Angle Of Direction Change Research Articles

The agility demands of Australian football: a notational analysis

ABSTRACT Agility is essential to success in Australian football (AF). However, the nature of agility events in competition is currently unknown. This study analysed in-game 1v1 agility events to identify the movement and cognitive demands of agility in elite AF. The study described the technique, the angle of change of direction (COD), and the approach speed. Cognitive demands were inferred by recording inter-athlete position and deceptive manoeuvres. Findings revealed sidestepping to be commonly used for both attacking and defending athletes. However, attacking athletes were substantially more likely to use the sidestep technique than their defending counterparts (74% vs 39% of the time). Analysis of movement speeds indicated a preference for submaximal approaches. Further, the movement technique was varied, with the angle of directional change particularly diverse. Overall, the notational analysis indicates a need for agility training and testing that reflects in-game agility demands. To achieve this, training and testing must allow for submaximal movement speeds, context-specific techniques, and the use of deceptive manoeuvres. Field-based or subjective assessment methods are proposed as viable testing alternatives. Further, the effectiveness of recorded deceptive actions suggests that athletes should be provided with training opportunities to practice fake disposals and fake CODs.

Forms of direction change during walking and effect on movement and reaction time.

[Purpose] To elucidate factors that affect walking before and after direction changes and their effects on reaction time by investigating different angles of direction changes. [Participants and Methods] A total of 29 healthy young males and females participated in this study. The task was to walk along a 20-m path and perform three direction changes while walking: straight walking, 45° direction change, and 90° direction change. Step length and probe reaction time (P-RT) were measured before and after the point of direction change. A two-factor repeated measures analysis of variance was applied to measure P-RT and step length before and after direction changes. [Results] A significant effect was observed for step length and P-RT immediately before and after direction changes. An interaction was also observed between the angle of direction change and the step length before and after the direction change. When compared with the straight walk, a significant effect was observed at 45° and 90° direction changes. [Conclusion] While walking, 90° direction changes are suggested to be more difficult than 45° direction changes, and 45° direction changes are more difficult than walking in a straight line.

Directional change of tracer trajectories in rotating Rayleigh-Bénard convection.

The angle of directional change of tracer trajectories in rotating Rayleigh-Bénard convection is studied as a function of the time increment τ between two instants of time along the trajectories, both experimentally and with direct numerical simulations. Our aim is to explore the geometrical characterization of flow structures in turbulent convection in a wide range of timescales and how it is affected by background rotation. We find that probability density functions (PDFs) of the angle of directional change θ(t,τ) show similar behavior as found in homogeneous isotropic turbulence, up to the timescale of the large-scale coherent flow structures. The scaling of the averaged (over particles and time) angle of directional change Θ(τ)=〈|θ(t,τ)|〉 with τ shows a transition from the ballistic regime [Θ(τ)∼τ^{c} with c=1] for τ≲τ_{η}, with τ_{η} the Kolmogorov timescale, to a scaling with smaller exponent c for τ_{η}≲τ≲T_{L}, with T_{L} the Lagrangian integral timescale. This scaling exponent is approximately constant in the weakly rotating regime (Rossby number Ro≳2.5) and is decreasing for increasing rotation rates when Ro≲2.5. We show that this trend in the scaling exponent is related with the large-scale coherent structures in the flow; the large-scale circulation for Ro≳2.5 and vertically aligned vortices emerging from the boundary layers (BLs) near the top and bottom plates and penetrating into the bulk for Ro≲2.5. In the viscous BLs, the PDFs of θ(t,τ) and scaling properties of Θ(τ) are in general different from those measured in the bulk and depend on the type of boundary layer, in particular whether the BL is of Prandtl-Blasius type (Ro≳2.5) or of Ekman type (Ro≲2.5). When it is of Ekman type, a stronger dynamic coupling exists between the BL and the bulk of the flow, resulting in similar scaling exponents in BL and bulk.

サイドステップおよびクロスステップによる走方向変換動作のキネマティクス的研究

Although a change in running direction is one of the most important skills for ball game players, there is little information on the techniques involved, and the criteria used for technical evaluation. The purposes of this study were to develop indices for evaluating the techniques involved in changing the direction of running (i.e. cutting motion), and to compare the motions used by skilled and less-skilled groups to gain insight into the cutting motion technique. Twenty male university players of several ball games participated as subjects. They performed three kinds of 30-m zigzag runs with directional changes in angle of 30, 60 and 90 degrees, using the side-step and cross-step techniques. Their motions were videotaped with two digital video cameras operating at 60 Hz for three-dimensional motion analysis. The running time was measured by an electric timing device with photocell sensors. The velocity of the center of gravity (CG), angle of direction change, and angles of shank inward lean and thigh were calculated. We developed a cutting motion index that was calculated from the distance between the CG positions before and after cutting, the horizontal velocity of the CG at the beginning of cutting, and the elapsed time during cutting. The index gives a ratio of the time estimated from the horizontal velocity of the CG at the beginning of cutting relative to the actual elapsed time. The major results are summarized as follows: 1) For zigzag runs except for a 60-degree change in direction in the cross-step technique, there was no significant relationship between the cutting motion index and the angle of direction change. 2) In the side-step technique, the acceleration of the CG, the extension of the knee and hip joints, and the maximal forward lean angular velocity of the thigh in the second support phase were larger in the skilled group than in the less-skilled group. 3) In the cross-step technique, the deceleration of the CG and the flexion of the knee joint were smaller, but the acceleration of the CG and the maximal forward lean angular velocity of the thigh in the second support phase were larger in the skilled group than in the less-skilled group. These results indicate that the technique used to maintain running speed can be evaluated by the cutting motion index, and that the angle of direction change can be used as an index of direction change for the cutting motion. In the side- and cross-step techniques, a fast forward lean of the support thigh in the second support phase is likely to be an effective motion for maintaining the speed of the CG. In the side-step technique, extension of the knee joint in the support phase increases the forward lean angular velocity of the thigh. A fast forward lean of the support leg is effective in the cross-step technique.

Two mechanisms underlying the effect of angle of motion direction change on colour–motion asynchrony

Under appropriate stimulus conditions, judgments about the degree of temporal synchrony in sequences containing rapid alternations of colour and motion direction imply a large apparent delay of motion perception relative to colour perception. Whether this colour–motion asynchrony results from the relative processing delay of different visual attributes, or from inappropriate matching of time markers assigned to first-order change of colour and position has been the subject of recent debate. Colour–motion asynchrony is significantly weakened when the angle of direction change is reduced from 180° (direction reversal) to a smaller change in direction. Although this finding has been interpreted to favour the processing delay hypothesis, here we show that it is consistent with the time marker account. First, the reported dependence on the motion direction angle was particularly strong for random-dot stimuli, but our results indicate that this may reflect the introduction of an artefact, motion streaks, that allows subjects to make a colour–orientation synchrony judgement rather than a colour–motion synchrony judgment for direction change angles other than 180°. Second, when we used streak-free plaid stimuli, a certain amount of angle dependence remained regardless of whether we asked the observers to judge the apparent binding or synchrony of colour and motion direction changes. The degree of direction change also affected reaction times, but the effect of apparent asynchrony for a direct comparison of sequences of 90° and 180° motion direction changes was very small, if at all present. These findings with plaid stimuli are consistent with the time marker account; in that we allow that the direction change angle can affect the time course of the recruitment of neural responses to the new direction of motion, which will have a consequential effect on the temporal location of salient features in the sequence of motion changes.

The Foraging Behavior of Semipalmated Sandpipers in the Upper Bay of Fundy: Stereotyped or Prey-Sensitive?

Videotapes of migrant Semipalmated Sandpipers foraging in the upper Bay of Fundy were analyzed to test for foraging behaviors sensitive to prey density. Over a range of prey densities, both the number of steps sec -1 and probes sec -1 increased with increasing prey density. However, the number of steps between probes was constant over the range of prey densities observed. The average angle of directional change during foraging and the number of turns min -1 were constant despite large differences in prey patchiness.

Processing of information about location during locomotion: Effects of a concurrent task and locomotion patterns

How maintenance of orientation during locomotion in unfamiliar environments is accomplished was investigated by having subjects walk behind a moving light line (1.12 m/sec) in a dark room and, from a stopping point, numerically estimate direction and distance to the starting point. Two linear distances (5.0–8.4 m) and the angle of direction change (45, 90, and 135 deg) were orthogonally varied as 12 locomotion patterns. Eight high‐school students were assigned to each of three conditions, two in which the starting point was invisible, one in which it was visible. In one of the former conditions the subjects counted backwards rapidly during walking. Lower accuracy and longer latency times were found in the counting condition whilst the other two conditions differed only slightly. The results suggested that accurate maintenance of orientation is achieved by recurrent encoding, coordination and decoding of information about direction change and locomotion distance, processes which demand central processing capacity and therefore are interfered with by a concurrent task.