The Hendra virus vaccine: perceptions regarding the role of antibody titre testing

OBJECTIVES

To elucidate veterinarians' and horse owners' perceptions towards the use of Hendra virus (HeV) antibody titre testing and how it influences veterinary advice.

METHODS

Six semi-structured phone interviews were conducted with veterinarians who have submitted samples for HeV antibody titre testing. Interviews were recorded, transcribed and thematically analysed to identify and report common themes within the data.

RESULTS

Veterinarians are predominantly using the titre tests as an alternative to vaccination due to clients' fear of vaccine reactions. The high cost of titre testing, the difficulty interpreting titre results and a lack of titre test recognition by authorities were the major barriers reported to using this test. Some veterinarians detailed difficulties communicating titre test procedures and results to their clients. The majority of veterinarians accepted titres of 64 or greater as evidence of protective immunity and would rely on those results for 12 months. However, there was discrepancy of these values and the level of confidence veterinarians had in interpreting the results of HeV antibody titre tests varied.

CONCLUSION

This study has provided an overview of the attitudes of horse owners and veterinarians towards HeV antibody titre testing. Although evidence for HeV vaccination titres as an indication of protective immunity is still inadequate, it will assist veterinarians in interpreting and communicating titre results.

Individuals with mild-to-moderate hip osteoarthritis walk with lower hip joint contact forces despite higher levels of muscle co-contraction compared to healthy individuals

OBJECTIVE

To compare hip joint contact forces (HJCF), hip muscle forces, and hip muscle co-contraction levels between individuals with mild-to-moderate hip osteoarthritis (OA) and healthy controls during walking.

DESIGN

Eighteen participants with mild-to-moderate hip OA and 23 healthy controls walked at a self-selected speed while motion capture and electromyographic data were synchronously collected. HJCF were computed using a calibrated electromyography-informed neuromusculoskeletal model. Hip joint contact forces, muscle forces, and co-contraction indices for flexor/extensor and adductor/abductor muscle groups were compared between groups using independent sample t-tests (P < 0.05).

RESULTS

There was no between-group difference in self-selected walking speed. On average, participants with hip OA walked with 11% lower first peak (mean difference 235 [95% confidence interval (CI) 57-413] N) and 22% lower second peak (mean difference 574 [95%CI 304-844] N) HJCF compared to controls. Hip muscle forces were also significantly lower in the hip OA compared to control group at first (mean difference 224 [95%CI 66-382] N) and second (mean difference 782 [95%CI 399-1164] N) peak HJCF. Participants with hip OA exhibited higher levels of hip muscle co-contraction in both flexor/extensor and adductor/abductor muscle groups. Consistent with existing literature, hip joint angles (extension, adduction) and external moments (flexion, extension, adduction) were lower in hip OA compared to controls.

CONCLUSION

Lower HJCF were detected in mild-to-moderate hip OA, primarily due to lower hip muscle force production, and despite higher levels of hip muscle co-contraction. Findings suggest that lower loading of the hip joint during walking is a feature of mild-to-moderate hip OA, which could have implications for the pathogenesis of hip OA and/or disease progression.

Using step width to compare locomotor biomechanics between extinct, non-avian theropod dinosaurs and modern obligate bipeds

How extinct, non-avian theropod dinosaurs locomoted is a subject of considerable interest, as is the manner in which it evolved on the line leading to birds. Fossil footprints provide the most direct evidence for answering these questions. In this study, step width-the mediolateral (transverse) distance between successive footfalls-was investigated with respect to speed (stride length) in non-avian theropod trackways of Late Triassic age. Comparable kinematic data were also collected for humans and 11 species of ground-dwelling birds. Permutation tests of the slope on a plot of step width against stride length showed that step width decreased continuously with increasing speed in the extinct theropods (p < 0.001), as well as the five tallest bird species studied (p < 0.01). Humans, by contrast, showed an abrupt decrease in step width at the walk-run transition. In the modern bipeds, these patterns reflect the use of either a discontinuous locomotor repertoire, characterized by distinct gaits (humans), or a continuous locomotor repertoire, where walking smoothly transitions into running (birds). The non-avian theropods are consequently inferred to have had a continuous locomotor repertoire, possibly including grounded running. Thus, features that characterize avian terrestrial locomotion had begun to evolve early in theropod history.

The influence of speed and size on avian terrestrial locomotor biomechanics: Predicting locomotion in extinct theropod dinosaurs

How extinct, non-avian theropod dinosaurs moved is a subject of considerable interest and controversy. A better understanding of non-avian theropod locomotion can be achieved by better understanding terrestrial locomotor biomechanics in their modern descendants, birds. Despite much research on the subject, avian terrestrial locomotion remains little explored in regards to how kinematic and kinetic factors vary together with speed and body size. Here, terrestrial locomotion was investigated in twelve species of ground-dwelling bird, spanning a 1,780-fold range in body mass, across almost their entire speed range. Particular attention was devoted to the ground reaction force (GRF), the force that the feet exert upon the ground. Comparable data for the only other extant obligate, striding biped, humans, were also collected and studied. In birds, all kinematic and kinetic parameters examined changed continuously with increasing speed, while in humans all but one of those same parameters changed abruptly at the walk-run transition. This result supports previous studies that show birds to have a highly continuous locomotor repertoire compared to humans, where discrete 'walking' and 'running' gaits are not easily distinguished based on kinematic patterns alone. The influences of speed and body size on kinematic and kinetic factors in birds are developed into a set of predictive relationships that may be applied to extinct, non-avian theropods. The resulting predictive model is able to explain 79-93% of the observed variation in kinematics and 69-83% of the observed variation in GRFs, and also performs well in extrapolation tests. However, this study also found that the location of the whole-body centre of mass may exert an important influence on the nature of the GRF, and hence some caution is warranted, in lieu of further investigation.

A systematic review of the effect of ageing and falls history on minimum foot clearance characteristics during level walking

Minimum foot clearance (MFC) is the minimum vertical distance between the lowest point of the foot of the swing leg and the walking surface during the swing phase of the gait cycle. MFC is a gait variable that is linked to the mechanism of a trip because reduced MFC for a given step during walking increases the susceptibility to tripping on an unseen obstacle or due to undetected changes in surface height. Given that tripping is a common cause of falls in older persons, this review was undertaken to determine whether ageing and/or history of falls in older adults influences MFC characteristics during level walking. Studies that assessed MFC characteristics including measures of central tendency (mean and/or median), variability (linear and non-linear measures) and shape (skewness, kurtosis) of the MFC distribution were included in the review. The final yield from a search of seven electronic research databases was 12 unique articles that met all the inclusion criteria. Ageing does not appear to alter measures of central tendency or shape of the MFC distribution. However greater MFC variability was observed in older compared to younger adults and older fallers compared to older non-fallers in the majority of studies. Greater MFC variability may contribute to increased risk of trips and associated falls in older compared to young adults and older fallers compared to older non-fallers.

Coordination of head and trunk accelerations during walking

The purpose of this study was to investigate the relationship between oscillatory dynamics of the head and trunk in each plane of motion during walking. Head and trunk accelerations of ten healthy subjects (age: 23 +/- 4 years) were measured in the vertical (VT), anterior-posterior (AP) and mediolateral (ML) directions using a pair of tri-axial accelerometers. All subjects performed five walking trials along a level 20 m walkway at their preferred gait velocity (1.30 +/- 0.15 m s(-1)). Acceleration data were analysed using power spectral, harmonic and regularity measures. Results indicated that: (1) oscillations of the head were smoother, with a greater proportion of power at lower frequencies than oscillations of the trunk, (2) differences in power spectral properties between the head and trunk were most pronounced in the ML direction, (3) coupling between VT-AP, VT-ML, and AP-ML accelerations were greater for the head than trunk, and (4) for both segments, the weakest coupling was observed for AP-ML acceleration relations. Overall, the results of this study suggest that accelerations of the head are significantly attenuated, and more tightly controlled, compared to accelerations of the lower trunk. This attenuation process was particularly evident for the ML direction, whereby head accelerations showed the greatest differences compared to ML accelerations at the trunk.

Upper body accelerations during walking in healthy young and elderly men

The purpose of the present study was to assess whether any differences existed in the upper body accelerations of young and elderly subjects during natural speed walking. Head and trunk accelerations in eight young subjects (aged 23+/-4 years) and eight healthy elderly subjects (aged 74+/-3 years) were measured during level walking on a 20 m walkway using a pair of tri-axial accelerometers. Heel contact and toe-off events were determined using a footswitch system embedded in the innersole of the right shoe. Gait measures assessed included; stride, stance and swing durations, cadence, gait velocity, step length and 3D head and trunk accelerations. All acceleration variables were normalised to walking speed before statistical analysis. The main findings of this study were: (1) the peak positive anterior-posterior (AP) trunk acceleration associated with push-off was significantly lower for elderly subjects, (2) the peak negative AP head and trunk accelerations following heel contact was significantly higher for elderly subjects, and (3) the time delay between trunk and head accelerations experienced in the AP direction was significantly lower for the elderly compared to the young group. Together, these results suggest that elderly subjects exhibit different patterns of upper body motion in the direction of travel compared to younger subjects. These differences are probably motivated by the need to maximise dynamic stability during critical parts of the gait cycle.

Rowing

The general aim of this study was to examine the relations between rigging set up, anthropometry, physical capacity, rowing kinematics and rowing performance. Fifteen elite single scullers participated in the experiment. Each sculler's preferred rigging set-up was quantified using measurements that included oar length, inboard, span, gearing ratio, swivel-seat height, footstretcher-seat height and distance, and footstretcher angles. Rowing performance was assessed using 2000 m race times from the Australian National Selection trials. Selected anthropometric, physical capacity and kinematic variables were also quantified. Several rigging variables were significantly correlated with each other, and with various anthropometric, physical capacity and kinematic variables. The individual variables that had the highest correlations with race time were 2 km ergometer time (r=0.90), mass (r=-0.87), height (r=-0.86), oar length (r = -0.85) and strength (r = -0.84). Overall results of this study indicated that the fastest rowers tend to be the largest and strongest, and that these larger body dimensions are reflected in the choice of rigging settings. Rigging set-up by itself should not be considered to be a primary determinant of rowing performance, but rather a consequence of faster rowers being larger and stronger and scaling their rigging set-up accordingly. To maximise rowing performance it appears important to tune the rigging of the boat to match the rower's size and strength.

Spinal loads during individual and team lifting

The aim of this experiment was to compare lumbar spinal loads during individual and team lifting tasks. Ten healthy male subjects performed individual lifts with a box mass of 15, 20 and 25 kg and two-person team lifts with a box mass of 30, 40 and 50 kg from the floor to standing knuckle height. Boxes instrumented with force transducers were used to measure vertical and horizontal hand forces, whilst sagittal plane segmental kinematics were determined using a video based motion measurement system. Dynamic L4/L5 torques were calculated and used in a single equivalent extensor force model of the lumbar spine to estimate L4/L5 compression and shear forces. A significant reduction in L4/L5 torque and compression force of approximately 20% was found during team lifts compared to individual lifts. Two main reasons for the reduced spinal loads in team lifting compared to individual lifting were identified: (1) the horizontal hand force (i.e. pulling force) was greater in team lifting, and (2) the horizontal position of the hands was closer to the lumbar spine during team lifts. The horizontal hand force and position of the hands had approximately equal contributions in reducing the spinal load during team lifting compared to individual lifting.

Swing phase mechanics of healthy young and elderly men

This study examined the effect of ageing on the swing phase mechanics of young and elderly gait. Sagittal plane marker trajectories and force plate data were collected while 10 young (24.9+/-0.9 years) and eight elderly (68.9+/-0.4 years) subjects walked at their preferred walking speeds. Comparison between young and elderly gait was made for a range of spatial-temporal, kinematic and kinetic variables with emphasis given to identifying possible differences at toe-off, minimum metatarsal-phalangeal joint clearance and heel contact. In order to control for the confounding effect of gait velocity on the dependent variables, a multivariate analysis of covariance was used to identify differences between the young and elderly subjects due to age. In contrast to studies that have reported lower preferred walking speeds in the elderly compared to the young [J.O. Judge, R.B. Davis III, S. Ounpuu, Step length reductions in advanced age: the role of ankle and hip kinetics, Journal of Gerontology: Medical Sciences 51 (1996) M303-312; D.C. Kerrigan, M.K. Todd, U. Della Croce, L.A. Lipsitz, J.J. Collins, Biomechanical gait alterations independent of speed in the healthy elderly: evidence for specific limiting impairments, Archives of Physical and Medical Rehabilitation 79 (1998) 317-322], no differences in walking speed nor in the spatial-temporal variables that determine walking speed were detected. The elderly were however, found to have a greater hip extension moment at the time of minimum metatarsal-phalangeal joint clearance, and a significantly higher anterior-posterior velocity heel contact velocity that was linked to a significantly higher shank and foot angular velocity at heel contact. Since many gait variables are highly correlated with walking speed [C. Kirtley, M.W. Whittle, R.J. Jefferson, Influence of walking speed on gait parameters, Journal of Biomechanical Engineering 7 (1985) 282-288; D.A. Winter, Biomechanical motor patterns in normal walking, Journal of Motor Behaviour 15 (1983) 302-330], differences between young and elderly gait found in the present study may therefore be attributed to ageing, rather than a secondary effect of differences in gait velocity.

Cardiovascular regulation during head-up tilt in healthy 20-30-year-old and 70-75-year-old men

This study compared the heart rate, finger arterial pressure (AP) and electromyographic (EMG) activity of selected anti-gravity muscles during the initial and prolonged phases of orthostatic stress in healthy young and older men. Beat-by-beat recordings of heart rate, finger systolic pressure, diastolic pressure and mean AP were made during supine rest and 5 min of 90 degrees head-up tilt (HUT) in 18 young (23+/-1 years) and 15 older (73+/-1 years) men. The EMG activity of the soleus, tibialis anterior and vastus medialis muscles was recorded. During the first 30 s following 90 degrees HUT (immediate response), the young men exhibited significant (P<0.05) decreases in finger systolic pressure, diastolic pressure and mean AP, followed by a sustained increase in finger AP during the 5 min following 90 degrees HUT (prolonged response). The immediate and prolonged finger AP and diastolic pressure responses were not significantly different (P>0.05) from the values at supine rest for the older men. The mean root mean square EMG activity of the soleus, tibialis anterior and vastus medialis muscles during 90 degrees HUT was not significantly different (P>0.05) from that at supine rest for either group. These results demonstrate that, when compared with healthy older men, young men show larger reductions in finger AP during the initial phase of orthostatic stress. However, during the prolonged phase of orthostatic stress, older men maintain resting finger AP, whereas young men demonstrate a reflex overshoot in finger AP. Finally, differences in lower-limb anti-gravity muscle activation do not account for the contrasting finger AP responses of healthy young and older men.

Lumbosacral loads in bedmaking

The purpose of this study was to determine whether the introduction of larger and heavier beds which were lower to the floor increased the physical stress on employees responsible for room cleaning and bedmaking in the hospitality industry. More specifically, this study assessed the effect of bed size (single, double and king) and bed height (460 and 560 mm) on dynamic and static estimates of L5/S1 compression force and static L5/S1 shear force for six simulated components of the overall bedmaking task. Results confirmed the view that static models severely underestimate the loads on the lumbar spine under inertial lifting conditions, and also indicated that: (i) tasks with the greatest hand loads were not necessarily associated with the greatest spinal loads due to differences in the way each task was performed; (ii) L5/S1 loads produced during bedmaking may exceed recommended safe lifting limits for certain task-size height combinations; and (iii) the use of larger and heavier beds in the hospitality industry imposes increased loads on the lumbar spine. The investigation of alternative work practices designed to minimise loads on the lumbar spine is recommended.

The dynamic loading response of surfaces encountered in beach running

The purpose of this study was to measure the response to dynamic loading of sand surfaces typically encountered in beach running. An instrumented drop test rig was constructed and used to guide a drop mass through impact with two surfaces (i) dry, uncompacted sand; and (ii) wet, compacted sand. Four drop masses (3.86, 7.24, 10.62 and 14.0 kg) were chosen and dropped from four different drop heights (100, 200, 300 and 400 mm) to represent the kinetic energies typically experienced during heelstrike in running. Accelerations were measured using a piezoelectric accelerometer and the trajectory of the drop head was measured using a displacement transducer. The following response variable were calculated for each trial: (i) peak impact force, (ii) mean impact force, (iii) impulse, (iv) total impact time, (v) rise time, (vi) fall time, (vii) maximum penetration, (viii) energy absorbed by the surface, and (ix) surface stiffness. Mean and peak impact forces were approximately 4 times greater for the wet surface while penetration, impact time and rise time were approximately 3-4 times greater for the uncompacted surface condition. The wet surface was also found to be 6 times stiffer than the uncompacted surface indicating the presence of water substantially altered surface compliance. Results are discussed in terms of their implications for performance and the potential for injury to athletes who run on these surfaces.

An injury profile of elite ironman competitors

An injury questionnaire was administered to the 30 elite ironman competitors (mean age = 25.7 +/- 4.6 yrs) participating in a commercially sponsored seven race national series. Responses provided retrospective data from the preceding three years indicating the type, location, frequency, cause and severity of injuries sustained by ironmen, and associated these injuries with particular race components (run, swim, board, ski). Twenty self-reported questionnaires were returned for analysis that described a total of 67 injuries incurred by 19 subjects. Results indicated the following: (i) the most frequently injured body parts were the knee (n = 18) and shoulder (n = 14) with the lower extremity accounting for 55% of all injuries reported; (ii) knee, shin and calf injuries had a significant association with the run component and upper extremity injuries had a significant association with the swim component; (iii) running was perceived to be the most injurious race component in terms of the frequency and severity of injury; (iv) overtraining was perceived to be the main cause of injury; (v) tendinitis was perceived to be the main type of injury; (vi) athletes adjusted their training mode to accommodate injury so that total training volume could be maintained; and (vii) injury did not result in withdrawal from competition. Further research investigating the techniques used in the ironman event and their relationship to injury is recommended.