Net ankle quasi-stiffness is influenced by walking speed but not age for older adult women

Collins, John D.; Arch, Elisa S.; Crenshaw, Jeremy R.; Bernhardt, Kathie A.; Khosla, Sundeep; Amin, Shreyasee; Kaufman, Kenton R.

doi:10.1016/j.gaitpost.2018.03.031

Cited by 21 publications

(17 citation statements)

References 34 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We found that the longitudinal stiffness increased with faster speed (p = 0.002), where the stiffness across the four speeds (0.4, 0.6, 0.8, and 1.0 statures/s) was: 153.48 ± 43.81, 156.22 ± 40.31, 187.27 ± 58.52, and 200.71 ± 58.83 N/cm. Our findings support the idea that humans can modulate stiffness of the lower extremity structures across a wide range of locomotor tasks, similar to how the entire leg can modulate stiffness when running on various surfaces [58], or how the ankle joint can modulate stiffness when walking faster [57, 61] or with added mass [57].…”

Section: Discussionsupporting

confidence: 82%

“…Furthermore, another feature that may be important for unpowered devices is the ability to change its stiffness depending on the walking task [70]. As our study, and other studies have found [57, 58, 61], the biological limbs have an inherent ability to modulate joint/limb stiffness based on the demands of locomotion. As such, a device that incorporates micro-motors to alter the stiffness characteristics [70, 71] may be a viable solution to replicate salient features of the biological foot and ankle system.…”

Section: Discussionmentioning

confidence: 57%

“…A torsional spring model has been used to describe the moment-angle relationship of the human ankle during stance phase of walking [39, 54–57]. An important characteristic of biological springs is the stiffness (or ‘quasi-stiffness’), as measured by the ratio of the peak force and displacement of the leg during running [51, 58–60], or by the ratio of the ankle joint moment and angular displacement during walking [39, 54, 55, 57, 61]. In line with these concepts, we quantified the longitudinal stiffness of the distal-to-shank structures, by computing the ratio of the peak force and total displacement (in the shank’s coordinate system).…”

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

The foot and ankle structures reveal emergent properties analogous to passive springs during human walking

2019

View full text Add to dashboard Cite

An objective understanding of human foot and ankle function can drive innovations of bio-inspired wearable devices. Specifically, knowledge regarding how mechanical force and work are produced within the human foot-ankle structures can help determine what type of materials or components are required to engineer devices. In this study, we characterized the combined functions of the foot and ankle structures during walking by synthesizing the total force, displacement, and work profiles from structures distal to the shank. Eleven healthy adults walked at four scaled speeds. We quantified the ground reaction force and center-of-pressure displacement in the shank’s coordinate system during stance phase and the total mechanical work done by these structures. This comprehensive analysis revealed emergent properties of foot-ankle structures that are analogous to passive springs: these structures compressed and recoiled along the longitudinal axis of the shank, and performed near zero or negative net mechanical work across a range of walking speeds. Moreover, the subject-to-subject variability in peak force, total displacement, and work were well explained by three simple factors: body height, mass, and walking speed. We created a regression-based model of stance phase mechanics that can inform the design and customization of wearable devices that may have biomimetic or non-biomimetic structures.

show abstract

Section: Discussionsupporting

confidence: 82%

Section: Discussionmentioning

confidence: 57%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

The foot and ankle structures reveal emergent properties analogous to passive springs during human walking

2019

View full text Add to dashboard Cite

show abstract

“…Several studies tried to extract the relationship between torques and angles of the hip [23, 24] or other lower body joints [64, 65] by assuming linear slop as quasi-stiffness between moments and angles. These researches are useful to design passive exoskeleton or prosthesis [66, 67].…”

Section: Discussionmentioning

confidence: 99%

A simple CPG-based model to generate human hip moment pattern in walking by generating stiffness and equilibrium point trajectories

Bahramian

Towhidkhah

Jafari

2019

Preprint

View full text Add to dashboard Cite

Equilibrium point hypothesis (its developed version named as referent control theory)presents a theory about how the central nerves system (CNS) generates human movements. On the other hand, it has been shown that nerves circuits known as central pattern generators (CPG) likely produce motor commands to the muscles in rhythmic motions. In the present study, we designed a bio-inspired walking model, by coupling double pendulum to CPGs that produces equilibrium and stiffness trajectories as reciprocal and co-activation commands. As a basic model, it is has been shown that this model can regenerate pattern of a hip moment in the swing phase by high correlation ሺ ߩ ൌ 0 . 9 7 0 ሻ with experimental data. Moreover, it has been reported that a global electromyography (EMG) minima occurs in the mid-swing phase when the hip is more flexed in comparison with the other leg. Our model showed that equilibrium and actual hip angle trajectories match each other in mid-swing, similar to the mentioned posture, that is consistent with previous findings. Such a model can be used in active exoskeletons and prosthesis to make proper active stiffness and torque.controls the body?" [3, 4]. These theories explain how the CNS can release from complex calculations to control movements. According to EPH, at the muscle level, the CNS only determines a specific threshold (ߣ) for muscle [5, 6]. If actual muscle length goes beyond the defined threshold, EMG activity emerges as a result of the gap between actual and threshold muscle lengths. To control the joint, two commands are defined by the CNS: reciprocal (R) command and co-activation (C) command [7]. If joint is considered as rotational spring, R and C commands determine equilibrium point and stiffness of the joint, respectively. In accordance with the referent control theory, for multi-joint system (e.g. leg), it is assumed that initially, global R and C commands are set by CNS, then, by few-to-many mappings, r and c commands for various joints are defined. Finally, ߣ s for agonist and antagonist muscles emerged from these r and c by another mapping [8]. This hierarchical system is effective for making coordination between different joints and muscles [9]. One of the powerful experimental evidence for this hierarchical referent system is the global EMG minima [10]. When the referent (R) and actual configurations approach meet each other, a minimum EMG activity occurs for most of the muscles involved in the task [10]. This phenomena has been confirmed by many studies on various tasks such as walking and jumping [10], monkeys head movement [11], Jete in ballet dancers [12], and hammering [13]. It is shown that during stepping forward, a global EMG minima occurred during mid-swing when the hip flexion of the swing leg is slightly more than the other leg [14].On the other hand, the behavior of the joints as a rotational spring have commonly been used for investigating the relationship between torque(s) and angle(s). These studies are applicable to design anthropomorphic biped robots [15][16][...

show abstract

“…In walking, k A increases with walking speed and positively correlates with positive work performed about the ankle during push-off 5,7 . In addition, the profile of k A across the stance phase mirrors that of net ankle moment and triceps surae muscle activation.…”

Section: Introductionmentioning

confidence: 99%

Activation-Dependent Changes in Soleus Length–Tension Behavior Augment Ankle Joint Quasi-Stiffness

Clark

Franz

2019

Journal of Applied Biomechanics

View full text Add to dashboard Cite

The triceps surae muscle-tendon units are important in governing walking performance, acting to regulate mechanical behavior of the ankle through interaction between active muscle and passive elastic structures. Ankle joint quasi-stiffness (the slope of the relation between ankle moment and ankle rotation, k A), is a useful aggregate measure of this mechanical behavior. However, the role of muscle activation and length-tension behavior in augmenting k A remains unclear. Here, 10 subjects completed eccentric isokinetic contractions at rest and at two soleus activation levels (25% and 75% isometric voluntary contraction-IVC) prescribed using electromyographic biofeedback. Ultrasound imaging quantified activation-dependent modulation of soleus muscle length-tension behavior and its role in augmenting k A. We found that soleus muscle stiffness (k M) and k A exhibit non-linear relations with muscle activation and were both more sensitive to the onset of activation than to subsequent increases in activation. Our findings also suggest that k A can be modulated via activation through changes in soleus muscle length-tension behavior. However, this modulation is more complex than previously appreciated-reflecting interaction between active muscle and passive elastic tissues. Our findings may have implications for understanding normal and pathological ankle joint function and the design of impedance-based prostheses.

show abstract

Net ankle quasi-stiffness is influenced by walking speed but not age for older adult women

Abstract: By determining that gait speed, not age, is related to NAS in older adults, this study represents the initial step towards objectively prescribing PD-AFO bending stiffness to achieve a targeted gait speed for older adults with plantar flexor weakness.

Cited by 21 publications

References 34 publications

The foot and ankle structures reveal emergent properties analogous to passive springs during human walking

The foot and ankle structures reveal emergent properties analogous to passive springs during human walking

A simple CPG-based model to generate human hip moment pattern in walking by generating stiffness and equilibrium point trajectories

Activation-Dependent Changes in Soleus Length–Tension Behavior Augment Ankle Joint Quasi-Stiffness

Contact Info

Product

Resources

About