Kaitlin M. Gallagher

The influence of a seated break on prolonged standing induced low back pain development

With the recent attention to ‘sitting disease’, health practitioners and scientists are promoting standing in the workplace to decrease sedentary time, despite a high prevalence of low back pain (LBP) development during prolonged standing. The purpose of this study was to assess how a seated break inserted between bouts of prolonged standing would influence LBP development, posture and movement. A total of 20 participants stood for 45 minutes, sat for 15 minutes and repeated this sequence while lumbar and thoracic angles were measured, and LBP visual analogue scale reports were taken. Of the sample, 55% participants reported LBP in standing. A stand to sit ratio of 3:1 did not provide lasting recovery of LBP from standing and pain developers utilised a limited range of their lumbar spine angle and increased thoracic extension, resulting in static postures that caused tissue aggravation that was not resolved after 15 minutes of sitting. Prolonged standing in the workplace has the potential to result in LBP for some workers and alternate ways to reduce sedentary time should be investigated. Practitioner Summary: Recommending standing to replace sitting should be undertaken with caution. A ratio of 3:1 (stand to sit) did not mitigate standing induced LBP. Practitioners should consider the interplay between standing and seated work and provide a variety of activities to reduce sedentary time tailored to work, preference and tolerance for an activity.

Possible mechanisms for the reduction of low back pain associated with standing on a sloped surface

Prolonged standing in an occupational setting has long been associated with the development of low back pain. In response to this, researchers have investigated various interventions that can alleviate low back pain and discomfort, such as anti-fatigue mats, shoe insoles, and more recently, sloped platforms. The purpose of this study was to investigate the effects of a sloped surface on kinematics and trunk muscle thickness during quiet and prolonged occupational standing. Eleven participants performed 1-min quiet standing tasks on three surfaces - level ground, incline, and decline - followed by 16-min of prolonged standing in each condition. Trunk, lumbar, and global pelvis angles were measured during each standing condition, and muscle thickness measurements of erector spinae and the lateral abdominal wall were taken during the quiet standing task. During quiet standing, there were systematic changes in trunk, lumbar, and pelvis angles with the different surfaces; however, these changes were not accompanied by systematic changes in muscle thickness. The responses found during the quiet standing were consistent during prolonged standing. As a result, the reduced perceived low back pain found when using sloped platforms is likely not the result of changes in morphology of the trunk musculature, but might be related to the altered kinematics caused by standing on these platforms.

Early static standing is associated with prolonged standing induced low back pain

Previous research points to the lack of movement during prolonged standing as a pre-disposing factor to low back pain (LBP). Such movements could be at the level of the lumbar spine or at the foot-ground interface. The primary purpose of this in vivo study was to determine if there were differences in magnitude, region, and frequency of movement patterns between non-pain developers (non-PDs) and standing induced pain developers (PDs). Thirty-two participants reported their LBP development using a visual analog scale over 2-h of prolonged standing. Time-varying lumbar spine kinematics were used to assess the magnitude and frequency of lumbar spine fidgets and shifts. Ground reaction forces were used to assess the magnitude and frequency of whole body weight transfers and anterior-posterior center of pressure movements. Fourteen of 32 participants (43.75%) were categorized as PDs. The first 15 min of standing distinguished the two pain groups, as non-PD performed a higher frequency of lumbar spine flexion/extension fidgets and large body weight transfers. Both of these differences may be pre-disposing factors for transient LBP development, as they both occurred prior to PDs reaching the 10mm visual analog scale threshold for LBP classification.

Is Standing the Solution to Sedentary Office Work

There has been a major shift toward office workstations that accommodate standing postures. This shift is attributable to negative health and musculoskeletal issues from sedentary exposures. However, changing exposures from sitting to standing does not eliminate these issues, as evidence indicates prolonged standing also induces problems. Reducing seated exposure and rotating frequently between sitting and standing has been shown to result in positive health outcomes, reduced discomfort, and increased work performance. Implementing sit-stand workstations has promise to mitigate work-related health issues, if the users are provided with training that includes accommodations for individual work patterns and preferences.

Effects of anterior shear displacement rate on the structural properties of the porcine cervical spine.

While the individual tissues of the vertebral joint demonstrate viscoelastic properties, the global viscoelastic properties of the lumbar vertebral joint are not well established. This study investigated how changes in displacement rate influenced the mechanical response of the porcine cervical spine (a surrogate or model for the human lumbar spine) exposed to acute anterior shear failure loading. Thirty porcine cervical spine specimens (15 C3-C4 and 15 C5-C6) were placed under a 1600 N compressive load and subsequently loaded in anterior shear to failure at one of three randomly assigned displacement rates (1 mm/s, 4 mm/s, or 16 mm/s). Ultimate anterior shear force, ultimate displacement, average stiffness, and energy stored until failure were calculated. Load rate in the elastic region was also calculated to compare the load rates used in this study to those used in previous studies. Changes in displacement rate affected the C3-C4 and C5-C6 specimens differently. C5-C6 specimens tested at 16 mm/s had an ultimate force that was 28% and 23% higher than at 1 (p=0.0215) and 4 mm/s (p=0.0461), respectively. The average stiffness to failure of the C5-C6 specimens tested at 16 mm/s was 52% higher than at 4 mm/s (p=0.0289). No such differences were found for the C3-C4 specimens. An increase in the anterior shear displacement rate did not necessarily demonstrate viscoelasticity of the vertebral joint. Specimen intervertebral levels were affected differently by changes in anterior shear displacement rate, which may have been a result of anatomical and postural differences between the two levels. Future studies should further investigate the effect of displacement rate on the spine and the inconsistencies between different specimen levels.

Computerised system for measurement of muscle thickness based on ultrasonography.

In this paper, a computerised system for measuring muscle thicknesses of the transverse abdominus (TrA), internal oblique and external oblique muscles based on ultrasonography is presented. The system is designed to allow for quantitative analysis of changes in muscle recruitment and activity, which facilitates the study of such changes and its relationship with low back pain. The abdominal muscle area was localised and imaged under different standing conditions using B-mode ultrasonography. To account for issues such as misalignments due to probe and subject motion as well as speckle noise inherent to ultrasonography, automatic ensemble registration is performed on the acquired images using a sequential quadratic programming approach based on a novel log-Rayleigh likelihood function. Regions of interest are then automatically identified based on the medial border of the TrA for the purpose of quantitative muscle thickness measurements. Experimental results show that the proposed system achieves registration errors of under 0.4 mm when compared with ground-truth measurements, as well as allow for the measurement of muscle thickness changes in the millimetre range. The proposed system is currently in operational use as an analysis tool for studying the relationship between abdominal muscle thickness changes and postural changes.

Foot Placement in Oblique Stair Descent

Extensive research has been conducted on stair safety as a loss of balance due to a misplaced step on a stair can result in a fall and serious injury. One aspect of stair safety that has not been well studied is oblique (angled) stair descent/ascent. Since oblique stair geometry affects the distance travelled and the theoretical symmetry of one’s stance, there are potential implications for fall risk. The purpose of this study was to investigate whether there are adaptations in foot placement that pedestrians demonstrate when descending stairs at oblique angles. Sixteen participants descended steps along two paths – 0 and 45 degrees. Kinematic data of the lower limbs were collected to calculate average step length, average step width, and toe placement. The data suggest that pedestrians compensate for angled descent by narrowing their step width and using a biased foot placement relative to the step edges, such that the inside foot (the foot furthest from the flared side) lands further forward on the step than the outside foot (the foot closest to the flared side). These variations from straight stair descent provide a more symmetric stance for oblique stair descent and may reflect adaptations to reduce the risk of a misstep.

Postural influence on the neutral zone of the porcine cervical spine under anterior-posterior shear load

Segmental instability, characterized by excessive or aberrant movement of the vertebrae can be assessed quantitatively using mechanical characteristics within a region of minimal resistance called the neutral zone. The diagnosis of instability is often used to decide whether or not to surgically fuse the vertebrae. Alterations in flexion/extension posture cause changes in both contact area and spacing between articulating facets that may lead to changes in the mechanical response of the functional spinal unit (FSU) within the neutral zone. This investigation quantified neutral zone (NZ) length under anterior and posterior shear loading and the influence of posture on the shear NZ characteristics of the vertebral joint. Thirty porcine cervical FSUs (15 C34 and 15 C56) were tested. Endplate area was calculated from measurements of the exposed endplates while facet angles were measured from X-rays taken in the transverse plane. Specimens were exposed to a 300 N compressive preload followed by a test to determine flexion/extension NZ limits. These limits were used as target angles during shear passive tests performed in extended and flexed postures. Displacement rate during shear passive tests was 0.2mm/s and five cycles of anterior-posterior shear were performed to a target of ±400 N in a randomized order of extended, neutral and flexed postures. Shear NZ length and average stiffness were quantified. Stiffness within the shear NZ was 67 N/mm in the neutral posture. Extended postures produced a 37% (p<0.0001) increase in shear stiffness within the NZ compared to both flexed and neutral postures. Posture did not influence shear NZ length. Therefore, a true region of zero stiffness does not exist during shear loading with a baseline compressive load. Neutral zone length for the porcine FSU exposed to shear load was not influenced, despite known changes in facet articulation, by changing posture. Average stiffness increased likely as a result of increased contact area and force in extension. The results from this investigation demonstrate that postural deviation of the vertebral joint is not likely a significant confounding factor when assessing segmental stability.

Gait adaptations to different paths of stair descent

Gait characteristics during stair descent have been characterized for a straight descent path; however, pedestrians are likely to encounter a variety of staircase designs that allow one to descend at an angle (i.e. an oblique or monumental staircase). The purpose of this study was to determine the temporospatial lower limb joint kinematics differences between descending a staircase on straight versus oblique descent paths. Sixteen subjects (8 males, 8 females) descended a staircase under three different conditions: straight descent and at a 25° and 45° angle compare to the straight path. Cycle time, cadence, speed, step width, and step length were significantly affected by descent angle, while the proportion of the cycle dedicated to the stance and swing phases remained constant over the descent paths. Peak knee flexion angle increased by approximately 2.5° in the 45° condition compared to the 0° condition (p=0.0044); however, the remainder of the time series was unchanged. A decreased step width and increased step length occurred to allow the foot to sufficiently clear the steps. Changes in the temporospatial variables, hip joint angle and a constant stance/swing proportion demonstrates that these adaptations may be made to maintain characteristics of the gait cycle and prevent subjects from adopting an unfamiliar gait pattern.

A radiographic assessment of lumbar spine posture in four different upright standing positions.

BACKGROUND Approximately 50% of a sample population will develop prolonged standing induced low back pain. The cause of this pain may be due to their lumbar spine posture. The purpose of this study was to investigate differences in lumbar posture between 17 participants categorized as a pain or non-pain developers during level ground standing. A secondary purpose was to evaluate the influence of two standing aids (an elevated surface to act as a foot rest and declined sloped surface) on lumbopelvic posture. METHODS Four sagittal plane radiographs were taken: a normal standing position on level ground, when using an elevated foot rest, using a declined sloped surface, and maximum lumbar spine extension as a reference posture. Lumbosacral lordosis, total lumbar lordosis, and L1/L2 and L5/S1 intervertebral joint angles were measured on each radiograph. FINDINGS There was a significant difference between the lumbosacral lordosis angle and L5/S1 angles in upright versus maximum extension; however, this was independent of pain group. The elevated surface was most effective at causing lumbosacral spine flexion. INTERPRETATION Potentially successful postures for eliminating low back pain during prolonged standing mainly influence the lower lumbar lordosis. Future work should assess the influence of hip posture on low back pain development during standing.