Effect of endpoint conditions on position and velocity near impact in tennis

Abstract

Smoothing to obtain accurate position and velocity data near impacts in sport biomechanics studies is complicated by the accelerations of impact, endpoint effects and the smoothing technique used. Wrist goniometric data with two levels of random noise added were used to examine three endpoint modelling conditions for obtaining accurate position and velocity data at impact in the tennis forehand. The common approach of smoothing through impact created distortions of the position signal up to 100 ms before impact and resulted in consistent underestimations (-3.2%) of wrist angle and angular velocity (-67.9%) at impact. New linear and polynomial extrapolation conditions smoothed with all techniques provided lower root mean squared errors than the smoothing-through-impact condition, with discrete wrist positions at impact within 1.1% of the criterion data. Both the new linear and polynomial conditions can be used to make more accurate angular position and velocity estimates for tennis impacts, whereas the smoothing-through-impact condition creates spurious decreases in speed before impact that in the past have been assumed to be aspects of skillful movement.

The effect of ball impact location on racket and forearm joint angle changes for one-handed tennis backhand groundstrokes

“…The methodology used to collect the data was appropriate with small reconstruction errors. Due to the difficulties of smoothing through an impact (Knudson, 1990;Knudson & Bahamonde, 2001) it was decided to use the raw data in this study; Figure 3 is typical and shows that smoothing the raw data would not have affected the findings. The tracking of the ball in a dynamic movement with reflective tape on the ball is challenging, and future studies should investigate whether curve fitting techniques could improve the tracking of the ball.…”

“…For each participant this resulted in a minimum of 24 successful trials. Each successful trial was analysed using a model created through Vicon Bodybuilder software with the raw marker data (Filtering kinematics data through the time of ball-racket impact can result in erroneous data (Knudson, 1990;Knudson and Bahamonde, 2001)). The model allowed ball-racket impact location to be calculated relative to the centre of the racket stringbed, by identifying the instant at which the centre of the ball was closest to the stringbed through computing the sum of squares distance from the centre of the ball to the four markers on the stringbed frame.…”

Rotation sequence to report humerothoracic kinematics during 3D motion involving large horizontal component: application to the tennis forehand drive

“…The follow-through began two frames after impact and lasted until the elbow reached its maximal height. Frames surrounding the impact were removed in order to prevent issues associated with data smoothing through the impact (Knudson & Bahamonde, 2001). Using such definitions, stroke phases were defined independently of humerothoracic angles.…”

Application of the Extrapolation Method to Motion Analysis of the Flat Power Serve in Tennis

“…A common solution to the problem of endpoint errors is to extrapolate 5 -20 points at the end of the raw data. A number of extrapolation methods have been proposed to correct endpoint error (Smith, 1989;Vint and Hinrich, 1996;Giakas, et al, 1998;Knudson and Bahamonde, 2001). Smith (1989), who tested the linear extrapolation, duplication and refl ection methods using the angular displacement data reported by Pezzack, et al, (1977), suggested that the refl ection method was somewhat superior to the linear extrapolation method.…”

“…In these studies, these extrapolation methods were not applied to practical biomechanical data. Knudson and Bahamonde (2001), who tested fi ve-point linear extrapolation and polynomial extrapolation using wrist goniometric angle data in the tennis forehand stroke, concluded that both extrapolation methods were effective for removing noise in the goniometric angle data. Moreover, Knudson and Bahamonde (2001) …”