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Heels Down During Jumps…Technique or Physics?

Posted By Samantha Panos on behalf of the IADMS Dance Educators' Committee, Friday, August 23, 2019
As dancers, we have all been told at one point to put our heels down when we land our jumps. As teachers, we may feel like we are constantly nagging our students to put their heels down. But why is preparing and landing from jumps with heels down important? Is it just good technique or does it play a larger role in performance capacity? 

First, it may be helpful to start with a brief review of lower leg anatomy. For the purposes of this post we will focus on the posterior (back) compartment of the leg and plantar (bottom) surface of the foot as the emphasis of this entry is on the importance of heels down. Additionally, the following concepts can also be applied to the anterior (front) thigh which I will reference briefly for a more complete picture. 

The posterior leg consists of two compartments of muscles, the superficial and deep posterior. The superficial compartment includes the gastrocnemius and soleus muscles which form the common Achilles or Calcaneal tendon, and attaches to the calcaneus (heel) bone. The resulting action of these muscles is planter flexion or “pointing” of the ankle. The soleus muscle is largely a postural muscle that is highly active in stabilizing the leg on the ankle while standing and balancing, while the gastrocnemius is a powerful muscle that plays a large role in high-velocity or forceful activities, such as jumping. The deep compartment includes the Flexor Hallucis Longus (FHL), Flexor Digitorum Longus (FDL) and the Tibialis Posterior (TP). The tendons of these muscles all pass behind the ankle, along the medial (inner) side, and enter the foot where they have various attachments as seen in Figure 1 below. These deep muscles have multiple actions but their common action is plantar flexion of the ankle.

 


 

Figure 1. Superficial Leg Compartment (Left two), Deep Posterior Compartment (middle), Plantar surface of foot (Right) showing the tendon attachments of the deep posterior compartment.

 

Next, let’s briefly review forces and energy. There are many types of forces that the body undergoes or can produce but for this article we will focus on tensile (tension) force. Tensile force is when a material, in this case muscles and tendons, is lengthened. The stretching or lengthening of muscles and tendons creates elastic or strain energy. Now, it is also important to understand that energy can neither be created or destroyed, it simply changes form. So, while the muscles and tendons are lengthened (tensile force) they are storing elastic potential energy and when they release and go back to their normal resting length, the energy transfers to kinetic energy. An example that is commonly used is a rubber band. Pull on the rubber band and you have elastic potential energy, let go of the band and kinetic energy is released. 


Now that you feel more comfortable with posterior leg anatomy, tensile force and transfer of energy, let’s move into the studio to see how everything connects!

Whether the allegro is to a heavy 4/4 or a brisk 6/8, technique tells us that you do a demi plie to prepare for and land from a jump. The demi plie is the most critical part of the jump as a whole because it is where the musculoskeletal system generates, stores and releases energy to perform the jump. In Figure 2 below, the red arrows are showing tensile forces in the leg during a demi plie. Again, for the purposes of this post we are focusing on the plantar surface of the foot and the posterior leg as they relate to the ankle joint (the arrow along the anterior thigh is showing that in a demi plie the quadriceps muscles and the quadriceps tendon are also under a tensile load, therefore the concepts of discussion and the importance of demi plie during jumps is also applied to this region and to the knee). As you can see in Figure 2, the plantar surface of the foot and posterior compartments of the leg are being stretched – they are under tensile load in a demi plie. Therefore, elastic potential energy is being stored in these compartments and is waiting to be released as kinetic energy during the jumping phase, only to land again in a demi plie and repeat the energy storage cycle. Having the heels down throughout the preparation and landing phase of the jump allows for this efficient transfer of energy back and forth and allows the tendons and muscles to undergo a full stretch-shortening cycle. A dancer that uses their plie and keeps their heels down will generate more power and be more physiologically efficient because they are properly utilizing and transferring their energy. You would be correct to expect that as a result this dancer will jump higher and have more endurance throughout the combination.

 


 

Figure 2. Force vectors indicating tensile forces in muscle groups during a demi plie.

 

 But now what happens when jumps are landed with heels off the ground? In this scenario the dancer will deplete themselves of all the benefits previously discussed. The muscles and tendons will still undergo a tensile load but of less magnitude, therefore less elastic potential energy will be stored and less will be released. Going back to the rubber band analogy, pull hard on the rubber band and it will shoot across the room when you release it, pull lightly (less stretch) and it will travel a shorter distance. Can you see how this is not optimal for your students or as a dancer yourself? Less potential energy means you will have to fight through the jumps and you will not recover in between each jump, in turn, fatiguing faster.

 

 Lastly, jumping with heels down will also help prevent injury by allowing for these compartments to go through their full stretch-shortening cycle. Landing with the heels up means the Achilles tendon and the smaller tendons of the deep posterior compartment do not get to fully lengthen during the impact of the landing. Repeated landing with heels up, such as during a petite allegro, means all the tendons of the posterior leg stay shortened to a degree and therefore are not able to absorb the force of impact, store adequate energy or release energy efficiently, so they are being taxed at a higher rate. Over time, this technique error will likely result in posterior leg/ankle overuse pathologies such as tendinitis including the most common Achilles tendinitis or the commonly under diagnosed FHL tendinitis as well as other inflammatory diagnoses. Dancers will complain of posterior ankle pain and most likely assume it is Achilles tendinitis which may or may not be the case, but addressing the proper use of their demi plie during jumps may help to calm or prevent the injury all together.

 

 Now, you may be thinking, does this information apply to other dance movements as well? Yes, it would. Consider repeated releve’s, pirouettes from fifth, fouette turns, etc. Any time the dancer is required to go from foot flat on the ground to demi pointe, full pointe or jumping, all of the information about the posterior compartments stretch-shortening cycle, tensile force, storage and transfer of energy is relevant in performance efficiency and prevention of injuries.

 

 

Recommended Readings

-Alexander RM. Tendon elasticity and muscle function. Comparative Biochemistry and Physiology Part A. 2002; 133:1001-1011.

-Kim S. An Effect of the Elastic Energy Stored in the Muscle-Tendon Complex at Two Different Coupling-Time Conditions During Vertical Jump. Advances in Physical Education. 2013;3(1):10-14.

-Silbernagel KG. Nonsurgical Treatment of Achilles Tendinopathy. In: Doral M., Karlsson J. (eds) Sports Injuries. Springer, Berlin, Heidelberg. 2014.

*Note: the recommended reading Nonsurgical Treatment of Achilles Tendinopathy is not to take the place of professional medical advice. If you or your dancer are experiencing posterior ankle pain, please seek medical attention from a physician or a Doctor of Physical Therapy to guide you through the appropriate treatment options for recovery. This reading is only intended to provide insight into the prevalence and potential causes of Achilles tendinopathy and to provide realistic expectations into recovery time frame.

 

Photo credits

Figure 1. Curtesy of Duke Anatomy Lab. Web.duke.edu

Figure 2. Panos, Samantha. (2006). The Physics of Ballet. (Unpublished Masters Thesis). University of Utah, Salt Lake City, Utah.

 

Samantha Panos PT, DPT, MFA is a dance educator, former dance teacher and Physical Therapist at Dynamic Physical Therapy in Salt Lake City, Utah whose goal is to educate and inspire young dancers, encourage cross training for overall dancer health and to reduce injury by promoting proper technique to achieve maximal physiologic efficiency and performance capacity.

 

 

 


Tags:  heels  jump  physics 

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Can Physics improve your pirouettes?

Posted By Margaret Wilson and Jennifer Deckert on behalf of the IADMS Dance Educators' Committee, Wednesday, January 23, 2019

Successful completion of a pirouette (turn on one leg) can sometimes feel like an impossible task, but understanding more about the mechanics behind the turn may help you find more stability, produce more rotations and have better balance.  There are several principles from physics that are useful in understanding the preparation and turning action in a pirouette.

1.     Torque – a turning force that helps start the turn

2.     Force couple – torque that is created in the placement of the legs and feet in the preparation for the turn

3.     Angular acceleration – how to build up turning speed

4.     Conservation of angular momentum – how to maintain the desired turning speed. 

 

Embed from Getty Images

 

But first, let’s examine Newton’s laws of motion to help put these principles into context and help describe our understanding of dance movement.  The first law has to do with inertia (the tendency to maintain the current state of motion or a resistance to change).  Newton's second law deals with acceleration and momentum and the third law describes action/reaction. Each of these laws comes into play in the preparation and continued turning motion in pirouette.  To start turning we must overcome inertia through the creation of torque – and we do this in the preparation for the turn.  While turns can start from a variety of positions of the legs, if we look at 4th position in external rotation, we can see easily see how the dancer creates torque to overcome inertia and begin the turn. The distance between the two feet, rotating away from each other creates an equal and opposite force which is transferred to the supporting leg in the turn. This generation of torque can be described as a force couple. In 4th position plié a moderate amount of torque is created, in 5th position, where the distance between the feet is very small, less torque is created. If a dancer takes an open fourth allongé (a lunge position where one leg is bent and the other extended), the torque generated is greater (Sugano and Laws 2002). 

 

Embed from Getty Images

 

The force couple and torque help start the turn, but angular acceleration also determined by the contribution of all related body parts in a turn.  For example, when the arms and legs are extended away from the center of the body, as when the arms and gesture leg are à la seconde, rotation is slower since more mass further away from the body’s center of rotation. As that mass gets pulled closer to the center of rotation, conservation of angular momentum dictates that the dancer must turn faster. Dancers can feel this when they pull their arms in tight, and it is clearly visible on a low-friction surface like when watching figure skaters.

 

Angular momentum is lost to friction – the amount of surface contact for the turning foot.  A dancer will experience less friction en pointe than on a low relevé in plié as is sometimes seen in a jazz turn. The interaction of the surface of the shoe and the floor also contribute to the coefficient of friction: a satin pointe shoe on a vinyl surface has relatively low friction when compared to a bare foot on the same surface. The more friction the slower the turn, and therefore fewer rotations are possible.

 

Take Away Ideas:

 

1)     Develop a strong supporting leg: In a pirouette the dancer is rotating around a vertical axis so balance in the turning position is important. Imura and Iino (2018) found that dancers need good strength in the supporting leg to help find balance and endurance for multiple revolutions. 

 

2)     Focus on the arms in the preparation –Kim, et al, (2015) found that skilled dancers generated larger vertical angular momentum by skillfully using rotation of the upper trunk and arms. The closing arm after the moment of inertia makes the largest contribution to whole-body angular momentum – not the arm that opens as the trunk begins to rotate.

 

3)     While the supporting leg should be strong, the body should be slightly relaxed.  The same is true in pirouette.  If a dancer holds the body rigid, the slightest displacement from equilibrium will cause gravity to exert a torque on the body, and the dancer will topple. Keeping the body somewhat relaxed enables the dancer to make the slight adjustments necessary to correct for small perturbations from balance.

 

Additional Reading:

1)     Laws, K. Physics and the Art of Dance (2002)

2)     Sugano A and Laws K.  Physical analysis as a foundation for pirouette training.  Med Probl Perfom Art, 17 (1) 29-32.

3)     Imura A. and Iino Y. Regulation of hip joint kinetics for increasing angular momentum. The results suggest that dancers need to regulate hip joint torques along with the thigh angles in the pirouettes depending on the number of revolutions. Human Movement Science 60(2018)18-31.

4)     Kim J, Wilson M, Singhal K, Gamblin S, Suh CY and Kwon YK Generation of vertical angular momentum in single, double and triple-turn pirouette en dehors in ballet.  Sports Biomechanics, Volume 13, 2014 - Issue 3

5)     Lott, MB and Laws KL The physics of toppling and regaining balance during pirouette.  Journal of Dance Medicine & Science 2012, 16(4) 167-174.

 

 

 

Margaret Wilson, PhD

Professor, University of Wyoming

 

Jennifer Deckert, MFA

Associate Professor, University of Wyoming

Margaret and Jennifer are the co-directors of the Dance Science Program at the University of Wyoming in Laramie, WY USA

 

Tags:  physics  pirouette  teachers  turn 

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