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Influence of time pressure and verbal provocation



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Eur J Appl Physiol 2002 87 257 263 DOI 10 1007 s00421 002 0611 7 O R I GI N A L A R T IC L E J Wahlstro m M Hagberg P W Johnson J Svensson D Rempel Influence of time pressure and verbal provocation on physiological and psychological reactions during work with a computer mouse Accepted 20 February 2002 Published online 22 May 2002 Springer Verlag 2002 Abstract The overall aim of this study was to investigate whether time pressure and verbal provocation has any e ect on physiological and psychological reactions during work with a computer mouse It was hypothesised that physiological reactions other than muscle activity i e wrist movements forces applied to the computer mouse would not be a ected when working under stressful conditions Fifteen subjects 8 men and 7 women participated performing a standardised textediting task under stress and control conditions Blood pressure heart rate heart rate variability electromyography a force sensing computer mouse and electrogoniometry were used to assess the physiological reactions of the subjects Mood ratings and ratings of perceived exertion were used to assess their psychological reactions The time pressure and verbal provocation stress situation resulted in increased physiological and psychological reactions compared with the two control situations Heart rate blood pressure and muscle activity in the rst dorsal interosseus right extensor digitorum and right trapezius muscles were greater in the stress situation The peak forces applied to the button of the computer mouse and wrist movements were also a ected by condition Whether the increases in the physiological reactions were due to stress or increased speed productivity during the stress situation is discussed In conclusion work with a computer mouse under time pressure and verbal provocation stress J Wahlstro m M Hagberg J Svensson Department of Occupational Medicine Sahlgrenska University Hospital St Sigfridsgatan 85 412 66 Go teborg Sweden E mail jens wahlstrom ymk gu se Fax 46 31 409728 P W Johnson Department of Environmental Health University of Washington Seattle WA USA D Rempel Ergonomics Program Division of Occupational Medicine University of California San Francisco USA conditions led to increased physiological and psychological reactions compared to control conditions Keywords Stress Electromyography Input device Video display terminal Physiological reactions Introduction Musculoskeletal symptoms of the neck and upper extremity associated with work with visual display units VDUs are common In 1999 approximately 60 of the Swedish work force used a VDU in their profession Statistics Sweden 2000 and it is believed that this gure is increasing It is thought that musculoskeletal symptoms among VDU operators have a multi factorial aetiology Non neutral wrist arm and neck postures workstation ergonomics duration of computer work and psychological and social factors such as time pressure and high perceived work load are believed to interact in the development of these symptoms Bongers et al 1993 Faucett and Rempel 1994 Experimental studies have shown that mental stress can induce muscle activity Ekberg et al 1995 Larsson et al 1995 Lundberg et al 1994 W rsted et al 1991 1994 W rsted and Westgaard 1996 In some of these experimental studies Ekberg et al 1995 Larsson et al 1995 Lundberg et al 1994 authors have used the Stroop Color Word Test CWT as a stressor and the outcome has primarily been muscle activity in the trapezius muscles Other authors have used a complex twochoice reaction time task W rsted and Westgaard 1996 W rsted et al 1991 1994 and focused on the muscle activity in the trapezius muscle but also measured muscle activity in other body regions The CWT and the two choice reaction time task require minimal physical activity during performance and are not easily transferred to real work situations using a VDU or a computer mouse The aim of this study was to investigate whether time pressure and verbal provocation have any e ect on 258 physiological and psychological reactions when working with a computer mouse It was also hypothesised that physiological reactions other than muscle activity i e wrist movements forces applied to the computer mouse would not be a ected when working under stressful conditions spectrum were calculated using the Polar software system and the LF HF ratio LF HF ratio was calculated together with the mean HR The HF component of the power spectrum re ects parasympathetic activity and the LF component re ects sympathetic activity with vagal modulation mental stress has been shown to lower HRV and e ect an increase in the LF HF ratio Kristal Boneh et al 1995 Blood pressure Methods Subjects Fifteen subjects 8 men and 7 women volunteered to participate in the study which had been approved by the Ethics committee Subjects from various occupations were recruited from the Sahlgrenska University Hospital Go teborg and former fellow students of two of the authors JS and JW The mean age was 30 years range 18 48 years the mean body mass index BMI was 23 5 range 20 28 and the median time with VDU work per week was 10 h range 2 80 h The subjects were all experienced computer mouse users and they all used their right hand to operate the mouse Prior to the study subjects were given written and verbal information explaining the experimental procedures None of the subjects used medication for hypertension or any other cardiovascular disease and they were all free of upper extremity musculoskeletal disorders as determined by an interview Experimental procedure An adjustable VDU workstation was set up and the subjects adjusted the table and chair to t their personal preferences A Macintosh computer with a 13 in 33 cm colour display and a standard keyboard was used Before the measurements subjects practised at the experimental workstation to familiarise themselves with the equipment and the task The subjects participated in a control situation Control 1 a stress situation Stress and at the end of the experiment a second control situation Control 2 In the control situations subjects edited eight ve line paragraphs of text two pages with no time constraints imposed In each line at a random location one to four characters were highlighted using coloured text Subjects were instructed to highlight the coloured characters with the computer mouse and then delete the characters by hitting the delete key on the keyboard with the hand operating the computer mouse Approximately


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