. B ish o p , B. (1974): N e u ro p h y sio lo g y o f M o to r R e ­ sp o n ses e v o k e d by V ib ra to ry S tim u la tio n . P h ysic a l T h e ra p y 54, 1273-1281. 2. B ish o p , B. (1975): P o s sib le A p p lic a tio n s o f V ib r a tio n in th e T r e a tm e n t o f M o to r D y s fu n c tio n s. P h ysic a l T h e ra p y 55, 139-143. 3. B rin k w o rth , K . E. (1975): T h e V i b r a to r — T h e r a ­ p e u tic T o o l o r A c a d e m ic T o y ? S .A .J. P h y s io th e ra p y 31, 3, 11-13. 4. M a rsd e n , C. D ., M e a d o w s, J. C. a n d H o d g s o n , H . J. F . (1969): O b s e rv a tio n s o f the R e fle x R e sp o n se to M u scle V ib ra tio n in M a n a n d its V o lu n ta ry C o n tro l. B rain 92, 829-864. 5. M a tth e w s , P . B. C. (1967): T h e R eflex E x c ita tio n o f S oleus M u scle o f th e D e c e re b ra te C a t c a u s e d by V ib ra tio n A p p lie d to its T e n d o n . J. P h ysio l. 192, 773-800. 6 . S tillm a n , B. C. (1970): V ib r a to r y M o to r S tim u la tio n — a P re lim in a ry R e p o rt. A u stra lia n J. P h y s io th e ra p y 16, 118-123. R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. )