Stiffness properties of the trunk in people with low back pain

The purpose of this study was to examine the dynamic properties of the trunk during unstable sitting and to determine differences between healthy and low back pain (LBP) participants.Participants sat on a custom-made chair that was able to swing freely in the sagittal plane. The chair was mounted on a force platform to measure loads acting at the trunk. Each participant was asked to find a balanced position after the chair was tilted backward and released. Movements of the trunk and chair were recorded. Effective moment of inertia, stiffness and damping coefficients were derived using a second order linear model. 10 participants were re-tested to assess reliability.Trunk stiffness was found increased for LBP subjects (p < .05) while no difference was found for damping coefficient. Gender and initial tilt angle did not affect viscoelastic properties of the spine.A second order linear model adequately described the biomechanical response of the trunk. It was shown that the trunk response was mainly elastic for all participants. The increase in trunk stiffness in LBP subjects could be a compensatory strategy to decrease pain and the risk of further injuries, but further investigations are needed to understand the nature of the viscoelastic alterations.     

Temporal order perception of auditory stimuli is selectively modified by tonal and non-tonal language environments

The close relationship between temporal perception and speech processing is well established. The present study focused on the specific question whether the speech environment could influence temporal order perception in subjects whose language backgrounds are distinctively different, i.e., Chinese (tonal language) vs. Polish (non-tonal language). Temporal order thresholds were measured for both monaurally presented clicks and binaurally presented tone pairs. Whereas the click experiment showed similar order thresholds for the two language groups, the experiment with tone pairs resulted in different observations: while Chinese demonstrated better performance in discriminating the temporal order of two “close frequency” tone pairs (600 Hz and 1200 Hz), Polish subjects showed a reversed pattern, i.e., better performance for “distant frequency” tone pairs (400 Hz and 3000 Hz). These results indicate on the one hand a common temporal mechanism for perceiving the order of two monaurally presented stimuli, and on the other hand neuronal plasticity for perceiving the order of frequency-related auditory stimuli. We conclude that the auditory brain is modified with respect to temporal processing by long-term exposure to a tonal or a non-tonal language. As a consequence of such an exposure different cognitive modes of operation (analytic vs. holistic) are selected: the analytic mode is adopted for “distant frequency” tone pairs in Chinese and for “close frequency” tone pairs in Polish subjects, whereas the holistic mode is selected for “close frequency” tone pairs in Chinese and for “distant frequency” tone pairs in Polish subjects, reflecting a double dissociation of function.     

Postural configuration affects the perception of earth-based space during pitch tilt

This study investigates the relative contribution of body parts in the elaboration of a whole-body egocentric attraction phenomenon previously observed during earth-based judgments. This was addressed through a particular earth-based task requiring estimating the possibility of passing under a projected line, imagining a forward horizontal displacement. Different postural configurations were tested, involving whole-body tilt, trunk tilt alone or head tilt alone. Two legs positions relative to the trunk were manipulated. Results showed systematic deviations of the subjective “passability” toward the tilt, linearly related to the tilt magnitude. For each postural configuration, the egocentric influence appeared to be highly dependent on the position of trunk and head axes, whereas the legs position appeared not relevant. When compared to the whole-body tilt condition, tilting the trunk alone consistently reduced the amount of the deviation toward the tilt, whereas tilting the head alone consistently increased it. Our results suggest that several specific effects from multiple body parts can account for the global deviation of the estimates observed during whole-body tilt. Most importantly, we support that the relative contribution of the body segments could mainly depend on a reweighting process, probably based on the reliability of sensory information available for a particular postural set.     

Differences in timing and magnitude of lumbopelvic rotation during active and passive knee extension in sitting position in people with and without low back pain: A cross-sectional study

Repetitive lumbopelvic rotation (LPR) during active limb movements has been indicated as a factor that contributes to low back pain (LBP). Prior studies suggest that people with LBP demonstrate greater and earlier LPR during limb movements in prone.We examined timing and magnitude of LPR during sitting active knee extension in people with and without LBP. We also investigated differences of LPR during active and passive knee extension in LBP group. 38 men (mean age: 38.4)10.6) years) with chronic mechanical LBP and 38 matched healthy men (mean age: 36.6(8.4) years) were examined. Kinematic data were collected by motion capture system and analyzed using OpenSim software. The difference between the start time of knee extension and start time of LPR was calculated and was normalized to knee extension movement time. Maximum angular displacement for LPR was also calculated across time.People with LBP demonstrated earlier LPR during knee extension than healthy subjects (P < 0.01). There was, however, no difference in maximum LPR between groups. LBP group also demonstrated greater and earlier LPR during active than during passive knee extension (P < 0.01).Earlier LPR during limb movements in sitting may be related to LBP. Quadriceps muscle activity and inefficient trunk muscles activation may contribute to early LPR in LBP group. A greater understanding of the factors that may contribute to early LPR during daily activities can provide information to guide rehabilitation treatment for people with LBP.     

“Posture first”: Interaction between posture and locomotion in people with low back pain during unexpectedly cued modification of gait initiation motor command

The ability to adapt anticipatory postural adjustments (APAs) in response to perturbations during single-joint movements is altered in people with chronic low back pain (LBP), but a comprehensive analysis during functional motor tasks is still missing. This study aimed to compare APAs and stepping characteristics during gait initiation between people with LBP and healthy controls, both in normal (without cue occurrence) condition and when an unexpected visual cue required to switch the stepping limb. Fourteen individuals with LPB and 10 healthy controls performed gait initiation in normal and switch conditions. The postural responses were evaluated through the analysis of center of pressure, propulsive ground reaction forces, trunk and whole-body kinematics, and activation onsets of leg and back muscles. During normal gait initiation, participants with LBP exhibited similar APAs and stepping characteristics to healthy controls. In the switch condition, individuals with LBP were characterized by greater mediolateral postural stability but decreased forward body motion and propulsion before stepping. The thorax motion was associated with forward propulsion parameters in both task conditions in people with LBP but not healthy controls. No between-group differences were found in muscle activation onsets. The results suggest that postural stability is prioritized over forward locomotion in individuals with LBP. Furthermore, the condition-invariant coupling between thorax and whole-body forward propulsion in LBP suggests an adaptation in the functional use of the thorax within the postural strategy, even in poor balance conditions.     

Learning melodies from non-adjacent tones

Language acquisition might heavily rely on statistical learning mechanisms. This has led many researchers to investigate the computational constraints that limit such learning. In particular, it has been argued that statistical relations among non-adjacent items cannot be tracked, as this might lead to a “computational explosion” making statistical learning intractable. In line with this view, previous research suggests that listeners cannot track relations among non-adjacent musical tones (Creel, Newport, & Aslin, 2004). Here I show that participants readily track non-adjacent tone relations when these are implemented in a musically meaningful way. Specifically, participants readily track non-adjacent tone relations in tonal melodies, but find it more difficult to track non-adjacent tone relations in random melodies, suggesting that non-adjacent relations are easier to track when listeners face “ecological”, musically meaningful stimuli.     

Muscle Stiffness in Down Syndrome and Other Mentally Handicapped Subjects

An attempt was made to determine the effects of strength training on elbow flexor stiffness of Down syndrome, non-Down syndrome mentally handicapped, and nonhandicapped subjects. It was hypothesized that stiffness would be affected by the training. Results showed that only half of the individual subjects increased their maximum voluntary contraction (MVC) level as a result of the training and that premeasures and postmeasures of MVC were not significantly different for any of the three groups. As expected, for both premeasures and postmeasures, nonhandicapped subjects had a significantly higher MVC than the other groups who were not significantly different. An important finding was that measures of stiffness (slopes of the IEMG × Torque) were not significantly different for the three groups. This finding is consistant with recent studies (Davis & Kelso, 1982; Shumway-Cook & Woollacott, in press) but raises serious doubts about the popularly held opinion that Down syndrome individuals are hypotonic. It was also found that both the Down syndrome and other mentally handicapped subjects produced significantly less torque at the maximum level than the nonhandicapped subjects. These findings suggest that deficits in mentally handicapping conditions result from a decrease in the range of a primary motor control parameter λ (see Feldman, 1986).     

Control of Equilibrium Position and Stiffness Through Postural Modules

If muscles are viewed as spring-like torque generators, then the integral of torque with respect to joint angle is the potential energy of that muscle. An energy function for the musculoskeletal system can be defined by summing the energy contribution of each muscle and the potential energy stored in the limb. Any local minimum in this energy landscape is a possible equilibrium position for the limb. The gradient of this function with respect to joint angles is a torque field, and the task of postural control is to find a set of muscle activations to produce a desired field. We consider one technique by which this approximation may be achieved: A postural module is defined as a synergy of muscles that produce a class of torque functions that converge at a constant equilibrium position, but whose stiffness at this position varies as a function of activation of the postural module. For a single-joint system, we show that through control of two such modules it is possible to produce any stiffness at any desired equilibrium position. To extend this scheme to a multijoint system, we initially derive the mechanical constraints on the shape of the restoring force field when a multijoint limb is displaced from equilibrium. Next, we consider voluntary control of the force field when the human arm is displaced from equilibrium: Mussa-Ivaldi, Hogan, and Bizzi (1985) have suggested that subjects are unable to voluntarily change the shape and orientation of the field, although they can readily scale it. This suggests existence of a limitation on the independent recruitment of arm muscles. We show, through simulation, that the inability to voluntarily control the shape and orientation of the restoring force field can be attributed to an organization of postural modules that act as local stiffness controllers. We propose that through coactivation, postural modules coarsely encode the work space and serve as an intermediate control system in the motor control hierarchy.     

Combined recruitment of two fixation chains during cyclic movements of one arm

Voluntary adduction-abduction movements of one arm in the horizontal plane discharge a reaction torque which would rotate the trunk in the direction opposite to arm acceleration. Rotation is impeded by muscular fixation chains that exert forces counterbalancing the reaction torque. We examined how two different fixation chains cooperate in stabilising the trunk during the above movements. Standing subjects (n = 6), with shoulders ante-flexed, performed cyclic adductions-abductions of the right arm (1.5 Hz) while grasping a fixed handle with the left hand. In this set-up, reaction torque is contrasted by: (1) a leg fixation chain, exerting on the ground a torque around the vertical axis (Tz), recorded by a force platform; and (2) a left arm fixation chain, exerting on the handle a force in the medial-lateral direction (Fh), recorded by a load cell. Subjects performed 20 trials (15 cycles each). It was found that Tz and Fh underwent sinusoidal changes at the same frequency as arm movements and contributed in counteracting the reaction torque. The intensity of the handle grip, monitored by EMG activity in the left Flexor Digitorum Superficialis, was changed from trial to trial and kept constant during each trial. As grip strength increased, Fh amplitude increased linearly while amplitude of Tz linearly decreased. In conclusion, voluntarily strengthening the handle grip progressively deviates the postural actions from the legs to the left arm.     

Visuomotor error augmentation affects mediolateral head and trunk stabilization during walking

Prior work demonstrates that humans spontaneously synchronize their head and trunk kinematics to a broad range of driving frequencies of perceived mediolateral motion prescribed using optical flow. Using a closed-loop visuomotor error augmentation task in an immersive virtual environment, we sought to understand whether unifying visual with vestibular and somatosensory feedback is a control goal during human walking, at least in the context of head and trunk stabilization. We hypothesized that humans would minimize visual errors during walking – i.e., those between the visual perception of movement and actual movement of the trunk. We found that subjects did not minimize errors between the visual perception of movement and actual movement of the head and trunk. Rather, subjects increased mediolateral trunk range of motion in response to error-augmented optical flow with positive feedback gains. Our results are more consistent with our alternative hypothesis – that visual feedback can override other sensory modalities and independently compel adjustments in head and trunk position. Also, aftereffects following exposure to error-augmented optical flow included longer, narrower steps and reduced mediolateral postural sway, particularly in response to larger amplitude positive feedback gains. Our results allude to a recalibration of head and trunk stabilization toward more tightly regulated postural control following exposure to error-augmented visual feedback. Lasting reductions in mediolateral postural sway may have implications for using error-augmented optical flow to enhance the integrity of walking balance control through training, for example in older adults.     

Stereoscopic shape discrimination is well preserved across changes in object size

A single experiment evaluated human observers’ ability to discriminate the shape of solid objects that varied in size and orientation in depth. The object shapes were defined by binocular disparity, Lambertian shading, and texture. The object surfaces were smoothly curved and had naturalistic shapes, resembling those of water-smoothed granite rocks. On any given trial, two objects were presented that were either the same or different in terms of shape. When the “same” objects were presented, they differed in their orientation in depth by 25°, 45°, or 65°. The observers were required to judge whether any given pair of objects was the “same” or “different” in terms of shape. The size of the objects was also varied by amounts up to ±40% relative to the standard size. The observers’ shape discrimination performance was strongly affected by the magnitude of the orientation changes in depth - thus, their performance was viewpoint dependent. In contrast, the observers’ shape discrimination abilities were only slightly affected by changes in the overall size of the objects. It appears that human observers can recognize the three-dimensional shape of objects in a manner that is relatively independent of size.     

Objects, events and "to be" verbs in Spanish--an ERP study of the syntax-semantics interface

In Spanish, objects and events at subject position constrain the selection of different forms of the auxiliary verb “to be”: locative predicates about objects require “estar en”, while those relating to events require “ser en”, both translatable as “to be in”. Subjective ratings showed that while the “object + ser + en” is considered as incorrect, the “event + estar + en” combination is also perceived as unacceptable but to a lesser degree. In an ERP study, we evaluated the impact of a purely semantic distinction (object versus events) on the subsequent processing of these auxiliary verbs followed by locatives in Spanish. For the “ser en” predicate, the P600 component was larger when the subject was an object than when it was an event. This P600 effect is consistent with an online repair of the defining predicate when it does not fit with the adequate semantic properties of the subject. On the other hand, for the “estar en” predicate, event subjects when compared to object subjects showed more positive ongoing amplitudes between 280 and 380 ms after the presentation of the “en” preposition, followed by a longer positive wave starting around 400 ms and lasting until 700 ms after the presentation of the following determiner, with central and frontal scalp distributions respectively. Thus, the different subject-predicate combinations, depending on the semantic features of the subjects, triggered syntactic reparatory processes at a structural level. These findings are consistent with an incremental interpretation of sentence meaning based on the interaction between syntactic and semantic information.     

The effects of trunk extensor and abdominal muscle fatigue on postural control and trunk proprioception in young,healthy individuals

The purpose of this study was to induce both trunk extensor and abdominal muscle fatigue, on separate occasions, and compare their effects on standing postural control and trunk proprioception, as well as look at the effects of a recovery period on these outcome measures. A total of 20 individuals participated, with 10 (5 males and 5 females) completing either a standing postural control or lumbar axial repositioning protocol. Participants completed their randomly assigned protocol on two occasions, separated by at least 4 days, with either their trunk extensor or abdominal muscles being fatigued on either day. Postural control centre of pressure variables and trunk proprioception errors were compared pre- and post-fatigue. Results showed that both trunk extensor and abdominal muscle fatigue significantly degraded standing postural control immediately post-fatigue, with recovery occurring within 2 min post-fatigue. In general, these degradative effects on postural control appeared to be greater when the trunk extensor muscles were fatigued compared to the abdominal muscles. No statistically significant changes in trunk proprioception were found after either fatigue protocol. The present findings demonstrate our body’s ability to quickly adapt and reweight somatosensory information to maintain postural control and trunk proprioception, as well as illustrate the importance of considering the abdominal muscles, along with the trunk extensor muscles, when considering the impact of fatigue on trunk movement and postural control.     

Effects of calcaneal eversion on three-dimensional kinematics of the hip, pelvis and thorax in unilateral weight bearing

Understanding the kinematic chain from foot to thorax will provide a better basis for assessment of malalignment of the body. The purpose of this study was to investigate the effects of induced calcaneal eversion on the kinematics of the hip, pelvis and thorax in three dimensions under unilateral weight-bearing. Twenty-eight healthy males were requested to stand on one leg under three conditions: normal (standing directly on the floor), and on wedges producing 5° and 10° calcaneal eversion. Recorded kinematic parameters included the angles of the hip joint, pelvis, and thorax in three dimensions. Eversion induced by wedges produced significant increases in hip flexion, hip medial rotation, pelvic anterior tilt, and thoracic lateral tilt and axial rotation to the standing side. In the frontal plane, pelvic lateral tilt to the standing side was decreased in 5° eversion condition compared with normal condition; conversely, it was increased in 10° eversion condition compared with 5° eversion condition. Arch height was negatively correlated with change in thoracic axial rotation to standing side from the normal to 10° eversion (r = −.528, p < .01). We concluded that induced calcaneal eversion affects the three-dimensional kinematics of the thorax through the hip joint and the pelvis.     

Multi-body dynamic coupling mechanism for generating throwing arm velocity during baseball pitching

The purpose of this study was to identify the detailed mechanism how the maximum throwing arm endpoint velocity is determined by the muscular torques and non-muscular interactive torques from the perspective of the dynamic coupling among the trunk, thorax and throwing and non-throwing arm segments. The pitching movements of ten male collegiate baseball pitchers were measured by a three-dimensional motion capture system. Using the induced-segmental velocity analysis (IVA) developed in this study, the maximum fingertip velocity of the throwing arm (MFV) was decomposed into each contribution of the muscular torques, passive motion-dependent torques due to gyroscopic moment, Coriolis force and centrifugal force, and other interactive torque components. The results showed that MFV (31.6 ± 1.7 m/s) was mainly attributed to two different mechanisms. The first is the passive motion-dependent effect on increasing the angular velocities of three joints (thorax rotation, elbow extension and wrist flexion). The second is the muscular torque effect of the shoulder internal rotation (IR) torque on generating IR angular velocity. In particular, the centrifugal force-induced elbow extension motion, which was the greatest contributor among individual joint contributions, was caused primarily by the angular velocity-dependent forces associated with the humerus, thorax, and trunk rotations. Our study also found that a compensatory mechanism was achieved by the negative and positive contributions of the muscular torque components. The current IVA is helpful to understand how the rapid throwing arm movement is determined by the dynamic coupling mechanism.     

Position of the egocentric reference and performance in line bisection and subjective vertical estimation tasks

Egocentric body coordinates such as the sagittal midline have been proposed to act as a reference for ballistic movements in extracorporeal space. Symmetrical functioning of the multiple neural structures processing sensory information would account for the normal sagittal position of the egocentric reference. According to this hypothesis a unilateral parietal lesion would induce a ipsilesional deviation which would prevent neglect patients from responding to stimuli that occur on that side. In this line of reasoning, an experimental manipulation of the position of the egocentric reference by way of a postural perturbation should have an effect on visuospatial tasks performance in normal subjects. Seventeen right-handed subjects were submitted in the dark to two visuomotor tasks: the adjustment of a luminescent rod to the vertical and the bisection of a luminescent line, either with the trunk and the head aligned at 0 degrees or with a 30 degrees trunk rotation to the right or to the left. Results revealed no significant effect of trunk rotation on the performance in both tasks. We discuss these findings and their implication for the understanding of the neglect syndrome.     

When global structure "Explains Away" local grammar: a Bayesian account of rule-induction in tone sequences

While many constraints on learning must be relatively experience-independent, past experience provides a rich source of guidance for subsequent learning. Discovering structure in some domain can inform a learner’s future hypotheses about that domain. If a general property accounts for particular sub-patterns, a rational learner should not stipulate separate explanations for each detail without additional evidence, as the general structure has “explained away” the original evidence. In a grammar-learning experiment using tone sequences, manipulating learners’ prior exposure to a tone environment affects their sensitivity to the grammar-defining feature, in this case consecutive repeated tones. Grammar-learning performance is worse if context melodies are “smooth” — when small intervals occur more than large ones — as Smoothness is a general property accounting for a high rate of repetition. We present an idealized Bayesian model as a “best case” benchmark for learning repetition grammars. When context melodies are Smooth, the model places greater weight on the small-interval constraint, and does not learn the repetition rule as well as when context melodies are not Smooth, paralleling the human learners. These findings support an account of abstract grammar-induction in which learners rationally assess the statistical evidence for underlying structure based on a generative model of the environment.     

Observed actions affect body-specific associations between space and valence

Right-handers tend to associate “good” with the right side of space and “bad” with the left. This implicit association appears to arise from the way people perform actions, more or less fluently, with their right and left hands. Here we tested whether observing manual actions performed with greater or lesser fluency can affect observers' space–valence associations. In two experiments, we assigned one participant (the actor) to perform a bimanual fine motor task while another participant (the observer) watched. Actors were assigned to wear a ski glove on either the right or left hand, which made performing the actions on this side of space disfluent. In Experiment 1, observers stood behind the actors, sharing their spatial perspective. After motor training, both actors and observers tended to associate “good” with the side of the actors' free hand and “bad” with the side of the gloved hand. To determine whether observers' space–valence associations were computed from their own perspectives or the actors', in Experiment 2 we asked the observer to stand face-to-face with the actor, reversing their spatial perspectives. After motor training, both actors and observers associated “good” with the side of space where disfluent actions had occurred from their own egocentric spatial perspectives; if “good” was associated with the actor's right-hand side it was likely to be associated with the observer's left-hand side. Results show that vicarious experiences of motor fluency can shape valence judgments, and that observers spontaneously encode the locations of fluent and disfluent actions in egocentric spatial coordinates.     

How do children aged 6 to 11 stabilize themselves on an unstable sitting device? The progressive development of axial segment control

Postural control continues to develop during middle childhood as shown by the decrease in body sway in stance between the ages of 5 and 11. Although head and trunk control is crucial for balance control during both static and dynamic activities, evaluating its specific development and its contribution to overall postural control is methodologically challenging. Here, we used an unstable sitting device adapted to ensure that only the axial segments could control the balance of the device and thus the balance of the upper body. This study aimed to assess the development of the postural stabilization of axial body segments during middle childhood. Thirty-six children (in three age groups: 6-7yo, 8-9yo, and 10-11yo) and 11 adults sat on the unstable sitting device and had to stabilize their axial segments under several conditions: a moderate vs. high level of balance challenge, and eyes open vs. eyes closed. Upper-body postural sway (area, mean velocity and root mean square (RMS) of the center of pressure (CoP) displacement) decreased progressively with age (6-7yo > 8-9yo > 10-11yo > adults), and this effect was accentuated when the balance challenge was high (for CoP area) or in the “eyes closed” condition (for CoP area and RMS). The stabilization strategies were assessed by anchoring indexes computed from three-dimensional kinematics. A progressive shift was showed, from an “en bloc” pattern at 6–7 years of age toward a more articulated (i.e. adult-like) pattern at 10–11. A head-on-space stabilization strategy first emerged at the age of 8–9. Middle childhood is an important period for the development of axial segment stabilization, which continues to mature until adulthood. This development might be related to the introduction and progressive mastery of feedforward sensorimotor processes and might contribute strongly to the development of overall postural control.     

Get an Apprenticeship before School Is Out: How German Adolescents Adjust Vocational Aspirations When Getting Close to a Developmental Deadline

Opportunities to attain important life goals are sequenced in age-graded trajectories that wax and wane throughout life. A prime example of such age-graded opportunity structures is the transition from school to work. The institutions of vocational training in Germany closely scaffold this transition and provide developmental deadlines for attaining the critical transition, namely finding an apprenticeship position. Adjustments of vocational aspirations are investigated with regard to the social prestige of three indicators of aspirations, “dream job,” “vocation I am interested in,” and apprenticeships applied for. Findings indicate that adolescents progressively adjusted their “dream job” to “job I am interested in” as the deadline approaches. Moreover, overall adolescents matched their school performance to the social prestige of apprenticeships for which they applied. Boys and girls whose motivational orientation did not match their gender prototype attained particularly high levels of achievement and aspiration.