The Biomechanics of a Tennis Forehand Daniel Lewis Biology 438 Prof. Rome April 10, 2012 Daniel Lewis The Biomechanics of a Tennis Forehand Slide 1 of 20

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 Daniel Lewis The Biomechanics of a Tennis Forehand Slide 2 of 20

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 Daniel Lewis The Biomechanics of a Tennis Forehand Slide 3 of 20

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. Daniel Lewis The Biomechanics of a Tennis Forehand Slide 4 of 20

My Forehand Stroke Daniel Lewis The Biomechanics of a Tennis Forehand Slide 5 of 20

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) Daniel Lewis The Biomechanics of a Tennis Forehand Slide 6 of 20

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 Daniel Lewis The Biomechanics of a Tennis Forehand Slide 7 of 20

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? Daniel Lewis The Biomechanics of a Tennis Forehand Slide 8 of 20

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 Daniel Lewis The Biomechanics of a Tennis Forehand Slide 9 of 20

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 Daniel Lewis The Biomechanics of a Tennis Forehand Slide 10 of 20

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 Daniel Lewis The Biomechanics of a Tennis Forehand Slide 11 of 20

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 Daniel Lewis The Biomechanics of a Tennis Forehand Slide 12 of 20

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 Daniel Lewis The Biomechanics of a Tennis Forehand Slide 13 of 20

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 Daniel Lewis The Biomechanics of a Tennis Forehand Slide 14 of 20

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 Daniel Lewis The Biomechanics of a Tennis Forehand Slide 15 of 20

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 Daniel Lewis The Biomechanics of a Tennis Forehand Slide 16 of 20

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. Daniel Lewis The Biomechanics of a Tennis Forehand Slide 17 of 20

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 69.8-88.7 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 Daniel Lewis The Biomechanics of a Tennis Forehand Slide 18 of 20

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 Daniel Lewis The Biomechanics of a Tennis Forehand Slide 19 of 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 65.10 (1997): 981-87. “Forehand Speed and Spin Rates of the ATP Stars.” Tennis Speed Blog Online. Web. 2011. 31 March 2012. <http://blog.tennisspeed.com /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): 51-66. Muscles in the Body Used in Tennis.” Livestrong Online. Web. 2011. 04 April 2012. <http://www.livestrong.com/article/105577-muscles-body-used-tennis/> Daniel Lewis The Biomechanics of a Tennis Forehand Slide 20 of 20