Stability as a constraint in sagittal plane human force exertion modeling

The stability constraints of a two-dimensional static human force exertion capability model (2DHFEC) were evaluated with subjects of varying anthropometry and strength capabilities performing manual exertions. The biomechanical model comprehensively estimated human force exertion capability under sagittally symmetric static conditions using constraints from three classes: stability, joint muscle strength, and coefficient of friction. Experimental results showed the concept of stability must be considered with joint muscle strength capability and coefficient of friction in predicting hand force exertion capability. Information was gained concerning foot modeling parameters as they affect whole-body stability. Findings indicated that stability limits should be placed approximately 37 % the ankle joint center to the posterior-most point of the foot and 130 % the distance from the ankle joint center to the maximal medial protuberance (the ball of the foot). 2DHFEC provided improvements over existing models, especially where horizontal push/pull forces create balance concerns.

Download Full-text

Effects of human stature and muscle strength on the standing strategies: A computational biomechanical study

Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine ◽

10.1177/0954411920914859 ◽

2020 ◽

Vol 234 (7) ◽

pp. 674-685

Author(s):

Mohammed N Ashtiani ◽

Mahmood-Reza Azghani ◽

Mohamad Parnianpour ◽

Kinda Khalaf

Keyword(s):

Muscle Strength ◽

Knee Flexion ◽

Inverse Dynamics ◽

Biomechanical Model ◽

Biomechanical Study ◽

The Body ◽

Whole Body ◽

Tall Stature ◽

Personal Factors ◽

Hamstring Muscles

It has been hypothesized that the muscular efforts exerted during standing may be altered by changes in personal factors, such as the body stature and muscular strength. The goal of this work was to assess the contribution of leg muscles using a biomechanical model in different physical conditions and various initial postures. An optimized inverse dynamics model was employed to find the maximum muscular effort in 23,040 postures. The simulation results showed that mid-range knee flexion could help the healthy and strong individuals maintain balance, but those with weaker muscle strength required more knee flexion. Individuals of weak muscular constitution as well as those with tall stature are at the highest risk of imbalance/falling. The number of imbalanced postures due to deficits in the calf and hamstring muscles was reduced by 7.5 times by strengthening the whole body musculature. The calf and the hamstring muscles play a key role in balance regardless of stature.

Download Full-text

Stability limits modulate whole-body motor learning

Journal of Neurophysiology ◽

10.1152/jn.00983.2010 ◽

2012 ◽

Vol 107 (7) ◽

pp. 1952-1961 ◽

Cited By ~ 13

Author(s):

Gregory C. Manista ◽

Alaa A. Ahmed

Keyword(s):

Postural Control ◽

Sagittal Plane ◽

Whole Body ◽

Robot Arm ◽

Anticipatory Control ◽

Upright Stance ◽

Anticipatory Postural Control ◽

Margin For Error ◽

Stability Limits ◽

Perturbation Direction

Our daily movements exert forces upon the environment and also upon our own bodies. To control for these forces, movements performed while standing are usually preceded by anticipatory postural adjustments (APAs). This strategy is effective at compensating for an expected perturbation, as it reduces the need to compensate for the perturbation in a reactive manner. However, it can also be risky if one anticipates the incorrect perturbation, which could result in movements outside stability limits and a loss of balance. Here, we examine whether the margin for error defined by these stability limits affects the amount of anticipation. Specifically, will one rely more on anticipation when the margin for error is lower? Will the degree of anticipation scale with the margin for error? We took advantage of the asymmetric stability limits (and margins for error) present in the sagittal plane during upright stance and investigated the effect of perturbation direction on the magnitude of APAs. We also compared anticipatory postural control with the anticipatory control observed at the arm. Standing subjects made reaching movements to multiple targets while grasping the handle of a robot arm. They experienced forward or backward perturbing forces depending on the target direction. Subjects learned to anticipate the forces and generated APAs. Although subjects had the biomechanical capacity to adapt similarly in the forward and backward directions, APAs were reduced significantly in the backward direction, which had smaller stability limits and a smaller margin for error. Interestingly, anticipatory control produced at the arm, where stability limits are not as relevant, was not affected by perturbation direction. These results suggest that stability limits modulate anticipatory control, and reduced stability limits lead to a reduction in anticipatory postural control.

Download Full-text

Using Biofeedback to Reduce Step Length Asymmetry Impairs Dynamic Balance in People Poststroke

Neurorehabilitation and Neural Repair ◽

10.1177/15459683211019346 ◽

2021 ◽

pp. 154596832110193

Author(s):

Sungwoo Park ◽

Chang Liu ◽

Natalia Sánchez ◽

Julie K. Tilson ◽

Sara J. Mulroy ◽

...

Keyword(s):

Angular Momentum ◽

Sagittal Plane ◽

Dynamic Balance ◽

Objective Measure ◽

Frontal Plane ◽

Step Length ◽

Berg Balance Scale ◽

Whole Body ◽

Functional Gait ◽

Full Body

Background People poststroke often walk with a spatiotemporally asymmetric gait, due in part to sensorimotor impairments in the paretic lower extremity. Although reducing asymmetry is a common objective of rehabilitation, the effects of improving symmetry on balance are yet to be determined. Objective We established the concurrent validity of whole-body angular momentum as a measure of balance, and we determined if reducing step length asymmetry would improve balance by decreasing whole-body angular momentum. Methods We performed clinical balance assessments and measured whole-body angular momentum during walking using a full-body marker set in a sample of 36 people with chronic stroke. We then used a biofeedback-based approach to modify step length asymmetry in a subset of 15 of these individuals who had marked asymmetry and we measured the resulting changes in whole-body angular momentum. Results When participants walked without biofeedback, whole-body angular momentum in the sagittal and frontal plane was negatively correlated with scores on the Berg Balance Scale and Functional Gait Assessment supporting the validity of whole-body angular momentum as an objective measure of dynamic balance. We also observed that when participants walked more symmetrically, their whole-body angular momentum in the sagittal plane increased rather than decreased. Conclusions Voluntary reductions of step length asymmetry in people poststroke resulted in reduced measures of dynamic balance. This is consistent with the idea that after stroke, individuals might have an implicit preference not to deviate from their natural asymmetry while walking because it could compromise their balance. Clinical Trials Number: NCT03916562.

Download Full-text

Effects of different vibration frequencies on muscle strength, bone turnover and walking endurance in chronic stroke

Scientific Reports ◽

10.1038/s41598-020-80526-4 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Zhenhui Yang ◽

Tiev Miller ◽

Zou Xiang ◽

Marco Y. C. Pang

Keyword(s):

Muscle Strength ◽

Bone Turnover ◽

Intervention Program ◽

Type I Collagen ◽

Chronic Stroke ◽

Medium Effect ◽

Whole Body ◽

Type I ◽

Leg Muscle ◽

Walking Endurance

AbstractThis randomized controlled trial aimed to evaluate the effects of different whole body vibration (WBV) frequencies on concentric and eccentric leg muscle strength, bone turnover and walking endurance after stroke. The study involved eighty-four individuals with chronic stroke (mean age = 59.7 years, SD = 6.5) with mild to moderate motor impairment (Fugl-Meyer Assessment lower limb motor score: mean = 24.0, SD = 3.5) randomly assigned to either a 20 Hz or 30 Hz WBV intervention program. Both programs involved 3 training sessions per week for 8 weeks. Isokinetic knee concentric and eccentric extension strength, serum level of cross-linked N-telopeptides of type I collagen (NTx), and walking endurance (6-min walk test; 6MWT) were assessed at baseline and post-intervention. An intention-to-treat analysis revealed a significant time effect for all muscle strength outcomes and NTx, but not for 6MWT. The time-by-group interaction was only significant for the paretic eccentric knee extensor work, with a medium effect size (0.44; 95% CI: 0.01, 0.87). Both WBV protocols were effective in improving leg muscle strength and reducing bone resorption. Comparatively greater improvement in paretic eccentric leg strength was observed for the 30 Hz protocol.

Download Full-text

Effects of whole-body vibration on quadriceps and hamstring muscle strength, endurance, and power in children with hemiparetic cerebral palsy: a randomized controlled study

Bulletin of Faculty of Physical Therapy ◽

10.1186/s43161-021-00023-1 ◽

2021 ◽

Vol 26 (1) ◽

Author(s):

Rania G. Hegazy ◽

Amr Almaz Abdel-aziem ◽

Eman I. El Hadidy ◽

Yosra M. Ali

Keyword(s):

Cerebral Palsy ◽

Physical Therapy ◽

Muscle Strength ◽

Whole Body Vibration ◽

Whole Body ◽

Controlled Study ◽

Control Group ◽

Hamstring Muscle ◽

Post Intervention ◽

Body Vibration

Abstract Background Hemiplegic cerebral palsy (CP) enormously affects the quadriceps and hamstring muscles. It causes weakness in the affected lower-extremity muscles in addition to muscle imbalance and inadequate power production, especially in the ankle plantar-flexor and knee extensor muscles. It also causes anomalous delayed myoelectrical action of the medial hamstring. A whole-body vibration (WBV) exercise can diminish muscle spasticity and improve walking speed, muscle strength, and gross motor function without causing unfavorable impacts in adults suffering from CP. Thus, the aim of this study is to investigate the impacts of WBV training associated with conventional physical therapy on the quadriceps and hamstring muscle strength, endurance, and power in children with hemiparetic CP. Results The post-intervention values of the quadriceps and hamstring muscle force, endurance, and power were significantly higher than the pre-intervention values for both groups (p = 0.001). The post-intervention values of the study group were significantly higher than the control group (quadriceps force, p = 0.015; hamstring force, p = 0.030; endurance, p = 0.025; power, p = 0.014). Conclusion The 8 weeks of WBV training that was added to traditional physical therapy was more successful in improving the quadriceps and hamstring muscle strength, endurance, and power in children with hemiparetic CP when compared to traditional physical therapy alone.

Download Full-text