Topic
Joint stiffness
About: Joint stiffness is a research topic. Over the lifetime, 1597 publications have been published within this topic receiving 32680 citations. The topic is also known as: stiffness of joint & Stiffness of joint, NEC, involving multiple sites in ICD9CM_2006.
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TL;DR: In this article, a linkage type element is developed for adding rock joint stiffness to the structural stiffness matrix describing the behavior of a system of rock blocks and joints and a new classification of joints is introduced, based on the application of the joint element to finite element analysis of structures in jointed rock.
Abstract: The representation of discontinuities in analysis of blocky rock is discussed. A linkage type element is developed for addition of rock joint stiffness to the structural stiffness matrix describing the behavior of a system of rock blocks and joints. Several basic problems of jointed rock are studied. These examples demonstrate the marked influence joints may have on the stress distribution, displacements, and failure pattern of an underground opening or other structures in jointed rock. A new classification of joints is introduced, based on the application of the joint element to finite element analysis of structures in jointed rock. Normal stiffness, tangential stiffness, and shear strength are used as parameters in the classification system. The methods discussed in this paper allow a jointed rock mass to be treated as a system of blocks and links. Just as analysis of a reinforced concrete building requires detailed knowledge of the behavior of concrete alone and steel alone, the joint stiffness approach calls for and uses detailed description of the behavior of rock blocks and rock joints independently.
1,186 citations
15 Mar 2004
TL;DR: The results indicate that a variable-impedance orthosis may have certain clinical benefits for the treatment of drop-foot gait compared to conventional ankle-foot orthoses having zero or constant stiffness joint behaviors.
Abstract: An active ankle-foot orthoses (AAFO) is presented where the impedance of the orthotic joint is modulated throughout the walking cycle to treat drop-foot gait. During controlled plantar flexion, a biomimetic torsional spring control is applied where orthotic joint stiffness is actively adjusted to minimize forefoot collisions with the ground. Throughout late stance, joint impedance is minimized so as not to impede powered plantar flexion movements, and during the swing phase, a torsional spring-damper control lifts the foot to provide toe clearance. To assess the clinical effects of variable-impedance control, kinetic and kinematic gait data were collected on two drop-foot participants wearing the AAFO. For each participant, zero, constant, and variable impedance control strategies were evaluated and the results were compared to the mechanics of three age, weight, and height matched normals. We find that actively adjusting joint impedance reduces the occurrence of slap foot allows greater powered plantar flexion and provides for less kinematic difference during swing when compared to normals. These results indicate that a variable-impedance orthosis may have certain clinical benefits for the treatment of drop-foot gait compared to conventional ankle-foot orthoses having zero or constant stiffness joint behaviors.
772 citations
TL;DR: The notion of joint stiffness as commonly studied in biomechanics and motor control is compared with the physical definition of stiffness and different terms are suggested in order to differentiate between experimentally observed relations between joint angle and torque that are likely to have different nature.
484 citations
TL;DR: Both joint stiffness and limb geometry adjustments are important in adjusting leg stiffness to allow similar hopping on different surfaces, and a computer simulation was used to examine the sensitivity ofLeg stiffness to the observed changes in ankle stiffness and touchdown knee angle.
Abstract: When humans hop in place or run forward, leg stiffness is increased to offset reductions in surface stiffness, allowing the global kinematics and mechanics to remain the same on all surfaces. The purpose of the present study was to determine the mechanism for adjusting leg stiffness. Seven subjects hopped in place on surfaces of different stiffnesses (23-35,000 kN/m) while force platform, kinematic, and electromyographic data were collected. Leg stiffness approximately doubled between the most stiff surface and the least stiff surface. Over the same range of surfaces, ankle torsional stiffness increased 1.75-fold, and the knee became more extended at the time of touchdown (2.81 vs. 2.65 rad). We used a computer simulation to examine the sensitivity of leg stiffness to the observed changes in ankle stiffness and touchdown knee angle. Our model consisted of four segments (foot, shank, thigh, head-arms-trunk) interconnected by three torsional springs (ankle, knee, hip). In the model, an increase in ankle stiffness 1.75-fold caused leg stiffness to increase 1.7-fold. A change in touchdown knee angle as observed in the subjects caused leg stiffness to increase 1.3-fold. Thus both joint stiffness and limb geometry adjustments are important in adjusting leg stiffness to allow similar hopping on different surfaces.
447 citations
TL;DR: In sprint running the spring-like behavior of the leg might be adjusted by changing the stiffness of the knee joint, which may depend on (constant) tendon stiffness because of its dominating role in triceps surae muscle-tendon unit.
Abstract: KUITUNEN, S., P. V. KOMI, and H. KYROLAINEN. Knee and ankle joint stiffness in sprint running. Med. Sci. Sports Exerc., Vol. 34, No. 1, 2002, pp. 166–173.IntroductionStiffness has often been considered as a regulated property of the neuromuscular system. The purpose of this study was to examine the
390 citations