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Biomedical subjects

A Pedotti

Publications and source records attributed to A Pedotti.

15 recordsLinked to original sources
PubMed1992

Motor strategies in landing from a jump: the role of skill in task execution.

A motor performance which involves multijoint coordination and belongs to the natural repertoire of motor behavior has been studied. Displacements have been related to EMG in the lower limb when taking off and landing from a jump down (45 cm) onto two surfaces of differing compliance in two populations of teenage girls: skilled and unskilled. To evaluate the performance, an index was defined taking into account: 1) the time required for reaching stability (1 body weight) after landing, and 2) the amount of sway during the stabilization time. Despite the apparent intra and inter subject similarities in performing the jump-down, slight differences were observed in both the kinematics and electromyogram patterns. During takeoff, two strategies were identified that were not related to either skill or landing surface compliance. The most common strategy, "Push Off", is characterized by almost full joint extension when departing from the jump platform and includes a swing period during flight. The other strategy, "Roll Off", is characterized by joint flexion at departure and continual extension during midflight. While the ankle dorsiflexor, tibialis anterior, is active in preparation for the takeoff phase in both strategies, it is followed by activation of the ankle plantarflexors, lateral gastrocnemious and soleus and the hip/knee musculature, rectus femoris, biceps femoris, and vastus lateralis, only in the push off strategy. The roll off strategy is characterized by a lack of other muscle activation prior to takeoff. At landing, regardless of the strategy used in takeoff, onset of muscles followed the same sequence for both landing surfaces; ankle musculature activity began first followed by activity in the knee and hip musculature. The onset of the musculature occurred closer to landing when landing on the more compliant surface. Skilled subjects were characterized by adjustments in amount of ankle extension present at landing and concomitant flexion post-landing with respect to landing surface. When landing on the rigid surface, the ankle was more plantarflexed and onset of the dorsiflexor occurred after that of the plantarflexors; on foam, dorsiflexor activity was coincident with the plantarflexors. Ankle joint range of motion post-landing was subsequently larger when landing on the rigid surface. In contrast, unskilled individuals used a default strategy for landing on both surfaces where the ankle position and movement was between that seen for the two conditions in the skilled individual. It is suggested the landing and takeoff phases are programmed independently in both skilled and unskilled subjects.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1992

Space coding by premotor cortex.

Many neurons in inferior area 6, a cortical premotor area, respond to visual stimuli presented in the space around the animal. We were interested to learn whether the receptive fields of these neurons are coded in retinotopic or in body-centered coordinates. To this purpose we recorded single neurons from inferior area 6 (F4 sector) in a monkey trained to fixate a light and detect its dimming. During fixation visual stimuli were moved towards the monkey both within and outside the neuron's receptive field. The fixation point was then moved and the neuron retested with the monkey's gaze deviated to the new location. The results showed that most inferior area 6 visual neurons code the stimulus position in spatial and not in retinal coordinates. It is proposed that these visual neurons are involved in generating the stable body-centered frame of reference necessary for programming visually guided movements.

Animals↗
PubMed1992

Coordination between equilibrium and head-trunk orientation during leg movement: a new strategy build up by training.

1. During unilateral leg movements performed while standing, it is necessary to displace the center of gravity toward the other leg to maintain equilibrium. In addition, the orientation of particular segments, such as the head and trunk, which are used as reference values for organizing the motor act, needs to be preserved. The aim of the present study was to investigate the coordination between movement, equilibrium, and local posture. 2. Experiments were carried out on standing subjects who were instructed to raise one leg laterally to an angle of 45 degrees in response to a light. Two sources of light placed in front of the subject indicated the side on which the movement was to be performed. Three main aspects of the posturokinetic sequence were investigated in two populations, naive subjects and dancers: 1) The body weight transfer toward the supporting leg was found to have two components: first, a "ballistic" one, initiated by a thrust exerted by the moving leg; and second, an "adjustment" component during which the displacement of the center of gravity (CG) reaches a final position (steady state). An early burst in the gastrocnemius medialis of the moving leg often precedes the onset of the center of pressure change. Two differences between naive subjects and dancers were observed: first, the new CG position was almost reached in one step very near to the end of the ballistic component and required only a short adjustment in dancers, whereas in naive subjects it was reached in two steps, including a much longer adjustment component. Second, the dancers were able to minimize the CG displacement toward the supporting side; this might be because they form a better internal representation of the biomechanical limits of stability because of their long training. 2) The onset of the lateral displacement of the malleolus marker of the moving leg always occurred when the body weight had almost completed its transfer to above the support foot. This shows that the positioning of the CG in a new position compatible with equilibrium maintenance was a prerequisite for the leg movement to be performed. The relative timing of events during the posturokinetic sequence was fairly fixed in the dancers, whereas it varied from one trial to another in the naive subjects. 3) The coordination between movement, equilibrium, and head-trunk orientation involves two control strategies. An "inclination" strategy was used by the naive subjects; this consisted of an external rotation of the supporting leg around the anteroposterior ankle joint axis. A counter-rotation at the neck level ensured the stability of the interorbital line in the horizontal plane.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1991

Normal gait is differentially influenced by the otoliths.

Postural control depends on the integration of vestibular, somatosensory and visual orientation signals. The otolith contribution to postural control is achieved by the integration of otolith inputs and peripheral afferent inputs involved in crossed reflex pathways. This study shows that a functional linkage between otolith signals and activity in lower limb muscles is detectable in normal human gait. The otolith input appears to dominate particularly the neck proprioceptive and gaze motor influences during normal gait. This is demonstrated by an increase of tibialis anterior muscle activity during retroflexion of the head/neck, leading to an increased stability and counteracting possible perturbations. It is also shown by decrease of coordination during the movement caused by larger displacement of the centre of gravity demonstrated in vector diagrams.

Biomechanical Phenomena↗
PubMed1991

Role of sinoaortic afferents in modulating BP and pulse-interval spectral characteristics in unanesthetized cats.

Sinoaortic denervation (SAD) is accompanied by an increase in blood pressure (BP) and a reduction in pulse-interval (PI) variance. Little is known, however, about the effect of SAD on the complex BP and PI variability pattern, which is identified by spectral analysis. In nine unanesthetized cats in which intra-arterial BP was monitored before and 7-10 days after SAD, spectral powers (estimated by fast Fourier transform) were calculated for the low frequency (LF, 0.025-0.07 Hz), midfrequency (MF, 0.07-0.14 Hz), and high frequency (HF, 0.14-0.60 Hz) band. The very low frequency (VLF) BP and PI components (VLF less than 0.025 Hz) were also estimated. SAD increased systolic BP variance and decreased PI variance. The reduction of PI variance was paralleled by significant and marked reductions in all PI powers including the VLF components. In contrast, the increase in systolic BP variance was accompanied by a marked increase in LF power, a decrease in MF power, and no change in HF power. The VLF BP components increased after SAD for frequencies between 0.025 and 0.0012 Hz, whereas a sudden marked reduction was observed below 0.0012 Hz. Similar results were obtained for diastolic BP powers. Thus the reduction in PI variance induced by SAD is paralleled by a reduction in all PI fluctuations identified by spectral analysis. This is not the case for the SAD-related increase in BP variance, which is accompanied by an increase, no change, or even a reduction in the different BP spectral components.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1991

[Strategies for simultaneous control of the equilibrium and of the head position during the raising movement of a leg].

The coordination between equilibrium control and the ability to maintain the position of given segments (head, trunk) was studied in standing subjects, instructed to raise one leg laterally at an angle of 45 degrees in response to a light. Two sources of light placed at eye level indicated the side on which the movement was to be performed. Two populations were compared: naive subjects and dancers. Two control strategies were identified. An "inclination" strategy was used by the naive subjects. This consisted of an external rotation of the body around the antero-posterior ankle joint axis; a counter-rotation of the head with respect to the trunk was observed, which ensured some stabilization in the horizontal plane of the interorbital line. A "translation" strategy was used by the dancers. Here the external rotation of the leg around the ankle joint was associated with a feed-forward counter-rotation of the trunk around the coxofemoral joint so that the horizontality of the interorbital line and the verticality of the trunk axis were maintained. This new coordination results from a long-term training and indicates that a new motor program has been elaborated.

Adult↗
PubMed1990

Sequential spectral analysis of 24-hour blood pressure and pulse interval in humans.

Blood pressure and pulse interval are characterized not only by erratic variations but also by rhythmic fluctuations at low-, mid-, and high-frequency (0.025-0.07, 0.07-0.14, and 0.14-0.35 Hz, respectively). However, information on these phenomena has largely been derived from analysis of short-term recordings taken in standardized laboratory conditions. In seven normotensive and 10 untreated mild essential hypertensive subjects, power spectrum analysis was performed on the intra-arterial blood pressure and pulse interval signal collected over a 24-hour period using the fast Fourier transform algorithm and splitting the recording into contiguous segments of 256 beats. About 70% of the segments were suitable for the analysis; the segments excluded for a nonstationary signal amounted to only 30%. All powers were characterized by a high segment-to-segment variability, but in each subject the mid- and high-frequency powers of diastolic blood pressure and the mid-frequency power of systolic blood pressure were markedly reduced during the night as compared with the daytime period, whereas the opposite occurred for the low- and high-frequency powers of the pulse interval. Over the 24-hour period, mid- and high-frequency powers of blood pressure were positively correlated to each other, but both accounted for less than 25% of the 24-hour blood pressure variance. No difference between mean normalized power values of normotensive and hypertensive subjects was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Postural synergies in axial movements: short and long-term adaptation.

Fast backward trunk movements are accompanied by hip, knee and ankle rotation which compensate for the backward shift of the center of gravity. The electromyographic pattern associated with the performance of these movements and the associated synergies consists of a fairly synchronous activation of the prime mover (erectores spinae) and the muscles situated at the back of the leg (hamstring, calf muscles). This pattern is called the "non anticipated pattern". The effect of training on the EMG pattern and on the subjects' mechanical performances was investigated by comparing a population of untrained subjects with one of highly trained gymnasts. A new EMG pattern was observed in the highly trained gymnasts, the "distally anticipated pattern" consisting of an early activation of the gastrocnemius, and in some subjects also of the hamstring, indicating that a long term adaptation had taken place. Performances expressed as a ratio between the displacement of the center of gravity projection onto the ground and the velocity of the movement were clearly better in the gymnasts. Short term adaptation was found to occur in the gymnasts and not in the untrained group when the movement was performed while standing on a narrow support. A suppression of the distal gastrocnemius burst occurred in the gymnasts from the first trial under the constrained standing condition whereas no change occurred in the untrained group. The flexibility of the EMG patterns associated with axial movements occurring either spontaneously or as a result of long or short term training is discussed.

Adaptation, Physiological↗
PubMed1989

24 h sequential spectral analysis of arterial blood pressure and pulse interval in free-moving subjects.

A procedure for the 24 h tracking of the 0.25, 0.1, and 0.05 Hz oscillations in blood pressure (BP) and pulse interval (PI) in ambulant subjects has been developed. It includes: 1) sampling of a 24 h intra-arterial BP recording, extraction of the systolic (S) and diastolic (D) BP and PI from each heart beat followed by storage into separate series; 2) high-pass filtering and a splitting of each series into consecutive records of 256 values; 3) estimation of power spectral density (PSD) via FFT in each stationary record, and finally, computation of the power of each target oscillation. Using this procedure we analyzed data from ten hospitalized free-moving subjects in whom BP was recorded by the Oxford technique. The results revealed different patterns of the 0.25, 0.1, and 0.05 oscillations over the day-night cycle, showing a differentiated involvement during the 24 h of the mechanisms responsible for such rhythmic phenomena. Moreover, in order to reinforce the meaning of the obtained results and to exclude the possible negative effects due to the drawbacks typical of the FFT algorithm, we also performed a second spectral estimate based on the AR modeling. The obtained results validates the FFT approach.

Blood Pressure Determination↗
PubMed1985

A new approach to analysis of the arterial baroreflex.

The arterial baroreflex is commonly evaluated by measuring the lengthening and shortening in pulse interval in response to changes in systolic (S) blood pressure (BP) induced by infusion of vasopressor and vasodepressor drugs. This method is simple but has important limitations: only a few observations can be made, reproducibility of the responses is far from optimal, interference by direct drug action on the sinus node and the baroreceptors cannot be excluded and the artificially induced stimuli only poorly mimic the naturally occurring pressor and depressor transients. A new approach was therefore pursued. Blood pressure was recorded intra-arterially for 3 +/- 0.4 h (mean +/- s.d) in 10 unanaesthetized, unrestrained cats and the recording was scanned by a computer to identify the spontaneous sequences of three or more consecutive beats in which SBP progressively rose and pulse interval progressively lengthened (type 1 sequence) or SBP progressively fell and pulse interval progressively shortened (type 2 sequences). Accurate beat-to-beat measurements of SBP and pulse interval were obtained by adopting a very narrow sampling interval of the BP trace, i.e. 1.6 ms real time. For each sequence the regression between the SBP values and the pulse internal values of the following cycle was calculated. In each cat a large number of three-beat sequences were found, the four-, five- and six-beat sequences being, however, progressively less common. All sequences had a high correlation coefficient (r > 0.9), type 1 having a greater slope than type 2 (14.1 +/- 2.5 versus 10.3 +/- 7.6 ms/mmHg, P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

A model of the mechanism controlling neuromuscular activation during ambulation based on feedback control hypothhesis.

As tested by many investigators, locomotor performance at steady state does not involve high conscious systems but takes place almost automatically. A great number of experiments on animals seem to demonstrate that the afferent proprioceptive signals play an important role in locomotion and that the higher nervous centers act in order to activate the lower control systems. On the basis of previous findings, we hypothesized that the descending signal from the higher nervous centers can lower the threshold of intervention of the proprioceptive signals on the alpha-motoneurons. The influences of the afferent signals on the various muscles enable them to realize the pattern of the basic muscular activity that we can record from walking subjects. A simulation of the model of human locomotion has been implemented on a digital computer and the theoretical results are compared with the experimental findings.

Afferent Pathways↗
PubMed1977

New procedure for evaluation of normal and abnormal gait.

In this paper a new procedure is presented that permits a quantitative clinical evaluation of an important aspect of human locomotion. It involves a spatio-temporal representation of the evolution of the group reaction vector (sagittal plane) for a single hind limb during the stance phase of a step. This representation is provided directly on line by use of a computer. Some preliminary results are presented for normal subjects and for patients with a variety of motor disorders.

Biomechanical Phenomena↗