Eric Berton

Judging where a ball will go: the case of curved free kicks in football

This study examined whether adding spin to a ball in the free kick situation in football affects a professional footballer’s perception of the ball’s future arrival position. Using a virtual reality set-up, participants observed the flight paths of aerodynamically realistic free kicks with (±600xa0rpm) and without sidespin. With the viewpoint being fixed in the centre of the goal, participants had to judge whether the ball would have ended up in the goal or not. Results show that trajectories influenced by the Magnus force caused by sidespin gave rise to a significant shift in the percentage of goal responses. The resulting acceleration that causes the ball to continually change its heading direction as the trajectory unfolds does not seem to be taken into account by the participants when making goal judgments. We conclude that the visual system is not attuned to such accelerated motion, which may explain why goalkeepers appear to misjudge the future arrival point of such curved free kicks.

Influence of additional load on the moments of the agonist and antagonist muscle groups at the knee joint during closed chain exercise

The present study investigated the influence of additional loads on the knee net joint moment, flexor and extensor muscle group moments, and cocontraction index during a closed chain exercise. Loads of 8, 28, or 48 kg (i.e., respectively, 11.1+/-1.5%, 38.8+/-5.3%, and 66.4+/-9.0% of body mass) were added to subjects during dynamic half squats. The flexor and extensor muscular moments and the amount of cocontraction were estimated at the knee joint using an EMG-and-optimization model that includes kinematics, ground reaction, and EMG measurements as inputs. In general, our results showed a significant influence of the Load factor on the net knee joint moment, the extensor muscular moment, and the flexor muscle group moment (all Anova p<.05). Hence we confirmed an increase in muscle moments with increasing load and moreover, we also showed an original more than proportional evolution of the flexor and extensor muscle group moments relative to the knee net joint moment. An influence of the Phase (i.e., descent vs. ascent) factor was also seen, revealing different activation strategies from the central nervous system depending on the mode of contraction of the agonist muscle group. The results of the present work could find applications in clinical fields, especially for rehabilitation protocols.

Optic variables used to judge future ball arrival position in expert and novice soccer players

Although many studies have looked at the perceptual—cognitive strategies used to make anticipatory judgments in sport, few have examined the informational invariants that our visual system may be attuned to. Using immersive interactive virtual reality to simulate the aerodynamics of the trajectory of a ball with and without sidespin, the present study examined the ability of expert and novice soccer players to make judgments about the ball’s future arrival position. An analysis of their judgment responses showed how participants were strongly influenced by the ball’s trajectory. The changes in trajectory caused by sidespin led to erroneous predictions about the ball’s future arrival position. An analysis of potential informational variables that could explain these results points to the use of a first-order compound variable combining optical expansion and optical displacement.

Effect of object width on precision grip force and finger posture.

This study aimed to define the effect of object width on spontaneous grasp. Participants held objects of various masses (0.75 to 2.25 kg) and widths (3.5 to 9.5 cm) between thumb and index finger. Grip force, maximal grip force and corresponding finger postures were recorded using an embedded force sensor and an optoelectronic system, respectively. Results showed that index finger joints varied to accommodate the object width, whereas thumb posture remained constant across conditions. For a given object mass, grip force increased as a function of object width, although this result is not dictated by the laws of mechanics. Because maximal grip force also increased with object width, we hypothesise that participants maintain a constant ratio between grip force and their maximal grip force at each given width. Altogether we conclude that when the task consists in manipulating objects/tools, the optimal width is different than when maximal force exertions are required.

An Integrated Approach toward Testing Sports Equipment (P260)

Recent improvements in material technology, together with generalization of testing, prototyping, and benchmarking, have impacted on performance in many sports. However, sports equipment properties are often tested through mechanically based standardized protocols. Such protocols would ignore the effects on equipment resulting from mechanically unpredicted manoeuvres performed by athletes aiming for performance, injury protection or comfort. Their use may thus turn out to be of limited use in the evolution of sports equipments towards perfection, as a first-rate equipment is not only the one including high-tech materials but also the one interacting in the best way with the athlete using it.

Effect of additional loads on torques during giant swing on the high bar

In Artistic Gymnastics the backward giant circle on the high bar is used to generate the angular momentum that the gymnast needs to perform certain release-regrasp and dismount skills. Due to muscle and joint redundancy, many different techniques could be used to perform this skill (Bernstein 1967). Yeadon and Hiley (2000) suggested that the choice of a particular technique could be due to limitations on the maximal torques that can be generated at the shoulder and hip joints. In order to test Yeadon’s hypothesis, one could increase the torques produced either at the shoulder or the hip joint to a level higher than that required to perform the task. To reach this objective, the present work used additional loads attached to the gymnast’s upper limbs, torso or lower limbs. In case Yeadon and Hiley’s hypothesis is confirmed, modification of kinematics should be observed depending on the load and it’s location.

Influence of object shape on musculoskeletal forces during grasping

Grasping an object for a precision task can be achieved with infinite configurations of joint angles and muscle forces that the central nervous system has to coordinate. This works aimed at studying how an object mass and width can affect the musculoskeletal organization and the repercussions it can have on potential injuries. To reach this objective, a 3D biomechanical modelling is proposed to determine the forces exerted in the thumb and index finger muscles during grasping an object. A static index/thumb pinching task was chosen as a generic example of common mode of object manipulations.

Effect of load on agonist and antagonist muscle moments during dynamic squats

More than simply increasing the activity of muscles, cocontraction has been reported to enhance movement accuracy as well as joint stability. Due to the indeterminacy associated to the estimation of agonist and antagonist moments, most of the studies regarding cocontraction are based upon EMG analysis, leading to possible meaningless results because of EMG artifacts, especially in dynamic conditions. To better understand the role of co-contraction during human movement, the aim of the present study is to investigate how load influence the co-activation of agonist and antagonist moments at the knee during dynamic half squats.