DROP JUMPS OR HURDLE JUMPING FOR VOLLEYBALL TRAlNlNG ?

Drop jumps and hurdle jumping are drills widely used in volleyball training. Selection of dropping height or hurdle jumping technique has often been based on traditions rather than detailed biomechanical analysis. This study was designed to compare volleyball spiking and blocking with the jumping drills mentioned above in relation to various kinematic and kinetic parameters and myoelectrical activity (EMG). Ten volleyball players ranging in age from 20 to 26 years with an average volleyball playing and training background of eight years volunteered as subjects. After warming up the subjects performed with maximal effort a total of 60 spikes, blocks and various jumping drills with a 30 s interval between each separate activity. The spikes were step-close and hop spikes, and the blocks were performed with and without side steps. The drop jumps (DJ) were performed from heights of 0.25 m, 0.45 m, 0.55 m and 0.85 m. The hurdles (height 1.0 m) were arranged so that the jrmpng was performed both with bilateral foot contacts with no steps between the hurdles and with one step between the hurdles. All takeoffs and landings were performed on force platforms so that three-dimensional ground reaction forces as well as contact and flight times could be measured for each jump. An electrical goniometer was used to detect knee angle data and EMG activity was registered from the knee, hip and ankle extensor and knee flexor musculature using surface electrodes. The block jumps showed the longest total contact times (337 -. 589 ms), followed by the spikes and hurdle jumping (254 - 329 ms) and the drop jumps (212 - 225 ms). Average eccentric ground reaction forces increased with dropping height (from 3177 to 4194 N) and were higher than for the hurdle jumping (21 15 - 3108 N), spike (2364 - 3005 N) or block jumps (1243 - 2219 N). During the eccentric phase of contact average knee angular velocity varied between 2.8 rad/s (block) and 5.3 rad/s (DJ05) and during the concentric phase of contact between 6.5 rad/s (block) and 9.1 rad/s (~145). Eccentric EMG activity in the drop jumps and hurdle jumping remained at the same level as in the spike jumps, while during the concentric phase, EMG activity in the hurdle jumping did not reach the levels measured during the spike, block and drop jumps. It is concluded that the utilisation of dropping above 0.45 m leads to high eccentric forces, which compared to hurdle jumping or to jumps performed from lower drop heights appear to yield no additional benefit in volleyball training and may actually have injurious effects on players

The Origin And Loss Of Periodic Patterning In The Turtle Shell

The origin of the turtle shell over 200 million years ago greatly modified the amniote body plan, and the morphological plasticity of the shell has promoted the adaptive radiation of turtles. The shell, comprising a dorsal carapace and a ventral plastron, is a layered structure formed by basal endochondral axial skeletal elements (ribs, vertebrae) and plates of bone, which are overlain by keratinous ectodermal scutes. Studies of turtle development have mostly focused on the bones of the shell; however, the genetic regulation of the epidermal scutes has not been investigated. Here, we show that scutes develop from an array of patterned placodes and that these placodes are absent from a soft-shelled turtle in which scutes were lost secondarily. Experimentally inhibiting Shh, Bmp or Fgf signaling results in the disruption of the placodal pattern. Finally, a computational model is used to show how two coupled reaction-diffusion systems reproduce both natural and abnormal variation in turtle scutes. Taken together, these placodal signaling centers are likely to represent developmental modules that are responsible for the evolution of scutes in turtles, and the regulation of these centers has allowed for the diversification of the turtle shell

Visualizing multi-dimensional pareto-optimal fronts with a 3D virtual reality system

In multiobjective optimization, there are several targets that are in conflict, and thus they all cannot reach their optimum simultaneously. Hence, the solutions of the problem form a set of compromised trade-off solutions (a Pareto-optimal front or Pareto-optimal solutions) from which the best solution for the particular problem can be chosen. However, finding that best compromise solution is not an easy task for the human mind. Pareto-optimal fronts are often visualized for this purpose because in this way a comparison between solutions according to their location on the Pareto-optimal front becomes somewhat easier. Visualizing a Pareto-optimal front is straightforward when there are only two targets (or objective functions), but visualizing a front for more than two objective functions becomes a difficult task. In this paper, we introduce a new and innovative method of using three-dimensional virtual reality (VR) facilities to present multi-dimensional Pareto-optimal fronts. Rotation, zooming and other navigation possibilities of VR facilities make easy to compare different trade-off solutions, and fewer solutions need to be explored in order to understand the interrelationships among conflicting objective functions. In addition, it can be used to highlight and characterize interesting features of specific Pareto-optimal solutions, such as whether a particular solution is close to a constraint boundary or whether a solution lies on a relatively steep trade-off region. Based on these additional visual aids for analyzing trade-off solutions, a preferred compromise solution may be easier to choose than by other means

The effect of landscape structure on dispersal distances of the Eurasian red squirrel

Landscape structure can affect dispersal and gene flow in a species. In urban areas, buildings, roads, and small habitat patches make the landscape highly fragmented and can inhibit movement and affect dispersal behavior. Similarly, in rural forested areas, large open areas, such as fields, may act as barriers to movement. We studied how landscape structure affects natal dispersal distances of Eurasian red squirrels (Sciurus vulgaris) in an urban area and a rural area in Finland, by monitoring juvenile red squirrels with radio telemetry. We observed extremely long dispersal distancesup to 16kmin the rural study area, but shorter distanceson average only half a kilometerin the urban study area. The landscape structure affected the eventual dispersal paths; in the rural landscape, dispersers favored spruce dominated areas and avoided fields along their dispersal route, although they occasionally even crossed wide fields. In the urban landscape, squirrels preferred areas with deciduous or coniferous trees. The movement steps made by dispersers were longer in the more hostile landscape compared to forested areas. Despite these effects on movement path, the landscape structure only had a minor effect on straight line dispersal distances moved from the natal nest. In other words, individuals moved longer distances and were likely to circumvent barriers in their path, but this did not affect how far they settled from their natal home. This result indicates that, although landscape structure has obvious effects on movement, it still may have only a small effect on other aspects of the population, for example, gene flow

Nitrous oxide fluxes from tropical peat with different disturbance history and management

Peer reviewe

The biological activity of serum bacterial lipopolysaccharides associates with disease activity and likelihood of achieving remission in patients with rheumatoid arthritis

Peer reviewe

The biological activity of serum bacterial lipopolysaccharides associates with disease activity and likelihood of achieving remission in patients with rheumatoid arthritis

Peer reviewe