Measures of postural steadiness are used to characterize the dynamics of the postural control system associated with maintaining balance during quiet standing. The objective of this study was to evaluate the relative sensitivity of center-of-pressure (COP)-based measures to changes in postural steadiness related to age. A variety of time and frequency domain measures of postural steadiness were compared between a group of twenty healthy young adults (21-35 years) and a group of twenty healthy elderly adults (66-70 years) under both eyes-open and eyes-closed conditions. The measures that identified differences between the eyes-open and eyes-closed conditions in the young adult group were different than those that identified differences between the eye conditions in the elderly adult group. Mean velocity of the COP was the only measure that identified age-related changes in both eye conditions, and differences between eye conditions in both groups. The results of this study will be useful to researchers and clinicians using COP-based measures to evaluate postural steadiness.

We applied functional magnetic resonance imaging (FMRI) to map the somatotopic organization of the primary motor cortex using voluntary movements of the hand, arm, and foot. Eight right-handed healthy subjects performed self-paced, repetitive, flexion/extension movements of the limbs while undergoing echo-planar imaging. Four subjects performed movements of the right fingers and toes, while the remaining subjects performed movements of the right fingers and elbow joint. There was statistically significant functional activity in the left primary motor cortex in all subjects. The pattern of functional activity followed a topographic representation: finger movements resulted in signal intensity changes over the convexity of the left motor cortex, whereas toe movements produced changes either at the interhemispheric fissure or on the dorsolateral surface adjacent to the interhemispheric fissure. Elbow movements overlapped the more medial signal intensity changes observed with finger movements. Functionally active regions were confined to the cortical ribbon and followed the gyral anatomy closely. These findings indicate that FMRI is capable of generating somatotopic maps of the primary motor cortex in individual subjects.

No abstract

The identification and characterization of age-related changes in postural steadiness will enhance our understanding of the postural control system, and may help to identify persons at risk for falls in the elderly population. This review includes a discussion of the methods that have been used to evaluate the static (postural steadiness) and dynamic (postural stability) performance of the postural control system. Time and frequency domain measures of postural steadiness are described. Research investigations of age-related changes in the postural control system, with an emphasis on postural steadiness evaluations, are discussed. Control systems and biomechanical models of the postural control system are described. Finally, the evaluation of bilateral asymmetries in postural sway and weight distribution, with a dual force plate balance platform, is briefly discussed. I. INTRODUCTION0 maintain standing balance, the postural control system T integrates information from the visual, vestibular, and proprioceptive systems. If one or more of these systems is impaired as part of the aging process, or in neurologic disease, then the postural control system must adjust the relative weighting factors of the inputs to maintain balance. Several studies have investigated the relative roles of the visual, vestibular, and proprioceptive systems in maintaining balance [12], [23], [59], [73], [95], [97]. Postural control is often discussed in terms of control systems theory [53],[HI, [137]. Johansson [53] reviewed topics related to human postural control, including biomechanics, neurophysiology, postural stability and steadiness, and postural control models.The performance of the postural control system is generally evaluated with measures of postural sway. As Maki summarized [72], postural sway has been characterized by the motion of body segments or joints, joint moments, EMG activity, and displacement of the center-of-pressure (COP) at the feet.