pressure ulcers are one of the most common secondary complications of spinal cord injury ( sci ) . increasing prevalence rates amongst individuals with sci are attributed to repeatedly spending prolonged periods of time in the seated position coupled with limited mobility and sensation . when sitting approximately 50% of body weight is concentrated over just 8% of body surface area , causing high interface pressure , consequently ischial tuberosity and sacral regions tend to suffer pressure ulceration the most [ 4 , 5 ] . these wounds disrupt life , often causing episodes of both physical and financial disability [ 6 , 7 ] . pressure ulcer care has a significant impact on health care expenses , costing an annual  1.42.1 billion to the national health service . prevention on the other hand has been reported to cost approximately one - tenth of these treatment costs . one of the most effective preventative methods in terms of cost and pressure relief is regular repositioning . within rehabilitation , individuals with sci are taught and encouraged to perform regular repositioning movements in order to redistribute the build - up of pressure around the ischial tuberosity and sacral regions . although recommended as often as every 1530 minutes , research has shown that concordance with regular repositioning is poor [ 12 , 13 ] . wheelchair users are reported to spend as much as 18 hours per day in their wheelchair , with many ( 54.7% ) repositioning less often than once an hour [ 12 , 13 ] . one potential alternative to improving concordance with these traditional repositioning methods would be to integrate such movements within everyday functional activities to make them a more natural part of everyday life . the annual communications market report   found that in the uk 8 out of 10 homes have internet access via a desktop or laptop computer . in 2011 , internet users were reported to spend an average of 23.5 hours per month online . furthermore , research has indicated that common occupations obtained by individuals with sci include office , finance , clerical , administrative , technical , and professional jobs [ 1517 ] , all of which require some form of computer use . physically , the demands of computer use are rated as one of the lowest amongst office tasks , requiring little body movement and exertion . thus it could be said that computer use , requiring a fairly static sitting posture , is a predominantly sedentary activity that consequently may increase the risk of pressure damage . therefore , as computer use is a popular activity amongst individuals with sci , used for both leisure and employment , and as computer use is thought to habitually restrict seated movement , the aims of this clinically based cohort study were twofold . the purpose of strand a was to investigate the current pressure relieving behaviours of sci individuals during everyday computer use , while strand b aimed to investigate the application of an ergonomically adapted computer - based activity to reduce interface pressure . recruitment and data collection took place in the regional spinal cord injury unit , musgrave park hospital , belfast health and social care trust . ethical approval was obtained from the office of research ethics committees , northern ireland , and research governance was provided by the research and development office of the belfast health and social care trust . a convenience sample of 14 subjects diagnosed with spinal cord injury ( 12 male , 2 female ; age range 2362 years ) was recruited to participate in this study ( table 1 ) . inclusion criteria required participants to be between 18 and 65 years of age , have a diagnosis of paraplegia or tetraplegia , and be current inpatients or outpatients of the regional spinal cord injury unit , musgrave park hospital , belfast . participants had to be able to safely perform a forward lean and be computer literate to a basic level to be included . informed written consent was gained by the researcher on commencement of the study , and participants were informed that they could withdraw from the study at any time . the xsensor x3 pressure mapping system , px100:36.36.02 ( xsensor technology corporation , calgary ) , consists of a thin , flexible pressure sensing mat and a hand held computer which graphically displays the distribution of interface pressure . the xsensor pressure mapping mat was set at a recording resolution of 1  hz and calibrated up to a maximum of 200  mmhg prior to each assessment . the activpal 3 accelerometer ( paltechnologies , glasgow ) , a triaxial activity monitor which uses piezoelectric accelerometers to measure movement in three perpendicular axes , was used to measure direction of movement . this device was chosen because of its compact size ( 5  3.5  0.7  cms ) and ability to respond accurately to gravitational and segmental movement acceleration   with a range of 2  g and a sensitivity of 5  hz when used as an inclinometer . participants used either a standard desktop computer or an ipad , depending on preference and fine motor skills .   throughout both strands a and b of the study , participants sat in their own wheelchair on their prescribed pressure relieving cushion and wore loose fitting clothing , for example , tracksuit bottoms . the xsensor pressure sensing mat was placed between the participant and the wheelchair cushion surface . an activpal3 accelerometer was attached to the participant 's sternum   using the hydrogel palstickies . the keyboard of the desktop computer was positioned with the home row ( row beginning a , s , d , f ) 19  cms from the front edge of the desk   in order to standardise the position for each participant . similarly , the ipad was also positioned 19  cm from the front edge of the desk . strand a. participants performed a self - selected computer - based activity for a one hour period . the frequency and type of repositioning movements performed throughout the one hour sitting period were determined by two methods : ( 1 ) through interface pressure mapping using the xsensor pressure mapping system and by ( 2 ) the researchers ' observational analysis of the type , timing , and frequency of participants ' movements . movements were categorised as either forward lean ; left lean ; right lean ; push - up ; other / task related movement such as typing or reading . each movement was timed from the second posture change took place until a different posture was adopted . interface pressure measurements for each movement were averaged and compared to periods of  normal upright sitting . strand b. participants positioned their wheelchairs at the desk as in strand a ; however , this time participants performed a computer - based activity of their choice for a 30 minute period , and the computer keyboard / ipad was positioned on a moveable tray which alternated between two positions : ( 1 ) their normal upright sitting position and ( 2 ) a forward leaning configuration normalised to each participants arm length ( 150%  arm length measured from acromion process to 2nd metacarpophalangeal joint ) . participants were instructed to sit in their  normal sitting position  and perform a computer activity of their own choice for a 10-minute period . the participant was then instructed to reach to and hold this 150% position , whilst continuing their computer activity for a further 5-minute period . the computer keyboard / ipad was then moved back to the original position , and both the 10-minute  normal sitting  and the 5-minute forward lean trials were repeated . measurement of interface pressure and trunk angle took place throughout this 30-minute period ( figure 1 ) . the primary outcomes of interest in this study were interface pressure and trunk angle . during both strand a and strand b , interface pressure measurements were investigated using the parameters of dispersion index , peak pressure index , and total contact area , which are defined as follows.dispersion index is the sum of the pressure distributed over the it regions divided by the sum of pressure readings over the entire mat , expressed as a percentage . peak pressure index is the highest pressure within a 9 - 10  cm area in the ischial region.total contact area is the area of the sensors with pressures reading 10  mmhg or above . dispersion index is the sum of the pressure distributed over the it regions divided by the sum of pressure readings over the entire mat , expressed as a percentage . peak pressure index is the highest pressure within a 9 - 10  cm area in the ischial region . total contact area is the area of the sensors with pressures reading 10  mmhg or above . the change in position of the participants ' trunk during each movement was measured using an activpal accelerometer - based sensor during both strands of the study . participant views of performing repositioning movements ; current computer usage ; and ease of performing the adapted activity were obtained using a short questionnaire at the end of strand b. all data were analysed using spss software version 17 . data recorded by the activpal 3 accelerometer was converted into degree and direction of postural movement using an  activpal2posture  algorithm . activpal3 reports 2  g accelerations in units between 1256 . orienting the activpal using the human figure on the unit , the x - axis points downward , y - axis points left , and the z - axis projects forward out of the body plane . using a custom script written in matlab , values from all three axes were converted into g units , and pitch angle was calculated using the equation : pitchangle = arctan(-zg , xg2+yg2)180/ , where xg , yg , and zg represent accelerations in the respective axes . ) strand a. pressure distribution patterns were visually examined to determine the frequency and type of movements . observational analysis confirmed the type and duration of movements categorised as follows : forward leans ; left lean ; right lean ; push - up ; other or task related movements such as typing and reading . interface pressure data were categorised into the following groups , dependent on the degree of unloading around the ischial tuberosity region between normal sitting and each movement using the pressure mapping graphical user interface ( gui ) : little or no change ( 025% ) , fair ( 2650% ) , moderate ( 5175% ) , and large or complete ( 76100% ) . strand b. a shapiro - wilk 's test revealed that raw data for the variables angle of trunk tilt , di , and ca during periods of normal sitting and periods of forward reach were normally distributed ; however , data for the ppi ( right and left ischial tuberosity ) were not . therefore , repeated measures anova was used to further investigate the normally distributed data , and skewed data were interpreted using the friedman test and post hoc analysis using individual wilcoxon signed rank tests . the relationship between trunk angle and interface pressure during repositioning movements in both strands all 14 participants completed strand a , 11 completed strand b , and 13 completed the self - report questionnaire . strand a. the frequency and type of movements performed by participants during the one hour period varied considerably ( table 2 ) . one participant executed 28 movements , and three participants performed no movements ( range 028 , median 5 movements ) during the 1 hour period . these included slight body movements to read the computer screen , talk to the researcher , type , and perform other automatic body functions / movements such as coughing and leg spasms . omitting the movements categorised as other or task related movements , participants performed a total of 49 movements ( range per participant 012 movements , median 3 movements ) . however , 42.86% of participants did perform at least 4 pressure relieving movements during the 1 hour period . on average , the first nontask related movement was performed after 26 minutes and 37 seconds , and the majority of movements ( 71.4% ) were held for less than 20 seconds , which is highly unlikely to be beneficial in terms of tissue reperfusion . no movement performed over the 1 hour period was categorised as relieving 75100% of interface pressures around the vulnerable ischial area , despite five of the participants performing  push - up  pressure reliefs during this time . the majority of all movements performed ( 84.4% ) were categorised as yielding less than 25% reduction in interface pressures when compared to normal sitting . thus , the effectiveness of the majority of weight shifts performed in terms of pressure relief was low ( figure 2 ) . a simple regression model , used to assess the ability of angle of trunk tilt to predict change in interface pressure using the parameters di , ppi , and ca , showed that a 1% increase in trunk angle was associated with a minimal change in the parameters , indicating a weak relationship .  
 strand b. a one way repeated measures anova revealed that reaching forward by 150% of arm length during a computer activity significantly reduced di ( p < 0.05 ) and angle of trunk tilt ( p < 0.05 ) compared to normal sitting . however , compared to normal a friedman test showed that reaching forward by 150% of arm length significantly reduced ppi for both the right and left ischial tuberosity regions compared to normal sitting ( p < 0.001 ) ( mean ppi for the right ischial tuberosity decreased from 86.14  mmhg to 41.61  mmhg , and mean ppi for the left ischial tuberosity decreased from 81.55  mmhg to 38.89  mmhg ) . this represents a reduction in interface pressure of approximately 52% as a result of the 150% forward lean . post hoc testing using individual wilcoxon signed rank tests confirmed these results ( p < 0.05 ) . however , despite the angle of trunk tilt changing by 26.6 on average between normal sitting and reaching forward by 150% , a simple regression model showed a weak correlation between di , ca , ppi , and angle of trunk tilt . a 1% increase in trunk angle was associated with a negligible change in di , ca , and ppi , indicating a weak relationship . ten participants ( 77% ) reported that they had never experienced a pressure ulcer , whilst three participants ( 23% ) had a history of pressure ulceration . of those participants who had experienced a pressure ulcer , the anatomical locations included : calves and heel , buttocks , and hip . the majority of participants ( n = 12 ) reported that they used a combination of traditional repositioning methods . the frequency of traditional repositioning movements reported varied considerably among participants , ranging from zero to approximately 60 daily , with the most popular method being a forward lean . seven participants ( 54% ) found reaching forward by 150% during the computer activity to have been an achievable task to perform , rating the task as very easy ( n = 1 ) , easy ( n = 4 ) , or slightly difficult ( n = 2 ) . in contrast , three of the participants ( 23% ) found this to be  difficult ,  with one participant reporting that the reach was  too far  and  not comfortable . three of the fourteen participants were unable to complete strand b , as their trunk stability would not sustain the forward reaching activity . the majority of participants ( n = 11 ; 85% ) concluded that it would be beneficial to incorporate pressure reliefs within an activity , such as computer use . likewise , the majority of participants ( n = 10 ; 77% ) also considered that incorporating pressure reliefs within an activity would make them easier to perform when compared to traditional pressure reliefs . the first aim of this study was to investigate the current pressure relieving behaviours of sci individuals during everyday computer use . during a 1-hour computer activity , the number of seated movements varied considerably across participants . however , during this time the most frequently adopted position was a normal sitting position . these results are agreeable with able bodied computer users , reported to favour the reclined sedentary normal sitting  posture when working intensively at the computer [ 25 , 26 ] . despite spending the majority of the working day in a  normal sitting posture ,  able bodied office workers have been found to change seated position approximately once per minute during a thirty - minute computer activity . though mainly task related movements , this is in stark contrast to the current study which found that sci subjects moved on average every 286.6 seconds ( approximately every 5 minutes ) , and three participants performed no movements at all within the one hour period . close examination of the effectiveness of movements performed within strand a of the current study , in terms of percentage unloading of the ischial tuberosities , showed that the majority of movements performed were ineffective in terms of pressure relief . only occasionally ( 4.9% of all movements performed ) did the movements generate  moderate  unloading of 5175% reduction in interface pressures . hence , although participants would have considered that seated movements were reducing interface pressures , analysis from pressure mapping revealed that these movements were ineffective for pressure relief . conversely , it could be argued that as interface pressure measurements were averaged over the duration of a movement from the initial posture change until a different posture was achieved , and brief episodes of complete unloading lasting 1 - 2 seconds may have been masked . however , it has been reported that tissue reperfusion rates for sci population can take up to 300 seconds ( 5 minutes ) ; therefore , it is unlikely that any minimal durations of complete unloading during a movement would have had any beneficial effect on tissue health in terms of reperfusion . as the majority of movements performed ( 84.8% ) produced minimal change in interface pressures , it can be concluded that the participants did not achieve the recommended four pressure relieving movements per hour , thus putting themselves at increased risk of tissue damage . these findings are comparable with previous research which found that , on average , most wheelchair users only reposition every 1 - 2 hours [ 12 , 13 , 28 ] . despite the varying frequency of movements performed during strand a , the effectiveness of the movements performed remained of low value in terms of pressure relief . furthermore , results from the questionnaire revealed that participants believed they performed many pressure relieving movements throughout their average day . considering the low pressure relieving value of the movements performed under observation , it would seem reasonable to question the worth of these movements currently being performed in  real life  as a preventative strategy for ulceration . the second aim of this study was to investigate the application of an ergonomically adapted computer - based activity to reduce interface pressure . strand b of this study found that incorporating a 150% forward reach into a computer activity significantly decreased interface pressure , by approximately 52% , at the ischial region . hence , reaching forward by 150% of arm length would be beneficial for reducing interface pressures for those at risk of tissue damage . results are compatible with those of previous studies , which showed that pressure relief occurred as a result of leaning forward [ 29 , 30 ] and during reaching activities [ 3133 ] . previous research reported that muscle and soft tissue deformations at the ischial tuberosity region decreased during a 40 forward lean ( 74% , 64% , resp . ) compared to a 20 forward lean , which slightly increased tissue deformations ( 79% , 67% , resp . ) for able bodied subjects . likewise , leaning forward by 45 produced the largest decreases in maximum pressure for children with myelomeningocele and able bodied comparisons . conversely , this study found that for a population of sci participants , a forward reach of 150% arm length , which produced an average change in trunk angle of 24 ( range 1535 ) was enough to significantly reduced interface pressures . it should be noted , however , that three of the fourteen participants could not complete strand b of the study due to poor trunk stability . furthermore , researchers observed that the forward reaching movement patterns performed by the sci participants differed considerably from those of able bodied or other disabled people . shoulder protraction was greatly increased in an effort to limit the amount of pelvic movement required , to help overcome trunk stability issues . despite this , responses from the majority who completed the questionnaire welcomed the idea of integrating weight shifts within a daily activity and believed that this would make pressure relieving movements easier to perform . however , although evidencing positive results for a 150% reach reducing interface pressures , this reduction was found to weakly correlate with a change in trunk angle . therefore angle of trunk tilt is not a reliable indicator of interface pressure unloading and should not be used as an assessment component within clinical practice . repositioning , whether performed independently by clients or with assistance from healthcare professionals or carers , is an important part of an effective pressure ulcer prevention strategy , with the aim of redistributing high interface pressure from the bony ischial tuberosity region to other less vulnerable areas . healthcare professionals advocate leaning forward as a form of pressure relief ; however , no specifications for the magnitude of forward lean required to redistribute pressure at the seating interface are currently recommended in guidelines . repositioning is a powerful and practical measure that is within the domain and control of all healthcare professionals , including nurses and occupational therapists who should encourage clients at risk of pressure ulceration to perform pressure relieving movements frequently . in addition , the incorporation of pressure relieving movements into daily activities should be explored in an effort to improve client concordance with national pressure relieving recommendations . a limitation of this study was the small sample size ( n = 14 ) , which may affect generalisability of the results and may have affected the relationship predicted by a simple regression model between the angle of trunk tilt and interface pressures . it could also be argued that  normal sitting behaviour  was recorded over a relatively short duration , thus the results for movement frequency during the 1 hour period may be over inflated . recording over a longer period of time may present different results of sitting behaviours within this population . additionally , the visual demands of the computer task during strand a may have played a role in the frequency of movements performed . furthermore , as interface pressure measurements were averaged over the duration of a movement from the initial posture change until a different posture was adopted , brief episodes of complete unloading lasting 1 - 2 seconds may have been masked . however , it is likely that such a minimal duration of complete unloading would have any beneficial effect on tissue health in terms of reperfusion . during strand b , the varying methods of reaching , including shoulder protraction and rotation , may have confounded results . it could also be argued that the presence of the researchers throughout the study may have skewed results ; however , the exact nature of the study was not disclosed to participants in an effort to minimise a hawthorne effect from occurring . this study investigated the current pressure relieving behaviours of sci individuals during everyday computer use , and explored the application of an ergonomically adapted computer - based activity to reduce interface pressure .   during a 1-hour computer activity , no participants adhered to national recommendations of performing pressure relieving movements as frequently or persistently as every 15 minutes . it is of note that the majority of movements performed were held for less than 20 seconds , which is highly unlikely to be beneficial in terms of tissue reperfusion . indeed , the effectiveness of these seated movements in practice for reducing interface pressures was found to be low , therefore questioning the pressure relieving value of currently recommended movements as a preventative strategy for ulceration . thus , further work is needed to investigate other methods of improving performance and concordance with repositioning methods among at risk populations . this study has shown that activity that incorporates a forward reach of 150% was capable of significantly reducing interface pressures in the ischial region . redistributing high interface pressure away from the bony ischial tuberosity region is important for reducing the risk of developing pressure ulcers during sitting . healthcare professionals , including nurses and occupational therapists , should encourage clients at risk of pressure ulceration to perform pressure relieving movements frequently . incorporation of pressure relieving movements , such as leaning / reaching forward , into everyday daily activities should be explored in an effort to improve client concordance with national pressure relieving recommendations .
background . 
 people with spinal cord injury ( sci ) are at increased risk of pressure ulcers due to prolonged periods of sitting . 
 concordance with pressure relieving movements is poor amongst this population , and one potential alternative to improve this would be to integrate pressure relieving movements into everyday functional activities . objectives . to investigate both the current pressure relieving behaviours of sci individuals during computer use and the application of an ergonomically adapted computer - based activity to reduce interface pressure . 
 design . 
 observational and repeated measures design . setting . regional spinal cord injury unit . participants . 
 fourteen subjects diagnosed with sci ( 12 male , 2 female ) . intervention.comparing normal sitting to seated movements and 
 induced forward reaching positions . 
 main outcome measures . 
 interface pressure measurements : dispersion index ( di ) , peak pressure index ( ppi ) , and total contact area ( ca ) . the angle of trunk tilt was also measured . 
 results . 
 the majority of movements yielded less than 25% reduction in interface pressure compared to normal sitting . reaching forward by 150% of arm length during an adapted computer activity significantly reduced di ( p < 0.05 ) , angle of trunk tilt ( p<0.05 ) , and ppi for both ischial tuberosity regions ( p < 0.001 ) compared to normal sitting . 
 conclusion . 
 reaching forward significantly redistributed pressure at the seating interface , as evidenced by the change in interface pressures compared to upright sitting .