- Research
- Open Access
Biomechanical analysis of different dynamic sitting techniques: an exploratory study
- Chun-Ting Li1,
- Yen-Nien Chen2, 3Email author,
- Yen-Ting Tseng1 and
- Kuen-Horng Tsai1Email authorView ORCID ID profile
- Received: 2 October 2017
- Accepted: 20 December 2018
- Published: 3 January 2019
Abstract
Prolonged static sitting in wheelchairs increases the risk of pressure ulcers. This exploratory study proposed three dynamic sitting techniques in order to reduce the risk of developing pressure ulcer during wheelchair sitting, namely lumbar prominent dynamic sitting, femur upward dynamic sitting, and lumbar prominent with femur upward dynamic sitting. The purpose of this study was to analyze the biomechanical effects of these three techniques on interface pressure. 15 able-bodied people were recruited as subjects to compare the aforementioned sitting techniques in a random order. All parameters, including dynamic contact area, dynamic average pressure, and dynamic peak pressure on backrest and seat were measured and compared. In result, when compared with lumbar prominent dynamic sitting, femur upward dynamic sitting and lumbar prominent with femur upward dynamic sitting appeared to yield significantly lower dynamic average and peak pressure on the back part of seat, and significantly higher dynamic average and peak pressure on the front part of seat. This study can serve as a reference point for clinical physicians or wheelchair users to identify a suitable dynamic sitting technique.
Keywords
- Pressure ulcers
- Wheelchair
- Dynamic sitting
- Interface pressure
Introduction
Wheelchairs are generally used by patients suffering from lower limb disorders. Studies have indicated that a prolonged static sitting in wheelchairs increases the risk of pressure ulcers [1–3]. It is most commonly induced by long-term stress concentration on ischial tuberosities, coccyx, or bony prominences can cause blockages in blood vessels of the surrounding tissues, affect the supply of nutrition to cells, and lead to cell necrosis [1, 2, 4, 5]. The wheelchair seating system is a crucial factor affecting the buttocks pressure [6–12].
Previous studies have reported that lumbar supports and cushions correct the problem of stress concentration at the ITs by redistributing stress on the back, buttocks, and thighs [6, 7]. However, these assistive devices cannot reduce the stress load caused by prolonged static sitting. Some studies have already proposed dynamic sitting techniques (DSTs) that are creatively designed with special purposes, experiments have also proven that these seating systems are able to periodically change sitting postures and reduce prolonged static sitting loads [13–15]. Nonetheless, the optimal movement strategy of DST to reduce the risk of developing pressure ulcers is still being debated.
Three different dynamic sitting techniques. Including the lumbar prominent dynamic sitting (LPDS), femur upward dynamic sitting (FUDS), and lumbar prominent with femur upward dynamic sitting (LFDS)
Methods
Subjects
Fifteen able-bodied people were recruited to participate in this exploratory study (8 men, 7 women; age, 22.5 ± 1.8 years; weight, 65.2 ± 10.6 kg; height, 168.5 ± 8.9 cm; body mass index, 22.8 ± 2.6 kg/m2). Subjects with preexisting musculoskeletal disorders and spinal pathologies were excluded. All subjects read and signed an informed consent form that explained the study objective and experimental protocol. This study was approved by the Institutional Review Board of National Cheng Kung University Hospital.
Experimental wheelchair
The researcher of this study designed an experimental wheelchair, which was installed with airbags providing adjustable support for lumbar and femur areas. The size of each airbag was 40 × 23 cm2. When filled with air, the airbags were 4 cm thick. A customized microprocessor was used to adjust the extent and cycle period of filling or deflating each airbag to periodically change the sitting postures. A 1-cm-thick foam pad was installed to the backrest and seat to minimize the discomfort caused by the surface discontinuity between the skin contact with the backrest and seat.
Experimental protocol
Before the experiment started, each subject was first asked to rest their upper body on the backrest and relax their arms on both sides. Moreover, they had to keep their thighs parallel to the ground, feet approximately shoulder-width apart and firm on the footrest, and eyes looking straight ahead [16, 17]. Afterward, the sequence of three DSTs was randomly drawn by each subject (illustrated in Fig. 1): (1) LPDS: An airbag providing adjustable support for lumbar area was placed at L3 (on the subject). The airbag configuration was periodically switched between deflated (0-cm-thick) and filled (4-cm-thick), alternating every 5 min, the total period of experiment lasted for 20 min. (2) FUDS: An airbag providing adjustable support for femur area was placed at the middle of the subject’s thighs. The airbag configuration was periodically switched between deflated (0-cm-thick) and filled (4-cm-thick), alternating every 5 min, the total period of experiment lasted for 20 min. (3) LFDS: This technique is a combination of the previous 2 techniques simultaneously. Between each DST experiment, the subject took a 5-min break during which they could stand up and walk around.
Data recordings and analysis
Two pressure mapping mats (Body Pressure Measurement System; Tekscan Inc, South Boston, Massachusetts, USA) were placed over the surface of the backrest and seat to measure the pressure distribution along the human-wheelchair interface. The pressure mapping mats comprised 2016 (48 × 42) measuring cells. Each measuring cell had a dimension of 10.16 × 10.16 mm2. The interface pressure parameters were calculated using the body pressure measurement system research software (BPMS, version 7.02C; Tekscan Inc, South Boston, Massachusetts, USA). Data were sampled at the frequency of 30 Hz. From the interface pressure recordings, the dynamic contact area (DCA), dynamic average pressure (DAP), and dynamic peak pressure (DPP) on the whole backrest (B-DCA, B-DAP, and B-DPP), the entire seat (S-DCA, S-DAP, and S-DPP), the back part of seat (BS-DCA, BS-DAP, and BS-DPP), and the front part of seat (FS-DCA, FS-DAP, and FS-DPP) were calculated. Each interface pressure parameter is given as the averaging value over the entire 20 min sitting trial.
Statistical analysis
The Statistics Package for the Social Sciences (SPSS, version 17; SPSS Institute, Chicago, IL, USA) was used for all statistical analyses. Firstly, the whole backrest (B-DCA, B-DAP, and B-DPP) and the entire seat (S-DCA, S-DAP, and S-DPP) were compared between the different DSTs (LPDS, FUDS and LFDS) by using a Friedman test. A post hoc test, Wilcoxon signed-rank test was used for detecting significant differences in the dependent variables across the tests. Secondly, the back part of seat (BS-DCA, BS-DAP, and BS-DPP) and the front part of seat (FS-DCA, FS-DAP, and FS-DPP) were compared between the three DSTs by using the same statistical methods as above. The statistical significance was set at P < 0.05.
Results
Results of interface pressure measurement on both the whole backrest and the entire seat
DSTs | B-DCA (cm2) | B-DAP (kPa) | B-DPP (kPa) | S-DCA (cm2) | S-DAP (kPa) | S-DPP (kPa) |
|---|---|---|---|---|---|---|
LPDS | 143.80 ± 61.70 | 2.93 ± 0.61 | 5.19 ± 1.63 | 837.80 ± 193.03 | 6.28 ± 0.85 | 41.77 ± 12.19 |
P * | 0.053 | 0.036 | 0.244 | 0.842 | 0.975 | 0.056 |
P † | 0.222 | 0.033 | 0.084 | 0.363 | 0.470 | 0.011 |
FUDS | 109.01 ± 67.56 | 2.55 ± 0.37 | 4.71 ± 2.59 | 823.06 ± 140.88 | 6.24 ± 0.61 | 37.58 ± 10.55 |
P ‡ | 0.005 | 0.010 | 0.047 | 0.629 | 0.648 | 0.807 |
LFDS | 176.02 ± 78.54 | 3.18 ± 0.71 | 6.04 ± 1.97 | 815.06 ± 184.13 | 6.38 ± 0.81 | 37.65 ± 12.83 |
P § | 0.022 | 0.006 | 0.028 | 0.936 | 0.948 | 0.006 |
Results of interface pressure measurement on both the back part of seat and the front part of seat
DSTs | BS-DCA (cm2) | BS-DAP (kPa) | BS-DPP (kPa) | FS-DCA (cm2) | FS-DAP (kPa) | FS-DPP (kPa) |
|---|---|---|---|---|---|---|
LPDS | 527.13 ± 64.00 | 8.11 ± 0.99 | 41.28 ± 12.35 | 342.13 ± 95.11 | 3.47 ± 0.56 | 6.55 ± 1.52 |
P * | 0.173 | 0.005 | 0.009 | 0.496 | 0.001 | 0.001 |
P † | 0.015 | 0.002 | 0.009 | 0.712 | 0.001 | 0.001 |
FUDS | 517.60 ± 80.16 | 7.13 ± 0.86 | 35.77 ± 10.80 | 350.00 ± 61.37 | 4.73 ± 0.42 | 9.97 ± 1.19 |
P ‡ | 0.069 | 0.460 | 0.875 | 0.932 | 0.154 | 0.065 |
LFDS | 495.73 ± 59.34 | 7.37 ± 1.14 | 36.88 ± 13.22 | 347.07 ± 83.07 | 4.88 ± 0.61 | 10.73 ± 1.66 |
P § | 0.031 | 0.001 | 0.004 | 0.819 | < 0.001 | < 0.001 |
Representative dynamic average pressure (DAP) and dynamic peak pressure (DPP) on the back part of seat (BS-DAP and BS-DPP) for a participant during lumbar prominent dynamic sitting (LPDS), femur upward dynamic sitting (FUDS), and lumbar prominent with femur upward dynamic sitting (LFDS) trial conditions
Discussion
This study examined and quantified the biomechanical effects of three DSTs, namely LPDS, FUDS, and LFDS, by measuring the interface pressure. The results of the experiments revealed that FUDS and LFDS periodically changed the interface pressure on the buttocks that can be used to reduce the risk of developing pressure ulcers. LPDS yielded the significantly lowest performance in interface pressure on the buttocks.
The weight of a wheelchair user is primarily supported by the backrest and seat. In addition, because the buttocks support most of the body weight, the stress of body weight is primarily focused on the ischial tuberosities and the surrounding soft tissues, increasing the likelihood of developing pressure ulcers there [8, 9, 18, 19]. Previous studies have indicated that increasing the stress load between the backrest and the front part of seat can assist in reducing the stress on the ischial tuberosities [8, 9]. The results of the interface pressure measurements illustrated that the three DSTs yielded significant differences in B-DAP values. LFDS yielded the significantly highest B-DAP values, LPDS the significantly medium, and FUDS the significantly lowest. Consequently, LFDS is more effective than LPDS and FUDS at shifting the sitting load from the seat to the backrest when dynamic alteration process. Moreover, compared with LPDS, FUDS and LFDS yielded significantly lower BS-DAP and BS-DPP values, and significantly higher FS-DAP and FS-DPP values. Regarding these parameters, there were no significant differences between FUDS and LFDS. Consequently, FUDS and LFDS are more effective than LPDS at shifting the sitting load from the back part of seat to the front part of seat when dynamic alteration process; periodically reduce the interface pressure on the buttocks.
In study limitations, the subjects in this study were able-bodied people rather than people with lower-limb disorders, because we concerned about the imposed physiological loads and danger on people with lower-limb disorders for this experiment that required extended processes and multiple sessions of repositioning. In addition, this study focused on reducing the risks of pressure ulcer from a preventive concept and expected participants who had healthy and functional torsos to reach the experiment target. Therefore, we decided to recruit able-bodied people who were not wheelchair users and eliminated those diagnosed with musculoskeletal disorders and spinal pathologies. If applying the study results to wheelchair users, their different pathological characteristics should be considered to ensure feasibility.
In conclusion, the results of this study suggested that FUDS and LFDS can be used to periodically change the distribution of interface pressure on the buttocks. This study can serve as a reference point for clinical physicians or wheelchair users to identify a suitable DST. Thus, further studies should focus on identifying the most adequate adjustment degree and cycle period of the dynamic alteration process.
Declarations
Authors’ contributions
All authors have made substantial contributions to the conception and design, acquisition, analysis and interpretation of data. All authors were involved in drafting the manuscript. All authors read and approved the final manuscript.
Acknowledgements
The authors are very grateful to the participants and staff who participated in this project.
Competing interests
The authors declare that they have no competing interests.
Availability of data and materials
The authors confirm that, for approved reasons, some access restrictions apply to the data underlying the findings. Ethical restrictions prevent public sharing of data. A deidentified data set is available upon request after approval from the Institutional Review Board. Requests for the data may be sent to the corresponding author.
Consent for publication
Consent for publication of individual data has been obtained from all the participants of the study.
Ethics approval and consent to participate
This study was approved by the Institutional Review Board of National Cheng Kung University Hospital and all the participants gave their informed consent.
Funding
This study was supported by Grant No. 104-2221-E-024-019-MY3 from the Ministry of Science and Technology, Taiwan.
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Authors’ Affiliations
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