Alexander P. Willmott

The planarity of the stickface motion in the field hockey hit

Abstract The field hockey hit is an important but poorly understood stroke. In this study, we investigated the planarity of the stickface motion during the downswing to better characterize the kinematics and to assess the suitability of planar pendulum models for simulating the hit. Thirteen experienced female field hockey players were filmed executing hits with a single approach step, and the kinematics of the centre of the stickface were measured. A method was developed for identifying how far back from impact the stickface motion was planar. Orthogonal regression was used to fit least-squares planes to the stickface path during sections of the downswing of varying length, with each section ending at impact. A section was considered planar if the root mean square residual between the stickface path and the fitted plane was less than 0.25% of the distance travelled by the stickface during that period. On average, the stickface motion was planar for the last 83 ± 12% of its downswing path, with the length of the planar section ranging from 1.85 m to 2.70 m. The suitability of a planar model for the stickface motion was supported, but further investigation of the stick and arm kinematics is warranted.

Kicking foot swing planes and support leg kinematics in rugby place kicking: Differences between accurate and inaccurate kickers

Abstract Place kicking is a complex whole-body movement that contributes 45% of the points scored in international Rugby Union. This study compared the kicking foot swing plane characteristics of accurate and inaccurate kickers, underpinned by differences in their support leg and pelvis kinematics at support foot contact, to identify key technique characteristics. Motion capture data (240 Hz) were collected from 33 experienced kickers, and distinct groups of accurate (n = 18) and inaccurate (n = 8) kickers were identified based on their performance characteristics. All accurate kickers were capable of kicking successfully from at least 33.3 m, whereas all inaccurate kickers would have missed left from distances greater than 30.7 m. The accurate group exhibited a moderately shallower swing plane inclination (50.6 ± 4.8° vs. 54.3 ± 2.1°) and directed the plane moderately further to the right of the target (20.2 ± 5.4° vs. 16.7 ± 4.1°). At support foot contact, the accurate group placed their support foot moderately less far behind the ball (0.08 ± 0.08 m vs. 0.12 ± 0.04 m) and positioned their centre of mass moderately further to the support leg side (0.77 ± 0.07 m vs. 0.72 ± 0.01 m) due to a moderately greater stance leg lean (29.3 ± 4.1° vs. 26.8 ± 3.2°). The kicking foot swing plane is highly planar in rugby place kicking but its orientation differs between accurate and inaccurate kickers. These plane characteristics may be controlled by support foot placement and support leg and pelvis kinematics at support foot contact.

Sociability modifies dogs’ sensitivity to biological motion of different social relevance

Preferential attention to living creatures is believed to be an intrinsic capacity of the visual system of several species, with perception of biological motion often studied and, in humans, it correlates with social cognitive performance. Although domestic dogs are exceptionally attentive to human social cues, it is unknown whether their sociability is associated with sensitivity to conspecific and heterospecific biological motion cues of different social relevance. We recorded video clips of point-light displays depicting a human or dog walking in either frontal or lateral view. In a preferential looking paradigm, dogs spontaneously viewed 16 paired point-light displays showing combinations of normal/inverted (control condition), human/dog and frontal/lateral views. Overall, dogs looked significantly longer at frontal human point-light display versus the inverted control, probably due to its clearer social/biological relevance. Dogs’ sociability, assessed through owner-completed questionnaires, further revealed that low-sociability dogs preferred the lateral point-light display view, whereas high-sociability dogs preferred the frontal view. Clearly, dogs can recognize biological motion, but their preference is influenced by their sociability and the stimulus salience, implying biological motion perception may reflect aspects of dogs’ social cognition.

Modelling error distribution in the ground reaction force during an induced-acceleration analysis of running in rear-foot strikers

ABSTRACT The objective of this study was to develop and evaluate a methodology for quantifying the contributions of modelling error terms, as well as individual joint torque, gravitational force and motion-dependent terms, to the generation of ground reaction force (GRF), whose true value can be measured with high accuracy using a force platform. Dynamic contributions to the GRF were derived from the combination of (1) the equations of motion for the individual segments, (2) the equations for constraint conditions arising from the connection of adjacent segments at joints, and (3) the equations for anatomical constraint axes at certain joints. The contribution of the error term was divided into four components caused by fluctuation of segment lengths, geometric variation in the constraint joint axes, and residual joint force and moment errors. The proposed methodology was applied to the running motion of thirteen rear-foot strikers at a constant speed of 3.3 m/s. Modelling errors arose primarily from fluctuations in support leg segment lengths and rapid movement of the virtual joint between the foot and ground during the first 20% of stance phase. The magnitudes of these error contributions to the vertical and anterior/posterior components of the GRF are presented alongside the non-error contributions, of which the joint torque term was the largest.

Using Marker-Based Motion Capture to Develop a Head Bobbing Robotic Lizard

Robotic animals are regularly used in behavioral experiments, typically in experimental interactions with individuals of the species they were modelled on. In order to do so successfully, these robots need to be designed carefully, taking into consideration the specific perceptual system of the model species. We used marker-based motion capture to measure head bobbing in a widely popular lizard species, bearded dragons, and found that head bobbing is highly stereotypic yet differs subtly when displayed towards males and females. These results were then used for the construction of a robotic lizard, with the aim to use it in behavioral and cognitive studies, focusing on social cognition. This is the first study to use motion capture of head bobbing in lizards to inform the design of a robotic animal.