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Body Position Affects Manual Dexterity

Buffington, Charles W. MD*; MacMurdo, Stanley D. MD*; Ryan, Christopher M. PhD

doi: 10.1213/01.ane.0000217124.94291.98
General Articles: Research Report

To evaluate the relationship between posture and psychomotor efficiency, 20 anesthesia providers performed a test requiring manual dexterity and eye-hand coordination while seated, kneeling, and standing bent forward at the waist. Performance on the Grooved Pegboard Test improved 6%–10% (P < 0.005) when subjects were seated compared to kneeling and standing bent at the waist, positions that the subjects rated as more painful and less comfortable than sitting. Sitting improved manual dexterity more in subjects with poor scores than it did in subjects with good performance. This study demonstrates improved manual dexterity in subjects seated in a comfortable position.

IMPLICATIONS: Manual dexterity is improved when subjects are seated in a comfortable position compared to kneeling or standing bent forward at the waist.

Departments of *Anesthesiology and †Psychiatry, University of Pittsburgh, Pittsburgh, Pennsylvania

Accepted for publication February 6, 2006.

Address correspondence and reprint requests to Charles W. Buffington, MD, N463 MUH, 200 Lothrop St., Pittsburgh, PA 15213. Address e-mail to

Anesthesia providers engage daily in tasks that require good eye-hand coordination, manual speed, and precision. Work constraints often demand that delicate tasks be done with the body in awkward positions. In this study, we explored the effect of body position on manual dexterity. One previous study has dealt with this issue (1) and found a small but significant decrease in performance when subjects were standing bent forward at the waist compared to standing with back straight or sitting. The subjects in this previous study were college-age students and mostly women, so the results may or may not apply to anesthesia practitioners because age and gender both affect performance (2). We were also interested in studying the effect of kneeling on manual dexterity because this position is often used when anesthesia practitioners start IV catheters.

There are several ways to measure manual dexterity. We selected the Grooved Pegboard Test (GPT), which has been used in employment settings to make vocational decisions about individuals’ ability to perform highly skilled tasks that require rapid eye-hand coordination and has also been used by neuropsychologists to evaluate patients suspected of experiencing psychomotor slowing secondary to brain dysfunction (3,4). A number of factors influence performance on the GPT, such as the subject’s age and gender (2). Performance with the preferred (dominant) hand is approximately 10% better than the nonpreferred hand (5). The effect of these factors was minimized in the current study by using a repeated-measures experimental design in which subjects used only their preferred hand and performed the GPT in three postures.

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The protocol was reviewed and approved by the IRB at the University of Pittsburgh, Pennsylvania. The study was open to all anesthesia practitioners from the Department of Anesthesiology, including residents and student Nurse Anesthetists. Twenty volunteers were recruited via a flyer broadcast as an e-mail message and were compensated for participating.

After informed consent was obtained, each subject completed a demographic questionnaire that included questions about handedness, previous brain injury, medications, and chronic diseases that might influence the interpretation of their GPT results. The questionnaire is reproduced in Table 1 along with the responses.

Table 1

Table 1

To determine whether any subject had clinically significant problems with visuoconstructional abilities, we administered the Rey Complex Figure Test (6). This well-known clinical task presents the subject with a complex geometric design and requires them to copy it, taking as much time as required. A licensed neuropsychologist (CMR), who was blinded to all other information and results, scored the Rey figures. Drawings were interpreted as “normal,” “borderline,” or “clearly abnormal.”

The GPT (model 32025; Lafayette Instruments, Lafayette, IN) is a well-established test of manual dexterity and psychomotor efficiency that has been used for more than three decades as part of standard neuropsychological evaluations (3,4). It consists of a metal board with a 5 × 5 matrix of slotted keyholes in which the slot is angled in different directions. Metal pegs with ridges along the side fit into the holes only if the ridge and slot are lined up properly. The subject picks up one peg at a time from a shallow storage dish located in the board above the matrix of holes and places it into a hole in a prescribed sequence. The score is the time in seconds required to insert all the pegs. We counted the number of pegs dropped during insertion and also determined the time required to remove the pegs one-by-one and return them to the storage dish. This latter measure provides an estimate of simple motor speed and has been recommended as an important new aspect of the GPT (7). Time to remove pegs shows the same effect of handedness and sex as peg insertion times (7).

The GPT is considered to be a measure of psychomotor efficiency, fine motor control, and eye-hand coordination because it requires the integration of visual information (viewing the slots in the board), kinesthetic information (fingertip orientation of the peg), fine motor dexterity (shifting the orientation of the peg to match the orientation of the slot in the board), and accuracy in placing the peg firmly into the keyhole. Insertion of pegs normally takes approximately 60 s in young subjects. The coefficient of variation is 15%. Insertion time increases approximately 2 s/decade in healthy subjects. Values are prolonged in subjects with diseases such as multiple sclerosis (mild, 88 ± 30 s; severe, 180 ± 100 s) or diffuse brain damage (125 ± 40 s) (3).

By way of introduction, each subject was shown the pegboard, instructed in its use, and allowed to perform the GPT once for practice. A single practice session results in improved speed on subsequent tests, but little further improvement with repetition is noted (5). All GPT tests were performed with the dominant hand. The nondominant hand was held loosely against the abdomen throughout a 120-s warm-up period and the test.

Three different positions were evaluated: seated, kneeling, and standing bent forward at the waist. Subjects were put into the 3 positions by the investigator and told to stay still for 120 s before doing the GPT. For the seated position, they sat in an erect posture in a sturdy metal chair that had a padded seat and back. The chair was placed close enough to the table that the subject could reach the pegboard easily. The table height was adjusted to have the forearms of the subject parallel with the floor. For the kneeling position, subjects knelt on a carpeted floor on either one knee or two. The pegboard was positioned in front of them at a height that allowed their forearms to be parallel to the floor when their backs were straight. For the standing position, subjects were asked to bend forward from the waist so that their backs were 45–70 degrees from erect. They were allowed to bend their knees if they wished. The work surface was low, resulting in a situation in which the forearms usually sloped down to the surface.

The first position was chosen at random by flipping a coin twice. The subject assumed the position for 120 s and remained in the position during the entire GPT (both inserting and removing pegs). A stopwatch was started on the command “Go!” and stopped when the last peg clicked in the hole. Similar points were used for timing peg removal.

After the test, the subjects were moved to a nearby table and seated in a comfortable chair. They completed a form asking them to rate the previous position on a 5-point scale (1 = strongly disagree, 2 = disagree, 3 = neutral, 4 = agree, and 5 = strongly agree) for the following statements: “That was easy;” “That was painful;” and “I was comfortable in that position.” They were allowed to rest in the chair until they relaxed and looked comfortable. The second posture was chosen by coin flip, and the process was repeated. The final posture was assigned by default.

After the 3 GPT tests and position rating scales were completed, the subjects were given $10 to compensate them for their time. The investigator made a seemingly offhand comment “That was interesting, wasn’t it?” and recorded any response that might influence the interpretation of the tests.

The data were entered into a spreadsheet (Excel; Microsoft, Redmond, WA). The order of positions was coded 1 (first) to 3 (last). Means and variance were calculated. There were no outliers; hence, all data were included in the analysis. One-way analysis of variance (ANOVA) for repeated measures was used to determine the overall significance of differences in insertion and removal time as a function of body position (GraphPad Prism Software, San Diego, CA). If a significant F ratio was obtained, a Newman-Keuls test was used for comparisons between pairs of positions. A P value of < 0.05 was considered significant. Linear regression analysis was used to test the strength of the relation between the average placement times for all three positions (used as a reflection of overall manual dexterity) versus the change from standing bent forward to sitting. This analysis was performed to see if subjects with high scores benefited from sitting more than subjects with low scores. Correlation was used to determine if responses to any of the items on the intake questionnaire were associated with insertion and removal times for all positions on the GPT. Data are presented as the mean ± 1 sd.

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Frequency distributions for responses to the items in the intake questionnaire are shown in Table 1. The average age was 40 years, with a range from 26 to 61 years old. Four subjects were women and the remainder men. Seventeen of the subjects were right-handed, and three were left-handed. Two claimed to be ambidextrous. Correlation analysis failed to find a significant association of age, sex, and handedness with insertion or removal times in all three positions on the GPT. In fact, none of the items in the Intake Questionnaire correlated with the measures of manual dexterity on the GPT.

Visuoconstructional skills, as measured by the Rey Complex Figure test, were classified as normal in 18 subjects and borderline in 2; however, there was no relationship between these ratings and performance on the GPT.

Each subject performed the GPT in all three positions and the order of positions was determined by coin flip. The order of positions was coded by assigning a value of 1 to the first position, 2 to the second, and 3 to the last. The average value for this order variable was between 1.95 and 2.05 (Table 2), indicating successful randomization. This decreased the likelihood that time or a practice effect confounded the results.

Table 2

Table 2

The time to insert pegs in the GPT is also given in Table 2. ANOVA for insertion time was highly significant (P < 0.0001). The insertion time was 6%–7% faster if the subject was seated compared with kneeling (P < 0.01) or standing bent forward (P < 0.01). Only a few subjects dropped a peg during the trials. Subjects removed the pegs 7%–10% faster in the seated or kneeling position than they did while standing bent forward (overall ANOVA significant at P < 0.0001; both comparisons significant at P < 0.001).

The subjective rating of the positions is shown in Figure 1. It is clear by inspection that the seated position was considered the most comfortable and least painful of the three positions studied. A plot of insertion time versus rating of position comfort is shown in Figure 2. Performance improved as the comfort of the subjects increased. The improvement in performance when sitting compared to standing bent forward was least in subjects with good manual dexterity and greatest in subjects with poor dexterity (Fig. 3).

Figure 1

Figure 1

Figure 2

Figure 2

Figure 3

Figure 3

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The results indicate that manual dexterity is best when the subject is seated in a comfortable position. We attempted to replicate positions that anesthesia providers often assume when starting IV or intraarterial lines or doing regional anesthesia blocks. We had the subjects assume a position and stay still for two minutes before performing the GPT to mimic the clinical situation of a moderately time-consuming procedure. It is likely that the impact of uncomfortable body position on performance would increase as the time holding that position increased, but we have no data to support this concept. It is also possible that a provider kneeling on a hard floor such as concrete or linoleum (as opposed to the carpeted floor used in the study) would find the position even more uncomfortable and possibly have a further decrement in performance as a result.

The GPT is performed with one hand, whereas most anesthesia procedures are done with two. In pilot studies, it became apparent that subjects tended to steady their bodies with the nondominant hand, a luxury that most anesthesia procedures do not allow. Hence, we had the subjects hold their nondominant hand against their abdomen in all positions in an attempt to get it out of the way and make the arm as comfortable as possible.

The results of the present study are comparable to those obtained by Westwood et al. (1) who used a different type of pegboard with fewer pegs yet found a 6%–7% increase in peg insertion time when their subjects were standing bent forward at the waist compared with either standing with back straight or sitting. The current study reinforces and extends these findings. Westwood et al.’s subjects were college-age and mostly women; ours were older (average 40 years old) and mostly men. In addition, we measured the time to remove pegs and found similar effects of body position. Removal time has been shown recently to be an important component of the test (7). Interestingly, we found no effect of age, sex, or Rey Complex Figure rating on performance, perhaps because our sample size was relatively small.

Our subjects practice anesthesia, a profession that requires good manual dexterity. It is possible that a similar effect of posture on manual dexterity might be found in other populations. Whether or not body position actually affects performance of clinical procedures will require further study. It was surprising that two of the subjects had borderline scores on the Rey Complex Figure test. Perhaps this was the result of inadequate motivation. Performance on the GPT may have also been biased by the motivation of individual subjects. We have no objective measures of motivation and can only assume that this factor would have affected performance in all three positions equally.

The data indicate that sitting improves poor performance more than it does good performance. The fastest scores came from a former Olympic-class boxer and varied less than one second between positions. The slowest scores came from an older clinician (age 58 yr) struggling with trifocal glasses. This illustrates that good vision is important for tasks requiring eye-hand coordination.

Several limitations of the study should be mentioned. Only one test of manual dexterity was used, and multiple psychomotor tests may have given a more complete picture of how body position affects manual dexterity. We did not study performance while standing with the back straight, a common clinical position. It is possible that erectness rather than comfort is the factor that mediates performance. In fact, our study demonstrates an association between poor performance and subjective measures of comfort and pain but does not prove causation. Finally, only 20 subjects were studied, and different results might have been obtained with a different or larger group of subjects.

Are there practical conclusions that should be drawn from the study? Circumstances beyond the practitioner’s control often dictate the position in which procedures are performed, but it may be possible to arrange the environment to improve comfort and working conditions. The addition of stools to an induction area in which lines are started and blocks are preformed is an example.

In conclusion, manual dexterity is better when the subject is seated compared to standing bent forward at the waist or kneeling, positions that were rated as less comfortable and more painful than sitting.

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© 2006 International Anethesia Research Society