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PubMed2004

Lifting over an obstacle: effects of one-handed lifting and hand support on trunk kinematics and low back loading.

Mechanical loading of the low back during lifting is a common cause of low back pain. In this study two-handed lifting is compared to one-handed lifting (with and without supporting the upper body with the free hand) while lifting over an obstacle. A 3-D linked segment model was combined with an EMG-assisted trunk muscle model to quantify kinematics and joint loads at the L5S1 joint. Peak total net moments (i.e., the net moment effect of all muscles and soft tissue spanning the joint) were found to be 10+/-3% lower in unsupported one-handed lifting compared to two-handed lifting, and 30+/-8% lower in supported compared to unsupported one-handed lifting. L5S1 joint forces also showed reductions, but not of the same magnitude (18+/-8% and 15+/-10%, respectively, for compression forces, and 15+/-17% and 11+/-14% respectively, for shear forces). Those reductions of low back load were mainly caused by a reduction of trunk and load moment arms relative to the L5S1 joint during peak loading, and, in the case of hand support, by a support force of about 250 N. Stretching one leg backward did not further reduce low back load estimates. Furthermore, one-handed lifting caused an 6+/-8 degrees increase in lateral flexion, a 9+/-5 degrees increase in twist and a 6+/-6 degrees decrease in flexion. Support with the free hand caused a small further increase in lumbar twisting. It is concluded that one-handed lifting, especially with hand support, reduces L5S1 loading but increases asymmetry in movements and moments about the lumbar spine.

Abdomen↗
PubMed2004

Paraspinal muscle reflex dynamics.

Neuromuscular control of spinal stability may be represented as a control system wherein the paraspinal muscle reflex acts as feedback response to kinetic and kinematic disturbances of the trunk. The influence of preparatory muscle recruitment for the control of spinal stability has been previously examined, but there are few reported studies that characterize paraspinal reflex gain as feedback response. In the current study, the input-output dynamics of paraspinal reflexes were quantified by means of the impulse response function (IRF), with trunk perturbation force representing the input signal and EMG the output signal. Surface EMGs were collected from the trunk muscles in response to a brief anteriorly directed impact force applied to the trunk of healthy participants. Reflex behavior was measured in response to three levels of force impulse, 6.1, 9.2 and 12.0 Ns, and two different levels of external trunk flexion preload, 0 and 110 N anterior force. Reflex EMG was quantifiable in response to 91% of the perturbations. Mean reflex onset latency was 30.7+/-21.3 ms and reflex amplitude increased with perturbation amplitude. Impulse response function gain, G(IRF), was defined as the peak amplitude of the measured IRF and provided a consistent measure of response behavior. EMG reflex amplitude and G(IRF) increased with force impulse. Mean G(IRF) was 2.27+/-1.31% MVC/Ns and demonstrated declining trend with flexion preload. Results agree with a simple systems model of the neuromechanical feedback behavior. The relative contribution of the reflex dynamics to spinal stability must be investigated in future research.

Adaptation, Biological↗
PubMed1999

Development of a set of equations describing joint trajectories during para-sagittal lifting.

Given a lifting task with predetermined starting and ending positions, the angular trajectories are usually very consistent with a distinctive pattern. This paper derives a set of equations that can describe the joint trajectories during a para-sagittal lifting task. Three optimal motion patterns were also expressed by the polynomials: minimal hand jerk, minimal center of gravity (CG) jerk, and minimal muscle utilization rate (MUR). The variability of the joint movements were synthesized by overlapping the optimal patterns.

Adult↗
PubMedDate not supplied

Air righting: role of the NMDA receptor channel and hippocampal LTP.

Air righting results in an animal turning over when it is dropped from a height in an inverted position. In the rat, air righting is a complex set of movements that depends only on an intact labyrinth and the normal vestibular input. Visual modulation of air righting does not develop until adulthood; and the ability to estimate the time to impact requires bilateral visual cues and indicates that air righting is a complex set of perceptually controlled movements and learning. The general purpose of this study was to determine the role of the NMDA receptor-ion channel on air righting and hippocampal LTP. Specifically: to measure the effects of various doses of CPP, an NMDA receptor antagonist, and MK-801, an ion channel blocker, on (a) air righting and (b) hippocampal LTP induction in medial perforant path-granule cell synapses. The following doses were used: CPP-0, 1, 5, and 10 mg/kg i.p.; MK-801-0. 0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 mg/kg i.p. Data were analyzed by appropriate ANOVAs and post hoc tests. Results were significant and demonstrate dose-dependent impairment of air righting and inhibition of LTP for both CPP and MK-801, implicating the role of the NMDA receptor and Na(+)/K(+)/Ca(2)+ channel in these effects. Air righting is a complex behavior and appears to be dependent upon NMDA mediated hippocampal LTP.

Analysis of Variance↗
PubMedDate not supplied

Motor dysfunction in a mouse model for Down syndrome.

Motor deficits are among the most frequently occurring features of Down syndrome (DS). Individuals with DS exhibit disturbances in the dynamics of movement production and postural control that are thought to have a significant impact in delaying their acquisition of motor skills. The origin of these deficits has been hypothesized to be cerebellar. The Ts65Dn mouse is the most robust and genetically sound animal model for DS currently available. Ts65Dn mice show many DS-like features, including significant learning deficits in different behavioral tasks and neurodegeneration of cholinergic neurons. In the present study, we investigate the motor function of these animals. We have analyzed hind paw print patterns during walking, running speeds, rotarod performance, grip force production, swim paths, and swimming speeds. Our results indicate that Ts65Dn mice present mild to severe dysfunction according to all of the above assessments. The most evident impairments presented by these mice were related to equilibrium and motor coordination, which agrees with reported clinical observations made on individuals with DS. Because none of these findings were readily apparent by simple inspection of these animals, these findings reiterate the need for a careful evaluation of any mutant mouse strain for which there is reason to suspect motor deficits. The identification of motor dysfunction in Ts65Dn mice may have important consequences for the interpretation of some previous assessments of learning and memory of these animals that assumed intact motor function, and further strengthens the use of this aneuploid mouse strain as a model for DS.

Animals↗
PubMed1989

The role of stretch and vestibulo-spinal reflexes in the generation of human equilibrating reactions.

Equilibrating reactions in standing humans were examined for evidence that either vestibulo-spinal or proprioceptive long loop stretch reflexes from ankle muscles, or both, are responsible for the control and organization of rapid postural responses. Specifically, the hypothesis was tested that the same postural response could be evoked by rotation of the support surface that mimics the ankle rotation occurring during support surface translations. Rotation perturbations evoked postural responses in leg and trunk muscles that were different in strategy, synergy and coactivation from translation responses, even though the short-latency response in the stretched triceps surae muscles was equal in latency and size. Movement patterns consisted of a stiffening strategy and hardly any compensating ankle rotation for rotation stimuli, and a multi-link strategy with motion focused about the neck, hip and ankle joints for translation stimuli. Dorsiflexion rotations caused earlier and stronger responses in tibialis anterior and quadriceps muscles just post to the onset of paraspinal muscles, whereas rearward translation activated soleus and abdominals strongest, both just prior to hamstring muscles. Correlated activation strengths of agonist and antagonist activity was a common feature for both types of perturbation, albeit, only in the ankle muscles for rotations and only in the trunk muscles for translations. These data suggest that sensory inputs, other than those generated in the lower leg predominate, in the triggering and modulation of equilibrating reactions. Possible candidates are those of the vestibular system or proprioceptive inputs from the trunk.

Humans↗
PubMed1993

Gating of reflexes in ankle muscles during human stance and gait.

Holding the body's centre of gravity steady represents the crucial variable for the stabilization of posture in upright stance in man. Results from two experimental approaches suggest that force-dependent receptors are required, in addition to the well-known systems involved in sway stabilization, for equilibrium control. One approach concerns bilateral leg muscle activation during stance. Unilateral or bilateral leg displacements were induced while subjects stood on a treadmill with split belts. A unilateral displacement induced a bilateral EMG response. During bilateral displacements the EMG activity was linearly summed or subtracted, depending on whether the legs were displaced in the same or opposite directions. Both legs acted in a cooperative manner: each limb affected the strength of muscle activation and the time-space behaviour of the other. This interlimb coordination is suggested to be mediated by spinal interneuronal circuits, which are themselves under supraspinal (e.g., cerebellar) control. The other approach concerns the modulation of postural reflexes under stimulated "microgravity" ir. water immersion. An approximately linear relationship was found between contact forces and impulse-directed EMG response amplitudes in the leg muscles. Out of water loading of the subjects resulted in no further increase of the response amplitude. It was concluded that the function of proprioceptive reflexes involved in the stabilization of posture depends on the presence of contact forces opposing gravity. Extensor load receptors are thought to signal changes of the projection of body's centre of mass with respect to the feet. The interaction of the afferent input from these receptors with the other systems involved in postural control is not yet fully understood.

Ankle↗
PubMed2002

Uranyl acetate-induced sensorimotor deficit and increased nitric oxide generation in the central nervous system in rats.

We investigated the effects of uranyl acetate on sensorimotor behavior, generation of nitric oxide and the central cholinergic system of rats. Male Sprague-Dawley rats were treated with intramuscular injection of 0.1 and 1 mg/kg uranyl acetate in water, daily for 7 days. Control animals received equivalent amount of water. The treatment was stopped after the seventh injection because the animals in the 1-mg/kg group appeared lethargic. The animals were maintained for an additional observation period of 30 days. The study was initiated as a dose-finding study that covered doses of 10 and 100 mg/kg, as well. However, all the animals in the 100-mg/kg treatment group died after the third and fourth injections, and all animals given 10 mg/kg died after the fifth and sixth injections. On Day 30 following the cessation of treatment, the sensorimotor functions of the animals in the 0.1- and 1-mg/kg treatment groups were evaluated using a battery of tests that included measurements of postural reflexes, limb placing, orientation to vibrissae touch, grip time, beam walking and inclined plane performance. The animals were sacrificed the same day and the cerebral cortex, brainstem, cerebellum and midbrain were dissected. The levels of nitric oxide as marker for increased oxidative stress, and the integrity of the cholinergic system as reflected in acetylcholinesterase (AChE) activity and m2 muscarinic acetylcholine receptors ligand binding, were determined. The data from behavioral observations show that there was a dose-related deficit at the 0.1- and 1-mg/kg treatment groups for inclined plane performance. Both doses reduced grip time, but there was no significant difference between the two doses. Similarly, both beam-walk score and beam-walk time were impaired at both doses as compared with the controls. A significant increase in nitric oxide was seen at 0.1 mg/kg dose in cortex and midbrain, whereas brainstem and cerebellum showed an insignificant decrease at both the doses. Similarly, there was no significant change in nitric oxide levels in kidneys and liver of the treated animals as compared with the controls. There was a significant increase in AChE activity in the cortex of the animals treated with 1 mg/kg uranyl acetate, but not in other brain regions. Ligand binding densities for the m2 muscarinic receptor did not show any change. These results show that low-dose, multiple exposure to uranyl acetate caused prolonged neurobehavioral deficits after the initial exposure has ceased.

Acetylcholinesterase↗
PubMed2002

Behavioral responses to stress following central and peripheral injection of the 5-HT(2) agonist DOI.

Evidence suggests that serotonin (5-HT) systems are involved in the regulation of an organism's response to stress. Experiments were conducted to evaluate the possibility that central (20, 100, or 200 microg icv), peripheral (0.1, 0.5, or 1.0 mg/kg sc), or combined central (200 microg) plus peripheral (0.1 mg/kg) injections of the selective 5-HT(2) agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI) would alter behavioral responses to stress in rats. Animals were evaluated during tail pinch stress, in an open field, and on a rotarod task. Across the three modes of administration (icv, sc, icv+sc), DOI resulted in a dose-related decrease in five of seven classes of behaviors observed during tail pinch. This reduction was most pronounced following subcutaneous injections, but occurred following intracerebroventricular and combined subcutaneous and intracerebroventricular injections as well. An additive effect of combined intracerebroventricular and subcutaneous administration was suggested by the fact that doses which were ineffective when given singly by these two routes resulted in a reduction in stress-evoked behavior when given together. Reduced responding seemed not to be attributable to general motoric impairment as DOI did not affect locomotion, grooming, or rotarod performance. The results suggest that activation of 5-HT(2) receptors produces an anxiolytic effect in rats subjected to acute tail pinch stress.

Amphetamines↗
PubMedDate not supplied

Motor coordination in weightless conditions revealed by long-term microgravity adaptation.

The functional approach to studying human motor systems attempts to give a better understanding of the processes behind planning movements and their coordinated performance by relying on weightlessness as a particularly enlightening experimental condition. Indeed, quantitative monitoring of sensorimotor adaptation of subjects exposed to weightlessness outlines the functional role of gravity in motor and postural organization. The recent accessibility of the MIR Space Station has allowed for the first time experimental quantitative kinematic analysis of long-term sensorimotor and postural adaptation to the weightless environment though opto-electronic techniques. In the frame of the EUROMIR'95 Mission, two protocols of voluntary posture perturbation (erect posture, EP; forward trunk bending, FTB) were carried out during four months of microgravity exposure. Results show that postural strategies for quasistatic body orientation in weightlessness are based on the alignment of geometrical body axes (head and trunk) along external references. A proper whole body positioning appears to be recovered only after months of microgravity exposure. By contrast, typically, terrestrial strategies of co-ordination between movement and posture are promptly restored and used when performing motor activities in the weightless environment. This result is explained under the assumption that there may be different sensorimotor integration processes for static and dynamic postural function and that the organisation of coordinated movement might rely stably on egocentric references and kinematics synergies for motor control.

Adaptation, Physiological↗
PubMedDate not supplied

Does the centre of mass remain stable during complex human postural equilibrium tasks in weightlessness?

In normal gravity conditions the execution of voluntary movement involves the displacement of body segments as well as the maintenance of a stable reference value for equilibrium control. It has been suggested that centre of mass (CM) projection within the supporting base (BS) is the stabilised reference for voluntary action, and is conserved in weightlessness. The purpose of this study was to determine if the CM is stabilised during whole body reaching movements executed in weightlessness. The reaching task was conducted by two cosmonauts aboard the Russian orbital station MIR, during the Franco-Russian mission ALTAIR, 1993. Movements of reflective markers were recorded using a videocamera, successive images being reconstructed by computer every 40ms. The position of the CM, ankle joint torques and shank and thigh angles were computed for each subject pre- in- and post-flight using a 7-link mathematical model. Results showed that both cosmonauts adopted a backward leaning posture prior to reaching movements. Inflight, the CM was displaced throughout values in the horizontal axis three times those of pre-flight measures. In addition, ankle dorsi flexor torques inflight increased to values double those of pre- and post-flight tests. This study concluded that CM displacements do not remain stable during complex postural equilibrium tasks executed in weightlessness. Furthermore, in the absence of gravity, subjects changed their strategy for producing ankle torque during spaceflight from a forward to a backward leaning posture.

Aerospace Medicine↗
PubMed2003

Closed-loop multivariable system identification for the characterization of the dynamic arm compliance using continuous force disturbances: a model study.

This study presents a new multivariable closed-loop identification technique for estimating the dynamic compliance of the multijoint human arm during posture maintenance. The method is designed for the application of continuous force disturbances that facilitate interaction of the limb with the environment. The dynamic compliance of the arm arises from different physiological mechanisms and is important for maintaining stable postures and to suppress disturbances. Estimates can be useful to analyze the ability of the nervous system to adapt the arm compliance to different types of disturbances and environments. The technique is linear and requires no a priori knowledge of the system. Linear system behavior is justified for posture tasks where the hand position deviates slightly from a reference position. Interaction results in a closed-loop configuration of arm and environment. The problem with previous methods is the restriction to open-loop systems. With the current technique, the dynamic arm compliance is separately estimated from the closed-loop. The accuracy of the identification technique is tested by simulations for different values of the dynamic compliance of the arm and environment and for different methodological parameters. It is concluded that the identification technique is accurate, even for short observation periods and severe noise.

Arm↗
PubMed2001

Effects of dentate nucleus lesions on spatial and postural sensorimotor learning in rats.

The role of the dentate nucleus on spatial orientation, assessed by the Morris water maze test, and on postural sensorimotor performance, assessed by vertical grid, suspended wire, and rotorod tests, was investigated. Bilateral electrolytic lesions of the dentate nucleus slowed down the acquisition of the hidden platform task of the Morris water maze, without affecting long-term retention, the probe trial, and the visuomotor guidance necessary for swimming toward a visible goal. In addition, reversal learning was impaired in the submerged platform condition. The lesions did not affect any of the motor performance scores. The selective impairment seen during acquisition of the hidden platform task is similar to that previously reported in rats with combined lesions of the cerebellar hemispheres and dentate, indicating a specific role for this region in spatial orientation.

Animals↗
PubMed2003

Behavioural changes induced by early and long-term gravito-inertial force modification in the rat.

The study concerns rats conceived, born and raised in a hypergravity environment (HG: 2 g) for 3 months using a centrifuge. They were then exposed to terrestrial gravity (1 g) and submitted to behavioural tests investigating their spontaneous locomotor activity (open-field), their posture (support surface), and their vestibular function (air-righting reflex). Performances were compared to age-matched control rats housed at 1 g for the same time period. Results showed static and dynamic behavioural deficits as early as the rats were exposed to normal gravity. They exhibited strongly increased motor activity in open-field, with longer travelled distances and more scattered trajectories; in addition, the HG rats displayed more numerous rearings than controls did. They showed postural changes characterized by an enlarged support surface and they did not succeed in the air-righting reflex, due to increased time-delay for head righting. None of these changes were permanent. Indeed, for all tests, the HG rats tested after 3 weeks spent in normal terrestrial gravity exhibited behaviours similar to those of the controls. HG-induced changes in the functional properties of the vestibular system may explain the deficits showed by the HG rats once exposed to normal gravity. The adaptation process to 1 g leading to the appearance of normal behaviour takes about 3 weeks. It likely implicates a central re-evaluation of the sensory inputs and an updating of the motor commands.

Adaptation, Physiological↗