Traumatic damage to the brainstem occurs frequently when the brain skull complex experiences injurious loading especially during those traumatic situations that produce diffuse axonal injury (DAI). DAI has been shown to be dependent on load direction and correlated with regional tissue deformation in response to rotational inertial loads. Possible mechanisms ...

Two-limb coordination of homologous and non-homologous effectors was examined during isofrequency (1:1) and multifrequency (2:1) conditions. The coordination patterns involved flexion and extension movements in the sagittal plane and were performed under unloaded and single-limb (right arm) loaded conditions. Previous studies suggested that the lower degree of 1:1 synchronization observed ...

A spring loaded tactile sensor with displacement sensing has been evaluated for non-invasive assessment of physical properties, stiffness and elasticity, of human skin in vivo. The tactile sensor consists of a peizoelectric vibrator (61 kHz) with a vibration pickup, electronics and PC with software for measurement of the change in ...

The physicochemically derived swelling stress in articular cartilage plays a crucial role in determining the pattern of stress sharing between the exudable fluid and the 'solid' components comprising its matrix. This pattern of stress sharing in turn influences the manner in which cartilage consolidates or deforms in compression via the ...

Disc-shaped specimens are frequently tested in order to establish an understanding of the properties of ceramic material. In this study three-dimensional finite element stress analysis has been used to investigate the loading characteristics of this shape of specimen and the effect of incorporating scratches and voids into its structure. The ...

Custom-designed miniature load-cells were inserted into the distal end of the ulna and the proximal end of the radius in ten fresh-frozen forearms from cadavera. The forces transmitted through the bones at these sites were measured under 134 newtons of constant axial load that was applied through the metacarpals as ...

To evaluate the mechanical effect of the direction of facet load on the isthmus stresses of the lower lumbar neural arch, stress analyses were performed by using three-dimensional finite element models of isolated L4 and L5 vertebrae with particular emphasis on accurate discretization of the posterior elements. The bilateral symmetric ...

Models of skeletal muscle based on its response to sinusoidal stimulation have been in use since the late 1960s. In these methods, cyclic excitation at varying frequencies is used to determine force or muscle length amplitude and phase as functions of excitation frequency. These functions can then be approximated by ...

The ability of the cat's ankle joint to track various input signals when controlled by electrically elicited motor unit recruitment, firing rate and antagonist muscle coactivation was examined. Pseudo-random, sinusoidal and staircase signals were used to control the soleus and tibialis anterior muscles isometrically and with a 250-g pendulum. Tracking ...

The anatomic architecture of connective tissue is dependent on the stresses associated with motion. Immobilization results in stress deprivation, causing structural changes in the tissue matrix. The structural changes that occur are due to the remodeling of tissue to its new resting length while being held immobile. The goal of ...

Past approaches for inducing protective stepping to preserve standing balance in humans have either lacked the flexibility of control over the initial conditions of falling, or involved considerable mass which limits mobility of the system. This report describes the design and function of a stepper motor closed-loop waist-pull system for ...

STUDY DESIGN: An electromyogram-assisted free-dynamic lifting model was used to quantify the patterns of complex spinal loads in subjects performing various lifting tasks. OBJECTIVES: To assess in vivo the three-dimensional complex spinal loading patterns associated with high and low risk lifting conditions that matched those observed in industrial settings. SUMMARY ...

Although a contracting muscle regulates its energy output depending on the load imposed on it ("Fenn effect"), the mechanism underlying the load-dependent energy output remains obscure. To explore the possibility that the mechanical efficiency, with which chemical energy derived from ATP hydrolysis is converted into mechanical work, of individual myosin ...

Experimental and theoretical methods were used to investigate the linearity of the stress response of articular cartilage to ramp and sinusoidal tests in confined compression, as well as the role of cartilage-porous platen and lateral confinement boundary conditions in determining material responses. With respect to linearity, we posed the question ...

This paper presents a silicon-based force sensor packaged in a flexible package and describes the sensors performance on human subjects. The sensing element consists of a circular silicon diaphragm (200-micron thick with a 2-mm radius) over a 10-micron sealed cavity with a solid Torlon dome providing force-to-pressure transduction to the ...

A finite element (FE) based scheme for modeling facet articulation in a spinal motion segment is proposed. The algorithm presented models the facet articulation as a nonlinear progressive contact problem. This algorithm is used to perform a nonlinear FE analysis of a complete L3-L4 motion segment. The role of facets ...

The evaluation of the effect of lifting belts on multijoint coordinated lifting performance has been limited. Thirteen subjects participated in two experiments: (a) fatiguing repetitive sagittal lifting and (b) asymmetric lifting. Both experiments were performed with and without the use of a common flexible lifting belt to determine the effect ...

The dynamic axial stiffness of the L2-3 motion segment subjected to vibratory loading under intact and injured states of the intervertebral disc was studied using an in vivo porcine model. Three groups of animals with the following states of the intervertebral discs were studied: intact disc, acutely injured disc, and ...

The composition and amount of extracellular matrix produced by chondrocytes are thought to be influenced by the stress and strain states in the vicinity of the chondrocytes. During daily activities, such as walking and running, articular joints are loaded dynamically. In the present study, a solution is proposed to simulate ...

The geometric and material properties of tendons and ligaments change during growth and development. While some of the changes occur in the absence of mechanical loading, normal development requires the mechanical stimulus provided by normal physical activity. We have developed an analytical framework for quantitatively describing changes in uniaxial tendon ...

OBJECTIVE: To compare the differences in lumbosacral spine forces under varying backpack loads. DESIGN: A biomechanical model was used to determine the changes in peak forces in the L5/S1 joint with increasing backpack loads during level walking. BACKGROUND: Most studies involving varying external backpack loads have been concerned mainly with ...

The motions of counterface articulation against the bearing surface of the acetabular liner strongly influence polyethylene wear debris production in contemporary total hip arthroplasty. However, the available body of relevant articular force and motion information is largely confined to resultant load excursions measured relative to instrumented femoral components, and/or to ...

PURPOSE: To abstract the essential elements of chiropractic prone leg checking and subject them to controlled, experimental parametric testing. DESIGN: Controlled, objective, repeated-measure analysis of the dynamic response of leg positions to distractive and compressive loading conditions. SETTING: Research laboratory in a chiropractic college. PARTICIPANTS: Twenty-five compression and 30 distraction ...

OBJECTIVE: The dynamic response and load sharing amongst passive elements of an L2-L3 motion segment during axial compressive cyclic loading was investigated. DESIGN: A validated viscoelastic nonlinear finite element model of L2-L3 was used for a detailed stress/strain analysis during axial cyclic loading. BACKGROUND: The repetitive loading of the spine ...

Collagen fibres form cross-helical, cross-ply or quasi-random feltworks in extensible connective tissues; strain-induced reorientation of these networks gives rise to the non-linear mechanical properties of connective tissue at finite strains. Such tissues are also generally viscoelastic (i.e. display time-dependent properties). The hypothesis that time-dependent reorientation of collagen fibres is responsible ...

STUDY DESIGN: A repetitive lifting test in the sagittal plane was performed with a submaximal load at a maximal lifting rate to understand the effects of fatigue on kinematic and kinetic measures of performance. OBJECTIVES: To quantify the effect of fatigue during a highly repetitive lifting task, in terms of ...

This study describes the effect of load magnitude, frequency and duration on proteoglycan (PG) biosynthesis and loss in mature bovine articular cartilage explants. Cultured full thickness cartilage discs were subjected to a continuously applied, uniaxial compressive cyclic load. The loads were applied using a sinusoidal waveform of 0.001, 0.01, 0.1 ...

In an attempt to understand better the contribution of the anteroinferior and posterosuperior popliteomeniscal fasciculi to lateral meniscus stability, we objectively evaluated the stability of the lateral meniscus before and after sequentially sectioning these fasciculi. In the biomechanical model, we attempted to account for the inherent limitations of arthroscopic evaluation ...

The relation between the eccentric force developed during a countermovement and the mechanical power output was studied in squatting exercises under nominally isotonic load (50% of 1-repetition maximum). The subjects (n = 5) performed squatting exercises with a countermovement at varied deceleration rates before lifting the load. The ground reaction ...

Repeated loading of the fingertips has been postulated to contribute to tendon and nerve disorders at the wrist during activities associated with prolonged fingertip loading such as typing. To fully understand the pathomechanics of these soft tissue disorders, the role of the fingertip pulp in attenuating the applied dynamic forces ...

Co-ordination of various components of the human body during the course of lifting are very complex and difficult to control. This study hypothesized that strategies used to control the motion patterns of the external load may be applied to control co-ordination and also to control the level of compressive force ...

OBJECTIVE: Characterization of the responses to spinal posteroanterior loading has involved measuring the gradient of the linear region of the force-displacement relationship between 30 N and 100 N of applied force. However, forces applied during manual assessment of stiffness may reach 300 N. This study investigated whether the force-displacement relation ...

OBJECTIVE: The purpose of this study was to investigate the effect of load rate on the mechanical characteristics of spinal motion segments under compressive loading. DESIGN: An in vitro experiment using a porcine model which ensured a homogeneous population for age, weight, genetic background and physical activity. BACKGROUND: Spinal motion ...

The aim of the present study was to evaluate quantitatively the change in stiffness of scalp flaps determined by increased loads of tension. Data were collected by stepwise loading 20 scalp flaps, created by a reversed-Y incision down to and through the galea aponeurotica together with undermining. In the layer ...

In a population of male workers in two ship maintenance companies (n = 32), a workplace survey was conducted in order to quantify their physical load. Postural load was measured by using the Ovako Working posture Analyzing System. During 7480 observations, working postures, exertion of force and working activities were ...

This paper presents the pilot procedures of a new in vivo experimental method for measures of local bone deformation on tibia. The tibia transducer consists of a strain gauge mounted on a surgical staple, and was designed to measure local bone deformation. Pilot measurements were undertaken during two standardized conditions ...

The study was carried out to determine the differences in the low-frequency dynamic mechanical properties of the guinea pig aorta and portal vein. Experiments were performed at five passive load levels in the aorta and at four levels in the portal vein. Sudden stretches 65 s in duration were imposed ...

Mechanical interactions between the polyethylene liner and the metal-backing play an important role in the load transfer and debris-generation mechanisms of an acetabular component. Insert thickness, cup orientation, and insert-shell interface conditions affect the resulting contact stresses at the articulating and backside surfaces of the polyethylene component. The objective of ...

It has been hypothesized that applied mechanical or osmotic loads which decrease cartilage volume by 5% or more are sufficient to relieve all collagen tensile forces, and that further changes in the applied load are completely supported by changes in proteoglycan osmotic pressure. In this view, cartilage should behave mechanically ...

Stability of the body during manual material handling is an important issue in the prevention of falls and over-exertion injuries. This research investigated stability limits while standing and holding loads in different positions relative to the body. Theoretically, the stability region is the full base of support defined by the ...

To provide a scientific basis for the design of bicycle pedals which possibly alleviate over-use knee injuries, two hypotheses were tested in the present study. The two hypotheses were: (1) that the three-dimensional pedal constraint loads; and (2) that the three-dimensional intersegmental knee loads would be reduced more significantly by ...

In locomotive activities, areas of cartilage in both the hip, and especially the knee, experience periods of complete unloading between loading cycles as contact is lost between opposing articulating surfaces. During these periods these cartilage sites experience load-free recovery. Therefore, it was decided to model as closely as possible the ...

INTRODUCTION:: Little information exits concerning the effect, if any, foot orthoses have upon how the foot is loaded during normal walking. The purpose of this study was to determine if there was a difference in the initiation of forefoot loading with different densities of foot orthoses. METHODS:: Ten volunteers (5 ...

Instrumentation was developed to apply controlled biaxial (normal and shear) forces to the skin of a human or animal subject. The instrument mimicked any reference waveform within the constraints of a bandwidth of 15 Hz, a maximum force of 20 N, and displacement ranges of 15 mm for the normal ...

Maximal load-lifting capacities of six ruby-throated hummingbirds (Archilochus colubris) were determined under conditions of burst performance. Mechanical power output under maximal loading was then compared with maximal hovering performance in hypodense gas mixtures of normodense air and heliox. The maximal load lifted was similar at air temperatures of 5 and ...

This Note describes the dynamic load sensors (DLS) spaceflight experiment that measured middeck astronaut-induced disturbances during the 14-day STS-62 Space Shuttle mission in March 1994. The DLS experiment was flown in conjunction with the reflight of the Middeck 0-Gravity Dynamics Experiment (MODE). The objective of MODE was to investigate effects ...

We investigated the issue of whether or not the CNS makes use of an internal model of the motor apparatus in planning and controlling arm movements. In particular, we tested the ability of subjects to predict different hand-held loads by examining grip force adjustments used to stabilize the load in ...

In some diseases affecting only 1 hip joint, it is necessary to keep the contact force between femoral head and acetabulum (hip joint force) permanently low at the affected side. Six subjects were examined while they were walking and carrying a load in 1 or 2 hands. It was determined ...

This study was directed at establishing the influence of dynamic loading situations on the sliding characteristics of the Gamma locking nail (Howmedica). It was postulated that the changing regions of load contact area that occur within the sliding mechanism during flexion and extension would favourably modify the jamming behaviour observed ...

Although explosive power in lower-body movements has been extensively studied, there is a paucity of research examining such movements in the upper body. This study aimed to investigate the influence of load and the stretch shortening cycle (SSC) on the kinematics, kinetics, and muscle activation that occurs during maximal effort ...