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. Author manuscript; available in PMC: 2016 May 24.
Published in final edited form as: Am J Occup Ther. 2009 Jul-Aug;63(4):386–397. doi: 10.5014/ajot.63.4.386

Potentially risky postural behaviors during worksite keyboard use

Nancy A Baker 1, Mark Redfern 2
PMCID: PMC4878151  NIHMSID: NIHMS539470  PMID: 19708467

Abstract

Objective

This study describes the frequency and distribution of potentially risky postural behaviors of keyboard users.

Method

Forty-three subjects’ keyboard postural behaviors were rated with the Keyboard – Personal Computer Style instrument (K-PeCS) while they worked at their own workstations. The frequency and distribution of keyboard postural behaviors, and the associations and differences between the right and left sides were assessed.

Results

Generally, each static body posture had a single criterion that occurred most frequently, (e.g. elbow flexion posture 80 – 120 degrees), while dynamic postures of the wrists and hands were distributed throughout their criteria. Right and left side postural behaviors were significantly associated for shoulder flexion, elbow flexion, hand displacement, wrist extension, forearm rotation, isolated 5th digit, MCP hyperextension, and wrist support use, and significantly different for hand displacement, isolated thumb, number of digits used, and MCP hyperextension.

Conclusion

Potentially problematic keyboard postural behaviors are common among keyboard users. Our results suggest that occupational therapists must systematically assess body, arm, wrist, and hand postures on both the right and left sides to be able to develop the most effective intervention strategies.

Keywords: Work, Health Behaviors, Task Performance and Analysis

Introduction

In their Centennial Vision the American Occupational Therapy Association (AOTA) identified work and industry, particularly work injury prevention, as one of the important emerging areas of practice in occupational therapy (Baum, 2006). One aspect of industrial injury prevention is ergonomics. Ergonomics focuses on evaluating the fit between the work environment and the worker with the goal of adapting the environment to prevent injury and to facilitate work participation at the highest possible level. One work environment which has been identified as having the potential to cause injury is the computer workstation (Wahlstrom, 2005). Occupational therapists are frequently asked to observe keyboard users’ to assess the effect that their computer workstations has on discomfort and injury, and to identify workstation interventions to reduce or prevent musculoskeletal disorders of the upper extremity (MSD-UE). Unfortunately, there is only limited information about the distribution of potentially risky postural behaviors assumed by keyboard users during worksite keyboard use, and no means to accurately document these potentially risky postural behaviors at the worksite.

Although many studies have focused on the association between postures and MSD-UE, there is only limited consensus concerning which postures place a keyboard user most at risk for MSDUE. However, researchers have developed some general information on potential risky postural behaviors in computer users. In general, computer users with a head tilt of less than 20 degrees (Baker, Sussman, & Redfern, 2008; Hunting, Laubli, & Grandjean, 1981; Lueder, 1996; McAtamney & Corlett, 1993; Szeto, Straker, & Raine, 2002) and shoulder flexion less than 20 degrees (Marcus et al., 2002; McAtamney & Corlett, 1993) appear to be less at less risk for MSD-UE then those with greater neck flexion postures. There is some disagreement in the literature concerning a “safe” elbow angle, some studies report that an elbow angle between 80 and 120 degrees is best (Faucett & Rempel, 1994; McAtamney & Corlett, 1993), while a recent longitudinal study by Marcus et al. (2002), reported that elbow angles in excess of 120 degrees were protective. The best wrist extension posture is also an area of debate, as some advocate a “neutral” wrist (Hedge & Powers, 1995; Simoneau, Marklin, & Berman, 2003), while some commonly used postural assessment tools, such as the RULA (McAtamney & Corlett, 1993) and the Strain Index (Moore & Garg, 1995), use 15 degrees as a cut-off point for low risk wrist extension postures. Ulnar wrist deviation of 20 degrees or more has been associated with MSDUE in computer users (Hunting et al., 1981). Optimal finger positions during keyboard use have not been well researched. Harding, Brandt, and Hillberry (1993) in their study on piano playing reported that a curved finger, with a metacarpophalangeal (MCP) flexion angle of between 40 and 65 degrees put the least stress on the MCP joint. They reported that a proximal interphalangeal (PIP) flexion angle of approximately 50 degrees and distal interphalangeal (DIP) flexion angle of approximately 25 degrees of flexion caused the least amount of force on the tendons and joints of the hand. Since piano playing is biomechanically similar to keyboarding, this research suggests that individuals using a keyboard should adopt a similar posture. Other keyboard postural phenomena that have been associated with MSD-UE are the tendency for some keyboard operators to maintain their fifth finger and/or thumb in hyperextension while typing (Pascarelli & Kella, 1993; Rose, 1991). Additional considerations in keyboard work are the use of an elbow, forearm, and/or wrist support during keying. Research on the utility of supporting the arm and/or wrist during keyboarding is equivocal. Studies suggest that while arm/wrist supports can decrease EMG outputs at the shoulder (Aaras, Ro, Fostervold, Thoresen, & Larsen, 1997; Fernstrom, Ericson, & Malker, 1994; Visser, De Korte, Van der Kraan, & Kuijer, 2000), they do not necessarily improve posture (Hedge & Powers, 1995) and may or may not reduce the incidence of MSD-UE (Bergquist, Wolgast, Nilsson, & Voss, 1995; Marcus et al., 2002; Rempel et al., 2006).

Studies have also reported differences between right and left side postural behaviors. In particular, differences appear to occur in wrist and hand postures. For example right and left wrist extension and ulnar deviation have been reported to be different (Simoneau, Marklin, & Monroe, 1999), although these differences have not always been significant (Serina, Tal, & Rempel, 1999). Baker et al. (2007) reported significant differences between the right and left hands for hand displacement, as well as for the thumb postures. Thus, keyboard users may have a greater potential risk for MSD-UE on one side than the other.

Much of the current literature on keyboard use has been done for the engineering community. There have been several studies which have described the mean postures of keyboard users (Baker et al., 2007; Baker & Cidboy, 2006; Marklin, Simoneau, & Monroe, 1999; Rose, 1991; Simoneau et al., 1999; Sommerich, Marras, & Parnianpour, 1996; Zecevic, Miller, & Harburn, 2000). These studies have identified that, on average, keyboard users position themselves in neutral, non-risky postures. However, studies have also suggested that while there is little variability within the postural behaviors of a single keyboard user (Baker et al., 2007; Ortiz, Marcus, Gerr, Jones, & Cohen, 1997), there is a great deal of variability between keyboard users (Psihogios, Sommerich, Mirka, & Moon, 2001; Simoneau et al., 1999; Sommerich et al., 1996). This variability between subjects suggests that some keyboard users may assume potentially risky postures, but the degree to which potentially risky postures are assumed may not be easily identified in studies which use mean postures, rather than the frequency and distribution of postures, as the outcome measure.

While research studies examining keyboard users’ mean postures have provided excellent information on general keyboard kinematics, they may not provide clinically applicable information about the frequency or distribution of a postural behavior during keyboard use. There are other aspects of keyboard kinematics studies which also make them less clinically useful. Keyboard kinematics studies generally use direct methods to obtain data (Li & Buckle, 1999). Direct methods, which measure kinematics by applying a measuring device, such as an electric goniometer or motion analysis device, to keyboard users’ extremities while they are typing, require a great deal of highly technical equipment. This is problematic for occupational therapists in two ways: most occupational therapists do not have access to this type of equipment, making it infeasible for occupational therapists to use these methods to obtain data and therefore directly compare their results to the literature; and studies using direct methods are almost always completed in a laboratory, where the equipment can be easily set up and used. Laboratory set-ups tend to be standardized to the subjects’ anthropometrics, and therefore are “ideal” workstation set-ups, promoting neutral postures. Even if subjects are instructed to set-up the laboratory workstation to match their own workstations, few appear willing or able to manipulate the laboratory office equipment to mimic their worksite set-up. This makes the results of these studies less applicable to “real world” interpretations. The information generated by direct methods, therefore, is often not feasible or useful for occupational therapists attempting to evaluate and intervene with clients.

Observational methods, those which use observation of subjects without the direct application of measuring equipment, provide more familiar and clinically applicable results. There has been only one study (Pascarelli & Kella, 1993) in which observational methods were used to provide a description of the frequency of potentially risky postural behaviors in a group of keyboard users with MSD-UE. While this study provided insights into keyboard use, the observational methods used to collect the data were not from a valid and reliable rating instrument, but more from the general observations made by the researchers. Occupational therapists need to have a systematic method to evaluate the whole body during keyboard use so that interventions can comprehensively address all risk factors. Until recently, there has been no reliable and valid observational method to assess and document keyboarding styles. There has been, therefore, a need for both a method to measure keyboarding style and data about the frequency and distribution of postural behaviors of keyboard users which can easily be translated to practice by occupational therapists.

This study is the first to use a valid and reliable observational method, the Keyboard – Personal Computer Style (K-PeCS) instrument (Baker & Redfern, 2005) to measure postural behaviors hypothesized to be potential risk factors for MSD-UE for keyboard users. The purpose of the study was to describe the frequency and distribution of postural behaviors of keyboard users while they worked at their own workstations. To further examine keyboard users’ postural behaviors, we calculated the associations and differences between the right and left sides during keyboard use. In addition to describing keyboarding postural behaviors, this paper provides readers with information about a reliable and valid observational method to measure keyboarding postural behaviors.

Methods

This descriptive study was approved by the University Institutional Review Board. Informed consent was obtained from all subjects prior to participation in the study.

Participants

Subjects were recruited from University student, faculty, and staff. To participate, subjects had to be between 18 and 65, of either sex, and be computer keyboard users. They were excluded if they had a fracture or traumatic injury which prevented them from using bilateral upper extremities. However, they were not excluded if they experienced musculoskeletal discomfort or had a diagnosed MSD-UE.

Instruments

Subject's keyboarding styles were rated using the K-PeCS, a 19-item criterion-based observational tool that documents the frequency of stereotypical postural behaviors during keyboarding (Baker & Redfern, 2005). The items of the K-PeCS have been divided into three general categories: 1) items of static posture (items 1, 3, 4, 5); 2) items of dynamic posture (items 8, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19); and 3) items of tension and force (items 2, 6, 7, 9) (Table 1). Most items are measured separately for the right and left sides. Items on the K-PeCS generally have 3 types of ratings (See Figures 1-5 for rating criteria). Some items are rated as “yes/no” (i.e. the behavior occurs or does not occur) (items 2, 6, 7, 12, 18, 19). Some items are rated using frequency ratings. The most common frequency ratings are “never” (0% of the time), “occasionally” (1 – 30% of the time), “frequently” (31% to 99% of the time), and “always” (100% of the time)” (items 10, 11, 13, 14, 17). Item 8's frequency rating is slightly modified to “occasionally” (0 – 30% of the time), “often” (31% - 75% of the time), and “most of the time (>75% of the time). Other items are rated as one of several possible ranges (items 1, 3, 4, 5, 9). Two items have unique ratings: item 15 for which the rater counts the number of digits used to activate the keys; and item 16 for which the rater identifies if the right thumb, right index, or some other method is used to activate the space bar.

Table 1.

Items and outcomes being measured by the K-PeCS

# Item Outcome being measured
Items of static posture
1 Torso angle Generally, what is the angle of the keyboard user's torso to the horizontal plane?
3 Neck flexion angle Generally, what is the displacement angle and position of the head?
4 Shoulder flexion angle Generally, what is the flexion angle of the shoulders?
5 Elbow flexion angle Generally, what is the angle of the elbows?
Items of Dynamic Posture
8 Hand displacement Does the keyboard user move his/her hands while typing?
10 Wrist ulnar angle Does the keyboard user exceed 20° of ulnar deviation?
11 Wrist extension angle Does the keyboard user exceed 15° of wrist extension?
12 Forearm rotation Does the keyboard user ever rotate his/her forearm (increase pronation or supination)?
13 Isolated 5th digit Does the keyboard user isolate the 5th digit?
14 Isolated thumb Does the keyboard user isolate the thumb?
15 # of digits to type How many digits does the keyboard user use to strike the keys?
16 Space bar activation What finger does the keyboard user use to strike the space bar?
17 MCP hyperextension Does the keyboard user hyperextend the MCP joints?
18 PIP/DIP curve Are the keyboard user's PIP/DIP joints generally curved (>25°) or generally straight (<25°)?
19 DIP hypermobility Do the DIP joints ever “collapse” when the fingers strike the keys (hypermobility)?
Items of Tension and Force
2 Back rest use Does the keyboard user rest at least 2/3 of the back against the back rest while using the computer?
6 Forearm support use Does the keyboard user support his/her forearms/elbows on an arm rest or table?
7 Wrist support use Does the keyboard user support his/her wrist(s) on the wrist pad or table?
9 Force Generally, what kind of force does the keyboard user use to strike the keys?
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MCP = metacarpophalangeal; PIP = proximal interphalangeal; DIP = distal interphalangeal

Figure 1.

Figure 1

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The distribution of ratings on the K-PeCS for Items of Static Posture (items 1, 3, 4, 5)

Figure 5.

Figure 5

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The distribution of the ratings of the K-PeCS for Items of Tension and Force (2, 6, 7, 9)

Overall, the K-PeCS has been shown to have good inter- and intra-rater reliability (inter-rater Intraclass Correlation Coefficients (ICC) = 0.90, p <.001; intra-rater ICC = 0.92, p < .001 (Baker, Cook, & Redfern, in press). Most individual items on the K-PeCS have from good to excellent reliability, although five items fell below ICC = .75. The K-PeCS has also been found to have content and criterion-based validity (Baker et al., in press; Baker & Redfern, 2005).

Procedures

Forty-three subjects were videotaped in their workplace at their own computer workstation while typing a standard document which was long enough to require at least 10 minutes of continuous typing. Each workstation was unique to the individual participant. There was no equipment that was constant in all workstations, and no attempt was made to set-up the work environment to reduce potentially risky postures, as the purpose of the study was to describe the frequency and distribution of postural behaviors of typical keyboard users while they used their workstations as usual. The workers’ hands were recorded using 3 digital video cameras for approximately 10 minutes, one camera focused on a lateral view of the right hand, one camera focused on a lateral view of the left hand, and the third camera focused on both hands from overhead. Additionally, still camera photographs of the full left and right body were taken to help rate items 1 through 6 (See Table 1). Each subjects’ recordings were processed into a 3-minute clip, 1 minute each of overhead, right and left data. Data from approximately the same timeframe was used for each view so that the clip presented differing aspects of the same minute of time. These clips and the still photographs were rated twice by the same rater experienced in using the K-PeCS. Intra-rater reliability was calculated using ICC's and good to excellent reliability was obtained. In order to improve accuracy, all data between the two rating sessions were assessed for agreement. Where there was disagreement between the ratings for an item, the subject's video recordings were re-assessed and a final determination of the correct rating was completed. In some cases it was impossible to obtain both the right and left still photographs due to space constraints: most workstations allowed us to access at least one side, but only 13 stations allowed us to obtain complete data for both the right a left full body postures. For sides where we did not have enough space to obtain a photograph, we used live K-PeCS ratings obtained while the keyboard user was being videotaped. These live ratings were all completed by one expert rater.

Data analysis

Data were statistically analyzed using SPSS 14.0. Descriptive frequency statistics for the KPeCS were completed to provide information on the distribution and frequency of each item. Where appropriate, the data for the right and left sides were compared using the non-parametric marginal homogeneity test, which calculates a chi-square (X2) critical value, to examine differences in the distribution of the K-PeCS score between the right and left sides and Spearman's rank correlations rho (ρ) to examine the linear relationship between the right and left sides. Bonferroni's correction was not used even though we did multiple tests, as we were not interested in testing the universal hypothesis, but in testing the differences in each test (Perneger, 1998). To help control for a Type I error we set alpha to a more stringent ≤ .01.

Results

Forty-three subjects participated in this study. The sample was primarily female (84%), Caucasian (84%) with a mean age of 45.7 (±8.7) years. Subjects had been using a computer at work for a mean of 14.2 (±6.6) years. Mean computer use was 6.3 (±2.0) hours per day, and ranged from 3 to 12 hours of daily use. Subjects reported they used their keyboard on average 60% of the time and the mouse 40% of the time. More than half reported taking a touch typing course (58%). When asked to rate their overall typing speed, 30% reported themselves as fast typists (>60 words per minute [wpm]), 40% reported themselves as moderate typists (40-60 wpm), 19% reported themselves as slow typists (<40 wpm), and 12% were not sure of their speed.

Most items were well-populated with ratings distributed in all criteria (Figures 1-5). Five items had a criterion where no subject ratings occurred, with 3 of the items having ratings for that item on one side of the body but not the other. The items with no subjects rated as performing a criterion were: torso angle, supine and number of digits used to type, both 1 digit and 2 digits.

Items of static body postures had one criterion that occurred most frequently (Figure 1). Most keyboard users sat in an upright position (67%), with shoulder flexion between 0 and 20 degrees (L = 67%; R = 63%) and elbow flexion between 80 and 120 degrees of flexion (L = 74%; R = 72%). Neck flexion postures were generally either less than 10 degrees (33%) or between 11 and 20 degrees (40%).

Dynamic postures rated using a frequency score were generally distributed throughout the range (Figures 2-4). Items rated as occurring or not occurring clustered around the “no” criterion: forearm rotation (no: L = 95%; R = 84%); distal interphalangeal (DIP) hypermobility (no: L = 86%; R = 95%) (Figures 2 and 3). Most, but not all, keyboard users activated the spacebar with the right thumb (79%). There was a distribution of the number of fingers used, with all subjects using at least 3 fingers on each hand during keyboarding, and most using 4 or 5. Many subjects maintained the 3rd – 5th digits in positions of tension such as MCP hyperextension or 5th digit isolation (Figure 6a). Almost all subjects isolated the 5th digit to some degree (Figure 6a) (never isolated: L = 12%; R = 21%) (Figure 3). There was also variability in finger postures, with about half the subjects hyperextending the right and left 4th MCP joints and the right 5th MCP joints (Figure 6b) at least occasionally, while 72% of subjects hyperextended the left MCP joints at least occasionally (Figure 4). Subjects did not generally maintain digits in a straight posture, although 33% subjects had a straight right 5th digit. Thumb isolation was less common than 5th digit isolation, particularly on the right side (never: L = 56%; R = 81%) (Figure 3). There was some variability across subjects for items of tension and force which rated support use (backrest support, forearm support and wrist support). Subjects about equally did or did not use a backrest (yes: 47%) (Figure 5). While most subjects generally did not use forearm support (70%), they were more likely to use a wrist rest on the left side than on the right (L = 58%; R = 47%). About half of the subjects used moderate force while keying (47%).

Figure 2.

Figure 2

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The distribution of the ratings of the K-PeCS for Items of Dynamic Posture (items 8, 10, 11, 12)

Figure 4.

Figure 4

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The distribution of the ratings of the K-PeCS for Items of Dynamic Posture (items 17, 18)

Figure 3.

Figure 3

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The distribution of ratings of the K-PeCS for Items of Dynamic Posture (items 13, 14, 15, 16, 19)

Figure 6.

Figure 6

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Examples of common postures: 6a - Examples of thumb and 5th digits isolation (items 13 & 14); 6b - Example of hyperextension of the 4th and 5th MCP joints (item 17)

In a secondary analysis we examined the associations and differences between the right and left sides across subjects. For items of static posture, large significant correlations were found between the right and left elbow and right and left shoulder postures (Table 2). Large significant correlations were also found between the right and left sides for wrist support use (Table 2). For items of dynamic posture, significant moderate correlations were found between the right and left sides for hand displacement, wrist extension, forearm rotation, and isolated 5th digit. There were smaller but still significant correlations between the sides for MCP joint hyperextension for all but the 3rd digit. The degree of association increased progressively from the 4th to 5th digits (Table 2). Associations between right and left side for wrist ulnar angle, isolated thumb, number of digits used, 3rd digit MCP hyperextension, 3rd and 4th digits PIP/DIP curve, and DIP hypermobility were all non-significant (Table 2).

Table 2.

Linear correlations and difference between the right and left sided items during keyboard use

Spearman's rho right to left χ2 right vs. left
# Item ρ(rho) p p
1 Torso angle --- --- ---
3 Neck flexion angle --- --- ---
4 Shoulder flexion angle .67 <.001 .32
5 Elbow flexion angle .68 <.001 .71
8 Hand displacement .58 <.001 .01
10 Wrist ulnar angle .27 .08 .60
11 Wrist extension angle .49 .001 .77
12 Forearm rotation .50 .001 .03
13 Isolated 5th digit .43 .004 .10
14 Isolated thumb .02 .88 .002
15 # of digits used to type −.18 .24 .003
16 Space bar activation --- --- ---
17 MCP hyperextension 2nd 0 0 0
3rd .37 .02 .05
4th .43 .004 .004
5th .56 <.001 <.001
18 PIP/DIP curve 2nd 0 0 0
3rd −.02 .88 1.0
4th .31 .04 .32
5th .37 .01 .13
19 DIP Hypermobility .23 .14 .10
2 Back rest use --- --- ---
6 Forearm support use --- --- ---
7 Wrist support use .67 <.001 .03
9 Force --- --- ---
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MCP = metacarpophalangeal; PIP = proximal interphalangeal; DIP = distal interphalangeal

There were significant differences between the right and left side for hand displacement, number of digits, isolated thumb, and MCP joint hyperextension for digits 4-5 (Table 2). The right hand tended to displace more frequently than the left, and more subjects used 5 digits when keying with the right hand. Subjects were more likely to isolate the left thumb than the right and hyperextend the left MCP joints than the right.

In summary, the keyboard users in this study generally assumed a neutral static posture of the neck, body, and arm, but tended to assume a variety of dynamic postures along the spectrum of neutral postures to postures which were potentially risk factors for MSD-UE. About half of these keyboard users used supports (backrest, forearm, and/ or wrist) and more than half used minimal to moderate force to strike the keys. There were significant correlations in postures between the right and left side except for ulnar angle, isolated thumb, number of digits used, 3rd digit MCP hyperextension, 3rd and 4th digits PIP/DIP curve, and DIP hypermobility. Keyboard users were significantly different in their right and left postures for hand displacement, number of digits, isolated thumb, and MCP joint hyperextension for digits 4-5.

Discussion

The distribution of postures identified by this method suggests that for some items most subjects worked in positions that placed them in neutral, non-risky postures. These items distributions were concentrated in one criterion (items 1, 4, 5, 6, 9, 12, 14, 15, 16, 18, 19 in Table 1). The common measures were: seated upright (item 1), shoulder flexion less than 20 degrees (item 4), and elbow postures between 80 and 120 degrees (item 5). Most subjects did not use any forearm support (item 6) They used the keyboard with moderate force (item 9), did not change their forearm rotation angle (item 12), did not isolate their thumb (item 14), used 4 digits to activate the keys with the left hand, and 5 digits with the right (item 15) with this difference probably due to the fact that they activated the space bar with their right thumb (item 16). They usually typed with curved PIP/DIP joints (item 18) and rarely demonstrated hypermobility of the 5th digit (item 19). The use of a backrest (item 2) was one item that did not follow this pattern of data concentrating under one criterion for an item. The use of a backrest was essentially equally distributed between those who did and did not use one. Other items (items 7, 8, 10, 11, 15, 13, 14, 17 in Table 1) demonstrated relatively equal distributions of subjects engaging in that behavior. Examples are hand displacement (item 8) or ulnar deviation past 20 degrees (item 10). These results suggest that these items, many of which have been identified as potential risks factors for MSD-UE, are well distributed throughout the computer using population during worksite keyboard use.

Many postures and behaviors were significantly positively associated between the right and left side, a phenomenon described by other studies (Baker et al., 2007; Marklin et al., 1999; Simoneau et al., 1999). The only items for which significant associations were not found were ulnar angle, isolated thumb, number of fingers used to type, 3rd MCP hyperextension, 3rd and 4th digit PIP/DIP curve and DIP hypermobility. The low association between the right and left side for isolated thumb was not unexpected (See Figure 6a for an example of thumb isolation). Seventy-nine percent of subjects use their right thumb to activate the space bar, while the left thumb is generally not active at all. Thus, the left and right thumbs are not engaged in symmetrical typing activities. The low association between the number of digits used between the right and left sides may also be related to space bar activation. Most individuals use 4 digits on the left hand (81%) but most use 4 or 5 digits on the right hand (35% and 58% respectively). The association between the right and left side was not significant for ulnar deviation. This non-significant association is supported by other literature on keyboard use which has reported that the right and left wrists are often asymmetrical for ulnar deviation (Simoneau et al., 1999). The lack of symmetry between the right and left for DIP hypermobility is probably representative of the rarity of this phenomenon. Only 5% of the sample demonstrated DIP hypermobility on the right and only 14% of the sample demonstrated DIP hypermobility on the left.

Not only were significant moderate positive associations found between the right and left sides for many items, significant differences between the right and left sides were also found for many of the same items. The reason an item could be both significantly associated and significantly different is due to the distribution of criteria for the right and left side of each item. To clarify this concept, we present examples of the right and left distribution of criteria for hand displacement, and 4th and 5th MCP hyperextension in Table 3. In these distributions a majority of the pairs fall along the diagonal of each table (the concordant squares which indicate a match between the left and right sides). However, those pairs that fall off the diagonal (the discordant square which indicate no match between the left and right sides) have a different distribution on the right and left. For hand displacement, for example, the discordant pairs tend to cluster in the “occasional” column for the left side, while the discordant pairs tend to cluster in the “most of the time” row on the right. That the majority of the data is in the concordant squares makes the data significantly linearly associated, while the different distribution of the right and left sides in the discordant squares makes the data significantly different.

Table 3.

Items on the K-PeCS which were both significantly linearly associated (Spearman's rho) and significantly different (Chi Square) (both p ≤.01)

Left hand displacement
Occ Often Most Total
Right hand displacement Occ 13 2 0 15
Often 5 4 2 11
Most 4 5 8 17
Total 22 11 10 43
Left 4th MCP hyperextension
Nev Occ Freq Alw Total
Right 4th MCP hyperextension Never 10 5 6 0 21
Occ 4 4 5 2 15
Freq 1 0 2 2 5
Alway 0 0 1 1 2
Total 15 9 14 5 43
Left 5th MCP hyperextension
Nev Occ Freq Alw Total
Right 5th MCP hyperextension Never 10 5 6 0 21
Occ 2 3 6 2 13
Freq 0 1 6 0 7
Alway 0 0 0 2 2
Total 12 9 18 4 43
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MCP = metacarpophalangeal

It is interesting to note that the significant differences in body postures and actions found in this study were not for the items related to the body or even motions of the wrists, as indicated by Simoneau and Marklin (1999). Instead, most differences occurred in the actions of the fingers and hands. For all subjects, the keyboard was placed on a horizontal surface. To access the keyboard with the hands, the body and arms would have to assume a symmetrical posture. The difference noted between the right and left sides for hand use are probably related to the job tasks required for each hand during typing (Dennerlein & Johnson, 2006). The right hand is not only used to activate the letter keys, but is the hand generally used to activate the space bar (item 16), and access the “enter”, “backspace”, and “delete” keys. It therefore tends to have a greater amount of hand displacement (item 8). Because the right side does activate the space bar, more people use all 5 fingers on the right hand when using the keyboard and fewer people isolate their right thumb, as they are positioning it over the space bar in preparation to strike it.

The differences in the right and left hand for MCP hyperextension is less easy to explain, as it is not clear why individuals hyperextend their MCP joints while using a keyboard (Figure 6b). Some degree of MCP hyperextension appears to be a common action during keyboard use (Figure 4). Rose (1991) suggested that individuals using a flat keyboard must extend their 3rd, 4th and 5th digits up to 75% of their range in order to position these digits on the same plane as the thumb and therefore in line with the keyboard. This need to be on the same plane for keyboarding tasks, however, does not explain why the two hands are not symmetrical for MCP hyperextension. Further study of this postural behavior is important to understand why people hyperextend their MCP joints and why they may hyperextend more frequently on the left.

The K-PeCS instrument appears to be a sensitive tool with which to document computer keyboard style. On average, an assessment could be completed in under 10-minutes, and was easy to use both for “live” or videotaped images. The data generated by the K-PeCS has been shown to be reliable and valid (Baker et al., in press), are easily interpreted by occupational therapists, and provide clinically relevant results that could help occupational therapists to decide on intervention strategies for clients at risk.

Limitations: As this study is a descriptive study of a relatively small sample of keyboard users, it may not generalize well to other populations outside of this University environment. This study cannot suggest that any of these postural behaviors cause, or even aggravate, MSD-UE; only that in this sample, certain postural behaviors were more common than others, and that the epidemiological literature has identified these postural behaviors as potential risk factors for MSD-UE. As this study only examined a single time point, we cannot attempt to determine whether the postural behaviors changed over time due to factors such as fatigue. In addition, we did not attempt to analyze the data to identify underlying causes, such as the environmental set-up or the subject's anthropometrics, of any postural behavior. We did not have photographs of both the right and left sides of many participants in order to assess static body postures of both the right and left shoulder and arms. Static posture ratings for work sites where we could not take a still photograph were completed live, and were not checked for their reliability. Although the K-PeCS has been found to be a reliable tool, certain items have lower intra-rater reliability. Force, isolated thumb, wrist ulnar angle, and PIP/DIP angles have demonstrated only moderate, rather than good to excellent intra-rater reliability. We have tried to control for this lower reliability by double rating items then coming to a consensus for any items where ratings did not match.

Conclusions and Implications for Practice

The participants in this study commonly demonstrated potentially risky keyboard postural behaviors, particularly in the hands and fingers. Based on these results, it is recommended that occupational therapists systematically assess body, arm, wrist, and hand postures on both the left and right sides to develop the most effective intervention for each client. Other postural behaviors, such as extremes of posture for the neck and torso, are uncommon, suggesting that occupational therapists must be vigilant to identify if they occur. While most research has focused on body and wrist postures, this research indicates that potentially risky finger and hand postural behaviors occur frequently. Occupational therapists evaluating keyboard users should examine not only the postures of the body, but also wrist and finger postures to determine if, and how often, a client assumes a potentially risky postural behavior.

We found that keyboard users tended to be symmetrical in their body and arm postures, and less symmetrical in how they used their hands and fingers to operate the keyboard. Occupational therapists need to assess both the left and right sides of the body while evaluating a client using a keyboard to determine variations in performance by side. Performances that differ on the right and left side may require different interventions.

The AOTA Centennial Vision explicitly identifies the need for “science-driven and evidence-based profession“ (Baum, 2006). Until now occupational therapists who have engaged in ergonomic assessment and interventions for computer keyboard workstations have had no scientific method to assess keyboard use, and have had no information about the frequency and distribution of potentially risky postural behaviors in keyboard users. This study provides occupational therapists with information about a clinically useful tool which can be used to document the types of postural behaviors which occur prior to implementing workstation redesign. Through accurate identification of client specific problem areas, the occupational therapist can more efficiently and effectively implement interventions which will reduce potential risk factors. In addition occupational therapists can re-assess the success of their interventions by re-evaluating keyboard users’ postural behaviors after the intervention has been completed. The use of a standardized observational method to ascertain and document keyboard style has the potential to improve the overall practice of office worksite intervention. This study also provides occupational therapists with baseline information of the prevalence of certain types of postural behaviors during computer use. This information will help to make occupational therapists more sensitive to the variety of computer related postures and more vigilant in identifying them for intervention.

Acknowledgements

The authors would like to acknowledge the support of Grant #K01 OH007826 from the National Institute for Occupational Safety and Health, and the University of Pittsburgh Central Research Development Fund. They would also like to thank Dr Jack Dennerlein, Dr Rakie Cham, Dr Caroline Sommerich, Erin Hale, Norman Gustafson, and Emily Eckel for their assistance in developing the K-PeCS.

Contributor Information

Nancy A. Baker, Department of Occupational Therapy, University of Pittsburgh, Pittsburgh, PA.

Mark Redfern, Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA.

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