Ergonomics

ISSN: 0014-0139 (Print) 1366-5847 (Online) Journal homepage: http://www.tandfonline.com/loi/terg20

Application of a novel spinal posture and motion measurement system in active and static sitting Esther Pries, Marcel Dreischarf, Maxim Bashkuev & Hendrik Schmidt To cite this article: Esther Pries, Marcel Dreischarf, Maxim Bashkuev & Hendrik Schmidt (2015) Application of a novel spinal posture and motion measurement system in active and static sitting, Ergonomics, 58:9, 1605-1610, DOI: 10.1080/00140139.2015.1019938 To link to this article: http://dx.doi.org/10.1080/00140139.2015.1019938

Accepted online: 25 Feb 2015.Published online: 20 Mar 2015.

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Date: 24 September 2015, At: 09:19

Ergonomics, 2015 Vol. 58, No. 9, 1605–1610, http://dx.doi.org/10.1080/00140139.2015.1019938

SHORT COMMUNICATION Application of a novel spinal posture and motion measurement system in active and static sitting Esther Pries1, Marcel Dreischarf2, Maxim Bashkuev3 and Hendrik Schmidt* Julius Wolff Institute, Charite´ – Universita¨tsmedizin Berlin, Campus Virchow-Klinikum, AugustenburgerPlatz 1, 13353 Berlin, Germany

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(Received 6 June 2014; accepted 11 February 2015) The quantification of work-related musculoskeletal risk factors is of great importance; however, only a few tools allow objective, unrestricted measurements of spinal posture and motion in workplaces. This study was performed to evaluate the applicability of the Epionics system in a sedentary workplace. The system is mobile and wireless and assesses lumbar lordosis, pelvic orientation and spinal motion, without restricting subjects in their movements. In total, 10 males were monitored while sitting for 2 h on static and dynamic office chairs and on an exercise ball, to evaluate the effect of dynamic sitting. The volunteers were able to perform their work unhampered. No differences among the tested furniture could be detected with respect to either the lordosis or the number of spinal movements after habituation to the furniture; however, differences in pelvic orientation were statistically significant. The results of the present study indicate that Epionics may be useful for the quantitative assessment of work-related risk factors. Practitioner Summary: Only a few tools allow objective, unrestricted measurements of spinal posture and motion in the workplace. Epionics SPINE measures lumbar lordosis, pelvic orientation and spinal motion under nearly unrestricted conditions and can be used to quantify work-related musculoskeletal risk factors. We demonstrated the use of this tool in the workplace-analysis. Keywords: workplace evaluation; ergonomics; active sitting; lumbar spine; pelvic orientation

1.

Introduction

Sophisticated diagnostic tools that objectively determine spinal posture and quantify the lumbar motion of employees at work are required for evidence-based ergonomic interventions for preventing work-related musculoskeletal disorders. Such tools could help to quantify risk factors and objectively evaluate individual prevention measures in the workplace. Although there are a number of systems available to non-invasively determine the motion and posture of the spine, there are only a few tools that allow for unhampered, long-term measurements during daily workplace activities. Established tools, such as Vicon (Levine et al. 2007), Zebris (Vogt et al. 2000), Formetric 4D (Drerup and Hierholzer 1994), MediMouse (Mannion et al. 2004), CA-6000 (Dvora´k et al. 1995), lumbar motion monitors (Ferguson and Marras 2004), fibre-optic sensors (Williams, Haq, and Lee 2010) and inertia-based sensing systems (Goodvin et al. 2006), can be used to analyse spinal posture and motion and have been successfully applied in clinical, rehabilitative and sports medical settings. Their applicability in the workplace, however, is limited because some of these tools are neither mobile nor wireless, whereas others require constant exposed visibility of the back, making unhampered analysis (e.g., with the subject wearing ordinary working clothes or sitting on a chair with a backrest) almost impossible. Moreover, the aforementioned systems have not been used to measure and quantify non-standardised dynamic spinal motion in long-term measurements in the workplace. Tools that are currently used for workplace analyses, such as CUELA (Freitag et al. 2007) and 3D-SpineMoveGuard (Wunderlich et al. 2011), allow determination of non-standardised dynamic motion but are of limited practicality as they are uncomfortable to wear or allow for measurements only under laboratory conditions. The ‘Epionics SPINE’ is mobile and wireless, can be worn under working clothes, enables the assessment of spinal and pelvic posture and can be used to quantify spinal motion for up to 24 h (Consmu¨ller et al. 2012; Rohlmann et al. 2014). This system may be an addition to the current tools in the field of quantitative measurements in the workplace; however, the applicability of the system, which was originally developed solely for clinical use, has not previously been investigated for ergonomic purposes. This study was performed to evaluate the applicability of Epionics in a sedentary workplace, as many employees spend more than 70% of their time seated (Stamatakis et al. 2013), and to assess the effect of dynamic seating furniture on spinal motion and posture.

*Corresponding author. Email: [email protected] q 2015 Taylor & Francis

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2. Methods 2.1. Measuring system

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Epionics consists of two flexible sensor strips, which are placed into two hollow plasters attached to the back paravertebrally at a distance of 7.5 cm from the midline on each side, with the most caudal sensor at the level of the posterior superior iliac spine (Figure 1). Each sensor strip consists of twelve sensor segments of 2.5 cm in length, which employ strain-gauge technology to assess the lumbar spinal posture indicated by lumbar lordosis. Additionally, a tri-axial acceleration sensor is located at the lower end of each sensor strip to assess the pelvic orientation (‘a,’ Figure 1) and thus determine the spatial position of the sensor relative to the vertical direction (the direction of the earth’s gravitational force; ‘g,’ Figure 1 middle). The sensor strips are connected to a storage unit (size: 12.5 £ 5.5 cm; mass: 80 g) that stores data with a frequency of 50 Hz. The sensor strips exhibit high accuracy and repeatability, (ICC . 0.98), with test-retest reliability ICCs of . 0.98 (Taylor, Consmu¨ller, and Rohlmann 2010). 2.2. Participants In total, 10 males (mean age: 32.3 years, height: 181.6 cm, weight: 77.8 kg, BMI: 23.6 kg/m2) were monitored while sitting on various types of seating furniture. The subjects had no history of low back pain and had never demonstrated allergic reactions to plaster strips. The study was approved by the Ethics Committee of the Charite´ – Universita¨tsmedizin Berlin (registry number EA4/011/10). The procedure was explained to the volunteers, and they provided written informed consent. 2.3. Protocol Using the Epionics SPINE, the volunteers underwent a reference measurement including upright sitting on a stool and relaxed standing. Afterwards, they sat for 2 h on the following types of seating furniture at their work desks: 1. Static office chair (STATIC) . An office chair with a fixed backrest and a static seat pan. 2. Dynamic office chair (DYNAMIC)

Figure 1. The Epionics SPINE system and its individual components (hollow plasters, sensor strips, acceleration sensors and storage unit) affixed to a volunteer’s back. Demonstration of the assessment of the total lordosis angle, which is the sum of all lordotically curved segments during standing (average lordosis range highlighted in orange: S1– S6) as well as the orientation of the pelvis given by ‘a’, with respect to the vertical direction (the direction of the earth’s gravitational force; ‘g’).

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. An office chair with adjustable backrest, which allowed the forward displacement of the seat pan when the backrest was tilted backward. 3. Exercise ball (BALL) . An exercise ball (approximately 65 cm in diameter) suitable for individuals of heights between 175 cm and 190 cm. The chairs and ball were individually adjusted in height in accordance with ergonomic guidelines (ISO 9241-5 1998). To obtain information regarding habituation effects, the volunteers continued to use the balls for 2 weeks, after which time the 2-hour measurement was repeated. 2.4.

Data analyses

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2.4.1. Reference measurement Total lumbar lordosis was calculated in standing and sitting positions by summing the segments that were lordotically curved while standing (averaging data from corresponding left and right sensors; Figure 1) using MATLAB R2009b (TheMathsWorks, Inc., Natick, MA, USA). This lordosis was subsequently used as a reference to quantify the spinal motion. 2.4.2. Posture over 2 h The mean total lordosis and pelvic orientation were determined and compared among the different types of seating furniture. 2.4.3. Motion over 2 h The difference between the instantaneous total lordosis and the reference lordosis was calculated for each time point, resulting in a curve depicting the change in lordotic angle over time (Figure 2(a)). After the data were filtered using an

Figure 2. (a) Illustration of a profile of a sitting measurement, depicting the change in instantaneous total lordosis among different sitting positions. Examples are presented for upright, extended and flexed positions, for which the changes in lordosis angle (y axis) are plotted against time (x axis). (b) The box demonstrates the algorithm for counting movements. The local minima and maxima of the curve were determined, and only the differences between them that were larger than 58 were considered to quantify the spinal motion.

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eighth-order low-pass Butterworth filter with a cut-off frequency of 5 Hz to reduce noise (small changes such as those induced by breathing), the local minima and maxima were determined, and any differences between them that were larger than 58 were considered to quantify the spinal motion (Figure 2(b)). Three classes of postural changes were investigated: small (58– 108), moderate (108– 158) and large (158– 208). Using SPSS 21.0 (Chicago, IL, USA), descriptive statistics were determined and normal distribution was tested using the Kolmogorov–Smirnov test. Repeated measures ANOVA was performed, followed by post hoc analysis using the Bonferroni test. 3.

Results

None of the volunteers displayed an allergic reaction to the plaster strips. All of them were able to perform their work unhindered, wearing normal clothes. There were no system malfunctions. All analysed data were normally distributed.

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3.1.

Posture

While sitting in the workplace on all furniture types, the volunteers exhibited significantly smaller lordosis in comparison with that observed in the upright sitting position during the reference measurement. Among the types of seating furniture, no significant differences in lordosis were observed (Figure 3(a)). The pelvis was significantly more backward oriented when the subjects were sitting in either of the office chairs compared with the reference measurement. Furthermore, the orientation of the pelvis during sitting differed significantly between the exercise ball and the office chairs (Figure 4(b) – (c)); while seated on the ball, the volunteers exhibited a more forward orientation of the pelvis compared with the orientation observed while sitting on the chairs. 3.2. Motion In the first measurement (BALL (1st)), a significant increase in the number of movements was observed for the exercise ball compared with both office chairs (Figure 3(b) – (d)). However, after 14 days of habituation on the ball (BALL (2nd)), no significant increase in the number of movements was detected.

Figure 3. (a) Mean total lumbar lordosis during standing and sitting (data from reference measurement) as well as the mean total lumbar lordosis during 2 h of sitting on the various types of seating furniture. (b – d) Number of movements during 2 h of sitting on the various types of seating furniture for small (58– 108), moderate (108 2158) and large (158 2208) postural changes. The error bars represent standard deviations. The p-values are based on Bonferroni post hoc analysis.

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Figure 4. (a,b) Side-view of the mean spinal posture and the mean pelvic orientation during reference measurements and during 2 h of sitting on the static chair (STATIC), the dynamic chair (DYNAMIC) and the exercise ball during the first (BALL (1st)) and second measurement (BALL (2nd)) (the graphical depiction of the sensor strips in space is labelled in mm). (c) Pelvic orientation was determined by the acceleration sensors (angle change in space with respect to the vertical direction [the direction of the earth’s gravitational force]). The error bars represent standard deviations. The p -values are based on Bonferroni post hoc analysis.

4. Discussion This study evaluated the applicability of a new measurement tool that allows long-term measurements under nearly unrestricted conditions and could provide an addition to the field of quantitative measurements of posture and motion in the workplace. Because Epionics was originally developed for the clinical assessment of patients’ ranges of motion, some limitations on its use in ergonomics remain. For the ergonomic application of the system in the present study, it was necessary to develop additional MATLAB routines to extend the clinical analysis. The system is currently unable to evaluate combined movements, such as upper body rotation or lateral bending, both of which are relevant ergonomic risk factors. The system cannot automatically differentiate among major postures, such as sitting, standing and lying, leading to limited applicability in workplaces where such position changes occur often. Moreover, although several studies have demonstrated that the posture and motion measured on the back and the spine are correlated (Adams et al. 1986; Stokes, Bevins, and Lunn 1987; Guermazi et al. 2006), it should be noted that this system determines the shape of the back rather than the spine directly. Ergonomists advocate dynamic sitting, but the amount of motion necessary remains unknown. The results of the present study indicate that motion while sitting was not substantially affected by motion-promoting interventions, a result that is consistent with previous studies (Ellegast et al. 2012; Grooten et al. 2013). Although this was a preliminary study with a limited sample size, the results reveal large inter- and intra-subject variability and highly individualised responses (e.g., in spinal posture) to the various types of seating furniture, thereby substantiating the need for employee-individualised analyses to evaluate preventative measures. In summary, the results of the present study indicate that Epionics may be useful for the quantitative assessment of spinal posture and motion in the field of workplace health promotion or for future ergonomic research. Disclosure statement Esther Pries is a scientific advisor for Epionics Medical GmbH; what however, did not influence the results of the present study. The company Epionics Medical GmbH played no role in study design, data collection and analysis, the decision to publish, or the preparation of the manuscript.

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Funding This study was financially supported by the Bundesinstitut fu¨r Sportwissenschaft, Bonn, Germany (MiSpExNetwork).

Notes 1. 2. 3.

Email: [email protected] Email: [email protected] Email: [email protected]

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Application of a novel spinal posture and motion measurement system in active and static sitting.

The quantification of work-related musculoskeletal risk factors is of great importance; however, only a few tools allow objective, unrestricted measur...
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