Questo articolo mette a confronto un rovescio ad una mano di una giocatrice "normale" con quello della Henin per valutare quali siano le differenze sostanziali. L'articolo è molto interessante ma purtroppo (almeno per ora) non siamo in grado di fornirvi la traduzione in italiano.
Tratto da www.tenniscruz.com
Autore: Dr. Calvin Nii
See how Dr. Calvin analyses the tennis backhand topsin of Carlyn a run of the mill tennis player. How he compares it to Justine Henin's powerful professional topspin backhand and what adjustments should Carlyn make to bring her tennis to professional level.
Read this article patiently and you may find things about tennis strokes you never even thought they existed. Sergio Cruz
SECTION I: PLAYER INFORMATION
Player Name: Carlyn
Gender: Female
Age: 22
Ranking: Not active
Stroke type: One-handed Backhand (Right-Handed)
Submitted Video Format: PAL Standard (25 fps; AVI format); modified front perspective
SECTION II: QUALITATIVE VIDEO EVALUATION
Summary: The submitted video showed Carlyn a young female player executing a one-handed, topspin backhand with her right hand in what appears to be a training situation. Qualitatively, the stroke mechanics of the player reflect the technical elements of a very sound, biomechanically-efficient, one-handed topspin backhand.
The still image sequence below shows each of the main phases of the player’s one-handed topspin backhand stroke. The core elements and characteristics of the stroke movements are listed below in each of the image captions.
We prepared a still image sequence from the video sample of Carlyn's one-handed topspin backhand to qualitatively analyze the technical elements of her stroke.
Our overall impression is that she executes nearly all of the key technical elements of a traditional one-handed topspin backhand (Eastern Backhand grip, high racket preparation, impact well in front of the body, and a classical, low-to-high swing path) at a very high level. In particular, we noticed her excellent, athletic ready position, solid overall balance and very steady head position throughout the stroke. All of these are crucial, yet often underappreciated elements in the proper execution of any stroke.
We did not observe any significant technical flaws or errors in the execution of this stroke.
 |
|
|
| A. Ready Position | B. Completed Backswing | C. Initiation of Forward Swing to Impact |
| Full Eastern backhand grip (1) | Square to slightly closed hitting stance (3) | Back leg flexed, front knee aligned higher than the back knee (6) |
Athletic Ready Position: weight on balls of feet, knees flexed slightly, non-dominant hand on racket throat (2)
| Full hip and shoulder turn (4) | Full hip and shoulder turn (4) Level to slightly upward shoulder plane (front shoulder higher than rear) during the forward swing (7) |
| Supporting the racket with the non-dominant hand in the backswing phase (5) | Square to slightly closed racket face just before initiation of the forward swing (8) | |
D. Impact Position |
E. Post-Impact Position |
6. Follow-through |
| Contact point well in front of the front hip (9) | Very stable lower body during forward swing (12) | Full follow-through with the racket hand finishing above shoulder level (15) |
| Racket face slightly closed at impact (10) | Non-dominant arm remains parallel to upper body during forward swing (13) | Good balance through all stroke phases (16) |
| Minimal shoulder movement during forward swing (11) | Classical, 45 to 60º upward swing path (14) |
Summary: The submitted video showed Carlyn executing a right-handed, one-handed topspin backhand in what appears to be a training situation. Overall, this player demonstrated virtually all of the key technical elements of a very sound, biomechanically-efficient, traditional one-handed topspin backhand.
Section 3: BVM Analysis of the one-handed backhand of Carlyn:
Now, let’s look at the BVM analysis of Carlyn.
Figure 1. BVM kinematic chain analysis of Carlyn's one-handed topspin backhand.
Carlyn clearly demonstrates an optimal, traditional kinematic chain that demonstrates the stereotype body movement sequence of a skilled athleteexecuting a swinging movement where the hip segment (1) reaches its maximum speed first, followed by the shoulder (2), the hand (3), and finally the racket (4).
Carlyn has the characteristic pattern of a biomechanically efficient and effective (stroke) movement where each body segment used in the stroke accelerates, peaks, then decelerates before this pattern repeats in the next segment of the (stroke) movement. This sequence of movements results in a continuous transfer of energy/speed from each body segment into ball impact.
The first interesting feature of this player’s kinematic chain is the sudden deceleration of the racket between the 1.05 to 1.15 second timepoints of the graph (see image below; racket speed is the purple trace, hand speed is red; shoulder speed is blue and hip speed is green).
Figure 2. Close-up of racket deceleration (arrow) just before starting the forward swing.
This deceleration was due to the player moving the racket downward to align the racket face with the path of the oncoming ball. After this “falling” of the racket, the player then accelerated forward to contact—seen as the sharp rise in racket speed (purple line).
The second interesting feature that we observed from BVM analysis is a second firing of the hip segment (Figure 3) AND the shoulder segment (Figure 4)occurring just before impact.
Figure 3. Unknown player demonstrates second firing of the hip segment.
This second firing of the hip and shoulder segment is a phenomenon that we have observed in the swinging movements of elite-level tennis, golf and baseball athletes, and apparently can only be detected using our BVM method of biomechanical analysis.
Figure 4. Unknown player demonstrates second firing of the shoulder segment.
Traditional biomechanical analysis of athletic movements have almost exclusively relied on measurements of rotational speed, not linear (translational) speed like BVM, and have failed to resolve/reveal this novel movement pattern: multiple body segments accelerating simultaneously, at multiple times during the overall movement sequence. What traditional, rotation speed-based analyses have shown is that only a single body segment (i.e. the racket segment) is accelerating (to maximum speed), at any one time in the overall movement sequence (see Appendix for an explanation of traditional, rotation speed-based, kinematic chain analysis).
What then is so interesting or useful to the athlete about the ability to accelerate their body segments more than once in executing a stroke, pitch, or swing?
The answer is: this ability to accelerate multiple body segments simultaneously, as well as accelerate them more than once in the overall movement sequence—rather than a single body segment at any one point—enables the athlete to deliver more energy to impact and thereby increase the overall power level of the stroke.
Rather than relying solely on the energy of the hands and arms to transfer energy to the ball, elite athletes are able to combine integrate and therefore combine the energy and force of their entire upper body from hips to shoulders and deliver it to the ball at impact.
Section 4. BVM Analysis of the one-handed topspin backhand of Justine Henin:
Figure 5. BVM analysis of the Henin one-handed topspin backhand (Indian Wells 2006).
Now, for the purposes of comparison, let’s take a look at a BVM analysis of a top player’s one-handed topspin backhand. We did a BVM analysis of the one-handed topspin backhand of former WTA #1 and 7-time Grand Slam singles champion, Justine Henin. What’s interesting is that like Carlyn, Henin is able to fire multiple body segments simultaneously in her overall movement sequence of her topspin backhand stroke.
Specifically, Henin accelerates fires her hips andher shoulder, as well as her hand and racket simultaneously as she accelerates her racket to contact. And, like Carlyn, Justine Henin demonstrates a “double firing” of her shoulders in this particular sequence.
Section 5. Comparison of the Henin and Unknown Player Backhands:
1. Henin hits a faster ball than the Unknown Player: The main difference between the backhands of the two players lies in the higher body segment speeds achieved by Henin compared to the Unknown Player. Based on the analysis here, Henin takes about 0.2 seconds to accelerate to impact after completing her backswing, whereas Carlyn takes 0.4 seconds, a difference of 50 percent. Henintherefore showed much higher hip, shoulder, hand and racket speeds compared to the Carlyn.
Based on these body segment speed differences, we wanted to estimate the ball speed of each player’s backhand using BVM. There were certain technical complications in estimating the ball speed for Carlyn because of the partial front view perspective of her video, yet we were still able to determine that her ball speed was approximately 69.2 KPH. In contrast, Henin’s ball speed was 91.6 KPH. The difference in ball speed between these two players is over 30 percent!
2. Henin demonstrates simpler and more integrated body movements than Carlyn: Another difference between the two players revealed by BVM analysis was that Henin’s kinematic chain appears to contain fewer movements overall and less variation in body segment speeds compared to the kinematic chain of Carlyn.
What explains these differences is difficult to evaluate without knowing the exact situation each player faced when the video was taken. The Henin video was taken during about halfway into her stroke warmup with a hitting partner preceding a tournament match. In contrast, Carlyn appears to be striking a fed ball, perhaps in a pure training session. These types of situational differences may account for the speed differences observed here, nevertheless, the qualitative aspects as well as the biomechanical characteristics of the stroke mechanics of the two players are quite similar overall. The most intriguing difference between the kinematic chains of the two players is that Henin’s peak shoulder speed occurred at virtually the exact same time she achieved peak racket speed. It appears that:
Henin is able to integrate the shoulder movement in her stroke sequence where she accelerates her shoulder segment at just about the same time as her racket achieves its maximum speed at impact.
In contrast, Carlyn demonstrated less integration of body segment movement, and demonstrated a more traditional kinematic sequence where the shoulder reached peak speed well before peak racket speed and impact were achieved (see below).
What this means is that Carlyn is transferring force and energy from her racket alone (her shoulder and hip reached their peak speed earlier and were already decelerating, having completed their energy transfer) to impact. Carlyn is essentially striking the ball using only her hand and racket while the rest of her body remains passive—having already “released” their stored energy through her kinematic chain. In contrast, Henin can transfer energy from BOTH her racket AND her shoulder simultaneously into the ball at impact.
In other words, Henin is capable of transferring energy to impact using two body segments, instead of just one segment like Carlyn. This extra energy that’s transferred by integrating a second body segment at the moment of contact may explain Henin’s higher ball speed off of the racket compared to Carlyn.
Summary: Regardless of the exact explanation for the difference in the ball speed between the two players, we conclude that Carlyn needs to increase her racket speed—and therefore, her ball speed—if she wants to perform at the same level as today’s touring professionals. Based on what we observed from the video, it appeared that both players were recorded in a warm-up situation, and even then, Henin’s power level is significantly higher than Carlyn.
Our stroke speed measurements and observations over the past 3 years of hundreds of professional, US collegiate and National and International junior players show that this difference in racket and ball speed is the major physical, performance difference that separates top professional players from lower-level professional players (Challenger and Futures competitors) and top junior players.
If Carlyn has aspirations to compete on the WTA Tour, she needs to significantly improve her racket speed on her backhand.
Section 6IV: Suggestions for Improvement
Overall, Carlyn has mastered the fundamental mechanics of a traditional, one-handed topspin backhand. The one-handed topspin backhand techniques shedemonstrated here in her video would enable the her to be a compete successfully as a regional or national high-level tournament competitor.
However, in order for her to be successful at a world-class level (i.e. WTA Tour level), she needs to improve her racket and ball speed. She needs to increase her racket speed by at least 20 percent to approach the racket and ball speeds of today’s WTA competitors. If Carlyn does not increase her stroke speed, she will find it very difficult to be competitive with the top tennis players in the world today.
We offer the following suggestions to help this player increase their racket speed:
Recommendation 1. Train with the SpeedChain to increase racket speed:The first recommendation we can make to help her increase her racket and ball speed is to train her backhand using the Tennis SpeedChain. She is the optimal candidate for this novel form of movement-specific, speed-strength training because she already has very sound stroke technique and the impact of SpeedChain will be very rapid based on our experience with players of her demonstrated skill level. We predict that she will be able to increase her racket and ball speed by at least 25 percent in 4 to 6 weeks of SpeedChain training.
We do have a few recommendations for Carlyn that we believe will raise the performance level of her already masterful stroke even higher.
1) Recommendation 2. Increase the width of the hitting stance: E.
Even taking into account the camera perspective (front view at what appears to be a 45º angle to the player), this player could widen her hitting stance (left photo below) enabling her to stabilize her body and maintain better balance through the stroke. A wider stance (right photo of Henin’s backhand stance) would also promote greater racket extension through the contact zone, and increase the stability of the racket at contact (increasing energy transfer to the ball at impact).
Recommendations 3 and 4. Us e a shallower swing path to increase shot speed and penetration combined with a closed racket face at impact to generate increased topspin:
Carlyn demonstrated the conventional 45 to 60º, -upward swing path and square racket face at impact that’s characteristic of the classic traditional, one-handed topspin backhand technique (see below). This type of swing path creates a traditional shot trajectory that produces high net clearance (1.5 to 2.0 meters over the net) and relatively heavy topspin (between 2000 to 2500 RPM) at rally speeds of 95 to 110 KPH.
Another characteristic of many of today’s touring professionals is that the swing path that they use on both the topspin backhand and forehand have become much shallower—between 30 and 45º upward—compared to the recent past (see Henin below).
This shallower swing path creates a more penetrating overall shot trajectory (the “flat topspin” trajectory referred to by the Germans; net clearance = 1.1 to 1.4 meters), with even greater spin rates (2500 to 3000 RPM) at even higher rally speeds (110 to 130 KPH).
Typically, this shallower path is created mainly by: 1) aligning the racket no more than one or two to three ball diameters below the impact point and 2) keeping the racket hand at or below shoulder level at the highest point the follow-through phase of the stroke.
2) Close the racket face more before initiating the forward swing.
Traditionally, topspin production was achieved by making contact with the ball with a square racket face using a fairly steep, upward swing path.
Today, players appear to rely more on tilting the racket face forward at impact (between 5 and 10º forward) to produce (heavy) topspin. This method of topspin production appears to mesh better with the faster racket speeds and shallower swing paths used by today’s players (see Henin below; image is 1 frame before impact).
The simplest way to assure a forward-tilting (or “closed”) racket face at impact is the make sure that the racket face is closed just before initiating the forward swing. The natural articulation and arrangement of the various arm and shoulder joints cause the hand and racket to “open” (supinate) when executing a tennis groundstroke—both backhand and forehand—so to create a square or closed racket face at contact, the racket face must start in a closed position at the start of the forward swing.
By observation of various touring professionals, to create a (slightly) closed racket face—between 5 and 10º closed—at impact on the backhand, the racket is/ should be closed between 20 to 30º at the very beginning of the forward swing (see Henin below). On the forehand, the racket can start from a much more closed position—for example, Federer’s racket is often nearly parallel to the court surface just before he begins his forward swing—than the backhand to achieve the same amount of closure at impact.
Given the fact that top professional tournament competitors today are hitting their shots with more power than ever before, increasing spin production is crucial to their ability to maintain maximum control over their ever -more powerful shots.
SECTION 7V. FINAL SUMMARY AND CONCLUSIONS:
In conclusion, the one-handed topspin backhand executed by Carlyn demonstrated a fundamental mastery of both the qualitative and quantitative characteristics typical of the traditional variation of this stroke. However, there was a major difference in the power level of this player’s stroke and that of a top professional player. The suggestions for improvement offered here are solely intended to increase the performance level of this/her current stroke tomatch/meet the performance trends/characteristics demonstrated by the one-handed topspin backhand techniques used by today’s top touring professionals. .
APPENDIX: A BRIEF EXPLANATION OF BVM EVALUATION OF STROKE BIOMECHANICS
Summary: We used BioVideoMechanics (BVM™) to analyze the kinematic chain (see Note below) used by the player to execute their strokes. We measured the translational (= linear, not rotational) speeds of the major body parts or “segments” used by this player to execute their one-handed topspin backhand to evaluate the overall biomechanical efficiency (force transfer potential) of the stroke.
We developed BVM™ to provide qualitative (visual appearance of body positions and movement patterns) and quantitative (speed of body movements, angles of motion, etc.) information about the specific movement sequence of the various body parts and segments used in the overall stroke movement.
In a biomechanically-efficient stroke, the traditional biomechanical analysis using rotational speed around various body joints to produce a graph (see next) that shows the body segments firing in a sequence where the peak speed of each segment occurs in this order:
1) hip;
2) shoulder;
3) hand and
4) racket/club/bat/etc.
Traditional kinematic chain analysis graph of a swing movement (golf) based on rotational speed measurements (brown-club; blue-hand; green-shoulders; red-hips).
This graphical profile of the body segments used in a stroke or swing movement reflects the sequential transfer of energy generated by one “link” in this overall chain of linked movements from one link to another. The optimum coordination (timing) of these body segments and their movements enables the body to efficiently transfer energy and therefore, power up through the body, moving from one body segment to the next. Each movement in the sequence builds upon the previous movement and each contributes to the generation of racket speed.
NOTE: In using the term “kinematic chain”, we are trying to stay with the convention used in biomechanics. The term “kinematic chain” refers to movement analysis based solely on movement speed versus the term “kinetic chain” which is used when both movement speed and the actual force/power output produced by the movement are measured. As we are basing our analysis on movement speeds alone (no forces were measured), we are studying the “kinematic chain” of this stroke.
Nessun commento:
Posta un commento