Werner Helsen

The relative age effect in youth soccer across Europe

The potential asymmetries in the birth-date distributions of youth soccer players across ten European countries (2175 age citations) were considered. First, we examined the birth-dates of players representing national youth teams in international competitions. Second, the birth-dates of players representing professional club teams in international youth tournaments were analysed. Kolmogorov-Smirnov tests were used to assess differences between observed and expected birth-date distributions. Regression analyses were employed to examine the relationship between month of birth and number of players in the different samples. The results showed an over-representation of players born in the first quarter of the selection year (from January to March) for all the national youth selections at the under-15 (U-15), U-16, U-17 and U-18 age categories, as well as for the UEFA U-16 tournaments and Meridian Cup. Players with a greater relative age are more likely to be identified as “talented” because of the likely physical advantages they have over their “younger” peers. Some options for reducing the relative age effect are offered.

A multidimensional approach to skilled perception and performance in sport

SUMMARY Three experiments examined the relative importance of attributes determined largely by the eAciency of the visual/central nervous system versus cognitive domain-specific skills, in the determination of expertise in soccer. In Experiment 1, expert and intermediate soccer players were assessed on various non-specific abilities including: processing (simple reaction time, peripheral reaction time, visual correction time), optometric (static, dynamic and mesopic acuity), and perimetric parameters (horizontal and vertical peripheral range). In Experiment 2, domain-specific variables were assessed including complex decision speed and accuracy, number of visual fixations, fixation duration, and fixation location in solving game problems. Stimuli were initially presented by slides (Experiment 2) and later by 16 mm film (Experiment 3). Eye movements were recorded and analysed. A stepwise discriminant analysis of both non-specific abilities and soccer-specific skills revealed an average squared canonical correlationa 0.84, with the significant step variables all being domain-specific skills. Copyright # 1999 John Wiley & Sons, Ltd.

The influence of relative age on success and dropout in male soccer players

The consistent asymmetry in the birth‐date distribution of senior professional soccer players has led us to investigate whether similar asymmetries emerge throughout youth categories in soccer. Birth dates were considered for professional players, national youth teams, youth players transferred to top teams, and regular youth league players. Kolmogorov Smirnov tests assessed differences between observed and expected birth‐date distributions. Regression analyses examined the relationship between month of birth and number of participants at various levels of play in soccer. Results indicated that youth players born from August to October (the early part of the selection year), beginning in the 6–8 year age group, are more likely to be identified as talented and to be exposed to higher levels of coaching. Eventually, these players are more likely to be transferred to top teams, to play for national teams, and to become involved professionally. In comparison, players born late in the selection year tended to dropout as early as 12 years of age. Recommendations suggest a review of the 24‐month age band and current methods for talent detection and selection. Am. J. Hum. Biol. 10:791–798, 1998.

Chapter 7 The Relationship between Expertise and Visual Information Processing in Sport

Publisher Summary This chapter explains the differences between experts and nonexperts in processing the acquired visual information by means of more cognitive, “software” dimensions. It is shown that expertise in more cognitive domains, such as chess or the solving of mathematical problems, is based on the acquisition of, the rapid access to, and the efficient use of semantically rich and, therefore, complicated networks of domain-specific declarative and procedural knowledge. From this theoretical background, the question is posed whether experts in a particular sport discipline differ from nonexperts in the amount and the type of knowledge they possess and in the way the information is processed. These studies have attempted to compare the knowledge base of experts and nonexperts within particular skill domains. To obtain better insight into problem-solving skills and processes in the acquisition of expertise in a sport discipline, a conceptual framework is sketched based on research on the acquisition of expertise in explicitly cognitive problem-solving tasks, such as chess or the solving of mathematical problems. The results of the sport-specific tasks provide insight into the knowledge structure of players with differing experiential background and how changes occur as a result of increasing expertise. Both the construction of declarative knowledge and the ability to “compile” and “tuning” are considered as “software” attributes. They can be studied by means of the indirect and direct paradigms and research techniques.

Effect of a change in selection year on success in male soccer players.

Since 1997 and following the guidelines of the International Football Association, the Belgian Soccer Federation has used January 1st as the start of the selection year. Previously, August 1 was the start. This shift prompted an investigation of changes in birth‐date distributions throughout youth categories for 1996–1997 compared to the 1997–1998 competitive years. Birth dates were considered for national youth league players, ages 10–12, 12–14, 14–16, and 16–18 years. Kolmogorov Smirnov tests assessed differences between observed and expected birth‐date distributions. Regression analyses examined the relationship between month of birth and number of participants both before and after the August to January shift. Results indicated that from 1996 to 1997, youth players born from January to March (the early part of the new selection year) were more likely to be identified as “talented” and to be exposed to higher levels of coaching. In comparison, players born late in the new selection year (August to October) were assessed as “talented” in significantly lower proportions. Specific suggestions are presented to reduce the relative age effect. Am. J. Hum. Biol. 12:729–735, 2000.

Eye-hand coordination in goal-directed aiming.

In a number of studies, we have demonstrated that the spatial-temporal coupling of eye and hand movements is optimal for the pickup of visual information about the position of the hand and the target late in the hands trajectory. Several experiments designed to examine temporal coupling have shown that the eyes arrive at the target area concurrently with the hand achieving peak acceleration. Between the time the hand reached peak velocity and the end of the movement, increased variability in the position of the shoulder and the elbow was accompanied by a decreased spatial variability in the hand. Presumably, this reduction in variability was due to the use of retinal and extra-retinal information about the relative positions of the eye, hand and target. However, the hand does not appear to be a slave to the eye. For example, we have been able to decouple eye movements and hand movements using Müller-Lyer configurations as targets. Predictable bias, found in primary and corrective saccadic eye movements, was not found for hand movements, if on-line visual information about the target was available during aiming. That is, the hand remained accurate even when the eye had a tendency to undershoot or overshoot the target position. However, biases of the hand were evident, at least in the initial portion of an aiming movement, when vision of the target was removed and vision of the hand remained. These findings accent the versatility of human motor control and have implications for current models of visual processing and limb control.

Coupling of Eye, Finger, Elbow, and Shoulder Movements During Manual Aiming

Abstract Temporal and spatial coupling of point of gaze (PG) and movements of the finger, elbow, and shoulder during a speeded aiming task were examined. Ten participants completed 40-cm aiming movements with the right arm, in a situation that allowed free movement of the eyes, head, arm, and trunk. On the majority of trials, a large initial saccade undershot the target slightly, and 1 or more smaller corrective saccades brought the eyes to the target position. The finger, elbow, and shoulder exhibited a similar pattern of undershooting their final positions, followed by small corrective movements. Eye movements usually preceded limb movements, and the eyes always arrived at the target well in advance of the finger. There was a clear temporal coupling between primary saccade completion and peak acceleration of the finger, elbow, and shoulder. The initiation of limb-segment movement usually occurred in a proximal-to-distal pattern. Increased variability in elbow and shoulder position as the movement progressed may have served to reduce variability in finger position. The spatial-temporal coupling of PG with the 3 limb segments was optimal for the pick up of visual information about the position of the finger and the target late in the movement.

Temporal and spatial coupling of point of gaze and hand movements in aiming.

Temporal and spatial coordination of both point of gaze (PG) and hand kinematics in a speeded aiming task toward an eccentrically positioned visual target were examined with the Optotrak 3D movement analysis system in tandem with the ASL head-mounted eye tracker. Subjects (N = 10) moved eyes, head, hand, and trunk freely. On the majority of trials, the PG pattern was a large initial saccade that undershot the target slightly, then 1 or more smaller corrective saccades to reach the target. The hand exhibited a similar pattern of first undershooting the target and then making small corrective movements. Previously (W. F. Helsen, J. L. Starkes, & M. J. Buekers, 1997), the ratio of PG and total hand response time (50%) was found to be an invariant feature of the movement. In line with those results, a striking temporal coupling was found between completion of the primary eye saccade and time to peak acceleration for the limb. Spatially, peak hand velocity coincided with completion of 50% of total movement distance. Those findings support a 2-component model of limb control.

The Impact of Specific High-Intensity Training Sessions on Football Referees’ Fitness Levels:

Background In comparison to the amount of literature that has examined the match demands of football refereeing, there has been little attempt to assess the impact of high-intensity training. Purpose The main goals were to get a better understanding of the long-term effect of specific intermittent training. Study Design The authors examined the cardiovascular strain of specific high-intensity training sessions and also their impact on referees’ fitness levels. Methods To examine the physical workload during intensive intermittent training sessions, heart rates were recorded and analyzed relative to the referees’ maximum heart rate (HRmax). To assess the referees’ fitness levels, the Yo-Yo intermittent recovery test was used. Results Both the pitch- and track-training sessions were successful in imposing an appropriate high intensity load on the referees, at 86.4 ± 2.9% and 88.2 ± 2.4% HRmax, respectively. Following 16 months of intermittent high-intensity training, referees improved their performance on the Yo-Yo intermittent recovery test by 46.5%, to a level that is comparable with professional players. Conclusions As match officials are subjected to a high physical load during matches, they should follow structured weekly training plans that have an emphasis on intensive, intermittent training sessions.

Recognizing Biological Motion and Emotions from Point-Light Displays in Autism Spectrum Disorders

One of the main characteristics of Autism Spectrum Disorder (ASD) are problems with social interaction and communication. Here, we explored ASD-related alterations in ‘reading’ body language of other humans. Accuracy and reaction times were assessed from two observational tasks involving the recognition of ‘biological motion’ and ‘emotions’ from point-light displays (PLDs). Eye movements were recorded during the completion of the tests. Results indicated that typically developed-participants were more accurate than ASD-subjects in recognizing biological motion or emotions from PLDs. No accuracy differences were revealed on two control-tasks (involving the indication of color-changes in the moving point-lights). Group differences in reaction times existed on all tasks, but effect sizes were higher for the biological and emotion recognition tasks. Biological motion recognition abilities were related to a person’s ability to recognize emotions from PLDs. However, ASD-related atypicalities in emotion recognition could not entirely be attributed to more basic deficits in biological motion recognition, suggesting an additional ASD-specific deficit in recognizing the emotional dimension of the point light displays. Eye movements were assessed during the completion of tasks and results indicated that ASD-participants generally produced more saccades and shorter fixation-durations compared to the control-group. However, especially for emotion recognition, these altered eye movements were associated with reductions in task-performance.