This study was designed to examine the importance of vision to corrective processes associated with a mechanical perturbation to the limb during goal-directed aiming. With a hand held stylus, under vision and no vision conditions, performers reached to a target represented by the intersection of perpendicular lines. The stylus was connected to an air compressor and engineered such that 80 ms following movement initiation reaches were perturbed by a short air burst either in the direction of, or opposite to, the movement. Spatial position analysis of the limb at early kinematic landmarks revealed that the single direction bursts were successful in advancing and hindering the movement progress. Furthermore, within subject trial-to-trial variability analysis indicated that performers adopted different control strategies for dealing with the perturbations depending on the availability of vision. The present findings suggest that a continuous form of online control is exercised during the early portions of the aiming trajectories. This form of control may be mediated by visual or proprioceptive information.
Lawrence E. M. Grierson, Claudia Gonzalez and Digby Elliott
Walter Herzog, Timothy Koh, Evelyne Hasler and Tim Leonard
We hypothesize that the neuromuscular system is designed to function effectively in accomplishing everyday movement tasks. Since everyday movement tasks may vary substantially in terms of speed and resistance, we speculate that agonistic muscles contribute differently to varying movement tasks such that the mechanical, structural, and physiological properties of the system are optimized at all times. We further hypothesize that a mechanical perturbation to the musculoskeletal system, such as the loss of an important joint ligament or the change of a muscle’s line of action, causes an adaptation of the system aimed at reestablishing effective function. Here. we demonstrate how the specificity of the cat ankle extensors is used to accommodate different locomotor tasks. We then illustrate how the loss of an important ligament in the cat knee leads to neuromuscular adaptation. Finally, we discuss the adaptability of skeletal muscle following an intervention that changes a muscle’s line of action, moment arm, and excursion.
Rhodri S. Lloyd, Jon L. Oliver, Gregory D. Myer, Mark B. De Ste Croix, Josh Wass and Paul J. Read
control that may be associated with injury risk. Screening assessments that involve repeated jumping tasks also require athletes to respond to movement perturbations and forces. 12 The tuck jump assessment (TJA) is a practical field-based test that uses this approach and has been developed to identify