Kappa Delta Award. Low back pain and whole body vibration

City bus seat vibration analysis using 6-axis accelerometer and gyroscope sensors

This paper analyses different modes and cycles of seat vibration in city buses by analysing acceleration peak magnitudes and their trends and fluctuations in the time domain. The purpose is to find peak vibration modes that exist in the driving patterns of city buses. Analysing peaks in a time series is essential for many applications specifically in vibration analysis because they represent significant events. Using a 6-axis inertial measurement unit device which has accelerometer and gyroscope sensors data were collected from a number of city buses operating. By applying algorithmic filters the g-force peaks present in different acceleration modes were analysed. The particularity of city bus seat vibration and g-force acceleration levels due to effective acceleration in 3-axes are presented and discussed, namely: longitudinal (forward motion), lateral (side-to-side) and vertical (bounce mode) accelerations. It was found that the bus seat root mean square acceleration magnitude of approximately 0.33 g occurred from the major acceleration cycles during bus running. In longitudinal, lateral and vertical directions, 20% of peak acceleration cycles were above 0.20 g, 0.18 g and 0.27 g respectively. Jerk may be a better indicator of passenger discomfort. The results from this study can provide future reference to research directions into understanding city bus seat vibration levels in longitudinal, lateral and vertical directions and also initiatives to mitigate excess bus seat vibration for the riders.

Complex Neck Loading and Injury Tolerance in Lateral Bending With Head Rotation From Human Cadaver Tests

Advancements in automated vehicles may position the occupant in postures different from the current standard posture. It may affect human tolerance responses. The objective of this study was to determine the lateral bending tolerance of the head-cervical spine with initial head rotation posture using loads at the occipital condyles and lower neck and describe injuries. Using a custom loading device, head-cervical spine complexes from human cadavers were prepared with load cells at the ends. Lateral bending loads were applied to prerotated specimens at 1.5 m/s. At the occipital condyles, peak axial and antero-posterior and medial-lateral shear forces were: 316-954 N, 176-254 N, and 327-508 N, and coronal, sagittal, and axial moments were: 27-38 N·m, 21-38 N·m, and 9.7-19.8 N·m, respectively. At the lower neck, peak axial and shear forces were: 677-1004 N, 115-227 N, and 178-350 N, and coronal, sagittal, and axial moments were: 30-39 N·m, 7.6-21.3 N·m, and 5.7-13.4 N·m, respectively. Ipsilateral atlas lateral mass fractures occurred in four out of five specimens with varying joint diastasis and capsular ligament involvements. Acknowledging that the study used a small sample size, initial tolerances at the occipital condyles and lower neck were estimated using survival analysis. Injury patterns with posture variations are discussed.

Feasibility of a Capacity Building Organizational Intervention for Worker Safety and Well-being in the Transportation Industry: Pivoting to Address the COVID-19 Pandemic and Social and Political Unrest in Chile

OBJECTIVE

This study developed, implemented, and evaluated the feasibility of executing an organizational capacity building intervention to improve bus driver safety and well-being in a Chilean transportation company. Method: Through an implementation science lens and using a pre-experimental mixed methods study design, we assessed the feasibility of implementing a participatory organizational intervention designed to build organizational capacity. Result: We identified contextual factors that influenced the intervention mechanisms and intervention implementation and describe how the company adapted the approach for unexpected external factors during the COVID-19 pandemic and social and political unrest experienced in Chile. Conclusions: The intervention enabled the organization to create an agile organizational infrastructure that provided the organization's leadership with new ways to be nimbler and more responsive to workers' safety and well-being needs and was robust in responding to strong external forces that were undermining worker safety and well-being.

Effect of Wheels, Casters and Forks on Vibration Attenuation and Propulsion Cost of Manual Wheelchairs

Manual wheelchair users are exposed to whole-body vibrations as a direct result of using their wheelchair. Wheels, tires, and caster forks have been developed to reduce or attenuate the vibration that transmits through the frame and reaches the user. Five of these components with energy-absorbing characteristics were compared to standard pneumatic drive wheels and casters. This study used a robotic wheelchair propulsion system to repeatedly drive an ultra-lightweight wheelchair over four common indoor and outdoor surfaces: linoleum tile, decorative brick, poured concrete sidewalk, and expanded aluminum grates. Data from the propulsion system and a seat-mounted accelerometer were used to evaluate the energetic efficiency and vibration exposure of each configuration. Equivalence test results identified meaningful differences in both propulsion cost and seat vibration. LoopWheels and SoftWheels both increased propulsion costs by 12-16% over the default configuration without reducing vibration at the seat. Frog Legs suspension caster forks increased vibration exposure by 16-97% across all four surfaces. Softroll casters reduced vibration by 11% over metal grates. Wide pneumatic 'mountain' tires showed no difference from the default configuration. All vibration measurements were within acceptable ranges compared to health guidance standards. Out of the component options, softroll casters show the most promising results for ease of efficiency and effectiveness at reducing vibrations through the wheelchair frame and seat cushion. These results suggest some components with built-in suspension systems are ineffective at reducing vibration exposure beyond standard components, and often introduce mechanical inefficiencies that the user would have to overcome with every propulsion stroke.

Vibrotactile somatosensory stimulus to assist the transition from level walking to stair ascent in the elderly: a pilot study

Background

Although, in daily living, almost all stair ambulation is conducted posterior to level walking, or vice versa, there are only a few studies related to the transition compared to the studies on steady-state stair walking.

Furthermore, neuromotor control in the instant of the transition is different from that of the steady-state stair walking. However, there are only a few studies investigating the transition from level walking to stair ascent in the elderly by comparing with young adults, and there is no study on the assistance of the transition movement in the elderly who are experiencing neurophysiological changes.

Thus, this pilot study aimed to compare the flat surface-to-stair ascent transition by the elderly to that seen in young adults, and to investigate how vibrotactile somatosensory stimulus (VSS), which has a positive effect on muscle performance and gait, affects the transition tasks in elderly people.

Results

In the first half of the stance phase, the elderly exhibited a higher moment and power of the hip extensor and a less moment and power of the knee extensor compared with young adults. In the second half of the stance phase, positive plantar-flexor power and support moment was higher in the elderly. In addition, during the single-limb support phase, dorsiflexion was maintained in the elderly, whereas young adults appeared to have decreased dorsiflexion.

When the VSS was applied, the moment and power of the hip extensor, the plantar-flexor moment, and the support moment in the entire of the stance phase were increased. In addition, it was found that the degree of the kinetics parameters was different depending on the frequencies of the VSS.

Conclusions

This pilot study has revealed evident biomechanical differences between elderly people and young adults during the transition from level walking to stair ascent. Additionally, it has shown that the VSS may accentuate the features of the transition movement of the elderly and regulate joint kinetics. The results of the present pilot study can provide a base for further research and understanding of movement, which can be utilized in designing assistance aids for the elderly.

Trial registration

CRIS, KCT0005434, Registered 25 September 2020, Retrospectively registered.

Estimating whole-body vibration limits of manual wheelchair mobility over common surfaces

Whole-body vibration (WBV) experienced during manual wheelchair use was quantified across several types of terrain (tile, sidewalk, decorative bricks, expanded metal grates). Over-ground travel was controlled using a robotic propulsion system. Vibrations along the vertical axis were measured with a triaxial accelerometer mounted to the seat of the wheelchair. Root-mean-square acceleration values were compared to the health guidance exposure limits established by the European Council using the WBV calculator tool published by the Health and Safety Executive (HSE). Vibrations along the vertical axis were well below the exposure values associated with health risks. Even the most aggressive tactile surface (grates) tested in this study would require more than 14 h of daily travel to reach the "exposure action value," and more than 24 h would be required to reach the "exposure limit value". Considering the average cumulative duration of active self-propulsion among manual wheelchair users is around an hour or less, none of the tested conditions were deemed unsafe or damaging.

Exposure to Whole-Body Vibration in Commercial Heavy-Truck Driving in On- and Off-Road Conditions: Effect of Seat Choice

Trucking is a key industry in Canada with around 180 000 professional drivers. As an industry it has a disproportionately high injury claim rate, particularly for back injuries. Whole-body vibration (WBV) can contribute to the onset and development of low back disorders, and is a well-documented exposure among driving professions. A widely adopted WBV mitigation measure focuses on hydraulic and/or pneumatic passive suspension systems both in the driver's seat and underneath the vehicle cab. Passive suspension 'air-ride' seats are the current industry standard but new technologies such as the electromagnetic active vibration cancelling (EAVC) seats offer potentially substantial improvements in WBV reduction. In this paper, we evaluate and compare four commonly used truck seats (three air-ride, one EAVC) for their vibration damping characteristics and WBV exposure attenuation in on- and off-road conditions. We recruited 24 professional truck drivers who drove 280 km (mixed on-road and off-road) in ore-haul trucks under four different seating conditions. Following the ISO 2631-1 WBV standard, vibration measurements were made on the cab floor and seat pad, and 8-h average weighted vibration (A(8)) and 8-h vibration dose values (VDV(8)) were calculated, as well as the Seat Effective Amplitude Transmissibility (SEAT), and daily vibration action limits (DVALs). These measures were compared between seat types, as well as road conditions. The EAVC seat gave best performance for both A(8) (0.27 m s-2) and VDV(8) (6.6 m s-1.75). The EAVC also had the highest SEAT of the seats tested (36.2%) and the longest DVAL. However, among the three passive air-suspension seats, two showed significantly reduced A(8) (0.43 and 0.44 m s-2) and VDV(8) (9.1 and 9.3 m s-1.75) exposures relative to the third passive air-suspension seats [A(8) (0.54 m s-2) and VDV(8) (11.1 m s-1.75)]. These differences in exposures among the three passive air-suspension seats resulted in varying DVAL times, with the worst performing seat reaching the DVAL after only 6.3 h of driving. There was also a seat by road type interaction; there were performance differences between the passive air-suspension seats on-road, but not off-road. The observed reduction of the WBV exposures measured from the EAVC seat was consistent with previous results. But we showed that there can also be substantive differences among seats that are the current industry standard. These differences were more evident on-road than off-road, which suggests that more work needs to be done to understand seat performance characteristics, and in matching the correct seat technology to the driving task. We demonstrated that WBV exposures in current industry conditions may exceed health-based exposure limits; this has policy relevance because WBV exposures are linked to prevalent and costly adverse health conditions in a working population that is ageing. Increased WBV measurement collection is recommended to ensure the anticipated exposure attenuations are achieved when seats are relied upon as an engineered control against WBV.

Working Conditions Influencing Drivers' Safety and Well-Being in the Transportation Industry: "On Board" Program

The conditions of work for professional drivers can contribute to adverse health and well-being outcomes. Fatigue can result from irregular shift scheduling, stress may arise due to the intense job demands, back pain may be due to prolonged sitting and exposure to vibration, and a poor diet can be attributed to limited time for breaks and rest. This study aimed to identify working conditions and health outcomes in a bussing company by conducting focus groups and key informant interviews to inform a Total Worker Health^® organizational intervention. Our thematic analysis identified three primary themes: lack of trust between drivers and supervisors, the scheduling of shifts and routes, and difficulty performing positive health behaviors. These findings demonstrate the value of using participatory methods with key stakeholders to determine the unique working conditions and pathways that may be most critical to impacting safety, health, and well-being in an organization.

Psychological Effects of Heart Rate and Physical Vibration on the Operation of Construction Machines: Experimental Study

BACKGROUND

A construction method has emerged in which a camera is installed around a construction machine, and the operator remotely controls the machine while synchronizing the vibration of the machine with the images seen from the operator's seat using virtual reality (VR) technology. Indices related to changes in heart rate (HR) and physical vibration, such as heart rate variability (HRV) and multiscale entropy (MSE), can then be measured among the operators. As these indices are quantitative measures of autonomic regulation in the cardiovascular system, they can provide a useful means of assessing operational stress.

OBJECTIVE

In this study, we aimed to evaluate changes in HR and body vibration of machine operators and investigate appropriate methods of machine operation while considering the psychological load.

METHODS

We enrolled 9 remote operators (18-50 years old) in the experiment, which involved 42 measurements. A construction machine was driven on a test course simulating a construction site, and three patterns of operation-riding operation, remote operation using monitor images, and VR operation combining monitor images and machine vibration-were compared. The heartbeat, body vibration, and driving time of the participants were measured using sensing wear made of a woven film-like conductive material and a three-axis acceleration measurement device (WHS-2). We used HRV analysis in the time and frequency domains, MSE analysis as a measure of the complexity of heart rate changes, and the ISO (International Standards Organization) 2631 vibration index. Multiple regression analysis was conducted to model the relationship among the low frequency (LF)/high frequency (HF) HRV, MSE, vibration index, and driving time of construction equipment. Efficiency in driving time was investigated with a focus on stress reduction.

RESULTS

Multiple comparisons conducted via the Bonferroni test and Kruskal-Wallis test showed statistically significant differences (P=.05) in HRV-LF/HF, the vibration index, weighted acceleration, motion sickness dose value (MSDVz), and the driving time among the three operation patterns. The riding operation was found to reduce the driving time of the machine, but the operation stress was the highest in this case; operation based on the monitor image was found to have the lowest operation stress but the longest operation time. Multiple regression analysis showed that the explanatory variables (LH/HF), RR interval, and vibration index (MSDVz by vertical oscillation at 0.5-5 Hz) had a negative effect on the driving time (adjusted coefficient of determination R2=0.449).

CONCLUSIONS

A new method was developed to calculate the appropriate operating time by considering operational stress and suppressing the physical vibration within an acceptable range. By focusing on the relationship between psychological load and physical vibration, which has not been explored in previous studies, the relationship of these variables with the driving time of construction machines was clarified.

Assessment of physical work demands of long-distance industrial gas delivery truck drivers

AIM

The aim of this study was to assess the work-related physical demands of long-distance truck drivers employed by a large gas delivery company in Canada.

METHODS

A total of 15 truck drivers participated in a data collection that included self-reporting assessments, field observations, and direct measurements to describe daily tasks organization, postural demands, physical workload, and force exertions.

RESULTS

Truck drivers' work was characterized by long working days ranging from 9.9 to 15.1 h (mean = 11.4 h), with half (49%) of the total working time spent behind the wheel. The overall workload as measured by relative cardiac strain (18.7% RHR) was found excessive for the long term given the shift duration. Peaks of heart rate in excess of 30 beats per minute above the daily average occurred mainly while operating valves and handling heavy hoses during gas deliveries. The task of delivering gas at a client's site required a moderate work rate on average (8.3 mlO₂/kg/min) requiring 24.4% or maximum work capacity on average.

CONCLUSION

Based on multiple data sources, this study highlights the risks of over-exertion and of excessive physical fatigue in the truck drivers' work that are coherent with the high prevalence of self-reported musculoskeletal pain in this group of workers.

Prevalence of work related musculoskeletal disorders among occupational bus drivers of Karnataka, South India

BACKGROUND

Work-related health problems result in an economic loss of 4-6% in GDP (Gross domestic Product) of the most countries. In the industrialized countries, 1/3rd of the health-related absence to duty are due to musculoskeletal disorders. Professional driving is one such occupation which looks like sedentary occupation, but involves many risk factors that contribute to work-related musculoskeletal disorders (WMSD) due to its nature of working and work environment. This research describes the various risk factors associated with WMSDs and their effects on drivers health.

OBJECTIVE

To assess the prevalence of WMSD and its associated risk factors among the bus drivers of Karnataka State Road Transport Corporation (KSRTC), Karnataka.

METHODS

Subjects considered in this study are 301 full-time bus drivers from the central division KSRTC which consists of 6 depots in Bengaluru. Information regarding reported WMSD symptoms during immediate past 7 days to 12 months, the intervention of WMSD in their day-to-day life and the overall comfort of the body are determined through Standardized Nordic Questionnaire and also by direct observation. The survey questionnaire is conducted by face to face interview.

FINDINGS

From the statistical analysis, it is found that around 55.8% of the study population has experienced WMSD. The prevalence of WMSD is most common in the age group of 29-39 years (53.5%) followed by the age group of >40 years.

CONCLUSION

In this study, some of the work-related and lifestyle/health-related factors show significant association with WMSD in bus drivers of Karnataka. Musculoskeletal disorders can be prevented by designing the driver's workspace ergonomically so that the design suits to all sorts of drivers and the drivers should also be trained on basics of vehicle ergonomics (posture, seat adjustments, in-vehicle controls adjustments).

INTERPRETATION

KSRTC should educate drivers on the basics of vehicle ergonomics, harmful use of tobacco/alcohol, unhealthy food habits and also to involve in physical exercise at least 75-150 mins weekly. If not, the trend of drivers suffering from WMSD belonging to mid-age will increase exponentially.

SCOPE FOR FUTURE WORK

Statistical result and direct observation insist on undertaking further studies on ergonomic interventions at driver's cabin, lifestyle/occupational health factors which mitigate WMSD in different parts of the body during driving.

A Systematic Literature Review of Various Control Techniques for Active Seat Suspension Systems

Drivers of heavy trucks are exposed to large amounts of vibration which can lead to serious health risks. Many suspension systems/methods can be used to isolate these transmitted vibrations, such as vehicle suspension systems, cabin suspension systems and seating suspension systems. The central idea of the work is to identify the research gaps and raise our future research questions in this specific area. The novelty of this paper is proposing a model predictive controller for active vibration control of seating suspension systems. A systematic literature review of the existing work of the vibration control of seating suspension systems has been conducted. Various control techniques that are used in the seating suspension systems have been summarized and evaluated. This paper focusses on the biodynamic model of the driver and seat for the first step needed in the design of the seating suspension system. Then, it illustrates the different types of the system vibration controls and their performance evaluation methods. At the end, the paper details several active seating suspension systems including their actuation system structures and control algorithms which are used in the heavy vehicle trucks.

Evaluation of commercially available seat suspensions to reduce whole body vibration exposures in mining heavy equipment vehicle operators

As mining vehicle operators are exposed to high level of Whole body vibration (WBV) for prolonged periods of time, approaches to reduce this exposure are needed for the specific types of exposures in mining. Although various engineering controls (i.e. seat suspension systems) have been developed to address WBV, there has been lack of research to systematically evaluate these systems in reducing WBV exposures in mining heavy equipment vehicle settings. Therefore, this laboratory-based study evaluated the efficacy of different combinations of fore-aft (x-axis), lateral (y-axis), and vertical (z-axis) suspensions in reducing WBV exposures. The results showed that the active vertical suspension more effectively reduced the vertical vibration (∼50%; p's < 0.0001) as compared to the passive vertical suspension (10%; p's < 0.11). The passive fore-aft (x-axis) and lateral (y-axis) suspension systems did not attenuate the corresponding axis vibration (p's > 0.06) and sometimes amplified the floor vibration, especially when the non-vertical vibration was predominant (p's < 0.02). These results indicate that there is a critical need to develop more effective engineering controls including better seat suspensions to address non-vertical WBV exposures, especially because these non-vertical WBV exposures can increase risks for adverse health effects including musculoskeletal loading, discomfort, and impaired visual acuity.

Intervertebral Disk Nutrients and Transport Mechanisms in Relation to Disk Degeneration: A Narrative Literature Review

Objective

The purpose of this paper was to review the literature regarding the mechanisms leading to degeneration in intervertebral disks and to discuss contributing mechanical and biological factors.

Methods

The inclusion criteria for the literature review were research studies conducted in the last 3 decades with free full-text available in English. Review articles and articles pertaining to temporomandibular joints and joints of the body other than the intervertebral disk were excluded. The following databases were searched: PubMed, EBSCOhost, and Google Scholar through September 9, 2016.

Results

A total of 57 articles were used in this review. Intervertebral disk cells require glucose for sustainability and oxygen to synthesize matrix components. Nutrients enter the disk via 2 vascular supply routes: capillary beds of end plates and the peripheral annulus fibrosus. Solute size, shape and charge, compression, and metabolic demand all influence the efficiency of nutrient transport, and alterations of any of these factors may have effects on nutrient transport and, potentially, disk degeneration.

Conclusions

Progressive nutrient transport disruptions may actively contribute in advancing the phases of degenerative disk disease. Such disruptions include dysfunctional loading and spinal position, lack of motion, high frequency loading, disk injury, aging, smoking, an acidic environment, and a lack of nutrient bioavailability.

A Study on the Improvement of Walking Characteristics of the Elderly with Vibration Stimuli Applied to the Tibialis Anterior Tendon

The purpose of this study was to identify the gait pattern of the elderly with aging and to analyze the elderly's gait changes by the focal tendon vibratory stimulation. A total of 10 elderly males and 15 young adult males participated in this study. Using 3D motion analysis, we analyzed that difference between the elderly gait and young adults gait and the changes of the elderly gait by applying focal vibratory stimuli. As a result, specifically in the early stance, the elderly's gait was more flexed and the lower extremity extensors of the elderly worked harder. When the focal vibratory stimuli were applied, joint angle of the elderly was induced to that of the young adults. There was a reduction in demands for supporting bodies and progressing gait in the stance phase. This means that focal vibratory stimuli affect the gait of the elderly. Also, the changes of the gait of the elderly varied according to the characteristics of the focal vibratory stimuli. This implies that the activity of the motor may be dependent on vibratory stimuli characteristics.

Matrix homeostasis within the immature annulus fibrosus depends on the frequency of dynamic compression: a study based on the self-developed mechanically active bioreactor

Evidence suggests that mechanical load is related to structural destruction of disk annulus fibrosus (AF) either in adult disk degeneration or in child disk acute injury. Both biochemical and biomechanical properties are different between immature and mature disks. However, the effects of mechanical compression on immature AF are not fully clear. This study was to investigate the effects of a relatively wide range of dynamic compressive frequency on matrix homeostasis within the immature AF. Immature disks from pig (3-4 months) were randomly assigned into the control group (non-compression) and compression groups (0.1, 0.5, 1.0, 3.0 and 5.0 Hz). All disks were bioreactor-cultured for 7 days. AF matrix production was evaluated by histology, gene expression, glycosaminoglycan (GAG) content, hydroxyproline (HYP) content and immunohistochemistry. Generally, no obvious difference was found in HE staining between control group and compression groups. However, alcian blue staining indicated proteoglycan content in the 5.0-Hz group was decreased compared with the control group and other compression groups. Similarly, a catabolic remodeling gene expression profile with the down-regulated matrix genes (aggrecan, collagen I and collagen II) and tissue inhibitor of metalloproteinases (TIMP-1 and TIMP-3) and the up-regulated matrix catabolic enzymes (ADAMTS-4 and MMP-3) was found in the 5.0-Hz group. Further analysis indicated that GAG content, HYP content and aggrecan protein deposition were also decreased in the 5.0-Hz group. Hence, we concluded that matrix homeostasis within the immature AF was compressive frequency dependent, and the relatively higher frequency (5.0 Hz) is unfavorable for matrix production within the immature AF. These findings will contribute to further understanding of the relationship between mechanical compression and immature AF biosynthesis.

Whole-body vibration induces pain and lumbar spinal inflammation responses in the rat that vary with the vibration profile

Whole-body vibration (WBV) is linked epidemiologically to neck and back pain in humans, and to forepaw mechanical allodynia and cervical neuroinflammation in a rodent model of WBV, but the response of the low back and lumbar spine to WBV is unknown. A rat model of WBV was used to determine the effect of different WBV exposures on hind paw behavioral sensitivity and neuroinflammation in the lumbar spinal cord. Rats were exposed to 30 min of WBV at either 8 or 15 Hz on days 0 and 7, with the lumbar spinal cord assayed using immunohistochemistry at day 14. Behavioral sensitivity was measured using mechanical stimulation of the hind paws to determine the onset, persistence, and/or recovery of allodynia. Both WBV exposures induce mechanical allodynia 1 day following WBV, but only the 8 Hz WBV induces a sustained decrease in the withdrawal threshold through day 14. Similarly, increased activation of microglia, macrophages, and astrocytes in the superficial dorsal horn of the lumbar spinal cord is only evident after the painful 8 Hz WBV. Moreover, extracellular signal-regulated kinase (ERK)-phosphorylation is most robust in neurons and astrocytes of the dorsal horn, with the most ERK phosphorylation occurring in the 8 Hz group. These findings indicate that a WBV exposure that induces persistent pain also induces a host of neuroimmune cellular activation responses that are also sustained. This work indicates there is an injury-dependent response that is based on the vibration parameters, providing a potentially useful platform for studying mechanisms of painful spinal injuries. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1439-1446, 2016.

The Impact of Posture on the Mechanical Properties of a Functional Spinal Unit During Cyclic Compressive Loading

To assess how posture affects the transmission of mechanical energy up the spinal column during vibration, 18 porcine functional spinal units (FSUs) were exposed to a sinusoidal force (1500 ± 1200 N) at 5 Hz for 120 min in either a flexed, extended, or neutral posture. Force and FSU height were measured continuously throughout the collection. From these data, specimen height loss, dynamic stiffness, hysteresis, and parameters from a standard linear solid (SLS) model were determined and analyzed for differences between postures. Posture had an influence on all of these parameters. In extension, the FSU had higher dynamic stiffness values than when neutral or flexed (p < 0.0001). In flexion, the FSU had higher hysteresis than both an extended or neutral posture (p < 0.0001). Height loss was greatest in a flexed posture and smallest in an extended posture (p < 0.0001). In extension, the series spring element in the SLS model had a stiffness value higher than both flexed and neutral posture conditions, whereas the stiffness in the parallel spring was the same between extension and neutral (p < 0.01), both higher than in flexion. Viscosity coefficients were highest in extension compared to both flexed and neutral (p < 0.01). Based on these results, it was determined that posture had a significant influence in determining the mechanical properties of the spine when exposed to cyclic compressive loading.

Dynamic Compression Effects on Immature Nucleus Pulposus: a Study Using a Novel Intelligent and Mechanically Active Bioreactor

BACKGROUND

Previous cell culture and animal in vivo studies indicate the obvious effects of mechanical compression on disc cell biology. However, the effects of dynamic compression magnitude, frequency and duration on the immature nucleus pulposus (NP) from an organ-cultured disc are not well understood.

OBJECTIVE

To investigate the effects of a relatively wide range of compressive magnitudes, frequencies and durations on cell apoptosis and matrix composition within the immature NP using an intelligent and mechanically active bioreactor.

METHODS

Discs from the immature porcine were cultured in a mechanically active bioreactor for 7 days. The discs in various compressive magnitude groups (0.1, 0.2, 0.4, 0.8 and 1.3 MPa at a frequency of 1.0 Hz for 2 hours), frequency groups (0.1, 0.5, 1.0, 3.0 and 5.0 Hz at a magnitude of 0.4 MPa for 2 hours) and duration groups (1, 2, 4 and 8 hours at a magnitude of 0.4 MPa and frequency of 1.0 Hz) experienced dynamic compression once per day. Discs cultured without compression were used as controls. Immature NP samples were analyzed using the TUNEL assay, histological staining, glycosaminoglycan (GAG) content measurement, real-time PCR and collagen II immunohistochemical staining.

RESULTS

In the 1.3 MPa, 5.0 Hz and 8 hour groups, the immature NP showed a significantly increase in apoptotic cells, a catabolic gene expression profile with down-regulated matrix molecules and up-regulated matrix degradation enzymes, and decreased GAG content and collagen II deposition. In the other compressive magnitude, frequency and duration groups, the immature NP showed a healthier status regarding NP cell apoptosis, gene expression profile and matrix production.

CONCLUSION

Cell apoptosis and matrix composition within the immature NP were compressive magnitude-, frequency- and duration-dependent. The relatively high compressive magnitude or frequency and long compressive duration are not helpful for maintaining the healthy status of an immature NP.

Occupational driving as a risk factor for low back pain in active-duty military service members

BACKGROUND CONTEXT

Although occupational driving has been associated with low back pain, little has been reported on the incidence rates for this disorder.

PURPOSE

To determine the incidence rate and demographic risk factors of low back pain in an ethnically diverse and physically active population of US military vehicle operators.

STUDY DESIGN/SETTING

Retrospective database analysis.

PATIENT SAMPLE

All active-duty military service members between 1998 and 2006.

OUTCOME MEASURES

Low back pain requiring visit to a health-care provider.

METHODS

A query was performed using the US Defense Medical Epidemiology Database for the International Classification of Diseases, Ninth Revision, Clinical Modification code for low back pain (724.20). Multivariate Poisson regression analysis was used to estimate the rate of low back pain among military vehicle operators and control subjects per 1,000 person-years, while controlling for sex, race, rank, service, age, and marital status.

RESULTS

A total of 8,447,167 person-years of data were investigated. The overall unadjusted low back pain incidence rate for military members whose occupation is vehicle operator was 54.2 per 1,000 person-years. Compared with service members with other occupations, motor vehicle operators had a significantly increased adjusted incidence rate ratio (IRR) for low back pain of 1.15 (95% confidence interval [CI] 1.13-1.17). Female motor vehicle operators, compared with males, had a significantly increased adjusted IRR for low back pain of 1.45 (95% CI 1.39-1.52). With senior enlisted as the referent category, the junior enlisted rank group of motor vehicle operators had a significantly increased adjusted IRR for low back pain: 1.60 (95% CI 1.52-1.70). Compared with Marine service members, those motor vehicle operators in both the Army, 2.74 (95% CI 2.60-2.89), and the Air Force, 1.98 (95% CI 1.84-2.14), had a significantly increased adjusted IRR for low back pain. The adjusted IRRs for the less than 20-year and more than 40-year age groups, compared with the 30- to 39-year age group, were 1.24 (1.15-1.36) and 1.23 (1.10-1.38), respectively.

CONCLUSIONS

Motor vehicle operators have a small but statistically significantly increased rate of low back pain compared with matched control population.

Health risks of vibration exposure to wheelchair users in the community

OBJECTIVE

The purpose of this study was to evaluate whole-body vibration (WBV) exposure to wheelchair (WC) users in their communities and to determine the effect of WC frame type (folding, rigid, and suspension) in reducing WBV transmitted to the person.

DESIGN

An observational case-control study of the WBV exposure levels among WC users.

PARTICIPANTS

Thirty-seven WC users, with no pressure sores, 18 years old or older and able to perform independent transfers.

MAIN OUTCOME MEASURES

WC users were monitored for 2 weeks to collect WBV exposure, as well as activity levels, by using custom vibration and activity data-loggers. Vibration levels were evaluated using ISO 2631-1 methods.

RESULTS

All WC users who participated in this study were continuously exposed to WBV levels at the seat that were within and above the health caution zone specified by ISO 2631-1 during their day-to-day activities (0.83 ± 0.17 m/second(2), weighted root-mean-squared acceleration, for 13.07 ± 3.85 hours duration of exposure). WCs with suspension did not attenuate vibration transmitted to WC users (V = 0.180, F(8, 56) = 0.692, P = 0.697). Conclusions WBV exposure to WC users exceeds international standards. Suspension systems need to be improved to reduce vibrations transmitted to the users.

Safety and severity of accelerations delivered from whole body vibration exercise devices to standing adults

OBJECTIVES

Whole body vibration devices are used as a means to augment training, and their potential to treat a range of musculoskeletal diseases and injuries is now being considered. The goal of this work is to determine the degree to which acceleration delivered by whole body vibration devices at the plantar surfaces of a standing human is transmitted through the axial and appendicular skeleton, and how this mechanical challenge corresponds to the safety threshold limit values established by the International Standards Organization ISO-2631.

DESIGN

Non-blinded laboratory assessment of a range of whole body vibration devices as it pertains to acceleration transmission to healthy volunteers.

METHODS

Using skin and bite-bar mounted accelerometers, transmissibility to the tibia and cranium was determined in six healthy adults standing on a programmable whole body vibration device as a function of frequency and intensity. Measures of transmissibility were then made from three distinct types of whole body vibration platforms, which delivered a 50-fold range of peak-to-peak acceleration intensities (0.3-15.1 gp-p; where 1g is Earth's gravitational field).

RESULTS

For a given frequency, transmissibility was independent of intensity when below 1g. Transmissibility declined non-linearly with increasing frequency. Depending on the whole body vibration device, vibration ranged from levels considered safe by ISO-2631 for up to 8h each day (0.3 gp-p @ 30 Hz), to levels that were seven times higher than what is considered a safe threshold for even 1 min of exposure each day (15.1 gp-p @ 30 Hz). Transmissibility to the cranium was markedly attenuated by the degree of flexion in the knees.

CONCLUSIONS

Vibration can have adverse effects on a number of physiologic systems. This work indicates that readily accessible whole body vibration devices markedly exceed ISO guidelines for safety, and extreme caution must be practiced when considering their use.

Challenges and strategies in the repair of ruptured annulus fibrosus

Lumbar discectomy is the surgical procedure most frequently performed for patients suffering from low back pain and sciatica. Disc herniation as a consequence of degenerative or traumatic processes is commonly encountered as the underlying cause for the painful condition. While discectomy provides favourable outcome in a majority of cases, there are conditions where unmet requirements exist in terms of treatment, such as large disc protrusions with minimal disc degeneration; in these cases, the high rate of recurrent disc herniation after discectomy is a prevalent problem. An effective biological annular repair could improve the surgical outcome in patients with contained disc herniations but otherwise minor degenerative changes. An attractive approach is a tissue-engineered implant that will enable/stimulate the repair of the ruptured annulus. The strategy is to develop three-dimensional scaffolds and activate them by seeding cells or by incorporating molecular signals that enable new matrix synthesis at the defect site, while the biomaterial provides immediate closure of the defect and maintains the mechanical properties of the disc. This review is structured into (1) introduction, (2) clinical problems, current treatment options and needs, (3) biomechanical demands, (4) cellular and extracellular components, (5) biomaterials for delivery, scaffolding and support, (6) pre-clinical models for evaluation of newly developed cell- and material-based therapies, and (7) conclusions. This article highlights that an interdisciplinary approach is necessary for successful development of new clinical methods for annulus fibrosus repair. This will benefit from a close collaboration between research groups with expertise in all areas addressed in this review.

Whole-body vibration: is there a causal relationship to specific imaging findings of the spine?

STUDY DESIGN

Systematic review.

OBJECTIVE

To perform a systematic review of the available literature for those studies that evaluated the role of whole-body vibration (WBV) on the spine, using imaging modalities as well as an estimation of WBV exposure.

SUMMARY OF BACKGROUND DATA

Numerous comparative studies have reported a possible association between the occurrence of spinal symptoms and exposure to WBV. These exposures have commonly been examined in the work environment largely through self-reported questionnaires only. From a scientific perspective, the majority of studies emphasize symptoms and lack objective medical evidence, such as spinal imaging, to help establish a specific spinal disorder. Because both neck and low back pain comprise symptoms that can arise from a host of factors including age, a casual link between spinal disorders and WBV cannot be affirmed.

METHODS

MEDLINE and EMBASE were searched for studies related to WBV and spinal symptoms, diagnosis, and/or disorders. Our searches were limited to studies published prior to August 2011. The resulting 700 citations (after excluding 354 duplicates) were then screened by 3 independent reviewers on the basis of the following predetermined inclusion and exclusion criteria: inclusion-clinical studies with imaging evaluation (radiographs, computed tomographic scans, and/or magnetic resonance images) and documented WBV exposure (occupation, amount of WBV, and/or duration); exclusion-reliance solely on self-reporting of symptoms (neck pain, low back pain, and/or sciatica), those articles based on a clinical diagnosis without use of imaging, and in vitro/animal/biomechanical studies.

RESULTS

Only 7 studies met the inclusion criteria for this systematic review. Included were 5 retrospective cohort and 2 cross-sectional studies. Although mixed results and conclusions were found, the majority of studies did not identify an association between WBV exposure and an abnormal spinal imaging finding indicating damage of the spine. We should also stress that each included study has limitations secondary to quantifying WBV exposure accurately, both as a single encounter and as a total exposure over years.

CONCLUSION

Based on our results from this systematic review, no causality can be shown between WBV and abnormal spinal imaging findings. With the conflicting data available in the literature, WBV has not been established as a cause for objective spinal pathological changes on a scientific basis.

Multi-factorial causative model for back pain management; relating causative factors and mechanisms to injury presentations and designing time- and cost effective treatment thereof

Back pain resolution has not statistically improved over many years with some literature suggesting chronic back pain to be increasing. From a search of literature on causes, events, mechanisms, factors and treatment for back pain, a model is developed that relates causes of back injury to factors that result in pain through two primary mechanisms; muscle fatigue and muscle/tendon/connective tissue strain or sprain with other main mechanisms being diminished reactivity and strength, changes in tendon/tissue mechanical properties and fear of back pain recurrence/fear of movement following a back pain episode. The model highlights the fact that back pain/injury is multi-factorial with numerous circular relationships. Therefore treatment should also be multi-factorial; a combination of physical and psychological therapy with attention to mechanisms at work or in daily living that exacerbate the injury and delay recovery thereof. Exercise is one method that can reduce muscle imbalance, improve resilience to muscle fatigue, and address reactivity and strength. More importantly, eccentric exercise can rectify musculotendinous or connective tissue injury which plays a role in prolonging the back injury cycle. Posture is identified as a causative factor for back pain with the time exposure for posture representing the largest portion of daily activities. From literature and from clinical observation, treatment methods can be improved and incorporated into integrated multi-modal programs. An integrated exercise program that commences with motor control exercise and progresses into functional movement is suggested. Furthermore a modification of the McKenzie extension movement may benefit back injury rehabilitation for a majority of lower back pain patients. Otherwise the sit-to-stand movement is a regular and frequent exacerbating mechanism of back pain and likely continuously tears connective tissue during the movement thus prolonging the cycle of back pain and can be addressed instantly with a modification in sit-to-stand technique.

Wavelet analysis of lumbar muscle oxygenation signals during whole-body vibration: implications for the development of localized muscle fatigue

The objective of this study was to assess the effects of whole-body vibration (WBV) on lumbar muscle oxygenation oscillations in healthy men based on the wavelet transform of near-infrared spectroscopy signals. Twelve healthy participants were exposed to WBV at frequencies of 3, 4.5 and 6 Hz while muscle oxygenation signal was monitored before, during and recovery from WBV. With spectral analysis based on wavelet transform of NIR signal, six frequency intervals were identified (I, 0.005-0.0095 Hz; II, 0.0095-0.02 Hz; III, 0.02-0.06 Hz; IV, 0.06-0.16 Hz; V, 0.16-0.40 Hz and VI, 0.40-2.0 Hz). It was found that the muscle oxygenation oscillations at 4.5 Hz in the frequency intervals I, II and III was lower during WBV compared with that of at 3 Hz. Present results demonstrated WBV at 4.5 Hz induced lower oscillatory activities than that of at 3 Hz. The lower oscillatory activities might indicate a decrease in the efficiency of oxygen supply to the oxygenated tissue and such mechanism might contribute to the development of local muscle fatigue.

The effects of dynamic loading on the intervertebral disc

Loading is important to maintain the balance of matrix turnover in the intervertebral disc (IVD). Daily cyclic diurnal assists in the transport of large soluble factors across the IVD and its surrounding circulation and applies direct and indirect stimulus to disc cells. Acute mechanical injury and accumulated overloading, however, could induce disc degeneration. Recently, there is more information available on how cyclic loading, especially axial compression and hydrostatic pressure, affects IVD cell biology. This review summarises recent studies on the response of the IVD and stem cells to applied cyclic compression and hydrostatic pressure. These studies investigate the possible role of loading in the initiation and progression of disc degeneration as well as quantifying a physiological loading condition for the study of disc degeneration biological therapy. Subsequently, a possible physiological/beneficial loading range is proposed. This physiological/beneficial loading could provide insight into how to design loading regimes in specific system for the testing of various biological therapies such as cell therapy, chemical therapy or tissue engineering constructs to achieve a better final outcome. In addition, the parameter space of 'physiological' loading may also be an important factor for the differentiation of stem cells towards most ideally 'discogenic' cells for tissue engineering purpose.

Does vibration influence the initiation of intervertebral disc herniation? An examination of herniation occurrence using a porcine cervical disc model

STUDY DESIGN

In vitro biomechanics, randomized control trial.

OBJECTIVE

The objectives of this study were 2-fold: first, to determine the effect of exposure to axial vibration on the initiation and progression of disc herniation; second, to determine the effect of vibration exposure and the presence of disc damage on the mechanical properties of individual lamella from the annulus.

SUMMARY OF BACKGROUND DATA

Vibration exposure has been linked to a higher reporting of low back pain and disc herniation via epidemiological studies. However, these studies are unable to determine causal relationships. In vitro tissue experimentation assists in determining if certain exposures, for example vibration, actually lead to herniation.

METHODS

A total of 20 porcine (aged, 6-8 months; similar skeletal development as an adolescent human) functional spine units (FSU) were subjected to repetitive flexion-extension (6000 cycles), which has been shown to produce intervertebral disc herniation. While being exposed to the repeated flexion/extension, 10 FSUs were statically compressed under 1400 N (control group) and the other 10 were cyclically compressed (1260-1540 N) at a frequency of 5 Hz (vibration group). Post collection, intervertebral discs were dissected and individual lamella of the annulus was tested under uniaxial tension to failure (tension applied perpendicular to the orientation of the collagen fibers) to isolate the mechanical properties of the intralamellar matrix.

RESULTS

Of the 10 control FSUs, 4 had evidence of herniation initiation while 8 of the 10 vibrated FSUs showed herniation initiation (P ∇ 0.01). No significant differences in disc height loss or FSU stiffness were observed between the control and vibrated groups. Further, no signficant differences were observed between the 2 groups for any of the single lamella mechanical properties.

CONCLUSION

This study confirmed that vibration is a causal mechanical risk factor that significantly increases the occurrence of herniation.

The combined effects of limited nutrition and high-frequency loading on intervertebral discs with endplates

STUDY DESIGN

Whole ovine caudal intervertebral discs were cultured under simulated-physiologic or high-frequency loading and either sufficient or limited nutrition for 7 days.

OBJECTIVE

To study the effect of high-frequency loading under sufficient or limited glucose conditions and to investigate the additive effects of load and nutrition on cell survival, gene expression, and cell activity after 7 days of culture.

SUMMARY OF BACKGROUND DATA

Limited nutrition and certain mechanical stimuli are generally believed to be etiologic factors for disc degeneration. Although these effects and their interactions have been demonstrated in cell culture, no investigations have been reported in entire discs.

METHODS

Discs were maintained in a whole organ culture bioreactor system under simulated-physiologic (0.2 Hz) or high-frequency (10 Hz) loading, in media with either limited (2 g/L) or sufficient (4.5 g/L) glucose concentration. After 7 days, cell viability, relative gene expression, newly synthesized chondroitin sulfate content, glycosaminoglycan synthesis rate, and disc morphology were assessed after culture and compared with fresh tissue.

RESULTS

Culture under either limited glucose or high-frequency loading conditions led to a significant drop in cell viability. Combined treatment with limited glucose and high-frequency loading resulted in an additive increase in cell death in both the anulus fibrosus and nucleus pulposus and in an increase in MMP13 gene expression.

CONCLUSION

Supporting in vivo studies and cell culture experiments, high-frequency loading simulating vibration conditions shows detrimental effects on intervertebral disc cells in whole organ culture. The effect on cell viability was exacerbated by limited nutrition culture. However, neither frequency nor limited glucose affected cell metabolism, measured by glycosaminoglycan synthesis rate. Longer culture periods may be required to detect changes at the extracellular matrix level.

Car driving with and without a movable back support: Effect on transmission of vibration through the trunk and on its consequences for muscle activation and spinal shrinkage

The aim of this study was to test the effect of a movable backrest on vibration transmission through the trunk during driving and on the physiological consequences thereof. Eleven healthy male subjects drove for about 1 h on normal roads with a movable and with a fixed backrest while surface electromyography (EMG) was measured at the level of the fifth lumbar vertebra (L5) and vertical accelerations were measured at the seat, backrest and at the spine at the levels of the second sacral vertebra (S2) and seventh cervical vertebra (C7). The movable backrest significantly reduced accelerations at C7 by up to 11.9% at the 5 Hz frequency band. The movable backrest also significantly reduced the coherence and transmission between S2 and C7 accelerations, but not the differential motion between these sensors. EMG at both sides of L5 was on average 28% lower when using the movable backrest. Spinal shrinkage was unaffected by backrest type. It is concluded that a movable backrest reduces the transmission of vibration through the trunk and that it reduces low back EMG. Car driving is associated with the risk of developing low back pain and this may be related to exposure to whole body vibration. This study found an effect of a simple ergonomics measure on the transmission of vibration through the trunk as well as on back muscle activation.

Functional changes in cerebral and paraspinal muscle physiology of healthy women during exposure to whole-body vibration

The objective of this study was to investigate the effects of whole-body vibration on multiple tissues simultaneously in fourteen healthy women. On three separate days, participants were exposed to frequencies, 3, 4.5, or 6 Hz (at 0.9 g(r.m.s) acceleration in vertical direction) per day on a simulator for 16 min. While sitting 'with' and 'without' backrest support, participants also performed handgrip contractions for 1 min. Cerebral and lumbar muscle oxygenation and blood volume responses were measured using near-infrared spectroscopy. Cardiorespiratory responses were collected using a metabolic cart. In general, cerebral and cardiorespiratory responses increased with vibration compared to without vibration, whereas in the lumbar region oxygenation and blood volume responses decreased. Greatest cerebral responses were observed at 6 Hz (P<0.05). When compared to exposure to vibration without performing work, significant decrease in lumbar responses was observed during handgrip contractions in both conditions of sitting 'with' and 'without' a backrest (P<0.05). Such decreases in the lumbar responses suggest postural load due to prolonged sitting combined with physical activity during vibration, might reduce vascular supply to the paraspinal muscles. This study reiterates the importance of understanding the physiological basis for various health disorders in women due to exposure to whole-body vibration.

Work-related musculoskeletal disorders in urban bus drivers of Hong Kong

INTRODUCTION

Work-related musculoskeletal disorders (WMSD) affect workers in many occupations including drivers of large vehicles. Urban bus drivers have been found to have high prevalence rates of back problems in overseas studies. Hong Kong is a densely populated city and has a large number of double-deck buses that constitute a major means of public transportation. The present study aimed at investigating the prevalence and characteristics of WMSD in male and female bus drivers who operate double-deck buses in Hong Kong.

METHOD

Altogether 481 bus drivers (404 males, 77 females) participated in the study that consisted of a questionnaire survey as well as physical assessment. The questionnaire included questions on work, musculoskeletal complaints and perceived occupational risk factors associated with each discomfort. Physical assessment consisted of measurement of lumbar spine mobility, hand grip strength, sit-and-reach test, and observation of standing and sitting postures.

RESULTS

The results showed generally the male drivers had longer years of work experience but their daily workloads were similar to the females. On the average drivers worked 9-10 h per day, with 5 days on and 1 day off. Neck, back, shoulder and knee/thigh areas had the highest 12-month prevalence rates ranging from 35% to 60%, and about 90% of the discomfort was related to bus-driving. Occupational factors of prolonged sitting and anthropometric mismatch were perceived to be most related to musculoskeletal discomfort. On physical examination, grip strength was significantly related to neck and shoulder discomfort.

CONCLUSIONS

The present results showed high prevalence rates of WMSD among bus drivers in Hong Kong which warrants further investigation.

Frequency response of pig intervertebral disc cells subjected to dynamic hydrostatic pressure

The pathogenesis of vibration-induced disorders of intervertebral disc at the cellular level is largely unknown. Dynamic loads with frequencies close to that of the in vivo human spine resonant frequency (4-6 Hz) have a destructive effect, which may induce extracellular disc matrix (ECM) degradation. To investigate this issue, three-dimensional (3D) alginate cultures of normal pig intervertebral disc nucleus and inner annulus cells were tested under dynamic hydrostatic loading. Alginate cultures of each region were divided into six groups; five groups were exposed to cyclic hydrostatic pressures of frequencies 1, 3, 5, 8, and 10 Hz with the same amplitude (1 MPa), and group 6 was the control group (no loading). Cultures of different groups were loaded for 3 days (30 min daily) in a hydraulic chamber. Effects of loading frequency on disc collagen and protein metabolism were investigated by measuring 3H-proline-labeled proteins associated with the cells in the extracellular matrix and release of 3H-proline-labeled molecules into culture medium. The results indicated a poor synthesis rate and more degradation near the 5 Hz frequency. The repeatability of experiments was verified by performing two experiments with the same protocol. Both experiments indicated that a threshold frequency of around 5 Hz disrupted protein metabolism.

In vivolumbar erector spinae oxygenation and blood volume measurements in healthy men during seated whole-body vibration

Exposure to whole-body vibration is implicated as one of the occupational risk factors for lower back disorders; however, its influence on the lumbar muscle physiology is still poorly understood. The objective of this study was to investigate the effects of backrest support and hand grip contractions on lumbar muscle oxygenation and blood volume responses during seated whole-body vibration using continuous dual-wave near-infrared spectroscopy. Thirteen healthy men were exposed to frequencies of 3, 4.5 and 6 Hz on a vibration simulator, in randomized order on separate days. Each day the duration of the protocol was 30 min. During the fifth minute of vibration 'with' and 'without' backrest support, participants performed maximal rhythmic hand grip contractions for 1 min. In general, erector spinae oxygenation and blood volume showed a trend to decrease with vibration exposure compared to the control condition. However, these responses were not influenced by the change in vibration frequency (P > 0.05). Sitting without backrest resulted in a greater decrease in oxygenation (by 27%, P = 0.02) and blood volume (by 11%, P = 0.05) than with backrest, implying a deficiency in oxygen supply owing to the sitting posture. Compared to the vibration-only condition, hand grip work decreased both oxygenation (by 22%, P = 0.003) and blood volume responses (by 13%, P = 0.04), suggesting that postural load due to prolonged sitting combined with physical activity during vibration might further burden paraspinal muscles. The influence of adipose tissue thickness of the lumbar muscle on optically derived oxygenation and blood volume changes was inconclusive.

Status of activator methods chiropractic technique, theory, and practice

OBJECTIVE

To provide an historical overview, description, synthesis, and critique of the Activator Adjusting Instrument (AAI) and Activator Methods Chiropractic Technique of clinical assessment.

METHODS

Online resources were searched including Index to Chiropractic Literature, EBSCO Online, MANTIS, CHIROLARS, CINAHL, eJournals, Ovid, MDConsult, Lane Catalog, SU Catalog, and Pubmed. Relevant peer-reviewed studies, commentaries, and reviews were selected. Studies fell into 2 major content areas: instrument adjusting and the analysis system for therapy application. Studies were categorized by research content type: biomechanical, neurophysiological, and clinical. Each study was reviewed in terms of contribution to knowledge and critiqued with regard to quality.

DISCUSSION

More than 100 studies related to the AAI and the technique were found, including studies on the instrument's mechanical effects, and a few studies on clinical efficacy. With regard to the analysis, there is evidence for good reliability on prone leg-length assessment, but to date, there is only 1 study evaluating the Activator Methods Chiropractic Technique analysis.

CONCLUSION

A body of basic science and clinical research has been generated on the AAI since its first peer-reviewed publication in 1986. The Activator analysis may be a clinically useful tool, but its ultimate scientific validation requires testing using sophisticated research models in the areas of neurophysiology, biomechanics, and statistical analysis.

Acute physiological responses in healthy men during whole-body vibration

OBJECTIVE

The influence of backrest support and handgrip contractions on acute metabolic, respiratory, and cardiovascular responses were evaluated in 13 healthy men during exposure to whole-body vibration (WBV).

METHODS

Following assessment of aerobic fitness during arm cranking, subjects were exposed to frequencies 3, 4.5, and 6 Hz with 0.9 g(r.m.s) acceleration magnitude on a vibrating base in randomized order, on separate days. Each exposure included 6 min baseline without WBV, 8 min of WBV exposure either 'with' or 'without' backrest, 4 min recovery, followed by 8 min of WBV with opposite backrest condition, and 4 min recovery. During the final minute of WBV, subjects performed right hand maximal rhythmic handgrip contractions for one minute. During baseline and before completion of WBV session 'with' and 'without' backrest, cardiac output was estimated indirectly by carbon dioxide rebreathing.

RESULTS

At 3 and 4.5, and 3 and 6 Hz, absolute and relative oxygen uptake demonstrated significantly greater responses during sitting 'without' backrest than 'with' backrest (P<0.01). At 3 and 4.5 Hz, heart rate and oxygen pulse responses were significantly greater during WBV combined with handgrip contractions than during WBV alone (P<0.01), demonstrating physical work during WBV will enhance greater metabolic responses. Stroke volume was the lowest at 4.5 Hz (P<0.01). Influence of aerobic fitness was evident only in absolute oxygen uptake, oxygen pulse, and ventilation volume (P<0.01).

CONCLUSIONS

This study demonstrates that subjects exposed to physical work during WBV will experience greater metabolic responses compared to WBV alone, and the physiological responses during WBV resemble to that of a light physical work. Despite low metabolic rates during WBV, the effect of aerobic fitness suggests the importance of physical activity in occupations exposed to WBV.

Does a rolling floor reduce the physical work demands and workload, and increase the productivity of truck drivers handling packed goods?

A PCM rolling floor (RF) was developed to reduce the risk of musculoskeletal complaints among truck drivers. The RF can be used to move packed goods automatically in and out of the cargo space. The efficacy of this intervention on physical work demands, energetic and perceived workload and productivity was evaluated by comparing nine truck drivers working with a RF and a traditional, non-moving floor during a working day. Since the RF was not used during the loading process, no effects were found. The RF reduced the unloading process by 8 min, decreased the frequency of lifting and setting down goods by 24%, decreased the frequency of handling goods below knee level by 79%, and decreased the frequency of entering the cargo space by 45%. No effect was found on the energetic and perceived workload. The RF resulted in a small increase in productivity.

Reducing whole-body vibration and musculoskeletal injury with a new car seat design

A new car seat design, which allows the back part of the seat (BPS) to lower down while a protruded cushion supports the lumbar spine, was quantitatively tested to determine its effectiveness and potentials in reducing whole-body vibration (WBV) and musculoskeletal disorders in automobile drivers. Nine subjects were tested to drive with the seat in: 1) the conventional seating arrangement (Normal posture); and 2) the new seating design (without BPS (WO-BPS) posture). By reducing contact between the seat and the ischial tuberosities (ITs), the new seating design reduced both contact pressure and amplitude of vibrations transmitted through the body. Root-mean-squared values for acceleration along the z-axis at the lumbar spine and ITs significantly decreased 31.6% (p < 0.01) and 19.8% (p < 0.05), respectively, by using the WO-BPS posture. At the same time, vibration dose values significantly decreased along the z-axis of the lumbar spine and ITs by 43.0% (p < 0.05) and 34.5% (p < 0.01). This reduction in WBV allows more sustained driving than permitted by conventional seating devices, by several hours, before sustaining unacceptable WBV levels. Such seating devices, implemented in large trucks and other high-vibration vehicles, may reduce the risk of WBV-related musculoskeletal disorders among drivers.

Mechanical damage to the intervertebral disc annulus fibrosus subjected to tensile loading

Damage of the annulus fibrosus is implicated in common spinal pathologies. The objective of this study was to obtain a quantitative relationship between both the number of cycles and the magnitude of tensile strain resulting in damage to the annulus fibrosus. Four rectangular tensile specimens oriented in the circumferential direction were harvested from the outer annulus of 8 bovine caudal discs (n = 32) and subjected to one of four tensile testing protocols: (i) ultimate tensile strain (UTS) test; (ii) baseline cyclic test with 4 series of 400 cycles of baseline cyclic loading (peak strain = 20% UTS); (iii & iv) acute and fatigue damage cyclic tests consisting of 4 x 400 cycles of baseline cyclic loading with intermittent loading to 1 and 100 cycles, respectively, with peak tensile strain of 40%, 60%, and 80% UTS. Normalized peak stress for all mechanically loaded specimens was reduced from 0.89 to 0.11 of the baseline control levels, and depended on the magnitude of damaging strain and number of cycles at that damaging strain. Baseline, acute, and fatigue protocols resulted in permanent deformation of 3.5%, 6.7% and 9.6% elongation, respectively. Damage to the laminate structure of the annulus in the absence of biochemical activity in this study was assessed using histology, transmission electron microscopy, and biochemical measurements and was most likely a result of separation of annulus layers (i.e., delamination). Permanent elongation and stress reduction in the annulus may manifest in the motion segment as sub-catastrophic damage including increased neutral zone, disc bulging, and loss of nucleus pulposus pressure. The preparation of rectangular tensile strip specimens required cutting of collagen fibers and may influence absolute values of results, however, it is not expected to affect the comparisons between loading groups or dose-response reported.

[Evaluation of forklift trucks operated in dockyards for reducing exposure to whole-body vibration]

Our preceding study revealed that many fork-lift truck drivers in Japanese dockyards suffer from fatigue symptoms such as low back pain (LBP). It has been suggested that exposure to whole-body vibration (WBV) is a cause of their LBP. Using forklift models manufactured from 1982 to 2000, we measured and evaluated the vibration of forklift trucks operated in dockyards, adopting experimental procedures based on the European Standard. We investigated various factors related to WBV, with the main focus on attenuating seat vibration. This study showed that (1) the seats did not attenuate vibration in the vertical direction, (2) forklift trucks and their seats had not improved in terms of WBV attenuation for a decade, (3) some forklift trucks in which the seat suspension could no longer be adjusted to the driver's weight continued to be used without being repaired, and impractical seat adjustment methods were adopted, and (4) the seats did not attenuate vertical vibration well in the most undesirable frequency range. We conclude that forklift trucks and especially their seats should urgently be improved with regard to WBV attenuation in order to prevent LBP in forklift truck drivers.

Intra-rater reliability of electromyographic recordings and subjective evaluation of neck muscle fatigue among helicopter pilots

The aim was to evaluate the reliability of a method of measuring neck muscle fatigue among helicopter pilots.

METHOD

Surface EMG from three areas in the neck region, bilaterally, was recorded among 10 male helicopter pilots while they were performing isometric contractions in flexion and extension for 45 s, sustaining a force representing 75% of maximum strength in a seated position. Perceived fatigue was rated using the Borg CR-10 scale. The test was repeated twice the first day and then two additional times with one-week intervals. Variables analyzed were the slope of the median frequency change, the normalized slope, and the ratings after 15, 30 and 45 s; and also the initial median frequency (IMDF). The intra-class correlation (ICC) and the measurement error (S(w)), intra- and inter-day were calculated statistically.

RESULTS

The best reliability for the slope was found for the 45 s intra-day analysis taking all measurements into account (ICC 0.65-0.83). The reliability after 30 s was poorer but still acceptable (ICC 0.52-0.71). For the subjective ratings, the highest reliability was found after 30 s inter-day (ICC 0.86-0.88). IMDF showed generally high reliability for the intra-day analyses (ICC 0.63-0.80).

CONCLUSION

The method is reliable for use in further research. Since performing a contraction of 75% of maximum was quite strenuous, we recommend that the protocol be shortened to 30 s.

Mechanical conditions that accelerate intervertebral disc degeneration: overload versus immobilization

STUDY DESIGN

A review of the literature on macromechanical factors that accelerate disc degeneration with particular focus on distinguishing the roles of immobilization and overloading.

OBJECTIVE

This review examines evidence from the literature in the areas of biomechanics, epidemiology, animal models, and intervertebral disc physiology. The purpose is to examine: 1) what are the degeneration-related alterations in structural, material, and failure properties in the disc; and 2) evidence in the literature for causal relationships between mechanical loading and alterations in those structural and material properties that constitute disc degeneration.

SUMMARY OF BACKGROUND DATA

It is widely assumed that the mechanical environment of the intervertebral disc at least in part determines its rate of degeneration. However, there are two plausible and contrasting theories as to the mechanical conditions that promote degeneration: 1) mechanical overload; and 2) reduced motion and loading.

RESULTS

There are a greater number of studies addressing the "wear and tear" theory than the immobilization theory. Evidence is accumulating to support the notion that there is a "safe window" of tissue mechanical conditions in which the discs remain healthy.

CONCLUSIONS

It is concluded that probably any abnormal loading conditions (including overload and immobilization) can produce tissue trauma and/or adaptive changes that may result in disc degeneration. Adverse mechanical conditions can be due to external forces, or may result from impaired neuromuscular control of the paraspinal and abdominal muscles. Future studies will need to evaluate additional unquantified interactions between biomechanics and factors such as genetics and behavioral responses to pain and disability.

Physiological Effect of Vibrations on Tractor Drivers under Variable Ploughing Conditions

The vibration conditions to which tractor operators are subjected are complex and varied with multi axis translation and rotational vibration inputs to different parts of the body. Working under such conditions may lead to human fatigue and other driving related hazards. The present research was carried out to study the operators under varying conditions of vibration while driving a tractor with and without farm equipment on different fields. Test runs were conducted in wet and dry fields to determine the levels of vibration generated at different engine speeds. On the basis of this study three levels of vibration namely 2.5, 3.5 and 5.0 m/s(2) were selected. Five subjects, all males, with no experience in the field of tractor driving participated in the study. The data were analyzed on the basis of three factor repeated measure kind of experimental design. The results showed that the main effects of farm equipment and the vibration level were statistically significant but the effect of field type was found to be statistically non-significant. The results of the study call upon the ergonomists to design and develop a tractor where the driver may be relieved of vibration induced stresses. Front loading of farm equipment is recommended for improved visibility and better working posture.

Predictors of back pain in a general population cohort

STUDY DESIGN

The study used longitudinal data from the first and second cycles (1994-1995 and 1996-1997) of the Canadian National Population Health Survey.

OBJECTIVE

Our objective was to derive prediction models for back pain in the general male and female household populations.

SUMMARY OF BACKGROUND DATA

Little is known about the predictors of back pain in the general population. Most previous studies focused on specific occupational groups and used a cross-sectional or case-control design.

METHODS

The study cohort consisted of all respondents aged 18+ years who reported no back problems in the 1994-1995 National Population Health Survey cycle (N = 11,063). Potential predictors of chronic back pain were classified into nine groups and entered into stepwise logistic regression models. Bootstrap methods were used to derive the final models and assess their predictive power.

RESULTS

The overall incidence of back pain was 44.7 per 1,000 person-years and was higher in women (47.0 per 1,000 person-years) compared with men (42.2 per 1,000 person-years). In men, significant predictors of back pain were age (peak effect in 45-64 years), height, self-rated health, usual pattern of activity (especially heavy work), yard work or gardening (negative association), and general chronic stress. In women, significant factors were self-reported restrictions in activity, being diagnosed with arthritis, personal stress, and history of psychological trauma in childhood or adolescence.

CONCLUSIONS

Overall health and psychosocial factors are important predictors of back pain in both men and women. Other risk factors differ between the two sexes.

Effect of dynamic hydrostatic pressure on rabbit intervertebral disc cells

The pathogenesis of vibration-induced disorders of intervertebral disc at the cellular level is largely unknown. The objective of this study was to establish a method to investigate the ranges of constructive and destructive hydrostatic loading frequencies and amplitudes in preventing or inducing extracellular disc matrix degradation. Using a hydraulic chamber, normal rabbit intervertebral disc cells were tested under dynamic hydrostatic loading. Monolayer cultures of disc outer annulus cells and 3-dimensional (3-D) alginate cultures of disc nucleus pulposus cells were tested. Effects of different loading amplitudes (3-D culture, 0-3 MPa; monolayer, 0-1.7 MPa) and frequencies (1-20 Hz) on disc collagen and protein metabolism were investigated by measuring 3H-proline-labeled proteins associated with the cells in the extracellular matrix and release of 3H-proline-labeled molecules into culture medium. High frequency and high amplitude hydrostatic stress stimulated collagen synthesis in cultures of outer annulus cells whereas the lower amplitude and frequency hydrostatic stress had little effect. For the same loading duration and repetition, neither treatment significantly affected the relative amount of protein released from the cell layers, indicating that protein degradation and stability were unaffected. In the 3-D nucleus culture, higher amplitude and frequency increased synthesis rate and lowered degradation. In this case, loading amplitude had a stronger influence on cell response than that of loading frequency. Considering the ranges of loading amplitude and frequency used in this study, short-term application of high loading amplitudes and frequencies was beneficial in stimulation of protein synthesis and reduction of protein degradation.