Biomedical subjects

Oron Levin

Publications and source records attributed to Oron Levin.

12 recordsLinked to original sources

PubMed2006

Relationship of chronic ankle instability to muscle activation patterns during the transition from double-leg to single-leg stance.

BACKGROUND: Impaired muscle activation may predispose subjects to develop chronic ankle instability. It has been suggested that impairments are found not only in structures around the injured ankle but also around the more proximal joint complexes. HYPOTHESIS: Subjects with chronic ankle instability were expected to show later onset times for lower limb and trunk muscle activation when compared with control subjects. They were expected to show less variability in muscle activation patterns compared with the control group. STUDY DESIGN: Controlled laboratory study. METHODS: Thirty control subjects and 10 subjects with chronic ankle instability participated in the study. The onset of muscle activity of 14 muscles of the lower limb and trunk was measured during the transition from a double-leg stance position to a single-leg stance position in eyes-open and eyes-closed test conditions. RESULTS: Subjects with chronic ankle instability showed significantly later onset times for the ankle, hip, and hamstring muscles compared with control subjects. They used a similar muscle activation pattern in both test conditions, whereas control subjects adjusted their activation pattern according to the condition. CONCLUSIONS: Differences in muscle activation patterns between subjects with chronic ankle instability and control subjects occur not only around the ankle but also around other joints. Subjects with chronic ankle instability show less variability in muscle activation patterns between test conditions. CLINICAL RELEVANCE: Knowledge of muscle activation patterns in the whole lower limb and trunk in noninjured subjects and the differences found in chronic ankle instability subjects broadens the physical therapy approach to the treatment of chronic ankle instability.

Adult↗

PubMed2006

Whole-body-vibration-induced increase in leg muscle activity during different squat exercises.

This study analyzed leg muscle activity during whole-body vibration (WBV) training. Subjects performed standard unloaded isometric exercises on a vibrating platform (Power Plate): high squat (HS), low squat (LS), and 1-legged squat (OL). Muscle activity of the rectus femoris, vastus lateralis, vastus medialis, and gastrocnemius was recorded in 15 men (age 21.2 +/- 0.8 years) through use of surface electromyography (EMG). The exercises were performed in 2 conditions: with WBV and without (control [CO]) a vibratory stimulus of 35 Hz. Muscle activation during WBV was compared with CO and with muscle activation during isolated maximal voluntary contractions (MVCs). Whole-body vibration resulted in a significantly higher (p < 0.05) EMG root-mean-square compared with CO in all muscle groups and all exercises (between +39.9 +/- 17.5% and +360.6 +/- 57.5%). The increase in muscle activity caused by WBV was significantly higher (p < 0.05) in OL compared with HS and LS. In conclusion, WBV resulted in an increased activation of the leg muscles. During WBV, leg muscle activity varied between 12.6 and 82.4% of MVC values.

Adult↗

PubMed2005

Kinesthetic, but not visual, motor imagery modulates corticomotor excitability.

The hypothesis that motor imagery and actual movement involve overlapping neural structures in the central nervous system is supported by multiple lines of evidence. The aim of this study was to examine the modulation of corticomotor excitability during two types of strategies for motor imagery: Kinesthetic Motor Imagery (KMI) and Visual Motor Imagery (VMI) in a phasic thumb movement task. Transcranial magnetic stimulation (TMS) was applied over the contralateral motor cortex (M1) to elicit motor evoked potentials (MEPs) in the dominant abductor pollicis brevis (APB) and abductor digiti minimi (ADM). In a separate experiment, transcutaneous electrical stimuli were delivered to the median nerve at the dominant wrist, to elicit F-waves from APB. Imagined task performance was paced with a 1 Hz auditory metronome, and stimuli were delivered either 50 ms before (ON phase), or 450 ms after (OFF phase), the metronome beeps. Recordings were also made during two control conditions: Rest, and a Visual Static Imagery (VSI) condition. Significant MEP amplitude facilitation occurred only in APB, and only during the ON phase of KMI. F-wave persistence and amplitude were unaffected by imagery. These results demonstrate that kinesthetic, but not visual, motor imagery modulates corticomotor excitability, primarily at the supraspinal level. These findings have implications for the definition of motor imagery, and for its therapeutic applications.

Adult↗

PubMed2005

Effects of interlimb and intralimb constraints on bimanual shoulder-elbow and shoulder-wrist coordination patterns.

The present study addressed the interactions between interlimb and intralimb constraints during the control of bimanual multi-joint movements. Participants performed eight coordination tasks involving bilateral shoulder-elbow (expt I) and shoulder-wrist (expt II) movements. Three principal findings were obtained. First, the principle of muscle homology (in-phase coordination), giving rise to mirror symmetrical movements with respect to the midsagittal plane, had a powerful influence on the quality of interlimb coordination. In both experiments, the accuracy and stability of inter- and/or intralimb coordination deteriorated as soon as the antiphase mode was introduced in one or both joint pairs. However, the mutual influences between bilateral distal and proximal joint pairs varied across coordination tasks and effectors. Second, the impact of intralimb coordination modes on the quality of intralimb coordination was inconsistent between adjacent (expt I) and non-adjacent joint (expt II) combinations. Third, the mode of interlimb coordination affected the quality of intralimb coordination, whereas strong support for the converse effect was not obtained. Taken together, these observations point to a hierarchical control structure whereby interlimb coordination constraints have a stronger impact on the global coordination of the system than intralimb constraints, whose impact is substantially dependent on effector and task. The finding that intralimb coordination is subordinate to interlimb coordination during the production of bimanual multi-joint coordination patterns indicates that symmetry is a major organizational principle in the neural control of complex movement.

Adult↗

PubMed2005

Interactions between interlimb and intralimb coordination during the performance of bimanual multijoint movements.

The simultaneous performance of movements involving different effectors gives rise to neural and biomechanical interactions between and within limbs. The present study addressed the role of interlimb and intralimb constraints during the control of bimanual multijoint movements. Thirteen participants performed eight tasks involving the bilateral elbows and wrists under different coordination conditions. With respect to interlimb coordination, coordination patterns referred to the in-phase and anti-phase coordination modes, involving the simultaneous timing of homologous versus non-homologous muscles, respectively. With respect to inter-segmental (intralimb) coordination, the isodirectional mode referred to simultaneous flexions and extensions in the ipsilateral wrist and elbow joints, whereas the non-isodirectional mode involved simultaneous flexion in one joint together with extension in the other joint, or vice versa. The analysis of the data focused upon measures of relative phasing between proximal and distal joints within a limb as well as between the homologous joints of both limbs. With respect to interlimb coordination, findings revealed that adoption of the in-phase mode resulted in a higher quality of interlimb coordination than the anti-phase mode. However, the mode adopted in the distal joints had a larger impact on the quality of interlimb coordination than the mode adopted in the proximal joints. More specifically, in-phase coordination of the distal joints had a positive, and anti-phase coordination a negative, influence on the global coordinative behavior of the system. Minor effects of intralimb coordination modes on interlimb coordination were observed. With respect to intralimb coordination between the ipsilateral elbow and wrist, the isodirectional mode was performed with higher stability than the non-isodirectional mode. The mode of interlimb coordination also affected the quality of intralimb coordination, such that generating anti-phase coordination patterns in the distal joints had a negative influence on the accuracy and stability of intralimb coordination. Taken together, the present findings suggest a hierarchical structure whereby interlimb coordination constraints have a stronger impact on the global coordinative behavior of the system than intralimb coordination constraints. Moreover, the global coordinative state of the system is more affected by the coordination between the distal than between the proximal joints. Overall, the findings suggest that the mirror-image symmetry constraint has a powerful influence on bimanual multijoint coordination.

Arm↗

PubMed2004

Bimanual coordination involving homologous and heterologous joint combinations: when lower stability is associated with higher flexibility.

Variability in behavior is often put in an unfavorable light as a marker of lack of skill. Here, we provide evidence that increased variability during preferred patterns of coordination is associated with higher flexibility in adopting new patterns. Twelve right-handed subjects performed cyclical bimanual flexion and extension patterns with four homologous and six heterologous joint combinations involving shoulder, elbow, wrist, and finger movements. Preferred (isofrequency) as well as less preferred (multifrequency) coordination patterns were studied. The findings revealed less accurate and less stable 1:1 coordination patterns during heterologous as compared to homologous limb segment combinations. Conversely, coordination patterns with a 2:1 frequency ratio were performed more accurately and more consistently during heterologous as compared to homologous conditions. Accordingly, a lower degree of coupling between effectors during performance of preferred coordination patterns was associated with more successful performance of less familiar patterns. This suggests that variability may promote the creative exploration of new performance modes.

Adult↗

PubMed2003

Bimanual coordination: constraints imposed by the relative timing of homologous muscle activation.

It has often been supposed that patterns of rhythmic bimanual coordination in which homologous muscles are engaged simultaneously, are performed in a more stable manner than those in which the same muscles are activated in an alternating fashion. In order to assess the efficacy of this constraint, the present study investigated the effect of forearm posture (prone or supine) on bimanual abduction-adduction movements of the wrist in isodirectional and non-isodirectional modes of coordination. Irrespective of forearm posture, non-isodirectional coordination was observed to be more stable than isodirectional coordination. In the latter condition, there was a more severe deterioration of coordination accuracy/stability as a function of cycling frequency than in the former condition. With elevations in cycling frequency, the performers recruited extra mechanical degrees of freedom, principally via flexion-extension of the wrist, which gave rise to increasing motion in the vertical plane. The increases in movement amplitude in the vertical plane were accompanied by decreasing amplitude in the horizontal plane. In agreement with previous studies, the present findings confirm that the relative timing of homologous muscle activation acts as a principal constraint upon the stability of interlimb coordination. Furthermore, it is argued that the use of manipulations of limb posture to investigate the role of other classes of constraint (e.g. perceptual) should be approached with caution because such manipulations affect the mapping between muscle activation patterns, movement dynamics and kinematics.

Adult↗

PubMed2003

Corticospinal excitability changes following prolonged muscle tendon vibration.

The present experiment addressed the time course of corticospinal excitability changes following interventional muscle tendon vibration. Using transcranial magnetic stimulation, motor evoked potentials of the flexor carpi radialis and extensor carpi radialis brevis muscle were recorded for a period of 60 min after cessation of vibration (80 Hz, 0.5 mm, 30 min) to the distal wrist flexor tendons. A delayed corticospinal excitability increase in both the vibrated and non-vibrated antagonistic muscle was observed, with lasting levels of facilitation for the latter. No changes were observed following interventional cutaneous vibration. These results underscore a facilitatory influence of prolonged Ia-afferent activation on corticospinal excitability. Findings are discussed in light of recent advances in promoting motor recovery after brain injury by somatosensory stimulation.

Adult↗

PubMed2003

High-frequency transcranial magnetic stimulation of the supplementary motor area reduces bimanual coupling during anti-phase but not in-phase movements.

Previous electrophysiological and neuroimaging studies have provided evidence that the supplementary motor area (SMA) has an important role in the control of bimanual coordination. The present experiment investigated the effects of high-frequency repetitive transcranial magnetic stimulation (rTMS) over the SMA region on kinematic variables during cyclical bimanual coordination, with a particular focus on the quality of coordination. Subjects performed metronome-paced trials of in-phase and anti-phase bimanual index-finger movements at near-maximal cycling frequency. During movement execution, rTMS (20 Hz, 0.5 s, 120% hand motor threshold) was applied over one of three positions in the sagittal midline 2.0, 4.0 and 6.0 cm anterior to the primary motor leg area. Sham rTMS was included as a control condition. After rTMS, the mean relative phase error between hands increased, but only in the anti-phase trials. The maximum increase in phase error occurred immediately after rather than during the rTMS train. The effect was largest after stimulation 4 or 6 cm anterior to the leg area of the primary motor cortex. We did not observe any changes in the variability of relative phase or in cycle duration or movement amplitude. Findings are discussed in light of recent functional models on the role of the SMA in bimanual movement control.

Adult↗

PubMed2003

Directional interference during bimanual coordination: is interlimb coupling mediated by afferent or efferent processes.

The role of afferent information in bimanual directional interference was studied by means of a modulation of the response-produced information in one of both limbs. In Experiment 1, visual information was either present, withdrawn, or shown with a directional transformation on a LCD screen. In Experiment 2, the technique of muscle tendon vibration was used to bias the kinesthetic afferent information associated with movement. The findings revealed strong evidence for directional interference between both limbs. Nevertheless, no evidence could be advanced that the observed interference from the right onto the left limb movement was modulated by manipulation of the afferent sources of information. It is concluded that directional interference primarily emerges at the efferent level of movement planning and organization.

Adult↗

PubMed2003

Joint torques during sit-to-stand in healthy subjects and people with Parkinson's disease.

OBJECTIVES: To compare lower limb joint torques during sit-to-stand in normal elderly subjects and people with Parkinson's disease, using a developed biomechanical model simulating all phases of sit-to-stand.Design. A cross-sectional study utilizing a Parkinsonian and a control group. BACKGROUND: Subjects with Parkinson's disease were observed to experience difficulty in performing sit-to-stand. The developed model was used to calculate the lower limb joint torques in normal elderly subjects and subjects with Parkinson's disease, to delineate possible causes underlying difficulties in initiating sit-to-stand task. METHODS: Six normal elderly subjects and seven age-matched subjects with Parkinson's disease performed five sit-to-stand trials at their self-selected speed. Anthropometric data, two-dimensional kinematic and foot-ground and thigh-chair reactive forces were used to calculate, via inverse dynamics, the joint torques during sit-to-stand in both before and after seat-off phases. The difference between the control and Parkinson's disease group was analysed using independent t-tests. RESULTS: Both control and Parkinson's disease groups had a similar joint kinematic pattern, although the Parkinson's disease group demonstrated a slower angular displacement. The latter subjects produced significantly smaller normalized hip flexion torque and presented a slower torque build-up rate than the able-bodied subjects (P<0.05). CONCLUSION: Slowness of sit-to-stand in people with Parkinson's disease could be due to a reduced hip flexion joint torque and a prolonged rate of torque production.

Ankle Joint↗

PubMed2002

Directional invariance during loading-related modulations of muscle activity: evidence for motor equivalence.

In the present study, we investigated the influence of external force manipulations on movements in different directions, while keeping the amplitude invariant. Subjects ( n=10) performed a series of cyclical anteroposterior, mediolateral, and oblique line-drawing movements (star drawing task) with their dominant limb in the horizontal plane. To dissociate kinematics from the underlying patterns of muscle activation, spring loading was applied to the forearm of the moving limb. Whereas spring loading of the arm resulted in considerable changes in the overall amount of muscle activation in the elbow and shoulder muscles, invariance was largely maintained at the kinematic level. Subjects produced the required movement directions and amplitudes of the star drawing largely successfully, irrespective of the force bias induced by the spring. These observations demonstrate motor equivalence and strengthen the notion that the spatial representation of drawing movements is encoded in the higher brain regions in a rather abstract form that is dissociated from the concrete muscle activation patterns underlying a particular movement direction. To achieve this goal, the central nervous system shifted between two or more muscle grouping strategies to overcome modulations in the interaction among posture-dependent (joint stiffness), dynamic (inertial), and elastic (spring) torque components in the joints. Spring loading induced general changes in the overall amount of EMG activity, which was largely muscle but not direction specific, presumably to represent the posture-dependent biasing force of the spring. Loading was mainly shown to increase muscle coactivation in the elbow joint. This indicates that the subjects tended to increase stiffness in the elbow to compensate for changes in the spring bias forces in order to minimize trajectory errors. Changes in muscle grouping of the shoulder antagonists were mainly a consequence of movement direction but were also affected partly by loading, presumably reflecting the influence of dynamic force components. Taken together, the results confirmed the hypothesis that changes of movement direction and direction of force in the end-effector generated specific sets of muscle grouping to overcome the dynamic requirements in the joints while keeping the kinematics largely unchanged. This suggests that directional tuning in muscle activity and changes in muscle grouping reflects the formation of appropriate internal models in the CNS that give rise to motor equivalence.

Adult↗