Pause time alters the preparation of two-component movements.

Targeted reciprocal aiming movements are pervasive in everyday life, but it is unclear how the timing parameters between task elements affect the preparation of these movements. This study used a loud (124 dB) startling acoustic stimulus (SAS) to probe how changes in the pause time between the outward and return components of a reciprocal aiming task affected the preparatory state of the motor system. Participants performed a visually guided wrist extension-flexion task to a target located at 20° from the start position and were instructed to pause the movement within the wrist extension target zone for either 50, 200, or 500 ms. A SAS was presented during 25 % of trials before either the onset of the wrist extension (out) or flexion (return) components of the task to determine how motor preparation was affected by task requirements. Results showed that the presentation of a SAS prior to the initial outward movement led to significantly earlier onsets of both the outward and return components (p < .05), indicating that the pause time in the planned action was pre-planned. For the longer (200, 500 ms) pause-time conditions, a SAS delivered prior to returning from the target region triggered the return portion of the movement early. These findings suggest that the shortest pause-time movement (50 ms) was preplanned as a single action, whereas for reciprocal movements with longer pause times at least the initial part of the movement and the timing of the pause were preplanned and integrated, while the return portion was more independent.

Muscle contribution to elbow joint valgus stability.

Repetitive valgus stress of the elbow can result in excessive strain or rupture of the native medial ulnar collateral ligament (MUCL). The flexor-pronator mass (FPM) may be particularly important for elbow valgus stability in overhead-throwing athletes. The aim of this study was to identify the relative contribution of each muscle of the FPM--that is, the flexor carpi ulnaris (FCU), flexor digitorum superficialis (FDS), flexor carpi radialis (FCR), and pronator teres (PT)--and of the extensor-supinator mass, including the extensor carpi ulnaris (ECU), extensor digitorum communis (EDC), extensor carpi radialis longus and brevus, and brachioradialis, to elbow valgus stability at 45 degrees and 90 degrees of elbow flexion angles. Eight fresh-frozen elbow specimens (mean age at death, 73.75 +/- 14.07 years) were tested. With the skin and subcutaneous tissue removed but all muscles left intact, each individual muscle of the FPM and extensor-supinator mass was loaded at 3 levels of force. During loading, strain on the MUCL and the kinematics of the elbow were measured simultaneously. Kinematic measurements were later repeated when the MUCL was fully cut. At 45 degrees and 90 degrees of elbow flexion, individual loading of the FCU, FDS, and FCR caused significant relief to the MUCL whereas the PT produced no significant change. Furthermore, of these flexor muscles, the FCU provided the greatest MUCL relief at both 45 degrees and 90 degrees . In contrast, loading of the ECU at 45 degrees of elbow flexion produced a significant increase in MUCL strain. All FPM muscles caused significant elbow varus movement at both 45 degrees and 90 degrees when loaded individually. At 90 degrees , the FCU created more motion than both the FCR and PT but not the FDS, and the FDS created more motion than the PT. The EDC and ECU created significant valgus movement at 45 degrees and 90 degrees , which became insignificant when the MUCL was transected. Our study suggested that the FCU, FDS, and FCR may function as dynamic stabilizers, with the FCU being the primary stabilizer for elbow valgus stability, incorporating with the MUCL for all tested joint configurations. Our findings also suggest that the ECU and EDC increased MUCL strain and elbow valgus movement at both 45 degrees and 90 degrees .

Development of a device for measurement of multi-directional isometric trunk kinetics in a seated position.

Trunk torque is typically quantified in a single plane. This is not ideal since any unmeasured coupled trunk kinetics in other directions, than the intended one, could affect the accuracy and reliability of the strength measurements as well as the ability to corroborate findings with electromyographic recordings. Therefore, an isometric device that simultaneously records trunk kinetics across planes has been developed to aid in the research of trunk control in both the healthy or impaired populations. This device utilizes a six degree-of-freedom load cell and custom designed frame to attach individuals while in the sitting position. The performance of the device was tested in six healthy controls and while using two protocols. The device was able to detect coupled trunk kinetics during maximum lateral flexion and axial twisting torque generation. It also allowed the implementation of a multi-axis isometric protocol showing that subjects were able to generate larger amounts of axial torque during sub-maximal trunk extension compared to sub-maximal trunk flexion. In conclusion, the device and mechanical transformations discussed in this article will aid in the interpretation of multi-directional isometric trunk kinetics in a wide range of populations.

Quantitative analysis of static sitting posture in chronic stroke.

Unsupported sitting requires postural stability of the trunk which is also necessary for almost all activities in daily living, yet there is a lack of research dealing with the persistence of trunk impairment post-stroke using quantitative methodologies. Therefore, the purpose of this study was to investigate unsupported sitting in individuals with chronic stroke by analyzing center of pressure (COP) signals from a force platform. Ten healthy control subjects and ten chronic stroke subjects sat on a chair without a footrest that was placed on top of a force platform. Trials consisted of eyes closed, staring at a target, and COP feedback. COP signals were analyzed using spatial and temporal techniques. Compared to controls, stroke group had larger sway area and larger displacements in all conditions (p<0.05) and less sample entropy (p<0.05) in eyes closed and target conditions. In feedback conditions, both groups had decreased sway area and maximum displacements along with stroke group having increased sample entropy (p<0.05). Our data suggest that trunk control, necessary for unsupported sitting, is impaired well into the chronic stage of stroke onset. Further investigations of sitting should be conducted for better understanding balance deficits under conditions localized to the trunk musculature.