Performance Analysis of Surfing: Rodeo Clown Flip

Anyone who has seen a surfer or skateboarder pull off a flying aerial move is amazed that a human can do such an incredible trick. Although we are all completely dumbstruck by the performance of these maneuvers, these sports often have an unfair reputation of not being truly professional. We often consider these athletes to simply be kids who have spent too much time playing around on the beach.

Surfing and Skateboarding are no longer sports dominated by athletes with talent only. These professional athletes spend many hours training. Professional surfers now spend almost as much time out of the surf, working out (often with trainers) on balance balls, with weights, and in the gym and swimming pool. They do thorough warm up sessions before going out to compete and often also have cool down routines for after a surf.

The use of scientific analysis in surfing has been long in coming. There are a number of reasons for this and I won't give you a history of soul surfing, but the main reason is the difficulty of doing any physiological or biomechanics testing on a surfer. Because surfers do their sport in water and shifting, changing waves (size, direction, steepness...), it is very difficult to test them in the same conditions and obtain relevant scientific results.

Recently, for the first time a team of scientists joined some professional surfers in the Mentawais and recorded their paddle speed, surfing speed and heart-rate during surfing sessions. They also took blood samples to monitor lactic acid build-up and hydration data. These scientists were able to provide the surfers with some physiological and performance data which will surely help them to train better for competition.

Using video to analyze surfing is another way in which these athletes and other non-professional surfers could improve their performance. The professional surfers get lots of video of their performances from all different angles and we hope they use this information to make improvements. Of course, because of the changing waves and the 3 dimensional nature of surfing (moving up and down, forward and sideways), it is difficult to make comparisons with video.

As we looked through some of the video from the surfing trip to the Mentawais, we found one of Jordy Smith of South Africa, performing a Rodeo Clown Flip. We won't try to describe the move here. At about the same time at a competition in the Maldives, an American surfer, Patrick Gudauskus was completeing the first ever rodeo clown in competition. We have decided to look at both these videos and compare their performances. Jordy's wave is the first video and then Pat's wave is the first part of the second video.





Once you get over being completely amazed that surfers can do such things on a wave, take a closer look.

The first thing you will notice is that Jordy is on a much bigger wave than Pat and this can make comparison difficult. We can still look at the technique though and we will do this in stages.

1. The Setup: Jordy launches into his rodeo clown with his board facing almost vertically up at the sky, while Pat's board is about 30 degrees from the vertical when he launches. This may be because of the size of the wave. However, what is obvious is how this affects the height of the flip. Jordy's vertical entry helps project him higher into the air.
2. The Take Off: Here both Jordy and Pat transfer their weight onto their back foot. This helps them launch the board out of the water, bring the board up to their hands for the grab and creates the rotation by pushing on the back of the board.
3. The Grab and Spin: Once again they both use a similar technique here. They both grab the board quickly once they are in the air and begin their rotation. Some of their rotation has come from the back foot pushing on the board but once they are in the air they both use their heads to complete the spin. Watch how they both turn their heads to their left (the direction of spin) . If they did not use their heads to turn they would not be able to complete the spin.
4. The Top of the Flip: As they spin around both surfers actually travel upward to their high point. The high point of the flip is determined by the surfers maximum height above the wave. It is obvious here that Jordy is much higher than Pat throughout the flip. At the top, Jordy's body and board are well above the wave (we can see sky and clouds between him and the wave). Pat's board and body are at just about the height of the wave. Although in this case it does look like Jordy is much higher we need to clarify this by pointing out that Jordy is on a bigger wave (this is not controlled by the surfer) and the camera angle filming these two flips is not the same and therefore the camera angle used to film Jordy's flip may be making it look much higher than it was.
5. The Landing: The landing of course is dependent on all the other factors that occurred before, including the take off, spin and height. Jordy has rotated further and is still above the wave as he prepares to land. He therefore needs to stretch out his legs to find his landing and ride out of it. Pat, on the other hand has not been able to rotate as far, because he did not get the same height above the wave. He is forced to land low down, but by landing with knees bent and hands still on the board he too is able to ride out.
   

So both of these flips were spectacular and although they looked different they were actually performed with similar techniques and there is a lot to learn by analyzing the videos.

Unfortunately, those of us who surf for fun and do not have sponsors, do not have too many opportunities to see ourselves in action. You can however set up a camera on a beach or get someone to film you from the beach. Try to get video looking straight out at the wave from the beach. It is difficult to analyze your performance when studying video that was filmed at an angle to the wave. It is also useful to have some sort of calibration scale that can be used to measure height (as we did in a previous post on Measuring Jump Height). Of course if you can get more than one camera setup you can really take a look at your technique from multiple views, which makes sense for a sport such as surfing.

We love to hear your comments or suggestions. Let us know what you think or what you want to see posted.

Cricket Bowling: Video Analysis of a Throwing Action

On the Video Analysis of Sports we are excited to show how video can be used to improve your performance in almost any sport. We are also interested when video or motion capture is used to study the intricacies of laws in sports.

This week Dudley came across an article about the use of a motion capture system to study the bowling action of a cricketer, http://www.gulfnews.com/sport/Cricket/10308342.html . For many years there has been controversy over legal bowling actions and numerous players have been called for suspect bowling. In fact the leading wicket taker in world cricket, Muttiah Muralitharan, was regularly called for a suspect action, early in his career. With the performance of 3D motion capture studies at the University of Western Australia, his action was finally ratified and was no longer called into question.

For those of you who know very little about cricket, here is a link with a brief explanation http://uk.cricinfo.com/link_to_database/ABOUT_CRICKET/EXPLANATION/ .
Bowling is the action of pitching the ball at the wicket (see link above) in an attempt to beat the batter.

There is a law in international cricket that the angle of the bowling arm (arm with the ball) cannot straighten more than 15 degrees during the final part of the bowling motion before releasing the ball. If it does then this motion can be considered illegal and in the end can result in a player being suspended from International cricket until he corrects his action.

It therefore makes perfect sense that video analysis is used to evaluate a cricket bowler's action before they are suspended. In fact the maximum change in angle was increased to 15 degrees based on a study using 3D motion capture analysis. Motion capture and biomechanical tests proved that it is almost impossible to bowl the ball without some flex or bending at the elbow and in 2004, it was discovered that many bowlers in International cricket flex their elbow more than the previously set limit during their bowling motion.

With video analysis we can:

1. Capture the motion with high speed cameras, so we can assess the motion frame-by-frame and concentrate on the part of the bowling action that is relevant.
2. Set up our cameras appropriately so we get a good view of the arm and how and where it bends.
3. Measure the change in angle of the arm using mathematical concepts rather than "eyeballing" it.
4. Capture the bowling action using multiple cameras to obtain a 3D view of the action and find the physical change in elbow angle rather than a 2D simple angle assessment.
   

The International Cricket Council (ICC) actually appoints a panel of human movement specialists to assess any possibly illegal bowling actions. This panel is instructed to use video and motion capture to analyze a suspect player's bowling and present their findings to a review board.

Here is a video of Muttiah Muralitharan bowling and taking the last few wickets on his way to the world record. His once suspect bowling delivery called the "doosra" is the first delivery you will see. In full speed and with the naked eye, it certainly looks like he is throwing the ball (straightening his arm by more than 10 degrees), but further investigation using 3D motion capture proved that this was not the case.

It is commendable that the ICC uses motion capture and technology to evaluate a rule that could cost a player his career. There are not many sports in which the player's action can be called into question; but all sports can benefit from some form of video analysis to improve players' performances.

If you have some sports video or are interested in analysis of a particular sport, let us know with a comment or send us an email.