Variation of COP and the COM During Pointe
Biomechanics (fall 2023)
Introduction:
There are extreme technical demands of ballet particularly during pointe work. The intricate control of the dancer's center of pressure is a pivotal element influencing stability and balance. Exploring COP and COM variations during pointe can help explain the biomechanics underlying ballet technique but also helps unveil crucial insights for performance enhancement and injury prevention.
In this experiment, we used motion capture technology and force plate analysis to look into the variations of COP and COM during different positions. By using high-precision motion capture data with force plate measurements, this experiment aims to decipher the subtleties in COP shifts and look into the dynamics between foot pressure distribution and body alignment during these ballet movements.
Understanding the COP variations during pointe work is essential not only for dancers striving for technical excellence but also for dance educators, physiotherapists, and researchers aiming to optimize training methodologies and injury mitigation strategies. This study aims to bridge the gap between ballet and the scientific precision of biomechanical analysis, unveiling the intricate subtleties shaping the artistry of pointe work through a lens of quantitative analysis and technological innovation.
Some studies have been done on this topic, and we used A Biomechanical Analysis of Ballet Dancers on Pointe to base our experiment. Both our study and theirs studied dancers “during the pointe maneuver… In this maneuver, the dancer lifts the heel completely off the floor until the weight is fully supported by the toes.” There have also been many articles and papers on the health risks of pointe work, for example, The Pressure Pointe.
Methods:
Before data collection, 13 reflecting markers were placed on the test subject. The reflecting markers were placed on the left and right shoulders, sides of the hips, sides of the knees, sides of the ankles, toes, and heels, and one on the middle of the back. We had to slightly adjust the placement of the ankle, toes, and heel markers while wearing the pointe shoes. Some of these markers kept falling off because they would get pushed off as the feet contorted. This exemplifies the unnatural movement of ballet. Using 12 VICON cameras to record the movement, the test subject went on pointe in second, third, fifth, and parallel positions. These positions are seen in the figure below
Results:
Discussion:
In Table 1 above the left side of the stabilogram is the flat foot and then the right side is when the subject is on their toes in parallel position. These graphs show the shift in the center of pressure from flat feet to solely on their toes. Both subjects are similar in height and body proportion so their movements are similar. This can be seen by both subjects' COP moving around 10-15m each.
We used inverse dynamics to examine the torque at the ankle joint which creates the motion. The ankle torque for the parallel position can be seen in Table 2. The first downward spike is the movement up onto your toes and the second downward spike is the movement from your toes back to flat feet. From these graphs, we can see that the ankle experiences a massive spike in torque over a very short time.
There are some sources of error in this experiment. The first being for our test subjects we used two dancers who haven’t done pointe work in a few years. Their technique is less refined and their skill levels may vary, so the results might be different if we used a current pointe dancer. The main source of error is our units. Visually the results look as expected but the units are too large to be in the context of our movement. We are uncertain if these units are correct and dancers experience these large forces in their small movements or if there is a conversion error. However, from all of this, we can conclude that a dancer's feet experience a lot of pressure and torque while en pointe. A potential application would be to analyze how making changes to the pointe shoe will make pointe work more comfortable and less injury-prone.