The influences of string tension and frame stiffness on racquet and ball motions, and on impact loads at the elbow joint during the tennis backhand drive
Shin, In-Sik
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https://hdl.handle.net/2142/19087
Description
Title
The influences of string tension and frame stiffness on racquet and ball motions, and on impact loads at the elbow joint during the tennis backhand drive
Author(s)
Shin, In-Sik
Issue Date
1989
Doctoral Committee Chair(s)
Groppel, J.
Department of Study
Kinesiology and Community Health
Discipline
Kinesiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Applied Mechanics
Education, Physical
Engineering, Biomedical
Language
eng
Abstract
The motion of the ball and frame during and just after impact was inferred from the acceleration-time change of an accelerometer instrumented impactor pendulum, and the strain-time change of the frame during the clamped racket impact. The impulsive loads acting on the elbow joint were estimated by adopting an inverse dynamic analysis (impulse-momentum equation) for the racket and forearm during the backhand drive.
The stiffness and string tension conditions tested in the experiment were 5450 and 7540 N/m crossed with 178,245, and 311 N, respectively for the two phases of tests. Generally, the impulse of the first acceleration spike was not consistently affected by the string tension and frame stiffness. However, at the slowest impact speed, high string tension and flexible frame significantly reduced the impulse on the ball. This specific result was partly consistent with the impulse measured in actual backhand drive impact where only the tighter string reduced the impulse applied to the ball. Although the mean impulses produced by the stiff frame were larger than those by flexible frame at the tested string tensions, the difference was not significant.
The mean linear and angular impulses acting on the elbow joint during backhand drive were 0.804 N $\cdot$ sec and 0.416 N $\cdot$ sec, respectively, with large variability in the measures. The approximated peak impulsive force and moment was 144 N and 78 Nm respectively. The effect of different string tension and frame stiffness on the impulsive loads at the elbow joint during backhand drive was not significant.
Recommendations. A lighter impactor would improve the applicability of the impactor pendulum results to actual racket and ball interaction. A set of 3-D impulse-momentum equations need to be developed for incorporation into 3-D motion analysis.
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