Human-Factors & Ergonomics Research
An Ergonomic Evaluation of Performance, Posture & Comfort
Is the new trend of active sitting and active standing in the workplace really benefiting human health and productivity?
The project objective was to work with the designers of these two products to translate their goals into an improved user experience.
Core Chair Research & Recommendations
Active Sitting | Active sitting is being touted as a new alternative to traditional sedentary seating - promising relief from aches and an opportunity to burn calories during the workday. As an increased number of users turn towards “active sitting” to alleviate pain and discomfort, and integrate activity into sedentary work lifestyles, non-traditional seating must be developed to accommodate new levels of motion and flexibility.
However there is debate about how active “active” seating really is.
Grooten et al (2013) conducted an experiment with thirteen participants who performed a keyboard-writing task during the five different conditions in random order: sitting on a stool without a backrest (BACK APP) in both a stable (FIX) and unstable mode (UNS), a saddle-formed stool without a backrest (SAD), a conventional office chair (OFF) and standing (STA). Data collected was analysed regarding posture, postural sway and trunk muscle activity. Surprisingly, less postural sway and less muscle activity were observed during the conditions that encourage active sitting, compared with sitting on a conventional office chair.
The Core Chair's design evaluation goals include:
1. Efficiency: How well the product is working
2. Effort: considerations would involve assessing the amount of effort required in
3. Maintaining proper posture while seated on the chair
4. Switching back and forth between “active sitting” and keeping still
5. Operating the controls of the dynamic chair
6. Mobility while remaining seated between zones in the workspace
7. Maintenance of the chair
8. Assembling the new product
This goals are evaluated in terms of performance, comfort, and posture.
Methods | A true experiment was conducted to investigate the effects of the CoreChair on two aspects of computer task performance. Participants completed a task while sitting in the CoreChair, as well as sitting in a control chair (the Humanscale Freedom). In this within-subjects design, each participant was exposed to all sitting conditions while performing Shenwen Liu’s Homing Task to measure two dependent variables, typing efficiency CORE CHAIR: AN ERGONOMIC ANALYSIS 5 and mousing efficiency (in ms). To account for any carryover effects, presentation of the sitting conditions, as well as presentation of the apparatus’ within each condition, was counterbalanced across participants.
Participants | Eleven graduate students (5 males and 7 females) in DEA 6510 at Cornell University participated in this study as part of a course requirement. Any previous injuries, including back and wrist injuries, were disclosed before the procedure.
Apparatus & Setting | Participants were run individually using a desktop computer in the testing room – an ergonomics lab at Cornell University. The room was selected as it included an adjustable desk to facilitate both the sitting conditions. The space is a fully interior space without any windows, and fit a desk and chair with an adjacent space to store the other conditions when not in use. The flooring was linoleum tile, allowing movement for the position of the chairs if the user needed to make adjustments and shift positions throughout the procedure. Additionally the space had room to set up three cameras to monitor posture data, one below the desk to monitor the feet, and two on tripods view the side of the participant and the back of the participant.
Participant’s anthropometrics data was collected at the test setting using a tape measure. Each participant’s height, weight, sitting elbow height, and sitting eye height were measured to make proper adjustments to the desk and the chairs during the test. As shown in the Table 1, the average of the measures were determined by gender: males (average height = 182.9cm, weight = 68.1kg, sitting eye height = 125.5cm, sitting elbow height = 68.4cm, and seat height = 51.1cm) and females (average height = 164.0cm, weight = 56.4kg, sitting eye height = 117.1cm, sitting elbow height = 59.5cm, and seat height = 49.6cm). All of the seating heights in the seated positions were measured in respect to the human scale freedom chair.
Moreover, the height adjustability range of Core Chair and the control chair was measured in order to evaluate whether the height of the chair supports all range of users. The seat height was also measured using a tape measure. The results showed that the seat height of Core Chair ranged from 48 cm to 53 cm, which allowed 5 cm increment of seat height adjustment from the lowest to the highest. The level of seat height may vary depending on the model of Core Chair. On the other hand, the height of Humanscale Freedom Chair which was used as a control chair ranged from 38 cm to 53 cm with 15 cm adjustability of seat height. Based on the data, it was found that participant’s seating height ranged from 42 cm to 53 cm. This indicated that the lowest seat height of Core Chair was higher than the lowest height of a participant.
1. Latency for typing will be higher in the Core chair than the control chair.
2. Latency for mouse clicks will be higher in the Core chair than the control chair.
As for the data generated by the performance test in three levels of the independent conditions (control chair, CoreChair in a locked position, and CoreChair unlocked), one-way repeated measures ANOVA was adopted to determine the existence of any differences between the means of latency in the three conditions.In order to conduct an one-way ANOVA, assumptions for outliers, normality, and sphericity need to be satisfied.
Therefore, the Shapiro-Wilk’s test of normality was conducted to see if the data met the aforementioned assumptions. The analysis process and specific data would be described in the following paragraphs. Typing Task All typing data for the CoreChair and the control chair was positively skewed and failed to pass Shapiro-Wilk’s test of normality (p < .05). There were two outliers in the unlocked CoreChair condition. When square-root and logarithmic transformations failed to correct the skewedness, an inverse transformation was applied, and the transformed data now passed Shapiro-Wilk’s test of normality (p > 0.05) with no outliers. Participants completed the typing task fastest in the control chair (M = 1582.5 ms, SD = 166.6) than in the CoreChair in the locked position (M = 1674.5 ms, SD = 184.1) and the unlocked CoreChair (M = 1643.6 ms, SD = 154.0). Mauchly's test of sphericity indicated that the assumption of sphericity had been violated for both the original data and the transformed data. A repeated-measures ANOVA using the Greenhouse-Geisser correction did not indicate any statistically significant difference between the seating types, F(1.682, 16.820) = 0.665, p = .502
1) The frequency of reported pain will be less with the Core Chair than the control chair.
2) The intensity of reported pain will be less with the Core Chair than the control chair.
3) The overall comfort will be less and fatigue will be more in the Core Chair than the control chair.
The frequency of reported pain was calculated by the number people who reported pain in certain regions of the body after testing conditions. The intensity of reported pain was a follow up question of the frequency of reported pain; if a subject reported that they had pain, he or she was then asked about the intensity of pain in the selected regions of the body. It calculated by the average pain level on a scale of 0 - 10 for each body part. Moreover, we expected to see lower comfort and higher fatigue rates when a person was sitting on the Core Chair than the control chair. Since Core Chair is an active sitting ergonomic chair that involves dynamic movement of your core muscles, it is supposed to add a moderate fatigue in the short term. However, in the long term, we expect them to be less fatigue and more comfortable as people would get used to sitting on the dynamic chair.
1) There will be dynamic movement in the core chair compared to the control chair.
2) The rotational tilt will retain perpendicular posture of the spine and hips in order to accommodate a forward incline during typical indoor office work.
3) The seat will allow participants to reach proper resting posture.
Results Using RULA, it was determined that the dynamic core chair had, on average, lower scores, which signified that it provided a seating condition that was better suited for a more neutral posture that does not put more musculoskeletal tension on the upper limbs, specifically the upper CORE CHAIR: AN ERGONOMIC ANALYSIS 19 arms. However, it is important to note that these differences were very minimal, a mere fraction of a difference to be exact. Therefore it is important to consider the statistical significance of these findings before jumping to conclusions. As such, although posture is improved, the improvement is marginal.
Expand on our study:
More participants need to be formally recruited for better sample.
Long term effect need to be considered
Variety of tasks that capture individual chair components’ performance
Comparative study of different dynamic chairs in the market to assess relative performance of products
Other areas of interest:
The range of height adjustment is not sufficient according to our anthropometric data.
Lever control should be more adjusted to arm length and reachability.
Castors on the CoreChair are easier to move, which is desirable in a workplace chair to facilitate ease and flexibility of movement.
However this may deter balance during CoreFit routine, for example when in the plank position, as a result of which the user may incur injury.
Locking mechanism be incorporated into the casters.
Next Steps: Comparing the Ergonomic Benefits of Active Sitting vs. Active Standing
This project will continue with a second round of data collection to compare the ergonomic benefits of active sitting, active standing against standing and sitting in a non-ergonomic seat. The next round of data will include measures of comfort, balance and adjustability.