Biomedical subjects

M C Do

Publications and source records attributed to M C Do.

At least 19 recordsLinked to original sources

PubMed2004

Postural sway increase in low back pain subjects is not related to reduced spine range of motion.

This study questioned whether postural sway increase in low back pain subjects was related to impaired spine mobility, and especially to a decrease in the range of motion, which was assumed to represent structural spine stiffness. Ten low back pain subjects and ten healthy control subjects performed spine flexion-extension and spine side bending tests, and standing posturographic examination in different experimental conditions. Low back pain subjects showed increased postural sway along the antero-posterior axis and reduced side bending, i.e. posturographic and range of motion parameters varied in the opposite direction. Moreover, no correlation was found between these two types of parameters. Although significant, the slight decrease in spine side bending did not seem sufficiently great to disturb the low amplitude movements that maintain postural equilibrium. Hence, it was concluded that postural sway increase in low back pain is not related to a reduced spine range of motion, but might be linked to an increase in muscular active tension, which reduces dynamic mobility capacity.

Adult↗

PubMed2002

Are stance ankle plantar flexor muscles necessary to generate propulsive force during human gait initiation?

The study examined whether the generation of the forward propulsive force (PF) during gait initiation resulted mainly from the electromyogram activity of stance ankle plantar flexor muscles (APF) which 'push' on the ground as is generally claimed in the literature. Six unilateral above-knee amputees performed a specific gait initiation protocol, i.e. they were asked to walk as fast as possible from an upright posture. Data from a force platform were collected and processed to obtain gait parameters (centre of mass (CoM) acceleration, anteroposterior (A/P) progression velocity, step length, etc.). The results showed that the A/P CoM velocity at the time of foot-off differed depending on the state of the lower limb (sound or prosthetic limb) performing the step. However, the A/P velocity of the CoM reached at the time of foot contact was similar whatever the state of the lower limb initiating the gait. Thus, the absence of ankle and knee muscles did not affect the velocity of body progression, i.e. the generation of the PF in gait initiation. Furthermore, the comparable slopes of the A/P velocity between the stance sound limb and the stance prosthetic limb suggest that the organization of the motor synergy underlying the production of the PF remained the same and did not directly involve the APF. However, other mechanisms could explain PF generation. PF could be generated by the swing leg oscillation, by the trunk movement, or by other mechanisms such as the energy transfer and the exchange of gravity potential energy into kinetic energy.

Adult↗

PubMed2001

In a complex sequential movement, what component of the motor program is improved with intensive practice, sequence timing or ensemble motor learning?

We investigated whether the higher maximum speed of complex athletic movements attained by experts compared with novices might solely be ascribed to the acquisition of a more efficient timing of the initiation of the simple movements that comprise complex sporting gestures. Six novices in fencing and five experts in fencing performed three experimental series: 7 trials of touche, 7 trials of lunge (control series) and 50 trials of lunge + touche (test series), where the touche and lunge were initiated with different chronological sequences imposed by the experimenter. The lunge and the touche can be assimilated to a fast forward step and to a pointing task, respectively. We compared the maximum speed of touche between the two groups, recorded by an accelerometer fixed to the hand guard of the foil, and the speed of the centre of mass obtained from a force plate. The speed of the centre of mass was not statistically different between the two groups in the control and in the test series. The maximum speed of touche was not statistically different between the two groups in the control series. In contrast, in the test series, the maximum speed of touche was higher in the fencers' than in novices' groups, while the timing of initiation of the lunge and the touche was similar. The results of the test series show that the higher maximum speed of touche of fencers compared with novices cannot solely be ascribed to the acquisition of a more efficient initiation timing in motor programming. In a complex fencing gesture, the higher maximum speed of touche following intensive practice is discussed with regard to the inhibition of negative effects linked to the "refractory period" associated with the initiation of two closely spaced motor programs.

Adult↗

PubMed2000

Are there anticipatory segmental adjustments associated with lower limb flexions when balance is poor in humans?

For a leg raising task performed in a sagittal plane, it has been shown that body balance instability can suppress anticipatory postural adjustments (APAs). The aim of this study was to determine whether the global (centre of mass) postural adjustments were replaced by local (segmental) ones, which were compensating each other and resulting in a lack of global APAs. Six healthy subjects must perform a lower limb flexion from two initial postures, corresponding to a bipedal (Fbu) and an unipedal (Fuu) stance. Kinematics of postural adjustments were recorded with accelerometers. The results showed that in Fbu the kinematics have large durations of APAs, contrary to Fuu where there are none. They showed also that during the voluntary movement the magnitudes of the segmental postural accelerations were equal or superior in Fuu than in Fbu on the anteroposterior and lateral axes, where balance is poor. Also while, on the contrary, the magnitudes are reversed on the vertical axis. These results suggest that firstly: (1) the absence of APAs can correspond to a strategic response for weak postural base configuration and secondly; (2) the local postural accelerations, depending to the axes, are linked to two different functions: to maintaining the balance and to performing the focal movement.

Biomechanical Phenomena↗

PubMed2000

In fencing, does intensive practice equally improve the speed performance of the touche when it is performed alone and in combination with the lunge?

Global movements are generally composed of several simple movements. In this study we tested the hypothesis that the effects of practice on the performance of a simple movement cannot be highlighted when it is performed alone but only when it is part of a global movement. For this purpose we examined the performance of the touche movement in fencing, in terms of maximal speed of the foil, when it is performed alone and in combination with the lunge. The touche can be assimilated to a pointing task towards a target while the lunge can be assimilated to a forward stepping movement. Four international class fencers and five novices were tested. The results show that 1) the performance in the isolated touche condition was comparable between the two test populations, 2) the performance was higher in the expert population compared to the novice population in the sequential touche + lunge condition, and 3) the velocity of the centre of mass at the time of the peak velocity of the touche was higher in the expert population than in the novice population in the sequential touche + lunge condition. In line with Bernstein's concepts on the effects of practice on motor control it is suggested that the experts exploit to advantage the forces developed during the lunge whereas the novices do not.

Adult↗

PubMed1999

Do centrally programmed anticipatory postural adjustments in fast stepping affect performance of an associated "touche" movement?

Ensuring maximum speed in executing a sequence of two voluntary movements requires the second movement to be triggered only after some delay. This is due to the existence of a "relative refractory period." If the second movement is initiated during the refractory period, its speed decreases (movement time increases). In the present study we tested the existence of a refractory period during the execution of a sequence of movements involving both the upper and the lower limbs. More precisely, we examined whether the maximal speed of the touche fencing movement is affected by the anticipatory postural adjustments (APA) preceding a voluntary lunge. The touche and the lunge are similar to a pointing task and a stepping forward movement, respectively. touche consists of hitting a target with a foil at maximal velocity. The results show that (a) when the touche was initiated prior to the onset of the APA of the lunge, the maximal foil velocity remains similar to that of an isolated touche, and (b) when the touche is initiated during the development of the APA of the lunge, the maximal foil velocity is lower than in the isolated touche. Furthermore, the maximal foil velocity decreases with the temporal progression of the APA and reaches its minimal value when initiated at the time of voluntary lunge execution ('foot off'). The discussion suggests that the centrally programmed APA that are elicited in the stepping forward movement induces a refractory period which affects performance of the pointing task.

Adult↗

PubMed1999

Factors influencing the quick onset of stepping following postural perturbation.

It has been shown that the stepping to recover balance following a forward fall occurs at a constant time (on average 293 ms) (Do et al. Journal of Biomechanics 15, 1982, 933-939). In this study, we tested the hypothesis according to which programming to make fast movement could trigger the movement earlier than when programming self-pace movement. The same experimental paradigm of forward fall was used (see Do et al., 1982) to induce stepping. Different extents of stepping were manipulated by instructions: Subjects were instructed to step to recover their balance naturally (control condition); to make shorter steps than in the control condition; longer steps; faster steps. Lastly, a fast step was also induced by the biomechanical constraint on the initial posture, i.e. by inclining the subject forward at his maximum capacity. Data were collected from 12 subjects. The variables analyzed were the onset latency of step execution and other classical parameters (time of heel-contact, duration of the swing phase, step length, center of mass progression velocity, and step velocity). The results showed that the onset of stepping was unchanged in the longer- and faster-step conditions, relative to the control condition (mean control value = 280 ms). In contrast, the onset of stepping was significantly earlier in the short-step condition, and when the initial inclination was greater (250 and 252 ms, respectively). The swing phase duration in these two conditions averaged 140 and 185 ms, was significantly shorter than in the other conditions, whereas step length was obviously expected to be shorter in the shorter-step condition and longer in the longer-step condition than in the other conditions. Step length was similar between the other conditions. We conclude that neither step length or step velocity programming could induce an earlier onset latency of stepping. Step programming in relation to these specific instructions seemed to concern the extent of step execution and not the time of triggering of the stepping. We suggest that the control of short swing phase duration resulted in an earlier onset latency of stepping to recover the balance. This control depends on the combination of biomechanical constraints and cognitive processes, including subject's interpretation of the instructions and evaluation of the risk of fall.

Adult↗

PubMed1997

[Increase of the contraction of the stance soleus muscle in human does not delay the swing phase in step elicited by forward fall].

In this study it was examined in man whether tension increase in the extensor muscles of the stance foot delays the stance to swing transition, as suggested by some observations made in cats. Steps reproducibly elicited by forward fall were studied. Increase in muscle tension was obtained by electrical stimulation of the tibial nerve during the last third of the first step stance phase with trains of five rectangular pulses, 1 ms in duration, at 20 Hz, whose intensity was sufficient for eliciting maximal responses in the stance Soleus muscle (e.m.g. M responses). Trials with and without electrical simulation were randomly carried out in five healthy subjects who had consented to take part in the experimentation. The stance to swing transition was characterized by the time of activation of the Tibialis anterior muscle of the stance foot and by the time of clearance of this foot from the ground. It was found that maximal contractions of the stance Soleus muscle did not change these times. Thus, in contradiction to some observations made in spinal and decerebrated cats, tension increase in the stance Soleus in man during steps elicited by a forward fall does not delay the transition to the swing phase.

Accidental Falls↗

PubMed1996

Changes in motor activity and biomechanics during balance recovery following cutaneous and muscular deafferentation.

The effects of lower limb deafferentation were examined during execution of a balance recovery step following a forward fall induced by release of an initial inclined posture. The subjects were healthy control subjects and patients with a unilateral loss of the Achilles tendon reflex following S1 radiculitis. Deafferentation of healthy subjects was obtained by unilateral leg ischemia (four subjects) and by foot anesthesia (five subjects). The balance recovery step was characterized by the surface electromyographic (EMG) activity of right and left soleus and tibialis anterior muscles and the kinetics of the center of gravity and center of foot pressure. Experimentally induced and pathological deafferentation decreased the EMG activity of the ipsilateral soleus and lowered the vertical ground reaction force. The lower limb motor activity was more affected by loss of muscle proprioceptive afferents than by loss of plantar cutaneous afferents. Patients showed early and bilateral changes in soleus and tibialis activities, whichever side was affected. The step length of patients was also shorter than that of controls, but it remained similar before and after deafferentation in the healthy subjects. The results are discussed in terms of ipsilateral and crossed pathway connections and functional adaptive strategies.

Achilles Tendon↗

PubMed1992

Effects of reducing plantar support on anticipatory postural and intentional activities associated with flexion of the lower limb.

This study examines the anticipatory dynamics of the center of gravity and the EMG activity of ipsi- and contralateral (to the moving leg) soleus (SOL) and tibialis anterior (TA) in flexion of the lower limb executed from different plantar support surfaces. Subjects were standing initially on a plane surface or a surface reduced to two narrow rods under the moving or stance foot. Reduction of the plantar support surface under the moving limb induced a decrease in the anticipatory activity of both TA and in the intentional ipsilateral SOL EMG activity, but the anticipatory activity of SOL did not change. The lateral and vertical accelerations of the center of gravity decreased. When the reduction was under the stance limb, the biomechanical traces did not change markedly and the EMG activity was similar to that of the control situation. The differential effects in EMG activity, depending on whether the reduced plantar surface was under the moving or the stance side, suggest that tonic plantar stimulation induces complex reflex actions on muscles involved in the preparation and execution of voluntary movement. The functional demand could explain the gating from one motor organization to another.

Adult↗

PubMed1992

Do fast voluntary movements necessitate anticipatory postural adjustments even if equilibrium is unstable?

Anticipatory postural adjustments (APA) were studied in maximum velocity flexion of lower limb from two initial postures, a bipedal stance (Fbu) and unipedal stance (Fuu). In Fbu, the dynamics of center of gravity (CG) and ankle and hip muscle EMG activity showed large APA. In contrast, in Fuu there were no APA, the CG dynamics and the ankle EMG activity started at the same time as the intentional movement while the hip EMG activity started some 30 ms before the thigh flexion. The knee flexion velocity was lower in Fuu than in Fbu (7 rd/s versus 12 rd/s). These results suggest that fast voluntary movements do not require APA when the postural equilibrium is unstable, and that an alternative strategy is used. The absence of APA in Fuu, in contrast to the presence of APA in Fbu, suggests that the postural command and the focal one are time-locked and organized in a parallel process.

Electromyography↗

PubMed1991

Is balance or posture at the end of a voluntary movement programmed?

Two leg movements, differing only by the final balance conditions, were analysed to determine whether the final body posture or the equilibrium were taken into account by the motor programming. The test movement was a flexion-extension of a lower limb executed at maximal velocity. The initial body posture was bipedal, while the final one was either bipedal or unipedal. The biomechanical and electromyographic data showed significant differences between parameters of the two movements. The results indicate that the final body equilibrium is the major parameter controlled.

Biomechanical Phenomena↗

PubMed1991

Motor compensatory reactions following a forward fall in subjects with unilateral abolition of the triceps-surae H reflex.

The electromyograms of the right and left soleus and tibialis anterior muscles of 6 subjects with unilateral abolition of Achilles tendon reflex due to S1 radiculitis were recorded during a forward fall involving stepping to recover balance. Each subject took part in two series of experiments, one in which the step was performed with the unaffected leg and a second in which the affected leg was used. A unilateral deficiency of peripheral proprioceptive afferents affected ankle muscles EMG activities bilaterally, except for the EMG activity of the soleus of the starting foot. The tibialis anterior of both the affected and the unaffected side, showed either a normal pattern (i.e. a phasic contraction after soleus contraction stopped), or an early contraction. On the stance side, the early contraction was associated with a depressed soleus EMG activity. Some abnormal motor patterns could be due to the ipsilateral deficiency of the Ia inhibitory projection from soleus to tibialis anterior. The presence of abnormal patterns on the unaffected side indicates that the motor activity in one lower limb can be modified by a loss of peripheral afference in the contralateral limb. This suggests that crossed pathways between lower limbs are involved in balance recovery movement.

Achilles Tendon↗

PubMed1991

The influence of a reduced plantar support surface area on the compensatory reactions to a forward fall.

The influence of altered plantar support area on the compensatory reactions to forward fall was studied. The forward fall was provoked from an initial forward inclined posture, and balance was recovered by making steps. Alteration of the support area was unilateral and was obtained using two rods on which the subject stood. The rods were under either the starting foot or the stance foot. The configuration of the plantar support area, flat or reduced, did not change the latency of Soleus electromyographic activity. In contrast, the unilateral reduction of the plantar support area had powerful bilateral effects on the magnitude of Soleus activity. The reduction of the plantar support area on the swing side significantly reduced the ipsilateral Soleus response. The reduction of plantar support area on the stance side did not alter the initial part of the ipsilateral soleus response, but did change the late response (corresponding to the unipedal stance). Reduction of plantar support surface area resulted in earlier step execution and earlier heel-contact, i.e. faster balance recovery. These changes suggest that there is an integration of the spinal reflexes, as well as the stepping motor program.

Ankle↗

PubMed1991

Control of gait initiation.

The initiation of gait from a standing posture by 6 subjects, who took controlled-length steps, was analyzed. Using an inverted pendulum model, we found that the duration of gait initiation was independent of gait velocity. This finding suggests that subjects' biomechanical constants are the determining factors for initiating movement. Both the instantaneous velocity of the center of gravity at the end of the first step (resulting in the propulsive forces measured on the ground) and the steady-state velocity (resulting in the step length and frequency) varied with step length, whereas step frequency did not. But step frequency and progression velocity were linked, for step frequency always increased in parallel with increased progression velocity. We interpret the correlation between velocity and frequency variations to be a peripheral expression of the posturodynamic control of the step parameters by the progression forces.

Journal Article↗

PubMed1990

Influence of plantar cutaneous afferents on early compensatory reactions to forward fall.

The influence of cutaneous afferents in the compensatory reactions to a forward fall was investigated. Modification of cutaneous afferent activity was obtained in two different ways: first, by varying the initial pedal support conditions, secondly by anesthetizing the plantar foot sole. The initial pedal support conditions were: 1) bipedal posture, 2) unipedal posture, with contact and 3) unipedal posture, without contact. Nine healthy subjects participated in the control (without anesthesia) experimental session, of which three subjects participated in a session where the plantar sole was anesthetized. The compensatory reactions to a perturbation of balance of a subject initially with a bipedal stance, showed synchronized EMG activity in both Soleus muscles, starting on average at 59 ms, and a burst of EMG activity in the Tibialis Anterior of the starting foot after 200 ms. When the subject was in unipedal posture, the EMG responses on the side which was without support, showed several modifications: the EMG burst in Soleus was strikingly depressed, the response in Tibialis Anterior appeared earlier (mean latency 90 ms) and its magnitude was enhanced. When this foot was in contact with a rigid support, the Soleus showed a short burst of activity and the activity in Tibialis Anterior started at a mean latency of 150 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1988

Compensatory reactions in forward fall: are they initiated by stretch receptors?

Electromyographic activities from soleus and tibialis anterior muscles of 12 healthy subjects and 3 patients with vestibular syndrome, together with onset of movement of the head and leg were recorded during balance recovery. The disequilibrium was induced from initial forward inclination of the body. Soleus of the oscillatory foot showed brisk activity starting 59 msec (mean latency) after the perturbation and lasting 100-120 msec. Soleus of the stance foot showed similar activity, except that its duration was longer. The antagonist muscle activities started 5-20 msec later and showed similar time courses but of smaller amplitude. Ischaemia of the leg did not modify the latency. The onset of head movement was 10-20 msec after the perturbation, and those of leg were 70-90 msec. The results suggest that the early motor responses of the balance recovery were neither triggered by discharges from soleus group I and group II afferents, nor from vestibular cues, but could possibly originate in receptors located at the abdominal or lumbar level.

Action Potentials↗

PubMed1986

When and how does steady state gait movement induced from upright posture begin?

The aim of this research was to study when and how the stationary process of gait begins when walking starts from upright posture. The subject initially stood up on a large force plate, then walked. Three conditions of speed (slow, normal, fast) were examined. Five subjects participated in the experiment. A total of 105 trials were performed. The results show that, at the end of the first step, the progression velocity of the center of gravity is not significantly different from the mean progression velocity of gait during the second step of gait and that the time necessary to reach steady state gait from initial posture phase is constant. Furthermore, the frequency of the first step, when compared to published values of the steady state gait frequency, is not significantly different from these frequencies. It can be concluded that the aim of the gait initiation process is to place the subject in steady-state gait within the first step, in an invariant time which is dependent only on the body segment parameters of each subject.

Gait↗