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Biomedical subjects

T Pozzo

Publications and source records attributed to T Pozzo.

At least 37 records · Page 2Linked to original sources
PubMed1998

Hand trajectory formation during whole body reaching movements in man.

End-effector trajectory formation was studied during a reaching movement using the whole body. The movements of various parts of the body were measured with the optoelectronic ELITE system. Wrist reaching movement paths showed noticeable curvatures. The analysis of various marker onset latencies revealed that the wrist was the last to move, always after the head, knee or trunk, suggesting a subordinate role of the focal component with respect to the primary role of the equilibrium component. These results suggest that reaching wrist movements are subjected to whole-body equilibrium constraints in addition to constraints placed upon end-effector kinematics or the dynamic optimization of upper-limb movements.

Adult↗
PubMed1998

The representation of gravitational force during drawing movements of the arm.

The purpose of the present experiment was to study the way in which the central nervous system (CNS) represents gravitational force (GF) during vertical drawing movements of the arm. Movements in four different directions: (a) upward vertical (0 degrees), (b) upward oblique (45 degrees), (c) downward vertical (180 degrees) and (d) downward oblique (135 degrees), and at two different speeds, normal and fast, were executed by nine subjects. Data analysis focused upon arm movement kinematics in the frontal plane and gravitational torques (GTs) exerted around the shoulder joint. Regardless of movement direction, subjects showed straight-line paths for both speed conditions. In addition, movement time and peak velocity were not affected by movement direction and consequently changes in GT, for both speeds tested. Movement timing (evaluated through the ratio of acceleration time to total time) changed significantly, however, as a function of movement direction and speed. Upward movements showed shorter acceleration times when compared with downward movements. Concerning the four directions, movements made at 0 degrees and 45 degrees differed significantly from those made at 135 degrees and 180 degrees. Drawing movements executed at rapid speed presented similar acceleration and deceleration times compared with movements executed at normal speed, which showed greater acceleration than deceleration times. In addition, the form of velocity profiles (assessed through the ratio of maximum to mean velocities), was significantly modified only with movement speed. Results from the present study suggest that GF is efficiently incorporated into internal dynamic models that the brain builds up for the execution of arm movements. Furthermore, it seems that GF not only is a mechanical parameter to be overcome by the motor system but also constitutes a reference (vertical direction), both of which are represented by the CNS during inverse kinematic and dynamic processes.

Adult↗
PubMed1998

Hand trajectories of vertical arm movements in one-G and zero-G environments. Evidence for a central representation of gravitational force.

The purpose of the present experiment was to study the way in which the central nervous system (CNS), represents gravitational force during vertical arm pointing movements. Movements in upward (against gravity) and downward (with gravity) directions, with two different mass loads (hand empty and with a hand-held 0.5-kg weight) were executed by eight subjects in a normal gravitational environment. Movements by two cosmonauts, in the two directions, were also tested in a state of weightlessness. Analyses focused upon finger trajectories in the sagittal plane. Subjects in a normal gravitational environment showed curved paths for both directions and weight conditions. In addition, downward movements showed significantly smaller curvatures than upward movements. Movement times were approximately the same for all the experimental conditions. Curvature differences between upward and downward movements persisted during space flight and immediately postflight. Movement times from both cosmonauts increased slightly during flight, but returned to normal immediately on reentry in a one-G environment. Results from the present study provide evidence that gravity is centrally represented in an anticipatory fashion as a driving force during vertical arm movement planning.

Adult↗
PubMed1998

The sensorimotor and cognitive integration of gravity.

In order to demonstrate that gravity is not only a load acting locally and continuously on the body limbs, but is also used by higher levels of the nervous system as a dynamic orienting reference for the elaboration of the motor act, a review of several experiments conducted both in 1 g and 0 g are presented. During various locomotor tasks, the strategy that consists of stabilizing the head with respect to gravity illustrates one of the solutions used by the CNS to optimize the control of dynamic equilibrium. A question which remains to be solved when considering experimental results obtained in weightlessness concerns, however, the maintenance of motor schema that has evolved under normal gravity. Results have suggested that the concept of conservative processes, that would adapt postural control to weightlessness by using previously learned innate strategies, must be reconsidered during goal-oriented tasks. In fact, it is proposed that when conservative processes and existing solutions derived from a repertoire of terrestrial postural strategies do not provide efficient output, the CNS has to create novel strategies through a slow learning process. As with the study of postural control, three-dimensional arm reaching movements also illustrate the central representation of gravity. Indeed, gravity can be regarded as either initiating or braking arm movements and, consequently, may be represented in the motor command at the planning level. Finally, from a prospective point of view, there is a need to determine new experimental paradigms in order to study the specific motor control of man in space. It is suggested that the formulation of experimental paradigms should not consider man in space simply as a terrestrial biped.

Arm↗
PubMed1998

A kinematic comparison between elderly and young subjects standing up from and sitting down in a chair.

BACKGROUND AND AIMS: The transfer from sitting to standing and back to sitting as the two phases of the same task has never been studied in elderly people. The purposes of this study were to analyse and compare kinematic features of the whole task (standing up and sitting down) and to determine whether there are age-related differences upon movement kinematics in healthy elderly persons during the whole sequence (standing up and sitting down). METHODS: The movements of various parts of the body were measured with a 100 Hz television image analyser that computed the co-ordinates of small reflective markers glued onto the skin of the subjects. The task was conducted using an armless chair set to 100% of knee height under four conditions: at normal speed in light, at normal speed in the dark, at fast speed in light and at fast speed in the dark. TYPE OF STUDY: Laboratory study. RESULTS: In young subjects, the task was characterized by similar acromion trajectories and angular displacement of trunk in standing up and sitting down and by a stabilization of the head in space during the two phases. However, the time required to achieve the movement was found to be greater in sitting down than in standing up, and an adjustment of velocity appeared in final part of the movement before reaching the chair. In sitting down, as in carrying out a pointing task of upper limb, an adjustment was required to achieve accuracy. This feature was not found in standing up. Age-related differences appeared to be more important during sitting down than during standing up. Moreover, deterioration of head stability was found in elderly subjects, particularly when the task was achieved rapidly and in darkness. CONCLUSION: There is a relationship between changes in the motor control of the task, which appeared during periods of potential postural instability, and the effects of ageing on postural stability.

Activities of Daily Living↗
PubMed1998

[Drawing movements and gravitational force: central or peripheral regulation?].

Drawing arm movements in four different directions: a) upward vertical (0 degree), b) upward oblique (45 degrees), c) downward vertical (180 degrees) and d) downward oblique (135 degrees), and at two different speeds, normal and fast, were executed by eight subjects. Movements of the arm were recorded using an optoelectronic (2 TV, 100 Hz) system which allowed the computer reconstruction of joint motion. Analyses focused upon pen kinematics in the frontal plane. Velocity profiles were unimodal for all conditions. The ratio of acceleration time to total movement time changed significantly as a function of the direction and the speed of the movement. Movement time and was not affected by movement direction and consequently changes in gravitational torques, for both speeds tested. Results from this study provide indirect evidence that the CNS executes movements by taking advantage of gravitational force.

Adult↗
PubMed1997

Evidence of a preprogrammed deactivation of the hamstring muscles for triggering rapid changes of posture in humans.

Normal subjects were asked to make rapid flexions of the legs from a stationary initial standing posture in a self-paced mode. Because this movement implicates a rapid change in posture, questions were asked about the type of central command which must include the rupture of the erect posture and the accomplishment of the goal directed movement. Movements of the different segments of the body were recorded and analyzed using the optoelectronic ELITE system. Electromyographic (EMG) activities of 8 muscles of the lower limb on one side were recorded, rectified and integrated. The time relationships of the different EMG signals (activation or deactivation) were analyzed with respect to selected kinetic measures of the related segments of the body. In the majority of the subjects, before the movement onset, EMG events included a specific deactivation of the tonic EMG activity of the semimembranous (SM) and semitendinous (ST) muscles (time onset relative to the onset of the legs flexion: -196.9 +/- 96.4 ms and -180.5 +/- 89.7 ms, respectively). A second event was a phasic activation of the tibialis anterior (TA) muscle (time onset: -60.5 +/- 117.6 ms). Conjugate cross-correlation analysis of these EMG signals demonstrated the existence of a common coordinated strategy between the deactivation of the hamstring and the TA activation. Even though a small horizontal displacement of the head was recorded prior to leg movement, it occurred too late to induce deactivation of the hamstring muscles. These results demonstrate that for rapid legs flexion, where the gravity forces are the main source of joint angle acceleration, the deactivation of the SM and ST muscles acts in conjunction with the phasic activation of the TA. The preprogrammed deactivation of the SM and ST muscles represents the early phase of the central command to switch from the standing to the squatting posture.

Adult↗
PubMed1996

[Effects of aging on standing up and sitting down. Kinematic analysis].

Standing up from and sitting down to a chair are a challenging task for many elderly persons. The purpose of this study was to analyse the effects of ageing in kinematic features of each phase of motion. The study was performed on 7 young subjects (22.8 +/- 1.5 years) and 5 healthy elderly subjects (73.2 +/- 5.5 years). The kinematics of the movement were analysed by mean of an optical automatic TV processor (Elite system). Eight reflective markers were placed on left side of body. The elderly subjects showed modifications of velocity profiles of trunk and knee during the two phases of movement, an important need for an adjustment of velocity before seat-on and an inability to increase the velocity of trunk displacement in space. We suggested that these differences between young and elderly subjects, well seen during standing to sitting down, were related to deficits in postural control ability.

Adult↗
PubMed1996

[Search of gravity force in the planning of arm pointing movements].

Arm movements in two directions (downward assisted by gravity and upward against gravity) with three different loads (no load 0.5 and 1 kg) were studied in six subjects. Movements of the arm were recorded using an optoelectronic (2 TV, 100 Hz) system which allowed the computer reconstruction of joint motion. Analyses focused upon finger kinematics in the sagittal plane. Subjects showed curved paths for both directions and load conditions. The path's curvature changed significantly only as a function of the direction of the movement. Velocity profiles were unimodal for all conditions. Upward movements showed greater deceleration than acceleration times in contrast to downward movements which presented more symmetrical velocity profiles. The ratio of acceleration time to total movement time changed significantly only as a function of the direction of the movement but not as a function of the load. Results from this study provide indirect evidence that the CNS executes movements by taking advantage of gravity force.

Adult↗
PubMed1995

Head and trunk movements in the frontal plane during complex dynamic equilibrium tasks in humans.

Eight normal human subjects were asked to maintain monopodal equilibrium on a narrow beam (task 1) or bipodal equilibrium on an unstable rocking platform (task 2) for 5 s. Each task was performed under four experimental conditions: (1) in light, (2) in darkness, (3) in light while subject had to hold a full cup of water, and (4) as in 3, but with additional instructions to fix the gaze on the cup. The movements of the trunk and head in the frontal plane were recorded by means of a 50-Hz TV image analyzer that computed the coordinates of small reflective markers glued on the skin of the subjects. On the beam the trunk was inclined on the side of the supporting foot (13 +/- 9 degrees), on the rocking platform the mean trunk orientation during the tests was nearly vertical (2 +/- 7 degrees). Nevertheless, in both tasks the mean head position was the same and close to vertical: 1.5 +/- 4 degrees on the rocking platform and 1.5 +/- 5 degrees on the beam. For both tasks and all experimental conditions the head remained stabilized relative to vertical, despite large translations in the frontal plane. Standard deviations of head orientation from its mean value were 2.8 +/- 2 degrees for task 1 and 2 +/- 1.5 degrees for task 2. The changes of trunk orientation were significantly higher: 6.2 +/- 4.8 degrees and 4.5 +/- 4 degrees, respectively. The differences in angular stability of head and trunk, measured through the standard deviations of angular displacements, were especially pronounced in trials with large trunk movements. It was concluded that head angular stabilization, providing the central nervous system with necessary visual and vestibular references, is essential for effective dynamic postural control in the frontal plane during complex equilibrium tasks.

Adult↗
PubMed1994

[Vestibular rehabilitation of patients suffering of vertigo: literature review and personal experience].

The paper reports the results of a study on the effectiveness of vestibular rehabilitation therapy in patients suffering from vertigo, mostly in those cases in which spontaneous compensation is only slight or not achieved at all. The main aim or rehabilitation training is to foster functional compensation between the two vestibular hemisystems. Fifty patients were divided into two groups: those with labyrinthine vertigo, who underwent therapy which included vestibular habituation training (VHT); those with disequilibrium, who received balance coordination training. The results turned out successfully in 75% of those patients belonging to the first group, whereas patients in the second group showed relevant improvement of subjective symptoms related to imbalance, confirmed by the results of post-urographic assessment. Moreover, the severity of vertigo decreased by about 50% with regard to initial intensity after the first week of treatment and reduced considerably by the end of the second week.

Adult↗
PubMed1992

[Vestibular studies: current status, prospects].

Equilibrium is based on gaze stabilization. Clinical examinations currently test, individually the three components involved in equilibrium: vestibular, visual and proprioception. New investigations are being developed to test equilibrium dynamic conditions. After briefly reviewing vestibular physiology, under the authors discuss the various tests of vestibular function and equilibrium.

Eye Movements↗
PubMed1991

Head stabilization during various locomotor tasks in humans. II. Patients with bilateral peripheral vestibular deficits.

This experiment, which extends a previous investigation (Pozzo et al. 1990), was undertaken to examine how head position is controlled during natural locomotor tasks in both normal subjects (N) and patients with bilateral vestibular deficits (V). 10 normals and 7 patients were asked to perform 4 locomotor tasks: free walking (W), walking in place (WIP), running in place (R) and hopping (H). Head and body movements were recorded with a video system which allowed a computed 3 dimensional reconstruction of selected points in the sagittal plane. In order to determine the respective contribution of visual and vestibular cues in the control of head angular position, the 2 groups of subjects were tested in the light and in darkness. In darkness, the amplitude and velocity of head rotation decreased for N subjects; these parameters increased for V subjects, especially during R and H. In darkness, compared to the light condition, the mean position of a line placed on the Frankfort plane (about 20-30 degrees below the horizontal semi-circular canal plane) was tilted downward in all conditions of movement, except during H, for N subjects. In contrast, this flexion of the head was not systematic in V subjects: the Frankfort plane could be located above or below earth horizontal. In V subjects, head rotation was not found to be compensatory for head translation and the power spectrum analysis shows that head angular displacements in the sagittal plane contain mainly low frequencies (about 0.3-0.8 Hz). The respective contribution of visual and vestibular cues in the control of the orientation and the stabilization of the head in space is discussed.

Adult↗
PubMed1991

Head stabilization during locomotion. Perturbations induced by vestibular disorders.

Head kinematics was studied in 10 normal subjects (NS) and 7 patients (P) with bilateral vestibular deficit while they executed various locomotor tasks. The movement of the body was recorded with a video system which allowed a computer reconstruction of the motion of joint articulations and other selected points on the body in three dimensions. Analyses focus on head translation along the vertical axis and rotation in the sagittal plane. Two conditions were studied: free walking (W) and hopping (H). The subjects were tested in light and in darkness. In NS, while walking in darkness, mean head position was tilted downward. In contrast, this flexion was not systematic in P. Darkness did not significantly influence the amplitude and velocity of head angular displacement during W, but, during H the amplitude decreased by 37% for NS. During H in darkness, head stabilization decreased for P. These results suggest that head kinematics, during natural locomotor tasks, could be used to evaluate vestibular deficiencies.

Adult↗
PubMed1990

Head stabilization during various locomotor tasks in humans. I. Normal subjects.

Head kinematics were studied in ten normal subjects while they executed various locomotor tasks. The movement of the body was recorded with a video system which allowed a computer reconstruction of motion of joint articulations and other selected points on the body in three dimensions. Analyses focus on head translation along the vertical axis and rotation in the sagittal plane. This was done by recording the displacement of a line approximating the plane of horizontal semi-circular canals (the Frankfort plane: F-P). Four conditions were studied: free walking (W) walking in place (WIP) running in place (R) and hopping (H). In the 4 experimental conditions, amplitude and velocity of head translation along the vertical axis ranged from 1 cm to 25 cm and 0.15 m/s to 1.8 m/s. In spite of the disparities in the tasks regarding the magnitude of dynamic components, we found a significant stabilization of the F-P around the earth horizontal. Maximum amplitude of F-P rotation did not exceed 20 degrees in the 4 situations. Vertical angular velocities increased from locomotion tasks to the dynamic equilibrium task although the maximum values remained less than 140 degrees/s. Predominant frequencies of translations and rotations in all the tasks were within the range 0.4-3.5 Hz and harmonics were present up to 6-8 Hz. During walking in darkness, mean head position is tilted downward, with the F-P always below the earth horizontal. Darkness did not significantly influence the amplitude and velocity of head angular displacement during W, WIP and R, but during H the amplitude decreased by 37%. Residual head angular displacement is found to compensate for head translation during the 4 conditions. Our study emphasizes the importance of head stabilization as part of the postural control system and described as a basis for inertial guidance.

Adult↗
PubMed1989

Head kinematic during various motor tasks in humans.

Head kinematic during various motor tasks was studied in ten subjects. The movement of the body was recorded with a video system (E.L.I.T.E.) which allows a computer reconstruction of three-dimensional motion of selected points on the body. Analysis is focused on head rotation in the horizontal and vertical planes. The results demonstrate that the amplitude and the maximum velocity do not exceed respectively 38 deg/s and 185 deg/s. However the head is intermittently stabilized and the angle of this stabilization is dependent upon the task and related to the direction of gaze. Darkness had no significant effect on head rotational velocity during walking but caused a decrease in velocity during running and hopping. The results suggest that head stabilization (1) is related to an ocular fixation point in the direction of gaze in space and (2) is probably regulated on the basis of a predictive mode of sensory motor control.

Adult↗
PubMed1988

Contribution of eye positioning to control of the upside-down standing posture.

The present study attempts to clarify the relationship between eye and body positioning during an upside-down standing posture on the hands. In this posture the head was observed to be stable and the eyes were anchored to an earth-fixed target. We measured the variations of body sway when subjects displaced their gaze upward or downward from their anchoring position. They did this voluntarily under instruction, and involuntarily by means of base-down or base-up wedge prisms. Results show that the anchoring point chosen by the subjects corresponds to a perceived limit of their body sway. They suggest that vision is also used to convey the desired optimal zone for the center of gravity in cases where fine balance is required.

Eye Movements↗