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The principle of stability can be applied to almost all athletes no matter what sport or activity they are participating in. Stability is defined as resistance to both linear and angular acceleration, or resistance to disruption of equilibrium. In most cases, athletes are trying to increase their stability in order to prevent movement (ie. an offensive lineman in football is trying to get into a stable position in order to prevent the defensive lineman from pushing through them), however, in some cases, athletes are trying to become very unstable in order to improve movement (ie. sprinter or swimmer coming out of the starting blocks will become very unstable in the direction they are moving in order to have a more explosive start). We will come back to these examples later but it is important realize that there are several variables which can increase or decrease an athlete’s stability.

The first mechanical factor to consider is mass. When looking at an athlete’s mass, it is important to consider Newton’s 2nd Law of Motion, Force = Mass x Acceleration. Therefore, if an athlete has more mass, it will subsequently require more force to cause that athlete to accelerate. In terms of stability, this would suggest that a heavier athlete would have more stability than a lighter athlete due to the fact that it would be harder to push this athlete and cause movement (more difficult to disrupt their equilibrium). When looking at the mass of an athlete, there is very little which can be done to increase the athlete’s mass for improved stability.

The second factor to consider is the athlete’s base of support. An athlete’s base of support is the area enclosed by the outermost edges of the body in contact with the supporting surface. When you are standing on two feet, your base of support is the area between your two feet. In order to increase your base of support you could put one hand (three point stance) or both hands (four point stance) on the ground, however, if you wanted to decrease your base of support, you could stand on one foot. This is common in football players when they put their hands on the ground to increase their base of support.

The third factor to consider is the height of the athlete’s center of gravity. Your center of gravity when standing is located approximately at your belly button. When an athlete lowers there center of gravity they increase their stability and when they move their center of gravity upwards, they decrease their stability. The easiest way to improve an athlete’s stability is to encourage them to “flex” or “bend” their knees. If you are a running back in football preparing for a head on collision with a defensive end, in most cases you will have less mass then the opposing player, but you can lower you center of gravity to improve your chances of a successful outcome. This can be achieved by flexing at the hips and knees immediately before the collision.

The final factor to consider is the position of the center of gravity relative to the base of support. If an athlete positions there center of gravity directly in the middle of their base of support, they will be in the most stable position possible. However, if you move this center of gravity towards the outer most edge of the base of support you decrease your overall stability. An athlete can position their center of gravity towards the direction of force application (ie. the running back preparing to be hit by a defensive lineman might move their center of gravity towards the front edge of their base of support in order to be more stable in direction which the force application is coming from) or an athlete can position their center of gravity away from the direction of force application (ie. sprinter during the start will have their center of gravity in front of their feet and then lift the hands off the ground in order to be in a position where their center of gravity is outside of their base of support prior to applying force into the blocks with the feet).

Sport Specific Examples:

In the sport of hockey, athletes who skate in a low, flexed position are more stable and as a result more difficult to move off of the puck. A classic example of manipulating your stability in the sport of hockey is a forward driving to the net against a defenseman. Next time you get a chance to watch an NHL game, watch a player like Taylor Hall as he drives to the net. Taylor does an excellent job of getting into a low, flexed position with a wide base of support and he moves his center of gravity towards the inside edge of his base. These three motions make it extremely difficult for the defender to knock him off balance as the defender would have to move Hall’s center of gravity all the way across his wide base of support.

Stability plays an extremely important role in wrestling, mixed martial arts, judo, etc. In these combat sports, the athlete who is able to get into a low, flexed position with a wide base of support is in an advantageous position as this makes it very challenging on their opponent as they must match this low, flexed position.

When working with swimmers, the goal of the start is to have the athlete go from a very stable position to a very unstable position in the shortest time possible. Similar to the block start in sprinting, swimmers want to move their center of gravity well outside of their base of support (which immediately following the starters pistol should be the two feet at the back of the starting block as the hands are lifted off the ground) and towards the direction which they are travelling (towards the water). This motion allows the swimmer to be more explosive during the start as this instability helps to improve their force application.

For more information on the stability and how it applies to the sport you play or coach in, please contact us.

Brian Shackel, MSc