What are the Optimal Biomechanics of a Triple Axel in Figure Skating to Enhance Performance?

 

Introduction:

Figure skating competitions are run by the International Skating Union (ISU). The ISU world figure skating championship is an annual figure skating competition involving top figure skaters from around the world who compete for the title of world champion (Podolsky, 1990). This event has been hosted all around the world since 1896, with countries placing bids each year for the rights to hold these championships. Competitive figure skating includes four major disciplines: singles, pairs, dance and synchronized skating. In singles skaters performs alone on the ice and combines the highest level of athleticism with composition.

(International Skating Union, 2016)

Pair skating consists of a female skater and a male partner who perform in highly athletic and daring program. This is similar to ice dance which consists of a female ice dancer performing with a male partner in intricately choreographed programs that focus on precision and artistry. 

(International Skating Union, 2016)

(International Skating Union, 2016)

 

Synchronize skating is completed in teams of twenty and everyone performs in unison on the ice.

(International Skating Union, 2016)

Levels of Competition:

There are six levels of competition, with each increasing in difficultly and techniques. These levels start as low as juvenile and work towards becoming a master. The skating performance is judged according to a set of criteria that must be meet. Each section and every element of the sequence is judged and has a certain base value indicated in the Scale of Value (SOV) chart. Each judge on the panel identifies for each element one of the seven grades of execution with each of these grades having its own positive and negative numerical value. The grades of execution are determined by calculating the trimmed mean of the numerical values of grades awarded by the panel of judges. All four disciplines are judged differently and points are awarded based on jump combinations, jump sequences, combination lifts and any other addition elements added to the performance. In addition, points are delegated for performances that contain illegal movements or elements such as costumes, props, falls, late starts interruption in performance programs and music (International Skating Union, 2014).

Major Question:

(International Skating Union, 2016)

Figure skating is a sport which associates athletic competency with a sophisticated artistry (King, 2005). Figure skating includes many different techniques and some of the stunts can be quite challenging. A challenging manoeuvre which most ice skaters are unable to perform is the triple axel. This aerial stunt is an edge jump that is launched from the ice and contains a half an extra rotation to a normal jump in figure skating (King, 2005). This is where the idea of the triple jump was established from and this technique has 3.5 revolutions. The triple axel has four components these being, skating, the take off, the rotation or the flight and the landing. It is crucial that all these elements are performed correctly to ensure that the skater safely lands   and that the rotations are successful. In addition, the triple axel is very difficult as it is not similar to the other jumps performed in figure skating. The triple axel involves the skater taking off on the outside edge of their blade and going into a forward rotation (King, 2005). Additionally, the skater lands on the opposite foot which they took off from and this is what makes the triple axel so complex. This blog will look at what the optimal biomechanics of a triple axel are and how these can be used to enhance performance.  

The Answer:

Preparation Phase:

(International Skating Union, 2016)

Gliding:

Before the take off the skater must glide across the ice in preparation for the jump spin. This involves using the principles of kinetic energy, which is the energy associated with velocity of someone's body (Blazevich, 2013). If a person produces a greater power their body or object will attain a higher velocity, as it will have more kinetic energy (Blazevich, 2013). This is crucial in the preparation phase of the triple axel as the skater must gain as much kinetic energy as possible before the take off. If the skater has more kinetic energy in the preparation phase, they will be able to accelerate better off the ice, allowing more air time to perform the turn.

Stroking/Crossover:

It is important that the skater is accelerating fast in the preparation stage to allow them to generate speed, resulting in maximum height off the ground when executing their jump. The purpose of crossovers is to gather speed on the ice (Fortin, Harrington & Langenbeck, 1997). During a triple axel crossovers the skater counters clockwise in a backwards position and is used as the standard form of traveling in a circle. This technique involves the skater's upper body to be turned into the circle and the head to be turned to look over the right shoulder the direction in which they are traveling. From using this technique power is generated through the skater’s right leg as it pushes powerfully against the ice through hip and knee extension and plantar flexion before it is crossed over the left leg which is extended vigorously. This skill relates back to Newton's third law of motion stating that “for every action, there is an equal and opposite reaction” (Blazevich 2013).

Direction of Acceleration:

Controlling one’s center of mass is required to performed this skill. This is due to the skater  shifting his or her weight from one leg to the other as they cross over each other. From this, power and speed of this technique will arise from the scissor like motion produces with every stroke. In instances such as these is it okay for the centre of mass to be unbalanced when accelerating as it helps to allow center of mass to be moved backwards of the base of support, as it will cause a backwards rotation of the body. The skaters will generate more speed if their pre-extended knee angle were more acute as this knee extension will create a greater velocity along with the bald of the skate being more horizontally during push off stage. By crouching or bending forwards the skater is able to reduce their air resistance and this allows them to maintain a greater speed and power (Fortin, Harrington & Langenbeck 1997). The skater’s torso and head faces the direction of acceleration, this can help to increase their speed intern moving them faster along the ice with less force required and an increase in movement efficiency. Angular velocity plays an important part in the preparation stage of the triple axel and it is key for the skater to increase their angular velocity, as then angular momentum will be conserved. Most professional athletes have a tendency to enter the take off stage with a linear velocity of approximately five meters per second. In the preparation stage of the triple axel, the skater will turn their body form facing backwards to now facing forward as they move towards the take off phase. When the skater makes this turn, they will push off their left skate, as angular velocity refers to the rate of change in angle (Blazevich, 2013). 

Take Off Phase:

Applying Greater Force Off The Ice:

The triple axel jump in figure skating is heavily influenced by Newton's third law of motion. This law states that for every action, there is an equal and opposite reaction (Blazevich, 2013). This is very important in the take off stage of the triple axel leading into the spin. When a vertical force is applied to the ice the equal and opposite force stops the foot sinking into the ice. The ice exerts an equal and opposite reaction which can accelerate an ice skater forwards if the force is large enough to overcome their inertia. In order for the skater to jump to a greater height they need to overcome inertia by having a force applied against them (Blazevich, 2013). This can be achieved be applying large and well-directed force against the ice. Having an equal and opposite reaction with the ice will allow the figure skater to push up and forward from the ice to start their jump. Then the skater pushes down and back on their ice after their rotations to land successfully. In addition, the skater needs to follow Newton's first law in this stage to push against the ground with the same magnitude giving the propulsion of the jump. The skater must perform this on ice the ice against a surface which is difficult due to the fiction less nature of its surface. 

Producing Greater Power:

(International Skating Union, 2016)

Kinetic energy is associated with the velocity of someone's body (Blazevich, 2013). This energy is associated with motion and an object with a greater mass or velocity has a greater energy (Blazevich, 2013). Kinetic energy is critical in the take off phase of the triple axel and to increase the skater's performance, they need to maximize the amount of energy used. If the skater produces a greater power through their legs as they push off the ice, they will attain a higher velocity as they will have a higher amount kinetic energy. The greater mass in the legs will result in a higher take off for an object with greater mass has a greater energy. After an extensive amount of training figure skaters should be able to increase their fitness and perform take offs with the same amount of kinetic energy continuously.  

Conservation of Angular Momentum:

As previously stated, angular momentum is conversed during the take off phase of the triple axel. Angular momentum refers to any mass that moves with velocity (Blazevich, 2013). In the take off phase, generating angular momentum is important to allow it to be conversed. Before the skater jumps off the ice their body create torque which influences the axis of rotation. This torque provides angular impulse and this results in angular momentum being created. When the skater moves their free leg through during the propulsive phases of the triple axel jump, there is an increase in angular momentum. However, when the skater is just about to take off the ice there is a slight decrease in angular momentum.

Angular momentum equals moment of inertia added to angular velocity. When a mass is moving an angular velocity, it has angular momentum. This relates to the skater in the take off phase of the triple axel as prior to take off the skater's free leg is a maximum hip flexion and this contributes to angular momentum beginning to decrease, due to deceleration of the skater. The skaters arms are assisting in creating positive angular momentum, however this is not sufficient enough to maintain a constant angular momentum due to the free leg decreasing. Therefore, this results in angular momentum being decreased slightly just before take off. In addition, when performing a triple axel the movements of the arms are more influential than the legs in creating angular impulse. 

Angular momentum is a function of the moment of inertia and the angular velocity (Blazevich, 2013). When the moment of inertia is increased the angular momentum will remain the same. When a person starts to fall in any circumstance, they will have little angular momentum and the momentum will remain until  an external force acts to change it.  This is evident when the skater is swinging their arms vigorously and the body tends to rotate in the opposite direction as angular momentum is reduced. This is by applying a force (torque) which is similar to the spinning phase when the legs and arms are drawn into the body.

By the skater applying force against the ice angular momentum is generated. The ice then applies a ground reaction force onto the skater. From this the skater is able to gain angular momentum and the skater's axis of rotation needs to be correct otherwise they will not spin in the flight phase. The force being applied must cause a moment or torque in which means it must be applied a distance away from the axis of rotation. The larger the torque the greater the angular momentum will be. Angular momentum is generated prior to the toe-pick as the skater brings forward the left arm and moves the right arm forwards with an extended trunk.  As the skater is on the outside edge of their skate they are able to create angular impulse about the axis of rotation which transfers into angular momentum for the jump. By taking off the toe pick the skater is able to extend their trunk during the take off stage to generate vertical momentum for the jump phase. 

Differences in Techniques:

During the triple axel most skaters often utilize a skid during the take off phases. This results in them creating higher angular velocity at take off and allows them to rotate the 3.5 times during the flight phase. However, if the skater includes a skid there is a reduction in their speed and no gain in angular momentum. If the skater can incorporate this technique with a higher angular velocity and a smaller moment of inertia they will successfully complete the rotations required. The skater will often extend their knee and hip in order to bring the limbs closer to their axis of rotation. This will allow them to increase their angular velocity and ensure their body is tight to maximize their rate of spin in the jump phase of the triple axel. 

Flight Phase:

Body and Arm Position:

(International Skating Union, 2016)

During the flight phase of the triple axel, Newton's first law of motion is evident. This law states that an object will remain in motion until an external force is applied. When moment of inertia is decreased, angular velocity increases allowing angular momentum to be conserved. Moment of inertia refers to anything where a quantity is multiplied by distance (Blazevich, 2013). Inertia cannot be changed in value however it's effect can be manipulated. To create a faster spin the skater needs to hold their knees tight close together and their arms need to be tucked towards their chest as soon as the skater is vertically straight. The effect of moment of inertia is reduced when a skater places their arms closer to their body as it closer to the axis of rotation. The upper body would be moving in an upwards vertical motion due to straightening of the legs. If the skater is vertical this allows them to increase height on their jump, allowing them more time to perform the rotations. In addition, the skater needs to point their toes towards the ground to enable them to successfully propel upwards, for the moment of inertia is decreased. This allows them to generate a greater speed in order to successfully rotate the 3.5 times. In addition, this will allow the skater to increase their angular velocity when they take off the ice and once they are in the air they will continue to decrease their moment of inertia. By adopting a smaller moment of inertia the skater can increase their angular velocity through the flight phase, whilst they are still on the ice. Once the skater has reached the minimum moment of inertia attainable, based on their body size they can no longer attain higher amounts of angular velocity. This is due to the skater decreasing their moment of inertia, as their body is already in the tightness possible rotating position. This technique will allow the skater to successfully complete the high revolutions in the triple axel. 

Creating Greater Angular Velocity:

Angular velocity refers to the rate of change in angle (Blazevich, 2013). In the flight phase of the triple axel it is important that the skater generates higher velocity to allow them to complete the revolutions included during this stage. For the triple axel the skater must generate a greater angular momentum compared to single or double axel jumps. To complete the 3.5 turns the skater must balance the average angular velocity with the time in the air. For the skater to attain a greater angular velocity during the flight phases they will need to attain a minimum moment of inertia quicker when they are in the air. For optimal technique the skater should delay their landing by flexing their hips and knees during the last rotation. This allows the skater to rotate quicker thought the air and complete the maximum amount of revolutions, as it is creating a downward force against the ice. In addition, during the flight phase the skater will perform the spin in a tight position, but then they must flex their body in order to decrease angular velocity in preparation for landing.  At the same time the skater will flex at the hip and knee of the take off leg to alter its moment of inertia prior to and during the landing. This will enable them to slow down and to have successful landing.

Increasing Flight Time:

(International Skating Union, 2016)

The amount of time in the air which a skater has is very important in the triple axel, as it requires many rotations. During the flight phases of the triple axel all the joins in the kinetic chain, (feet, knees and hips) simultaneously extended vertically to generate higher cumulative forces. This results in a push like movement pattern which results in a higher overall force. in addition, flight time is dependent on the vertical velocity which the skater generates and the difference in centre of mass height at take off. 

Projectile motion is crucial in the flight phase to increase flight time. Projectile motion refers to the motion of an object which is projected at an angle into the air (Blazevich, 2013). This is influenced by the gravity and the air resistance of the object. In figure skating the skater can either move between horizontal and vertical, but gravity works to keep the body in a vertical motion. During the flight phase of the triple axel jump projectile motion is influencing how long the skater can stay in the air, before returning to the ice. This allows them to complete the rotations and keep their body vertical towards the ice.  In addition, the trajectory of the skater is influenced by projection speed and the height that an object is projected. This means the skater must aim to be as high as they can off the ice whilst rotating.

Landing Phase:

Some skaters are known to delay the landings of their jumps. This is achieved through hip and knee flexion just prior to landing as it will enable them to complete their last revolution (King, 2000). Once the skater has completed their rotation the next step is to land on the ice whilst still maintaining balance. In order for the skater to achieve this they must achieve a goal of decreasing the angular velocity in order for them not to continue to rotating once they have made contact with the ice.

A skater will typically land their jump on their right leg with their non-supported leg (left leg) being moved into complete hip hyperextension and complete knee extension positioning it parallel to the ice surface. Their arms are re positioning from being tucked into the chest to being flexed and abducted to 90 degrees at the shoulder. This will continue their moment of inertia of their upper limbs and acts as a form of balance. Centre of mass refers to the point at which the mass of the body is evenly distributed in all direction (Blazevich, 2013). Landing with a trunk flexion close to 30 degrees and 60 degrees of flexion on the knee and hip allows the skater to maintain their balance for their centre of mass will be situated between their base of support.

Additional Information:

Footwear Worn:
The skates which the skater wears are very important to their overall performance and are influenced by physics. The skates allow the skater to do two things, glide over the ice and push off the ice with the edge, which causes them to gain speed. In speed skating the skaters use clap skates to allow them to accelerate faster on the ice, however in figure skating a hollowed out blade is used. The blade has three parts and has a concave edge which allows the skater two edges to skate on. When the skater angles their foot outwards and extends their knee, the inside edge of the blade is placed on the ice and creates friction between the two of them. Fiction allows the skate to connect the ice and this gives the skater the resistance as they move. When the edge exerts a force onto the ice, fiction propels the skater forward. When the skater has low fiction with the ice it allows them to easily glide over the surface. In addition, the skate allows the skater to dig their skate into the ice in order to go around a turn, speed up or stop.

When a skater is at rest on the ice the fiction between the skater's blade and the ice is zero. Once the skater propels themselves forward by pushing off the ice with a force perpendicular to the skate blade they are able to move across the ice. When the skate is on the ice, there is less air flow. This allows the skater to stick on the surface for a longer period of time. In addition, when a skater pushes off with their rear leg, a perpendicular force is exerted on the skate by the ice. The force points forward as that is the direction of motion and this is what pushes the skater forward. As the skater moves across the ice they switch to the other leg, by pushing off the ice with that one and then the process is mirrored. If the skater pushes off the ice with a greater forward force they are able to accelerate faster across the ice and increase the component of force in the direction of motion. For a skater to maintain their balance when accelerating forward, the skater will crouch forward in the direction of motion. This will prevent them from falling backwards, due to the torque caused by the forward component of the force. When the skater is landing the ground reaction force end of their skate is bent, otherwise they would slow down.

How Else Can We Use This Information?

Dance:

Dance is very similar to the techniques of figure skating; however, it is not performed on the ice. The previous information can be transferred to certain dance techniques such as leaps, pirouettes and moving turns. Pirouettes require great balance and this is achieved when the bodies centre of mass lies within the base of support. If the centre of mass moves outside the base of support balance cannot be reached. When a dancer prepares for their turn their positioning is with arms put straight horizontal to the ground. From this, the dancer then makes their way to third position where take off begins. This is where they aim to produce a greater power through their legs through pushing off the floor to spring their body up into relive. The greater mass in the legs will result in more momentum with greater mass has a greater energy. As the dancer springs up their arms swing in to come close to their chest with elbows facing outwards decreasing their moment of inertia. As noted above the effect of moment of inertia is reduced when a skater places their arms closer to their body and their free leg is closer to the axis of rotation.

Ice Hockey and Speed Skating:

These biomechanical principles can also be applied to sports such as, ice hockey and speed skating. Both of these sports are played on ice, therefore how the player skates and the friction with the ice is similar. The low friction of the blade with the ice is what allows the hockey players and speed skaters to glide along the ice. This is similar to the previous statements above and how the skater prepares for the triple axel. The physical makeup of the ice also allows the skaters to dig in with their skate to either turn, speed up or stop whilst in a game situation or skating. For a hockey player to successfully retrieve a puck they must push off the ice with force perpendicular to the skate blade. As the friction of the blade is almost zero, this is the only way which they can propel themselves forward. Speed skaters use different skates, which can be referred to as clap skates to allow them to accelerate faster, as previously mentioned. On the contrary, hockey players have a slight hollow in the bottom of the blade. This creates sharp edges which grip onto the ice to allow the player from slipping.  In addition, this blade must be kept sharpened to maintain optimal performance to ensure the player's foot does not slip on the ice.



Reference List:

Blazevich, A. J. (2013). Sports biomechanics: the basics: optimising human performance. A&C Black.

Fortin, J. D., Harrington, L. S., & Langenbeck, D. F. (1997). The biomechanics of figure skating. Physical Medicine and Rehabilitation, 11, 627-648.

International Skating Union,. (2016). Home. ISU. Retrieved 10 June 2016, from http://www.isu.org/en/home

King, D. L. (2000). Jumping in figure skating. Zatsiorsky VM, Biomechanics in Sports: Performance Enhancement and Injury Prevention. Oxford: Blackwell Science, 312-325

King, D. L. (2005). Performing triple and quadruple figure skating jumps: implications for training. Canadian Journal of Applied Physiology, 30(6), 743-753.

Kuehn, K. (2015). Newton’s Laws of Motion. In A Student's Guide Through the Great Physics Texts (pp. 261-264). Springer New York.

Podolsky, A., Kaufman, K. R., Cahalan, T. D., Aleshinsky, S. Y., & Chao, E. Y. (1990). The relationship of strength and jump height in figure skaters. The American journal of sports medicine, 18(4), 400-405.

Smith, A. D. (2000). The young skater. Clinics in sports medicine, 19(4), 741-755.

By Kristie Sonntag and Juliet Rapetti.