Mark A. Scott

Learning from demonstrations: the role of visual search during observational learning from video and point-light models

In this study, we examined the visual search strategies used during observation of video and point-light display models. We also assessed the relative effectiveness of video and point-light models in facilitating the learning of task outcomes and movement patterns. Twenty-one female novice soccer players were divided equally into video, point-light display and no-model (control) groups. Participants chipped a soccer ball onto a target area from which radial and variable error scores were taken. Kinematic data were also recorded using an opto-electrical system. Both a pre- and post-test were performed, interspersed with three periods of acquisition and observation of the model. A retention test was completed 2 days after the post-test. There was a significant main effect for test period for outcome accuracy and variability, but observation of a model did not facilitate outcome-based learning. Participants observing the models acquired a global movement pattern that was closer to that of the model than the controls, although they did not acquire the local relations in the movement pattern, evidenced by joint range of motion and angle-angle plots. There were no significant differences in learning between the pointlight display and video groups. The point-light display model group used a more selective visual search pattern than the video model group, while both groups became more selective with successive trials and observation periods. The results are discussed in the context of Newells hierarchy of coordination and control and Scully and Newells visual perception perspective.

Body composition of English Premier League soccer players: Influence of playing position, international status, and ethnicity

Abstract Body composition is a key consideration in the physical make-up of professional soccer players. The aims of the present study were to determine whether the body composition of professional soccer players varied according to playing position, international status or ethnicity, and to establish which variables best distinguished the soccer players from a reference group. Body composition was assessed using dual-energy X-ray absorptiometry in 64 male professional soccer players. Measured variables included bone mineral density and the relative amounts of lean and fat mass. Data were analysed using analysis of variance and stepwise discriminant function. The soccer players recorded better values than a reference group (n = 24) for all body composition compartments. Percent lean mass and bone mineral density were the variables best able to identify the soccer players (95.5% correctly classified). Differences in body composition were evident between goalkeepers and outfield players, but not between outfield playing positions. No differences were found on the basis of international status. The non-Caucasian players demonstrated significantly lower percent body fat (9.2 ± 2.0%) than the Caucasian players (10.7 ± 1.8%). It was concluded that body composition is important for elite soccer players, but that homogeneity between players at top professional clubs results in little variation between individuals.

Expertise and the regulation of gait in the approach phase of the long jump.

In the approach phase of the long jump, athletes attempt to strike the take-off board accurately with minimum loss of speed, and in an optimum body position for take-off. Previous research has shown that skilled long jumpers demonstrate an ascending-descending trend of variability rather than a consistent pattern of foot placement over trials. The present study examined whether non-long jumpers showed a similar pattern of variability in footfall placement between trials to skilled long jumpers. Consistency of foot placement over trials for non-long jumpers (n = 11) was determined using a panned video camera. Digitization of the foot position provided toe-board distances during the run-up phase. Our results showed that non-long jumpers have a similar pattern of descending variability near to the take-off board to expert long jumpers, suggesting the use of visual regulation. However, in comparison to more skilled subjects, non-long jumpers accumulated a considerably larger maximum mean standard deviation in footfall placement between trials (58 cm). Since non-long jumpers had no previous task-specific training, these data extend our current understanding of the regulation of goal-directed gait.

Quantification of the typical weekly in-season training load in elite junior soccer players

Abstract We examined the typical weekly training load experienced by elite junior soccer players during the in-season competitive period. Altogether, eight under-14 (U14), eight under-16 (U16) and eight under-18 (U18) players were monitored over a 2-week period during the first month of the 2010–11 competitive season. This time period included one competitive match per week. Physiological loading was monitored using heart rate (HR) and ratings of perceived exertion (RPE). Training and match loads were calculated by multiplying the global session RPE and duration (session-RPE). Total weekly training load (training and match) increased with age (U14, 2524 ± 128 arbitrary units [AU]; U16, 2919 ± 136 AU; U18, 3948 ± 222 AU; P < 0.05). Differences in the daily training load across the training week were also evident in the older age group relative to both U14 and U16. The amount of time engaged in low (<50% HRmax) and high (>90% HRmax) intensity activity during training and match-play was significantly lower and higher respectively in the U18 compared to the U14 group (P < 0.05). When comparing activity, the intensity (% HRmax) of field training (U18, 69 ± 2%; U16, 74 ± 1%; U14, 74 ± 2%) was significantly lower compared to match-play (U18, 81 ± 3%; U16, 84, ± 2%; U14, 83 ± 2) across all age groups (P < 0.05). Findings demonstrate that age related differences in the volume and intensity of weekly in-season training load are evident amongst elite professional junior soccer players. These differences may reflect a systematic approach to the long-term physical development of elite junior players.

The efficacy of demonstrations in teaching children an unfamiliar movement skill: The effects of object-orientated actions and point-light demonstrations

Abstract In Experiment 1, adult and child participants were instructed to imitate a video model performing a bowling action with or without a ball. Participants imitated the action with greater accuracy without a ball and in general adults were more accurate than children. In Experiment 2, adults and children were shown a video or point-light display of the bowling action. There was no difference in movement form between the adult point-light and video groups. In contrast, children were poorer at reproducing the action when viewing point-light compared with video sequences (P < 0.05). The novel point-light display hindered the childrens ability to provide conceptual mediation between the presented information and action requirements. In Experiment 3, a child point-light group was provided with perceptual-cognitive training. The perceptual-cognitive training group demonstrated better movement reproduction than a group who viewed the point-light displays with no training (P < 0.05), although there were no differences between participants who received training and those who viewed a video. Children are able to perceive and use relative motion information from a display after some general training, and the effectiveness of demonstrations needs to be judged relative to the task context.

Age-related differences in vision and proprioception in a lower limb interceptive task: the effects of skill level and practice.

Abstract This study examined age-related differences in the role of visual proprioception during a lower limb interceptive action and how this varies as a function of skill and practice. In Experiment 1, skilled and less-skilled 8-, 10-, and 12-year-old boys controlled a soccer ball using their preferred foot under full vision and when sight of the effector was occluded. With the exception of the high-skilled 12-year-olds and low-skilled 8-year-olds, participants showed a decrement in performance when denied access to visual proprioception. In Experiment 2, the effect of practicing under different informational constraints was examined for 12 year-old boys. Children performed varying amounts of practice under full vision, or in a condition where sight of the foot was occluded, before being transferred to the alternative viewing condition. Participants who practiced under occluded viewing conditions showed greater relative improvement in performance over practice and transfer sessions compared with a full vision control group. Some support is provided for the manipulation of visual informational constraints as an effective pedagogical approach to motor learning.

How Well do Skinfold Equations Predict Percent Body Fat in Elite Soccer Players

The use of generic equations for estimating percent body fat from skinfold thicknesses can be criticised when applied to specific sports. The present aims were to compare existing methods of using skinfold data and to derive an equation for predicting body fat values in professional soccer players. Forty-five professional soccer players (24.2 +/- 5.0 years; 82.0 +/- 8.5 kg; 1.82 +/- 0.07 m) participated. Skinfold thicknesses were assessed at eight sites for the application of existing prediction equations. Skinfold data were also utilised to determine a novel soccer-specific equation. All players had a reference estimate of percent fat by dual-energy x-ray absorptiometry (DXA). The existing skinfold equations differed from the DXA-referenced values by varying degrees, the equation of Withers et al. (1987) demonstrating the lowest bias and highest relationship and agreement with DXA. Regression analysis resulted in an equation incorporating anterior thigh, abdominal, triceps and medial calf sites, accounting for 78.4% variance in DXA criterion values.

Transfer and motor skill learning in association football

Transfer of learning involves the influence of previous experiences on the performance or learning of new skills. It is defined as a gain (or loss) in the capability for performance on one task as a result of practice on another. The aim of the study was to examine the degree of transfer between various association football skills. Twenty intermediate male players participated in the study. During pre- and post-training tests, participants juggled a football as many times as possible within 30 s using feet or knees. Further tests required participants to control an approaching football inside a restricted area using the preferred and non-preferred kicking leg. Following performance on the pretest, two matched skill groups were obtained. One group participated in a 4-week training period in which feet-only ball juggling was practised for 10 min daily, while the remaining group acted as a control. Trained participants exhibited superior post-test performance on knee juggling and ball control with preferred and non-preferred leg tasks relative to the control group (p< 0.05). Findings indicate positive transfer of learning from juggling practice with the feet to juggling with the knees and a football control task. Implications for theory and practice are highlighted.

Demonstration as a rate enhancer to changes in coordination during early skill acquisition

Abstract We compared the nature and rate of change in intra-limb coordination in participants who observed a video model (model) with those who practised based on verbal guidance only (control). Sixteen male novices threw a ball towards a target with maximal velocity using a back-handed, reverse baseball pitch. Participants in the model group immediately changed their intra-limb relative motion to more closely resemble the models relative motion pattern. This new coordination pattern, and concomitant changes in ball speed, was maintained throughout acquisition, without further change. In contrast, the control group showed no change in coordination or ball speed across acquisition. Our findings suggest that demonstrations act as a rate enhancer, conveying an immediate movement solution that is adopted early in acquisition. A model may constrain the learner to perceive and imitate the models relative motion pattern as suggested by Scully and Newell (1985). The stability of this new movement pattern questions accounts of learning, which suggest that prescriptive, directed learning may result in the “soft assembly” of an inaccurate and temporary movement solution.

Movement Deviation Profile: A measure of distance from normality using a self-organizing neural network

We introduce the Movement Deviation Profile (MDP), which is a single curve showing the deviation of an individuals movement from normality. Joint angles, recorded from typically developing children over one gait cycle, were used to train a self-organizing map (SOM) which then generated MDP curves for patients with gait problems. The mean MDP over the gait cycle showed a high correlation (r(2) = .927) with the Gait Deviation Index (GDI), a statistically significant difference between groups of patients with a range of functional levels (Gillette Functional Assessment Questionnaire Walking Scale 7-10) and a trend of increasing values for patients with cerebral palsy through hemiplegia I-IV, diplegia, triplegia, and quadriplegia. The small difference between the MDP and GDI can be explained by the SOMs method of operation comparing biomechanical patterns to the nearest abstract reference pattern, and its flexibility to compensate for temporal shifts in movement data. The MDP is an alternative method of processing complex biomechanical data, potentially supporting clinical interpretation. The electronic addendum accompanying this article is a standalone program, which can be used to calculate the MDP from gait data, and can also be used in other applications where the deviation of multi-channel temporal data from a reference is required.