Trunk posture affects upper extremity function of adults

This study examined the effects of various seated trunk postures on upper extremity function. 59 adults were tested using the Jebsen Taylor Hand Function Test while in three different trunk postures. Significant mean differences between the neutral versus the flexed and laterally flexed trunk postures were noted during selected tasks. Specifically, dominant hand performance during the tasks of feeding and lifting heavy cans was significantly slower while the trunk was flexed and laterally flexed than when performed in the neutral trunk position. Performance of the nondomi nant hand during the tasks of picking up small objects, page turning, as well as the total score was slower while the trunk was flexed compared to performance in the neutral trunk position. These findings support the assumption that neutral trunk posture improves upper extremity performance during daily activities although the effect is not consistent across tasks. Findings are discussed along with limitations and recommendations for research.     

Modification of impulse generation during piqué turns with increased rotational demands

During initiation of a piqué turn, a dancer generates impulse to achieve the desired lateral translation and whole-body rotation. The goal of this study was to determine how individuals regulate impulse generation when initiating piqué turns with increased rotational demands. Skilled dancers (n = 10) performed single (∼360°) and double (∼720°) piqué turns from a stationary position. Linear and angular impulse generated by the push and turn legs were quantified using ground reaction forces and compared across turn conditions as a group and within a dancer using probability-based statistical methods. The results indicate that as the rotation demands of the piqué turn increased, the net angular impulse generated increased whereas net lateral impulse decreased. Early during turn initiation, the free moment contributed to angular impulse generation. Later during turn initiation, horizontal reaction forces were controlled to generate angular impulse. As rotational demands increased, the moment applied increased primarily from redirection of the horizontal reaction force (RFh) at the push leg and a combination of RFh magnitude and moment arm increases at the turn leg. RFh at each leg were coordinated to limit unwanted net linear impulse. Knowledge of observed subject-specific mechanisms is important to inform the design of turning performance training tools.     

Effects of experimentally increased trunk stiffness on thorax and pelvis rotations during walking

Patients with non-specific low back pain, or a similar disorder, may stiffen their trunk, which probably alters their walking coordination. To study the direct effects of increasing trunk stiffness, we experimentally increased trunk stiffness during walking, and compared the results with what is known from the literature about gait coordination with, e.g., low back pain. Healthy subjects walked on a treadmill at 3 speeds (0.5, 1.0 and 1.5 m/s), in three conditions (normal, while contracting their abdominal muscles, or wearing an orthopedic brace that limits trunk motions). Kinematics of the legs, thorax and pelvis were recorded, and relative Fourier phases and amplitudes of segment motions were calculated. Increasing trunk stiffness led to a lower thorax–pelvis relative phase, with both a decrease in thorax–leg relative phase, and an increase in pelvis–leg relative phase, as well as reduced rotational amplitude of thorax relative to pelvis. While lower thorax–pelvis relative phase was also found in patients with low back pain, higher pelvis–leg relative phase has never been reported in patients with low back pain or related disorders. These results suggest that increasing trunk stiffness in healthy subjects causes short-term gait coordination changes which are different from those seen in patients with back pain.     

Changes in intersegmental dynamics over time due to increased leg inertia

The purpose of this study was to investigate the effects of asymmetrical loading on the intersegmental dynamics of the swing phase. Participants were asked to walk on a treadmill for 20 min under three loading conditions: (a) unloaded baseline, (b) 2 kg attached to the dominant limb’s ankle, and (c) post-load, following load removal. Sagittal plane motion data of both legs were collected and an intersegmental dynamics analysis of each swing phase was performed. Comparisons of steady-state responses across load conditions showed that absolute angular impulses of the loaded limb’s hip and knee increased significantly after load addition, and returned to baseline following load removal. Unloaded leg steady-state responses were not different across load conditions. However, after a change in leg inertia both legs experienced a period of adaptation that lasted approximately 40 strides before a steady state walking pattern was achieved. These findings suggest that the central nervous system refined the joint moments over time to account for the altered limb inertia and to maintain the underlying kinematic walking pattern. Maintaining a similar kinematic walking pattern resulted in altered moment profiles of the loaded leg, but similar moment profiles of the unloaded leg compared with the unloaded baseline condition.     

Trunk- and head-centred spatial coordinates do not affect free-viewing perceptual asymmetries

Turning the trunk or head to the left can reduce the severity of leftward neglect. This study sought to determine whether turning the trunk or head to the right would reduce pseudoneglect: A phenomenon where normal participants underestimate the rightward features of a stimulus. Participants made luminance judgements of two mirror-reversed greyscales stimuli. A preference for selecting the stimulus dark on the left was found. The effect of trunk-centred coordinates was examined in Expt. 1 by facing the head toward the display and turning the trunk to the left, right or toward the display. Head-centred coordinates were examined in Expt. 2 by directing the eyes toward the display and then turning the head and trunk. No effect of rotation was observed. It was concluded that the leftward bias for the greyscales task could be based on an object-centred attentional bias or left-to-right eye scanning habits.     

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.     

Twist within a somersault

The twisting somersault is a key skill in diving and gymnastics. The components of twist and somersault are defined with respect to anatomical axes, and combinations of multiples of half rotations of twist and somersault define specific twisting somersault skills. To achieve a twisting somersault skill twist must be continuous; otherwise oscillations in twist while somersaulting may be observed. The posture-dependent inertial properties of the athlete and the initial conditions determine if continuous or oscillating twist is observed. The paper derives equations for the amount of somersault required per half twist, or per twist oscillation, without making assumptions about the relative magnitudes of the moments of inertia. From these equations the skills achievable may be determined. The error associated with the common assumption that the medial and transverse principal moments of inertia are equal is explored. It is concluded that the error grows as the number of twists per somersault decreases, when the medial and transverse moments of inertia diverge, and when the longitudinal moment of inertia approaches either the medial or transverse moment of inertia. Inertial property data for an example athlete are used to illustrate the various rotational states that can occur.     

Perceived bending and stretching motions from a line of points

Abstract.— The aim of this investigation was to study to what extent bending and stretching motions can be accurately perceived. The (imaginary) "distal" stimuli were lines of points, either in bending motion with constant distances between adjacent points or in stretching motion with the same distances equal at each moment (thus making the relations between the distances constant). The proximal stimuli were produced by a computer, and the subject indicated the slant and curvature of the turning positions of the perceived motion. The result for the stimuli with motion towards the subject was that a majority of the percepts were rather close to the accurate value. That was not true, however, for the stimuli with motion away from the subject. All stimuli were ambiguous demonstrating that more information must be added to get unambiguity.     

Effects of moment of inertia on simple reaction time

Two experiments examined the effect of altering the moment of inertia within an anatomical unit on simple reaction time (SRT), premotor time (PMT), and motor time (MOT) during the initiation of a discrete rapid movement. In Experiment 1 (N = 14), moment of inertia of the forearm was increased with the addition of a weighted cuff fastened around the wrist. In Experiment 2 (N = 7), moment of inertia was altered by the addition of a weighted sleeve to the index finger prior to rapid extension of the digit. Results from both experiments were unequivocal. An increase in the moment of inertia resulted in a significant increase in SRT and MOT but had no significant effect on PMT. Within selected anatomical unites (forearm and index finger), an increase in the moment of inertia does not appear to require additional neuromotor programming time but does influence the overall duration of response initiation.     

Effects of sound frequency on behavioral and cardiac orienting in newborn and five-month-old infants

Alert newborn and 5-month-old infants' responsivity to variations in spectral composition of a rattle sound was examined. Each child received four stimulus conditions: low-, mid-, and high-frequency bandpass-filtered rattles and an unfiltered broadband rattle. Stimuli were played through a single loudspeaker laterally positioned, and head orientation and cardiac responses to sound were recorded. Compared to other stimuli, the low-frequency sound elicted less head turning in both age groups, with this effect exaggerated in younger infants. Head orientation toward the mid-frequency, high-frequency, and broadband stimuli did not differ with age. For all conditions, latency and duration of newborns' head turning was longer than that of 5-month-olds. Newborns responded with cardiac deceleration only on trials when they failed to turn. When head turns occurred, an acceleratory cardiac response was obtained. Five-month-olds responded with reliable cardiac deceleration irrespective of head turning toward the sound. Heart rate change did not vary as a function of frequency at either age, suggesting that all stimuli were equally effective in eliciting the infant's attention.     

Slower Reorientation of Trunk for Reactive Turning while Walking in Hemiparesis Stroke Patients

We examined the behavioral characteristics of reactive turning in hemiplegic stroke patients when they were informed of the turning direction just before turning was required at an unpredictable time. Eleven stroke patients and 20 healthy elderly control people were asked to initiate a turn as soon as a visual cue to inform them of the turning direction was activated unpredictably using a foot switch. Both the segmental reorientation and stepping type when turning 90° while walking were measured. The results indicated preserved segmental reorientation of the head and pelvis in stroke patients. Stroke patients showed delays in pelvic turning but not in head turning. Their delayed pelvic movement might be due to motor dysfunction and the time taken to ensure stability when deciding when to turn.     

Emotional inertia contributes to depressive symptoms beyond perseverative thinking

The autocorrelation or inertia of negative affect reflects how much negative emotions carry over from moment to moment and has been associated with increased depressive symptoms. In this study, we posed three challenges to this association by examining: (1) whether emotional inertia is relevant for depressive symptoms when assessed on a longer timescale than usual; (2) whether inertia is uniquely related to depressive symptoms after controlling for perseverative thoughts; and (3) whether inertia is related to depressive symptoms over and above the within-person association between affect and perseverative thoughts. Participants (N = 101) provided ratings of affect and perseverative thoughts for 100 days; depressive symptoms were reported before and after the study, and again after 2.5 years. Day-to-day emotional inertia was related to depressive symptoms over and above trait and state perseverative thoughts. Moreover, inertia predicted depressive symptoms when adjusting for its association with perseverative thoughts. These findings establish the relevance of emotional inertia in depressive symptoms independent of perseverative thoughts.     

Which mechanical invariants are associated with the perception of length and heaviness of a nonvisible handheld rod? Testing the inertia tensor hypothesis

It has been suggested that the inertia tensor governs many instances of haptic perception. However, the evidence is inconclusive because other candidate mechanical parameters (i.e., invariants) were not or were insufficiently controlled for in pertinent experiments. By independently varying all candidate mechanical parameters, the authors were able to test the role of the inertia tensor relative to that of other mechanical parameters. The results showed that length perception during rod wielding is not governed by the inertia tensor alone but also by the static moment. In contrast to previous reports, length perception during rod holding and heaviness perception during rod wielding were found to be unrelated to the inertia tensor and strongly related to the static moment.     

Emotional inertia prospectively predicts the onset of depressive disorder in adolescence

Emotional inertia refers to the degree to which a person's current emotional state is predicted by their prior emotional state, reflecting how much it carries over from one moment to the next. Recently, in a cross-sectional study, we showed that high inertia is an important characteristic of the emotion dynamics observed in psychological maladjustment such as depression. In the present study, we examined whether emotional inertia prospectively predicts the onset of first-episode depression during adolescence. Emotional inertia was assessed in a sample of early adolescents (N = 165) based on second-to-second behavioral coding of videotaped naturalistic interactions with a parent. Greater inertia of both negative and positive emotional behaviors predicted the emergence of clinical depression 2.5 years later. The implications of these findings for the understanding of the etiology and early detection of depression are discussed.     

Decision making at a crossroad: why to go straight ahead,retrace a path,or turn sideways?

In order to uncover processes in the acquisition of spatial representation, we tested voles, jirds, and mice in a dark grid maze—a relatively homogenous environment comprising 16 identical equispaced crossroads and similar choice of paths at each crossroad. The three species initially displayed a tendency to retrace sections of their recently traversed path, perhaps indicating exploration and learning of an unfamiliar environment by virtue of repetition. All three species displayed the same decision making at crossroads. They had an equal tendency to progress forward, turn sideways, or turn back to retrace their path upon the first arrival at each crossroad. Over repeated visits to the same crossroad, however, progressing forward increased along with a decrease in turning back, but there was no change in the incidence of turning sideways. It is suggested that progressing forward is easier than making turns, since the latter oblige the navigator to remember the location of turning in order to retrace or integrate the path and remain oriented. The incidence of turning sideways, in being more difficult than forward progression and retracing, yet necessary in a restricted maze space, did not change over repeated visits to crossroads. Altogether, decision making at a crossroad may be described as going straight ahead for simplicity, retracing a path to memorize it, or turning sideways at a constant rate. The present tests in the grid maze illustrate how tangible entities (crossroads, paths) are integrated during the early phase of acquiring an abstract representation (map) of the maze.     

Control of lateral weight-transfer initiation during sitting

Whereas many researchers have examined the transition from quiet posture to dynamic state, study of the initiation of lateral weight-transfer during sitting has only begun recently. This action is included in many tasks performed in our daily living, i.e., reaching, dressing, looking backwards, lying down, and shuffling the buttocks. The present study was designed to describe lateral weight-transfer movements of healthy adults, kinematically and kinetically, and to clarify the strategies and speed dependency of lateral weight-transfer initiation during sitting. Seven healthy Japanese male students without orthopaedic or neurological disorders participated. Their lateral weight-transfer movements were measured during sitting, using two force platforms and a 3-dimensional analysis system. Analysis showed that there appear to be two strategies for the initiation of the task: one is the lateral bending of trunk toward the weight-transfer side, and the other is a coordinated reciprocal leg action of both legs. A combination of these strategies is used in a trade-off fashion during natural motions. These results are clinically important for the assessment and therapy of patients with sitting problems.     

Haptic perception of partial-rod lengths with the rod held stationary or wielded

Three experiments on the haptic perception of partial-rod lengths are reported. The rods were gripped between the two ends and held horizontal. The subjects held the rods stationary; the distribution of mass of the segment in front of the hand was fixed, while the distribution of mass of the segment behind the hand was varied. Perceived forward length was found to be significantly affected by the distribution of mass of the backward segment. Similar results were obtained when the rods were wielded. The results indicated that partial-rod lengths are specified by functions of mechanical perturbations acting on the hand, and not ay the breaking up of the first moment of mass or the moment of inertia of the rod by attention as suggested previously by others. The results are also discussed with respect to invariant detection and attention.     

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.     

Perceiving extents of rods by wielding: haptic diagonalization and decomposition of the inertia tensor

We report two experiments on the length-perception capabilities of the hand-related haptic subsystem. On each trial, a visually occluded rod was wielded by the subject at a position intermediate between its two ends. The position was either 1/2 or 3/4 of the rod's length. On two-thirds of the trials, a weight was attached to the rod at a point either above or below its center of gravity and not coincident with the hand's position. In Experiment 1, the subject's task was to perceive the distance reachable with the portion of the rod extending beyond the position of the grasp. In the second experiment, the subject's task was to perceive the distance reachable with the entire rod if it were held at its proximal end. In Experiment 1, perceived reaching distance was a function of the moment of inertia of the amount of rod forward of the grasp about an axis through the proximal end of the rod segment. In Experiment 2, perceived reaching distance was a function of the moment of inertia of the entire rod about the given axis of rotation intermediate between the rod's ends. The results are discussed in terms of (a) the notion of smart perceptual instruments capitalizing on invariant properties of the inertia tensor and (b) how the haptic decomposition of moments of inertia follows the principle of equivalence of forces.     

How trunk turns affect locomotion when you are not looking where you go

How well do we maintain heading direction during walking while we look at objects beside our path by rotating our eyes, head, or trunk? Common experience indicates that it may be fairly hazardous not to look where you are going. In the present study, 12 young adults walked on a treadmill while they followed a moving dot along a horizontal line with their gaze by rotating primarily either their eyes, head, or trunk for amplitudes of up to 25 degrees . During walking the movement of the center of pressure (COP) was monitored using force transducers under a treadmill. Under normal light conditions, the participants showed little lateral deviation of the COP from the heading direction when they performed the eye or head movement task during walking, even when optic flow information was limited. In contrast, trunk rotations led to a doubling of the COP deviation in the mediolateral direction. Some of this deviation was attributed to foot rotation. Participants tended to point their feet in the gaze direction when making trunk turns. The tendency of the feet to be aligned with the trunk is likely to be due to a preference to have feet and body in the same orientation. Such alignment is weaker for the feet with respect to head position and it is absent with respect to eye position. It is argued that feet and trunk orientation are normally tightly coupled during gait and that it requires special abilities to move both segments independently when walking.