Ankle Muscle Stiffness Alone Cannot Stabilize Balance During Quiet Standing

2002 ◽  
Vol 88 (4) ◽  
pp. 2157-2162 ◽  
Author(s):  
Pietro G. Morasso ◽  
Vittorio Sanguineti
Keyword(s):  
Normal Subjects ◽  
Realistic Model ◽  
Muscle Stiffness ◽  
The Body ◽  
Quiet Standing ◽  
Control Input ◽  
Mechanical Instability ◽  
Ankle Muscles ◽  
Ankle Muscle ◽  
Restoring Forces

This communication addresses again the hypothesis that the stabilization of balance during quiet standing is achieved by the stiffness of ankle muscles without anticipatory active control. It is shown that a recently proposed method of estimating ankle stiffness directly from the analysis of the posturographic data is incorrect because it ignores the modulation of motoneuronal activity and grossly overestimates the real range of values in relation with the critical value of stiffness. Moreover, a new simulation study with a realistic model of ankle muscles demonstrates the mechanical instability of the system when there is no anticipatory control input. However, the simulations also suggest that in normal subjects the active stiffness mechanisms of stabilization have similar weights in determining the restoring forces that are necessary for preventing the body from falling.

scholarly journals Can Muscle Stiffness Alone Stabilize Upright Standing?

1999 ◽  
Vol 82 (3) ◽  
pp. 1622-1626 ◽  
Author(s):  
Pietro G. Morasso ◽  
Marco Schieppati
Keyword(s):  
Center Of Pressure ◽  
Center Of Mass ◽  
Muscle Stiffness ◽  
The Body ◽  
Ankle Muscles ◽  
Upright Standing ◽  
Stiffness Control ◽  
Control Patterns ◽  
Physiological Values

A stiffness control model for the stabilization of sway has been proposed recently. This paper discusses two inadequacies of the model: modeling and empiric consistency. First, we show that the in-phase relation between the trajectories of the center of pressure and the center of mass is determined by physics, not by control patterns. Second, we show that physiological values of stiffness of the ankle muscles are insufficient to stabilize the body “inverted pendulum.” The evidence of active mechanisms of sway stabilization is reviewed, pointing out the potentially crucial role of foot skin and muscle receptors.

Ankle Muscle Stiffness in the Control of Balance During Quiet Standing

2001 ◽  
Vol 85 (6) ◽  
pp. 2630-2633 ◽  
Author(s):  
David A. Winter ◽  
Aftab E. Patla ◽  
Shirley Rietdyk ◽  
Milad G. Ishac
Keyword(s):  
Linear Regression ◽  
Muscle Stiffness ◽  
Quiet Standing ◽  
New Technique ◽  
Ankle Moment ◽  
Ankle Stiffness ◽  
Ankle Muscle ◽  
Stiffness Control ◽  
A New Technique ◽  
Elastic Elements

This research presents new data and reanalyzed information to refute the criticisms of our model of stiffness control during quiet standing. A re-review of their references to biomechanical research on muscle ankle stiffness confirmed muscle stiffness estimates of the ankle series elastic elements that agreed closely with our estimates. A new technique is presented that directly estimates the muscle stiffness from the ankle moment (N · m) and sway angle (deg). The linear regression of 10 subjects standing quietly for 10 s estimated the stiffness (N · m/deg) to be safely above the gravitational spring. The R 2 scores for this linear regression averaged 0.92, confirming how closely the model approached a perfect spring that would have an R 2 = 1. These results confirm our model of a simple muscle stiffness control and refutes the criticisms.

scholarly journals Effects of vibration rolling on ankle range of motion and ankle muscle stiffness in stroke patients: a crossover study

2020 ◽  
Author(s):  
Se-Ju Park ◽  
So-In Lee ◽  
Ho-Jin Jeong ◽  
Byeong-Geun Kim
Keyword(s):  
Range Of Motion ◽  
Crossover Design ◽  
Ankle Dorsiflexion ◽  
Muscle Stiffness ◽  
Lateral Stiffness ◽  
Stroke Patients ◽  
Ankle Stiffness ◽  
Ankle Muscles ◽  
Significant Difference ◽  
Ankle Muscle

Abstract Background: Vibration stimulation has emerged as a treatment tool to aid spasticity during physical therapy. However, the benefits of vibration rolling (VR) on interventions for stroke patients are unclear. This study aimed to investigate the effect of VR intervention on the range of motion (ROM) and ankle stiffness in stroke patients. Methods: In this crossover design study, seven stroke patients completed two test sessions (one VR and one non-VR [NVR]) in a randomized order, with 48 h of rest between each session. Participants completed intervention and its measurements on the same day. The measurements included ankle dorsiflexion and plantarflexion ROM and stiffness of ankle muscles, including the tibialis anterior and gastrocnemius lateral and medial muscles. Results: After VR, ankle dorsiflexion ROM, gastrocnemius lateral stiffness, and gastrocnemius medial stiffness improved significantly (all P < 0.05). After NVR, only gastrocnemius lateral stiffness improved significantly (P < 0.05). Furthermore, compared with the change values for ankle dorsiflexion ROM and gastrocnemius lateral stiffness, VR showed a more significant difference than NVR (P < 0.05).Conclusions: VR improved ankle ROM and muscle stiffness. Therefore, we suggest that practitioners should consider VR as an intervention to increase dorsiflexion ROM and gastrocnemius stiffness in stroke patients.

Active head movements facilitate compensation for effects of prism displacement on dynamic gait12

2006 ◽  
Vol 16 (1-2) ◽  
pp. 29-33
Author(s):  
Kim R. Gottshall ◽  
Michael E. Hoffer ◽  
Helen S. Cohen ◽  
Robert J. Moore
Keyword(s):  
Head Movement ◽  
Sensory Modality ◽  
Normal Subjects ◽  
The Body ◽  
Head Movements ◽  
Head Motion ◽  
Control Group ◽  
Entire Body ◽  
Group 3 ◽  
Group 2

Study design: Four groups, between-subjects study. Objectives: To investigate the effects of exercise on adaptation of normal subjects who had been artificially spatially disoriented. Background: Many patients referred for rehabilitation experience sensory changes, due to age or disease processes, and these changes affect motor skill. The best way to train patients to adapt to these changes and to improve their sensorimotor skills is unclear. Using normal subjects, we tested the hypothesis that active, planned head movement is needed to adapt to modified visual input. Methods and measures: Eighty male and female subjects who had normal balance on computerized dynamic posturography (CDP) and the dynamic gait index (DGI), were randomly assigned to four groups. All groups donned diagonally shift lenses and were again assessed with CDP and DGI. The four groups were then treated for 20 min. Group 1 (control group) viewed a video, Group 2 performed exercise that involved translating the entire body through space, but without separate, volitional head movement, Group 3 performed exercises which all incorporated volitional, planned head rotations, and Group 4 performed exercises that involved translating the body (as in Group 2) and incorporated volitional, planned head motion (as in Group 3). All subjects were post-tested with CDP and DGI, lenses were removed, and subjects were retested again with CDP and DGI. Results: The groups did not differ significantly on CDP scores but Groups 3 and 4 had significantly better DGI scores than Groups 1 and 2. Conclusions: Active head movement that is specifically planned as part of the exercise is more effective than passive attention or head movements that are not consciously planned, for adapting to sensorimotor change when it incorporates active use of the changed sensory modality, in this case head motion.

COMPARISON OF CARDIAC MAGNETIC FIELD DISTRIBUTIONS DURING DEPOLARIZATION AND REPOLARIZATION

2003 ◽  
Vol 13 (12) ◽  
pp. 3783-3789 ◽  
Author(s):  
F. E. SMITH ◽  
P. LANGLEY ◽  
L. TRAHMS ◽  
U. STEINHOFF ◽  
J. P. BOURKE ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Field Distribution ◽  
Normal Subjects ◽  
The Body ◽  
Magnetic Field Distribution ◽  
T Wave ◽  
High Magnetic Field Strength ◽  
The Magnetic Field

Multichannel magnetocardiography measures the magnetic field distribution of the human heart noninvasively from many sites over the body surface. Multichannel magnetocardiogram (MCG) analysis enables regional temporal differences in the distribution of cardiac magnetic field strength during depolarization and repolarization to be identified, allowing estimation of the global and local inhomogeneity of the cardiac activation process. The aim of this study was to compare the spatial distribution of cardiac magnetic field strength during ventricular depolarization and repolarization in both normal subjects and patients with cardiac abnormalities, obtaining amplitude measurements by magnetocardiography. MCGs were recorded at 49 sites over the heart from three normal subjects and two patients with inverted T-wave conditions. The magnetic field intensity during depolarization and repolarization was measured automatically for each channel and displayed spatially as contour maps. A Pearson correlation was used to determine the spatial relationship between the variables. For normal subjects, magnetic field strength maps during depolarization (R-wave) showed two asymmetric regions of magnetic field strength with a high positive value in the lower half of the chest and a high negative value above this. The regions of high R-wave amplitude corresponded spatially to concentrated asymmetric regions of high magnetic field strength during repolarization (T-wave). Pearson-r correlation coefficients of 0.7 (p<0.01), 0.8 (p<0.01) and 0.9 (p<0.01) were obtained from this analysis for the three normal subjects. A negative correlation coefficient of -0.7 (p<0.01) was obtained for one of the subjects with inverted T-wave abnormalities, suggesting similar but inverted magnetic field and current distributions to normal subjects. Even with the high correlation values in these four subjects, the MCG was able to identify differences in the distribution of magnetic field strength, with a shift in the T-wave relative to the R-wave. The measurement of cardiac magnetic field distribution during depolarization and repolarization of normal subjects and patients with clinical abnormalities should enable the improvement of theoretical models for the explanation of the cardiac depolarization and repolarization processes.

scholarly journals Men and women do not have the same relation between body composition and postural sway

2015 ◽  
Vol 32 (02) ◽  
pp. 093-097 ◽  
Author(s):  
A. Alonso ◽  
L. Mochizuki ◽  
N. Luna ◽  
A. Canonica ◽  
R. Souza ◽  
...  
Keyword(s):  
Body Composition ◽  
Body Mass ◽  
Bone Mineral ◽  
Postural Sway ◽  
Multiple Linear Regression Model ◽  
The Body ◽  
Lower Limbs ◽  
Quiet Standing ◽  
Mineral Density ◽  
Men And Women

Abstract Introduction: The aim of the present study was to evaluate the influence of body composition on the postural sway during quiet standing. Our hypothesis is that men and women do not have the same relation between body composition and postural sway during quiet standing. Materials and Methods: Participated in the study 50 men and 50 women; age range: 20-40 years old. The main outcome measures were: Body composition (bone densitometry), percentage of fat (% fat) tissue (g), fat (g), lean mass (g), bone mineral content (g) and bone mineral density (g/cm2); Anthropometry: body mass (kg), height (cm), length of the trunk-head (cm), length of lower limbs (cm). The following indices were calculated: body mass index (BMI) (kg/m2) and Postural balance test - center ofpressure displacement. Results: The correlation analysis showed low correlations between postural sway and anthropometric variables. The multiple linear regression model showed that the body composition and the anthropometry were able to explain only men's postural sway. Conclusion: The postural sway is sex type dependent. Men and women have different relations between body composition and postural sway. Only male's body composition affected the body sway.

Kinetic analysis of zinc metabolism and its regulation in normal humans

1986 ◽  
Vol 251 (2) ◽  
pp. R398-R408 ◽  
Author(s):  
M. E. Wastney ◽  
R. L. Aamodt ◽  
W. F. Rumble ◽  
R. I. Henkin
Keyword(s):  
Compartmental Model ◽  
Additional Data ◽  
Normal Subjects ◽  
The Body ◽  
Whole Body ◽  
Zinc Metabolism ◽  
Zinc Intake ◽  
Normal Humans ◽  
Taste And Smell ◽  
Oral Supplement

Zinc metabolism was studied in 32 normal volunteers after oral (n = 25) or intravenous (n = 7) administration of 65Zn. Data were collected from the blood, urine, feces, whole body, and over the liver and thigh regions for 9 mo while the subjects consumed their regular diets (containing 10 mg Zn ion/day) and for an additional 9 mo while the subjects received an exogenous oral supplement of 100 mg Zn ion/day. Data from each subject were fitted by a compartmental model for zinc metabolism that was developed previously for patients with taste and smell dysfunction. These data from normal subjects were used to determine the absorption, distribution, and excretion of zinc and the mass of zinc in erythrocytes, liver, thigh, and whole body. By use of additional data obtained from the present study, the model was refined further such that a large compartment, which was previously determined to contain 90% of the body zinc, was subdivided into two compartments to represent zinc in muscle and bone. When oral zinc intake was increased 11-fold three new sites of regulation of zinc metabolism were identified in addition to the two sites previously defined in patients with taste and smell dysfunction (absorption of zinc from gut and excretion of zinc in urine). The three new sites are exchange of zinc with erythrocytes, release of zinc by muscle, and secretion of zinc into gut. Regulation at these five sites appears to maintain some tissue concentrations of zinc when dietary zinc increases.

A Nonlinear Optimal Control Approach for the Vertical Take-off and Landing Aircraft

2021 ◽  
pp. 2150012
Author(s):  
G. Rigatos
Keyword(s):  
Optimal Control ◽  
Control Method ◽  
Nonlinear Optimal Control ◽  
The Body ◽  
Algebraic Riccati Equation ◽  
Control Input ◽  
Time Step ◽  
Control Approach ◽  
Vtol Aircraft ◽  
Optimal Control Approach

The paper proposes a nonlinear optimal control approach for the model of the vertical take-off and landing (VTOL) aircraft. This aerial drone receives as control input a directed thrust, as well as forces acting on its wing tips. The latter forces are not perpendicular to the body axis of the drone but are tilted by a small angle. The dynamic model of the VTOL undergoes approximate linearization with the use of Taylor series expansion around a temporary operating point which is recomputed at each iteration of the control method. For the approximately linearized model, an H-infinity feedback controller is designed. The linearization procedure relies on the computation of the Jacobian matrices of the state-space model of the VTOL aircraft. The proposed control method stands for the solution of the optimal control problem for the nonlinear and multivariable dynamics of the aerial drone, under model uncertainties and external perturbations. For the computation of the controller’s feedback gains, an algebraic Riccati equation is solved at each time-step of the control method. The new nonlinear optimal control approach achieves fast and accurate tracking for all state variables of the VTOL aircraft, under moderate variations of the control inputs. The stability properties of the control scheme are proven through Lyapunov analysis.

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