From Rafael Nadal's first game of the US Open in 2010, there has been lots of talk about his improved serve speed. Although being the best player in the world, Rafa has never had the best serve or even one of the better serves in the game. This improved serving speed though, would put him into the same first serve speed range as Murray and Federer and make him even more threatening on hard court surfaces, the only surface on which he is not consistently dominant.
In the Wimbledon 2010 final against Tomas Berdych, Nadal had a 69% first serve percentage, averaging 115MPH, with a fastest serve at 127MPH. In his 4th round match at the 2010 US Open against Feliciano Lopez, Rafa hit 63% first serves in, averaged 118 MPH for his first serve and maxed out at 135MPH.
Although one game does not suggest a complete turn around, the stats listed above seem to be consistent for all matches that Nadal played in both Wimbledon 2010 and so far in the US Open 2010. The stats suggest that Rafa's serving percentage is a little lower in the US Open (4%), his average first serve speed is only slightly higher (3MPH) and only his fastest serve seems to be impressively different with an increase of 8 MPH.
Rumours abound as to how Nadal has improved his 1st serve speed. His coach Tony Nadal says he opened his grip more. Rafa himself says, nothing is different. John McEnroe seems to be completely flummoxed.
Looking at it this way maybe there is not much to be surprised about. Nadal has always used a lot of spin and control in his serve. This is good enough for the slower clay and grass courts and was good enough for the slower hard court of the Australian Open in 2009, but for the fast courts at Flushing Meadow, Nadal knows that a few fast serves and quick points will benefit his game more, saving his joints and energy.
Therefore we believe in everything Rafa and his uncle and coach Tony have said. He is not doing too much different except opening up his grip and attempting more flat and hard serves rather than spin. His 6'1 height and obvious strength suggest there is little reason that he cannot hit a 135MPH flat serve, if he attempts one. He may be losing a little accuracy and lowering his 1st serve percentage but if he wins the US Open 2010, it will all have been worth it.
Below is some slow motion video of Nadal serving during training. Watch the video and pause it just before he hits the ball.
Watch how his hand is gripping the racket and how the racket turns after he hits through the ball.
In the first three serves in this video Nadal hits across the ball, putting spin on his serve. We can see this by the way the racket turns after striking the ball. The last serve in the video seems to be a bit flatter and the racket turns slower and later. In all cases though the grip looks the same and fairly closed.
The video is from March 2009 and therefore probably does not show any changes that Nadal has made for the US Open 2010. It does show us that in the past Nadal has used a lot of spin and a closed grip. Flattening out his first serve on a few occasions therefore is the most likely explanation of his increased first serve speed at the US Open.
Thats right Roger Federer did it again. A shot between the legs at the US Open for a winner. In 2009 he played this shot against Djokovic in the semi-final. This time it was a lower ranked player he beat with the shot, but the shot itself was still one of pure genius.
In 2009, after watching his shot against Djokovic, we discussed how Federer actually practices a between the legs shot, so that when he pulls it off in a match it cannot be described as lucky. He knows how to play this shot and is probably even trying to hit a winner, so that he is not caught out of position.
On this website we love to compare athletes and performances. Having two examples of Federer's between the leg shot allows us to do a quick comparison.
Both shots are played as Roger runs backward to retrieve a ball that was lobbed over his head.
Versus Djokovic, Federer plays his shot behind the baseline. Djokovic is standing up at the net, so Roger needed to beat him with power and place it just wide enough.
Versus Brian Dabul in 2010, he plays the shot further behind the baseline than the shot in 2009. This time his opponent stays at the baseline and placement is more important. He needed to go deep into the corner with the shot to wrong foot Dabul and keep the ball out of his reach on the baseline.
Both shots though need to be played with power and in both cases we can see how Federer sets up with his feet and plays the shot with a lot of wrist action to create speed on the ball.
Take a look at the video below. A comparison is made by John Mcenroe near the end.
Federer gives us a great opportunity to analyze perfection. He practices perfect mechanics all the time and shots come naturally to him in the match because of all his practice and analysis.
Keep using your video camera to analyze and compare your performances.
Rafael Nadal has won the French Open Tennis tournament four times. He owes many of these wins to his exceptional top spin forehand. As he goes for his fifth title in 2010, we thought it would be interesting to analyze some video and describe why top spin wins on clay.
Tennis balls loose much of their speed when they bounce on clay tennis courts. This means that the powerfully hit flat shots that Roger Federer uses to destroy opponents on hard courts and grass lose much of their speed on clay. The ball also tends to bounce higher on clay. The flat forehand that normally stays low to the ground slows down and bounces higher, allowing the opponent to hit it back with interest.
Top spin is the effect on the tennis ball created when it rotates in the same direction that it is travelling. Top spin shots are ideal for clay:
Top spin shots can be hit higher over the net and deeper into the court. This is because the top spin makes the ball drop quickly with a downward force known as the Magnus Effect. The deeper you can push your opponent on a clay court the harder it is for them to play an offensive shot in return.
Top spin ensures that the ball bounces higher too. The top spin bounce along with the extra high bounce on clay results in a return shot that is hit at shoulder height or above making it much more difficult to return with power, especially with a one handed backhand like Federer's.
Top spin also creates a heaviness in the shot. As the ball is spinning toward your opponent and in the same direction as it travels, a well hit top spin shot will come onto the racket faster after the bounce. This is more evident when the shot is used on hard courts, but Nadal is powerful enough and creates sufficient top spin to have players comment on this aspect of his shot even on clay.
So now that we know what makes top spin effective on the clay at Roland Garros, lets take a look at Nadal's top spin forehand in slow motion in the video below.
Nadal imparts top spin on the ball by swing his racket from a low position to a high position, using the racket to skim over the ball and creating a rotation in the same direction as he is hitting.
As you watch the video notice how Nadal uses all his big body parts, hips, torso and shoulders to create the power in the shot and then uses the arm and racket to create the top spin and direction.
He starts by rotating his hips, torso and shoulders away from the ball as he brings his racket back to a low starting position.
He positions his feet and then starts by rotating his hips first, followed by his chest and shoulders toward the direction he plans to hit, using the kinematic sequence to create racket speed.
Now he can swing his arm and racket through the ball, using the power that was created by his body and the control created by his arm and wrist.
He swings the racket low to high, sliding the racket over the ball during the shot. Some call this a windshield wiper action. This action creates the top spin.
Nadal ends with the racket at shoulder height and over his right shoulder. Depending on the shot he sometimes follows through with the racket even higher than this.
Knowing why Nadals top spin forehand is so effective on clay and how he hits it is one thing, offering effective counter to such a shot is something else. Another French Open final between Nadal and Federer would be a great test of Nadals top spin and clay court skills versus Federer's creative and adaptive style. In previous years Nadal's top spin has won out, but Federer has 16 Grand Slams and is playing better than ever.
Many writers describe Roger Federer's game as "classic," but what exactly does this mean? The word itself means "something that is a perfect example of a particular style, something of lasting worth or with a timeless quality" (Wikipedia).
With video analysis, we can easily compare Federer's style of play with previous generations' players by viewing them side-by-side, looking at stillshots of key positions, and synchronizing the video to a particular event (e.g., impact). Below we have a video comparing Federer's game to a champion of the past, Bjorn Borg.
The key positions shown here are: Preparation (a.k.a. Loading Phase), Contact, and Follow-through. During the Preparation phase, both players bend their knees and rotate their upper bodies, building up potential energy. They're also using an open stance, meaning their front foot is not positioned across their body. The second key position shown in the video is Contact; and it's noted that both players impart topspin on the ball by brushing up the back of the ball from a low to high position. The final key position is the Follow-through. Because they swung from low to high, both players' racquets end up across their bodies from somewhat of a windshield wiper motion.
What makes the similarity between these two players' styles so interesting is how different their racquets are. The physical properties of the racquets are quite different, including the size, weight, material, and string; and these differences undoubtedly affect the types of shots a player can make on a ball. But despite these differences in racquet technology, Federer's technique on this forehand is extremely similar to Bjorn Borg's, and that is one of the things that makes his game classic.
The backhand tennis stroke has transformed incredibly since the 1980's and now the majority of men and most of the women players use a two handed backhand. In fact in men's Tennis only Federer of the top players playing the 2010 Australian Open this week, uses a one handed stroke.
The backhand can be used for a variety of shots and there are distinct advantage of a two handed backhand over a one handed backhand in most instances. Damir Popadic breaks it down shot by shot on the ITF coaching website and suggests which shot is better and why.
Return of Serve - Two handed is better as it allows the player to use a short back swing and to play the stroke with an open stance (hips facing forward).
Running backhand - Two handed is better as a single handed stroke requires better positioning. A one handed stroke requires a rotation of the hips and shoulders and a longer back swing making it more difficult to hit on the run.
Approach shot (to the net) - Two handed shot allows the shot to be hit with an open stance which gives the player more time to approach the net. The player does not need to complete his rotation before approaching the net as he would with a one handed shot.
Low balls - Two handed shot allows for more stability and it is easier to scoop the ball up with a stable base. The one hand shot will be difficult to control.
Short low balls - Popadic suggests that neither shot has the edge here, but the one handed shot has the advantage of reach and with a strong wrist a satisfactory shot could be played.
Very wide balls - here again Popadic gives no advantage either way, but just like the short low ball, the one handed shot has the extra reach and a strong wrist action (such as Federers) could produce a fantastic shot.
Balls hit at the body - Here the single handed backhand has the definite advantage. With a single handed shot the player is able adjust his racket position enough to block the ball back.
Slice shot - Now here is a shot that can only be played one handed. This is also an important shot for defense and staying in a rally. It is also a great shot to use to change the pace of a point. There is no good way to play this shot two handed and therefore even a player with a two handed backhand will need to play the slice one handed.
It seems from Damir Popadic's analysis that the two handed stroke must be far superior to the one handed backhand. However we all know the world number 1 tennis player, Roger Federer, uses one hand and seems to have as much power and precision as the other top 10 players using two hands.
Most pundits though believe that Rafael Nadal and Andy Murray's two handed backhand is better than Federer's one handed version. But lets take a look at two down the line drives, one from Federer and the other from Andy Murray. Although I believe Nadal has the best backhand in tennis today, it is more difficult to make a comparison because he is a left hander.
Although both these videos show a backhand drive down the line, you will notice that they are not filmed from the ideal position and Federer's shot is from a waist high ball, while Murray is hitting a ball around chest high.
It is interesting to note that with a backhand drive both players need to setup correctly, turning their hips and shoulders 90 degrees to the direction in which they are going to hit the ball and taking big backswings. It looks as if Federer's backswing is bigger than Murray's, but with the different camera angles it is not possible to be definitive here. So the two handed advantage of a more balanced, open stance does not apply when comparing these two backhands as both players use a closed stance.
Watching the shot itself, we see Federer rotate his hips and shoulder further away from the court to create potential energy (wind up) just before the shot. He then swings through the ball using both his hips and shoulders to create power, hitting the ball almost in line with his body to ensure that it goes straight down the line and not cross court.
Murray on the other hand rotates 90 degrees to the court in preparation for the shot but then does not rotate further away to increase his potential energy. This is a result of the two handed grip he uses and possibly also because the ball is bouncing high. You will see that although he does rotate his shoulders toward the ball, it is not nearly as much as Federer's rotation. Instead he create power by using both arms to hit the shot. He too meets the ball with the racket in line with his body.
The follow through of both players is also of interest. Federer follows through all the way opening up his shoulders and finishing with his racket above his head. Murray's follow through is almost as big but he does not take the racket high above his head because both hands are on the racket.
So which backhand is better? Federer is using his whole body, with a big back swing and follow through and lots of rotation to create power. He needs, and does have a strong wrist and forearm and is able to control the ball with that strength. Murray uses his two hands to control the shot, but also needs to take a big back swing and follow through and to rotate his shoulders in order to create power. He supplements that rotation power by using both hands.
Both backhands are powerful and precise. When Federer's backhand goes wrong though it can go horribly wrong, but if he gets it right with timing and position he is often hitting a winner. Murray is less likely to hit a wild backhand shot.
Federer though seems to have a much wider variety of backhand shots than Murray or even Nadal for that matter. Nadal and Murray may hit heavier backhand topspin shots, but Federer seems to be able to flick and block and change his shot whenever he pleases.
As the two handed backhand seems to be more efficient and better for players with less racket control and wrist strength (everyone other than Federer), it is likely that we will see less players using a one handed backhand. For now we can enjoy watching Federer's backhand mastery and compare it to the awesome power and control of Nadal's and Murray's.
As the 2009 US Open continues, the top 4 ranked players, Roger Federer, Andy Murray, Rafael Nadal and Novack Djokovic are all still in with a chance of winning. To win against the likes of these Tennis greats, the players have to have a complete play list of different shots. One of the most lethal is the drop shot. Federer in particular loves the drop shot as a major attacking weapon.
The drop shot can be used to win a point outright, but it can also be used to draw your opponent to the net and set yourself up for a passing shot or to simply get your opponent winded by making them run up to net in an attempt to recover the point. Playing a good drop shot requires not only executing the shot itself but also determining the best time to execute the shot.
Here is some video of Federer with some sublime drop shots. As you watch the video take note of Roger's court position, how he swings the racket and the court position of his opponent in each case.
We can pick out a few tips from analyzing this video.
Federer usually plays his drop shot when he is just on the baseline or somewhere between the service line and the base line. It is much more difficult to play the shot when you are way behind the baseline. This is because the ball will need to travel further and it will also give your opponent more time to get to the net to hit a return shot.
His opponent in each point is usually way behind the baseline when the drop shot is played. His opponents therefore need to cover much more ground if they want to catch up to the shot.
Points 1 and 2 above actually work in combination, because as one player begins to attack , he moves forward and plays close to the baseline, pushing his opponent further behind the baseline. Therefore a drop shot is seldom played as a defensive shot.
In each shot Federer cuts under the ball to create backspin. He angles his racket and slices under the ball as if he is trying to chop the bottom of the ball off. Back spin ensure that the ball dies (does not bounce high or forward) once it lands on the other side of the net. This will further reduce the chances of his opponent reaching the shot. Cutting under the ball will also slow the flight of the ball down allowing it to drop closer to the net.
Roger has a great drop shot but he is successful with it because he knows when to play it. Using video analysis we can learn from Roger and practice incorporating the drop shot into our own games.
The US Open Tennis 2009 is in full swing. Once again the likes of Federer, Nadal and Murray are playing well and the men's championships looks set for an exciting second week. We know and have seen how video analysis can be used to analyze a tennis players performance, but it can also be used in real time or almost real time to track the ball and even make close line calls. Of course I am talking about the "Shot Spot" or Hawk-Eye system.
If you have watched any Major Tennis since 2006, you will know exactly what Hawk-Eye is. The Hawk-Eye is used to make decisions on line calls that are challenged by the tennis player. Each player (or team if playing doubles) can challenge a line call on any point. They get a maximum of 2 incorrect challenges each set. If the set goes to a tie break an extra challenge is allowed. Basically the Hawk-Eye challenge enables the tennis players to use technology to challenge line calls they think are incorrect.
The technology being used by the Hawk-Eye system is Video Analysis. Here is how it works.
Multiple cameras are placed around the court and players. These cameras are usually placed high up, so that there is less chance that a player will be blocking the ball from the camera view.
Multiple cameras are used to ensure accuracy of tracking the ball and to account for possible occlusion (the ball being hidden from the camera view by the players body...)
The system uses at least 4 high speed video cameras, with a capture rate presumed to be 500 frames per second.
The camera position is calibrated to determine its position in space and relative to the other cameras in the system. The lines on the court are also used in calibration and to compensate for any camera movement.
The center of the ball is tracked in 2D by each camera. The ball therefore is like a reflective marker or point on the body. Using the information from all the cameras, the Hawk-Eye system then triangulates the 3D position of the ball.
This process is done for each captured frame so that a trajectory of the ball can be created and then overlayed on an animated background containing the lines of the tennis court.
Finally the skid and compression of the ball is measured by examining the position and trajectory of the ball prior to the bounce and its position and trajectory after the bounce. In this way they can determine how long the ball was on the ground and how it skidded over the ground.
The Hawk-Eye system is said to have an accuracy of 3.6 mm.
I believe that the use of video technology in this way is great for the sport of tennis and for the players piece of mind as well as spectator enjoyment. However we have seen a number of controversial calls with the Hawk-Eye system. Take a look at video of 2 big ones here.
In this first video we see a very tight call for Mikhail Youzhny over Rafael Nadal at Dubai in 2007.
This second video is from the Wimbledon final in 2007. Rafael Nadal benefiting from a very close one over Roger Federer.
In both cases we would have to say that the ball likely looked out to the lines judge who made the call. In both cases the player is most likely only challenging the call because it is a crucial point (Yozhny vs Nadal - Set Point, Nadal vs Federer - Break point). The Hawk-Eye system suggests that in both cases these calls were measured as being 1mm IN, meaning the ball was 1mm from being out.
Have a look what the manufacturers of Hawk-Eye have to say about these two controversial calls at here.
Could Hawk-Eye have been wrong in either or both of these calls and what does it mean that it is 2-3 mm accurate but can suggest that the ball was in by only 1mm?
Here are some points that may effect the accuracy of the system.
The camera capture rate of 500 frames per second may be too slow for the hard hitting tennis game of today. Andy Roddick has recorded a fastest serve at 155 mph and ground strokes are often hit with a similar speed. Assuming a capture speed of 500 frames per second or 1 frame every 0.002 seconds, the ball will have moved about 139 mm for every video frame. This may not be sufficient data to determine the position of the ball to within 1 mm.
The more cameras that are used the better the chance of tracking the ball and the higher the accuracy. However there are possibilities of occlusion by players, tennis rackets and the net, which will lead to reduced accuracy.
High speed video capture also needs excellent lighting. We have discussed the importance of lighting for high speed capture in a previous post . Therefore the system will work best under a roof with artificial bright lighting and will possibly have a problem tracking the ball outdoors, particularly when there is cloud cover or as it gets later into the evening.
Assuming everything is perfect for capture, the center of the ball has to be identified as accurately as possible too. If a camera sees the ball at a funny angle or partly occluded the center may not be correctly defined by this one camera and the position of the ball will be inaccurate.
The skid and compression of the ball is being estimated and extrapolated based on the trajectory of the ball before and after the bounce. Any inaccuracies in tracking the position and flight of the ball will become larger during an extrapolation (estimation of the movement).
The Hawk-Eye system may not be perfect but it is definitely a step up from the eyeball view of a line judge, particularly when the ball is moving at high speed. We believe Hawk-Eye has improved the line calls in Tennis and this is great for the players and spectators alike. However it still leaves room to debate exciting points and close matches. Enjoy the US Open Tennis and hopefully we will not see any controversial Hawk-Eye calls.
Last week, Roger Federer won the Western & Southern Financial Group Masters tournament for the third time. Only Mats Wilander, Andre Agassi, and Pete Sampras have done the same (Wilander actually won it four times). This tournament is part of a series of tournaments leading up to the US Open, and the players use it as an opportunity to reacquaint themselves to the hardcourt surface. After having been in a bit of a slump, partly due to injuries and a formidable opponent by the name of Rafael Nadal, Federer appears to have returned to winning form as of late, and is once again considered a favorite in the upcoming US Open.
Although Federer's serve is quite respectable in terms of speed (averaging around 120 mph for his first serve), it is his ability to disguise the spin and direction that make it extremely effective. As Federer has demonstrated, blistering serves can be returned consistently if the returner can anticipate where the ball will be hit. By keeping his opponents from being able to easily read his serve, adjusting the pace only increases Federer's effectiveness.
One of the main ways Federer is able to disguise his serves is with a consistent toss. As is true with most sports, keeping your eyes on the ball throughout a point/play is one of the basic concepts that helps you play well; tennis is no different, and a server can give away a lot of information about the type of serve he will hit by significantly moving his toss around. By tossing the ball in the same location, and instead adjusting his swing path to direct the ball and apply various spins, Federer gives his opponents just a fraction less time to anticipate where the ball will go; and at 120 mph, that lost time can make a big difference whether the serve is returned successfully.
Of course, just knowing your serve's effectiveness can be improved by having a consistent toss is only half the battle; having the ability to do this and make minor adjustments to your swing path/grip (not to mention having perfect timing) are just some of the skills that separate us amateurs and weekend warriors from the pros. Below is a slow-motion video of one of Federer's serves at Wimbledon. Enjoy, and learn what you can from perhaps the greatest tennis player of all time (to this date, anyway - keep practicing kids!).
Every year around May the pro tennis players make the switch from the hard courts in the US to the clay courts of Europe in their quest to be the world's best. Playing on clay forces the players to make changes in their game and as we know not many players are able to adapt completely and win on both the hard and clay court surfaces. Amongst the men, only Rafa Nadal has proved he can win consistently on both, while the women have only seen Steffi Graf and Martina Navratilova as perfect examples.
The differences between playing on a hard or grass court and on clay are are logical as well as tactical. Here are a few:
The clay court is softer and therefore puts less stress on the players' joints.
The ball moves slower on most clay courts than on hard courts. This means players cannot dominate with their serves.
The ball "sits up" more on clay, which means that it seems to hang in the air ready to be hit. This is why players hit more topspin shots on clay.
Baseline ground strokes are much more prevalent than volleys on clay because of the reasons described above. The players find it difficult to hit a good approach shot. Failure to hit a good approach may allow their opponent to have a chance to hit a passing shot.
Top players slide into shots on clay. This is more difficult to do on other surfaces.
We are going to analyze the slide shot on a clay surface. Players slide on clay so that they can change direction more quickly after hitting their shot. It's easier to stop and turn on hard courts because of the surface's friction; however clay courts can be slippery, and once a player stops running and positions his feet to hit a shot, his momentum will cause him to slide on the surface.
Therefore if the player does not slide correctly he will overrun the ball or cramp his shot. Assuming he was able to return the ball effectively he would then need to stop his momentum so he could return to the middle of the court and prepare for the next shot.
Let's look at some video. We found some video of one of the greatest female tennis players, Steffi Graf, sliding on a clay court. Watch it below:
We can see Steffi running and sliding into a forehand and then doing the same for a backhand. We can also see that she uses the slide to help her change direction and prepare for her next shot. In both her forehand and her backhand, she slides first and hits the shot at the end of the slide. This means she is hitting the shot from a set position.
We also note that after sliding and hitting the shot she no longer has any momentum carrying her further away from the center of the court. She can now recover quickly and get ready for the next shot. Watch how she is slides into her forehand and is able to quickly recover and get ready to run for the next shot, the backhand. Once again she slides before hitting the backhand and easily changes directions to get back into position to hit the winner against Monica Seles who is approaching the net in this point.
Before starting to slide we also see that Steffi positions her feet correctly in preparation to hit the shot she wants. She does not try to reposition her feet once she is sliding and before hitting the shot.
Our video analysis of Steffi Graf sliding on a clay court gives us some insight on how to slide correctly on clay. Here are some pointers:
Slide before hitting the shot. This means your timing has to be perfect so that you slide into the correct position to hit a good shot.
The slide is about recovery and changing direction. Therefore you do not want to continue to slide after you have hit the shot. After hitting the shot you need to be almost stationary so that you can push off and recover for the next shot. Once again timing is critical here.
Get your feet into the correct position to hit the shot you want, before starting your slide. Once you are sliding you will find it difficult to change your stance without messing up the shot or falling over.
You need to be able to slide for both forehand and backhand shots. If you cannot slide in one direction then your opponent may be able to take advantage of this weakness. Therefore when you practice sliding on clay, practice sliding to hit a forehand as well as a backhand.
This year's French Open Tennis has already begun and we are excited to watch the likes of Rafael Nadal and Roger Federer, Serena Williams and Safina. We will be watching as they slide around the courts and looking for more clues to how to slide effectively on clay.
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This last weekend, we once again had the pleasure of watching Tiger Woods playing in a Major Golf Tournament, the 2009 Masters. He injured his knee prior to the 2008 US Open, and the last we saw of him was winning that tournament in a lot of pain.
He may not have won this year's Masters tournament, but his swing truly is exceptional and it is always worth taking a look at some video and snapshots of his swing to do some video analysis. So why does Tiger Woods have a perfect golf swing? The answer is TIMING.
Tiger shows an almost perfect example of a concept we discussed in our last post with Andy Murray's serve. Tiger creates club head speed by perfectly sequencing and timing the movement of his knees, hips, shoulders, wrists and club. In golf, this is known as the kinematic sequence. The kinematic sequence in a golf swing is a little different to that of a tennis serve, but in the end the idea for both is to create club head speed or racquet head speed by storing and then transferring energy from hips to shoulders to club or racquet, with perfect timing.
Let's have a look at Tiger Woods' swing in slow motion. We have seen this video before, but it is a really good one. In this video we have a side-on view of Tiger's swing (side-on to the direction he will hit) and we can see the club throughout the swing. This makes it a great video to analyze. The video was also filmed with a high speed camera with a high shutter speed, which is why we can see the club so clearly in each frame, even through ball impact.
OK lets analyse this swing by looking at the way Tiger stores and transfers energy to the ball through the golf club. If you stop the video at 0:33 seconds, you will see that Tiger is now at the top of his back swing. During his back swing he turned his hips and his shoulders away from the direction in which he will be hitting in order to store up energy for his swing.
Play the video from here and we will see how his hips start to move earlier and quicker than his upper body and that his shoulders are left behind. Tiger is starting his kinematic sequence by unwinding his back swing. The timing is important and he leads with his hips in order to create more separation between his hips and shoulders and therefore create more energy to be transferred.
His shoulders then follow and at ball strike we see that Tiger's hips are now facing the target while his shoulders are almost facing directly at the camera. This perfect timing has allowed him to transfer all the energy from his back swing, first to his hips and then from his hips to his shoulders.
Here are two images of Tiger at the top of his back swing and at ball strike, created with some free video analysis software and images of Tiger's swing.
Although these are 2 different swings, we can see how Tiger creates separation between his hips and shoulders in the image on the left and how his hips are turned toward the target at ball strike in the image on the right. The shoulders have rotated quickly as they follow in sequence from the hips, in fact they have caught up with the hips as energy was transferred from hips to shoulders and the hip rotation has slowed while the shoulder rotation has sped up. The angle between the hips and shoulders at ball strike is now much less than at the start of the down swing and we can see this in the images above.
Of course the golf swing does not end with the shoulders and there are still numerous places where the timing can be off and the golfer can lose club head speed. In the video above we can look at time 00:41 seconds and we can see that Tiger's wrists are still cocked. As we play forward from this point we will see the wrists release, transferring the energy from the shoulders and arms to the wrists and on to the club and club head at ball strike.
This last sequence happens very quickly and the golfer's timing has to be perfect. Tiger Woods is the master of this timing and we look forward to seeing more video of his swing now that he is back from injury.
Send us your comments and let us know what you think of our posts. We look forward to hearing from our readers.
Welcome to the Video Analysis of Sports blog. As this is our first article, we will take this opportunity to introduce ourselves.
We (Dennis and Dudley) have a combined 20 years experience in motion capture and biomechanics with a special interest in sports performance and injury prevention. Through our consulting company Sadaka, LLChttp://www.sadakallc.com ,we offer services to sports professionals, sports equipment manufacturers, hospitals and motion analysis software and hardware companies. Some of our past clients include Titleist, FootJoy, Warrior Hockey, National Pitching Association, NASA, ShrinersChildrens Hospital and Vicon Motion Systems.
Video analysis of sports performance is often the domain of professional athletes and large companies or research institutions. This analysis is done with expensive 3D video camera equipment and complicated software to ensure high speeds and accuracy. However there are some basic techniques that can be used by any individual to evaluate their own performance and get great results using a simple digital video camera and a little understanding of biomechanics. The video camera will require a small cost (we will discuss what makes a good camera in a future posting), but we will supply you with much of the biomechanics understanding for free on this blog.
Reviewing video clips can be a great way to provide coaching feedback to players, as well as a means to emulate one's favorite athletes. Whether you're a professional all-star, high school athlete, or weekend warrior, seeing yourself from a different perspective can help improve your performance and/or minimize your chances of injury.
So in this first posting, we'll start right at the beginning and describe what features make a sports clip suitable for video analysis of an individual, and what you can do to ensure the clips you film will meet those requirements. Future postings will demonstrate the various levels of analysis that can be performed on suitable videos, using a range of available software, from basic free software to detailed 3D analysis.
What makes a good sports clip? A good sports clip of an individual shows the athlete's full range of motion (ROM) during an action, with the camera positioned such that angles can be accurately calculated (this will be discussed in more detail later). Filming the athlete's ROM can be accomplished by simply zooming out or moving the camera backwards until all the desired features are in the viewer. In general, it's recommended to have the camera as close to the athlete as possible and still capture the entire ROM, as this will make the most use of the camera sensor's resolution. For example, if we were to capture a basketball player dunking the ball we would want to ensure that our camera can see the complete action from take off until the player puts the ball in the net. Our camera would therefore need to see the ground at the take off point as well as some space above the rim of the the net.
Another important factor in obtaining a great sports clip is to make sure that your camera is stationary. There are some motion capture software available that can handle a moving camera, but for now we suggest that the camera is mounted on a tripod and is not moved while the video clip is being filmed. This means that you should ensure the full ROM (described above) can be captured in this one shot.
How you can film useful footage: Camera placement In general, most sports clips we watch on tv are best suited for analyzing strategy and teamwork because they provide an overall picture of many or all of the competitors and the playing field. However, when it comes to analyzing an individual's performance or technique, it's not only important to focus the camera on the single athlete, but the angle we film from must also be taken into account. It's best to use "orthogonal angles", meaning the camera is directly in front of, behind, or to the side of the athlete. Golf coverage usually does a nice job of this, providing shots of the golfer either "face-on" or "down-the-line". Here's a great face-on view of Tiger Woods' swing:
And here is a down-the-line shot of his swing:
Notice these cameras are level with the golfer; they're not filmed at an upward or downward angle, meaning it's possible to accurately calculate some angles, if that's what is desired from the analysis.
Background/contrast Although the above clip is a beautiful view of Tiger's swing, the footage could have been improved by having him wear clothes that were a different color from the background. Black clothing with a black background can make it difficult to accurately evaluate the amount of hip and shoulder rotation - two commonly analyzed characteristics of a golf swing. Not that having a solid black background is a bad thing though; on the contrary, if you can manage to film your athlete with a solid-colored background, you are well on your way to filming some nice footage for analysis.
Lighting As is true with taking most photos, it's ideal to position the camera and athlete such that the light source (e.g., the sun) is behind the camera and illuminates the athlete. This will provide a crisp view of the athlete, and will allow you to use a more open setting on the camera's aperture.
Now that you're up to speed on the basics of filming great video for analysis, grab your video camera and start practicing! Follow our regular blog postings, and see how you can create your own analyses of your videos, using a variety of software packages.
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