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.
We know why you visit our blog, to learn how to capture and analyze sports performance. Today we present our first videos and some biomechanical analysis done with free video analysis software.
Before we begin, we want to remind you that our intention is to show you the tools you can use for the video analysis of sports. We are biomedical engineers who have done research and work in sports performance analysis, but no one can be an expert on all sports. Therefore, although our biomechanical analysis is correct, our coaching tips (which we will minimize) should be evaluated with a professional coach in the appropriate sport, and must be evaluated on an athlete-by-athlete basis.
With the NCAA basketball tournaments about to begin and the regular season of the NBA about to end, we know many of you are spending a lot of time either watching or playing basketball. In honor of March Madness, our videos this week are of a basketball free throw. We have video of two subjects with very different techniques shooting a free throw. We have set up our camera on the side of the subject, as we wanted to evaluate the subjects ball release angle. The two videos can be seen below. Notice that both the free throw shooters are right-handed therefore it would have been more appropriate for us to shoot the video from the other side of the court, so that we would have a clear view of the right arm. However, in this case, lighting conditions and other background interference meant that shooting from the left side of the athlete would result in a sharper image to analyse. We were, however, lucky that in both videos we can see enough of the shooting arm and ball to evaluate the release angle that we are interested in.
With these two independent videos there is already so much we can analyze. We can see that Subject 1 jumps quite high off the ground for his free throw and also falls forward, while Subject 2 goes up on his toes. As the camera was set up in almost the same position, we can immediately notice that Subject 2 is quite a bit taller than Subject 1 and we can take that into account in our assessment. Subject 1 is jumping in order to gain more height on his free throw. This is causing the ball to come out of his hand at a flatter angle.
A feature of many free video analysis software is that we can compare two subjects side by side. When comparing 2 subjects, it is important to also synchronize the video to a specific event. In our comparison video below, we have synchronized the two subjects' free throws at the point of ball release. We need to synchronize video for comparison because not all videos are the same length, as some subjects may take longer to shoot their free throw than others. If we tried to analyze two videos of free throws that were not synchronized, we would have a very difficult time ensuring that we could see both subjects releasing the ball at the same time. The free video analysis software we used allows us to synchronize side by side video, but not to save it out as an avi. We therefore used a well-known video analysis software to create the synchronized view you see below:
If you are a basketball coach, you can probably see a few things that can be improved for both
Subject 1 and Subject 2. Please send us your comments or coaching tips if you have suggestions. We however are going to suggest some improvements for subject 1 based on a little bit more video analysis we did with a free video analysis software package.
Here are two freeze frame images of Subject 1 (top) and Subject 2. Using free video analysis software, we have calculated the angle of release for both subjects, and zoomed in on their arms and the ball at this release point. Subject 1 released the ball at 48 degrees to horizontal while Subject 2 released the ball at 79 degrees to the horizontal.
Now for some basic physics. The diameter of the basketball rim should be exactly twice the diameter of the basketball. In other words, two basketballs can fit through the hoop at the same time (if everything is perfect and there is no net). During a free throw or any basketball shot from the outer court, we are throwing the ball on an arc. The ball needs to move forward as well as up (for most of us) to get it into the net. The ball can either move on a flatter arc (Subject 1) or on a steeper arc (Subject 2). On a flatter arc the ball will not go as high but will move forward further and quicker; on a steeper arc, the ball will go higher and not as far. This means a free throw on a steeper arc will come down straighter and take advantage of the size of the basketball rim, while a flatter free throw will need to be far more accurate as a ball moving forward is more likely to hit the rim.
Subject 1 should try to put his free throw on a higher arc to take advantage of the physics described above. He can see immediately from this video analysis that his free throw is at a 30 degree flatter angle at release than Subject 2 and while practicing his free throws, should concentrate on releasing the ball on a higher angle. Once Subject 1 has some time to practice, we will get another video of him and see how he has improved.
Hope you enjoyed this first full Video Analysis. Remember that you too can do this type of in-depth analysis. All you need is a video camera and a little understanding. Follow us to get more tips, tricks, and understanding in using your video camera to analyze different sports.
We are happy to answer any questions or hear from you, please leave us a comment.
Posts
