Motor abundance and control structure in the golf swing

Evaluation of shaft angle to ball-to-target line as a predictor of horizontal delivery plane angle in the golf swing

The shaft angle to the ball-to-target line at various points in the golf swing is used by coaches as an indication of the horizontal delivery plane angle (HPA). The aim of the current study was to understand to what degree this simplified method of using the shaft orientation can predict the orientation of the HPA. Fifty-two male golfers hit 40 drives each in an indoor biomechanics laboratory. Between-subject regression models were created for the relationship between the HPA and the shaft angle to the ball-to-target line at three different swing positions. Additionally, single subject regression models were created for each subject for the small variables. The only significant between-subjects regression model was for mid-downswing (Adjusted R2 = 89.5%, RMSE = 2.41°); however, this was deemed not accurate enough to distinguish differences between typical driver and wedge HPA. The only shaft position to have significant single-subject regression models for all participants was mid-downswing. The mean RMSE for those models was determined to be low enough to distinguish typical driver and wedge swing planes within individuals. Overall, the shaft angle was only deemed accurate enough to predict the HPA within individual subjects, and only for mid-downswing.

Extracting proficiency differences and individual characteristics in golfers' swing using single-video markerless motion analysis

In this study, we analyzed golfers' swing movement to extract differences in proficiency and individual characteristics using two-dimensional video data from a single camera. We conducted an experiment with 27 golfers who had a wide range of skill levels, using a 7-iron; we acquired video data with a camera on the sagittal plane. For data extraction, we used pose estimation (using HRNet) and object detection (using DeepLabCut) methods to extract human-joint and club-head data. We examined the relationship between proficiency and individual characteristics vis-à-vis forward tilt angle and club trajectory. The results showed that the stability and reproducibility of the forward tilt angle are characteristics of proficiency. Highly skilled golfers showed low variability and high reproducibility between trials in forward tilt angle. However, we found that club trajectory may not be a characteristic of proficiency but rather an individual characteristic. Club trajectory was divided roughly into clockwise rotation and counterclockwise rotation. Thus, the analysis based on video data from a single markerless camera enabled the extraction of the differences in proficiency and individual characteristics of golf swing. This suggests the usefulness of our system for simply evaluating golf swings and applying it to motor learning and coaching situations.

A distal external focus of attention facilitates compensatory coordination of body parts

Many studies have shown that focusing on an intended movement effect that is farther away from the body (distal external focus) results in performance benefits relative to focusing on an effect that is closer to the body (proximal external focus) or focusing on the body itself (internal focus) (see, Chua, Jimenez-Diaz, Lewthwaite, Kim & Wulf, 2021). Furthermore, the advantages of a distal external focus seem to be particularly pronounced in skilled performers (Singh & Wulf, 2020). The present study examined whether such benefits of more distal attentional focus may be associated with enhanced functional variability. Volleyball players (n = 20) performed 60 overhand volleyball serves to a target. Using a within-participants design, the effects of a distal external focus (bullseye), proximal external focus (ball) and an internal focus (hand) were compared. The distal focus condition resulted in significantly higher accuracy scores than did the proximal and internal focus conditions. In addition, uncontrolled manifold analysis showed that functional variability (as measured by the index of synergy) was greatest in the distal focus condition. These findings suggest that a distal external focus on the task goal may enhance movement outcomes by optimising compensatory coordination of body parts.

The relationship between skill and ground reaction force variability in amateur golfers

It is accepted that highly skilled golfers are more consistent in their clubhead presentation and shot outcomes than their lesser skilled counterparts. However, the relationships between movement variability, outcome variability and skill in golf are not particularly well understood. This study examined the ground reaction force variability of one-hundred and four amateur golfers for shots with drivers and 5-irons. Principal component analysis was used as a data reduction technique and allowed all three components of ground reaction force to be considered together. There were statistically significant trends for the higher skilled golfers to display lower variability in two of the five principal components (driver) and four of the five principal components (5-iron). A similar trend was also observed in the other principal components, but these trends were not statistically significant. Intra-individual variability was much lower than inter-individual variability across all golfers; the golfers were each relatively consistent in maintaining their own ground reaction force patterns. Lower variability in ground reaction forces may partly explain how highly skilled golfers maintain lower variability in shot outcomes.

One more time about motor (and non-motor) synergies

We revisit the concept of synergy based on the recently translated classical book by Nikolai Bernstein (On the construction of movements, Medgiz, Moscow 1947; Latash, Bernstein's Construction of Movements, Routledge, Abingdon 2020b) and progress in understanding the physics and neurophysiology of biological action. Two aspects of synergies are described: organizing elements into stable groups (modes) and ensuring dynamical stability of salient performance variables. The ability of the central nervous system to attenuate synergies in preparation for a quick action-anticipatory synergy adjustments-is emphasized. Recent studies have demonstrated synergies at the level of hypothetical control variables associated with spatial referent coordinates for effectors. Overall, the concept of synergies fits naturally the hierarchical scheme of control with referent coordinates with an important role played by back-coupling loops within the central nervous system and from peripheral sensory endings. Further, we review studies showing non-trivial changes in synergies with development, aging, fatigue, practice, and a variety of neurological disorders. Two aspects of impaired synergic control-impaired stability and impaired agility-are introduced. The recent generalization of the concept of synergies for non-motor domains, including perception, is discussed. We end the review with a list of unresolved and troubling issues.

Multifractality in postural sway supports quiet eye training in aiming tasks: A study of golf putting

The 'quiet eye' (QE) approach to visually-guided aiming behavior invests fully in perceptual information's potential to organize coordinated action. Sports psychologists refer to QE as the stillness of the eyes during aiming tasks and increasingly into self- and externally-paced tasks. Amidst the 'noisy' fluctuations of the athlete's body, quiet eyes might leave fewer saccadic interruptions to the coupling between postural sway and optic flow. Postural sway exhibits fluctuations whose multifractal structure serves as a robust predictor of visual and haptic perceptual responses. Postural sway generates optic flow centered on an individual's eye height. We predicted that perturbing the eye height by attaching wooden blocks below the feet would perturb the putting more so in QE-trained participants than participants trained technically. We also predicted that QE's efficacy and responses to perturbation would depend on multifractality in postural sway. Specifically, we predicted that less multifractality would predict more adaptive responses to the perturbation and higher putting accuracy. Results showed that lower multifractality led to more accurate putts, and the perturbation of eye height led to less accurate putts, particularly for QE-trained participants. Models of radial error (i.e., the distance between the ball's final position and the hole) indicated that lower estimates of multifractality due to nonlinearity coincided with a more adaptive response to the perturbation. These results suggest that reduced multifractality may act in a context-sensitive manner to restrain motoric degrees of freedom to achieve the task goal.

Consistent Hand Dynamics Are Achieved by Controlling Variabilities Among Joint Movements During Fastball Pitching

This study aimed to determine whether covariations among joint movements are utilized to stabilize hand orientation and movement and to determine which of the upper or lower extremities make effective use of the covariation. Joint angles during pitching were measured in 12 skilled baseball pitchers, using a motion capture system. The joint angles in 10 successful trials were used for the reconstructed motions. The reconstructed motion in the first condition was the same as for the measured motion. In the second condition, the reconstructed motion was generated with joint angles that were pseudo-randomly selected to artificially break off covariation in the measured joint-angle combination. In the third and fourth conditions, the reconstructed motions were generated with the same joint-angle combinations as the measured angles in the throwing arm and the stride leg, respectively, but pseudo-randomly selected in the other joint angles. Ten reconstructed motions were generated for each condition. Standard deviations (SDs) of hand orientation and movement direction were calculated and compared among the conditions. All SDs for the first condition were the smallest among the conditions, indicating that the movements in the measured condition used the covariation in joint angles to make the hand movement stable. The results also illustrated that some SDs in the fourth condition were smaller than those in the third condition, suggesting that the lower extremity made effective use of the covariation. These results imply that it is necessary not only to reduce variability in each joint but also to regulate joint movements to stabilize hand orientation and movement.

Differences in kinematics and driver performance in elite female and male golfers

The aim of this study was to compare swing kinematic differences between women and men and investigate which variables predict clubhead speed (CHS) and carry distance (CD) whilst accounting for individual variation.

METHODS

Swing kinematics and driver performance data were collected on 20 (10 women) elite golfers (HCP 0.7 ± 1.4). We used Bayesian T-test for between sex comparison of swing kinematics and Bayesian Analysis of covariance (ANCOVA) to produce general linear models for CHS and carry distance for elite female and male golfers separately.

RESULTS

There was strong evidence that the driver performance variables CHS and CD were decreased in women compared to men, and two kinematic variables; time to arm peak speed downswing and angular wrist peak speed were slower in women. The ANCOVAs identified very strong to overwhelming evidence that participant as a fixed factor was a determinant of CHS for both women and men but was not a determinant of CD.

CONCLUSION

when looking to enhance driver performance among high-level golfers, coaches should be aware that variables that determine CHS and CD differ among women and men and if the aim is to improve CHS coaches should not forget the importance of individual swing characteristics.

An Uncontrolled Manifold Analysis of Arm Joint Variability in Virtual Planar Position and Orientation Telemanipulation

OBJECTIVE

In teleoperated robot-assisted tasks, the user interacts with manipulators to finely control remote tools. Manipulation of robotic devices, characterized by specific kinematic and dynamic proprieties, is a complex task for the human sensorimotor system due to the inherent biomechanical and neuronal redundancies that characterize the human arm and its control. We investigate how master devices with different kinematics structures and how different task constraints influence users capabilities in exploiting arm redundancy.

METHODS

A virtual teleoperation workbench was designed and the arm kinematics of seven users was acquired during the execution of two planar virtual tasks, involving either the control of position only or position-orientation of a tool. Using the uncontrolled manifold analysis of arm joint variability, we estimated the logarithmic ratio between the task irrelevant and the task relevant manifolds ( R_v).

RESULTS

The R_v values obtained in the position-orientation task were higher than in the position only task, while no differences were found between the master devices. A modulation of R_v was found through the execution of the position task and a positive correlation was found between task performance and redundancy exploitation.

CONCLUSION

Users exploited additional portions of arm redundancy when dealing with the tool orientation. The R_v modulation seems influenced by the task constraints and by the users possibility of reconfiguring the arm position.

SIGNIFICANCE

This paper advances the general understanding of the exploitation of arm redundancy in complex tasks, and can improve the development of future robotic devices.

Uncontrolled manifold analysis of joint angle variability during table tennis forehand

This study was conducted with the objective of evaluating the variance structure of the trunk and racket arm joint angles in table tennis topspin forehand using the uncontrolled manifold (UCM) approach, regarding racket orientation as the task variable. Nine advanced and eight intermediate male collegiate table tennis players performed the topspin strokes against backspin balls. The trunk, upper limb, and racket were modeled as six rigid-link segments with a total of 16 rotation degrees of freedom. The UCM analysis was conducted using 30 trial datasets per participant to quantify the degree of redundancy exploitation needed to stabilize the vertical and horizontal angles of the racket. Irrespective of the performance level, the variance of the joint angle vector increased towards ball impact. The degree of redundancy exploitation increased towards ball impact. As a result, the variability of the racket angles was minimal at impact. Both groups of players used the relative movement between the racket and the hand to stabilize the racket angles at ball impact. The variance of the joint angle vector that affected the vertical racket face angle at ball impact was significantly smaller for advanced players than for intermediate players, and the degree of redundancy exploitation to stabilize that angle at impact tended to be larger for the advanced players. The ability to use the redundancy of the joint configuration to stabilize the vertical racket face angle at impact may be a critical factor that affects performance level.