IMPROVING TUMBLE TURN PERFORMANCE IN SWIMMING – ABOUT THE IMPACT OF WALL CONTACT TIME AND TUCK INDEX

Race time can be shortened by improving turn performance in competitive swimming, but this requires insight into the optimal turn technique. This study aimed to experimentally investigate the effect of wall contact time (WCT) and Tuck Index on the tumble turn performance. Eighteen Dutch national level swimmers participated and conducted tumble turns with three different WCTs and Tuck Indices. The results showed that a sufficiently long WCT that allows time to generate a high push-off force at the end of the wall contact when the body is in a proper streamlined position. The results also showed that it is possible to recommend an optimal Tuck Index for individual swimmers, which might help to improve their tumble turn and thus their race performance. These results should be verified by an intervention study in which the swimmers are trained to perform the tumble turn with the recommended WCTs and Tuck Indices

Understanding inconsistent step-length asymmetries across hemiplegic stroke patients: Impairments and compensatory gait

Background. In hemiplegic gait, step length typically differs in magnitude between paretic and nonparetic sides. However, the direction of step-length asymmetry varies across stroke patients. Objective. The study sought to understand directional variations in step-length asymmetry in terms of asymmetries in forward foot placement relative to the trunk and trunk progression. Methods. A total of 10 hemiplegic stroke patients and 9 healthy elderly controls walked at a self-selected comfortable speed while pelvic and heel marker positions were recorded. Step length, forward foot placement relative to the trunk, and trunk progression of paretic and nonparetic steps were quantified, as well as the asymmetries therein. Results. The 3 asymmetry indices in question varied within individual patients and occasionally fell within control reference ranges, whereas directional variations across stroke patients were observed for asymmetries in step length and forward foot placement only. Despite heterogeneity in asymmetry across patients, step-length asymmetry was determined by the sum of asymmetries in forward foot placement and trunk progression. Asymmetries in trunk progression and forward foot placement were negatively correlated. No significant association was observed between step-length asymmetry and any other asymmetry index. Conclusions. Step-length asymmetry was accounted for by asymmetries in forward foot placement and trunk progression, whereas their relative contribution accounted for directional variations in step-length asymmetry. Partitioning of step-length asymmetry further helped to identify individual impairments and compensatory gait strategies. An encompassing hemiplegic gait evaluation should therefore include an assessment of foot positioning relative to the trunk

HOW CRITICAL IS THE CHOICE OF DISTANCE-BASED MEASURES IN STUDYING TUMBLE TURN PERFORMANCE?

The turn is a crucial part of swim races and therefore requires systematic investigation. Yet, many different measures of turn performance are used in the literature. This study aimed to examine the level of agreement and the sensitivity of six fixed-distance based performance measures of the tumble turn. Tumble turn data of 10 Dutch elite level swimmers were analysed using those measures. The overall level of agreement was high between all measures (R ranging from 0.91 to 0.99). However, if the swimmers were ranked according to each of those measures, not all performance measures resulted in the same ranking. In particular, the rankings for measures with an exist distance of 10 m deviated from those for measures with an exit distance of 5 or 15 m. This finding suggests that the performance measures of interest are sensitive to different phases of the turn

In-plane field-induced vortex liquid correlations in underdoped Bi_2Sr_2CaCu_2O_8+\delta

The effect of a magnetic field component parallel to the superconducting layers on longitudinal Josephson plasma oscillations in the layered high temperature superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ is shown to depend on the thermodynamic state of the underlying vortex lattice. Whereas the parallel magnetic field component depresses the Josephson Plasma Resonance (JPR) frequency in the vortex solid phase, it may enhance it in the vortex liquid. There is a close correlation between the behavior of microwave absorption near the JPR frequency and the effectiveness of pancake vortex pinning, with the enhancement of the plasma resonance frequency occurring in the absence of pinning, at high temperature close to the vortex melting line. An interpretation is proposed in terms of the attraction between pancake vortices and Josephson vortices, apparently also present in the vortex liquid state.Comment: 8 pages, 7 Figures, submitted to Phys. Rev.

Informational and Neuromuscular Contributions to Anchoring in Rhythmic Wrist Cycling

Continuous rhythmic movements are often geared toward particular points in the movement cycle, as evidenced by a local reduction in trajectory variability. These so-called anchor points provide a window into motor control, since changes in the degree of anchoring may reveal how informational and/or neuromuscular properties are exploited in the organization of rhythmic movements. The present experiment examined the relative contributions of informational timing (metronome beeps) and neuromuscular (wrist postures) constraints on anchoring by systematically varying both factors at movement reversal points. To this end, participants cycled their right wrist in a flexed, neutral, or extended posture, either self-paced or synchronized to a metronome pacing peak flexion, peak extension, or both peak flexion and extension. The effects of these manipulations were assessed in terms of kinematics, auditory-motor coordination, and muscle activity. The degree of anchoring seen at the reversal points depended on the degree of compatibility of the prevailing configuration of neuromuscular and informational timing constraints, which had largely independent effects. We further observed systematic changes in muscular activity, which revealed distinct contributions of posture- and muscle-dependent neuromuscular properties to motor control. These findings indicate that the anchor-based discretization of the control of continuous rhythmic wrist movements is determined by both informational timing and neuromuscular constraints in a task-specific manner with subtle interactions between the two, and exemplify how movement variability may be exploited to gain such insights

How intrinsically motivating are swimming instructors/lessons in the Netherlands? An observational study through the lens of self-determination theory

BackgroundIt is desirable that (more) children continue swimming after having completed their swimming lessons to preserve their swimming skills and water safety, and as part of an active, healthy lifestyle. This may be encouraged by stirring children's intrinsic motivation for swimming during swimming lessons. However, it is currently unknown how intrinsically motivating swimming lessons are in Western countries.PurposeThis study examined to what extent swimming instructors in the Netherlands cater to the basic needs of autonomy, competence, and relatedness, which, according to Self-Determination Theory (SDT), promote intrinsic motivation. Additionally, it examined whether an SDT-based teaching program prompts instructors to better meet these needs, and to what extent the teaching program, the education and experience of the instructor, and the group size predict the employment of SDT in swimming lessons.MethodsA total of 128 swimming lessons given by equally many instructors were observed in the Netherlands and rated on a modified version of the SDT teaching style scale to assess autonomy, competence, and relatedness support. The swimming lessons referred to four teaching programs, one of which was explicitly based on SDT.ResultsInstructors exhibited autonomy-thwarting, weakly competence-supportive, and relatedness-supportive behaviors. The SDT-based teaching program scored higher on the provision of autonomy, competence, and relatedness in lessons. This finding was significant for autonomy. Teaching program was the only significant predictor of SDT employment by instructors.ConclusionFurther improvement is desirable in catering to the basic needs, particularly autonomy, which can be achieved by deliberately implementing the principles of SDT into teaching programs for swimming

A Re-Appraisal of the Effect of Amplitude on the Stability of Interlimb Coordination Based on Tightened Normalization Procedures

The stability of rhythmic interlimb coordination is governed by the coupling between limb movements. While it is amply documented how coordinative performance depends on movement frequency, theoretical considerations and recent empirical findings suggest that interlimb coupling (and hence coordinative stability) is actually mediated more by movement amplitude. Here, we present the results of a reanalysis of the data of Post, Peper, and Beek (2000), which were collected in an experiment aimed at teasing apart the effects of frequency and amplitude on coordinative stability of both steady-state and perturbed in-phase and antiphase interlimb coordination. The dataset in question was selected because we found indications that the according results were prone to artifacts, which may have obscured the potential effects of amplitude on the post-perturbation stability of interlimb coordination. We therefore redid the same analysis based on movement signals that were normalized each half-cycle for variations in oscillation center and movement frequency. With this refined analysis we found that (1) stability of both steady-state and perturbed coordination indeed seemed to depend more on amplitude than on movement frequency per se, and that (2) whereas steady-state antiphase coordination became less stable with increasing frequency for prescribed amplitudes, in-phase coordination became more stable at higher frequencies. Such effects may have been obscured in previous studies due to (1) unnoticed changes in performed amplitudes, and/or (2) artifacts related to inappropriate data normalization. The results of the present reanalysis therefore give cause for reconsidering the relation between the frequency, amplitude, and stability of interlimb coordination

Improving tumble turn performance in swimming—the impact of wall contact time and tuck index

Race time can be shortened by improving turn performance in competitive swimming, but this requires insight into the optimal turn technique. The aim of the present study was to examine the effect of Wall Contact Time (WCT) and Tuck Index on tumble turn performance and their interrelations by experimentally manipulating both variables, which has not been done in previous research. Eighteen Dutch national level swimmers (FINA points 552 ± 122) performed tumble turns with three different WCTs (shorter, preferred, longer) and three different Tuck Indices (higher, preferred, lower), which were recorded by four underwater cameras and a wall-mounted force plate. Linear kinematic and kinetic variables, including the approach velocity (Vin), wall adaptation time (Tadapt), percentage of active WCT (aWCT), peak push-off force (FPeak) and exit velocity (Vexit), were extracted from the recordings and analyzed statistically, using the 5 m round trip time (5mRTT) as performance measure. The results indicated that the WCT should be sufficiently long to generate a high push-off force at the end of wall contact when the body is in a streamlined position. This led to a significantly shorter 5mRTT than a shorter or longer WCT. A linear mixed effect model yielded negative significant effects of WCT (−4.22, p < 0.001), FPeak (−2.18, p = 0.04), Vin (−4.83, p = 0.02), Tadapt (−2.68, p = 0.002), and Vexit (−9.52, p < 0.001) on the 5mRTT. The best overall turning performance was achieved with a Tuck Index of 0.7, which suggests that some of the participating swimmers could benefit from adapting their distance to the wall while turning, as was exemplified by calculating the optimal Tuck Index for individual swimmers. These results underscore the importance of WCT and Tuck Index vis-à-vis tumble turn performance, as well as their interrelations with other performance determining variables in this regard

Visuomotor transformation for interception: catching while fixating

Catching a ball involves a dynamic transformation of visual information about ball motion into motor commands for moving the hand to the right place at the right time. We previously formulated a neural model for this transformation to account for the consistent leftward movement biases observed in our catching experiments. According to the model, these biases arise within the representation of target motion as well as within the transformation from a gaze-centered to a body-centered movement command. Here, we examine the validity of the latter aspect of our model in a catching task involving gaze fixation. Gaze fixation should systematically influence biases in catching movements, because in the model movement commands are only generated in the direction perpendicular to the gaze direction. Twelve participants caught balls while gazing at a fixation point positioned either straight ahead or 14° to the right. Four participants were excluded because they could not adequately maintain fixation. We again observed a consistent leftward movement bias, but the catching movements were unaffected by fixation direction. This result refutes our proposal that the leftward bias partly arises within the visuomotor transformation, and suggests instead that the bias predominantly arises within the early representation of target motion, specifically through an imbalance in the represented radial and azimuthal target motion

Visual and musculoskeletal underpinnings of anchoring in rhythmic visuo-motor tracking

Anchoring, that is, a local reduction in kinematic (i.e., spatio-temporal) variability, is commonly observed in cyclical movements, often at or around reversal points. Two kinds of underpinnings of anchoring have been identified—visual and musculoskeletal—yet their relative contributions and interrelations are largely unknown. We conducted an experiment to delineate the effects of visual and musculoskeletal factors on anchoring behavior in visuo-motor tracking. Thirteen participants (reduced to 12 in the analyses) tracked a sinusoidally moving visual target signal by making flexion–extension movements about the wrist, while both visual (i.e., gaze direction) and musculoskeletal (i.e., wrist posture) factors were manipulated in a fully crossed (3 × 3) design. Anchoring was affected by both factors in the absence of any significant interactions, implying that their contributions were independent. When gaze was directed to one of the target turning points, spatial endpoint variability at this point was reduced, but not temporal endpoint variability. With the wrist in a flexed posture, spatial and temporal endpoint variability were both smaller for the flexion endpoint than for the extension endpoint, while the converse was true for tracking with the wrist extended. Differential anchoring effects were absent for a neutral wrist posture and when gaze was fixated in between the two target turning points. Detailed analyses of the tracking trajectories in terms of velocity profiles and Hooke’s portraits showed that the tracking dynamics were affected more by wrist posture than by gaze direction. The discussion focuses on the processes underlying the observed independent effects of gaze direction and wrist posture on anchoring as well as their implications for the notion of anchoring as a generic feature of sensorimotor coordination