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Articles by Victor S. Gurfinkel in JoVE
JoVE Clinical and Translational Medicine
שיטה למדוד טון של שרירים נטיית ציר וסמוך
1Department of Biomedical Engineering, Oregon Health and Science University, 2UCL Institute of Neurology, Queen Square, 3Department of Neurology, Oregon Health and Science University
פיתחנו מכשיר (טוויסטר) ללמוד את הרגולציה על פעילות השריר טוניק במהלך תחזוקה יציבה פעיל. טוויסטר אמצעי התנגדות torsional ותגובות שרירי בנושאים עומד במהלך סיבוב של ציר הגוף. המכשיר ניתן להגדיר בגמישות ללמוד היבטים שונים של בקרה טוניק פני הצוואר, גזע, ו / או ירכיים.
Other articles by Victor S. Gurfinkel on PubMed
Motor Coordination Can Be Fully Understood Only by Studying Complex Movements
In this chapter, we use the sit-up to illustrate the complexity of coordination in movements that involve many muscles, joints, degrees of freedom, and high levels of muscle activity. Complex movements often involve the body axis. In addition to the intentional, focal part of any voluntary movement, complex movements also include "associated movements" that are not consciously controlled, but are necessary for the movement to succeed. Some associated movements serve a purpose, and others may not. During sitting up, the leg-lift is a purposive associated movement, whereas three-joint flexion is a non-purposive associated movement. The control of complex movements is also likely to be complex and, we argue, is hierarchically controlled. Associated movements may, themselves, be hierarchically organized and triggered by lower brain structures, local changes in neuronal excitability, and sensory feedback. Complex movements typically involve a high level of mobility. Because this mobility can lead to instability, anticipatory postural adjustments, a type of purposive associated movement, are commonly used to regulate posture. Thus, a number of important aspects of motor coordination can only be revealed by the study of complex movements.
Scaling and Non-scaling of Muscle Activity, Kinematics, and Dynamics in Sit-ups with Different Degrees of Difficulty
The purpose of this study was to investigate how the CNS adjusts motor patterns for variants of a complex axial movement-the sit-up. Adjustments were induced by changing the support surface contact and mass distribution of the body. Healthy adults performed straight-legged sit-ups, 3 s in duration, with support added to or removed from the lumbar trunk, or with mass added to the head or to the legs. Each of these interventions either increased or decreased the difficulty of the task. The study addressed the extent to which changes in sit-up difficulty are compensated by scaling of muscle activity, kinematics, and dynamics versus the extent to which they are compensated by changing discretely the motor pattern. The analysis of muscle activity, kinematics, and dynamics focused on the first 30-40% of the sit-up-the trunk flexion phase-since this is the most critical part of the movement. Our results demonstrate that, in some respects, sit-up kinematics and dynamics scaled with difficulty, but in other respects, they did not. Muscle activity also scaled, in many respects, but in more difficult sit-ups, abdominal flexor activity decreased instead of increased. Non-scaling changes in these parameters suggest that complex movements, such as the sit-up, may require discrete changes in motor pattern in order to deal with large loads, which challenge the available leverage.
Reduced Performance in Balance, Walking and Turning Tasks is Associated with Increased Neck Tone in Parkinson's Disease
Rigidity or hypertonicity is a cardinal symptom of Parkinson's disease (PD). We hypothesized that hypertonicity of the body axis affects functional performance of tasks involving balance, walking and turning. The magnitude of axial postural tone in the neck, trunk and hip segments of 15 subjects with PD (both ON and OFF levodopa) and 15 control subjects was quantified during unsupported standing in an axial twisting device in our laboratory as resistance to torsional rotation. Subjects also performed six functional tests (walking in a figure of eight [Figure of Eight], Timed Up and Go, Berg Balance Scale, supine rolling task [rollover], Functional Reach, and standing 360-deg turn-in-place) in the ON and OFF state. Results showed that PD subjects had increased tone throughout the axis compared to control subjects (p=0.008) and that this increase was most prominent in the neck. In PD subjects, axial tone was related to functional performance, but most strongly for tone at the neck and accounted for an especially large portion of the variability in the performance of the Figure of Eight test (r(OFF)=0.68 and r(ON)=0.74, p<0.05) and the Rollover test (r(OFF)=0.67 and r(ON)=0.55, p<0.05). Our results suggest that neck tone plays a significant role in functional mobility and that abnormally high postural tone may be an important contributor to balance and mobility disorders in individuals with PD.
Prolonged Weight-shift and Altered Spinal Coordination During Sit-to-stand in Practitioners of the Alexander Technique
The Alexander Technique (AT) is used to improve postural and movement coordination and has been reported to be clinically beneficial, however its effect on movement coordination is not well-characterized. In this study we examined the sit-to-stand (STS) movement by comparing coordination (phasing, weight-shift and spinal movement) between AT teachers (n=15) and matched control subjects (n=14). We found AT teachers had a longer weight-shift (p<0.001) and shorter momentum transfer phase (p=0.01), than control subjects. AT teachers also increased vertical foot force monotonically, rather than unweighting the feet prior to seat-off, suggesting they generate less forward momentum with hip flexors. The prolonged weight-shift of AT teachers occurred over a greater range of trunk inclination, such that their weight shifted continuously onto the feet while bringing the body mass forward. Finally, AT teachers had greatly reduced spinal bending during STS (cervical, p<0.001; thoracic, p<0.001; lumbar, p<0.05). We hypothesize that the low hip joint stiffness and adaptive axial postural tone previously reported in AT teachers underlies this novel "continuous" STS strategy by facilitating eccentric contractions during weight-shift.
Foot Anatomy Specialization for Postural Sensation and Control
Anthropological and biomechanical research suggests that the human foot evolved a unique design for propulsion and support. In theory the arch and toes must play an important role, however, many postural studies tend to focus on the simple hinge action of the ankle joint. To further investigate the role of foot anatomy and sensorimotor control of posture, we quantified the deformation of the foot arch, as well as studying the effects of local perturbations applied to the toes (TOE) or 1(st)/2(nd) metatarsals (MT) while standing. In sitting position, loading and lifting a 10kg weight on the knee respectively lowered and raised the foot arch between 1-1.5mm. Less than 50% of this change could be accounted for by plantar surface skin compression. During quiet standing, the foot arch probe and shin sway revealed a significant correlation, which shows that as the tibia tilts forward the foot arch flattens and vice versa. During TOE and MT perturbations (a 2-6mm upward shift of an appropriate part of the foot at 2.5mm/s), EMG measures of the tibialis anterior and gastrocnemius revealed notable changes and the RMS variability of shin sway increased significantly, these increments being greater in the MT condition. The slow return of RMS to baseline level (>30s) suggested that a very small perturbation changes the surface reference frame which then takes time to reestablish. These findings show that rather than serving as a rigid base of support, the foot is compliant, in an active state, and sensitive to minute deformations. In conclusion, the architecture and physiology of the foot appear to contribute to the task of bipedal postural control with great sensitivity.
