1. The Biomechanics of a Tennis Forehand
Daniel Lewis
Biology 438
Prof. Rome
April 10, 2012
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2. Basic Principles Definition of the Forehand Other types of shots:
Struck with the dominant hand
Easiest and most natural, fundamental type of stroke
Usually hit with topspin
Other types of shots:
Backhand
Lob
Serve
Slice
Smash
Volley
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3. Five Steps of the Forehand
1) Positioning: Get into position 2) Stance: Turn your shoulders and, with help of your opposite arm, start bringing the racquet back
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4. Five Steps of the Forehand (cont’d)
3) Backswing: Swing the racquet straight back or in a loop style. 4) Forward swing: Swing the racquet head into the ball, extending the arm completely. 5) Follow-through: Finish the stroke over the opposite shoulder.
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5. My Forehand Stroke
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6. Body Co-Coordination Chain
Forehand relies on a “kinetic chain of events”
“The segments of the body act as a system of chain links whereby the force generated by one link, or body part, is transferred in succession to the next link” - J. Groppel (1984)
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7. Muscles Used for Power Generation
Legs and feet – pushing off
Feet push off the ground
Lower legs (calves), upper legs (quadriceps and hamstrings), and gluteus maximus
Hips and core – rotation
Hips (adductors and abductors), core (obliques and abdominals), and upper body (pectorals)
Upper body – following through
Upper body (pectorals), shoulder (deltoids), upper arm (biceps), forearm (brachialis), and hand
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8. Research Questions
At which point during the motion are the wrist speed and racket head speed at a maximum? Which is faster during contact with the ball, wrist or racket head speed?
What is the ball speed of my forehand, and how does it compare to those of players at other levels?
How much kinetic energy from the racket is transferred to the ball during the stroke?
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9. Measured Racket Head Speed
Used center of percussion to measure racket speed.
The racket head speed during contact was found to be 16.2 m/s (36.4 MPH).
Absolute maximum velocity was found to be 18.9 m/s (42.2 MPH) – .048 sec after contact
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10. Measured Wrist Speed
Wrist speed during contact was found to be 8.7 m/s (19.5 MPH)
Absolute maximum velocity was found to be 9.9 m/s (22.2 MPH) – .008 sec before contact
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11. Racket Head Speed vs. Wrist Speed
“The racket tip or head moves faster than the rest of the racquet or any part of the body.” – ITF (2007)
Body moves slower to allow the racquet head whip through the ball during contact.
“The stopping of the shoulders speeds up the next segment, the elbow, then the wrist, then the racquet and finally the racquet tip. The subsequent stopping of each body segment accelerates the speed of the next segment.” – ITF (2007)
Location
Speed During Contact
Maximum Speed During Stroke
Racket Head
36.4 MPH
42.2 MPH
Wrist
19.5 MPH
22.2 MPH
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12. Measured Ball Speed
Comparison of my forehand speed to results of a speed stroke survey
At the 2011 US Open, James Blake recorded the fastest ever forehand at 125 MPH
Player
Ball Speed
Daniel Lewis
51.6 MPH
High School player
46.1 MPH
NCAA Division I player
78.5 MPH
Roger Federer
75.8 MPH
Andy Murray
69.8 MPH
Rafael Nadal
88.7 MPH
Novak Djokovic
78.2 MPH
Andy Roddick
88.5 MPH
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13. Kinetic Energy Transfer to Ball
Kinetic energy of the racket head = ½ x massracket x (velocityracket)2
= (.5*.056*(46.2)^2) = 59.6 J
Kinetic energy of the ball = ½ x massball x (velocityball)2
= (.5*0.23*(16.3)^2) = 31.1 J
KEball/KEracket = 31.1/59.6 = 0.52
Only 52% of kinetic energy of the racket head is transferred to the ball upon contact
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14. Racket-Ball Contact as a Collision
Kinetic energy is not conserved
Semi-elastic collision
Examples of sources of kinetic energy loss
Racket
Racket strings
Topspin/backspin
Sound
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15. Measured Impulse on Ball
Impulse = Δp = massball x velocityball = 2.6 kg m/s
Average force on ball = Δp / timecontact = 2.6 / .006 s = 430 N
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16. Linear and Angular Momentum
Linear Momentum
Developed through the forces generated from the ground as you step forward and transfer your body weight from the back leg to the forward leg
Angular Momentum
Developed from the ground reaction forces (GRF)
Produces a sequence of body rotations (legs, hips, trunk, upper limb, and racket)
Trunk rotation is correlated with racket velocity (about 10%)
Used in the pre-stretching of the shoulder muscles to allow them to produce a larger tension
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17. Physics of Topspin Application of Bernoulli’s Law
A topspin shot is hit by sliding the racquet up and over the ball as it is struck.
The shot dips down after impact and also bounces at an angle lower to the ground than a flat shot.
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18. Summary and Conclusions
At which point during the motion are the wrist speed and racket head speed at a maximum? Which is faster during contact with the ball, wrist or racket head speed?
The racket speed is higher than the wrist speed, and both reach their maximum values near time of contact with ball
What is the ball speed of my forehand, and how does it compare to those of players at other levels?
My forehand speed was 51.6 MPH, compared to 46.1 MPH (HS), 78.5 MPH (NCAA D1), and MPH (ATP)
How much kinetic energy from the racket is transferred to the ball during the stroke?
Only 52% of the kinetic energy is transferred
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19. Further Investigation
Possible topics for study
Effect of different tennis racket parameters
Head size, string tension, racket material
Example: Hypercarbon (Ultra High Modulus Graphite)
Effect of various types of stances on power generation
Current research in the field
Electromyography to study muscle recruitment patterns
Correlation between forehand motions and injury frequency
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20. References
Bahamonde, R. “Biomechanics of the Forehand Stroke.” ITF CSSR 24.1 (2007): 6-8.
“Biomechanics of Tennis: An Introduction.” ITF Coaches Education Program Level 2 Coaching Course (2007): 1-47.
Brody, H. “The Physics of Tennis: the Ball-Racket Interaction.” American Journal of Physics (1997):
“Forehand Speed and Spin Rates of the ATP Stars.” Tennis Speed Blog Online. Web March < /2011/01/forehand-speed-and-spin-rates-of-atp.html>
Ivancevic, T. “Biomechanical Analysis of Shots and Ball Motion in Tennis and the Analogy with Handball Throws.” Physical Education and Sport 6.1 (2008):
Muscles in the Body Used in Tennis.” Livestrong Online. Web April <
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