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DEVELOPING BETTER ATHLETES ONE STRIDE AT A TIME

This principle seems relatively straight forward upon first glance, but there are some key features to focus on when applying this principle to your sport. Liner motion is motion along a line that may be straight or curved, with all parts of the body moving in the same direction at the same speed.

Running is most likely the best example of Principle #5 as it is true linear motion. When an athlete is running, the primary direction of force application is down into the ground and in the backwards direction. If you look at the runner who is “bouncy” they most often are applying too much force down into the ground which results in them becoming more of a vertical projectile, however, if you look at the runner who has no vertical deviation of their center of gravity, they are applying force primary in the backwards direction. This relationship also holds true when looking at long jumpers vs. high jumpers. A long jumper will apply more of their force backwards, causing them to be more of a horizontal projectile, while a high jumper will apply more of their force down into the ground in order to become a vertical projectile.

An interesting example of this principle which might fall under the area of “movement usually” occurs in the direction opposite to that of the applied force is skating in hockey. If you look at the below image you will gain a greater understanding of an example where the direction of force application might not cause motion in the opposite direction.

Skating Ice Pattern.jpg

When you watch a highly skilled hockey player skate down the ice going from a stationary position into maximum velocity, it is fair to say that the player will skate in almost a perfect straight line. With that being said, based on Principle #5, the direction of force application should occur 90 degrees to the direction of travel (or the push off skate should move directly behind the athlete into true hip extension). However, if you look at the tracings on the ice in the image above you will see that the force application angle moves from 90 degrees to the direction of travel to 45 degrees to the direction of travel. This change in push off angle does not cause a change in the direction which the hockey player is heading. Furthermore, when you factor in Newton’s 3rd Law of Motion that for “every action there is an equal and opposite reaction” you can begin to discuss the use of the arms in the skating stride. I think most people would agree that a runners direction of force application is directly backwards (in the sagittal plane) and as a result, the runners arms should move primarily in the forwards/backwards direction in order to improve the rhythm of the runner and increase the force which can be applied to the ground. When you bring this same concept to a hockey player, you will notice that the direction of force application is 45 degrees to the direction of travel. What does this mean for the arm swing? Should the arms move opposite to the direction of travel or opposite to the direction of force application? I am of the belief that the arm swing should move forwards and across the front of the athletes body as the push off skate is moved backwards and away from the athlete’s midline. For more information on this debate, review the article written by Dr. Marion Alexander from the University of Manitoba:

http://www.coachesinfo.com/index.php?option=com_content&view=article&id=...)

and the video by Dr. Michael Bracko from The Hockey Institute:

http://www.youtube.com/watch?feature=player_embedded&v=TrAAoE039Vk).

Definitely food for thought for those hockey players, parents and coaches! Feel free to pass your comments onto me regarding this debate…..

Thanks,
Brian Shackel, MSc