Movement Coupling at the Ankle During the Stance Phase of Running

The purpose of this study was to quantify movement coupling at the ankle during the stance phase of running using bone-mounted markers. Intracortical bone pins with reflective marker triads were inserted under standard local anaesthesia into the calcaneus and the tibia of five healthy male subjects. The three-dimensional rotations were determined using a joint coordinate system approach. Movement coupling was observed in all test subjects and occurred in phases with considerable individual differences. Between the shoe and the calcaneus coupling increased after midstance which suggested that the test shoes provided more coupling for inversion than for eversion. Movement coupling between calcaneus and tibia was higher in the first phase (from heel strike to midstance) compared with the second phase (from midstance to take-off). This finding is in contrast to previous in-vitro studies but may be explained by the higher vertical loads of the present in-vivo study. Thus, movement coupling measured at the bone level changed throughout the stance phase of running and was found to be far more complex than a simple mitered joint or universal joint model

Effects of Foot Orthoses on Skeletal Motion During Running

Objective. To quantify the effects of medial foot orthoses on skeletal movements of the calcaneus and tibia during the stance phase in running. Design. Kinematic effects of medial foot orthoses (anterior, posterior, no support) were tested using skeletal (and shoe) markers at the calcaneus and tibia. Background. Previous studies using shoe and skin markers concluded that medially placed orthoses control/reduce foot eversion and tibial rotation. However, it is currently unknown if such orthoses also affect skeletal motion at the lower extremities. Methods. Intracortical Hofman pins with reflective marker triads were inserted under standard local anesthetic into the calcaneus and tibia of five healthy male subjects. The three-dimensional tibiocalcaneal rotations were determined using a joint coordinate system approach. Eversion (skeletal and shoe) and tibial rotation were calculated to study the foot orthoses effects. Results. Orthotic effects on eversion and tibial rotations were found to be small and unsystematic over all subjects. Differences between the subjects were significantly larger (pp\u3c0.05). Conclusions. This in vivo study showed that medially placed foot orthoses did not change tibiocalcaneal movement patterns substantially during the stance phase of running. Relevance Orthoses may have only small kinematic effects on the calcaneus and tibia (measured with bone pins) as well as on the shoes (measured with shoe markers) during running of normal subjects. Present results showed that orthotic effects were subject specific and unsystematic across conditions. It is speculated that orthotic effects during the stance phase of running may be mechanical as well as proprioceptive

Instabilities and Oscillations in Isotropic Active Gels

We present a generic formulation of the continuum elasticity of an isotropic crosslinked active gel. The gel is described by a two-component model consisting of an elastic network coupled frictionally to a permeating fluid. Activity is induced by active crosslinkers that undergo an ATP-activated cycle and transmit forces to the network. The on/off dynamics of the active crosslinkers is described via rate equations for unbound and bound motors. For large activity motors yield a contractile instability of the network. At smaller values of activity, the on/off motor dynamics provides an effective inertial drag on the network that opposes elastic restoring forces, resulting in spontaneous oscillations. Our work provides a continuum formulation that unifies earlier microscopic models of oscillations in muscle sarcomeres and a generic framework for the description of the large scale properties of isotropic active solids.Comment: 13 pages, 5 figure

A Multisegment Dynamic Model of Ski Jumping

This paper presents a planar, four-segment, dynamic model for the flight mechanics of a ski jumper. The model consists of skis, legs, torso and head, and anns. Inputs include net joint torques that are used to vary the relative body configurations of the jumper during fiight. The model also relies on aerodynamic data from previous wind tunnel tests that incorporate the effects of varying body configuration and orientation on lift, drag, and pitching moment. A symbolic manipulation program, "Macsyma," is used to derive the equations of motion automatically. Experimental body segment orientation data during the fiight phase arc presented for three ski jumpers which show how jumpers of varying ability differ in flight and demonstrate tlie need for a more complex analytical model than that previously presented in the literature. Simulations are presented that qualitatively match the measured trajectory for a good jumper. The model can be used as a basis for the study of optimal jumper behavior in fiight which maximizes jump distance

QUANTITATIVE HEMISPHERIC EEG DIFFERENCES BETWEEN NORMAL SUBJECTS AND TEMPORAL EPILEPTICS

Verbal function disorders have often been found in left temporal lobe epileptics, but is not known whether they are due to the brain lesion giving rise to the epileptic seizures or whether the epilepsy itself plays a direct, if partial, role. This study exploited the method of EEG asymmetry during cognitive tasks, considering only patients with normal CT scans to eliminate possible brain lesion interference. The EEG signal from P4-02 and P3-01 derivations during verbal and non-verbal tasks was analyzed in 18 patients with left temporal lobe epilepsy. The R/L log increase during the verbal task observed in a group of normal subjects was not present in the epileptic patients. There were no differences corresponding to seizure frequency among the epileptics, but a longer history of the disease tended to make for greater alterations in task-dependent EEG asymmetry