Tuesday, November 10, 2009

Analyzing Dane Reynolds in Slow Motion

Sometimes it is simply fun to see a pro athlete perform in slow motion. Usually though we can learn a lot from watching him or her in such detail.

Surfing is one of those sports that lends itself well to photographs and video clips. The action is usually intense and the surfers positions so contorted that it is a wonder to see them perform. Of course because their movements are often quick and dynamic, it is difficult to analyze their motion at normal speed. Recently there have been attempts to analyze professional surfing from a scientific stand point of physiology and biomechanics. Check out a previous article we wrote about a trip to the Mentawai islands.

Recently the Quicksilver surfing team was in Mexico and took along a high speed vision research camera. This super slow motion camera can record at high resolution up to a frame rate of 7530 frames per second. We do not know the frame rate used to record this video clip, it is most likely at around 1000 fps. This does not sound like a lot when we consider that golf swings seen with the Swing Vision system are often recorded at 10X this frame rate. However it is generally accepted that the fastest movement that a human can make can be recorded at 250 fps, therefore a high speed capture at 1000 fps is 4X the fastest movement that the surfer can make. The reason Swing Vision uses a higher frame rate for golf is to capture the golf club and ball, which can move much faster than any part of the human body.

The video shows Dane Reynolds performing an aerial surfing move in Mexico, recorded by the Vision Research Camera.

Analyzing Dane's performance to learn how we can perform a similar move is easier because of the high speed footage. Lets take a look at some critical points.
  • Dane starts by balancing his center of mass (the center of all the masses and positions of all his limbs) between his feet, which are toward the back of the board. We can see that his weight is at the back of the board by noticing how the nose of the board is sticking up out of the water. We also see him leaning into the face of the wave so that he can turn quickly to launch into his aerial move.
  • Mid way up the face of the wave, Dane applies more pressure to his back foot, shifting his center of mass further back. We see his front knee straighten and his head lift up eyeing his take off point. The movement prepares him to almost jump off the wave with his back foot when he reaches the top.
  • At take off Dane pushes his back foot almost straight (jumping). He does this to launch the board into the air and also to bring it up closer to his hands so that he can grab it.
  • Once in the air, just off the wave we can see how Dane pushes the board around with his back foot, while bending his front knee. He also lifts his head up and forward as if he is trying to peer over the top of his board. This enables him to get the rotation needed to bring his body on top of his board so that he can set up for the landing. In fact it almost looks like he is climbing up his floating board with his hand.
  • Now that he is in the air and has got back on top of the board he needs to prepare for the landing. This time, unlike when he was riding the wave at the beginning, he positions his center of mass over the middle of the board. This will give him a bigger landing area. If he positioned himself over the back of the board as he did at the start, the board would most likely slip forward and out from under him on landing.
  • On landing he stretches out his legs to reach for the top of the wave and then allows them to bend to absorb the landing impact. Notice how his arms are in an equal and opposite balancing position over the center of his board to keep his weight centered.
  • Interestingly on his landing we can see the flex or wobble of the board itself, which probably gives him a little more shock absorption.
  • Finally riding out we can see that Dane's body is leaning backward a little and the board is sliding out forward. This is probably a result of his not having his center of mass directly over the center of the board at landing. However Dane quickly recovers by bending his knees and moving his arms forward to once again position himself over the center of the board and ride out.
Breaking down a movement using high speed video footage can be very instructive. If you are a surfer, we hope you were able to pick up a few tips. If you are not a surfer, take a look around for high speed video footage of your sports and see what you can learn from the pros. If you have any suggestions of high speed video you would like us to analyze let us know. We enjoy hearing your comments.

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