Video Analysis of the Back Flip

When most people think of the Olympic Games, the first sport that comes to mind is Gymnastics. Supremely strong and fit athletes flying through the air, somersaulting and twisting. The sport defies gravity and leaves us all in awe.

The sport of Artistic Gymnastics is performed by moving the body, often through the air, and there are no rackets, bats or balls involved. Because of this, video analysis of different gymnastics movements can provide excellent coaching and feedback for the athlete. Gymnastics is all about the technique. By applying the correct technique and timing, the athlete will achieve the desired results. In most cases, there are no outside influences and therefore good biomechanics will result in good performance.

As a young gymnast myself, I watched and analyzed countless hours of my own technique on video. It really is very easy to set up. Most gymnastics moves take place in a small area, so you only need to ensure that the camera is set up so you can see the complete movement in the field of view and also that the camera is set up at the correct angle to analyze the movement you want to assess.

In college, I continued to analyze my own and my teammates gymnastics technique using video. One very common analysis we did was of the standing back flip. Many gymnastics elements have the back flip as a core component. A double back flip is simply 2 back flips in a row without touching the ground in between, a full in - full out is a double back flip with a twist in each of the flips. The list goes on, but what is important is that the technique used to start a back flip is the same technique that is used to begin many of these other flipping and twisting maneuvers.

Capture video to analyze your back flip requires some easy setup:

1. Set up your video camera, so that the gymnast is standing sideways to the camera. Most of the analysis of a back flip is done in this side on (sagittal) view, such as jump height, lean and rotation.
2. Remember to fill the field of view. You do not want your camera to be too far away so you have a lot of empty space around your subject. You also do not want it too close, so that the gymnast jumps out of the camera view. A little trick to know, is that most cameras have a rectangular field of view (they are wider than they are high). So flip the camera on its side to get closer to the gymnast but still be able to capture the height of his flip. If you do decide to flip your camera on its side, make sure you have some video editing software that will allow you to view the video right way up, otherwise it may be difficult to view properly.
3. Set your gymnast up with a plane background (such as a white wall) behind them in the image. This will allow you to mark a specific height on the wall and thereby measure their height.
4. If you really want to measure angles of the joints, such as the knee or hip, it is best to mark these points with a bold marker pen so that you can see them in the video.

Lets take a look at some video I found on YouTube. The video also give you some instructions on how to do a good back flip. The video camera itself is not setup in the optimal position to make good measurements of the gymnasts jump height, rotation or proper take off technique, but it is still easy to see that he has good technique.

This gymnast really does a very good standing back flip. The most important part being the take off which will allow the gymnast to perform any variation on his back flip from there.

There are 3 phases to the back flip take off:

1. The loading phase: In this phase the gymnast bends his knees and swings his arms backward in preparation. The idea is to create the energy needed to jump up into the air and rotate over in the flip. By swinging his arms backward and bending his knees, the gymnast is loading up with potential energy. As the video points out , you do not want to bend your knees too much or you will need to use the energy to get yourself back into a good load position for the take off.
2. The take off phase: Now the gymnast drives his arms upward and straightens his knees quickly as he jumps off the ground. The head is very important in this phase of the take off. If you throw your head backward , you may create a lot of rotation but you will not be able to jump as high. Therefore it is important to keep the head looking forward and still. Coaches suggest that the optimum angle of lean for the take off is between 75 and 80 degrees from the floor. The gymnast in this video looks to have this angle perfected.
3. The tuck: For the last part of the flip, the gymnast needs to rotate over so that he can land back on his feet. If the take off is good, then this part should be easy. By taking off leaning slightly backward (angle of 75 to 80 degrees), you have already created the rotation you require and all you need to do is bring your knees up to your chest. By bringing your knees up you will increase this rotational speed and easily complete the flip.

OK, before you try a back flip on your hardwood floors, remember that it takes practice and numerous drills before most gymnasts are doing good back flips. If you are intent on learning one, then get into a gym with mats or a foam pit and a coach. Then get out your video camera and film yourself to see what you are doing and correct your biomechanics from there.

From personal experience, I will say it is well worth the effort to learn how to do a good back flip.

If you are a gymnastics fan, look out for video from the 2009 US Gymnastics Championships starting today in Dallas, Texas. You can watch a live webcast at http://www.usa-gymnastics.org/events/2009/visachamps/webcast.php .

How Beach Volleyball Players Jump!

Playing volleyball on the beach is a fun (albeit tiring) way to spend a day in the sun. For those of us who haven't played in a while, it's always a bit of a shock to realize just how difficult it is to jump on the sand. At first glance, the nets don't look all that high and you think to yourself, "Is this regulation? This looks too easy." But when you make that first attempt at a spike, it's immediately apparent the game isn't as easy as the pros on TV make it out to be.

One study suggests that if you can jump and reach 10 feet in a gym, you can expect to only reach 9 feet on the sand. So why is it so much more difficult to jump in the sand, compared to jumping in a gym? The answer is quite obvious: when jumping on the sand, your feet sink into the ground so there's less of a reaction pushing back on your feet, reducing how high you can elevate. In the gym, the floor does sink in a bit when you push off, but the floorboards spring back to their original position, pushing you off the ground for a nice jump. But sand doesn't have this springlike property; for the most part, it just gives way to the downward force you apply with your feet.

Understanding why it's more difficult to jump in the sand allows us to make some educated changes to our technique that may give us better results (i.e., higher elevation).

• Take a little hop into a flat-footed position before jumping. The landing from the hop will compact the sand beneath your feet, giving you a stable platform from which to jump. The compacted sand will also increase the sand's reaction force to your push off, and will act a little more like the gym's surface (not a lot, but every bit helps). Landing flat-footed (as opposed to the front parts of your feet) increases the surface area in contact between your feet and the sand, minimizing how far you'll sink into the sand.


• Get your back and arms into it. Bend at the waist a little, and swing your arms back during the loading phase of the jump. Building up this potential energy is a recommended technique when jumping on any surface, but it's especially important when you can't just rely on getting good push off the ground. Swinging your arms upward during the jump not only helps elevate you off the ground, it also gets your arms into position for a block or spike.


• Jump upward, not outward. Your body can only produce so much force to propel itself; so if you use some of that force to jump forward, not as much of the force will be used to elevate yourself and you won't be able to reach as high a point during the jump. Again, this is true regardless of what surface you're playing on; but on the sand, where the ability to jump high is really valued, it's that much more important to get as much as you can out of each attempt.

While there's no guarantee you'll be able to elevate as high as the professional beach volleyball players, employing some of these techniques may help you get a little more out of your time on the beach. If you're interested in using video to calculate how high you can jump in the sand, please read our recent posting on that topic: http://videosportsanalysis.blogspot.com/2009/06/measuring-your-vertical-leap-using.html

Below is a highlight video from a beach volleyball tournament in southern California. It's not an ideal video clip, in that the camera doesn't seem to be mounted on tripod, but you can clearly view the concepts described above. Enjoy!

Andy Murray's Tennis Serve

Last week, Rafael Nadal won the 2009 BNP Paribas Tennis Tournament at Indian Wells, California, defeating Andy Murray easily in the final.

As we watched the tournament, we heard frequent discussions of Murray's second serve, and that if he could develop a better second serve he would be almost unstoppable. Of course, he was almost unstoppable at Indian Wells, but did lose badly in the final, mostly because of poor serving. In that final match against Nadal, he lost his service games four times and won only 6 of 16 (38%) of his 2nd serve points. Let's take nothing away from Nadal though; he has the best return game in tennis, possibly the best ever.

All tennis players, including beginners, know the importance of the serve. A good serve can result in easy points and puts pressure on an opponent. The first and second serves in tennis usually have different goals. With your first serve, you want to win the point with an ace, service winner, or at least put your opponent in a defensive position for the next shot. The first serve is generally flat and fast, and you can take more risk, knowing you have an attempt at a 2nd serve if you need it. The second serve is your backup safety. Your priority is to get the second serve in and start the point. If you miss the second serve, you will double fault and give your opponent a free point. Most tennis players put a lot more spin on the second serve, but this tends to reduce the speed of the serve.

Because of the slower pace, the second serve often gives the receiver plenty of time to get into position to hit an aggressive return. However, if you can make your second serve look similar to your first serve, at least in terms of the service motion, you can make it difficult for the receiver to predict the speed (and type of spin) of the serve, and you may retain a significant advantage, even as you serve slower and with more control.


We found some video of Andy Murray's first serve and decided to look at it from a biomechanics point of view. This video is set up very well for video analysis. The camera is set up along the baseline, which allows us to get a side-on view of Andy during his serve. We can also see the complete service motion in the video, including the racquet head, and can see the racquet make contact with the ball. It would have been great if we could've seen the complete ball toss (the ball goes out of the top of the screen) and if the camera had been stable and mounted on a tripod; but in general, this is good video sports analysis footage.



The power in the tennis serve, like many throwing or hitting sports (baseball hitting and pitching, football throw, and golf) is created by a chain of events. Each part of the body loads up with energy and transfers its energy to the next link in the chain. The timing of this energy transfer is critical to creating racquet head speed and therefore a good, fast serve.

In Andy's serve, we see how he starts with his knee bend as he throws the ball up. You may also notice that as he bends his knees his hips turn away from the court. He then transfers this energy now stored in his hips by bringing his back foot up to his front foot and rotating his hips into the court. Once again notice that as he rotates his hips back into the court, his shoulders now rotate away. This counter rotation in both hips and then shoulders creates the potential for racket head speed; Andy is coiled up and ready to explode his racket toward the ball.

As he does this, he releases the potential energy, rotates his shoulders back into the court, and throws his racket at the ball. All these energy transfers add up to create the speed with which he will hit his serve. If his timing is off, his speed will not be as high.

The ball toss is, of course, just as important. If you do not throw the ball consistently, it will be very diffcult to perfect the timing of your kinetic chain (described above). Andy's ball toss is high and a falls about a foot inside the court. If you want to hit a good hard serve, the ball needs to be in front of you, so that your body and racquet are moving forward when the ball is struck. If the ball toss is directly above your head, it is much more difficult to get theball moving forward with as much pace.

Ok, so Andy has a great first serve, and we can see that here. It is his second serve that the commentators were discussing. Unfortunately, we were unable to find any good footage of his second serve to compare it to his first serve. We are sure his coach is working hard on improving his kinetic chain sequence and timing to make it more difficult for his opponents to read his second serve.

Please post comments and let us know what you think, or whether you have any questions or suggestions. We would be delighted to hear from you.