Exploration of collective tactical variables in elite netball: An analysis of team and sub-group positioning behaviours.

Collective tactical behaviours are aspects of player interactions that are particularly important in netball, due to its unique restrictions on player movement (players unable to move when in possession of the ball and positional spatial restrictions). The aim of this study was to explore variables representing collective tactical behaviours in netball. A local positioning system provided player positions of one team throughout seven elite-level netball matches. The positions were analysed to provide mean, variability (standard deviation) and irregularity (normalised approximate entropy) for each attack and defence possession (470 and 423, respectively) for the team and positional subgroups (forwards, midcourts and defenders) for 10 position-related variables. Correlational analyses showed collective tactical variables could be grouped as lateral and longitudinal dispersion variables. The variables were each analysed after log transformation with a linear mixed model to compare attack and defence and to estimate standardised effects on attack and defence of possession outcome, possession duration, score difference, match time, opposition strength and season time. During attack, the team and all sub-groups adopted greater lateral dispersion between players, while on defence there was generally greater longitudinal dispersion. The team also showed increased longitudinal dispersion when home and opposition possessions ended in a score. Additionally, greater irregularity was observed in active sub-groups (forwards on attack, defenders on defence). Score difference and opposition strength had trivial-small but generally unclear effects. In conclusion, these effects show that analysis of player positions on attack and defence is a promising avenue for coaches and analysts to modify collective tactical behaviours in netball.

Applying common filtering processes to Global Navigation Satellite System-derived acceleration during team sport locomotion.

This study aimed to observe whether there were substantial differences in acceleration during team-sport locomotion between GNSS manufacturers. Speed and acceleration were obtained from 7 professional rugby league athletes via 2 GNSS manufacturers (GPSports EVO, 10 Hz and STATSports Apex, 10 Hz) worn together during the same training sessions (n = 13). Raw GNSS data were exported from respective proprietary software and a 1 Hz, 4th-order Butterworth filter applied, with differences in speed and acceleration calculated between manufacturers. To determine the difference in acceleration and speed, a root mean square deviation (RMSD) was used. Linear mixed models were used and no substantial differences were found between manufacturers in raw and filtered speed variables. RMSD for average acceleration (m · s-2) decreased from raw (RMSD: 1.77 ± 0.37 m · s-2) to those seen at the filtered (RMSD: 0.27 ± 0.23 m · s-2) and twice filtered (0.24 ± 0.23 m · s-2) variables. Raw average acceleration (m · s-2) was substantially higher in Apex compared to EVO (Difference (Diff); CI: -0.82; -0.84 to -0.80). Following application of the common filter there was no substantial difference between GNSS models for average acceleration (Diff; CI: -0.04; -0.04 to -0.04). Acceleration variables derived from each manufacturer's proprietary software were substantially different.

Criterion Validity of Catapult ClearSky T6 Local Positioning System for Measuring Inter-Unit Distance.

The validity of a local positioning system (LPS) to measure inter-unit distance was investigated during a team sport movement circuit. Eight recreationally active, female indoor team-sport players completed a circuit, comprising seven types of movements (walk, jog, jump, sprint, 45° change of direction and shuffle), on an indoor court. Participants wore a receiver tag (ClearSky T6, Catapult Sports) and seven reflective markers, to allow for a comparison with the reference system (©Vicon Motion Systems, Oxford Metrics, UK). Inter-unit distance was collected for each combination of participants. Validity was assessed via root mean square error, mean bias and percentage of variance accounted for, both as an overall dataset and split into distance bands. The results presented a mean root mean square error of 0.20 ± 0.05 m, and mean bias detected an overestimation for all distance bands. The LPS shows acceptable accuracy for measuring inter-unit distance, opening up opportunities to utilise player tracking for tactical variables indoors.

Key parameters of the swimming start and their relationship to start performance.

The swimming start is typically broken into three sub-phases; on-block, flight, and underwater phases. While overall start performance is highly important to elite swimming, the contribution of each phase and important technical components within each phase, particularly with the new kick-start technique, has not been established. The aim of this study was to identify technical factors associated with overall start performance, with a particular focus on the underwater phase. A number of parameters were calculated from 52 starts performed by elite freestyle and butterfly swimmers. These parameters were split into above-water and underwater groupings, before factor analysis was used to reduce parameter numbers for multiple regression. For the above-water phases, 81% of variance in start performance was accounted for by take-off horizontal velocity. For the underwater water phase, 96% of variance was accounted for with time underwater in descent, time underwater in ascent and time to 10 m. Therefore, developing greater take-off horizontal velocity and focussing on the underwater phase by finding the ideal trajectory will lead to improved start performance.

The reliability of an instrumented start block analysis system.

The swimming start is highly influential to overall competition performance. Therefore, it is paramount to develop reliable methods to perform accurate biomechanical analysis of start performance for training and research. The Wetplate Analysis System is a custom-made force plate system developed by the Australian Institute of Sport--Aquatic Testing, Training and Research Unit (AIS ATTRU). This sophisticated system combines both force data and 2D digitization to measure a number of kinetic and kinematic parameter values in an attempt to evaluate start performance. Fourteen elite swimmers performed two maximal effort dives (performance was defined as time from start signal to 15 m) over two separate testing sessions. Intraclass correlation coefficients (ICC) were used to determine each parameter's reliability. The kinetic parameters all had ICC greater than 0.9 except the time of peak vertical force (0.742). This may have been due to variations in movement initiation after the starting signal between trials. The kinematic and time parameters also had ICC greater than 0.9 apart from for the time of maximum depth (0.719). This parameter was lower due to the swimmers varying their depth between trials. Based on the high ICC scores for all parameters, the Wetplate Analysis System is suitable for biomechanical analysis of swimming starts.

How does drag affect the underwater phase of a swimming start?

During the underwater phase of the swimming start drag forces are constantly acting to slow the swimmer down. The current study aimed to quantify total drag force as well as the specific contribution of wave drag during the underwater phase of the swimming start. Swimmers were towed at three different depths (surface, 0.5 m, 1.0 m) and four speeds (1.6, 1.9, 2.0, 2.5 m · s(-1)), totaling 12 conditions. Wave drag and total drag were measured for each trial. Mixed modeling and plots were then used to determine the relationships between each towing condition and the amount of drag acting on the swimmer. The results of this study show large decreases in total drag as depth increases, regardless of speed (-19.7% at 0.5 m and -23.8% at 1.0 m). This is largely due to the significant reduction in wave drag as the swimmers traveled at greater depth. It is recommended that swimmers travel at least 0.5 m below the surface to avoid excessive drag forces. Swimmers should also perform efficient breakouts when transitioning into free swimming to reduce the duration spent just below the surface where drag values are reported at their highest.

Comparing three underwater trajectories of the swimming start.

UNLABELLED: Once a swimmer enters the water they will not increase velocity, instead they will decelerate. One factor that will influence the velocity maintained during the underwater phase is the trajectory the swimmer adopts. OBJECTIVES: Once a swimmer enters the water they will not increase velocity, instead they will decelerate. One factor that will influence the velocity maintained during the underwater phase is the trajectory the swimmer adopts. This study aimed to identify how different underwater trajectories affect start time in elite swimmers. METHODS: Fourteen swimmers performed three dives: a shallow dive with little underwater time (Dive 1), a flatter dive with intermediate time underwater (Dive 2) and a deep dive with lengthy underwater time (Dive 3). The proprietary 'Wetplate' analysis system was used to collect performance time (time to 15 m) and other dive parameters. RESULTS: A mixed modelling approach found Dive 1 was significantly slower than Dive 2 and 3 (time to 15 m). This indicated that both a shallow or deep dive slowed overall performance, with shallower dives adversely affecting performance the most. CONCLUSIONS: On average, using a flatter trajectory with a maximum depth of -0.92 ± 0.16 m similar to Dive 2 may prove to be beneficial to start performance. More research is needed to examine the interaction between drag and depth for individual swimmers to better understand the mechanisms influencing these findings and to further explore the notion of an ideal underwater trajectory.

Kinematics of primate midfoot flexibility.

This study describes a unique assessment of primate intrinsic foot joint kinematics based upon bone pin rigid cluster tracking. It challenges the assumption that human evolution resulted in a reduction of midfoot flexibility, which has been identified in other primates as the "midtarsal break." Rigid cluster pins were inserted into the foot bones of human, chimpanzee, baboon, and macaque cadavers. The positions of these bone pins were monitored during a plantarflexion-dorsiflexion movement cycle. Analysis resolved flexion-extension movement patterns and the associated orientation of rotational axes for the talonavicular, calcaneocuboid, and lateral cubometatarsal joints. Results show that midfoot flexibility occurs primarily at the talonavicular and cubometatarsal joints. The rotational magnitudes are roughly similar between humans and chimps. There is also a similarity among evaluated primates in the observed rotations of the lateral cubometatarsal joint, but there was much greater rotation observed for the talonavicular joint, which may serve to differentiate monkeys from the hominines. It appears that the capability for a midtarsal break is present within the human foot. A consideration of the joint axes shows that the medial and lateral joints have opposing orientations, which has been associated with a rigid locking mechanism in the human foot. However, the potential for this same mechanism also appears in the chimpanzee foot. These findings demonstrate a functional similarity within the midfoot of the hominines. Therefore, the kinematic capabilities and restrictions for the skeletal linkages of the human foot may not be as unique as has been previously suggested.

Monitoring the effect of race-analysis parameters on performance in elite swimmers.

UNLABELLED: Time trials are commonly used in the lead-up to competition. A method that evaluates the relationship between time trial and competition performance in swimming would be useful for developing performance-enhancement strategies. PURPOSE: To use linear mixed modeling to identify key parameters that can be used to relate time-trial and competition performance. METHODS: Ten swimmers participated in the study. Each swimmer was analyzed during 3 time trials and 1 competition. Race video footage was analyzed to determine several key parameters. Pooling of strokes and distances was achieved by modeling changes in parameters between time trials and competition within each subject as linear predictors of percent change in performance using mixed modeling of log-transformed race times. RESULTS: When parameters were evaluated as the effect of 2 SD on performance time, there were very large effects of start time (2.6%, 90% confidence interval 1.8-3.3%) and average velocity (-2.3%, -2.8% to -1.8%). There was also a small effect for stroke rate (-0.6%, -1.3% to 0.2%). Further analysis revealed an improvement in performance time of 2.4% between time trials and competition, of which 1.8% (large; 1.4-2.1%) was due to a change in average velocity and 0.9% (moderate; 0.6-1.1%) was due to a change in start time; changes in remaining parameters had trivial effects on performance. CONCLUSION: This study illustrates effective analytical strategies for identifying key parameters that can be the focus of training to improve performance in small squads of elite swimmers and other athletes.

A procedure to refine joint kinematic assessments: Functional Alignment.

Functional Alignment is a new method to determine the orientation of a joint's primary rotational axis and the associated movement. It employs three unique concepts. First, data analyses are based upon assessment of spatial positions and not upon movement in a time sequence. Second, analyses are conducted on derived joint rotation matrices instead of tracked markers. This permits reanalysis of published biomechanical results and, therefore, provides a basis for unifying perspectives among different research efforts. Finally, the independent perspectives of the move and base segments require the analysis to use two unique descriptors of the joint axis orientation. These two mathematically necessary descriptors are also shown to be obtainable without reference to the original marker data. The combination of these approaches provides opportunities for additional comparisons of kinematic joint features that have been heretofore underappreciated.

Kinematic comparison of the preferred and non-preferred foot punt kick.

Kicking with the non-preferred leg is important in Australian Football and becoming important in the rugby codes. The aim of this study was to examine differences between preferred and non-preferred leg kicking in the drop punt kick. Seventeen elite Australian Football players performed kicks with the preferred and non-preferred leg. Optotrak Certus collected kinematic data of the kick leg and pelvis (200 Hz) from kick leg toe-off until ball contact. Foot speed, knee and shank angular velocity at ball contact, and pelvis range of motion were significantly larger for the preferred leg (P < 0.05). In contrast, hip and thigh angular velocity at ball contact and hip range of motion were significantly larger for the non-preferred leg. This indicates different movement patterns, with preferred-leg kicks making greater use of the pelvis, knee, and shank while non-preferred leg kicks rely relatively more on the hip and thigh (P < 0.05). Reasons for this difference might be due to locking degrees of freedom or sub-optimal sequencing in the non-preferred leg. The thigh-knee continuum identified by Ball ( 2008 ) was also evident in this study. Findings have implications for training non-preferred leg kicking for performance and injury prevention.

Effects of footwear on comfort and injury in professional rugby league.

The aim of this study was to determine the effectiveness of a tailored footwear programme on lower-limb comfort in professional rugby league players. The study was conducted over 30 weeks and involved two professional teams (n = 59 players) from the Australian National Rugby League competition. One team was assigned to a footwear programme (intervention), while players from the control group continued usual practices of self-selected footwear. The tailored footwear programme consisting of player education, prescription of footwear, and frequent rotation of footwear resulted in a lower incidence of injury and higher comfort ratings. The intervention group had fewer lower-limb injuries (P = 0.005; Cohen d = 0.72) and higher comfort ratings (P < 0.001, Cohen d = 1.24) than the control group. Specifically, the intervention group reported a lower incidence of poor comfort events (mean = 3.8, s = 2.7) than the control group (mean = 7.9, s = 3.7). Observations also included fewer time loss events in the intervention (mean = 6.3, s = 4.8) than the control group (mean = 11.0, s = 6.3) and reduced injuries per 1000 h in the intervention (24.79/1000) than the control group (30.76/1000). These findings should help medical advisers improve footwear comfort in sportspeople and so reduce the incidence of related injuries.

Golf styles and centre of pressure patterns when using different golf clubs.

When using a driver, the centre of pressure of a golfer shows a pattern that is characteristic of one of two distinct swing styles: the "front foot" style or the "reverse" style. The aim of this study was to establish whether these two swing styles are also evident when using other clubs, and if so, to determine whether golfers use the same swing style when using different clubs. Forty-six professional, amateur, and recreational golfers performed swings to hit a ball into a net placed 3 m away. Ten swings were performed for each of the driver, 3-iron, and 7-iron while standing on two force plates. The position of the golfer's centre of pressure parallel with the line of shot and relative to the feet was quantified at eight swing events that were identified from 200-Hz video. Cluster analysis confirmed that the front foot and reverse styles were evident in all three clubs, and most of the golfers (96%) used the same swing style for all three clubs. Golfers that used the reverse swing positioned their centre of pressure nearer to their toes at ball contact compared with golfers that used the front foot swing.

Intrarater and interrater reliability of 22 clinical measures associated with lower quarter malalignment.

OBJECTIVE: The purpose of this study was to assess the intrarater and interrater reliability of a broad range of techniques commonly used to assess the lower quarter. METHODS: A test-retest single group design was used to investigate the intrarater and interrater reliability of 22 lower quarter evaluation measures. Two raters conducted each measure twice on a total of 18 unimpaired subjects with an average age of 23.7 years. This study was conducted in the Human Performance Research laboratory in a university setting. Intraclass correlation coefficients were used to assess reliability of continuous variables, and weighted kappa was used to assess nominal or ordinal results. RESULTS: Side differences were not found (P > .05); thus, data for right and left legs were pooled (n = 36) where applicable. Intraclass correlation coefficient and weighted kappa results ranged from a low of 0.06 to a high of 0.99. Intrarater reliability results were generally higher than interrater reliability results. CONCLUSION: Many of the clinical measures demonstrated good overall reliability. For those tests where acceptable intrarater and interrater reliability cannot be demonstrated, additional training of raters, modification of the technique, or elimination of the technique's use should be considered.

Statistical analysis of the three dimensional joint complex.

Although three-dimensional data capture has become routine, statistical methods that take appropriate advantage of these multivariate data have not been widely developed. Researchers frequently rely on multiple isolated univariate statistical methods in the analysis of a joint's several axes of rotation and their associated motions. This approach reflects an inherent flaw in that it fails to appreciate the unbreakable link among these descriptors. We propose a new analytical perspective. Borrowing from the techniques of geometric morphometrics, data that describe multiple joint axis orientations and the motions about them are converted into a shape, an axis triangle, that is viewable in a three-dimensional space. In this format, multivariate statistical analyses can be conducted using conventional analytical packages. The axis triangle technique represents a significant advance over current analytical approaches in that it provides an encompassing method of appreciating joint rotations, as well as comprehensive consideration of joint function by linking rotational axis orientations with associated motion patterns.

On the problems of describing joint axis alignment.

Each three-dimensional joint possesses at least one potentially oblique axis of rotation. Several systems are used to express joint axis alignment. One system, designated the plane projection (PP) method, describes angles based on orthogonal projections onto two, of the three, anatomical planes. Alternatively, a joint axis may be described in two different ways using two sequential Cardan angle rotations. These expression systems all lay claim to similar descriptive labels, such as deviation and elevation. Difficulties arise as researchers use these various methods to compare their own data to the results of others. A joint axis alignment, described as 27 degrees deviation and 41 degrees elevation in PP, differs by as much as 6 degrees when expressed as Cardan angles. Differences among expression systems increase as the joint axis alignment becomes more oblique -- eventually differing by as much as 75 degrees . This paper explores implications for this lack of congruence among the joint axis expression systems. Effective steps in dealing with these issues begin with recognizing the existence and extent of the problem. The paper provides a common set of algorithms to illustrate and alleviate the possible problems associated with the exchange of joint axis alignment data.

Body sway, aim point fluctuation and performance in rifle shooters: inter- and intra-individual analysis.

In this study, we examined the relationships between body sway, aim point fluctuation and performance in rifle shooting on an inter- and intra-individual basis. Six elite shooters performed 20 shots under competition conditions. For each shot, body sway parameters and four aim point fluctuation parameters were quantified for the time periods 5 s to shot, 3 s to shot and 1 s to shot. Three parameters were used to indicate performance. An AMTI LG6-4 force plate was used to measure body sway parameters, while a SCATT shooting analysis system was used to measure aim point fluctuation and shooting performance. Multiple regression analysis indicated that body sway was related to performance for four shooters. Also, body sway was related to aim point fluctuation for all shooters. These relationships were specific to the individual, with the strength of association, parameters of importance and time period of importance different for different shooters. Correlation analysis of significant regressions indicated that, as body sway increased, performance decreased and aim point fluctuation increased for most relationships. We conclude that body sway and aim point fluctuation are important in elite rifle shooting and performance errors are highly individual-specific at this standard. Individual analysis should be a priority when examining elite sports performance.

Documentation and three-dimensional modelling of human soleus muscle architecture.

The purpose of this study was to visualize and document the architecture of the human soleus muscle throughout its entire volume. The architecture was visualized by creating a three-dimensional (3D) manipulatable computer model of an entire cadaveric soleus, in situ, using B-spline solid to display muscle fiber bundles that had been serially dissected, pinned, and digitized. A database of fiber bundle length and angle of pennation throughout the marginal, posterior, and anterior soleus was compiled. The computer model allowed documentation of the architectural parameters in 3D space, with the angle of pennation being measured relative to the tangent plane of the point of attachment of a fiber bundle. Before this study, the only architectural parameters that have been recorded have been 2D. Three-dimensional reconstruction is an exciting innovation because it makes feasible the creation of an architectural database and allows visualization of each fiber bundle in situ from any perspective. It was concluded that the architecture is non-uniform throughout the volume of soleus. Detailed architectural studies may lead to the development of muscle models that can more accurately predict interaction between muscle parts, force generation, and the effect of pathologic states on muscle function.

First Prize: Central motor excitability changes after spinal manipulation: a transcranial magnetic stimulation study.

BACKGROUND: The physiologic mechanism by which spinal manipulation may reduce pain and muscular spasm is not fully understood. One such mechanistic theory proposed is that spinal manipulation may intervene in the cycle of pain and spasm by affecting the resting excitability of the motoneuron pool in the spinal cord. Previous data from our laboratory indicate that spinal manipulation leads to attenuation of the excitability of the motor neuron pool when assessed by means of peripheral nerve Ia-afferent stimulation (Hoffmann reflex). OBJECTIVE: The purpose of this study was to determine the effects of lumbar spinal manipulation on the excitability of the motor neuron pool as assessed by means of transcranial magnetic stimulation. METHODS: Motor-evoked potentials were recorded subsequent to transcranial magnetic stimulation. The motor-evoked potential peak-to-peak amplitudes in the right gastrocnemius muscle of healthy volunteers (n = 24) were measured before and after homolateral L5-S1 spinal manipulation (experimental group) or side-posture positioning with no manipulative thrust applied (control group). Immediately after the group-specific procedure, and again at 5 and 10 minutes after the procedure, 10 motor-evoked potential responses were measured at a rate of 0.05 Hz. An optical tracking system (OptoTRAK, Northern Digital Inc, Waterloo, Canada [<0.10 mm root-mean-square]) was used to monitor the 3-dimensional (3-D) position and orientation of the transcranial magnetic stimulation coil, in real time, for each trial. RESULTS: The amplitudes of the motor-evoked potentials were significantly facilitated from 20 to 60 seconds relative to the prebaseline value after L5-S1 spinal manipulation, without a concomitant change after the positioning (control) procedure. CONCLUSIONS: When motor neuron pool excitability is measured directly by central corticospinal activation with transcranial magnetic stimulation techniques, a transient but significant facilitation occurs as a consequence of spinal manipulation. Thus, a basic neurophysiologic response to spinal manipulation is central motor facilitation.