The Kinematics of False Intent Conveyed by Deceptive Sidestep Actions.

Researchers have identified kinematic differences between deceptive and non-deceptive rugby reorientation actions. However, the honest and deceptive signals corresponded to 'deception detection' (accuracy increasing) rather than signals that caused deception (accuracy decreasing). In this study, statistical parametric mapping and multilevel modelling were applied to examine the kinematic differences between sidestep and non-deceptive actions during the time window of deception. The analysis compared three-dimensional motion capture data from 144 deceptive actions and 144 genuine actions performed by six high-skilled rugby players. Results indicated that the kinematics of deceptive actions were characterized by a combination of exaggerated head roll, outside foot and centre-of-mass displacement, and attenuated thorax roll and yaw relative to genuine actions. These are candidate sources for the cause of deception, either individually or in combination with other sources. Furthermore, the results indicate that previously identified 'honest' signals may not be reliable sources of information earlier in the action sequence.

Where in a time constrained throwing task is the speed-accuracy trade-off?

Previous research on fielding in cricket and baseball has focused on the technique and speed-accuracy trade-off of the throw in isolation from a typical sequence of fielding actions; approach, gather and throw. The present study aimed to determine whether a speed-accuracy trade-off existed in fielding and where within the above sequence the trade-off occurs. Participants, who were elite cricketers, were required to run to a stationary ball and throw to the centre of a target in order to run-out a virtual batter. High-speed video was used to record the time of approach, time in contact with, and time of flight of the ball. Two-way ANOVAs were used to determine differences in group (gender) and condition (instructions to prioritise speed or accuracy). A speed-accuracy trade-off was found, with both groups being quicker in the approach and spending less time in contact with the ball in the speed condition; however, the horizontal velocity of the throw remained the same in both conditions. It was proposed the drop in accuracy in the speed condition may be associated with less time spent aiming. It was found that instructions triggered a change in throwing technique for 31% of the participants, which requires further investigation.

Strategies for Controlling a Whole-Body Task With Uncertain Initial Conditions: Application to the Upstart on Bars.

The upstart is commonly used on bars in artistic gymnastics following a release and regrasp skill, where the gymnast will perform a flighted element before catching the bar. The variability of the flighted element leads to varying initial conditions prior to the upstart. The aim of the study was to understand how technique can be manipulated in order to ensure success at the task despite this variability. More specifically, the study aimed to quantify the ranges of initial angular velocity a gymnast could cope with in an upstart using (a) a fixed timing technique, (b) with one additional parameter to modify timings as a function of initial angular velocity, and (c) a further additional parameter to extend the range. Relationships were established, using computer simulation modeling, between the movement pattern parameters, which defined the technique, and the initial angular velocity of the upstart. A two-parameter relationship outperformed both the one-parameter relationship and the fixed timing solution in terms of the range of initial angular velocities the model could cope with. One of the two parameters governed the time by which the initiation of the shoulder extension should be reduced as a function of increased initial angular velocity, and the other parameter performed the same function for the remaining timing parameters at the hip and shoulder. The present study suggests that gymnasts, and, therefore, humans, may be able to modify movement patterns to cope with uncertain initial conditions using a relatively small number of parameters.

Earlier detection facilitates skilled responses to deceptive actions.

High-skilled and recreational rugby players were placed in a semi-immersive CAREN Lab environment to examine susceptibility to, and detection of, deception. To achieve this, a broad window of seven occlusion times was used in which participants responded to life-size video clips of an opposing player 'cutting' left or right, with or without a deceptive sidestep. Participants made full-body responses to 'intercept' the player and gave a verbal judgement of the opponent's final running direction. Response kinematic and kinetic data were recorded using three-dimensional motion capture cameras and force plates, respectively. Based on response accuracy, the results were separated into deception susceptibility and deception detection windows then signal detection analysis was used to calculate indices of discriminability between genuine and deceptive actions (d') and judgement bias (c). Analysis revealed that high-skilled and low-skilled players were similarly susceptible to deception; however, high-skilled players detected deception earlier in the action sequence, which enabled them to make more effective behavioural responses to deceptive actions.

A kinetic and kinematic comparison of the two-footed and step-out back handsprings on the balance beam.

The back handspring is one of the most commonly performed skills on the balance beam in women's gymnastics. Despite this, quantitative research on the beam has often been overlooked. This study aimed to investigate the kinetic and kinematic variables during the performance of two back handspring techniques on the beam: the back handspring with two footed landing and the back handspring step-out. A modified balance beam was fixed to a force plate with an isolated mat for landing to allow analysis of the take-off and hand contact phases. Kinetic and kinematic data were recorded for twelve gymnasts performing both techniques. No statistically significant differences between techniques were found during take-off. However, average peak vertical and horizontal ground reaction forces (4.1 bodyweights ± 1.1 BW, and 0.7 BW ± 0.2 BW, respectively) were higher and time to peak force shorter during the hand contact phase for the two footed variant. A more vertical trajectory, along with a greater hand contact ground reaction force were found in comparison to the back handspring performed on the floor. These results highlight the need for more specific investigation to understand the factors which could contribute to reducing the load faced during balance beam performance.

Control of a Whole-Body Task with Uncertain Initial Conditions: Application to the Upstart On Bars.

The aim was to determine whether operating a feedforward schema for generating movement pattern parameters was more successful than an open loop strategy for coping with uncertain initial conditions. A computer simulation model was used to determine the optimal solutions that maximised the likelihood of performing a successful upstart. Feedforward schema were established between movement pattern parameters and initial angular velocity. The success of modifying a pre-planned movement pattern based on the parameter relationships (feedforward) was compared with optimal solutions unable to adapt (open loop) to initial angular velocity. The open loop solution was successful 28% and 20% of the time for a full strength (elite) and weaker gymnast. The feedforward strategy had success rates of 99% and 96% respectively.

The effect of uphill and downhill slopes on centre of pressure movement, alignment and shot outcome in mid-handicap golfers.

The aim of the study was to examine changes in centre of pressure (COP) movement, alignment and shot outcome during golf shots from flat, uphill, and downhill slopes by mid-handicap golfers. Twelve male golfers hit balls with a six-iron from the flat and 5° slopes while kinematics and kinetics of the swing were collected. A launch monitor measured performance outcomes. A shift in the COP was found during the backswing when playing on a slope, but disappeared during the downswing. Golfers attempted to align the body perpendicular to the slope at the start of the swing resulting in COP movement towards the lower foot, but were not able to maintain this throughout the swing, like low handicap golfers. There was no significant difference in stance width, but golfers placed the ball closer to the uphill foot on a slope. Ball speed was not significantly affected by the slope, but launch angle and ball spin were. Golfers were more likely to hit shots to the left from an uphill slope and to the right for a downhill slope. No consistent compensatory adjustments in alignment at address were found, with differences in final ball position due to lateral spin.

Effect of racket-shuttlecock impact location on shot outcome for badminton smashes by elite players.

A logarithmic curve fitting methodology for the calculation of badminton racket-shuttlecock impact locations from three-dimensional motion capture data was presented and validated. Median absolute differences between calculated and measured impact locations were 3.6 [IQR: 4.4] and 3.5 [IQR: 3.5] mm mediolaterally and longitudinally on the racket face, respectively. Three-dimensional kinematic data of racket and shuttlecock were recorded for 2386 smashes performed by 65 international badminton players, with racket-shuttlecock impact location assessed against instantaneous post-impact shuttlecock speed and direction. Mediolateral and longitudinal impact locations explained 26.2% (quadratic regression; 95% credible interval: 23.1%, 29.2%; BF10 = 1.3 × 10131, extreme; p < 0.001) of the variation in participant-specific shuttlecock speed. A meaningful (BF10 = ∞, extreme; p < 0.001) linear relationship was observed between mediolateral impact location and shuttlecock horizontal direction relative to a line normal to the racket face at impact. Impact locations within one standard deviation of the pooled mean impact location predict reductions in post-impact shuttlecock speeds of up to 5.3% of the player's maximal speed and deviations in the horizontal direction of up to 2.9° relative to a line normal to the racket face. These results highlight the margin for error available to elite badminton players during the smash.

Functional variability in the takeoff phase of one metre springboard forward dives.

In springboard diving consistency of body orientation at water entry is necessary for a good dive and is likely to be dependent on the consistency of conditions at takeoff. The aim of the present study was to investigate whether a diver modifies his technique from dive to dive during the board contact phase in order to be more consistent at takeoff in one metre springboard forward dives. Two-dimensional video analysis was used to calculate orientation and configuration angles of 12 forward pike dives and 12 forward 2½ somersault pike dives, performed by an international diver. A computer simulation model of a diver and springboard during board contact was used to obtain matching simulations of the performances and to calculate the rotation potential (angular momentum × flight time) for each dive. Simulations were used to determine the variation in conditions at maximum board depression arising from variation in touchdown conditions, and the variation in takeoff conditions arising from the variability in conditions at maximum board depression. A comparison of the simulated and performance variations implied that adjustments were made during the board contact phase for both the pike dives and the 2½ somersault pike dives. In the board depression phase, adjustments reduced the variability in the mass centre horizontal velocity at the lowest point. In the board recoil phase, adjustments reduced the variability in the horizontal velocity and rotation potential at takeoff.

How do technique and coordination change during learning of a whole-body task: Application to the upstart in gymnastics.

When learning swinging skills on a bar there has been conflicting advice in the research literature regarding whether to coach the "gold standard" technique to novices. The present study aimed to determine how technique (joint angle time histories) and (inter-limb) coordination changed as novice gymnasts learned a fundamental gymnastics skill (the upstart). It was hypothesised that both technique and coordination would become more like an expert as learning progressed. Eight novice gymnasts, unable to perform an upstart, underwent four months of training, with the number of successful upstarts out of 10 recorded at the start and then every month subsequently. In the first and last sessions motion capture was used to determine joint kinematics. Root mean squared differences for the joint angle time histories and continuous relative phase at the shoulder and hip were calculated between the novices and an expert gymnast. As training progressed technique and coordination became more like the expert gymnast. The more successful novices were better able to time their actions within the swing than the less successful novices. Gymnastics coaches teach towards a "gold standard" technique since being successful at the skill is not the only goal, as considerations for future skill development are made.

Functional variability in the flight phase of one metre springboard forward dives.

In springboard diving, low variability in takeoff conditions and in the somersault orientation angle at water entry is to be expected since consistency and accuracy are necessary for a good dive. A diver's adjustment of body configuration during flight may be a deliberate compensation for variations in takeoff conditions, leading to increased joint angle variability and decreased entry angle variability. The aim of this research was to investigate the extent to which a diver pre-plans the aerial phase and then makes adjustments in flight to control the entry angle in one metre springboard forward dives. Performances of 15 forward pike dives and 15 forward 2½ somersault pike dives, performed by an international diver were video recorded at 250 Hz. Joint centres during flight were digitized and their spatial coordinates were subsequently reconstructed using the Direct Linear Transformation in order to determine orientation and configuration angles. A computer simulation model was used to investigate the effects of variability in takeoff conditions and configuration variability in flight on the variability of the orientation angle at water entry. The amount of variation in the somersault orientation angle at entry as determined using simulations based on the variability in the takeoff conditions was four times greater than the variation in the recorded performances. It was concluded that the diver used open loop control for the first half of the flight phase and subsequently used feedforward and feedback control to make timing adjustments of hip and arm angles to reduce the variability of his entry orientation angle.

The Effect of Uphill and Downhill Slopes on Weight Transfer, Alignment, and Shot Outcome in Golf.

The aim of the study was to examine changes in weight transfer, alignment, and shot outcome during golf shots from flat, uphill, and downhill slopes. Twelve elite male golfers hit 30 shots with a 6-iron from a computer-assisted rehabilitation environment used to create 5° slopes while collecting 3-dimensional kinematics and kinetics of the swing. A launch monitor measured performance outcomes. A shift in the center of pressure was found throughout the swing when performed on a slope, with the mean position moving approximately 9% closer to the lower foot. The golfers attempted to remain perpendicular to the slope, resulting in weight transfer toward the lower foot. The golfers adopted a wider stance in the sloped conditions and moved the ball toward the higher foot at address. Ball speed was not significantly affected by the slope, but launch angle and ball spin were. As the coaching literature predicted, golfers were more likely to hit shots to the left from an uphill slope and to the right from a downhill slope. No consistent compensatory adjustments in alignment at address or azimuth were found, with the change in final shot dispersion resulting from the lateral spin of the ball.

Balance control strategies during perturbed and unperturbed balance in standing and handstand.

Insights into sensorimotor control of balance were examined by the assessment of perturbed and unperturbed balance in standing and handstand postures. During perturbed and unperturbed balance in standing, the most prevalent control strategy was an ankle strategy, which was employed for more than 90% of the time in balance. During perturbed and unperturbed balance in handstand, the most prevalent control strategy was a wrist strategy, which was employed for more than 75% of the time in balance. In both postures, these strategies may be described as a single segment inverted pendulum control strategy, where the multi-segment system is controlled by torque about the most inferior joint with compensatory torques about all superior joints acting in the same direction to maintain a fixed orientation between superior segments. In contrast to previous literature, surprisingly little time was spent in a mixed strategy, representing less than 1% of time in standing balance and approximately 2% of time in handstand balance. Findings indicate that although the central nervous system may employ a number of control strategies during a trial, these strategies are employed individually rather than simultaneously.

What governs successful performance of a complex whole body movement: The Kovacs release-regrasp on horizontal bar?

The Kovacs is a release and regrasp skill performed on the horizontal bar in men׳s artistic gymnastics. It is a popular skill in elite competitive gymnastics with over 40% of male gymnasts performing a variation of the Kovacs at the London 2012 Olympics. In the qualifying competition 84% of Kovacs were successfully regrasped, with the remaining 16% resulting in a fall. The aim of the present study was to determine why some gymnasts are more successful than others at regrasping the bar, with a secondary aim to determine how a less successful gymnast could alter his technique in order to become more successful. Nine performances of the Kovacs by each of two gymnasts, one 100% successful and one 11% successful, were analysed to determine differences in release and regrasp parameters. The technique of the less successful gymnast was optimised using a computer simulation model to increase the percentage of catches (success rate). The successful gymnast had larger and more consistent release windows and a radial velocity towards the bar at regrasp. The less successful gymnast had higher horizontal velocity at release and a mean radial velocity away from the bar at regrasp. Optimising his simulated technique increased the rate of success from 11% to 93%. The actions prior to release were performed earlier than in the recorded performances leading to a more vertical path of the mass centre at release and a radial velocity towards the bar at regrasp.

The role of functional variability in a whole body co-ordinated movement - Application to high bar giant circles.

When performing a giant circle on high bar a gymnast flexes at the hips in the lower part of the circle, increasing the kinetic energy, and extends in the upper part of the circle, decreasing the kinetic energy. In order to perform a sequence of giant circles at even tempo, any variation in angular velocity at the end of the flexion phase needs to be reduced by the end of the extension phase. The aim of this study was to determine the nature and contribution of such adjustments. A computer simulation model of a gymnast performing giant circles on high bar was used to investigate strategies of (a) fixed timing of the extension phase (feedforward control) and (b) stretched timing in order to extend at the same point of the giant circle (feedforward with additional feedback control). For three elite gymnasts fixed timing reduced the angular velocity variation on average by 36% whereas stretched timing reduced the variation by 63%. The mean reduction for the actual gymnast techniques was 61%. It was concluded that both feedforward and feedback control strategies are used by gymnasts for controlling such movements.

Evaluating feedback time delay during perturbed and unperturbed balance in handstand.

Feedback delays in balance are often assessed using muscle activity onset latencies in response to discrete perturbations. The purpose of the study was to calculate EMG latencies in perturbed handstand, and determine if delays are different to unperturbed handstand. Twelve national level gymnasts completed 12 perturbed and 10 unperturbed (five eyes open and five closed) handstands. Forearm EMG latencies during perturbed handstands were assessed against delay estimates calculated via: cross correlations of wrist torque and COM displacement, a proportional and derivative model of wrist torque and COM displacement and velocity (PD model), and a PD model incorporating a passive stiffness component (PS-PD model). Delays from the PD model (161±14ms) and PS-PD model (188±14ms) were in agreement with EMG latencies (165±14ms). Cross correlations of COM displacement and wrist torque provided unrealistically low estimates (5±9ms). Delays were significantly lower during perturbed (188±14ms) compared to unperturbed handstand (eyes open: 207±12ms; eyes closed: 220±19ms). Significant differences in delays and model parameters between perturbed and unperturbed handstand support the view that balance measures in perturbed testing should not be generalised to unperturbed balance.

Investigating optimal technique in the presence of motor system noise: application to the double layout somersault dismount on high bar.

Minimising joint torque is often used as an optimisation criterion when investigating human movement. Alternatively, an aspect of performance may be chosen to be maximised when investigating sporting movements. The aim of the study was to optimise the technique in the backward giant circle prior to a double layout somersault dismount from the high bar using various criteria to determine which best characterised the technique adopted by a gymnast. Ten recorded gymnast trials were used to determine bar release parameters and the level of noise in the gymnast's movements. A computer simulation model of a gymnast and bar was used to optimise giant circle technique under three criteria: minimising joint torques, maximising the release window and maximising success in the presence of motor system noise. Local and global optimisations of technique were performed using the three criteria starting from the average technique of the 10 recorded trials. All global optimum solutions diverged from the gymnast's technique. The local optimum for maximising success in the presence of noise had a success rate comparable with the global optimum (98% vs. 100%, respectively). It is concluded that the gymnast's technique is characterised by maximising success despite operating with motor system noise.

Optimal technique for maximal forward rotating vaults in men's gymnastics.

In vaulting a gymnast must generate sufficient linear and angular momentum during the approach and table contact to complete the rotational requirements in the post-flight phase. This study investigated the optimization of table touchdown conditions and table contact technique for the maximization of rotation potential for forwards rotating vaults. A planar seven-segment torque-driven computer simulation model of the contact phase in vaulting was evaluated by varying joint torque activation time histories to match three performances of a handspring double somersault vault by an elite gymnast. The closest matching simulation was used as a starting point to maximize post-flight rotation potential (the product of angular momentum and flight time) for a forwards rotating vault. It was found that the maximized rotation potential was sufficient to produce a handspring double piked somersault vault. The corresponding optimal touchdown configuration exhibited hip flexion in contrast to the hyperextended configuration required for maximal height. Increasing touchdown velocity and angular momentum lead to additional post-flight rotation potential. By increasing the horizontal velocity at table touchdown, within limits obtained from recorded performances, the handspring double somersault tucked with one and a half twists, and the handspring triple somersault tucked became theoretically possible.

The influence of touchdown conditions and contact phase technique on post-flight height in the straight handspring somersault vault.

In vaulting the gymnast must generate sufficient linear and angular momentum during the approach and table contact in order to complete the rotational requirements in the post-flight phase. This study investigated the effects of touchdown conditions and contact technique on peak post-flight height of a straight handspring somersault vault. A planar seven-segment torque-driven computer simulation model of the contact phase in vaulting was evaluated by varying joint torque activation time histories to match three performances of a straight handspring somersault vault by an elite gymnast. The closest matching simulation was used as a starting point to optimise peak post-flight height of the mass centre for a straight handspring somersault. It was found that optimising either the touchdown conditions or the contact technique increased post-flight height by 0.1m whereas optimising both together increased post-flight height by 0.4m above that of a simulation matching the recorded performance. Thus touchdown technique and contact technique make similar contributions to post-flight height in the straight handspring somersault vault. Increasing touchdown velocity and angular momentum lead to additional post-flight height although there was a critical value of vertical touchdown velocity beyond which post-flight height decreased.

Determining the solution space for a coordinated whole body movement in a noisy environment: application to the upstart in gymnastics.

The upstart is a fundamental skill in gymnastics, requiring whole body coordination to transfer the gymnast from a swing beneath the bar to a support position above the bar. The aim of this study was to determine the solution space within which a gymnast could successfully perform an upstart. A previous study had shown that the underlying control strategy for the upstart could be accounted for by maximizing the likelihood of success while operating in a noisy environment. In the current study, data were collected on a senior gymnast and a computer simulation model of a gymnast and bar was used to determine the solution space for maximizing success while operating in a noisy environment. The effects of timing important actions, gymnast strength, and movement execution noise on the success of the upstart were then systematically determined. The solution space for the senior gymnast was relatively large. Decreasing strength and increasing movement execution noise reduced the size of the solution space. A weaker gymnast would have to use a different technique than that used by the senior gymnast to produce an acceptable success rate.