On-line trajectory modifications of planar, goal-directed arm movements.

Sometimes a goal-directed arm movement has to be modified en route due to an unforeseen perturbation such as a target displacement or a hand displacement by an external force. In this paper several aspects of that modification process are addressed. Subjects had to perform a point-to-point movement task on a computer screen using a mouse-coupled pointer as the representation of the hand position.

(In)dependent limbs during discrete bi-manual movements.

During discrete bi-manual pointing movements the two hands start highly correlated and gradually decorrelate throughout the movement. In this work we studied whether this decorrelation can be postponed by imposing temporal and spatial constraints at the end of the movement. We compared a simple ballistic bi-manual pointing movement with (i) bi-manually grasping a small object between the two stretched index fingers and with (ii) bi-manually pointing with end time synchronisation on a sound pulse.

Relation between torque history, firing frequency, decruitment levels and force balance in two flexors of the elbow.

By means of intramuscular electromyographic recordings, we studied the firing frequencies and recruitment/decruitment thresholds of individual motor units in two elbow flexors, the biarticular biceps brachii muscle and the monoarticular brachioradialis muscle. Subjects had to perform isometric contractions with increasing elbow flexion torque until a specific peak torque level was reached. The torque level was kept constant for 6 s during which firing frequencies were measured.

A comparison of curvatures of left and right hand movements in a simple pointing task.

Human arm movements towards visual targets are remarkably reproducible in several tasks and conditions. Various authors have reported that trajectories of unconstrained point-to-point movements are slightly curved, smooth and have bell-shaped velocity profiles. The hand paths of such movements show small - but significant - curvatures throughout the workspace.

A new method to study shape recovery of red blood cells using multiple optical trapping.

In this new method for studying the shape recovery of deformed red blood cells, three optical traps ("optical tweezers") induce a parachute-shaped red cell deformation, which is comparable to the deformation in small capillaries. The shape recovery is recorded, and a relaxation time is obtained for each individual red blood cell. The sensitivity of this technique for the detection of differences in relaxation times is demonstrated on subpopulations of density-separated red blood cells: "young" cells have shorter (162 ms) and "old" cells have longer (353 ms) relaxation times compared with the total population (271 ms).