Correlations Between Young Dancers’ Ankle Flexibility to their Jump Height and Side Dominance

6 December 2022

Rebecca Sharp

Table of Contents

Introduction…………………………………………………………………2-3

Methodology………………………………………………………………..4

Results………………………………………………………………………5-7

Discussion…………………………………………………………...………7-8

Limitations and Conclusions…………………………………………...……8

Introduction:

Also known as the Calcaneal Tendon, the Achilles Tendon is the tissue that connects the calf muscles, the gastrocnemius and soleus muscles, to the bones in the ankle, the calcaneus. This tissue is responsible for lifting the heel off of the ground while walking, running, or jumping as well as many other activities and it is therefore incredibly important in daily life as well as in dancers. While the Achilles can handle up to four times its body weight in pressure, it is a common site for injury among dancers and other athletes. (“Achilles Tendon: Function, Anatomy and Common Conditions”). Dancers particularly partake in a lot of activities that require both ankle strength and ankle flexibility, so the health of this tendon is imperative. It is also important to understand both the activity that dancers perform, and how consistent it is on their dominant and non-dominant sides. Inconsistent training on either side can lead to an increased risk of injury according to the Cleveland Clinic, and injuries in the areas of the Achilles can be life-altering (“Achilles Tendon: Function, Anatomy and Common Conditions”). Young dancers in particular are important to observe, as pubescent children are still growing, while simultaneously putting large amounts of impact and training on their Achilles tendon, and may not fully understand their bodies and limits.

In this case, the flexibility that is discussed is the combination of the elongation of the gastrocnemius, the soleus, and the Achilles tendon as a whole. This flexibility can be an aspect of a dancer or other athlete’s performance, particularly in jumping. At the University of Alabama in Huntsville, research was conducted on male collegiate Track and Field and Basketball athletes to determine the importance of Achilles length in predicting jump potential. Similarly to many dancers, these athletes specifically train in a way to increase their vertical jump, which makes this study ideal for comparison as there is a lack of research for this topic in dancers. The length of each athletes’ Achilles tendon was measured, and a device was used to determine vertical jump potential in each athlete over multiple trials. This observational study found a “moderate-to-large positive correlation” in Achilles tendon length and vertical jump potential, meaning that the longer a person’s achilles tendon is, the more likely they are to have a higher vertical jump potential, and vice-versa. While this is not an experimental study, it can still provide a lot of information as it relates to the length of the tendon, a genetic trait that cannot be trained. However, it is impossible in this study for them to exclude the possibility that those with larger Achilles tendons train vertical jumps more, so there can only be a correlation between the two, and it is not proven that a longer Achilles causes a higher vertical jump potential.

During the present study, it was discovered that each dancer had a more flexible ankle on their dominant side (figure 4). This discovery led to further research, and while there is little research on specifically the ankles of dancers’ and their side dominance, there has been research on standing stability and its relationship with side dominance. A study was conducted on healthy adults to determine the effects of side dominance on standing stability. Using plates measuring pressure on each side, the researchers were able to discover that higher rates of pressure occurred on the dominant side. The conclusion of that study was that “results suggest that side-dominance affects biomechanical and neuromuscular control strategies during unilateral standing” (Négyesi, J et al 2022). While this study can show a favoring in stability on the dominant side, there is no way to fully understand the favoring of one side during a dancers’ training. Oftentimes, dancers and other athletes will train more on their dominant side because it is more enjoyable to achieve a more successful result. Therefore a discovery in higher ankle flexibility may be due to genetics or a greater amount of training, as this is an observational study it is impossible to know definitively.

Methodology:

In order to conduct this study, done on recreational dancers participating in three or more styles of dance ages 11-17, a detailed consent form was sent home with each student to get signed and dated by a parent or guardian approving that they consented to their childs’ age, height, ankle flexibility, jump height, and side dominance being recorded. When discussing ankle flexibility as it relates to the gastrocnemius, soleus, and achilles tendon as a whole, the angle that can be created between the ground behind the foot and the center of the lower portion of the leg, is a viable way to achieve an estimated overall measurement of the degree of flexibility. Therefore, the higher the degree of the angle, the more flexibility there is in that direction of motion in the ankle. This was measured using a goniometer, a simple instrument that measures angles between two sides off of a circular base (in this case, the circular base was positioned on the lateral malleolus, the bony projection on the outside of the ankle). This angle was recorded on both the left and right leg, and the dominant side of each dancer was recorded. The dancer's age as well as height was recorded as well. Lastly each dancer stood in first position of the feet facing a blank wall with their first metatarsal six inches away from the wall. They then each raised their dominant arm as high as possible and placed the sticky note on the wall with their feet fully on the ground. Then, in order to measure jump height, each dancer performed a demi-plie with proper technique (knees over toes and heels remaining on the ground in order to get the best possible measurement as it compares to ankle flexibility). They used the power they could obtain from a demi plie and their feet to jump with an outstretched hand and place a second sticky note as high as they could on the wall. The difference between the two sticky notes was used to measure how high they could vertically jump. This data was all recorded in inches to the hundredth decimal place to obtain as accurate a measure as possible.

Results:

Each figure below displays a particular arrangement of data to display the results of each measured combination of data.

In the twelve dancers studied, there was no observable correlation between ankle flexibility and jump height (figure 1). There was a weak negative correlation between height and ankle flexibility, meaning that the taller dancers in general had less ankle flexibility (figure 2). There was a moderate positive correlation between age and average ankle flexibility, meaning that older dancers had more flexibility in their ankles than younger dancers (figure 3). All but two of the dancers had a significantly greater amount of flexibility in their dominant ankle (figure 4).

Discussion:

While the hypothesis of this study was that dancers with more flexible ankles would be correlated to dancers with higher jumps, this hypothesis was not supported. While the hypothesis was also not refuted, there is not enough data, and likely not enough subjects, to directly support or refute the data. An interesting note to be made however, is that according to an identical twin study, recreational activity can actually make tendons stiffer than those without regular recreational activities (Sichting, F et al 2022). It would be interesting to study the ankle flexibility and its relation to jump height in children in other or no recreational activities.

Not taking into consideration jump height, a strange result was found that while taller dancers had less ankle flexibility than their shorter counterparts, older dancers generally had more ankle flexibility. This could be due to a variety of factors, particularly age itself or an improvement in technique of training of ankle flexibility that may come with age.

The most significant overall discovery was that the majority of dancers had a more flexible dominant side ankle. Some of these numbers were significant, and the smallest difference was 0, with only two dancers having equal flexibility. During the study, sometimes the right ankle was measured first and sometimes the left, eliminating bias in that realm. As discussed, many people have a stronger dominant foot, and it is likely these dancers are not training their non-dominant side as much as their dominant foot. This information is incredibly useful to know as it can help the teachers of these dancers as well as any other teacher to focus more on putting an emphasis on the equality of training each side, as there is a measurable difference in results.

Limitations and Conclusions:

There were several limitations and opportunities for bias in this study. This study was only conducted by one person, making a blind or double blind observation impossible. It is also not experimental which is important to remember, nothing can be proven in the realm of causation, only in correlation. There was also a very small sample size available, making the statistical significance very low, and it can apply only to this specific group of dancers alone. In addition all dancers are right-side dominant, making an understanding of the full scope of side dominance in the study impossible.

However, despite the limitations or opportunities for bias, the study was ultimately successful and saw little correlation between ankle flexibility and jump height, but yielded a different important observation in the inconsistent flexibility between dominant and non-dominant ankles in these young dancers.

References

“Achilles Tendon: Function, Anatomy and Common Conditions.” Cleveland Clinic, https://my.clevelandclinic.org/health/body/21927-achilles-tendon.

Sichting, F., Kram, N. C., & Legerlotz, K. (2022). An Identical Twin Study on Human Achilles Tendon Adaptation: Regular Recreational Exercise at Comparatively Low Intensities Can Increase Tendon Stiffness. Frontiers in physiology, 12, 777403. https://doi.org/10.338 9/fphys.2021.777403

Alrefai, Mohamad; Claytor, Richard; and New, Brianna (2021) "The Usefulness of Achilles Tendon Length in Predicting Jump Potential in Male Collegiate Basketball and Track and Field Athletes," Perpetua: The UAH Journal of Undergraduate Research: Vol. 4: Iss. 2, Article 1.

Négyesi, J., Petró, B., Salman, D. N., Khandoker, A., Katona, P., Wang, Z., Almaazmi, A. I. S. Q., Hortobágyi, T., Váczi, M., Rácz, K., Pálya, Z., Grand, L., Kiss, R. M., & Nagatomi, R. (2022). Biosignal processing methods to explore the effects of side-dominance on patterns of bi- and unilateral standing stability in healthy young adults. Frontiers in physiology, 13, 965702. https://doi.org/10.3389/fphys.2022.965702