An investigation to determine the kinematic variables associated with the production of topspin in the tennis groundstrokes

The ability to impart topspin to the ball when playing forehand and backhand groundstrokes can give a tennis player a tactical advantage in a rally. Recent developments in racket technology and tactical approaches to the game have increased the prevalence of topspin strokes. However, there is a limited scientific knowledge base for players and coaches to draw upon when seeking to improve this aspect of the game. Many of the kinematic analyses into tennis groundstrokes were conducted more than ten years ago, with measurement techniques that may not have accurately measured the anatomical rotations important for generating racket velocity. It has only recently been possible to measure the spin rate of a ball, and this has not been investigated in relation to the kinematics of a player. This study aimed to make an important contribution to the knowledge of tennis professionals by establishing which kinematic variables are related to the production of high ball spin rates resulting from topspin strokes. In order to achieve this aim, consideration was given to the accurate measurement of the joint rotations of the player in all planes of movement and the quantification of the ball spin rate. This information was used to answer three further questions; what are the kinematic differences between flat and topspin groundstrokes, how do these differences relate to the spin rate of the ball and how do these findings relate to individual players? Joint rotations were calculated based on three-dimensional data captured from twenty participants playing flat and topspin forehand and backhand strokes. The resulting ball spin rate was captured using a high-speed camera. The participants produced larger ball spin rates when playing the topspin strokes, indicating that they were able to produce spin if required. Analysis of the joint rotations revealed that there were adaptations in the stroke in order to achieve the higher spin rates. The adaptations were not uniform among participants, but did produce similar alterations in racket trajectory, inclination and velocity for the topspin strokes. It was these measures that were found to be the strongest predictors of ball spin rates, accounting for over 60 % of the variation in ball spin rate in the forehand stroke and over 70% in the backhand. Case study analyses confirmed the importance of the optimal racket kinematics at impact and provided models of technique throughout the forward swing of each stroke. This study has made a contribution to the knowledge of generating topspin in the tennis groundstrokes by establishing the parameters that predict high spin rates and applying them to analyses of individual players. In doing so, this investigation has also demonstrated methodology that is capable of accurately measuring the joint rotations associated with tennis strokes, and suggested a method by which the spin rate of the ball can be calculated

QUANTIFYING AXIAL ROTATION OF UPPER EXTREMITY SEGMENTS

The calibrated anatomical systems technique (CAST) (Cappozzo et al, 1995) is an established method in gait and lower limb analyses. Its application to 6-degrees-of-freedom kinematic analyses and reduction of soft tissue artefact could make it particularly useful in quantifying axial rotation of the upper extremity. Such rotations have been established as being important in generating racket-head velocity in a variety of racket skills (Marshall and Elliott, 2000). The present study assesses the accuracy of CAST in quantifying the rotation of the forearm

EQUESTRIAN RIDER TRUNK-PELVIS STRATEGIES CAN BE IDENTIFIED USING SELF-ORGANISING MAPS

The purpose of the study was to explore whether equestrian riders can be grouped by their trunk-pelvis movement strategy. Riders (n = 40) with national or international competition experience in dressage were measured using motion capture on a riding simulator for ten seconds of simulated medium and extended trot. Trunk and pelvic pitch trajectories were filtered, time-normalised to the riding simulator’s vertical displacement cycle, and scaled. A self-organising map, with subsequent k-means clustering, identified three groups of rider-trunk pelvis movement. These groups related to the relative timing between peak posterior trunk and pelvis pitch. The study identified movement-based classifications of riders for future studies, which may have implications for rider injury risk and training

Predicting impact shock magnitude: which ground reaction force variable should we use?

Peak tibial acceleration (PTA) measured using accelerometers attached to the musculoskeletal system is considered the most effective method of quantifying impact shock magnitude as a result of footstrike during running. Ground Reaction Forces (GRFs) measured using force plates are also widely used to predict PTA. However it is not clear which is the most effective GRF variable to use. This has led to different variables being reported within biomechanics literature. This study aimed to identify which GRF variable is the most suitable for consistent and accurate prediction of impact shock magnitudes. Thirteen participants (10 male and 3 female) took part in this study. Simultaneous tibial accelerations and GRF information were recorded as participants ran at 4.0ms-1+5% over a force platform. The relationship between various GRF parameters including, average vertical loading rates, peak instantaneous vertical loading rates (PIVLR), event times were compared to tibial shock magnitudes using Pearson correlations

Coordination variability reveals the features of the 'independent seat' in competitive dressage riders.

The rider's ability to consistently coordinate their movements to their horse is a key determinant of performance in equestrian sport. This study investigated the inter-segmental coordination variability between the vertical displacement of a riding simulator and the pitch rotation of 28 competitive female dressage riders' head, trunk, pelvis, and left foot, in simulated medium and extended trot. A statistical non-parametric mapping three-way repeated-measures ANOVA investigated the influence of gait, competition level and segment on coordination variability. There was a significant main effect of gait and segment (p = 0.05), however, no significant effect of competition level. In medium trot, simulator-pelvis coupling was significantly (p < 0.001) less variable than simulator-head, -trunk, and -foot couplings. Significantly greater coordination variability of simulator-head and -foot relative to the trunk and pelvis suggested that riders can maintain stability in the saddle with their trunk and pelvis while allowing greater variability of their head and foot coupling to the simulator's vertical displacement. It is proposed that stronger coupling of the rider's pelvis relative to their other segments is one facet of the equestrian dressage skill of the independent seat. However, greater perturbations during simulated extended trot may necessitate a decrease in the independence of the rider's seat