Search Results

You are looking at 1 - 10 of 12 items for

  • Author: David Elliott x
  • Refine by Access: All Content x
Clear All Modify Search
Restricted access

A. Mark Williams and David Elliott

The effects of anxiety and expertise on visual search strategy in karate were examined. Expert and novice karate performers moved in response to taped karate offensive sequences presented under low (LA) and high anxiety (HA). Expert performers exhibited superior anticipation under LA and HA. No differences were observed between groups in number of fixations, mean fixation duration, or total number of fixation locations per trial. Participants displayed scan paths ascending and descending the centerline of the body, with primary fixations on head and chest regions. Participants demonstrated better performance under HA than under LA. Anxiety had a significant effect on search strategy, highlighted by changes in mean fixation duration and an increase in number of fixations and total number of fixation locations per trial. Increased search activity was more pronounced in novices, with fixations moving from central to peripheral body locations. These changes in search strategy with anxiety might be caused by peripheral narrowing or increased susceptibility to peripheral distractors.

Restricted access

David A. Le Clair and Digby Elliott

This study examined the extent to which individuals with Down syndrome benefit from visual and verbal advance information about a manual aiming movement. Adults with Down syndrome as well as control subjects with and without mental handicaps performed 10.5-cm manual aiming movements with their preferred hand. On each trial subjects were cued about the specific movement either visually or verbally. On different trial blocks, the cue provided either 50% or 80% certainty. Nonhandicapped control subjects initiated and completed their manual aiming movements more quickly than subjects with mental handicaps. As well, individuals with Down syndrome were found to be slower and more variable in reaction time than participants in the other mentally handicapped group when valid information was provided verbally but not when the cue was provided visually. These results are consistent with the proposal that atypical hemispheric lateralization for speech perception associated with Down syndrome disrupts communication between functional systems responsible for processing of verbal language and organizing movement (Elliott & Weeks, 1993b).

Restricted access

Greg Anson, Digby Elliott, and Davids

Since the middle of the nineteenth century, movement scientists have been challenged to explain processes underlying the control, coordination, and acquisition of skill. Information processing and constraints-based approaches represent two distinct, often perceived as opposing, views of skill acquisition. The purpose of this article is to compare information processing and constraints-based approaches through the lens of Fitts’ three-stage model and Newell’s constraints-based model, respectively. In essence, both models can be identified, at least in spirit, with ideas about skill described by Bernstein (1967, 1996). Given that the product of “skill acquisition” is the same, although the explanation of the processes might differ, it is perhaps not surprising that similarities between the models appear greater than the differences. In continuing to meet the challenge to explain skill acquisition, neural-based models provide a glimpse of the cutting edge where behavior and biological mechanisms underpinning processes of control, coordination, and acquisition of skill might meet.

Restricted access

Flavio T.P. Oliveira, Digby Elliott, and David Goodman

Anecdotal and scientific evidence suggest humans tend to undershoot targets in rapid movements. We investigated whether this undershoot bias derives from energy minimization mechanisms. Participants performed 200 trials of two tasks: (1) a simple slider push to a target, and (2) a modified version of (1), designed so overshooting was less energy consuming than undershooting. Results support that the undershoot bias found in (1), as well as the overshoot bias found in (2), results from an energy minimization mechanism. Energy minimization might be inherent to biological systems. Movement biases were undesirable for maximal performance. Nonetheless, participants presented biases despite financial incentives to perform maximally. Participants did, however, appear sensitive to systematic errors produced by the attraction to less energy costly responses. We suggest that the motor system is constrained such that maximal performance trades off with energetic optimality although humans are able to learn and compensate for the energy minimization biases.

Restricted access

Avish P. Sharma, Adrian D. Elliott, and David J. Bentley

Context:

Road cycle racing is characterized by significant variability in exercise intensity. Existing protocols attempting to model this aspect display inadequate variation in power output. Furthermore, the reliability of protocols representative of road cycle racing is not well known. There are also minimal data regarding the physiological parameters that best predict performance during variable-power cycling.

Purpose:

To determine the reliability of mean power output during a new test of variable-power cycling and establish the relationship between physiological attributes typically measured during an incremental exercise test and performance during the variable-power cycling test (VCT).

Methods:

Fifteen trained male cyclists (mean ± SD age 33 ± 6.5 y, VO2max 57.9 ± 4.8 mL · kg−1 · min−1) performed an incremental exercise test to exhaustion for determination of physiological attributes, 2 VCTs (plus familiarization), and a 30-km time trial. The VCT was modeled on data from elite men’s road racing and included significant variation in power output.

Results:

Mean power output during the VCT showed good reliability (r = .92, CV% = 1.98). Relative power during the self-paced sections of the VCT was most correlated with maximal aerobic power (r = .79) and power at the second ventilatory threshold (r = .69). Blood lactate concentration showed poor reliability between trials (CV% = 13.93%).

Conclusions:

This study has demonstrated a new reliable protocol simulating the stochastic nature of road cycling races. Further research is needed to determine which factors predict performance during variable-power cycling and the validity of the test in monitoring longitudinal changes in cycling performance.

Restricted access

Aaron Chin, David Lloyd, Jacqueline Alderson, Bruce Elliott, and Peter Mills

The predominance of upper-limb elbow models have been based on earlier lower-limb motion analysis models. We developed and validated a functionally based 2 degree-of-freedom upper-limb model to measure rotations of the forearm using a marker-based approach. Data were collected from humans and a mechanical arm with known axes and ranges of angular motion in 3 planes. This upper-limb model was compared with an anatomically based model following the proposed ISB standardization. Location of the axes of rotation relative to each other was determined in vivo. Data indicated that the functional model was not influenced by cross-talk from adduction-abduction, accurately measuring flexion-extension and pronation-supination. The functional flexion-extension axis in vivo is angled at 6.6° to the anatomical line defined from the humeral medial to lateral epicondyles. The pronation-supination axis intersected the anatomically defined flexion-extension axis at 88.1°. Influence of cross-talk on flexion-extension kinematics in the anatomical model was indicated by strong correlation between flexion-extension and adduction-abduction angles for tasks performed by the subjects. The proposed functional model eliminated cross-talk by sharing a common flexion axis between the humerus and forearm. In doing so, errors due to misalignment of axes are minimized providing greater accuracy in kinematic data.

Restricted access

David Whiteside, Bruce Elliott, Brendan Lay, and Machar Reid

The importance of the flat serve in tennis is well documented, with an abundance of research evaluating the service technique of adult male players. Comparatively, the female and junior serves have received far less attention. Therefore, the aims of this study were to quantify the flat serve kinematics in elite prepubescent, pubescent, and postpubescent female tennis players. Full body, racket, and ball kinematics were derived using a 22-camera Vicon motion capture system. Racket velocity was significantly lower in the prepubescent group than in the two older groups. In generating racket velocity, the role of the serving arm appears to become more pronounced after the onset of puberty, whereas leg drive and “shoulder-over-shoulder” rotation mature even later in development. These factors are proposed to relate to strength deficits and junior players’ intentions to reduce the complexity of the skill. Temporally, coupling perception (cues from the ball) and action (body movements) are less refined in the prepubescent serve, presumably reducing the “rhythm” (and dynamism) of the service action. Practically, there appears scope for equipment scaling to preserve kinematic relevance between the junior and senior serve and promote skill acquisition.

Restricted access

Marc R. Portus, David G. Lloyd, Bruce C. Elliott, and Neil L. Trama

The measurement of lumbar spine motion is an important step for injury prevention research during complex and high impact activities, such as cricket fast bowling or javelin throwing. This study examined the performance of two designs of a lumbar rig, previously used in gait research, during a controlled high impact bench jump task. An 8-camera retro-reflective motion analysis system was used to track the lumbar rig. Eleven athletes completed the task wearing the two different lumbar rig designs. Flexion extension data were analyzed using a fast Fourier transformation to assess the signal power of these data during the impact phase of the jump. The lumbar rig featuring an increased and pliable base of support recorded moderately less signal power through the 0–60 Hz spectrum, with statistically less magnitudes at the 0–5 Hz (p = .039), 5–10 Hz (p = .005) and 10–20 Hz (p = .006) frequency bins. A lumbar rig of this design would seem likely to provide less noisy lumbar motion data during high impact tasks.

Restricted access

Michael Koh, Leslie Jennings, Bruce Elliott, and David Lloyd

The Yurchenko layout vault is the base vault from which more advanced forms of the Yurchenko family of vaults have evolved. The purpose of the study was to predict an individual’s optimal Yurchenko layout vault by modifying selected critical mechanical variables. The gymnast’s current performance characteristics were determined using the Peak-Motus video analysis system. Body segment parameters were determined using the elliptical zone mathematical modeling technique of Jensen (1978). A 5-segment computer simulation model was personalized for the gymnast comprising the hands, upper limbs, upper trunk, lower trunk, and lower limbs. Symmetry was assumed, as the motion was planar in nature. An objective function was identified which translated the subjective points-evaluation scheme of the Federation of International Gymnastics (FIG) Code of Points to an analytic expression that was mathematically tractable. The objective function was composed of performance variables that, if maximized, would result in minimal points being deducted and bonus points being allocated. A combined optimal control and optimal parameter selection approach was applied to the model to determine an optimum technique. The predicted optimal vault displayed greater postflight amplitude and angular momentum when compared with the gymnast’s best trial performance. Increased angular velocity, and consequently greater angular momentum at impact and greater shoulder flexion angle at impact with the horse, were related with this optimum technique. The impact phase therefore serves to increase the angular momentum during horse contact. Since the optimized parameters at impact with the horse were within the accepted physical capacity limits observed for the individual, the predicted vault is viable.

Restricted access

Alasdair R. Dempsey, Bruce C. Elliott, Bridget J. Munro, Julie R. Steele, and David G. Lloyd

Anterior cruciate ligament (ACL) injuries are costly. Sidestep technique training reduces knee moments that load the ACL. This study examined whether landing technique training alters knee moments. Nineteen team sport athletes completed the study. Motion analysis and ground reaction forces were recorded before and after 6 weeks of technique modification. An inverse dynamic model was used to calculate three-dimensional knee loading. Pre- and postintervention scores were compared using paired t tests. Maximal knee flexion angle during landing was increased following training. There was no change in valgus or flexion moments, but an increase in peak internal rotation moment. This increase in internal rotation moment may increase the risk of ACL injury. However, the increased angle at which the peak internal rotation moment occurred at follow up may mitigate any increase in injury risk by reducing load transmission.