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Experimental evaluation of a new morphological approximation of the articular surfaces of the ankle joint.
Related Articles

Experimental evaluation of a new morphological approximation of the articular surfaces of the ankle joint.

J Biomech. 2017 Jan 07;:

Authors: Belvedere C, Siegler S, Ensini A, Toy J, Caravaggi P, Namani R, Giannini G, Durante S, Leardini A

Abstract
The mechanical characteristics of the ankle such as its kinematics and load transfer properties are influenced by the geometry of the articulating surfaces. A recent, image-based study found that these surfaces can be approximated by a saddle-shaped, skewed, truncated cone with its apex oriented laterally. The goal of this study was to establish a reliable experimental technique to study the relationship between the geometry of the articular surfaces of the ankle and its mobility and stability characteristics and to use this technique to determine if morphological approximations of the ankle surfaces based on recent discoveries, produce close to normal behavior. The study was performed on ten cadavers. For each specimen, a process based on medical imaging, modeling and 3D printing was used to produce two subject specific artificial implantable sets of the ankle surfaces. One set was a replica of the natural surfaces. The second approximated the ankle surfaces as an original saddle-shaped truncated cone with apex oriented laterally. Testing under cyclic loading conditions was then performed on each specimen following a previously established technique to determine its mobility and stability characteristics under three different conditions: natural surfaces; artificial surfaces replicating the natural surface morphology; and artificial approximation based on the saddle-shaped truncated cone concept. A repeated measure analysis of variance was then used to compare between the three conditions. The results show that (1): the artificial surfaces replicating natural morphology produce close to natural mobility and stability behavior thus establishing the reliability of the technique; and (2): the approximated surfaces based on saddle-shaped truncated cone concept produce mobility and stability behavior close to the ankle with natural surfaces.

PMID: 28093261 [PubMed - as supplied by publisher]




Shear and pressure under the first ray in neuropathic diabetic patients: Implications for support of the longitudinal arch.
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Shear and pressure under the first ray in neuropathic diabetic patients: Implications for support of the longitudinal arch.

J Biomech. 2016 Dec 29;:

Authors: Davis B, Crow M, Berki V, Ciltea D

Abstract
OBJECTIVE: To assess dynamic arch support in diabetic patients at risk for Charcot neuroarthopathy whose arch index has not yet shown overt signs of foot collapse.
METHODS: Two indirect measures of toe flexor activation (ratios: peak hallux pressure to peak metatarsal pressure - Ph/Pm; peak posterior hallux shear to peak posterior metatarsal shear - Sh/Sm) were obtained with a custom built system for measuring shear and pressure on the plantar surface of the foot during gait. In addition, the tendency of the longitudinal arch to flatten was measured by quantifying the difference in shear between the 1st metatarsal head and the heel (Sflatten) during the first half of the stance phase. Four stance phases from the same foot for 29 participants (16 control and 13 neuropathic diabetic) were assessed.
RESULTS: The peak load ratio under the hallux (Ph/Pm) was significantly higher in the control group (2.10±1.08 versus 1.13±0.74, p=0.033). Similarly, Sh/Sm was significantly higher in the control group (1.87±0.88 versus 0.88±0.45, p=0.004). The difference in anterior shear under the first metatarsal head and posterior shear under the lateral heel (Sflatten) was significantly higher in the diabetic group (p<0.01). Together these findings demonstrate reduced plantar flexor activity in the musculature responsible for maintaining the longitudinal arch.
CONCLUSIONS: With no significant difference in arch index between the two groups, but significant differences in Ph/Pm, Sh/Sm and Sflatten the collective results suggest there are changes in muscle activity that precede arch collapse.

PMID: 28093260 [PubMed - as supplied by publisher]




Suspending loads decreases load stability but may slightly improve body stability.
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Suspending loads decreases load stability but may slightly improve body stability.

J Biomech. 2016 Dec 08;:

Authors: Ackerman J, Potwar K, Seipel J

Abstract
Here, we seek to determine how compliantly suspended loads could affect the dynamic stability of legged locomotion. We theoretically model the dynamic stability of a human carrying a load using a coupled spring-mass-damper model and an actuated spring-loaded inverted pendulum model, as these models have demonstrated the ability to correctly predict other aspects of locomotion with a load in prior work, such as body forces and energetic cost. We report that minimizing the load suspension natural frequency and damping ratio significantly reduces the stability of the load mass but may slightly improve the body stability of locomotion when compared to a rigidly attached load. These results imply that a highly-compliant load suspension could help stabilize body motion during human, animal, or robot load carriage, but at the cost of a more awkward (less stable) load.

PMID: 28093259 [PubMed - as supplied by publisher]




Stooping, crouching, and standing - Characterizing balance control strategies across postures.
Related Articles

Stooping, crouching, and standing - Characterizing balance control strategies across postures.

J Biomech. 2017 Jan 06;:

Authors: Weaver TB, Glinka MN, Laing AC

Abstract
BACKGROUND: While stooping and crouching postures are critical for many activities of daily living, little is known about the balance control mechanisms employed during these postures. Accordingly, the purpose of this study was to characterize the mechanisms driving net center of pressure (COPNet) movement across three postures (standing, stooping, and crouching) and to investigate if control in each posture was influenced by time.
METHODS: Ten young adults performed the three postures for 60s each. Kinetic signals were collected via a force platform under each foot. To quantify mechanisms of control, correlations (CorrelLR) were calculated between the left and right COP trajectories in the anterior-posterior (AP) and medio-lateral (ML) directions. To examine the potential effects of time on balance control strategies, outcomes during the first 30s were compared to the last 30s.
RESULTS: CorrelLR values did not differ across postures (AP: p = 0.395; ML: p = 0.647). Further, there were no main effects of time on CorrelLR (AP: p = 0.976; ML: p = 0.105). A significant posture-time interaction was observed in the ML direction (p = 0.045) characterized by 35% decreases in CorrelLR over time for stooping (p = 0.022).
CONCLUSION: The dominant controllers of sway (i.e., AP: ankle plantar/dorsi flexors; ML: hip load/unload mechanism) are similar across quiet stance stooping, and crouching. Changes in ML control strategies over time suggests that fatigue could affect prolonged stooping more so than crouching or standing.

PMID: 28093258 [PubMed - as supplied by publisher]