Biomedical subjects

Marco Schieppati

Publications and source records attributed to Marco Schieppati.

28 records · Page 2Linked to original sources

PubMed2003

Effects of leg muscle tendon vibration on group Ia and group II reflex responses to stance perturbation in humans.

Stretching the soleus (Sol) muscle during sudden toe-up rotations of the supporting platform in a standing subject evokes a short-latency response (SLR) and a medium-latency response (MLR). The aim of the present investigation was to further explore the afferent and spinal pathways mediating the SLR and MLR in lower limb muscles by means of tendon vibration. In seven subjects, toe-up or toe-down rotations were performed under: (1) control, (2) continuous bilateral vibration at 90 Hz of Achilles' tendon or tibialis anterior (TA) tendon, and (3) post-vibration conditions. Sol and TA background EMG activity and reflex responses were bilaterally recorded and analysed. Toe-up rotations induced SLRs and MLRs in Sol at average latencies of 40 and 66 ms, respectively. During vibration, the latency of both responses increased by about 2 ms. The area of the SLR significantly decreased during vibration, regardless of the underlying background activity, and almost returned to control value post-vibration. The area of Sol MLR was less influenced by vibration than SLR, the reduction being negligible with relatively high background activity. However, contrary to SLR, MLR was even more reduced post-vibration. Toe-down rotations induced no SLR in the TA, while a MLR was evoked at about 81 ms. The area of TA MLR decreased slightly during vibration but much more post-vibration. SLRs and MLRs were differently affected by changing the vibration frequency to 30 Hz: vibration had a negligible effect on the SLR, but still produced a significant effect on the MLR. The independence from the background EMG of the inhibitory effect of vibration upon the SLR suggests that vibration removes a constant amount of the Ia afferent input. This can be accounted for by either presynaptic inhibition of group Ia fibres or a 'busy-line' phenomenon. The differential effect of vibration on SLRs and MLRs is compatible with the notions that spindle primaries have a higher sensitivity to vibration than secondaries, and that group II afferent fibres are responsible for the production of the MLR. The decrease of MLRs but not SLRs after vibration is discussed in terms of an interaction between peripheral and central drive on group II interneurones in order to produce sufficient EMG activity to maintain a given postural set.

Achilles Tendon↗

PubMed2003

Comparison of Cawthorne-Cooksey exercises and sinusoidal support surface translations to improve balance in patients with unilateral vestibular deficit.

OBJECTIVE: To compare the effectiveness of vestibular rehabilitation by using Cawthorne-Cooksey exercises with that of instrumental rehabilitation. DESIGN: The main study (n=32) used a pre-post rehabilitation (A-B) design; the ancillary studies used a subset of 11 patients 1 month before rehabilitation versus pre-post rehabilitation (A-A-B design) and 9 patients pre-post rehabilitation versus 1 month after (A-B-B design). SETTING: Division of physical therapy and rehabilitation at a scientific institute in Italy. PARTICIPANTS: Patients (Cawthorne-Cooksey, n=17; instrumental rehabilitation, n=15) with a complete or incomplete unilateral vestibular lesion due to ischemic, inflammatory, cranial nerve VIII sectioning, or unknown cause. INTERVENTIONS: Cawthorne-Cooksey exercises or instrumental rehabilitation training consisting of standing with eyes open (EO) or closed (EC) on a platform moving, relative to the subjects, in the anteroposterior (AP) or mediolateral direction, at a sinusoidal translation frequency of 0.2 or 0.6Hz; training sessions for both interventions were twice daily, 30 minutes per session, for 5 days. MAIN OUTCOME MEASURES: Body sway and subjective score of sway during quiet stance with EO or EC, with feet 10cm apart (FA) or together (FT); the standard deviation of the AP displacement of the malleolus, hip, and head during AP platform translations; the Dizziness Handicap Inventory (DHI); and performance-oriented evaluation of balance and gait (according to Tinetti). RESULTS: Both interventions improved patients' balance. Under each postural and visual condition, both groups showed reduction in body sway, and the post rehabilitation sway values approached those observed in normal subjects; improvement was significantly better for instrumental rehabilitation under FA EO, FA EC, and FT EC conditions. All patients reported a subjective feeling of increased steadiness. Sway recorded 1 month before treatment did not differ from that at the start of treatment. The follow-up evaluation showed persistence of effect. Parallel to the improved stability, a decrease in the SD of the displacement of hip and head in balancing on the movable platform was present in both groups; improvement was better in the instrumental rehabilitation group than the Cawthorne-Cooksey group under the EC condition. Balance and gait assessment improved to the same extent in both groups. Scores on the physical, functional, and emotional questions of the DHI improved significantly in both groups after treatment, but to a larger extent in the instrumental rehabilitation patients. CONCLUSIONS: Both Cawthorne-Cooksey and instrumental rehabilitation are effective for treating balance disorders of vestibular origin. Improvement affects both control of body balance and performance of activities of daily living. The larger decrease in body sway and greater improvement of DHI after instrumental rehabilitation suggests that it is more effective than Cawthorne-Cooksey exercises in improving balance control.

Activities of Daily Living↗

PubMed2003

Human walking along a curved path. I. Body trajectory, segment orientation and the effect of vision.

Task-related characteristics of gait and segment orientation during natural locomotion along a curved path have been described in order to gain insight into the neural organization of walking. The locomotor task implied continuous deviation from straight-ahead, thereby requiring continuous adjustment of body movement to produce and assist turn-related torques. Performance was compared to straight-ahead locomotion. Subjects easily reproduced both trajectories with eyes open (EO). The actual-to-required trajectory difference increased blindfolded (BF), more so during turning. Stride length was unchanged for the outer but decreased for the inner leg. The feet anticipated subsequent body rotation by pivoting toward the inner side of the curve at heel strike. A shift of body centre of mass and trunk roll toward the inner side accompanied turning. The head turned more than dictated by the heading change, and the absolute range of yaw oscillation increased. Head yaw anticipated body yaw by approximately 200 ms. Despite the minor effect of vision on the behaviour of all other segments, a difference in head pitch occurred between EO and BF; with EO, the head was flexed (P < 0.01), as to look at the path, while pitch was negligible with BF. In general, the changes in the amplitude of head, trunk and feet movements proved to be well related to the kinematics of the steering body, and constituted a sort of basic library of motor synergies.

Adult↗

PubMed2003

Human walking along a curved path. II. Gait features and EMG patterns.

We recorded basic gait features and associated patterns of leg muscle activity, occurring during continuous body progression when humans walked along a curved trajectory, in order to gain insight into the nervous mechanisms underlying the control of the asymmetric movements of the two legs. The same rhythm was propagated to both legs, in spite of inner and outer strides diverging in length (P < 0.001). There was a phase lag in limb displacement between the inner and outer leg of 7% of the total cycle duration (P = 0.0001). Swing velocity was greater for outer than inner foot (P < 0.001). The duration of the stance phase diminished and increased in the outer and inner leg (P < 0.01), respectively, and was associated with trunk leaning toward the inside of the path. Muscle activity was not dramatically altered during curved walking. The amplitude of soleus burst during stance increased in the outer (P < 0.05) and decreased in the inner leg (P < 0.05), without changes in timing. Tibialis anterior activity increased in both legs during the swing phase (P < 0.05); it was advanced on the outer and delayed on the inner side (P < 0.01; 2% of the cycle). The peroneus longus burst decreased in both legs, but more in the inner than the outer leg, and lasted longer in the inner leg at the onset of swing. Closing the eyes did not affect the gait pattern and muscle activity during turning. The command to walk along a curved path may exploit the basic mechanisms of the spinal locomotor generator, thereby limiting the computational cost of turning.

Adult↗

PubMed2002

Trajectories of arm pointing movements on the sagittal plane vary with both direction and speed.

Five subjects performed arm upward and downward movements at different speeds (movement duration ranged from 0.26 to 1.2 s). Fingertip paths, velocity profiles and muscle activation patterns of arm and forearm were computed. Inspection of the electromyograph (EMG) revealed that for relatively slow speeds (>0.7 s) and for both directions, only the flexor muscles were active, mainly the anterior deltoid, for motor (upward) and braking action (downward) respectively. However, where gravity was no longer sufficient to accelerate downward and decelerate upward movements (<0.7 s), both flexors and extensors muscles were active. Path curvature and position of maximum deviation from straightness were lower for downward than for upward movements. In addition, the position of maximum deviation from straightness became progressively higher with increase in duration for both upward and downward movements. The ratio of acceleration duration to total movement duration was greater for downward than upward directions for all the range of speeds. The ratio of maximum to mean velocity was similar for upward and downward movements but decreased with decrease in speed. The results indicate that the brain accomplishes arm movements in the vertical plane with different planning processes for movements with or against gravity. Furthermore, they provide evidence that both gravitational and inertial forces are determinant for arm trajectory generation in the vertical plan.

Adult↗

PubMed2002

Does order and timing in performance of imagined and actual movements affect the motor imagery process? The duration of walking and writing task.

The purpose of the present study was to investigate the effects on the duration of imagined movements of changes in timing and order of performance of actual and imagined movement. Two groups of subjects had to actually execute and imagine a walking and a writing task. The first group first executed 10 trials of the actual movements (block A) and then imagined the same movements at different intervals: immediately after actual movements (block I-1) and after 25 min (I-2), 50 min (I-3) and 75 min (I-4) interval. The second group first imagined and then actually executed the tasks. The duration of actual and imagined movements, recorded by means of an electronic stopwatch operated by the subjects, was analysed. The duration of imagined movements was very similar to those of actual movements, for both tasks, regardless of either the interval elapsed from the actual movements (first group) or the order of performance (second group). However, the variability of imagined movement duration was significantly increased compared to variability of the actual movements, for both motor tasks and groups. The findings give evidence of similar cognitive processes underlying both imagination and actual performance of movement.

Adult↗

PubMed2002

Variability in a dynamic postural task attests ample flexibility in balance control mechanisms.

When humans stand upright on a platform that sinusoidally translates in the anterior-posterior direction, the movements of upper and lower body segments are appropriately coordinated, in order to keep the body within its limits of stability. A significant fluctuation in this behaviour is evident across subjects and perturbation conditions. The inter- and intrasubject variability in the body segment kinematics, as occurs during repeated trials across different conditions, is quantitatively described here. Twenty normal subjects stood upright with eyes open (EO) or eyes closed (EC) on a platform moving to-and-fro in the horizontal plane for 30 s, at a frequency of 0.2 and 0.6 Hz, with a peak-to-peak amplitude of 6 cm. Each subject made two trial repetitions for each visual and frequency condition. The last 20 s of each trial was acquired. The displacement of markers fixed on the lateral malleolus, hip and head was sampled at a frequency of 50 Hz. An index of the 'average' displacement of each marker during the trial was the standard deviation (SD) of its anterior-posterior displacements, calculated across the acquired trial cycles. The cross-correlation (CC) between pairs of marker displacement traces gave an indication of the degree of coupling of the body segments. All subjects showed two basic modes of coping with the perturbation, depending on the availability of the visual input: with EO, they tended to stabilize the head in space; with EC, the head oscillated in the anterior-posterior direction more than hip and platform. Within this general behaviour, the values of the SD of horizontal displacement of head and hip marker traces varied within an ample range during different trials of the same perturbation condition. Even within a single trial there was an ample variability of the body segments' position. In spite of this, neither head nor hip ever bypassed the anterior or posterior limits of stability. Remarkably, the range of variability of the whole population of normal subjects, both across and within trials, was analogous to the range of variability of single subjects across numerous trials. This large variability notwithstanding, it appeared that the relationship of head to hip SD across trials was almost constant, independent of visual and perturbation frequency condition. The results show that there exist a large variety of dynamic postures, rather than one particular configuration, which assure stability. The findings also suggest a neural or biomechanical constraint underlying the operations of the equilibrium control strategy.

Adolescent↗

PubMed2002

Imagined and actual arm movements have similar durations when performed under different conditions of direction and mass.

Several experiments have suggested that similar physiological substrates are involved in movement execution and motor imagery, and that the same laws of movement control apply to both processes. Using a mental chronometry paradigm, we examined the effects of movement direction and added mass on the duration of actual and imagined movements. Six subjects executed or imagined arm movements in the sagittal and horizontal plane, in three different loading conditions: without added mass, and with an added mass of 1 and 1.5 kg. The duration of both actual and imagined movements was measured by an electronic stopwatch. The actual movements were significantly increased in duration as a function of mass, for both movement directions. However, direction per se had no effect on duration. The duration of imagined movements was very similar to that of actual movements whatever the subject and mass and direction condition. These results show that both inertial and gravitational constraints are accurately incorporated in the timing of the motor imagery process, which appears therefore to be functionally very close to the process of planning and performing the actual movement.

Adult↗

PubMed2002

Neck muscle vibration and spatial orientation during stepping in place in humans.

Unilateral long-lasting vibration was applied to the sternomastoid muscle to assess the influence of asymmetric neck proprioceptive input on body orientation during stepping-in-place. Blindfolded subjects performed 3 sequences of 3 trials, each lasting 60 s: control, vibration applied during stepping (VDS), and vibration applied before stepping (VBS). VDS caused clear-cut whole body rotation toward the side opposite to vibration. The body rotated around a vertical axis placed at about arm's length from the body. The rotation did not begin immediately on switching on the vibrator. The delay varied from subject to subject from a few seconds to about 10 s. Once initiated, the angular velocity of rotation was remarkably constant (about 1 degrees /s). In VBS, at the beginning of stepping, subjects rotated for a while as if their neck were still vibrated. At a variable delay, the direction of rotation reversed, and the effects were opposite to those observed during VDS. Under no condition did head rotation, head roll, or lateral body tilt accompany rotation. The results confirm and extend the notion that the neck proprioceptive input plays a major role in body orientation during locomotion. The body rotation does not seem to depend on the same mechanisms that modify the erect posture; rather, the asymmetric neck input would seem to modify the egocentric body-centered coordinate system.

Adult↗

PubMedDate not supplied

Trunk muscle proprioceptive input assists steering of locomotion.

During locomotion, human subjects navigate in their environment and choose the direction by means of the internal representation of space that is continuously updated by sensory input. Aim of this study was to assess whether trunk proprioceptive information plays a role in the definition of the reference frame for orientation. Unilateral trunk muscle vibration was applied during locomotion along a straight path in seven subjects. Vibration was administered either from the onset or in the middle of a seven-step task, under eyes-open (EO) or blindfolded condition. The deviation of the walking trajectory was quantified by the distance of the seventh from the first foot print along the medio-lateral axis. Foot angles and stride lengths were computed for all foot-falls. Vibration produced a clear-cut deviation from the straight-ahead direction when delivered in the middle of blindfolded locomotion. With EO the deviation was much smaller. A mild deviation was obtained in blindfolded condition when vibration started at the onset of locomotion. All deviations from the straight-ahead were accompanied by coherent changes in foot orientation on the ground. Trunk proprioception plays a major role in the definition of locomotor trajectory. Trunk input seems to be weighted against vision and whole-body kinematic information.

Analysis of Variance↗