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Biomedical subjects

C Frigo

Publications and source records attributed to C Frigo.

12 recordsLinked to original sources
PubMed1991

Lower extremity angle measurement with accelerometers--error and sensitivity analysis.

Closed-loop control techniques for the restoration of locomotion of paraplegic subjects are expected to improve the quality of functional neuromuscular stimulation (FNS). We investigated the use of accelerometers for the assessment of feedback parameters. Previously, the possibility of angle assessment of the lower extremities using accelerometers, but without integration, was demonstrated. The current paper evaluates and assesses this method by an error and sensitivity analysis using healthy subject data. Of three potential error sources, the reference system, the accelerometers, and the model assumptions, the last was found to be the most important. Model calculations based on data obtained by the Elite video motion analysis system showed the rigid-body assumption error to be dominant for high frequencies (greater than 10 Hz), with vibrations in the order of 1 mm resulting in errors of one radial or more. For low frequencies (less than 5 Hz), the imperfect fixation of the accelerometers combined with a nonhinge type knee joint gave an error contribution of +/- 0.03 rad. The walking pattern was assumed to be two-dimensional which was shown to result in an error of +/- 0.04 rad. Accelerations due to rotations of the segments could be neglected. The total error computed for low frequencies (+/- 0.07 rad) was comparable to the experimental difference between the current and the reference system.

Acceleration↗
PubMed1991

A motor programme for the initiation of forward-oriented movements in humans.

1. The EMG sequence activated before the initiation of a number of fast forward-oriented voluntary movements was analysed quantitatively in normal subjects. 2. The sequence consisted of an initial inhibitory component directed to the soleus motor nucleus, followed by a second excitatory one directed to the tibialis anterior (TA). 3. The spectrum of functional utilization included motor tasks in which the prime movers are leg and thigh muscles (initiation of gait, rising on tip-toes), thigh and trunk muscles (fast-forward bending of the trunk, standing up) and upper-limb muscles (forward throw or catch). 4. In a same motor task and across the different motor tasks, performed at various speeds, the latency of soleus inhibition and TA activation with respect to the onset of movement co-varied according to a linear function, indicating a close temporal correlation between the two components. 5. In all the movements investigated, the earliest mechanical effect was a backward displacement of the centre of foot pressure in the sagittal plane. 6. Soleus inhibition alone and TA burst alone were each able to produce a backward displacement of the centre of foot pressure, but the effect was significantly slower after soleus inhibition. 7. The spatio-temporal parameters of the sequence were modulated according to the pre-existing postural conditions. For the gait initiation protocol, increasing initial forward leaning led to a decrease in the amplitude of soleus inhibition and the TA burst, and to a change in their relative time delays. Modulation was different on the two sides. We could define a postural boundary as the degree of forward leaning beyond which the full sequence is no longer called into action. 8. The spatio-temporal parameters of the sequence were pre-set according to the requirements of the forthcoming movement. In the gait initiation protocol, the amplitude and synchronization of the TA burst were directly correlated with velocity of movement, while the relative delay between soleus inhibition and TA activation was inversely correlated. Modulation on the two sides differed. We could define a velocity boundary as the velocity of movement below which the full sequence is no longer called into action. 9. We suggest that the EMG sequence described can be considered a motor programme that, through direct action on the position of the centre of foot pressure (the variable primarily controlled), will precisely adjust the configuration of forces external to the body, allowing the contraction of the prime mover(s) to interact appropriately with them for the production of a specific, forward-oriented movement.

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

Muscular effort and musculo-skeletal disorders in piano students: electromyographic, clinical and preventive aspects.

An investigation was made on the relationship between music practice and musculo-skeletal disorders among piano students, with the main aim of developing health education programmes that would improve the performance and health of the students. The investigation covered three areas: (a) Analysis of study organization and main musculo-skeletal complaints achieved by a questionnaire distributed to all piano students at the Milan Conservatory. (b) Vocational electromyographic analysis of the effort exerted by the various muscle groups of the trunk, of the shoulder and shoulder blade girdle, and of the arm during performance of a standard set of piano exercises, an unseen passage and a passage of maximum difficulty. This analysis was made on a sample of six subjects. (c) A series of preventive measures was developed on the basis of a critical assessment of the results (38% of the students practised for excessively long periods without breaks; 62% had from 1 to 5 complaints, the most affected sites being the spine and the trapezius muscles). These consisted largely of a health education programme aimed at helping the students to suitably organize practice and rest periods and in instructing them in appropriate exercises for relaxation and stretching of overused muscle groups and strengthening the supporting muscle groups. Changes in lifestyle were also suggested.

Adolescent↗
PubMed1987

Forward and backward axial synergies in man.

Upper trunk and head forward and backward movements were analyzed in human subjects standing on a force platform. EMG of several flexor and extensor muscles was recorded together with the kinematics of the movement (EL.I.TE. system). It was found that upper trunk movements are accompanied by movements of hip and knees in the opposite direction, resulting in a slight displacement of the center of gravity projection on the ground. In fast movements, all the body segments were displaced at the same time, which suggests a feedforward control, whereas in slow movements, onset of displacement of the body segments was found to take place sequentially in a cranio-caudal direction. EMG analysis during fast movements revealed two different types of control, utilized in forward and backward movements. With forward bending movements the action of two sets of muscles could be recognized: the prime mover (R. Abd.), the activation of which was not correlated with that of the other muscles and preceded the onset of movement with a fairly constant lead, and a group of postural muscles, the activation (VM, TA) and inhibition (Sol) of which were closely correlated. By contrast, with backward movements, the prime mover (Er.S.) and the postural leg muscles (Hamstrings, Sol) were activated simultaneously. In both cases, a feedforward type of control is evident. Performance of the fast forward movements was accompanied by an initial forward displacement of the knee. The function of this phenomenon is discussed in term of a destabilizing action favouring the forward bending of the body or a prestretching of the knee extensor muscles increasing the strength of their subsequent contraction.

Adult↗
PubMed1987

Excitability of the soleus H-reflex arc during walking and stepping in man.

In eight normal subjects, the excitability of the soleus (Sol) H-reflex was tested in parallel with Sol length changes, EMGs of leg and thigh muscles and ground contact phases, during three different pacing movements: bipedal treadmill walking, single limb treadmill walking, and single-limb stepping on one spot. A computerized procedure was used which compensated for changes in stimulus effectiveness that occurred during free motion. In the three paradigms examined, significant excitability modulations were observed with respect to a control level determined in standing weight-bearing position. During bipedal treadmill walking, excitability was decreased in the early stance, maximally enhanced in the second half of the stance, and again decreased during the end-stance and the whole swing phase, with a minimum value around the toe off period. The main modulation pattern was retained during single-limb treadmill walking. During single-limb stepping on one spot, the stance-phase increase in excitability and the swing phase depression were still present. However, in the second half of the swing phase, reflex responsiveness returned to reference level, which was maintained during the subsequent contact period. Moreover, a decrease in reflex excitability was detected around the mid-stance. The time course of the described modulations was only partly correlated with the EMG and length changes of the Sol muscle. Furthermore, in the three movements tested, during the early stance phase, the excitability of the H-reflex arc did not correspond to the one expected on the basis of the available H-reflex studies performed under static conditions. It is suggested that, at least in certain stride phases (e.g. around the early contact period), an active regulation affects the transmission in the Sol myotatic arc during the pacing movements investigated.

Adult↗
PubMed1986

Speed-dependent variations of lower-limb joint angles during walking. A graphic computerized method showing individual patterns.

A method for obtaining a synthetic representation of the joint angle time-courses at different walking velocities is presented, based on a computerized procedure. Hip, knee and ankle joint angles are measured by electrogoniometric devices and checked on line for their reliability. One stride only for each walking speed is selected as representative of the adopted cadence. For each joint a tridimensional representation of angle time-course versus stride frequency or versus gait speed is performed so that speed-dependent variations can be analyzed. Ten normal (seven males and three females) and three prosthetized subjects have been tested by this method. In normal as well as in pathological subjects individual features could be easily detected and the method proved to be useful for a functional gait evaluation.

Adult↗
PubMed1985

Hindered muscle relaxation in spasticity: experimental evidence suggesting a possible pathophysiological mechanism.

In ten spastic patients and in an equal number of healthy controls, the relaxation phase occurring at the end of an isotonic voluntary contraction has been studied on soleus muscle using EMG and H-reflex methods. In the spastic group, the duration of motor unit-decruitment was consistently prolonged (from two to six times the control values). Moreover, the decrease in the excitability of the H-reflex arc, which normally accompanies the end of muscle contraction was delayed in time, reduced in amplitude or in some cases even absent. As a rule, patients in whom such release-associated inhibition (RAI) was lacking or severely reduced exhibited the longest motor unit-decruitment times, due to the interference of sustained clonic sequences. It is proposed that a lowered effectiveness of RAI might explain the clonic activity which frequently hinders voluntary muscle relaxation in spasticity.

Adult↗
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↗