Serve the only stroke in which the player has full control over its outcome. Bahamonde (2000) The higher the velocity, the smaller the margin of

Transcription

1 Lower Extremity Performance of Tennis Serve Reporter: Chin-Fu Hsu Adviser: Lin-Hwa Wang

2 OUTLINE Introduction Kinetic Chain Serve Types Lower Extremity Movement Summary Future Work

3 INTRODUCTION Serve the only stroke in which the player has full control over its outcome. Bahamonde (2000) The higher the velocity, the smaller the margin of error. Modern tactics tennis players hit the ball with both max. speed and with an acceptable level of control. Girard, Micallef & Millet (2007) Dynamic L/E motion is considered a precursor to high h speed trunk and U/E segment rotations, ti and thus the origin of the stroke's kinetic chain. Bahamonde et al.(2000); Elliott et al. (2003); Girard et al. (2005)

4 KINETIC CHAIN Any disruption to the kinetic chain could result in Legs/trunk increased loading of other Kinetic joints Energy in the sequence (%): (51) of Force movements. (%):% 729 (54) Kibler (1994) Kibler (1995) Catch up Break the link of proximal part Higher risk on the distal segments. Enhancement of the functional ability of distal segments Same level of energy at the end of the kinetic chain.

5 Examine the influence of restricted t knee motion during the serve. Flat serve with normal (normal serve, S N ) and restricted (restricted serve, S R ) knee motion. Girard (2007) Z X Y

6 Restriction of one or more joints can deteriorate the coordination of the other body segments. Kinetic Chain Miller (1980); Elliott (1986) Focus on the resultant muscle torque patterns. Internal Forces Miller (1980) As a paradigm for interrupting the normal mechanisms used by players to perform the serve, rather than to focus on the contribution of L/E.

7 S R may have in turn decreased the ability of the shoulder to rotate t rapidly internally. Quadriceps muscles stretched elastic energy Speed of leg extension was certainly near 0 at the beginning of the kinetic chain force production. The movement of the trunk was then limited.

8 Summary of section Knee flexion before extension A prerequisite for an efficient execution of the serve, whatever the performance level. The movement of L/E to produce an effective high-speed serve through possible mechanisms. Coordinated movement, elastic energy and muscle preload.

9 SERVE TYPES 1 st Serve: Flat / Power serve (min spin on ball). 2 nd Serve: Topspin / Slice serve (sidespin) / Kick serve (hit with maximum spin). Reid, Elliott & Alderson (2007) Flat serve 3.06 sec (± 0.32) Spine serve sec(± 0.39) Lo et al. (2004)

10 Spin Serve Flat Serve

11 The ball toss position Ball release (sec) Flat Serve: 1.14 ± 0.27 Spin Serve: ± Lo et al. (2004) FS further forward high horizontal racquet velocities. KS lateral higher right lateral racquet velocities. The 1 st and 2 nd serves were performed during tournament play and likely with varying tactical intent. Chow (2003)

12 Racket (sec ) drop wind up cocking Flat Serve: 160± 1.60 ± Spin Serve: Max. anterior force (N) 1.77 ± 0.15 FS (167.3 ± 46.7) > KS (160.4 ± 52.5) Average rate of max. anterior loading (N.s - 1 ) Cocking phase FS (208.3 ± 56.2) > KS (189.9 ± 55.9) Anterior capsule & ligaments of the glenohumeral l joint Lo et al. (2004) These passive structures play an important role in limiting anterior translation of the humeral head to mitigate the prospect of glenohumeral instability.

13 Forward swing Acceleration (sec) Peak internal rotation moment (Nm): FS (22.7 ± 76) 7.6), KS(235± (23.5 ± 54) 5.4) Independent of serve type. Mean compression force (N): FS (228.6 ± 52.4) > KS (210.7 ± 54.2) Flat Serve: 0.31 ± 0.04 Spin Serve: 0.31 ± 0.02 Lo et al. (2004) The rotator cuff the compressive force to centre the humeral head in the glenoid fossa.

14 At impact (alignment of the shoulders ) Right rotation (toward impact): FS (41.6 ± 18.5) > KS (33.4 ± 10.2) Left lateral flexion (tilt to the left): FS (41.7 ± 7.8) < KS (64.4 ± 14.3) Forward flexion (upright): FS (56.4 ± 15.1) 1) < KS (67.2 ± 94) 9.4) The forward swing (larger amounts of lateral trunk flexion and trunk rotation) FS More forward flexion KS

15 Total Serving Time (sec) Flat Serve: 3.06 ± 0.32 Spin Serve: 3.22 ± Follow-through Lo et al. (2004) Mean compression force (N) FS (87.1 ± 39.6) > KS (75.7 ± 32.5) Peak external rotation moment (Nm) FS (18.8 ± 10.0) > KS (14.7 ± 6.6) Deceleration of the continued internal rotation of the upper arm is facilitated by post-impact external rotation moments.

16 Motion of ankle Left foot Plantar flexion (5 ) flexion toward dorsifiexion (mid-racket drop) max. of 18 dorsiflexion (acceleration) tiptoe toward plantarflexion Right foot Dorsiflexion (5 ) max. of 10 dorsiflexion (acceleration) tiptoe toward plantarflexion max. of 20 plantarflexion before impact Lo et al. (2004)

17 Motion of knee bend (begin) bend (mid-racket drop) max. bend (Acceleration) straighten back before impact FS Max. of 30 bend KS (spin) Max. of 50 bend Lo et al. (2004)

18 Motion of hip: Bend all the way straighten to 0 before impact bend immediately after impact Left foot: Abduction 20 abduct (mid-racket drop) max. 10 of abduction (acceleration) abduct Right foot: Maintain natural abduct (mid-racket drop) max. 15 of abduction adduct Lo et al. (2004)

19 Motion of pelvis & trunk Pelvis Rotate external (begin), internal rotate internal (acceleration) Backward tilt (0-5 ) KS (spin) > FS Trunk Rotate external (begin) Dorsiflexion (reach max. before impact) KS (spin) around 25 VS. FS around 18 Right-side bend (end of acceleration): 25 of both Lo et al. (2004)

20 Summary of section The ball toss position The 1 st and 2 nd serves varying tactical intent Alignment of the shoulders at impact The forward swing FS More forward flexion KS The rotator cuff generate stability & decrease the risk of injury.

21 LOWER EXTREMITY MOVEMENT Foot-up (FU): the rear foot is moved forward next to the front one during the push-off. Foot-back (FB): the feet stay at the same relative level. e Minimal leg drive (ARM): with minimal L/E action. Girard et al. (2007); Reid et al. (2008) Effective drive (ES): knee flexion (> 10 ) Minimal drive (MS): knee flexion (< 10 ) Elliott et al. (2003)

22 Kinematics FU, FB & ARM ES drive: use the inertial transfer from the trunk to U/L and move the upper arm into a position of MER. Reid, Elliott & Alderson (2008) Less internal rotator torque to stop the external rotation. MS drive: primarily use the external rotators to achieve MER. Greater internal rotator torque to reverse the rotation of the upper arm. ES & MS FB stance At max. is probable external rotation by-product (MER) of this of racquet stance's hand. wider base of support permitting greater squat depth. Elliott et al. (2003) FU stance may account for some of the higher vertical ground-reaction forces

23 Leg-drive skill: No significant difference between ES & MS groups just recorded shoulder post-impact ball velocities (162 km h external rotation angle. -1 ). Be confounded by the group's misrepresentative It would thus appear that racket speed is generated classification of leg drive based on the players' independent of stance, but significantly affected by angles of front knee flexion angle at MER. differential leg drive. FU, FB & ARM Elliott (2003)

24 Kinetics ES & MS This reduction placed a less load on the joint during the concentric ti contraction ti of fth the muscles involved in rotating the upper arm in the swing to impact. Less load is thus evident with the group with the larger front knee flexion in performing an action.

25 ES & MS Training must be such that the muscles surrounding these joints are strengthened both in eccentric and concentric movement patterns to help pp protect the region from injury. Physical preparation must encompass all sections of the body kinetic chain

26 FU, FB & ARM Dominant internal rotation moments were produced to decelerate external rotation of the upper arm throughout the majority of the cocking phase.

27 The notion of selected rotator cuff eccentric muscle activity, horizontal adduction and internal rotation of humerus throughout this phase. IR (+)/ER(-)

28 Summary of section FU & FB Generate similar resultant pre-impact racket velocities. Devoid of a leg drive less capable of developing high h resultant t racket velocities. ES & MS With a smaller front knee flexion and thus less leg- drive loaded the shoulder and elbow joints with larger torques (MER). Develop an effective leg-drive to attain high velocities with as small a loading profile as possible.

29 SUMMARY Knee flexion before extension Different L/E activity Generate similar resultant pre-impact racket velocities. Non-effective drive Loaded the shoulder and elbow joints with larger torques (MER). FS vs. KS Ball toss position Varying tactical intent Alignment of the shoulder at impact The rotator t cuff generate stability & decrease the risk of injury.

30 FUTURE WORK Comparison of serve with FS & KS (spin) The different position on the baseline.

31 Thanks for your attentions