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The translating platform paradigm is widely used to investigate the regulation of upright standing and locomotion. This study investigated how the displacement waveform characteristics underlying the translating platform perturbation are revealed in the resulting postural response. Eight participants experienced a series of backward-directed perturbations using a hydraulically driven forceplate. Two ranges of platform displacement (5 and 15 cm) in combination with two peak velocities (40 and 60 cm/s) were achieved using three distinct waveforms for platform displacement: (a) RAMP: ramp onset and ramp offset, (b) Ramp-to-Parabola (R-P): ramp onset with parabolic offset and (c) SINE: sine-wave onset with sine wave offset. Our findings indicated that the unique and distinctive acceleration and deceleration characteristics that result from the three different platform displacement waveforms significantly altered the postural response to the perturbation.

Developmental changes in the kinematics and kinetics underlying balance control were studied in 61 children, 9 months to 10 years of age. The children were classified according to developmental milestones as standers; new, intermediate, and advanced walkers; runners-jumpers; hoppers; gallopers; and skippers. The children experienced support-surface translations of varying size and speed. Children with greater locomotor experience withstood larger balance threats without collapsing or stepping. Analyses of scaled trials (perturbations normalized in size to foot length and center of gravity height) revealed that improvement in balance was not related to initial configuration parameters surrounding the task (degree of crouch or lean). Children with advanced locomotor skills had faster recovery times and relatively larger muscle torques than children with less experience. Relative torque-time histories of the more experienced children began to match the adult response to similar perturbations. With increased experience and changing muscle torque regulatory abilities, balance skills became more robust.

The common platform translation paradigm used in balance control studies employs a disturbance event that applies non-muscular forces to the body for the duration of the disturbance. Previous research has explored the process of constructing the balance recovery by considering these perturbations to be trigger events, not events with an ongoing force application timeline. The purpose of this study was to quantify the effect of muscular and non-muscular torques on post-perturbation balance with particular interest in the role of the external perturbation in balance recovery. Five young adult males experienced backward translations of the support surface at three different speeds. Integration intervals were defined for each segment and angular impulses were calculated for a period of increasing angular momentum (destabilization), and a period of decreasing angular momentum (restabilization). Destabilization of distal segments was primarily due to impulse generated by the motion of the support surface. For the trunk, however, muscle and motion-dependent sources contributed most to increasing momentum. Restabilization of distal segments was achieved by muscle and platform impulses while trunk restabilization was achieved by muscle and motion-dependent terms in opposition to gravity. Increased platform speed resulted in increased muscular contribution only in the control of the trunk, while demand on distal musculature decreased with change in platform speed as the platform contribution to restabilization increased in these segments. Therefore, impulses from non-muscular sources, including the perturbation itself, are significant modifiers of the response to balance disturbances and must be accounted for in balance research.

This research was directed toward predicting postural equilibrium configurations in normal humans for asymmetric locations of the feet. The objective of the study was to identify trends in the variation of the location of ground center of pressure (COP) with increasing levels of asymmetry in the foot placement. The procedure developed here minimized the muscular effort (active torques) in the lower extremities while maximizing postural stability margins for given foot locations. Minimizing muscular effort led to fully extended knees, and maximal stability margin led to the COP moving toward the rear foot in asymmetric stance. A combined analytical-numerical optimization scheme was used to avoid singularities that can arise due to the fact that at equilibrium postural configurations, the torso lies at or near the workspace boundary of the lower extremities. Experiments were conducted and the results obtained were in keeping with the model predictions. This basic understanding of asymmetric stance is important for studying asymmetric postural mechanics in the presence of external disturbances, and for extending the results from normal subjects to humans at both ends of the life span.

Background: One of the key components of postural control is the motor system's ability to produce appropriate torques to counteract perturbations that may lead to a loss of balance. Evidence exists to show that there is an age-related decline in absolute strength and in the ability to rapidly produce torque. The relationship between age-related decreases in these voluntary torque production capabilities and the ability to rapidly produce torques in a reactive balance task has not been studied. Thus, the purpose of this study was to examine the magnitude and rate of torque production in younger and older adults under reactive balance conditions., Methods: Older (OA) and younger (YA) adults received forward and backward support surface translations of varying amplitudes and velocities. Maximum ankle muscle torque (maxMa) and rate of change of ankle muscle torque (Ma) following a perturbation were calculated., Results: Two balance responses emerged: a no-step and a step response. With increasing perturbation difficulty, YA and OA used different responses. The no-step and step responses were examined for age-group differences in the force characteristics. No significant age-group differences were found for maxMa or rate of change of Ma within either no-step or step responses., Conclusion: The results of this study suggest that neither the magnitude nor rate of ankle muscle torque production, as produced during the initial balance response in this set of reactive balance control tasks, determines the different balance responses seen in younger versus older adults.

Background: This study tested balance behavior of young adults and aging adults with and without balance problems in response to visual flow from a moving visual surround., Methods: Balance behavior was indexed by force plate measures of maximum anterior/posterior displacement of the center of foot pressure and horizontal shear forces. The sample included normal young adults (n = 13; mean age 23 years, +/- 7.5), normal aging adults (n = 13; mean age 76 years, +/- 6.5), and aging adults with balance problems not directly attributable to a diagnosable neurological disease or dysfunction (n = 13; mean age 79 years, +/- 5.8)., Results: The balance-affected aging group had statistically greater sway responses than the young group when the stimulus was unexpected (as in the first trial; p < .05). Some individuals in each group had large responses that were statistical outliers from the group median. The balance-affected group had significantly greater shear forces than the young group., Conclusions: Greater sway responses suggest over-reliance on visual cues for posture control in the balance-affected aging group, which may be related to underlying, borderline somatosensory deficits, as indicated by the patterns of subclinical indications for somatosensory impairments on neurological exams in this group. Visually sensitive postural control, however, may issue from several different underlying processes. Elevated shear forces during balance responses in the balance-affected group suggest a greater use of hip movements in addition to ankle movements for postural adjustments.