Running It!

How do you run the approach?

Entering And Leaving The Curve

It is important to get into and out of your curve smoothly and consistently. You should make the transition from a straight run to your curve by simply setting your foot a bit out of line with the straight path you were running. For example, if you want to start a turn to the left, place your foot a little to the right of where you would place it if you wanted to go straight. This will place your center of mass to the left of your center of support. In this condition, your body will begin to "fall" toward the left, thus placing you in a bank to the left.

Getting out of a turn is similar, but there is an additional force involved; the force that accelerates you toward the center of your curve and makes you turn. In this case you place your foot just inside the point you would have stepped if you were going to keep running in a circle. This will place your center of mass to the right of your center of support (considering both gravity and your acceleration in the turn). In this condition, your body will again begin to "fall", but this time toward the right, thus causing you to come out of the bank.

In this case, as you are coming out of your bank, you will be spinning clockwise with your foot restrained on the ground. Now imagine that you leave the ground when you reach an upright position. This clockwise spin will continue once you leave the ground because there is nothing to stop the spin.

This is exactly what should happen during your takeoff. You make the transition from your curve to traveling straight as you cross your takeoff foot. You leave the ground when your body is upright, and the spin you get from leaving the curve continues through your flight. This is the whole purpose of the curved approach - to allow you to develop a spin about an axis parallel to the bar, and at the same time be able to leave the ground with your body oriented vertically.

Whether you are entering your curve, or leaving it during your takeoff, you should do it smoothly. Be careful not to "cut" abruptly in the direction of your curve. The curve is there to get you leaning away from the bar. Cutting abruptly inside your curve will send you on a brand new, experimental approach path; not the desired effect during a track meet.

Foot Path VS CM Path

The path described above is the path taken by your CM (center of mass) across the ground. The path your feet take across the the ground is slightly different. In fact, the line of your foot path is whatever it needs to be to make your CM follow the approach path.

In the initial straight-run portion of the approach, the line of your foot path is the same as the CM path. That doesn't mean that your feet strike the ground exactly centered on that straight line; it means that the average position of your footprints is centered on that line. This is because we have one foot on the left side of our bodies and the other foot on the right side. To keep our balance as we run, our foot path wobbles back and forth across the straight line we are running. For simplicity when talking about the line of the foot path, I will generally ignore this wobble and talk about it specifically when the wobble is important.

When we run a curved path the curved line of the foot path is slightly outside the curved line taken by the CM. This is because in a curve your body is not oriented vertically as it is when running in a straight line. Instead, your body is banked (leaned) toward the center of the curve. Consequently, the CM tracks over the theoretical curve calculated by the High Jump Coach 2010 software. As you might imagine, it also means that the head tracks a bit inside the calculated curve.

The curved tracks of the head, CM, and feet all have the same center point. The difference in radius among these three curves depends on the speed of the jumper when running the curve. The faster the jumper runs, the greater the bank angle for a given curve radius. Higher bank angles yield greater differences among the head, CM, and foot curves.

When watching a jumper you can't know the speed they are running and, therefore, you can't know the difference in radius between the theoretical calculated curve and the foot path.

Figure 1:  The theoretical approach path which is calculated by HJC 2010 is shown in green. A representation of the foot path is shown in red. The radial displacement of the curved foot path from the theoretical curve is exaggerated for visual clarity.

 
Figure 2:  A block representation of the approach and takeoff. The magenta line represents the line of travel of the CM  (center of mass) which is directly above the theoretical approach path which is calculated by HJC 2010. The red line represents the offset of the foot path during the curve.




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