Kyphosed seated postures: extending concepts of postural health beyond the office

Active workstations: A literature review on workplace sitting

The purpose of this paper is to further understand current literature on prolonged sitting, sitting posture and active sitting solutions. This paper is divided into three sections: The first section (Part I) is a comprehensive overview of the literature on how a static prolonged seated posture can affect: spinal health, trunk posture, contact pressure/discomfort development and vascular issues. The second section (Part II) reviews and qualitatively compares the four working postures recognized in ANSI/HFES 100-2007: reclined sitting, upright sitting, declined sitting and standing. The final section (Part III) is a summary of research on active chairs that revolves around the two types of movement patterns: 1- sustaining continual movement over a range of postures, occasionally reaching neutral lordosis, and 2- maintaining high frequency and duration of daily light contractile activity in the legs (or lower limbs).

Differences in lumbar spine intradiscal pressure between standing and sitting postures: a comprehensive literature review

Background

Musculoskeletal disorders (MSDs), especially in the lumbar spine, are a leading concern in occupational health. Work activities associated with excessive exposure are a source of risk for MSDs. The optimal design of workplaces requires changes in both sitting and standing postures. In order to secure such a design scientifically proved quantitative data are needed that would allow for the assessment of differences in spine load due to body posture and/or exerted force. Intradiscal pressure (IP) measurement in the lumbar spine is the most direct method of estimating spinal loads. Hence, this study aims at the quantitative evaluation of differences in lumbar spine load due to body posture and exerted forces, based on IP reported in publications obtained from a comprehensive review of the available literature.

Methodology

In order to collect data from studies measuring IP in the lumbar spine, three databases were searched. Studies with IP for living adults, measured in various sitting and standing postures, where one of these was standing upright, were included in the analysis. For data to be comparable between studies, the IP for each position was referenced to upright standing. Where different studies presented IP for the same postures, those relative IPs (rIP) were merged. Then, an analysis of the respective outcomes was conducted to find the possible relationship of IPs dependent on a specific posture.

Results

A preliminary analysis of the reviewed papers returned nine items fulfilling the inclusion and exclusion criteria. After merging relative IPs from different studies, rIP for 27 sitting and 26 standing postures was yielded. Some of the data were useful for deriving mathematical equations expressing rIP as a function of back flexion angle and exerted force in the form of a second degree polynomial equation for the standing and sitting positions. The equations showed that for the standing posture, the increase in IP with increasing back flexion angle is steeper when applying an external force than when maintaining body position only. In a sitting position with the back flexed at 20°, adding 10 kg to each hand increases the IP by about 50%. According to the equations developed, for back flexion angles less than 20°, the IP is greater in sitting than in standing. When the angle is greater than 20°, the IP in the sitting position is less than in the standing position at the same angle of back flexion.

Conclusions

Analysis of the data from the reviewed papers showed that: sitting without support increases IP by about 30% in relation to upright standing; a polynomial of the second degree defines changes in IP as a function of back flexion for for both postures. There are differences in the pattern of changes in IP with a back flexion angle between sitting and standing postures, as back flexion in standing increases IP more than in sitting.

Evaluating the biomechanics of an in-between posture to create a multi-posture office environment

BACKGROUND

Prolonged sitting during work is common and has been shown to cause health issues. However, changing working postures has been reported to reduce musculoskeletal issues and impact other health issues; thus, there is a need for an office environment with multiple choices of working postures.

OBJECTIVE

The purpose of this study was to evaluate changes in body position, body loading, and blood perfusion while in a seated, standing, and new office seating position, termed the in-between position.

METHODS

Ground reaction forces, joint angles, pelvic tilt, openness angle (angle between the pelvis plane and thorax), and blood perfusion were evaluated for three positions. A motion capture system with markers was used to capture the position of anatomical landmarks. A six-axis force plate was used to collect the ground reaction forces, and a laser doppler perfusion monitor was used to obtain the blood perfusion.

RESULTS

Data showed that the in-between position articulated the hips, which provided a hip and lumbar position closer to a standing posture than a seated posture. The average vertical ground reaction force in the in-between position was larger than the seated position but significantly smaller than during standing (p < 0.0001). There were no significant differences in anterior/posterior ground reaction forces between the seated and the in-between positions (p = 0.4934). Lastly, blood perfusion increased during the dynamic transitions between positions indicating changes in blood flow.

CONCLUSION

The in-between position provides benefits of both standing (larger pelvic tilt and increased lumbar lordosis) and sitting (reduction in ground reaction forces).

Do different sit-stand workstations influence lumbar kinematics, lumbar muscle activity and musculoskeletal pain in office workers? A secondary analysis of a randomized controlled trial

Purpose. This study investigated the effect of different sit-stand workstations on lumbar spine kinematics, lumbar muscle activity and musculoskeletal pain. Methods. Thirty-two office workers were randomized to one of three sit-stand workstations (Group 1, ratio of minutes spent sitting to standing each hour at work 40:20, n = 8; Group 2, 30:30, n = 6; Group 3, 20:40, n = 7) and a control group (usual sitting, n = 11). Intervention groups (Groups 1, 2 and 3) were collapsed into one group for analysis (n = 21). Data on lumbar kinematics and muscle activity were only collected for 25 participants due to equipment availability. Results. Participants in the intervention group had lower overall lumbar spine flexion angles during the workday compared to the control group (mean difference 10.6°; 95% confidence interval [-18.1, -3.2]; p = 0.008; Cohen's d = 1.5). There were no between-group differences for the remaining kinematic measures (i.e., mean flexion angle in standing and sitting, mean side flexion angle in standing and sitting, and percentage of time in upright sitting), muscle activity or presence of musculoskeletal pain. Conclusions. Sit-stand workstations reduced overall lumbar spine flexion angles over the course of a workday but had no effect on other kinematic measures, lumbar spine muscle activity or musculoskeletal pain.Trial registration: Australian New Zealand Clinical Trials Registry identifier: ACTRN12615001018505..

Physiotherapist perceptions of optimal sitting and standing posture

BACKGROUND

Assessment of, and advice about, spinal posture is common when people with spinal pain present to physiotherapists. Most descriptions regarding optimal spinal posture have been qualitative in nature.

OBJECTIVES

To determine the beliefs of physiotherapists regarding optimal sitting and standing posture.

DESIGN

Online survey.

METHOD

544 Greek physiotherapists selected an optimal sitting (choice of seven) and standing (choice of five) posture, while providing justification for their choice.

RESULTS

Education regarding optimal sitting and standing posture was considered "considerably" or "very" important by 93.9% of participants. Three different sitting postures, and two different standing postures, were selected as the optimal posture by 97.5% and 98.2% of physiotherapists respectively. While this reflects a lack of complete consensus on optimal posture, the most commonly selected postures were all some variation of upright lordotic sitting, in contrast slouched spinal curves (sitting) or forward head posture (sitting and standing) almost never being selected as optimal. Interestingly, participants used similar arguments (e.g. natural curves, muscle activation) to justify their selection regardless of the spinal configuration of each selected posture.

CONCLUSIONS

These results reinforce previous data suggesting that upright lordotic sitting postures are considered optimal, despite a lack of strong evidence that any specific posture is linked to better health outcomes. While postural re-education may play a role in the management of spinal pain for some patients, awareness of such widespread and stereotypical beliefs regarding optimal posture may be useful in clinical assessment and management.

Assessment of the ergonomic risk from saddle and conventional seats in dentistry: A systematic review and meta-analysis

Objective

This study aimed to verify whether the saddle seat provides lower ergonomic risk than conventional seats in dentistry.

Methods

This review followed the PRISMA statement and a protocol was created and registered in PROSPERO (CRD42017074918). Six electronic databases were searched as primary study sources. The "grey literature" was included to prevent selection and publication biases. The risk of bias among the studies included was assessed with the Joanna Briggs Institute Critical Appraisal Tool for Systematic Reviews. Meta-analysis was performed to estimate the effect of seat type on the ergonomic risk score in dentistry. The heterogeneity among studies was assessed using I² statistics.

Results

The search resulted in 3147 records, from which two were considered eligible for this review. Both studies were conducted with a total of 150 second-year dental students who were starting their laboratory activities using phantom heads. Saddle seats were associated with a significantly lower ergonomic risk than conventional seats [right side (mean difference = -3.18; 95% CI = -4.96, -1.40; p < 0.001) and left side (mean difference = -3.12; 95% CI = -4.56, -1.68; p < 0.001)], indicating posture improvement.

Conclusion

The two eligible studies for this review provide moderate evidence that saddle seats provided lower ergonomic risk than conventional seats in the examined population of dental students.

Increased spinal height using propped slouched sitting postures: Innovative ways to rehydrate intervertebral discs

BACKGROUND

Upright and slouched sitting are frequently adopted postures associated with increased intradiscal pressure, spinal height loss and intervertebral disc pathology.

OBJECTIVES

To examine the effects of two sustained propped slouched sitting (PSS) postures on spinal height after a period of trunk loading.

METHODS

Thirty-four participants without a history of low back pain (LBP) were recruited (age 24.4 ± 1.6 years). Subjects sat in (1) PSS without lumbar support and (2) PSS with lumbar support for 10 min, after a period of trunk loading. Spinal height was measured using a stadiometer.

RESULTS

Mean spinal height increase during PSS without lumbar support was 2.94 ± 3.63 mm and with lumbar support 4.74 ± 3.07 mm.

CONCLUSIONS

Both PSS with and without lumbar support significantly increased spinal height after a period of trunk loading (p < 0.001). Such PSS postures can provide a valuable alternative to upright sitting and may be recommended for recovering spinal height in the working environment following periods of loading.

Computer-based estimation of the hip joint reaction force and hip flexion angle in three different sitting configurations

Sitting is part of our daily work and leisure activities and can be performed in different configurations. To date, the impact of different sitting configurations on hip joint loading has not been studied. We therefore evaluated the hip joint reaction force (HJRF) and hip flexion angle in a virtual representative male Caucasian population by means of musculoskeletal modelling of three distinct sitting configurations: a simple chair, a car seat and a kneeling chair configuration. The observed median HJRF in relation to body weight and hip flexion angle, respectively, was 22.3% body weight (%BW) and 63° for the simple chair, 22.5%BW and 79° for the car seat and 8.7%BW and 50° for the kneeling chair. Even though the absolute values of HJRF are low compared to the forces generated during dynamic activities, a relative reduction of over 50% in HJRF was observed in the kneeling chair configuration. Second, the hip flexion angles were both in the kneeling chair (-29°) and simple chair configuration (-16°) lower compared to the car seat and, as such, did not reach the threshold value for femoroacetabular conflict. In conclusion, the kneeling chair appears to hold the greatest potential as an ergonomic sitting configuration for the hip joint.

The effect of a corrective functional exercise program on postural thoracic kyphosis in teenagers: a randomized controlled trial

OBJECTIVE

To investigate the effects of a corrective functional exercise program on postural thoracic kyphosis in teenagers in China.

DESIGN

A single-blind randomized controlled trial including students with a thoracic kyphosis angle (TKA) >40° measured using the SpinalMouse.

SETTING

China Institute of Sport Science and three middle schools in Beijing, China.

SUBJECTS

A total of 181 subjects were included in this trial; of these, 164 subjects were included in the analyses (intervention group, n = 81; control group, n = 83).

INTERVENTION

The intervention group received a functional exercise program designed to correct postural thoracic kyphosis, and the control group received an exercise program designed in accordance with the state-regulated curriculum.

MAIN MEASURES

The primary outcome variable was TKA. Secondary outcome variables were lumbar lordosis angle (LLA), sacral angle (SA), and incline angle (INA) measured in the upright position; thoracic, lumbar, and sacral spine range of motion (ROM) and INA ROM (change in center of gravity) measured in the forward bending and extended positions; and changes in TKA, LLA, SA, and INA measured during the Matthiass test.

RESULTS

There were significant differences in pretest and posttest TKA in both groups (intervention group: pretest 47.09 ± 5.45, posttest 38.31 ± 9.18, P < 0.0001; control group: pretest 47.47 ± 6.06, posttest 43.59 ± 7.49, P < 0.0001). After adjustment for gender and pretest values, there were significant differences in posttest TKA, change in SA, and thoracic ROM in the intervention group compared to the control group ( P < 0.05).

CONCLUSION

The corrective functional exercise program designed for this study improved exaggerated thoracic kyphosis in teenagers.

Comparison of the BackJoy SitSmart Relief and Spine Buddy LT1 H/C Ergonomic Chair Supports on Short-Term Neck and Back Pain

OBJECTIVE

The purpose of this study was to perform a needs assessment to determine whether short-term use of BackJoy SitSmart Relief and Spine Buddy LT1 H/C chair supports influences neck, upper back, and lower back pain.

METHODS

Forty-eight college students (age, 27.5 ± 6.3 years; height, 1.72 ± 0.08 m; body mass, 78.7 ± 19.8 kg; time seated that day, 4.3 ± 2.8 hours; means ± SD) were recruited for this study. The Nordic Musculoskeletal Questionnaire was used to measure pain for the neck, upper back, and lower back regions. Subjects were randomized to sit in a stationary office chair for a single 12-minute period under 1 of 4 conditions: office chair only (control group), BackJoy SitSmart Relief and chair, freezer-cooled Spine Buddy LT1 H/C and chair, or microwave-heated Spine Buddy LT1 H/C and chair. Participants then completed a posttest Nordic Musculoskeletal Questionnaire. A between-within repeated-measures analysis of variance using the between-subject factor intervention (group) and within-subject factor time (baseline and posttest) was used to analyze study data.

RESULTS

The main effect of time across the whole sample was statistically significant for neck (P = .000), upper back (P = .032), and lower back (P = .000) pain; however, there was no statistically significant interaction effect between intervention and time. Thus, as long as participants sat down and rested, symptoms improved similarly across the different groups.

CONCLUSIONS

In this preliminary study, short-term and single use of a support product for an office chair had no additive effect on reducing neck and back pain.

How consistent are lordosis, range of movement and lumbo-pelvic rhythm in people with and without back pain?

BACKGROUND

Comparing movements/postures in people with and without lower back pain (LBP) may assist identifying LBP-specific dysfunction and its relationship to pain or activity limitation. This study compared the consistency in lumbo-pelvic posture and movement (range and pattern) in people with and without chronic LBP (>12 week's duration).

METHODS

Wireless, wearable, inertial measurement units measured lumbar lordosis angle, range of movement (ROM) and lumbo-pelvic rhythm in adults (n = 63). Measurements were taken on three separate occasions: two tests on the same day with different raters and a third (intra-rater) test one to two weeks later. Participants performed five repetitions of tested postures or movements. Test data were captured automatically. Minimal detectable change scores (MDC90) provided estimates of between-test consistency.

RESULTS

There was no significant difference between participants with and without LBP for lordosis angle. There were significant differences for pelvic flexion ROM (LBP 60.8°, NoLBP 54.8°, F(1,63) = 4.31, p = 0.04), lumbar right lateral flexion ROM (LBP 22.2°, NoLBP 24.6° F(1,63) = 4.48, p = .04), trunk right lateral flexion ROM (LBP 28.4°, NoLBP 31.7°, F(1,63) = 5.9, p = .02) and lumbar contribution to lumbo-pelvic rhythm in the LBP group (LBP 45.8 %, F(1,63) = 4.20, NoLBP 51.3 % p = .044). MDC90 estimates for intra and inter-rater comparisons were 10°-15° for lumbar lordosis, and 5°-15° for most ROM. For lumbo-pelvic rhythm, we found 8-15 % variation in lumbar contribution to flexion and lateral flexion and 36-56 % variation in extension. Good to excellent agreement (reliability) was seen between raters (mean r = .88, ICC (2,2)).

CONCLUSION

Comparisons of ROM between people with and without LBP showed few differences between groups, with reduced relative lumbar contribution to trunk flexion. There was no difference between groups for lordosis. Wide, within-group differences were seen for both groups for ROM and lordosis. Due to variability between test occasions, changes would need to exceed 10°-15° for lumbar lordosis, 5°-15° for ROM components, and 8-15 % of lumbar contribution to lumbo-pelvic rhythm, to have 90 % confidence that movements had actually changed. Lordosis, range of movement and lumbo-pelvic rhythm typically demonstrate variability between same-day and different-day tests. This variability needs to be considered when interpreting posture and movement changes.

Is There a Relationship Between Lumbar Proprioception and Low Back Pain? A Systematic Review With Meta-Analysis

OBJECTIVE

To systematically review the relationship between lumbar proprioception and low back pain (LBP).

DATA SOURCES

Four electronic databases (PubMed, EMBASE, CINAHL, SPORTDiscus) and reference lists of relevant articles were searched from inception to March-April 2014.

STUDY SELECTION

Studies compared lumbar proprioception in patients with LBP with controls or prospectively evaluated the relationship between proprioception and LBP. Two reviewers independently screened articles and determined inclusion through consensus.

DATA EXTRACTION

Data extraction and methodologic quality assessment were independently performed using standardized checklists.

DATA SYNTHESIS

Twenty-two studies (1203 participants) were included. Studies measured lumbar proprioception via active or passive joint repositioning sense (JRS) or threshold to detection of passive motion (TTDPM). Data from 17 studies were pooled for meta-analyses to compare patients with controls. Otherwise, descriptive syntheses were performed. Data were analyzed according to measurement method and LBP subgroup. Active JRS was worse in patients compared with controls when measured in sitting (standard mean difference, .97; 95% confidence interval [CI], .31-1.64). There were no differences between groups measured via active JRS in standing (standard mean difference, .41; 95% CI, -.07 to .89) or passive JRS in sitting (standard mean difference, .38; 95% CI, -.83 to 1.58). Patients in the O'Sullivan flexion impairment subgroup had worse proprioception than the total LBP cohort. The TTDPM was significantly worse in patients than controls. One prospective study found no link between lumbar proprioception and LBP.

CONCLUSIONS

Patients with LBP have impaired lumbar proprioception compared with controls when measured actively in sitting positions (particularly those in the O'Sullivan flexion impairment subgroup) or via TTDPM. Clinicians should consider the relationship between sitting and proprioception in LBP and subgroup patients to guide management. Further studies focusing on subgroups, longitudinal assessment, and improving proprioception measurement are needed.

Thoracic and lumbar posture behaviour in sitting tasks and standing: Progressing the biomechanics from observations to measurements

Few studies quantify spinal posture behaviour at both the thoracolumbar and lumbar spinal regions. This study compared spontaneous spinal posture in 50 asymptomatic participants (21 males) during three conditions: 10-min computer task in sitting (participants naïve to the measure), during their perceived 'correct' sitting posture, and standing. Three-dimensional optical tracking quantified surface spinal angles at the thoracolumbar and lumbar regions, and spinal orientation with respect to the vertical. Despite popular belief that lordotic lumbar angles are 'correct' for sitting, this was rarely adopted for 10-min sitting. In 10-min sitting, spinal angles flexed 24(7-9)deg at lumbar and 12(6-8)deg at thoracolumbar regions relative to standing (P < 0.001). When participants 'corrected' their sitting posture, their thoracolumbar angle -2(7)deg was similar to the angle in standing -1(6)deg (P = 1.00). Males were flexed at the lumbar angle relative to females for 10-min sitting, 'correct' sitting and standing, but showed no difference at the thoracolumbar region.

A sloped seat wedge can change the kinematics of the lumbar spine of seated workers with limited hip flexion

[Purpose] The purpose of this study was to determine whether a wedge type seat decreases the lumbar flexion angle of seated workers with limited hip flexion. [Subjects] Twelve sedentary workers with limited hip flexion were recruited. [Methods] Three seat surfaces were used: a level surface, a forward-inclining wedge, and a backward-reclining wedge. The angles of lumbar flexion and pelvic tilt were measured using a three-dimensional motion analysis system. Differences in kinematic data of the subjects seated on the three seat surfaces were analyzed using repeated one-way analysis of variance. [Results] The degree of lumbar flexion decreased significantly when using the forward-inclining wedge compared with the level surface and backward-reclining wedge. [Conclusion] These findings suggest that sitting on a forward-inclining wedge may be useful for minimizing the compensatory lumbar flexion of individuals with limited hip flexion who work in a seated position.

Specific flexion-related low back pain and sitting: comparison of seated discomfort on two different chairs

No study has examined the effectiveness of prescribing seating modifications according to the individual clinical presentation of people with low back pain (LBP). A dynamic, forward-inclined chair ('Back App') can reduce seated paraspinal muscle activation among pain-free participants. This study examined 21 participants whose LBP was specifically aggravated by prolonged sitting and was eased by standing. Low back discomfort (LBD) and overall body discomfort (OBD) were assessed every 15 min while participants sat for 1 h on both the dynamic, forward-inclined chair and a standard office chair. LBD increased significantly more (p = 0.005) on the standard office chair, with no significant difference (p = 0.178) in OBD between the chairs. The results demonstrate that, in a specific flexion-related subgroup of people with LBP, increased LBD during sitting can be minimised through modifying chair design. Mechanisms that minimise seated discomfort may be of relevance in LBP management, as part of a biopsychosocial management plan.

PRACTITIONER SUMMARY

This study examined low back discomfort (LBD) during a typing task among people with low back pain (LBP). Sitting on a dynamic, forward-inclined chair resulted in less seated LBD than sitting on a standard office chair. Further research is required to examine the long-term effectiveness of ergonomics interventions in LBP.

High frequency of McKenzie's postural syndrome in young population of non-care seeking individuals

OBJECTIVES

The role of postural loads as a risk factor for back pain and musculoskeletal symptoms is unclear. McKenzie proposed in his classification of mechanical syndromes a postural syndrome, in which people only develop symptoms from sustained loading, which is relieved by a change in position and has no effect on movement or function. Because of the low level disability with postural syndrome, it was suggested that few seek healthcare for this problem.

METHODS

This study used a two-stage process first to give a questionnaire to 100 students and staff from a university to determine who appeared to have postural syndrome, and then applied a physical examination to those who consented.

RESULTS

One hundred and thirty-eight were approached, of who 100 completed questionnaires and 66% appeared to have postural syndrome. Of the 66 who appeared to have postural syndrome, 37 consented to have a physical examination. Of the 37, 31 met the criteria for postural syndrome, with postural syndrome being significantly associated with pain on sustained loading and pain abolition on posture correction. Most postural syndrome was in the lumbar spine and associated with sitting, but other sites and causes were also noted.

DISCUSSION

This study lends credibility to McKenzie's postural syndrome, but also suggests this as a possible precursor for future more disabling or painful problems. Postural syndrome may not feature in those seeking professional healthcare, but is clearly highly prevalent in a young population.

A pilot investigation into the effects of different office chairs on spinal angles

PURPOSE

To investigate the effects of four office chairs on the postural angles of the lumbopelvic and cervical regions.

RESEARCH QUESTION

Which chair(s) produce an "ideal" spinal posture?

METHODS

An experimental same subject design was used involving healthy subjects (n = 14) who conducted a typing task whilst sitting on four different office chairs; two "dynamic" chairs (Vari-Kneeler and Swopper), and two static chairs (Saddle and Standard Office with back removed). Data collection was via digital photogrammetry, measuring pelvic and lumbar angles, neck angle and head tilt which were then analysed within MatLab. A repeated measures ANOVA with Bonferroni corrections for multiple comparisons was conducted.

RESULTS

Statistically significant differences were identified for posterior pelvic tilt and lumbar lordosis between the Vari-Kneeler and Swopper chairs (p = 0.006, p = 0.001) and the Vari-Kneeler and Standard Office chairs (p = 0.000, 0.000); and also for neck angle and head tilt between the Vari-Kneeler and Swopper chairs (p = 0.000, p = 0.000), the Vari-Kneeler and Saddle chairs (p = 0.002, p = 0.001), the Standard Office and Swopper chairs (p = 0.000, p = 0.000), and the Standard Office and Saddle chairs (p = 0.005, p = 0.001). This study confirms a within region association between posterior pelvic tilt and lumbar lordosis, and between neck angle and head tilt. It was noted that an ideal lumbopelvic position does not always result in a corresponding ideal cervical position resulting in a spinal alignment mismatch.

CONCLUSION

In this study, the most appropriate posture for the lumbopelvic region was produced by the Saddle chair and for the cervical region by both the Saddle and Swopper chairs. No chair consistently produced an ideal posture across all regions, although the Saddle chair created the best posture of those chairs studied. Chair selection should be based on individual need.

A methodology for quantifying seated lumbar curvatures

To understand the role seating plays in the support of posture and spinal articulation, it is necessary to study the interface between a human and the seat. However, a method to quantify lumbar curvature in commercially available unmodified seats does not currently exist. This work sought to determine if the lumbar curvature for normal ranges of seated posture could be documented by using body landmarks located on the anterior portion of the body. The development of such a methodology will allow researchers to evaluate spinal articulation of a seated subject while in standard, commercially available seats and chairs. Anterior measurements of boney landmarks were used to quantify the relative positions of the ribcage and pelvis while simultaneous posterior measurements were made of lumbar curvature. The relationship between the anterior and the posterior measures was compared. The predictive capacity of this approach was evaluated by determining linear and second-order regressions for each of the four postures across all subjects and conducting a leave-one-out cross validation. The relationships between the anterior and posterior measures were approximated by linear and second-order polynomial regressions (r(2 ) =  0.829, 0.935 respectively) across all postures. The quantitative analysis showed that openness had a significant relationship with lumbar curvature, and a first-order regression was superior to a second-order regression. Average standard errors in the prediction were 5.9° for the maximum kyphotic posture, 9.9° for the comfortable posture, 12.8° for the straight and tall, and 22.2° for the maximum lordotic posture. These results show predictions of lumbar curvature are possible in seated postures by using a motion capture system and anterior measures. This method of lumbar curvature prediction shows potential for use in the assessment of seated spinal curvatures and the corresponding design of seating to accommodate those curvatures; however, additional inputs will be necessary to better predict the postures as lordosis is increased.

Physiological measurements of tissue health; implications for clinical practice

Pressure mapping alone insufficiently describes tissue health. Comprehensive, quantitative non invasive assessment is crucial. Interface pressures (IPs) and transcutaneous blood gas levels [transcutaneous tissue oxygen (T(c) PO(2) )] were simultaneously assessed over both ischia and the sacrum to investigate the hypotheses: (i) tissue oxygenation decreases with sustained applied pressure; (ii) tissue oxygen and IP are inversely correlated in loaded soft tissues; (iii) multisite assessments are unnecessary because healthy individuals are symmetrical. Measurements were taken at 5-minute intervals for 20 minutes in both sitting and supine lying for a cohort of 20 able-bodied adults. There were no statistically significant changes over time for either variable in 96% of timepoint comparisons. Specifically, no significant differences were seen between 10 and 20 minutes in either position. These findings imply that a 10-minute assessment can reliably indicate tissue health and that tissue may adapt to applied load over time. No statistically significant correlations between T(c) PO(2) and IP were observed. However, the left and right ischia were significantly different for both variables in supine lying (P < 0.001) and for sitting IP (P < 0.010). Thus, even in this healthy cohort, postural symmetry was not observed and should not be assumed for other populations with restricted mobility. If a multisite technique cannot be used, repeated tissue health assessments must use the same anatomic location.