Biomedical subjects

T Pozzo

Publications and source records attributed to T Pozzo.

At least 19 recordsLinked to original sources

PubMed2006

Effect of fatigue on the precision of a whole-body pointing task.

We addressed the issue of the possible degradation of the aiming precision of a whole-body pointing task, when movement coordination is deranged by selective fatigue of the postural task component. The protocol involved continuous repetition (0.1 Hz frequency) of rapid whole-body pointing trials toward a target located beyond arm length, starting from stance and requiring knee flexion. Six healthy human subjects repeated the trials until exhaustion. Such repetition led to electromyography signs of fatigue in rectus femoris (active in body lowering and raising), but not in deltoid (prime mover for arm reaching component). Rectus femoris fatigue affected the equilibrium control strategy, since the anteroposterior displacement of the center of foot pressure was reduced during the fatigued compared with the initial trials. Conversely, the precision of the aiming movement was unaffected by the rectus femoris fatigue in spite of changes in finger trajectory. Trunk inclination at the end of whole-body pointing task and hip and shoulder marker trajectories were unaffected by rectus femoris fatigue. Control experiments were made, whereby fatiguing repetitions of the postural component of the task were performed without finger pointing, except in the first and last five complete whole-body pointing trials. The results were not different from those of the main protocol, except for a transient change in finger trajectory in the very first trial after fatigue. The CNS takes into account the state of postural muscles' fatigue and the concurrently ensuing equilibrium constraints in order to appropriately modify whole-body pointing strategy and keep pointing precision at the target.

Adult↗

PubMed2005

Improvement and generalization of arm motor performance through motor imagery practice.

This study compares the improvement and generalization of arm motor performance after physical or mental training in a motor task requiring a speed-accuracy tradeoff. During the pre- and post-training sessions, 40 subjects pointed with their right arm as accurately and as fast as possible toward targets placed in the frontal plane. Arm movements were performed in two different workspaces called right and left paths. During the training sessions, which included only the right path, subjects were divided into four training groups (n = 10): (i) the physical group, subjects overtly performed the task; (ii) the mental group, subjects imagined themselves performing the task; (iii) the active control group, subjects performed eye movements through the targets, (iv) the passive control group, subjects did not receive any specific training. We recorded movement duration, peak acceleration and electromyographic signals from arm muscles. Our findings showed that after both physical and mental training on the right path (training path), hand movement duration and peak acceleration respectively decreased and increased for this path. However, motor performance improvement was greater after physical compared with mental practice. Interestingly, we also observed a partial learning generalization, namely an enhancement of motor performance for the left path (non-training path). The amount of this generalization was roughly similar for the physical and mental groups. Furthermore, while arm muscle activity progressively increased during the training period for the physical group, the activity of the same muscles for the mental group was unchanged and comparable with that of the rest condition. Control groups did not exhibit any improvement. These findings put forward the idea that mental training facilitates motor learning and allows its partial transfer to nearby workspaces. They further suggest that motor prediction, a common process during both actual and imagined movements, is a fundamental operation for both sensorimotor control and learning.

Adult↗

PubMed2005

Effects of loss of metatarsophalangeal joint mobility on gait in rheumatoid arthritis patients.

OBJECTIVE: To evaluate the effects of loss of range of motion (ROM) of the metatarsophalangeal (MTP) joint on the kinematic parameters of walking in rheumatoid arthritis (RA) patients. METHODS: Inclusion of RA patients with inactive disease, no synovitis of the inferior limb and reduced ROM of the MTP joints. Evaluation of the ROM of the MTP dorsal and plantar flexion, and gait analysis using a three-dimensional computerized movement analysis. Calculation of gait parameters and maximal flexion and extension of the hips and knees during walking. Analysis 1 compared the ROM of dorsal and plantar flexion in patients with or without walking pain; 2 compared the gait parameters between patients and controls; 3 investigated a relationship between gait parameters and (i) the ROM of the MTP dorsal and plantar flexion and (ii) the pain at walking; 4 investigated the relationship between the ROM of the MTP dorsal and plantar flexion and maximal flexion and extension of the hip and knee joints during walking. RESULTS: Nine patients and seven controls were included. The MTP ROM was no different in patients presenting with or without pain at walking. The walking velocity was lower and the stride length shorter in patients than in controls. The walking velocity and the stride length were positively related to the MTP dorsal flexion ROM (r(2)=0.75 and 0.67). There was a negative relationship between maximal flexion of the knee and hips during walking and the underlying MTP dorsal flexion ROM (r(2)=0.67 and 0.54). CONCLUSION: In RA patients, reduced MTP dorsal flexion mobility induces changes in the walking parameters, including the kinematics of the overlying lower limb joints. Treatment of an RA-impaired forefoot should focus on MTP mobility as well as on pain.

Aged↗

PubMed2005

Kinematic and dynamic processes for the control of pointing movements in humans revealed by short-term exposure to microgravity.

The generation of accurate motor commands requires implicit knowledge of both limb and environmental dynamics. The action of gravity on moving limb segments must be taken into account within the motor command, and may affect the limb trajectory chosen to accomplish a given motor task. Exactly how the CNS deals with these gravitoinertial forces remains an open question. Does the CNS measure gravitational forces directly, or are they accommodated in the motor plan by way of internal models of physical laws? In this study five male subjects participated. We measured kinematic and dynamic parameters of upward and downward arm movements executed at two different speeds, in both normal Earth gravity and in the weightless conditions of parabolic flight. Exposure to microgravity affected velocity profiles for both directions and speeds. The shape of velocity profiles (the ratio of maximum to mean velocity) and movement duration both showed transient perturbations initially in microgravity, but returned to normal gravity values with practice in 0 x g. Differences in relative time to peak velocity between upward versus downward movements, persisted for all trial performed in weightlessness. These differences in kinematic profiles and in the torque profiles used to produce them, diminished, however, with practice in 0 x g. These findings lead to the conclusion that the CNS explicitly represents gravitational and inertial forces in the internal models used to generate and execute arm movements. Furthermore, the results suggest that the CNS adapts motor plans to novel environments on different time scales; dynamics adapt first to reproduce standard kinematics, and then kinematics patterns are adapted to optimize dynamics.

Adult↗

PubMed2005

[Ocular proprioception and developmental dyslexia. Sixty clinical observations].

PURPOSE: The objective of this study is to assess proprioception anomalies in postural deficiency syndrome in a group of children suffering from reading impairment. MATERIAL AND METHODS: Sixty male patients with an average age of 11 years and 9 months were included in the study. Initially, they were given a standardized neuropsychological examination, which confirmed the diagnosis of reading impairment. Then after filling out a questionnaire seeking a proprioceptive anomaly, the patients were subjected to a clinical ocular and postural examination consisting of nine precisely described steps. RESULTS: All of the patients recruited for the study presented clinical signs confirming a proprioception disorder found as a part of postural deficiency syndrome. CONCLUSION: This study opens a new direction for research concerning the origin and treatment of at least some reading-impaired children.

Adolescent↗

PubMed2004

Temporal relationship between postural and focal components of a whole-body reaching movement: a study case of short-term adaptation in microgravity condition.

In this study, the question of postural and focal components integration by the central nervous system (CNS) is investigated through whole body reaching task performance in microgravity. Because of the especially important difficulties suffered by one subject during parabolic flight, observation of temporal relationship evolution was allowed. From these results, short-term adaptation based on the restoration of this relationship could be postulated.

Adaptation, Physiological↗

PubMed2003

Similar planning strategies for whole-body and arm movements performed in the sagittal plane.

The present paper looks for kinematic similarities between whole-body and arm movements executed in the sagittal plane. Eight subjects performed sit-to-stand (STS) and back-to-sit (BTS) movements at their preferred speed in the sagittal plane. Kinematics analysis focused on shoulder motion revealed that STS was composed of a straight, forward displacement followed by a curved, upward displacement while BTS was characterized by a curved, downward and straight, backward displacement. Curvature of the upward displacement was significantly greater than the downward one. Analysis of shoulder-velocity profiles showed that movement duration was significantly longer for BTS compared with STS and that the shape of the velocity profiles changed when subjects performed an STS compared with a BTS movement. Velocity profiles of the upward and downward displacements also differed; the relative acceleration duration (acceleration duration divided by movement duration during the vertical motion) was smaller for the upward compared with the downward displacement. The present results are in accordance with previous findings concerning the execution of vertical arm movements and suggest that the CNS uses similar motor plans for the performance of arm and whole-body movements in the sagittal plane.

Adult↗

PubMed2002

Evidence of short-term adaptation to microgravity of neuromuscular synergy during a whole body movement.

Human, like any other animal systems, moves in the terrestrial gravity field and must learn gravity-related motor strategies during his ontogenetic development. Considering continuous gravity action upon body segments, movement involves particular muscle activation patterns depending on body orientation to gravity. Gravitational-altered environments provided by parabolic flight or orbital space mission offer a great opportunity to investigate how gravity is taken into account in posture and movement planning. Indeed, in a context where the mechanical constraints are modified, movement execution involves that new muscular activity have to be produced. Almost, only few studies in microgravity environment are included electromyographic analysis and this parameter is generally used only to confirm modification of the muscular activation patterns. This study is focused to analyse the adaptation capacity of the brain to a modified gravitational environment. In this aim, EMG activity have been recorded during a whole body movement execution in both normo- and microgravity environment during parabolic flight. This procedure allowed us to analyse the EMG patterns recorded during the very first moments of weightlessness. In this study are reported the results of this analyse.

Journal Article↗

PubMed2001

Continuous, bilateral Achilles' tendon vibration is not detrimental to human walk.

Sensory feedback from the moving limbs contributes to the regulation of animal and human locomotion. However, the question of the specific role of the various modalities is still open. Further, functional loss of leg afferent fibres due to peripheral neuropathy does not always lead to major alteration in the gait pattern. In order to gain further insight on proprioceptive control of human gait, we applied vibratory tendon stimulation, known to recruit spindle primary afferent fibres, to both triceps surae muscles during normal floor walk. This procedure would disturb organisation and execution of walking, especially if spindles fire continuously and subjects are blindfolded. Vibration induced significant, though minor, changes in duration and length of stance and swing phase, and on speed of walking and kinematics of lower limb segments. No effect was induced on angular displacement of the ankle joint or trunk and head kinematics. This paucity of effects was at variance with the perception of the subjects, who reported illusion of leg stiffness and gait imbalance. These findings would speak for a selective gating of Ia input during locomotion and emphasise the notion that the central nervous system can cope with an unusual continuous input along the Ia fibres from a key muscle like the soleus.

Achilles Tendon↗

PubMed2001

Simulating mechanical consequences of voluntary movement upon whole-body equilibrium: the arm-raising paradigm revisited.

Voluntary arm-raising movement performed during the upright human stance position imposes a perturbation to an already unstable bipedal posture characterised by a high body centre of mass (CoM). Inertial forces due to arm acceleration and displacement of the CoM of the arm which alters the CoM position of the whole body represent the two sources of disequilibrium. A current model of postural control explains equilibrium maintenance through the action of anticipatory postural adjustments (APAs) that would offset any destabilising effect of the voluntary movement. The purpose of this paper was to quantify, using computer simulation, the postural perturbation due to arm raising movement. The model incorporated four links, with shoulder, hip, knee and ankle joints constrained by linear viscoelastic elements. The input of the model was a torque applied at the shoulder joint. The simulation described mechanical consequences of the arm-raising movement for different initial conditions. The variables tested were arm inertia, the presence or not of gravity field, the initial standing position and arm movement direction. Simulations showed that the mechanical effect of arm-raising movement was mainly local, that is to say at the level of trunk and lower limbs and produced a slight forward displacement of the CoM (1.5 mm). Backward arm-raising movement had the same effect on the CoM displacement as the forward arm-raising movement. When the mass of the arm was increased, trunk rotation increased producing a CoM displacement in the opposite direction when compared to arm movement performed without load. Postural disturbance was minimised for an initial standing posture with the CoM vertical projection corresponding to the ankle joint axis of rotation. When the model was reduced to two degrees of freedom (ankle and shoulder joints only) the postural perturbation due to arm-raising movement increased compared to the four-joints model. On the basis of these results the classical assumption that APAs stabilise the CoM is challenged.

Arm↗

PubMed2001

Neck muscle vibration disrupts steering of locomotion.

Neck muscle vibration was applied to human subjects to assess the influences of neck abnormal proprioceptive input on the organization and execution of gait. Subjects walked blindfolded to a previously seen target, located straight ahead at ~4 m. Vibration was applied on the right side of the neck, both during and before walking. The variables measured were length, duration, and velocity of trajectory; relative and absolute frontal errors at target; and width of walking support base. Vibration applied during locomotion produced an undershoot of target and deviation of gait trajectory toward the side opposite to vibration. Vibration applied before locomotion produced no effect on length of trajectory but slowing of velocity and nonsystematic deviation. When vibration frequency was increased, the amplitude of the nonsystematic deviation increased. Vibration applied during or before stance trials had minor effects on body sway. Vibration before stance had no effect on the position of mean center of foot pressure, whereas vibration during stance displaced it to the side opposite to the vibrated muscle. We suggest that vibration during locomotion reduces length and velocity of trajectory because of a direct action on the locomotor centers and produces trajectory deviation related to its effect on stance. Vibration before locomotion causes a major, nonsystematic deviation from the planned trajectory, possibly connected to a disorientation of the internal references.

Adult↗

PubMed2001

[Vibration after effect during human walking].

Muscular vibration effects could usually persist after the end of the stimulation. The extinction of this after-effect was studied during human walk. Six subjects performed a locomotor task (six successive steps) under control, and after bilateral Achilles' tendon vibration (70 Hz). The step frequency was enhanced (diminution of the stance phase duration) whereas the stride length tended to decrease. The relative duration of the stance phase reached back normal values with repetitions. These results demonstrated that vibration-induced effects persevere after the end of the stimulation. In addition, owing to the dynamic of the re-adaptation process, they suggested that the muscular proprioceptive input could participate in both maintaining and regulating the locomotor rhythm.

Achilles Tendon↗

PubMed2000

Investigating centre of mass stabilisation as the goal of posture and movement coordination during human whole body reaching.

In the light of experimental results showing significant forward centre of mass (CoM) displacements within the base of support, this study investigated if whole body reaching movements can be executed whilst keeping the CoM fixed in the horizontal axis. Using kinematic simulation techniques, angular configurations were recreated from experimental data imposing two constraints: a constant horizontal position of the CoM and an identical trajectory of the hand to grasp an object. The comparison between recorded and simulated trials showed that stabilisation of the CoM was associated with greater backward hip displacements, which became more marked with increasing object distance. This was in contrast to recorded trials showing reductions in backward hip displacements with increasing distance. Results also showed that modifications to angular displacements were necessary only at the shoulder and hip joints, but that these modifications were within the limits of joint mobility. The analysis of individual joint torques revealed that the pattern and timing of simulated trials were similar to those recorded experimentally. Peak joint torque values showed particularly that keeping the CoM at a constant horizontal position resulted in significantly smaller ankle peak flexor and extensor torques. It may be concluded from this study that 'stabilising' the CoM during human whole body reaching represents a feasible strategy, but not the one chosen by subjects under experimental conditions. Our results also do not support the idea of the CoM as the stabilised reference value for the coordination between posture and goal-directed movements.

Adolescent↗

PubMed2000

Standing up from a chair as a dynamic equilibrium task: a comparison between young and elderly subjects.

The purpose of this study was to analyze and compare the features of center of mass (CoM) control along anterior/posterior axis in young and elderly subjects during sit-to-stand (STS). From a sitting position, seven healthy young subjects and seven healthy elderly subjects were asked to stand up from a chair under different experimental conditions (visual conditions: normal and blindfolded; speed: normal and as fast as possible). Analysis of results was based upon the concept of a "dynamic equilibrium area" (DEA), which in turn identified the dynamic limits of balance. The results showed that both the maximal CoM velocity in the horizontal axis and the CoM velocity at the instant of seat-off were found to be lower in elderly compared with young subjects. Concerning the maximal CoM velocity, the difference was increased under blindfolded condition. The position of CoM in the phase plane (i.e., velocity according to displacement) at the instant of seat-off was found to be shifted backward in elderly subjects. From these results we can deduce that age-related modifications can he observed in the control of the horizontal CoM motion during STS in healthy elderly subjects.

Adult↗

PubMed1999

Effects of kinematics constraints on hand trajectory during whole-body lifting tasks.

Trajectories of the hands and whole-body center of mass were studied during whole-body lifting tasks. The movements of different parts of the body were monitored with the ELITE system. Subjects were instructed to lift to shoulder height an object placed at one of two distances (5-45 cm) before them on the floor. The lifts were performed both with and without kinematics constraints (i.e. to produce a straight hand trajectory while lifting, and to lift without any instructions, respectively). Hand trajectories were roughly straight when performed under the constrained condition, but curved when performed without instruction. Hand velocity curves showed bell-shaped profiles. In both groups, body centers of mass (whole-body, upper and lower part) were calculated and their trajectories showed invariant sagittal displacements. These results support the idea that movement contributes to postural control and, reciprocally, that whole-body center of mass is a robust and controlled variable which plays an important role in hand trajectory formation.

Adult↗

PubMed1999

Does the coordination between posture and movement during human whole-body reaching ensure center of mass stabilization?

The whole-body center of mass (CoM) has been classically regarded as the stabilized reference value for human voluntary movements executed upon a fixed base of support. Axial synergies (opposing displacements of head and trunk with hip segments) are believed to minimize antero-posterior (A/P) CoM displacements during forward trunk movements. It is also widely accepted that anticipatory postural adjustments (APAs) create forces of inertia that counteract disturbances arising from the moving segment(s). In the present study, we investigated CoM stabilization by axial synergies and APAs during a whole-body reaching task. Subjects reached towards an object placed on the ground in front of them in their sagittal plane using a strategy of coordinated trunk, knee, and hip flexion. The reaching task imposed constraints on arm-trajectory formation and equilibrium maintenance. To manipulate equilibrium constraints, differing conditions of distance and speed were imposed. The comparison of distance conditions suggested that axial synergies were not entirely devoted to CoM stabilization: backward A/P hip displacements reduced as head and trunk forward A/P displacements increased. Analysis of upper- and lower-body centers of mass in relation to the CoM also showed no strict minimization of A/P CoM displacements. Mechanical analysis of the effects of APAs revealed that, rather than acting to stabilize the CoM, APAs created necessary conditions for forward CoM displacement within the base of support in each condition. The results have implications for the CoM as the primary stabilized reference for posture and movement coordination during whole-body reaching and for the central control of posture and voluntary movement.

Adolescent↗

PubMed1998

Effects of movement direction upon kinematic characteristics of vertical arm pointing movements in man.

Vertical arm pointing movements in two directions (upwards and downwards), imposing two different loads (unload and 0.5 kg) and speeds (normal and fast) have been studied in six subjects. Movements were recorded using an optoelectronic system. Data analysis concentrated upon finger-tip kinematics. Significant effects of movement direction were recorded upon velocity profiles. The acceleration time, computed relative to total movement time, was greater for downward movements than for upward movements. In contrast however, no effects of load or speed were observed. Movement time was not affected by movement direction or load, for both speeds tested. These results suggest different planning processes, for movements with and against gravity and indicate that gravitational force influences the processes controlling movement execution.

Acceleration↗

PubMed1998

The role of anticipatory postural adjustments during whole body forward reaching movements.

The purpose of this study was to examine the role of anticipatory postural adjustments (APAs) in the execution of forward oriented whole body reaching movements. From the standing position, eight healthy subjects were asked to reach an object placed at 45 cm from the feet, at both naturally paced and fast speeds. Electromyographic signals of six antagonistic muscles were analysed in conjunction with centre of mass (CM) displacements, centre of foot pressure displacements and resultant ground reaction forces. Results revealed that APAs created necessary angular momentum of body segments for effective task execution. These results suggest that APAs can initiate movements conducted from a fixed base of support, and in this context do not act solely to stabilize the CM.

Adaptation, Physiological↗