Lindgrenmidtgaard1474

Whole body digitizing used to calculate whole body center of mass (CM) variables from competitions is particularly time-consuming, and "shortcut" methods that substitute for it could expediate the calculation of spatiotemporal variables. The aim of this study was to measure the appropriateness of using the head as a proxy for the CM when calculating running velocity in competition. Fifty-six athletes in the IAAF World Championship marathons were recorded using two high-definition cameras (50 Hz) on two laps so that 112 running sequences were analyzed. The video files were imported into SIMI Motion and manually digitized. The horizontal running velocity during one gait cycle was obtained using four methods horizontal velocity of the CM; horizontal velocity of the head (raw data); horizontal velocity of the head (Butterworth filtered); and horizontal displacement of the head (a single measurement using SIMI Motion 3D still image measurement) divided by time taken. In comparison with the criterion CM measurements for mean horizontal velocity, the filtered head data had the best 95% confidence interval (95% CI) for intraclass correlation coefficient (ICC) (0.999 - 1.000), the least bias (-0.006 m/s), and the lowest root mean square difference (0.024 m/s). The filtered head condition also had the best 95% CI for ICC for maximum and minimum horizontal velocities during the stride (>0.988) and the lowest bias (-0.001 m/s and -0.003 m/s, respectively). With the application of an appropriate filter, the head is thus an excellent proxy for whole body CM velocity calculations.Information on the local stiffness characteristics of the intervertebral disc (IVD) is crucial for the understanding of its structure-function properties in health and disease and may improve numerical modeling. Previous studies have attempted to map local tissue stiffness by sectioning the disc and performing mechanical testing on these discrete tissue units, which is technically challenging and may bias the results. Shear wave elastography (SWE) represents a nondestructive alternative that can provide spatially continuous elasticity estimates. We investigated the feasibility of SWE for human intervertebral disc elasticity mapping in a laboratory setting. BOS172722 To this end, global spinal segment mechanical behavior was determined in 6 loading directions and served as ground truth data for the validation of the approach. Subsequently, the cranial spinal vertebra was removed and shear wave elastographic scans of the IVD were acquired. SWE-measurements were reconstructed into three-dimensional elastographic maps, discretized into distinct IVD regions and correlated with global segment mechanical parameters. SWE-derived Young's modulus estimates were compared among different regions and as a function of their state of degeneration. We found annulus shear wave speed to be moderately correlated with segment mechanical behavior irrespective of the loading direction whereas shear wave speed in the nucleus pulposus showed a very weak association (mean (SD) absolute Pearson correlation coefficients 0.51 (0.14) and 0.17 (0.12), respectively). Young's modulus mapping of the intervertebral disc revealed stiffness to be highest in the ventral annulus with a stiffness decrease both circumferentially towards the dorsal aspect as well as towards the center of the disc. SWE hence provides a valid alternative to disc sectioning and piecewise mechanical testing.

This study examined whether "hang", an extended period of greatly reduced or zero vertical velocity of the head and trunk created by inter-segmental interactions, would be seen during skilled volleyball player spike jumps.

Fifteen skilled volleyball hitters (eight men and seven women, age 23.26±3.22years, height 1.86±0.08m, mass 77.53±10.45kg) performed spike jumps in two hitting conditions, flexing their knees during flight as much as possible and not flexing their knees during flight. We analyzed the effect of knee flexion on the vertical and temporal components of the trajectories of the head, trunk, legs and wrist of the hitting arm to study the existence of "hang" and its underlying mechanisms.

With knee flexion, unlike no knee flexion, the head and trunk (HT) demonstrated "hang", characterized by a longer time of near-zero vertical velocity of the head and trunk near mid-flight (p<0.001). Analysis of the influence of the timing and extent of knee flexion on the HT center of mass trajectory revealed significant effects (p<0.001).Women demonstrated longer "hang" during flight than men. Athletes in this study hit the ball later in flight in the "hang" condition (p<0.001).

An extended period of reduced vertical velocity of the head and trunk near mid-flight resulted from knee flexion and then extension. This additional time at the peak of the jump could be useful to adjust to ball trajectory and to decide where, when and how to hit the ball.

An extended period of reduced vertical velocity of the head and trunk near mid-flight resulted from knee flexion and then extension. This additional time at the peak of the jump could be useful to adjust to ball trajectory and to decide where, when and how to hit the ball.Sea lice adhere to the body surface of host fish with a cephalothoracic sucker. Caligus adheres to this substrate using legs 2 and 3, and the action of cephalothoracic muscles. Lunules, small, paired, anterior sucker-like structures, have a vital function in the initial step of adhering and contain a unique endocuticule containing elements that may behave like active matter and serve as the actuating mechanism. Cuticular membranes bordering the cephalothorax have a unique endocuticule with an undulating dorsal surface and a smooth ventral surface. A high-speed camera revealed that this undulation likely facilitates rapid automatic application of the sucker to the substrate. The cuticular membranes on the posterior margin of the first exopodal segment of leg 2 have a specialized endocuticle with tubules each surrounded by fine fibers. This reinforcement helps them to generate a posteriorly-directed jet of water. Opening-closing of these membranes is controlled by postero-anterior motion of the distal exopodal segments of leg 2.