Frequency-domain patterns in foot-force line-of-action: an emergent property of standing balance control.

A recent line of work suggests that the net behavior of the foot-ground interaction force provides insight into quiet-standing-balance dynamics and control. Through human-subject experiments, Boehm et al. found that the relative variations of the center of pressure and force orientation emerge as a distinct pattern in the frequency domain, termed the "intersection-point (IP) height.

Human foot force suggests different balance control between younger and older adults.

Aging can cause the decline of balance ability, which can lead to increased falls and decreased mobility. This work aimed to discern differences in balance control between healthy older and younger adults. Foot force data of 38 older and 65 younger participants (older and younger than 60 yr, respectively) were analyzed.

Reliability and validity of the force intersection point in the assessment of human quiet standing balance.

Background: This study evaluated psychometric properties of the Intersection Point Height, derived from ground-on-feet force characteristics, as a tool for assessing balance control. We compare this metric with traditional center of pressure (CP) measurements.

Methods: Data from a public dataset of 146 participants, divided into younger (<60 years old) and older (≥60 years old) adults, were analyzed.

Frequency-dependent behavior of paretic and non-paretic leg force during standing post stroke.

Maintaining upright posture in quiet standing is an important skill that is often disrupted by stroke. Despite extensive study of human standing, current understanding is incomplete regarding the muscle coordination strategies that produce the ground-on-foot force (F) that regulates translational and rotational accelerations of the body. Even less is understood about how stroke disrupts that coordination.

Modulation of sagittal-plane center of pressure and force vector direction in human standing on sloped surfaces.

The multi-joint coordination responsible for maintaining upright posture in the standing human manifests in the pattern of variation of the support-surface force (F). Assessment of both the translational and rotational kinematics in the sagittal-plane requires understanding the critical relationship between the direction and location of F. Prior work demonstrated that band-pass filtered F direction and center-of-pressure (CoP) covary in time such that the F vector lines-of-action pass near a fixed point called an intersection point (IP).

The Utility of the 2-Minute Walk Test as a Measure of Mobility in People With Lower Limb Amputation.

Objectives: To establish reference values for the 2-minute walk test (2-MWT) distance and gait speed in people with a lower limb amputation (LLA) who are prosthetic ambulators. Also, to describe the differences in distance and gait speed between sexes, causes of amputation, levels of amputation, health risk classification, functional levels, and age groups.

Design: Cross-sectional study.

Biomechanics of Vertical Posture and Control with Referent Joint Configurations.

Our study compared the results of two methods of analysis of postural sway during human quiet standing, the rambling-trembling (-) decomposition and the analysis of the point of intersection of the ground reaction forces ( analysis). Young, healthy subjects were required to stand naturally and with an increased level of leg/trunk muscle co-activation under visual feedback on the magnitude of a combined index of muscle activation (muscle mode). The main findings included the shift of toward higher frequencies and strong correlations between and when the subjects stood with increased muscle co-activation.

Development of KIINCE: A kinetic feedback-based robotic environment for study of neuromuscular coordination and rehabilitation of human standing and walking.

Introduction: The objective of this article is to introduce the robotic platform KIINCE and its emphasis on the potential of kinetic objectives for studying and training human walking and standing. The device is motivated by the need to characterize and train lower limb muscle coordination to address balance deficits in impaired walking and standing.

Methods: The device measures the forces between the user and his or her environment, particularly the force of the ground on the feet () that reflects lower limb joint torque coordination.

Frequency-dependent contributions of sagittal-plane foot force to upright human standing.

Quiet standing is a mechanically unstable postural objective that humans typically perform with ease. Control of upright posture requires stabilization of both translational and rotational degrees-of-freedom that is accomplished by neuro-muscular coordination. This coordination produces a force at the ground-foot interface (F) that is quantified by magnitude, direction (θ), and point of application (center-of-pressure, CP).

Standing Balance on Unsteady Surfaces in Children on the Autism Spectrum: The Effects of IQ.

Background: Postural stability difficulties are commonly reported in people on the autism spectrum. However, it is unclear whether unsteady surfaces may exacerbate postural stability difficulties in children and adolescents with autism spectrum disorder (ASD). Understanding balance on unsteady surfaces is important because uneven surfaces are commonly encountered in daily life.

Post-Stroke Walking Behaviors Consistent with Altered Ground Reaction Force Direction Control Advise New Approaches to Research and Therapy.

Recovery of walking after stroke requires an understanding of how motor control deficits lead to gait impairment. Traditional therapy focuses on removing specific observable gait behaviors that deviate from unimpaired walking; however, those behaviors may be effective compensations for underlying problematic motor control deficits rather than direct effects of the stroke. Neurological deficits caused by stroke are not well understood, and thus, efficient interventions for gait rehabilitation likely remain unrealized.

Ankle torque control that shifts the center of pressure from heel to toe contributes non-zero sagittal plane angular momentum during human walking.

A principle objective of human walking is controlling angular motion of the body as a whole to remain upright. The force of the ground on each foot (F) reflects that control, and recent studies show that in the sagittal plane F exhibits a specific coordination between F direction and center-of-pressure (CP) that is conducive to remaining upright. Typical walking involves the CP shifting relative to the body due to two factors: posterior motion of the foot with respect to the hip (stepping) and motion of the CP relative to the foot (foot roll-over).

Mechanical interaction of center of pressure and force direction in the upright human.

Humans maintain upright bipedal posture by producing appropriate force against the environment through the interaction of neural controlled muscle force with the mechanics of the skeletal system. Characterizing these mechanics facilitates understanding of the neural control. We used a mechanical model of an upright human to analyze how the mechanical linkage aspects of the human body affect the force between the feet and the ground (F).

Force direction pattern stabilizes sagittal plane mechanics of human walking.

The neural control and mechanics of human bipedalism are inadequately understood. The variable at the interface of neural control and body mechanics that is key to upright posture during human walking is the force of the ground on the foot (ground reaction force, F). We present a model that predicts sagittal plane F direction as passing through a divergent point (DP) fixed in a reference frame attached to the person.

Task-dependent organization of pinch grip forces.

The organization of thumb and index finger forces in a pinch formation was investigated under conditions where kinetic constraints on interdigit force coupling were removed. Two visually guided isometric force tasks at submaximal levels were used to characterize the spatial and temporal aspects of interdigit force coupling. Task 1 provided an initial characterization of interdigit force coordination when the force relationship between the digits was not specified.

Afferent contributions to digit force coupling and force level variation during performance of non-lift pinch.

Afferent contributions to the coordination of thumb and index finger forces during non-lift pinch were studied using an anesthetization case study design. Two subjects, one performing with and without digital anesthetization and one with intact sensation, produced dynamic pinch forces against a stable object, with and without visual feedback. Error corrections were less frequent post-anesthetization, and the cross correlation between digit forces was lower when sensation was removed.

Direction of foot force for pushes against a fixed pedal: variation with pedal position.

The force that healthy humans generated against a fixed pedal was measured and compared with that predicted by four models. The participants (n = 11) were seated on a stationary bicycle and performed brief pushing efforts against an instrumented pedal with the crank fixed. Pushes were performed to 10 force magnitude targets and at 12 crank angles.

Foot force direction control during leg pushes against fixed and moving pedals in persons post-stroke.

The component of foot force generated by muscle action (F(m)) during pedaling in healthy humans has a nearly constant direction with increasing force magnitude. The present study investigated the effect of stroke on the control of foot force. Ten individuals with hemiparesis secondary to a cerebral vascular accident performed pushing efforts against translationally fixed and moving pedals on a custom stationary cycle ergometer.

Direction of foot force for pushes against a fixed pedal: role of effort level.

Control of the force exerted by the foot on the ground is critical to human locomotion. During running on a treadmill and pushing against a fixed pedal, humans increased foot force in a linear manner in sagittal plane force space. However, for pushes against a moving pedal, force output was linear for some participants but slightly curved for others.

Foot force direction in an isometric pushing task: prediction by kinematic and musculoskeletal models.

The abilities of a kinematic model and a muscle model of the human lower limb to predict the stereotyped direction of the muscular component of foot force produced by seated subjects in a static task were tested and compared. Human subjects ( n=11) performed a quasi-static, lower-limb pushing task against an instrumented bicycle pedal, free to rotate about its own axis, but with the crank fixed. Each pushing trial consisted of applying a force from the resting level to a force magnitude target with the right foot.

The control of foot force during pushing efforts against a moving pedal.

The muscle component of the force applied to a bicycle pedal (foot force) by seated humans provided insight into the organization of the motor system. Healthy adults ( n=11) pedaled a stationary cycle ergometer while attempting to match peak foot force magnitude to visually presented force targets (200, 250,., 650 N).

Characteristics of the force applied to a pedal during human pushing efforts: emergent linearity.

The force seated humans exert on a translationally fixed pedal (foot force) may be directed at any angle because the fixed distance between the seat and the pedal axis kinematically constrains the lower limb. The authors' objective in the present work was to characterize such force. Participants (N = 7) generated force with their lower limb by pushing against the pedal in the most comfortable manner.

Circulatory responses to voluntary and electrically induced muscle contractions in humans.

Background And Purpose: Transcutaneous electrical nerve stimulation (TENS) increases regional blood flow when applied at intensities sufficient to cause skeletal muscle contraction. It is not known whether increases in blood flow elicited by TENS differ from those caused by voluntary muscle contraction. The purpose of this study, therefore, was to compare the hemodynamic effects of these 2 types of muscle contraction.

Canine sternal force-displacement relationship during cardiopulmonary resuscitation.

A viscoelastic model developed to model human sternal response to the cyclic loading of manual cardiopulmonary resuscitation (CPR) [8] was used to evaluate the properties of canine chests during CPR. Sternal compressions with ventilations after every fifth compression were applied to supine canines (n = 7) with a mechanical resuscitation device. The compressions were applied at a nominal rate of 90/min with a peak force near 400 N.