Human Postural Control.

From ancient Greece to nowadays, research on posture control was guided and shaped by many concepts. Equilibrium control is often considered part of postural control. However, two different levels have become increasingly apparent in the postural control system, one level sets a distribution of tonic muscle activity ("posture") and the other is assigned to compensate for internal or external perturbations ("equilibrium").

Tonic and Rhythmic Spinal Activity Underlying Locomotion.

In recent years, many researches put significant efforts into understanding and assessing the functional state of the spinal locomotor circuits in humans. Various techniques have been developed to stimulate the spinal cord circuitries, which may include both diffuse and quite specific tuning effects. Overall, the findings indicate that tonic and rhythmic spinal activity control are not separate phenomena but are closely integrated to properly initiate and sustain stepping.

Tapping into rhythm generation circuitry in humans during simulated weightlessness conditions.

An ability to produce rhythmic activity is ubiquitous for locomotor pattern generation and modulation. The role that the rhythmogenesis capacity of the spinal cord plays in injured populations has become an area of interest and systematic investigation among researchers in recent years, despite its importance being long recognized by neurophysiologists and clinicians. Given that each individual interneuron, as a rule, receives a broad convergence of various supraspinal and sensory inputs and may contribute to a vast repertoire of motor actions, the importance of assessing the functional state of the spinal locomotor circuits becomes increasingly evident.

Lighten Up: Specific Postural Instructions Affect Axial Rigidity and Step Initiation in Patients With Parkinson's Disease.

Background: Parkinson's disease (PD) is associated with stooped postural alignment, increased postural sway, and reduced mobility. The Alexander Technique (AT) is a mindfulness-based approach to improving posture and mobility by reducing muscular interference while maintaining upward intentions. Evidence suggests that AT can reduce disability associated with PD, but a mechanism for this effect has not yet been established.

Light and heavy touch reduces postural sway and modifies axial tone in Parkinson's disease.

Background: Light touch with a stable object reduces postural sway by increasing axial postural tone in healthy subjects. However, it is unknown whether subjects with Parkinson's disease (PD), who have more postural sway and higher axial postural tone than healthy subjects, can benefit from haptic touch.

Objective: To investigate the effect of light and heavy touch on postural stability and hip tone in subjects with PD.

Method to measure tone of axial and proximal muscle.

The control of tonic muscular activity remains poorly understood. While abnormal tone is commonly assessed clinically by measuring the passive resistance of relaxed limbs, no systems are available to study tonic muscle control in a natural, active state of antigravity support. We have developed a device (Twister) to study tonic regulation of axial and proximal muscles during active postural maintenance (i.

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.

Contributions of skin and muscle afferent input to movement sense in the human hand.

In the stationary hand, static joint-position sense originates from multimodal somatosensory input (e.g., joint, skin, and muscle).

Progression of forearm intravenous regional anesthesia with ropivacaine.

The progression of sensory blockade in the hand following a forearm Bier block with ropivacaine is currently unknown. The hands of 10 healthy adult human subjects were anesthetized with ropivacaine, and their sensitivities to cold and touch were tested until the completion of anesthesia. On average, insensitivity to cold occurred uniformly throughout the hand within 9 mins; however, touch sensation was not complete until approximately 20 mins after injection.

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.

Parkinson's disease shows perceptuomotor asymmetry unrelated to motor symptoms.

Evidence of neglect symptoms in Parkinson's disease (PD) have been reported during visuoperceptual tasks and linked to side of disease onset. The goal of this study was to determine if in PD perceptual asymmetry is also evident in perceptuomotor tasks without visual input. The task was to point to a remembered straight-ahead (SA) target in peripersonal space.

Postural muscle tone in the body axis of healthy humans.

Across the entire human body, postural tone might play its most critical role in the body's axis because the axis joins the four limbs and head into a single functioning unit during complex motor tasks as well as in static postures. Although postural tone is commonly viewed as low-level, tonic motor activity, we hypothesized that postural tone is both tonically and dynamically regulated in the human axis even during quiet stance. Our results describe the vertical distribution of postural muscle tone in the neck, trunk, and hips of standing human adults.

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.

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.

Position sensitivity of human muscle spindles: single afferent and population representations.

The representation of joint position at rest and during movement was investigated in 44 muscle spindle primary afferents originating from the extensor carpi radialis brevis (ECRb) and extensor digitorum (ED) of normal human subjects. Position sensitivity was estimated for each afferent, and 43 of 44 were position sensitive. In each trial, six sequential ramp-and-hold movements (2-6 degrees, 2 degrees/s, total 24 degrees) flexed the relaxed wrist, beginning from the angle at which the afferent was just recruited.