The relationships between lumbar curves, pelvic tilt and joint mobilities in different sitting postures in young adult males

Alignment of the Sternum and Sacrum as a Marker of Sitting Body Posture in Children

An analysis of literature on the methods of assuming a sitting position and the results of our own research indicated the need to search for biomechanical parameters and existing relationships that would enable a description of sitting body posture. The purpose of this paper is to analyze the relationship between the alignment of the body of sternum and sacrum and the changes in the thoracic and lumbar spine curvatures in children. The study involved 113 subjects aged 9-13 years. A planned simultaneous measurement of the angle parameters of the alignment of the body of sternum and sacrum relative to the body's sagittal axis and the angle parameters of the thoracic and lumbar spine curvatures was performed during a single examination session. The proposed markers of alignment in the corrected sitting body posture are characterized by homogeneous results. A high measurement repeatability was observed when determining the corrected body posture in the study setting. It was noted that changes in the alignment of the body of sternum and sacrum resulted in changes in the thoracic kyphosis and lumbar lordosis angle values, which may be an important component of clinical observations of sitting body posture in children. Implementing the body of sternum alignment angle of about 64° relative to the body's sagittal axis in clinical practice as one of the objectives of postural education may be the target solution for sitting body posture correction in children.

Effects of seat height on whole-body movement and lower limb muscle power during sit-to-stand movements in young and older individuals

Sit-to-stand (STS) movements from low seat height are not easily executed by older individuals. Although young individuals increase their lower limb muscle power (LLMP) based on the product of the ground reaction force (GRF) and center of mass velocity (CoMv) during STS movement from a low seat height, it remains unclear whether seat height has an effect on LLMP during STS movement in older individuals. The present study aimed to investigate differences in the LLMP during STS movements when seat height is lowered between young and older individuals. Twelve older and twelve height-matched young individuals were instructed to perform STS movements from low (20 cm), middle (40 cm), and high (60 cm) seat heights. STS movement and GRF were obtained by a motion analysis system and force plates. In the low-seat-height condition, the forward and upward LLMPs and the upward CoMv were significantly lower in older individuals than those in young individuals, but the forward CoMv was not. The completion time of STS movement from a low seat height was significantly longer in older individuals than in young individuals. Our findings suggest that the slower upward CoMv due to the lower upward LLMP extends the completion time of STS movement from a low seat height in older individuals. Furthermore, in the low-seat-height condition, older individuals may move their center of mass (CoM) forward in a different way when compared with young individuals, and they may not use forward LLMP for moving CoM forward.

Changes in external ischial tuberosity width at varying trunk-thigh angles between sexes using two measurement methods

This study examined the influence of two methods and various trunk–thigh (TT) angles on external ischial tuberosity width (EITW) for 45 men and 45 women. In the experiment, the impress and seat pressure methods were applied at TT angles of 60°, 75°, 90°, and 105°. When the impress method was used, EITW remained highly consistent across the four measured TT angles with differences of 2.8 and 2.1 mm for men and women, respectively. Conversely, in the seated pressure method, EITW increased with TT angle such that differences in EITW across a full TT angle range were 11.5 and 11.7 mm for men and women, respectively. Irrespective of method, differences in EITW between genders measured approximately 12.6–13.7 mm across all TT angles. Correlation analyses revealed that hip circumference was positively related to EITW in all cases, whereas the relationship of hip width and depth with EITW varied by method and gender. Because of inherent differences in EITW between genders, these findings suggest that gender variability should be considered in seat cushion design.

Changes in Low Back Muscle Activity and Spine Kinematics in Response to Smartphone Use During Walking

STUDY DESIGN

Within-subject design of an experimental study.

OBJECTIVE

The aim of this study was to determine the effects of smartphone use on the activity level of the lumbar erector spinae muscles and spine kinematics during walking.

SUMMARY OF BACKGROUND DATA

Using a smartphone while walking makes the user hold the phone steady and look downward to interact with the phone. Walking with this non-natural posture of the head and the arms may alter the spine kinematics and increase the muscular load on the low back extensor muscles.

METHODS

Twenty healthy young individuals participated in the laboratory experiment. Each participant walked on a treadmill in five different conditions: normal walking without using a phone, conducting one-handed browsing while walking, two-handed texting while walking, walking with one arm bound, and walking with both arms bound. Spine kinematics variables and the myoelectric activity levels of the lumbar erector spinae muscles were quantified and compared between the five walking conditions.

RESULTS

Participants walked with significantly (P < 0.05) more thoracic kyphosis and lumbar lordosis when using a phone compared to when walking without using the phone. The median level of muscle activity was also 16.5% (browsing) to 31.8% (texting) greater for the two smartphone use conditions than for the normal walking condition, and the differences were significant (P < .05). Between the normal walking and the two bound arm walking conditions, no significant difference in the muscle activity was found.

CONCLUSION

Study results show that the concurrent use of a smartphone while walking could pose a larger muscular load to the lumbar erector spinae muscles than that of normal walking. Habitual use of a smartphone while walking could be a risk factor for low back musculoskeletal problems.Level of Evidence: N/A.

Effects of the posterior pelvic tilt sitting posture on thoracic morphology and respiratory function

[Purpose] We investigated how differences in pelvic angle in the posterior pelvic tilt sitting posture simultaneously affect the thoracic morphology and the respiratory function. [Participants and Methods] The participants were 18 healthy young males. We positioned the pelvis at 0°, 10°, 20°, and 30° of posterior tilt, following which the thoracic expansion volume ratio, thoracic spine tilt angle, and respiratory function were measured. We calculated the thoracic volume and thoracic spine tilt angle by measuring the amount of displacement of reflective markers attached to the thoracic area using the Vicon MX 3D-analysis system. Respiratory function was measured by spirometry. [Results] The expansion volume ratio decreased significantly in response to 10-30° posterior pelvic tilt sitting at the mid-thorax and 30° posterior pelvic tilt sitting at the lowest thorax. The upper thoracic spine level showed a change in anterior tilt at 10-30° posterior pelvic tilt sitting, whereas the lower thoracic spine level showed a change in posterior tilt at 30° posterior pelvic tilt sitting. Respiratory function was significantly lower at 30° posterior pelvic tilt sitting than at 0° posterior pelvic tilt sitting. A positive correlation between thoracic expansion volume ratio and respiratory function was found at 30° posterior pelvic tilt sitting. [Conclusion] Changes in thoracic spine tilt angle due to posterior pelvic tilt sitting may restrict the expansion of thoracic motion during respiration, thereby affecting respiratory function.

New insights into lumbar flexion tests based on inverse and direct kinematic musculoskeletal modeling

Measurement of maximal lumbar flexion is considered to be a crucial element in the assessment of lumbar spine mechanics in situations as diverse as physiotherapy, orthopaedics, ergonomics, sport or aging. However, currently, there is no consensus on a reference test. This study aims to characterise five maximal lumbar flexion tests (four classical tests and a new, specifically-developed test designed to constrain pelvic retroversion) based on a three-dimensional, participant-specific musculoskeletal model. Twenty-six male and female participants performed the five tests. Movements were modelled in OpenSim to estimate change in length in lumbar, hamstring and gluteus muscles, together with lumbar flexion and pelvic tilt. These so-called "inverse" kinematic results were compared using a two-way ANOVA (sex×test). In a second step, lumbar muscle change in length was computed using a direct kinematic method. Lumbar flexion and lumbar muscle change in length were found to be greater when participants were in seated postures, with little pelvic retroversion. Female participants were observed to have less lumbar flexion than male participants (77±14° and 91±12°, respectively). Hip extensor muscles (hamstrings and gluteus) were fully stretched during each of the five tests. Our results highlight the specific roles of hamstrings, gluteus and lumbar muscles into reaching maximal lumbar flexion. Coupling inverse and direct kinematic methods proved to be a useful tool to enhance our knowledge of lumbar tests. Our findings help to characterise the role of the muscles involved in lumbar flexion, and we propose some recommendations for improving and standardising these tests.

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.

ANALYSIS OF LUMBOSACRAL LORDOSIS USING STANDING LATERAL RADIOGRAPHS THROUGH CURVE RECONSTRUCTION

The consensus of the normal magnitude of lumbosacral curve has not been achieved. The Cobb's angle cannot depict the whole contour of this curve. For practical applications, a clearer image of these curves and their aging changes should be further investigated. This study aimed to provide a more consolidate concept of normal lumbosacral curves for clinician through a computerized reconstruction method.

Standing lateral radiographs of lumbosacral spine in 82 normal adults were used for reconstructing the sagittal lumbosacral curves. The geometric characteristics of these curves according to the gender and age groups were studied. Using standing lateral radiographs, reconstruction of the lumbosacral curves was performed through digitization, programming and computation. These curves and related parameters were normalized and averaged for analyzing the differences of gender and age.

The most anteriorward and horizontal vertebrae usually occurred on the L4 and L3 in any gender and age groups. The sacral inclination angle did not change obviously with the increasing ages. A tendency of L1 shifting backward was noted in the age groups of 40 to 60 and above 60 years old. The sagittal lumbosacral curves can be easily reconstructed by digitizing lateral radiographs, The aging changes of lumbosacral curves could be qualitatively described as the flattening of lower lumbar curve and the rearward inclination of upper lumbar curve. The changes occurred obviously above 40 years old. Although individual variations existed, the aging changes and the geometric characteristics such as the most anteriorward or horizontal vertebrae could be used as an important guideline during therapy or surgical correction.

Preferred seat orientation of senior high-school students

The height of the front of the seat is the primary determinant of appropriate seat size in the school setting. In the present study, this dimension was fixed at 445 mm and, using a brief adjustment period, students adjusted the angle of the seat to their preferred rear seat height (PRSH) under three fixed and one adjustable desk height conditions and for one desk height, under two time conditions. PRSH was significantly greater at an 800 mm desk height (454+/-14 mm) compared to 735 mm (447+/-15 mm) and 720 mm (444+/-16 mm). When desk height as well as rear seat height were adjustable, PRSH was 446+/-15 mm and preferred desk height 751+/-25 mm. Taller students or those with larger popliteal heights selected lower PRSHs at all desk heights, with PRSH more strongly related to popliteal height (r = -0.54 to -0.59) than stature (r = -0.44 to -0.50). No differences were found in PRSH between short (<5 min) and long (30 min) adjustment periods for the 735 mm desk height. The nearly horizontal seat positions found in this study were between those recommended by other authors.

Evaluation of spinal internal loads and lumbar curvature under holding static load at different trunk and knee positions

A study was performed to investigate how different trunk and knee positions while holding static loads affect the lumbar curvature and internal loads on the lumbar spine at L4-L5. Ten healthy male subjects participated in this study. Two inclinometers were used to evaluate the curvature of lumbar spine, lordosis, while a 3D static biomechanical model was used to predict the spinal compression and shear forces at L4-L5. Eighteen static tasks while holding three level of load (0, 10 and 20 kg), two levels of knee position (45 and 180 degrees of flexion) and three levels of trunk position (neutral, 15 and 30 degree of flexion) were simulated for 10 healthy male subjects. The results of this study revealed that the lordosis of lumbar spine changed to kyphosis with increasing weight of load from 0 to 20 kg in trunk flexion position (p<0.05), but in squatting position (45 degrees knee full flexion) the higher load did not affect the curvature. The results of this study suggested, at a more flexed trunk and standing position with higher loads both external moment and internal loads increased significantly at L4-L5 level but with 45 knee flexion external moment and compression force increased and shear force decreased significantly (p < 0.05). Subjects made more effort to maintain stability of the body in squat position. The highest external moment and compression force were computed at flexed knee and trunk position with highest loads. Hence holding weight in this position must be avoided by implementing ergonomic change to the workplace.

Stability of sitting postures: the influence of degrees of freedom

Observational studies of sitting have shown that, during spontaneous sitting, people adopt a variety of postures. Various researchers have formulated theories to explain why people adopt their sitting postures. Branton (1969) hypothesized that there is continual need for postural stability while sitting. Dempster (1955) stated that additional stability could be obtained through temporarily closing chains of body segments, or, in other words, through decreasing the number of degrees of freedom of the body. The present study elaborates on Dempster's theory. The aim of this study was to determine the influence of the degrees of freedom of the body on postural stability in sitting postures. For 21 different sitting postures, the total number of degrees of freedom was determined. Postural sway, a measure for postural stability, was determined using a 3D motion and position measurement system with ten healthy subjects. This study shows that the mean path length at the level of the second thoracic vertebra (PL0.05), a measure derived from postural sway, increases significantly (p < 0.0001) with an increase of the number of degrees of freedom of the body (DoFB). Closer examination of the data showed that a model taking into account only the degrees of freedom of the lumbar and thoracic spine and pelvis seems to be a better predictor of postural sway than the total number of degrees of freedom of the body.

Lumbopelvic kinematics and trunk muscle activity during sitting on stable and unstable surfaces

STUDY DESIGN

A single-group comparative study.

OBJECTIVES

To compare lumbopelvic kinematics and muscle activation patterns while sitting on stable and unstable surfaces.

BACKGROUND

Unstable surfaces are commonly used during the rehabilitation of certain low back pain disorders. The benefits postulated are increased muscle activity and facilitation of sustainable midrange positions via neuromuscular control. The use of unstable sitting devices in the workplace is controversial, as the postulated increase in muscle activity is thought to lead to a muscle fatigue/pain response. However, little evidence exists for or against the ability of these devices to alleviate or prevent spinal pain.

METHODS AND MEASURES

This study included 26 healthy adults (14 male, 12 female). Fastrak 3-dimensional motion analysis detected lumbar curvature, pelvic tilt, and postural sway during sitting on a stable and unstable surface over 5-minute periods. Surface electromyography was used to measure activity in the superficial lumbar multifidus, transverse fibers of internal oblique, and iliocostalis lumborum pars thoracis.

RESULTS

Spinal postures were similar for sitting on a stable and unstable surface. Significant increases in postural sway were detected (P = .013) in 3 dimensions of movement during sitting on an unstable surface. Gender differences were noted. No EMG amplitude or variance differences were detected between seating conditions.

CONCLUSIONS

Preliminary data show that sitting on unstable surfaces induces greater spinal motion, but does not significantly alter the lumbosacral posture nor the amount of activity in the superficial trunk muscles under investigation.

Scheuermann kyphosis: the importance of tight hamstrings in the surgical correction

STUDY DESIGN

A historic cohort study of the sagittal alignment in 33 consecutive patients with surgically corrected thoracic Scheuermann kyphosis.

OBJECTIVES

To determine if postsurgical imbalance, sagittal malalignment, and decreased lumbar-pelvic range of motion in patients with thoracic Scheuermann kyphosis is related to tight hamstrings.

SUMMARY OF BACKGROUND DATA

Tight hamstrings are a frequent sign in Scheuermann kyphosis. The importance of tight hamstrings in the surgical management of Scheuermann kyphosis has not yet been studied.

METHODS

Thirty-three patients with Scheuermann kyphosis were managed by surgical correction and fusion. Tight hamstrings, lumbar-pelvic range of motion, and sagittal balance were evaluated. Sixteen patients had tight hamstrings, and 17 patients had nontight hamstrings. Hamstrings were considered tight if the popliteal angle was >30 degrees.

RESULTS

Patients with tight hamstrings have a significantly greater risk of postoperative imbalance (P = 0.05), and these patients can only compensate for this risk by reducing their lumbar lordosis (P = 0.0227). Furthermore, the limitations in the lumbar and pelvic range of motion are predicted by tight hamstrings (P <or= 0.005).

CONCLUSION

Tight hamstrings can be considered as an important factor in the surgical management of thoracic Scheuermann kyphosis. Tight hamstring patients can be classified as "lumbar compensators" and as such are prone to overcorrection and imbalance. Preoperative assessment of the lumbar-pelvic range of motion and tight hamstrings should therefore be advised. Extensive fusion of the lumbar segments might compromise the lumbar compensation mechanism and induces further risk of imbalance.

Is the sagittal configuration of the cervical spine changed in women with chronic whiplash syndrome? A comparative computer-assisted radiographic assessment

OBJECTIVE

To reveal whether women with chronic whiplash-associated disorder (WAD) symptoms, grade I-II, demonstrate regional and/or segmental radiographic signs of altered cervical lordosis.

DESIGN

Case-control study.

SETTING

Radiography department at a university hospital.

PARTICIPANTS

Three age-balanced groups comprising 120 women. The case group included women with chronic whiplash syndrome (n = 41), and the control group included women with chronic insidious onset neck pain (n = 39) and an asymptomatic group (n = 40), who were given baseline data. The sample was referred from informed doctors and physiotherapists.

INTERVENTION

The women sat in a standardized sitting position and radiographs were taken in a lateral position with fluoroscopic control for alignment.

OUTCOME MEASURES

Two distinct measurements were taken; 1 of the angles of the upper and lower cervical curvatures, respectively, and 1 of the angles between the inferior borders of each pair of vertebrae in the lower cervical spine. The 3 groups were compared on the ratio of the lower to upper cervical spine angles and on the mean angular values for each segment in the cervical spine.

RESULTS

The whiplash group showed a decreased ratio between the lower versus upper cervical spine but comparisons between groups were not statistically significant. The whiplash group was in a significantly more flexed position at the C4-C5 level compared with the asymptomatic group (P =.007). The reliability measures have to be strengthened to render these results definitely conclusive.

CONCLUSION

The whiplash group exhibited a different configuration of cervical lordosis. This is clinically important and needs to be studied more closely.

Posterior pelvic tilt in patients with decreased lumbar lordosis decreases acetabular femoral head covering

The relationship between pelvic tilt and acetabular femoral head covering was determined in 38 patients with decreased lumbar lordosis. Posterior pelvic tilt and acetabular femoral head covering were measured on radiographs taken in both supine and standing positions. Previously reported normal values obtained from 96 patients were used as controls. Posterior pelvic tilt increased (P<.01) in patients with decreased lumbar lordosis and anterior acetabular femoral head covering decreased (P<.0001) compared with the controls. These differences were more remarkable in the standing position than in the supine position. Patients with decreased lumbar lordosis have decreased femoral head covering, especially in the standing position.

The relationship between tight hamstrings and lumbar hypolordosis in children with cerebral palsy

STUDY DESIGN

Retrospective clinical and radiographic review.

OBJECTIVE

To assess the influence of tight hamstrings on the sagittal alignment of the thoracic and lumbar spine in children with cerebral palsy.

SUMMARY OF BACKGROUND DATA

It is postulated that tight hamstrings may produce a hypolordosis of the lumbar spine. The abnormal sagittal contour of the spine may lead to increased stresses in the lumbar spine and subsequent pain and disability. This is of special concern in children with cerebral palsy who often have shortened spastic hamstring muscles.

METHODS

Twenty-one patients were evaluated, with a mean age of 9.4 years. Standing and sitting lateral spine films were obtained and the lumbar lordosis and thoracic kyphosis were measured using the Cobb method. The popliteal angle was measured to assess hamstring tightness, such that a large popliteal angle indicates tight hamstrings.

RESULTS

We found a statistically significant correlation between the sitting lumbar curve and popliteal angle (Pearson correlation value -0.77, P < 0.01). As the popliteal angle increased, the amount of lumbar lordosis decreased. This correlation was less significant when the patient was standing (Pearson correlation value -0.59).

CONCLUSION

This study demonstrates that there is a correlation between tight hamstrings, as measured by the popliteal angle, and decreasing lumbar lordosis, especially when sitting.

Sitting biomechanics part I: review of the literature

OBJECTIVE

To develop a new sitting spinal model and an optimal driver's seat by using review of the literature of seated positions of the head. spine, pelvis, and lower extremities.

DATA SELECTION

Searches included MEDLINE for scientific journals, engineering standards, and textbooks. Key terms included sitting ergonomics, sitting posture, spine model, seat design, sitting lordosis, sitting electromyography, seated vibration, and sitting and biomechanics.

DATA SYNTHESIS

In part I, papers were selected if (1) they contained a first occurrence of a sitting topic, (2) were reviews of the literature, (3) corrected errors in previous studies, or (4) had improved study designs compared with previous papers. In part II, we separated information pertaining to sitting dynamics and drivers of automobiles from part 1.

RESULTS

Sitting causes the pelvis to rotate backward and causes reduction in lumbar lordosis, trunk-thigh angle, and knee angle and an increase in muscle effort and disc pressure. Seated posture is affected by seat-back angle, seat-bottom angle and foam density, height above floor, and presence of armrests.

CONCLUSION

The configuration of the spine, postural position, and weight transfer is different in the 3 types of sitting: anterior, middle, and posterior. Lumbar lordosis is affected by the trunk-thigh angle and the knee angle. Subjects in seats with backrest inclinations of 110 to 130 degrees, with concomitant lumbar support, have the lowest disc pressures and lowest electromyography recordings from spinal muscles. A seat-bottom posterior inclination of 5 degrees and armrests can further reduce lumbar disc pressures and electromyography readings while seated. To reduce forward translated head postures, a seat-back inclination of 110 degrees is preferable over higher inclinations. Work objects, such as video monitors, are optimum at eye level. Forward-tilting, seat-bottom inclines can increase lordosis, but subjects give high comfort ratings to adjustable chairs, which allow changes in position.