EFFECTS OF SITTING AND STANDING WORK POSTURES ON SHORT-TERM TYPING PERFORMANCE AND DISCOMFORT

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1 Proceedings of the Human Factors and Ergonomics Society 2016 Annual Meeting 460 EFFECTS OF SITTING AND STANDING WORK POSTURES ON SHORT-TERM TYPING PERFORMANCE AND DISCOMFORT Gourab Kar and Alan Hedge Cornell University, Department of Design and Environmental Analysis, Ithaca, New York, USA The study evaluated effects of sitting and standing work postures on objective short-term computer typing performance and perceived discomfort. A randomized, repeated measures, study design was used to assess typing performance and perceived discomfort for 12 participants on a 15-minute computer-typing task. Typing performance was measured by number of characters typed and number of errors. Perceived discomfort was measured for the whole body, as well as for upper body and lower body, using a visual analog scale. Results suggest that for a short-term computer typing task, compared to a sitting work posture a standing work posture leads to fewer typing errors without impacting typing speed. Overall levels of perceived discomfort for the whole body are similar for sitting and standing work postures. However, for perceived discomfort there is an interaction of work posture and body region - upper body discomfort is higher in the sitting work posture while lower body discomfort is higher in the standing work posture. Copyright 2016 by Human Factors and Ergonomics Society. DOI / INTRODUCTION There is a growing body of evidence to suggest that chair sitting for prolonged durations is a health hazard (Thorp et al., 2011). Sedentary behavior has been associated with increased risk of cardiovascular disease (Warren et al., 2010), obesity (Proper et al., 2007; McCrady and Levine, 2009), weight gain (Brown et al., 2005), type-2 diabetes (Hu et al., 2003), and allcause mortality (Katzmarzyk et al., 2012; Chau et al., 2013). From an evolutionary biology perspective, humans were not designed to sit all day (Grimsrud, 1990). Sitting in a chair is not bad in moderation, but in excess is addictive and harmful. According to Dr. James Levine (2010), for every hour we sit, we lose two hours of our life. In recent years, given the increased attention to chronic disease and total mortality associated with prolonged sitting (Patel et al., 2010), sit-stand workstations have become popular in the workspace (Karakolis & Callaghan, 2014). These workstations feature variable-height work surfaces enabling users to alternate between sitting and standing work postures. However, there are mixed results of the effectiveness of sit-stand workstations in reducing 'sitting time' at work. While Alkhajah et al. (2012) report a significant reduction in sedentary time following the introduction of a sit-stand workstation, Gibson et al. (2012) did not find significant change in proportion of work time spent in sedentary behavior after introducing height-adjustable desks. Studies by Nerhood & Thompson (1994), Hedge & Ray (2004) and Vink et al. (2009) indicate that workers choose to stand for 20% to 30% of their day when provided with sit-stand workstations. While the adoption of sit-stand workstations in the office potentially improves energy expenditure by increasing standing time at work, Wilks et al. (2006) report non-compliance in use of sitstand workstations to vary work posture, between six months to a year after their installation in office environments. A systematic review of sit-stand workstations reveals that changing posture throughout the day while using a sit-stand workstation is likely to reduce discomfort when compared to seated only work (MacEwen et al., 2015). Although measuring discomfort is by nature subjective, there have been significant correlations between objective measures (e.g. pressure distribution) and subjective discomfort scores (De Looze et al., 2003). This correlation coupled with logistical limitations of worksite objective measures, has led to the adoption of perceived discomfort as a common outcome measure. Studies comparing sit-stand work interventions with sit-only work as control report reduced discomfort scores for the former (Karol & Robertson, 2015). However, there is paucity of data comparing discomfort scores between sitting and standing work postures while using a sit-stand workstation. Worker performance is another outcome measure used in assessing effectiveness of sit-stand workstations. A literature review of performance in sit-stand work compared to sit only work, reported mixed results (Karakolis & Callahan, 2014). Three of eight studies showed increase in performance for sitstand work when compared to sit only work (Dainoff, 2002; Hedge & Ray, 2004; Ebara et al., 2008). Four studies showed no effect on performance (Nerhood & Thompson, 1994; Hedge et al., 2005; Davis et al., 2009; Husemann et al., 2009), while the remaining study by Hasegawa et al. (2001) had mixed results - higher volume of work was performed for sitstand work posture, but with more errors. There have been few studies, if any, comparing the effects sitting and standing work postures on short-term computer typing performance. Given the serious health effects of sedentary behavior and the large number of people globally exposed to this heath risk, workspace interventions to promote postural variability are being increasingly adopted. The sit-stand workstation shows promise in promoting postural variability at work. However, the paucity of data comparing objective performance and perceived discomfort between sitting and standing work postures limits our understanding of the inter-relationships between posture, performance and discomfort in office work. Therefore, the aim of this study was to evaluate effects of sitting and standing work postures on short-term typing performance and perceived discomfort. We hypothesize that: (1) Short-term typing performance will not vary between the two work postures, i.e. there will be no main effect of work posture on short-term typing performance.

2 Proceedings of the Human Factors and Ergonomics Society 2016 Annual Meeting 461 (2) Overall perceived discomfort in standing work posture may be higher compared to sitting work posture, i.e. there will be a main effect of work posture on perceived discomfort scores. (3) Perceived discomfort scores for upper and lower body region will vary in relation to work posture, i.e. there will be an interaction of work posture and body region with regard to perceived discomfort scores. METHODS Participants Twelve male adults volunteered to participate in the study. They were recruited by circulated among graduate students in a large research university. Inclusion criteria were: at least 18 years old, a Body Mass Index (BMI) between 18 and 30, experience with computer typing tasks, involvement in physical activity or exercise (frequency: 1-5 sessions/week, duration: minutes/session), and no musculoskeletal health complaints. Computer experience, physical activity and musculoskeletal health were self-reported. (See Table 1 for details) All participants (Ps) signed an informed consent form at the beginning of the study. Table 1 - Participant Demographics Experimental Design Using a randomized repeated measures design, objective performance and perceived discomfort levels on a 15-minute typing task was assessed for two work postures in an office like laboratory environment. Each typing task was repeated twice in each work posture; order of tasks was randomized. Ps performed a total of four, 15-minute typing tasks. The two work postures seated work (SIT) and standing work (STA) was the independent variable. Dependent variables were shortterm typing task performance and perceived level of physical discomfort. Apparatus A 17-inch height-adjustable computer screen, keyboard and wired mouse (Dell products) were used for the study. For the SIT posture a fixed-height desk at 0.75 m from the floor level and an office chair (Herman Miller - Mirra 2) adjusted in height to fit each Ps body dimensions was used. For STA posture the fixed-height desk was supplemented by two raised surfaces at 1.00 m and 1.25 m heights from the floor level, to provide elevated surfaces for the keyboard and mouse, and to the monitor respectively. Tasks and Assessments The computer-typing task required Ps to copy text from a window in left half of the screen to a MS Word document in right half of the screen. Each mistyped word or punctuation was counted as one error. Computing task performance was operationalized by two measures (a) typing speed (# of characters typed) and typing error (# of mistyped words and punctuation). Perceived level of physical discomfort was operationalized using a Visual Analog Discomfort Scale (Straker et al., 1997). The 13-item discomfort scale enabled classification of discomfort scores by upper and lower body regions; a mean value of these scores provided the whole-body discomfort score. Procedure First, Ps signed the informed consent form and a researcher explained the experimental protocol. Next, a questionnaire administered to Ps documented their demographic characteristics, prior computer experience, level of physical activity and musculoskeletal health. Following this, Ps performed practice-typing trials in both work postures (SIT & STA) for 5 minutes each. Ps were then instructed to perform four typing tasks of 15-minutes duration each, based on a predetermined randomized sequence. They were instructed to type at a comfortable speed without worrying about spelling and punctuation errors. A 5-minute break was provided in between typing tasks; discomfort ratings were recorded at 5 instances - prior to start of the first task, and at end of each subsequent task. For each P, the complete experiment, including preparatory activities, typing sequences, rest-breaks, and filling out questionnaires, took 100 minutes. Data Analysis Statistical analyses were performed using Statistical Package for Social Sciences (SPSS) version Paired T- tests (two-tailed) were used to compare short-term typing performance (speed and errors) and perceived discomfort between seated work posture (SIT) and standing work posture (STA). Significance threshold was set at p < Objective performance and perceived discomfort values were plotted against 15-minute time intervals (t = 15, 30, 45 and 60 min) to compare temporal trends for SIT and STA work postures. RESULTS Performance Typing Speed Typing Speed. Short-term typing speed was measured as number of characters including blank spaces typed in 15 minutes. A paired t-test (two-tailed) was employed to compare mean values of short-term typing speed in the SIT and STA postures. There was no main effect of workstation condition on short-term typing speed (t = , p = ). (Figure 1) Practice Effect. There was evidence of a practice effect on short-term typing speed in both work postures. In case of SIT work posture, typing speed in second session (μ = ; σ = ) was marginally higher compared to first session (μ = ; σ = ). Similarly, for STA work posture,

3 Proceedings of the Human Factors and Ergonomics Society 2016 Annual Meeting 462 typing speed in second session (μ = ; σ = ) was marginally higher than first session (μ = ; σ = ). Typing Speed across Time. Mean typing speed was plotted across the four 15-minute sessions. For SIT posture, increase in typing speed was observed across the first three sessions, followed by a decrease in session four. Conversely, for STA posture a decrease in typing speed was observed in session two, followed by a steady increase in session three and four. (Figure 2) Conversely, for STA posture a decrease in typing errors was observed across first three sessions, followed by an increase in session four. (Figure 4) Figure 3 - Mean Typing Errors in SIT and STA Postures Figure 1 - Mean Typing Speed in SIT and STA Postures Figure 2 - Typing Speed across Time Performance Typing Errors Typing Errors. Typing Errors was measured by counting total number of mistyped words and punctuations in the typed document; a lower value of errors indicates higher accuracy. A paired t-test (two-tailed) comparing mean values of typing errors in SIT and STA postures indicated a main effect of work posture on typing errors (t = , p = ). On average, typing errors in STA posture (μ = 11.28; σ = 7.58) was significantly lower compared to the SIT posture (μ = 13.60; σ = 8.49). (Figure 3) Practice Effect. There was evidence of a practice effect on short-term typing errors in both work postures. For SIT work posture, typing errors in second session (μ = 14.75; σ = 9.49) was higher compared to first session (μ = 12.67; σ = 8.02). Similarly, for STA work posture, typing errors in second session (μ = 11.50; σ = 8.54) was marginally higher compared to first session (μ = 11.25; σ = 7.20). Typing Errors across Time. Mean number of typing errors was plotted across the four 15-minute sessions. For the SIT posture an increase in typing errors was observed across the first three sessions, followed by a decrease in session four. Figure 4 - Typing Errors across Time Perceived Discomfort Overall Discomfort. Overall discomfort was calculated by averaging scores from an 8-item discomfort measure; items on the measure were scored using a visual analog scale where: 0 = no discomfort, and 100 = extreme discomfort. A paired t-test (two-tailed) comparing mean values of perceived discomfort in the SIT and STA postures indicated no main effect of workstation condition on perceived discomfort (t = , p = ). (Figure 5) Discomfort across Body Region. Perceived discomfort scores were analyzed with respect to upper body (head and neck, shoulder and arm, lower back, elbow and forearm, wrist and hands) and lower body (hip, thigh and knee, leg and foot). There is an interaction of body region (upper or lower) with work posture (SIT or STA), i.e. effect of work posture on perceived discomfort score varies with the body region. A paired t-test (two-tailed) comparing mean values of perceived discomfort for upper body in SIT and STA work postures indicated a main effect of workstation condition on perceived discomfort scores (t = , p = ). Similarly, a paired t-test (two-tailed) comparing mean values of perceived discomfort for the lower body in SIT and STA work postures indicated a main effect of work posture on perceived discomfort scores (t = , p = ). (Table 2)

4 Proceedings of the Human Factors and Ergonomics Society 2016 Annual Meeting 463 Discomfort across Time. Mean perceived discomfort score was plotted across the four 15-minute sessions. For the SIT posture there was a decrease in perceived discomfort in the second session, followed by an increase in discomfort scores for session three and four. However, for the STA posture a consistent pattern of decrease in perceived discomfort score was observed across the four sessions. (Figure 6) Figure 5 - Overall Discomfort in SIT and STA Postures Table 2 - Interaction of Body Region and Work Posture Figure 6 - Perceived Discomfort across Time DISCUSSION Results partially confirm the first hypothesis, i.e. shortterm typing performance does not vary across SIT and STA postures. Mean typing speed in STA posture is similar to that for SIT work posture; difference of means is not statistically significant. However, mean typing errors for STA posture is significantly lower than that for SIT posture. While previous research suggests no significant changes in task performance between sitting and standing postures (Drury et al., 2008; Straker et al., 2009); analysis of typing errors in the present study suggests that accuracy in standing is significantly higher compared to sitting. The increase in typing accuracy maybe attributed to the finding that physiological arousal levels are higher in standing as compared to sitting (Ebara et al., 2008). The results do not confirm the second hypothesis, i.e. there is no main effect of workstation condition on overall perceived discomfort. While overall perceived discomfort scores are marginally higher in STA posture compared to SIT posture; difference of means is not statistically significant. Previous studies have compared sitting only work with sit-stand work to suggest a significant reduction in perceived discomfort for sitstand work (Roelofs & Straker, 2002; Hedge & Ray, 2004; Husemann et al., 2009). This study is unique in comparing perceived discomfort between SIT and STA postures to report non-significant difference in overall discomfort scores. With respect to perceived discomfort and body region, Roelofs & Straker (2002) found lower limb discomfort was greatest in the standing only posture. Additional studies have shown a strong association between low back pain and standing occupations (Andersen et al., 2007; Roelen et al., 2008) or prolonged constrained standing work (Nelson-Wong & Callaghan, 2010). Our findings are consistent with previous research and report a similar increase in mean discomfort score for the lower body region in STA posture. Results confirm the third hypothesis, i.e. there is an interaction of work posture and body region with regard to perceived discomfort. Findings suggest that for short-term typing tasks there is a tradeoff between perceived discomfort scores and the work posture adopted. Across equivalent tasks and durations, upper body discomfort is higher in SIT posture while lower body discomfort is higher in STA posture. To provide adequate context of the results, the following strengths of this study need to be discussed. First, the study was performed in a controlled, office-like laboratory environment with Ps performing short-term typing tasks. Second, while previous studies compared performance and discomfort between sitting only and sit-stand work, this is one of the first studies to independently compare performance and discomfort between SIT and STA work postures. Third, performance and discomfort have been analyzed both in terms of both overall scores as well as across intervals of 15 minutes each. This enables for analysis of both overall values, along with a temporal perspective on how performance and discomfort are impacted by the work posture in 15-minute time intervals. Fourth, the method of analysis adopted enabled short-term typing performance to be studied in terms of both speed and accuracy. Similarly, perceived discomfort was analyzed both in terms of individual body region and wholebody scores. These fine-grained analyses suggest that accuracy in a short-term typing task is significantly impacted by work posture, and that there is an interaction between work posture and body region for perceived discomfort scores. However, these strengths incorporate some limitations as well. First, evaluations were based on short-term typing tasks performed for 15-minute durations. This short duration may not offer ecologically valid results for typing performance generalizable across a typical workday. Second, repeated measures design employed provided evidence for practice effects. Third, choice of Ps and small sample size (n = 12) may reduce external validity of results. Ps were male, relatively young (mean age 27.6), lean (mean BMI 23.4) and fit (on average 45 minute exercise / week). Generalizing these results to the overall office population may be limited as performance and discomfort measures may be affected by gender, age and fitness levels. Fourth, Ps were a mix of touch typists (n = 3), hybrid typists (n =7) and hunt-and-peck typists

5 Proceedings of the Human Factors and Ergonomics Society 2016 Annual Meeting 464 (n = 2); different typing styles may have impacted results. Overall, these limitations provide context for interpreting results of this study. In conclusion, while uninterrupted chair-sitting is recognized as a health hazard, alternatives to the chair-sitting paradigm of work are not necessarily benign. Alternating between sitting and standing at work in the office is a viable and increasingly popular option, however there is scant data about how these two work postures impact performance and discomfort. This study reports on a preliminary research comparing short-term typing performance and perceived discomfort between sitting and standing work postures. Results suggest that for short-term computer typing tasks, a standing work posture provides for more accurate typing without reduction in typing speed. 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