Wednesday, July 28, 2010

Does Kicking Help to Paddle Faster in Surfing?

The world best surfer, Kelly Slater, whips around and starts paddling hard into a double overhead wave at Pipeline on the north shore of Oahu, Hawaii. His arms stroke deep into the water right next to the side of his board as he produces the speed needed to catch the fast moving wave beneath him. With another look at some video we also notice that he is kicking hard with his legs.

Getting up to speed

To catch a wave, a surfer needs to paddle the board fast enough to create the forward momentum that will ensure the wave carries the board and rider along with it and does not leave the surfer behind. The surfer must overcome the forces of inertia and gravity and match the speed of the wave as closely as possible. Large waves travel faster and therefore the board speed needs to be faster to catch these waves than to catch smaller waves.

A surfer increases his paddling speed by taking deep paddling strokes with arms close to the board and fingers together. This seems intuitive, but what about kicking hard? Does it really help to kick hard when paddling into a wave?

Slater kicks

In this video of Slater at the 2008 Pipeline Masters, watch how he paddles and kicks for every wave. From this video it is obvious that Slater kicks his legs when paddling into a large wave.

Why do surfers kick?

Kicking while paddling a surfboard has been carried over from freestyle swimming. A freestyle swimmer kicks:
  • To keep their bodies and legs floating high up in the water. This ensures the body maintains a straight line in the water, reducing drag.
  • To assist with body rotation and breathing. Breathing in freestyle swimming is timed with the kick.
  • Swimmers are taught to kick from the hips with slightly bent knees and an extended foot. Kicking from the hips produces the power which can translate into extra speed.
  • To increase swimming speed. Swimmers use a higher kick count to speed up in the water.
This may work for a freestyle swimmer, but a surfer may not get all the benefits listed above.
  • A surfer is lying on his board and is being kept afloat by the board itself, therefore kicking is not needed to stay afloat or to support the hips and legs.
  • Once again as the surfer is on his board with his head and chest up, he does not need to use a kick for breathing and he will certainly not want to rotate his body too much as that may destabilize him on the board.
  • On almost any surfboard that can be stood up on, the surfers hips will be pinned to the board while paddling and only his feet and knees will be in the water (depending on the length of the board). It is very difficult to kick from the hips while paddling a surfboard and therefore difficult to create the same kicking power as a freestyle swimmer.
Therefore the only advantage to kicking while paddling a surfboard may be to increase paddling speed.

Kicking increases paddling speed

A  2010 study done at Griffith University in the surfing Mecca of Queensland, Australia  - Loveless, D., Minahan, C. (2010). Two reliable protocols for assessing maximal-paddling performance in surfboard riders, Journal of Sports Sciences (in press), suggests that kicking while paddling gives the surfer a 9.2% increase in paddling speed over paddling with arms alone.

The study looked at eleven young competitive male surfers and tested them in a field test in a 25m pool. The participants were asked to paddle as hard as they could for 10 seconds. Their paddling speed was measured with a tether like device which was connected to their waste and pulled a cable attached to a spool. The spool contained holes 1cm apart and an infrared light measuring sensor recorded the speed at each interval that the light could pass through the holes. The faster the spool spins the faster the surfer is paddling.

Over this 10 second interval the surfers averaged 1.73 meters per second when paddling with arms alone and 1.89 meters per second when paddling with their arms and kicking hard too. A 9.2% improvement.

So kicking increases paddling speed and Kelly Slater kicks so it must be good.

Surfers don't paddle into a wave for 10 seconds.

If you surf you will know that most of the paddling you do is out to the line up or to get into position for a wave. The sudden burst of paddling to actually catch the wave is likely to last at most 2 or 3 seconds.

From the Griffith University study we can see that kicking while paddling adds speed and allows the surfer to cover more distance (0.8m-1.6m) over a 5 or 10 second period. This will definitely help a surfer get into position for a wave or win a paddle battle for priority during a surfing competition, but does it help a surfer when paddling to match the speed of a wave?

If we go back and analyze the video above we can see that Slater paddles and kicks to get into each of his waves for at most 2 seconds. Theses first 2 seconds of paddling from a resting position are used to get up to maximum paddling speed (this can be seen in the Griffith University study graph on page 54) and therefore the surfer does not get the same 9.2% benefit that he would get over a prolonged 10 second paddle. The advantage will be less and will depend on how much more acceleration can be gained by kicking.

The average advantage of kicking over a 10 second period therefore cannot be used as proof that kicking while paddling will help a surfer catch a fast moving wave.

To kick or not to kick

Unfortunately the Griffith University study does not compare the acceleration that can be gained by kicking while paddling but we can assume that there is an advantage here. Even if it takes the same amount of time, say 2 seconds, to reach maximum paddling speed with kicking and without, the fact that the maximum paddling speed with kicking is higher suggests that the acceleration with kicking will be greater. In other words a surfer kicking will get to a higher paddling speed in the same amount of time than a surfer that uses his arms only. And a higher paddling speed is better for catching larger waves.

The study and physics suggest that if a surfer can kick hard while paddling he will gain an advantage however small it may be. Of course if the kicking destabilizes the surfer on the board or disturbs their arm paddling rhythm then it may in fact reduce paddling speed and make it hard to catch the wave.

The size of the board is also a relevant factor in deciding whether to kick. A good kick can only be maintained on a shorter board where the surfers knees are in the water and not on top of the board. The surfer is already restricted in kicking from his hips as they lie on the board, if the board was also under his knees he would be forced to kick the surface of the water and create turbulence behind him rather than using his feet as paddles just beneath the surface of the water.

If you are a surfer and have a video camera, get into a pool with your surfboard and line up your camera on the side of the pool. Do not push off the pool wall, but paddle straight from a still start for a measured distance say 10 feet or 5 meters, using your arms only and then using your arms and kicking too. Measure and compare the time it took to cover the distance and the speed attained at the end of the distance using a basic video analysis software and see whether kicking to catch a wave would work for you. Let us know what you find out.


Jay said...

Great article Dudley! Very useful, and interesting. If only I could paddle like Slater....

Danielle said...

I enjoyed your analysis and review of my study and article - relating it to a real life surfing situation. Thanks - Danielle Loveless

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