Biomedical subjects

Y P Ivanenko

Publications and source records attributed to Y P Ivanenko.

At least 19 recordsLinked to original sources

PubMed2006

Motor patterns in human walking and running.

Despite distinct differences between walking and running, the two types of human locomotion are likely to be controlled by shared pattern-generating networks. However, the differences between their kinematics and kinetics imply that corresponding muscle activations may also be quite different. We examined the differences between walking and running by recording kinematics and electromyographic (EMG) activity in 32 ipsilateral limb and trunk muscles during human locomotion, and compared the effects of speed (3-12 km/h) and gait. We found that the timing of muscle activation was accounted for by five basic temporal activation components during running as we previously found for walking. Each component was loaded on similar sets of leg muscles in both gaits but generally on different sets of upper trunk and shoulder muscles. The major difference between walking and running was that one temporal component, occurring during stance, was shifted to an earlier phase in the step cycle during running. These muscle activation differences between gaits did not simply depend on locomotion speed as shown by recordings during each gait over the same range of speeds (5-9 km/h). The results are consistent with an organization of locomotion motor programs having two parts, one that organizes muscle activation during swing and another during stance and the transition to swing. The timing shift between walking and running reflects therefore the difference in the relative duration of the stance phase in the two gaits.

Adult↗

PubMed2005

Interaction of involuntary post-contraction activity with locomotor movements.

Involuntary post-contraction muscle activity may occur after performing a strong long-lasting (about 30 s) isometric muscle contraction (Kohnstamm phenomenon). Here we examined how this putative excitatory state may interact with a locomotor movement. The subjects stood upright and were asked to oppose a rotational force applied to the pelvis for about 30 s either in the clockwise or in the counterclockwise direction. After that, they were asked to perform various motor tasks with the eyes closed. During quiet standing, we observed an involuntary post-contraction torsion of the trunk. During walking, the post-contraction facilitatory effect of body torsion was not overridden by the voluntary activity, but instead significantly influenced the forward locomotor program such that subjects walked along a curved trajectory in the direction of the preceding torsion. In contrast, we did not observe any rotational component when subjects were asked to step in place. We conclude that the post-contraction rotational aftereffect does not transfer to just any motor task but apparently manifests itself in those movements that incorporate the activated axial muscle synergy or rotational component. We argue that central excitability changes following the voluntary effort may contribute to the phenomenon and highlight the role of tonic influences in fine-tuning of the spinal cord.

Adult↗

PubMed2005

Spinal cord maps of spatiotemporal alpha-motoneuron activation in humans walking at different speeds.

Functional MRI (fMRI) imaging of motoneuron activity in the human spinal cord is still in its infancy, and it will remain difficult to apply to walking. Here we present a viable alternative for documenting the spatiotemporal maps of alpha-motorneuron (MN) activity in the human spinal cord during walking, similar to the method recently reported for the cat. We recorded EMG activity from 16 to 32 ipsilateral limb and trunk muscles in 13 healthy subjects walking on a treadmill at different speeds (1-7 km/h) and mapped the recorded patterns onto the spinal cord in approximate rostrocaudal locations of the motoneuron pools. This approach can provide information about pattern generator output during locomotion in terms of segmental control rather than in terms of individual muscle control. A striking feature we found is that nearly every spinal segment undergoes at least two cycles of activation in the step cycle, thus supporting the idea of half-center oscillators controlling MN activation at any segmental level. The resulting spatiotemporal map patterns seem highly stereotyped over the range of walking speeds studied, although there were also some systematic redistributions of MN activity with speed. Bursts of MN activity were either temporally aligned across several spinal segments or switched between different segments. For example, the center of mass of MN activity in the lumbosacral levels generally shifted from rostral to caudal positions in two cycles for each step, revealing four major activation foci: two in the upper lumbar segments and two in the sacral segments. The results are consistent with the presence of at least two and possibly more pattern generators controlling the activation of lumbosacral MNs.

Action Potentials↗

PubMed2004

Five basic muscle activation patterns account for muscle activity during human locomotion.

An electromyographic (EMG) activity pattern for individual muscles in the gait cycle exhibits a great deal of intersubject, intermuscle and context-dependent variability. Here we examined the issue of common underlying patterns by applying factor analysis to the set of EMG records obtained at different walking speeds and gravitational loads. To this end healthy subjects were asked to walk on a treadmill at speeds of 1, 2, 3 and 5 kmh(-1) as well as when 35-95% of the body weight was supported using a harness. We recorded from 12-16 ipsilateral leg and trunk muscles using both surface and intramuscular recording and determined the average, normalized EMG of each record for 10-15 consecutive step cycles. We identified five basic underlying factors or component waveforms that can account for about 90% of the total waveform variance across different muscles during normal gait. Furthermore, while activation patterns of individual muscles could vary dramatically with speed and gravitational load, both the limb kinematics and the basic EMG components displayed only limited changes. Thus, we found a systematic phase shift of all five factors with speed in the same direction as the shift in the onset of the swing phase. This tendency for the factors to be timed according to the lift-off event supports the idea that the origin of the gait cycle generation is the propulsion rather than heel strike event. The basic invariance of the factors with walking speed and with body weight unloading implies that a few oscillating circuits drive the active muscles to produce the locomotion kinematics. A flexible and dynamic distribution of these basic components to the muscles may result from various descending and proprioceptive signals that depend on the kinematic and kinetic demands of the movements.

Adult↗

PubMed2003

Postural instability enhances motor responses to transcranial magnetic stimulation in humans.

Does the state of postural instability require a high hierarchical level of posture control? Electromyographic (EMG) activity of leg muscles was recorded during transcranial magnetic stimulation (TMS) of the motor cortex and electrical stimulation of the tibial nerve (H-reflex) in healthy subjects standing on a rigid floor and on a rocking platform. In the soleus muscle, TMS-evoked EMG responses increased considerably (2.2+/-1.1 times) when balancing on the rocking platform, whilst the H-reflex tended to decrease. The effect of support instability was specific to the muscles participating in the posture control. The results suggest that postural instability might change the state and the role of the motor cortex in equilibrium maintenance.

Adult↗

PubMed2002

Control of foot trajectory in human locomotion: role of ground contact forces in simulated reduced gravity.

We studied the changes of vertical contact forces, lower limb kinematics, and electromyographic activity (EMG) at different speeds and gravitational loads. To this end healthy subjects were asked to walk on a motorized treadmill while the percentage of body weight unloaded (body weight support, BWS) was modified in steps by means of a well-characterized unloading system. BWS was set at 0, 35, 50, 75, 95, or 100% of body weight. Walking speed was 0.7, 1.1, 2, 3, or 5 km/h. We found that changing BWS between 0 and 95% resulted in drastic changes of kinetic parameters but in limited changes of the kinematic coordination. In particular, the peak vertical contact forces decreased proportionally to BWS; at 95%-BWS they were 20-fold smaller than at 0% and were applied at the forefoot only. Also, there were considerable changes of the amplitude of EMG activity of all tested lower limb muscles and a complex re-organization of the pattern of activity of thigh muscles. By contrast, the corresponding variation of the parameters that describe shape and variability of the foot path was very limited, always <30% of the corresponding values at 0 BWS. Moreover, the planar co-variation of the elevation angles was obeyed at all speed and BWS values. Minimum variance of limb trajectory occurred at 3 km/h. At 100% BWS, subjects stepped in the air, their feet oscillating back and forth just above but never contacting the treadmill. In this case, step-to-step variability of foot path was much greater than at all other BWS levels but was restored to lower values when minimal surrogate contact forces were provided during the "stance" phase. The results did not depend on the specific instruction given to the subject. Therefore we conclude that minimal contact forces are sufficient for accurate foot trajectory control.

Adult↗

PubMed2002

Kinematic control of walking.

The planar law of inter-segmental co-ordination we described may emerge from the coupling of neural oscillators between each other and with limb mechanical oscillators. Muscle contraction intervenes at variable times to re-excite the intrinsic oscillations of the system when energy is lost. The hypothesis that a law of coordinative control results from a minimal active tuning of the passive inertial and viscoelastic coupling among limb segments is congruent with the idea that movement has evolved according to minimum energy criteria (1, 8). It is known that multi-segment motion of mammals locomotion is controlled by a network of coupled oscillators (CPGs, see 18, 33, 37). Flexible combination of unit oscillators gives rise to different forms of locomotion. Inter-oscillator coupling can be modified by changing the synaptic strength (or polarity) of the relative spinal connections. As a result, unit oscillators can be coupled in phase, out of phase, or with a variable phase, giving rise to different behaviors, such as speed increments or reversal of gait direction (from forward to backward). Supra-spinal centers may drive or modulate functional sets of coordinating interneurons to generate different walking modes (or gaits). Although it is often assumed that CPGs control patterns of muscle activity, an equally plausible hypothesis is that they control patterns of limb segment motion instead (22). According to this kinematic view, each unit oscillator would directly control a limb segment, alternately generating forward and backward oscillations of the segment. Inter-segmental coordination would be achieved by coupling unit oscillators with a variable phase. Inter-segmental kinematic phase plays the role of global control variable previously postulated for the network of central oscillators. In fact, inter-segmental phase shifts systematically with increasing speed both in man (4) and cat (38). Because this phase-shift is correlated with the net mechanical power output over a gait cycle (3, 4), phase control could be used for limiting the overall energy expenditure with increasing speed (22). Adaptation to different walking conditions, such as changes in body posture, body weight unloading and backward walk, also involves inter-segmental phase tuning, as does the maturation of limb kinematics in toddlers.

Animals↗

PubMed2000

The direction of postural instability affects postural reactions to ankle muscle vibration in humans.

Postural instability changes the weighting of different types of sensory information and the state of the equilibrium maintenance system. We have recently found that the effect of Achilles tendon vibration (so-called 'vibration-induced falling') strongly diminishes during unstable posture. However, it is unclear whether the state of postural instability has directionally specific or non-specific effects on the attenuation of proprioceptive influences from ankle muscles. To check this hypothesis, we varied the direction of support mobility and applied shank muscle vibration to subjects standing on a rocking platform movable in the sagittal, frontal or both directions. Postural reactions were present only on those supports that were stable in the sagittal direction. We suggest that the direction of postural instability affects information processing from ankle muscle receptors.

Adult↗

PubMed2000

Neck muscle vibration makes walking humans accelerate in the direction of gaze.

We studied the effect of the continuous vibration of symmetrical dorsal neck muscles in seven normal subjects during (a) quiet standing, (b) stepping in place movements and (c) walking on the treadmill. The experiments were performed in a darkened room and the subjects were given the instruction not to resist the applied perturbation. In one condition the velocity of the treadmill was controlled by feedback from the subject's current position. Head, trunk and leg motion were recorded at 100 Hz. In normal standing, neck vibration elicited a prominent forward body sway. During stepping in place, neck vibration produced an involuntary forward stepping at about 0.3 m s-1 without modifying the stepping frequency. If the head was turned horizontally 45 and 90 deg to the right or to the left, neck muscle vibration caused stepping approximately in the direction of the head naso-occipital axis. For lateral eye deviations, the direction of stepping was roughly aligned with gaze direction. In treadmill locomotion, neck vibration produced an involuntary step-like increase of walking speed (by 0.1-0.6 m s-1), independent of the initial walking speed. During backward locomotion, the walking speed tended to decrease during neck vibration. Thus, continuous neck vibration evokes changes in the postural reference during quiet standing and in the walking speed during locomotion. The results suggest that the proprioceptive input from the neck is integrated in the control of human posture and locomotion and is processed in the context of a viewer-centred reference frame.

Acceleration↗

PubMed2000

Lack of anticipatory gaze-orienting responses in patients with right brain damage.

OBJECTIVE: To study eye movements during cervical proprioceptive stimulation by passive body rotation in darkness, with the head held stationary, in patients with right brain damage and hemineglect. BACKGROUND: At very low frequency, this stimulation is reported to produce an illusion of head turning in space and eye deviations directed opposite to trunk rotation (in the direction of the illusory head rotation). METHODS: Ten normal subjects and seven patients with unilateral cerebral lesions (five right brain-damaged patients with mild to moderate visuospatial neglect, two left brain-damaged patients without neglect) were included in the study. Subjects were seated on a rotating chair. Stimuli consisted of slow sinusoidal passive trunk rotations (+/-30 degrees, 0.01 Hz) while the head was fixed in space. RESULTS: Eye movements directed opposite to trunk rotation were typical for normal subjects and for left brain-damaged patients. In contrast, all right brain-damaged patients showed either eye movements in the direction of trunk rotation or no eye deviations at all. CONCLUSION: This result could characterize a lack of anticipatory coordinating gaze behavior in patients with right brain damage.

Aged↗

PubMed2000

Spatial, not temporal cues drive predictive orienting movements during navigation: a virtual reality study.

A fundamental property of the human brain is the ability to make predictions of future sensory and motor events. We have recently found that steering manoeuvres when walking along curvilinear trajectories are controlled by an anticipatory guidance of the direction of head (and eyes). However it is unclear whether a time-related or space-related signal triggers such anticipatory head orienting movements. By simulating navigation along a multi-legged virtual corridor we show that anticipatory orienting movements are triggered (in standing subjects) by reaching specific locations rather than by the time to the approaching corridor's bend. Similar to what happens in car driving, specific spatial features of the route rather than time to collision seem to drive steering.

Adult↗

PubMed2000

Influence of leg muscle vibration on human walking.

We studied the effect of vibratory stimulation of different leg muscles [bilateral quadriceps (Q), hamstring (HS) muscles, triceps surae (TS), and tibialis anterior (TA)] in seven normal subjects during 1) quiet standing, 2) stepping in place movements, and 3) walking on the treadmill. The experiments were performed in a dimly illuminated room, and the subjects were given the instruction not to resist the applied perturbation. In one condition the velocity of the treadmill was controlled by a feedback from the subject's current position. In normal standing, TA vibration elicited a prominent forward body tilt, whereas HS and TS vibration elicited backward trunk or whole body inclination, respectively. Q vibration had little effect. During stepping in place, continuous HS vibration produced an involuntary forward stepping at about 0.3 m s(-1) without modifying the stepping frequency. When the subjects (with eyes closed) kept a hand contact with an external still object, they did not move forward but perceived an illusory forward leg flexion relative to the trunk. Q, TS, and TA vibration did not cause any systematic body translation nor illusory changes in body configuration. In treadmill locomotion, HS vibration produced an involuntary steplike increase of walking speed (by 0.1-0.6 m.s(-1)). Continuous vibration elicited larger speed increments than phasic stimulation during swing or stance phase. For phasic stimulation, HS vibration tended to be more effective when applied during swing than during stance phase. Q, TA, and TS vibration had little if any effect. Vibration of thigh muscles altered the walking speed depending on the direction of progression. During backward locomotion, the walking speed tended to decrease after HS vibration, whereas it significantly increased after Q vibration. Thus the influence of leg muscle vibration on stepping in place and locomotion differed significantly from that on normal posture. We suggest that the proprioceptive input from thigh muscles may convey information about the velocity of the foot movement relative to the trunk.

Adult↗

PubMed1999

Effect of gaze on postural responses to neck proprioceptive and vestibular stimulation in humans.

1. We studied the effect of gaze orientation on postural responses evoked by vibration of neck dorsal muscles or by galvanic stimulation of the vestibular system during quiet standing in healthy humans. Various gaze orientations were obtained by different combinations of horizontal head-on-feet (-90, -45, 0, 45, 90 deg) and eye-in-orbit (-30, 0, 30 deg) positions. The instantaneous centre of foot pressure was recorded with a force platform. 2. With a symmetrical position of the vibrator relative to the spine, neck muscle vibration elicited a body sway in the direction of the head naso-occipital axis when the eyes were aligned with it. The same result was obtained both during head rotations and when the head and trunk were rotated together. 3. For lateral eye deviations, the direction of the body sway was aligned with gaze orientation. The effect of gaze was present both with eyes open and eyes closed. After long-lasting (1 min) lateral fixation of the target the effect of gaze decreased significantly. 4. Postural responses to galvanic vestibular stimulation tended to occur orthogonal to the head naso-occipital axis (towards the anodal ear) but in eight of the 11 subjects the responses were also biased by the direction of gaze. 5. The prominent effect of gaze in reorienting automatic postural reactions indicates that both neck proprioceptive and vestibular stimuli are processed in the context of visual control of posture. The results point out the importance of a viewer-centred frame of reference for processing multisensory information.

Adult↗

PubMed1999

Non-specific directional adaptation to asymmetrical visual-vestibular stimulation.

Subjective estimates of passive whole-body rotations in darkness were evaluated before and after exposure to asymmetrical incoherent visual-vestibular stimulation (VVS). Two subjects who showed large capacity for adaptation to symmetrical incoherent VVS were enrolled in the study. Strikingly, after 45 min of asymmetrical left-right VVS, perception of rotation decreased equally for rotations to the right and to the left indicating that the calibration of vestibular sensory input for spatial orientation did not undergo a directional specific control.

Acoustic Stimulation↗

PubMed1999

Support stability influences postural responses to muscle vibration in humans.

We studied the effect of support stability on postural responses to the vibration of Achilles tendons and of neck dorsal muscles in healthy humans. For this purpose we compared postural responses on a rigid floor and on 6 cm high rocking supports (see-saws) of different curvatures (different radii: 30, 60 and 120 cm). The subject stood with eyes closed, the centre of the feet coincided with the centre of the see-saw. We recorded platform tilt, horizontal displacements of the upper body, ankle joint angle and activity of ankle joint muscles. On the rocking platform subjects maintained balance in a sagittal direction by making see-saw rotations placing the support under the body's centre of gravity. Equilibrium maintenance requires that the torque in the ankle joint increases during forward body displacements, as on the rigid floor, and be accompanied by a plantar flexion (not by a dorsiflexion) in the ankle joint. The directional dependence of vibration-induced reactions on the see-saw was the same (relative to space) as on the rigid floor: backward body displacement during Achilles tendon vibration and forward body displacement during neck muscle vibration. A decrease of support stability (with a decrease of the radius from 120 to 30 cm) diminished significantly the effect of Achilles tendon vibration and to a lesser extent the effect of neck muscle vibration. In contrast, the increase of platform stability by hand contact with a stable external object gave rise to prominent body sway in response to Achilles tendon vibration. Neck muscle vibration on the movable support provoked a quick initial forward body sway. This initial quick response was absent during vibration of the Achilles tendons. We conclude that postural responses to muscle vibration reflect the participation of different muscles in posture control and depend on the support properties. Support instability changes the role of proprioceptive information and the state of the system of equilibrium maintenance.

Achilles Tendon↗

PubMed1999

Eye movements during torso rotations in labyrinthine-defective subjects.

The aim of this study was to examine whether the chronic loss of vestibular function modifies perceptual and oculomotor responses during torso rotations in darkness. Subjects (4 patients with complete vestibular loss and 7 healthy volunteers) were seated on a rotating chair. Stimuli consisted of sinusoidal chair rotations (+/-30 degrees, 0.1 Hz and 0.011 Hz). We used 2 conditions: space stationary head (neck stimulation) and space stationary head and shoulders (torso stimulation). Horizontal eye deviations and slow component of eye movements were analysed. The results showed that eye movements and perception of head motion in space during neck stimulation were similar to those during torso stimulation both in normal and labyrinthine-defective (LD) subjects. During low-frequency chair rotations (0.011 Hz) all subjects perceived illusory head or head and shoulder rotation in space (as if the lower part of the body was stationary relative to the room) and shifted their gaze in the direction of illusory head rotation. In these conditions there was no significant difference in eye movements between normal and LD subjects. During higher frequency chair rotations (0.1 Hz), LD subjects had significantly larger eye deviations as well as increases in the gain of the slow component of eye movements relative to normals. In these conditions patients mostly perceived illusory head or head and shoulder rotation in space while normal subjects mainly perceived the head as stationary in space. The results indicate that 1) neck and torso rotations can evoke similar ocular responses in LD subjects, 2) the chronic loss of vestibular function modifies the representation of axial body segment motion relative to space.

Aged↗

PubMed1998

Eye-head coordination for the steering of locomotion in humans: an anticipatory synergy.

We investigated head and gaze orientation in six healthy volunteers walking along 90 degrees corner trajectories, both at light and with eyes closed. We found that head and eyes systematically deviated toward the future direction of the curved trajectory. Anticipation lead was about 1 s. Strikingly, the same behaviour was observed in darkness. In backward (BW) locomotion along the trajectory (from end- to start-point), gaze deviated toward the opposite direction, such that the forward locomotor pattern did not appear time-reversed. Orienting movements displayed higher amplitude, reproducibility and time lead in the forward (FW) direction at light. We suggest that anticipatory orienting synergies belong to the behavioural repertoire of human navigation and may reflect the need to prepare a stable reference frame for intended action.

Adult↗

PubMed1998

The vestibulo-ocular reflex and angular displacement perception in darkness in humans: adaptation to a virtual environment.

The vestibulo-ocular reflex (VOR) and angular displacement perception were measured in 25 healthy humans in darkness before and after exposure to incoherent visual-vestibular stimulation (VVS): 45 min of repeated passive 180 degrees whole-body rotations around the vertical axis concurrent with only 90 degrees rotation in a visual virtual square room. Large inter-individual variability was observed for both VOR gain and turning estimates. The individual VOR gains were not correlated with perceived angles of rotation either before or after VVS. After VVS, the angular displacement perception decreased by 24+/-16% while the VOR gain did not change significantly. The results suggest that adaptive plasticity in turning perception and adaptive plasticity in VOR might be independent of one another.

Adaptation, Physiological↗