Upsala J M e d Sci 91: 53-66, 1986 Perception of Efforts in Working Postures M . Wangenheim,' S. Carlsoo,' B. Nordgren,' and K. L i n r o t h 4 ' R e s e a r c h Foundation f o r Occupational Safety and Health in the Swedish Construction Industry and Department of Rehabilitation Medicine, University Hospital, Uppsala, 'Departnirnt of A n a t o m y , Karolinska Institute, Stockholm, 'Department of Rehabilitation Medicine, University Hospital, Uppsala, 4Research Foundation f o r Occupational Safety and Health in the Swedish Construction Industry, Sweden ABSTRACT The aim o f t h i s s t u d y i s t o o b t a i n an u n d e r s t a n d i n g o f t h e s u b j e c t i v e d i s c o m f o r t o f w o r k i n g p o s t u r e s and t h e degree o f p h y s i c a l e f f o r t t h e s e p o s t u r e s g i v e r i s e t o . 31 s t u d e n t s have r a t e d t h e i r p e r c e i v e d e x e r t i o n on Borg's s c a l e (1982) based on a c o l l e c t i o n o f photographs o f d i f f e r e n t work p o s t u r e s o f v a r y i n g c o m p l e x i t y , i n c l u d i n g a k i n a e s t h e t i c d e s c r i p t i o n ( 2 ) . Each one o f t h e 78 p o s t u r e s was h e l d f o r 45 seconds, w i t h r a t e d p e r c e i v e d e x e r t i o n (RPE) g i v e n a f t e r 15, 30 and 45 seconds. The whole t e s t s e r i e s was r e p e a t e d t w i c e . The r e s u l t s show t h a t i t i s p o s s i b l e t o e v a l u a t e d i f f e r e n t body p o s t u r e s b y RPE a c h i e v i n g a t o t a l r e l i a b i l i t y a - v a l u e o v e r 0.96. D e s p i t e t h e f a c t t h a t t h e r a t i n g p a t t e r n between t h e d i f f e r e n t p o s t u r e s was t h e same f o r a l l s u b j e c t s , i t i s shown t h a t each person assessed a c c o r d i n g t o a c e r t a i n i n d i v i d u a l l y - i n f l u e n c e d p a t t e r n . A c e r t a i n p e r s o n can f o r example, d e v i a t e c o n s i s t e n t l y t o w a r d s h i g h e r v a l u e s on Borg's s c a l e , a s o - c a l l e d " h i g h r a t e r " . F i n a l l y , t h e d i f f e r e n t p o s t u r e s were grouped a c c o r d i n g t o how t h e r a t i n g s changed i n t i m e ( r e g r e s s i o n s l o p e between t h e RPE's a f t e r 15, 30 and 45 seconds). The t h i r d - c l u s t e r , w h i c h showed a h i g h b a s i c r a t i n g - l e v e l and t h e g r e a t e s t r e g r e s s i o n s l o p e , i n c l u d e d o n l y extreme o u t e r l i m i t s o f movement. T h i s i n d i c a t e s t h a t t h e o u t e r l i m i t p o s t u r e s have a tendency t o s t a t i c l o a d and need t o be s t u d i e d b y more a d d i t i o n a l methods when r e m a i n i n g unchanged even f o r s h o r t p e r i o d s . 53 I N T R O D U C T I O N The a b i l i t y t o adapt and f r e e l y m a i n t a i n a body p o s t u r e , e.g. a p o s t u r e w i t h o u t e x t e r n a l s u p p o r t always i n v o l v e s a c e r t a i n degree o f p h y s i c a l s t r e s s . The degree o f s t r e s s d i f f e r s o f course from one p o s t u r e t o another. It i s t h e w e i g h t o f t h e d i f f e r e n t p a r t s o f t h e body, t h e s o - c a l l e d f u n c t i o n a l u n i t s (FU), and t h e energy r e q u i r e d t o make them move t h a t causes t h e s t r e s s . T h i s s t r e s s i n v o l v e s l o a d on j o i n t s and muscles. A s t h e t o r q u e around t h e j o i n t s changes, so does t h e p e r c e p t i o n o f e f f o r t o r d i s c o m f o r t . When making an ergonomical e v a l u a t i o n o f body p o s t u r e s o c c u r r i n g i n p h y s i c a l work, i n o t h e r words work postures, an anatomical / p h y s i o l o g i c a l a n a l y s i s should a1 so be performed p a r a l l e l t o a p s y c h o l o g i c a l s u b j e c t i v e assessment, t o come as c l o s e as p o s s i b l e t o a r e l i a b l e n d i a g n o s i s n (8). The aim o f t h i s study i s t o o b t a i n an u n d e r s t a n d i n g o f t h e s u b j e c t i v e d i s c o m f o r t o f working p o s t u r e s and t h e degree o f p h y s i c a l e f f o r t these p o s t u r e s g i v e r i s e t o . Carlsoo e t a1 ( 2 ) have d e s c r i b e d d i f f e r e n t work p o s t u r e s from a k i n a e s t h e t i c , t h a t i s anatomical p h y s i o l o g i c a l b a s i s . They d e s c r i b e t h e c h a r a c t e r i s t i c f e a t u r e s o f t h e muscular a c t i v i t y around t h e j o i n t s . Each p o s t u r e i s i l l u s t r a t e d by a s p l i t image p i c t u r e . I n o r d e r t o make t h e d e s c r i p t i o n s u f f i c i e n t l y d e t a i l e d w h i l e r e m a i n i n g a t t h e same t i m e easy t o f o l l o w , t h e body was d i v i d e d up on t h e b a s i s o f t h e g r e a t j o i n t s and j o i n t - s y s t e m s i n t o 14 " f u n c t i o n a l u n i t s " . The 14 FUs are: head/neck, b a c k / t r u n k and 12 e x t r e m i t y FUs. Each e x t r e m i t y has been broken down i n t o t h r e e p a r t s . Each p a r t covers one o f t h e t h r e e m a j o r j o i n t s as w e l l as t h e d i s t a l p a r t , shoulder/upper arm, elbow/forearm and so on. It i s these p i c t u r e s o f d i f f e r e n t p o s t u r e s f o r each FU which form t h e m a t e r i a l f o r s u b j e c t i v e e v a l u a t i o n o f e x e r t i o n i n t h e p r e s e n t study, Whatever ergonomic e v a l u a t i o n technique i s adopted, t h e purpose i s t o o b t a i n a q u a n t i t a t i v e and/or q u a l i t a t i v e e v a l u a t i o n o f even a complex 54 p o s t u r e . Q u e s t i o n n a i r e s a r e commonly-used f o r w o r k - p o s t u r e s e.g. i n o f f i c e s o r m o t o r v e h i c l e s . L a b o r a t o r y c o n s t r u c t i o n o f a r e p l i c a o f a work s i t u a t i o n and b i o m e c h a n i c a l a n a l y s i s i s a n o t h e r , more o b j e c t i v e method ( 3 ) . Man’s a b i l i t y t o grade and g i v e v e r b a l e x p r e s s i o n t o t h e d i s c o m f o r t and s t r e s s e x p e r i e n c e d i n d i f f e r e n t work p o s t u r e s has a l s o been employed as an i n v e s t i g a t i v e method ( 1 0 ) . Van Wely ( 1 0 ) has shown t h a t a h i g h degree o f c o r r e l a t i o n e x i s t s between s u b j e c t i v e p e r c e p t i o n o f a w o r k - p o s t u r e and t h e c o m p l a i n t s t o w h i c h i t g i v e s r i s e . Work p s y c h o l o g i s t Gunnar Borg (1) showed t h a t s u b j e c t i v e p e r c e p t i o n can be q u a n t i f i e d u s i n g a c a t e g o r y s c a l e w i t h r a t i o p r o p e r t i e s . I t i s t h i s method w h i c h has been used i n t h e p r e s e n t s t u d y . The s c a l e used i n t h e f o l l o w i n g t e s t s c o n s i s t s o f a l i m i t e d r a n g e o f numbers, 0-10. D i f f e r e n t v e r b a l e x p r e s s i o n s a r e c o r r e l a t e d t o t h e numbers. 0 r e p r e s e n t s n o t h i n g a t a l l , 0.5 e x t r e m e l y weak, 1 v e r y weak, 2 weak, 3 moderate, 4 somewhat s t r o n g , 5 s t r o n g , 7 v e r y s t r o n g and 1 0 e x t r e m e l y s t r o n g . The p e r c e i v e d e x e r t i o n t o w h i c h a p o s t u r e g i v e s r i s e , depends o f c o u r s e on whether t h e p o s t u r e i s momentary, f o r m i n g p a r t , f o r example, o f a sequence o f movements, o r o f l o n g e r d u r a t i o n ( 4 ) . I n t h e l a t t e r case, t h e i s o m e t r i c m u s c u l a r l o a d p l a y s such a d e c i s i v e and s p e c i a l r o l e i n t h e e v a l u a t i o n o f t h e work p o s t u r e t h a t a s p e c i a l s t u d y such as Rohmert (9) suggests, w o u l d be necessary. The s t u d y d e s c r i b e d be1 ow r e 1 a t e d o n l y t o m o m e n t a r i l y - a d o p t e d p o s t u r e s o f s h o r t d u r a t i o n . I n a p i l o t s t u d y t h e p o s t u r e s were e v a l u a t e d a f t e r 6 seconds. Whatever t h e r e s u l t s showed t h a t t h e t h r e s h o l d o f p e r c e p t i o n o c c u r s l a t e r . T h e r e f o r e e v a l u a t i o n was made a f t e r 15, 30 and 45 seconds. 55 MATERIAL AND METHODS The s u b j e c t s were 8 male students, aged 23-35 y e a r s and 20 female s t u d e n t s aged 20-38 y e a r s from t h e Physiotherapy Department, U n i v e r s i t y H o s p i t a l , Uppsala. None had any p r e v i o u s r e c o r d o f c o m p l a i n t s o f t h e muscul a r - s k e l e t a l system. The s u b j e c t s were asked t o t a k e up and h o l d t h e v a r i o u s p o s t u r e s d e s c r i b e d i n t h e p r e v i o u s l y mentioned c o l l e c t i o n o f p o s t u r e photographs. Each p o s t u r e was adopted from a symmetrical u p r i g h t stance a t r e s t , and compared w i t h t h i s stance. Though t h e l o w e r e x t r e m i t i e s as w e l l as t h e back a r e s u b j e c t t o s t r e s s due t o t h e f a c t t h a t t h e p o s t u r a l muscles a r e t o some e x t e n t a c t i v e i n t h e u p r i g h t stance, t h e h e a l t h y s u b j e c t does n o t p e r c e i v e t h i s as s t r e s s f u l as l o n g as t h e d u r a t i o n o f t h e p o s t u r e i s l i m i t e d t o 4 5 seconds. The degree o f e x e r t i o n o f t h e p o s t u r e has t h e r e f o r e been graded 0 i n t h e e v a l u a t i o n s c a l e g i v e n above. The p o s t u r e d i f f e r s from t h e i n t e r n a t i o n a l l y - a c c e p t e d anatomic p o s t u r e o n l y i n s o f a r as t h e arms hang f r e e by t h e s i d e s and are n o t , as i n t h e anatomic p o s t u r e , supined. The p o s t u r e s t h e s u b j e c t s were r e q u i r e d t o adopt a r e shown i n f i g s . 2-9. These a r e 10 d i f f e r e n t head postures, 8 shoulder-arm postures, 12 elbow postures, 9 h a n d - w r i s t postures, 10 back-trunk p o s t u r e s , 12 h i p p o s t u r e s , 13 knee p o s t u r e s and 5 f o o t postures. A l l 78 postures, were h e l d unchanged f o r 45 seconds. S o - c a l l e d normal p o s t u r e s ( f o r each FU) as w e l l as m i r r o r - i m a g e p o s t u r e s ( c r o s s e d - o u t i n f i g u r e s 2, 3 and 6) were n o t r a t e d . The s u b j e c t e v a l u a t e d t h e degree o f e x e r t i o n a s s o c i a t e d w i t h each p o s t u r e a f t e r 15, 30 and 45 seconds r e s p e c t i v e l y . The RPE was r a t e d a c c o r d i n g t o t h e p r e v i o u s l y mentioned s c a l e ad modum Borg ( 1 ) . B e f o r e t h e t e s t s began, each s u b j e c t was c a r e f u l l y i n s t r u c t e d i n t h e v a r i o u s p o s t u r e s and had an o p p o r t u n i t y t o p r a c t i s e u s i n g t h e s c a l e i n d i f f e r e n t t e s t s . I n t h e f i r s t t e s t an e v a l u a t i o n o f t h e area o f d i f f e r e n t g e o m e t r i c a l s u r f a c e s was made. I n t h e second t e s t d i f f e r e n t shades o f w h i t e and grey were evaluated. Taste t e s t s were a l s o performed u s i n g s o l u t i o n s o f v a r y i n g a c i d i t y . F i n a l l y t h e s u b j e c t s were asked t o demonstrate g i v e n percentage p a r t s o f t h e i r maximal s t r e n g t h o f g r i p and back e x t e n s i o n . 56 To p r e v e n t p e r c e p t i o n o f one p o s t u r e i n f l u e n c i n g e v a l u a t i o n o f t h e n e x t , t h e r e was c o n s t a n t v a r i a t i o n between t h e f u n c t i o n a l u n i t s employed and o f more and l e s s s t r e s s f u l p o s t u r e s . The whole s e r i e s was r e p e a t e d t w i c e . RESULTS An a n a l y s i s o f v a r i a n c e * was p e r f o r m e d on t h e e n t i r e m a t e r i a l , 78 body p o s t u r e s , 3 r a t i n g s ( 1 5 , 30 and 45 sec.) and two r e p e t i t i o n s o f t h e e n t i r e t e s t s e r i e s f o r 31 s u b j e c t s . The a n a l y s i s showed t h a t as expected, t h e r a t i n g s o f t h e d i f f e r e n t p o s t u r e s v a r i e d s i g n i f i c a n t ' l y (p