MAJOR QUESTION:

What are the optimal biomechanics for sprinting?

INTRODUCTION

Biomechanics is the study of sport science, which applies the laws of mechanics and physics to human athletic performance (Wood, 2010). It is concerned with the internal and external forces that act on the human body, causing optimal performance (Mac, 2015). Sport biomechanics is a vital tool for improving as an athlete, especially at a professional level. Through a series of key movement phases the optimal biomechanical techniques and principals in sprinting will be revealed in order to benefit anyone out there wishing to improve their own sprinting ability.

Here is a video clip of Usain Bolt, who is the fastest man in the world, clearly outlining the key biomechanics involved in sprinting.

Figure 1: Key Sprinting Biomechanics (Nick Warren, 2012).

THE ANSWER

STARTING POSITION COMING OUT OF BLOCKS

At the start of the race, mass is at rest. According to Newton’s first law of motion an object will remain at rest or continue to move with constant velocity as long as the net force equals zero. Therefore following Newton’s third Law of motion; for every action there is an equal and opposite reaction, the importance of the feet position becomes clear. Assistance from starting blocks increases horizontal velocity resulting in equal and opposite reaction from the body/legs pushing into the blocks and then propelling the body forward. Seen in figure 2 the arms need to be positioned vertically down from the shoulders, as the weight needs to be on the feet allowing more power to be generated for a exploding push off the blocks. For optimal push off power the front leg angle needs to be at 90 degrees and the back leg needs to be at 120 degrees with the centre of mass slightly to the back end of the athlete (seen in figure 3 & 4). This will allow optimal ground reaction force from the body to ground. The blocks are used to create more surface area for the feet to push off of. The more surface area the feet have to push off the more power is generated, creating a more powerful ground reaction. 

Figure 2: Arms positioned vertically down from athlete’s shoulders. (Kenny. J, 2015).

Figure 3: Front leg at 90 degrees. (Kenny. J, 2015).

Figure 4: Trailing leg at 120 degrees. (Kenny. J, 2015).

TAKE OFF PHASE

With good angle of projection a change in centre of mass is seen as the athlete is projecting forward. Therefore the centre of mass has moved from the back of the body to the front (figure 5). This is achieved through the torso being lifted to about a 35 degree angle, creating a straight line from head to toe (figure 6). With the centre of mass being transferred to the front of the body it allows a greater force generation, maximizing forward momentum. As the athlete explodes from the blocks the arm of the back leg needs to rapidly pull backward as well as the front arm rapidly swinging forward. The arms should be at a 90-degree angle for optimal force production resulting in optimal take off velocity. By shortening the levers (arms) at this particular angle it reduces moment of inertia increasing angular velocity, allowing a greater take off distance and stride length.

Figure 5: Relating to the change in COM.











Figure 6: Optimal angle for take off (Kenny. J, 2015). 

BODY POSITION IN DRIVE PHASE

The drive phase is seen through the first 10 meters of the race. This is where the body still needs to have quite a low centre of gravity with all forces propelling forward. This is achieved with the body still slightly bent forward, with the head and shins matching the torso angle, creating a straight line. With this angle more power is being generated in an upwards-forward motion. The athlete’s angular momentum does not want to be increased dramatically in this phase, as the forward momentum will be lost, resulting in it being directed upwards.  As the athlete continues, the torso, shins and head angular momentum slowly increases allowing the stance to open up. Figure 7 outlines these key forms through a short video clip below. 

Figure 7: This video shows the optimal body position in the drive phase (TV Athletic, 2012). 

LATERAL MOVEMENT

Lateral movement is important, as the athlete wants all the momentum progressing forward. Therefore all the levers and torque production needs to be moving in a straight line to decrease lateral movement. The arms become a major factor when trying to decrease lateral deviation, as they tend to encourage twisting in the upper body and hips. The arms should never cross the midline of the body. If the arms cross the midline of the athlete’s body it encourages the hips to rotate which in turn deviates the forward momentum across the body. This will burn more energy, whilst running a slower time. In figure 8 Michael Johnson perfectly outlines the importance of minimising lateral movement. He even states that Usain Bolt could run even faster if he focused on his lateral movement. 

Figure 8: At 5:52 the importance of lateral movement is explained by Michael Johnson (Muru, M. 2014).

FOOT GROUND CONTACT

The foot ground contact throughout the sprinting phase is very important in increasing acceleration. Newton’s third law of motion comes into discussion again in this phase, as the action of the foot making contact with the ground creates an opposite reaction. The athlete wants to be generating as much power forward to increase speed and acceleration. This is achieved through angular momentum. Firstly for this to occur the foot contact with the ground is excessively made with the toes. This is because it allows angle of the legs to continue to create forward momentum. The contact needs to be made directly below the hip as this further amplifies forward momentum. It is also important to make contact here as it is below the centre of mass allowing more drive. Applying this force over a period of time with as much ground contact as possible will generate higher speeds. A visual abstract of these key forms are seen in the short video clip in figure 9.  

Figure 9: This clip shows the correct way to make ground contact with a sprinters foot (Howcast, 2013).

HIGH KNEE DRIVE

The athlete needs to lift their knees in a high knee drive almost lateral to their hip or pivot point (figure 10). This movement action allows more force to be driven downwards, therefore penetrating into the ground, creating an equal ground reaction. This again follows Newton’s third law of motion. Pulling the knee in to the hips allows more force to be created, as this is the torque production point. This allows force to be applied over a period of time, creating more speed and acceleration. Lifting the knee closer to the centre of mass also decreases the moment of inertia allowing an increase in angular momentum, thus further creating a more powerful downwards push. 

Figure 10: The high knee drive is seen in Usain Bolts front knee. 

The knee is almost perfectly horizontal. 

SWINGING LEG BACK TO HIP

By swinging the leg backwards to the hip it allows the athlete to move forwards more quickly. The quicker an athlete swings their leg back and tucked up against their buttocks the more torque is developed by the hip muscles. This decreases the mass of the leg and ensures that the remaining mass is located as close to the hip as possible.  By doing the inertia is decreased due to the mass reduction. Keeping the leg directly behind the rear can allow the leg to swoop forward further increasing forward momentum. Figure 11 shows Usain Bolt perfecting this phase. 

Figure 11: Usain Bolt perfectly showing the swinging leg back to hip phase and the arm extension. 

REAR LEG EXTENSION

During the recovery phase the runners leg should extend as the other is preparing for the next driving phase. Athletes need to flex their leg to minimize the moment of inertia. This movement also increases angular velocity of the shins. The leg extension acts as a conservation of angular momentum because of the principal of Newton’s third law; for every angular action there is an equal and opposite angular reaction. The driving arm is moving at a high velocity so the leg straightens in order to stop the body from rotating. Therefore the increased angular momentum of the leg counteracts the moment of inertia. This can be seen in figure12 below. 

Figure 12: A perfect example of the rear leg extension seen in the woman's trailing leg.

ARM EXTENSION

As the aim of sprinting is to project forward as quickly as possible the body wants to stay in a still upright position. The key to sprinting efficiency is having a coordinated movement of arms and legs. For the body to stay balanced and control hip movement, the arms become a major factor. One arm is used as a conservation of angular momentum and the other is bent to reduce moment of inertia, therefore increasing angular velocity. This will allow for a quicker turn over. As driving leg is moving at a high velocity, the athlete needs to keep the body balanced and this is done through the increased angular momentum of the opposite arm (straightened arm). This will decrease hip rotation and body rotation, allowing an increase in forward momentum. An example of this is seen in figure 11.

LEAN

To go even further in improving athletes sprinting ability a lean can be used at the end of the race to reduce some critical milliseconds of their time, as seen in figure13 below. In the final driving phase of the sprint the angular momentum is decreased as the torso is slightly bent forward. The head is extended creating a longer lever. This allows a smaller angle of momentum in relation to the legs and the ground allowing for greater force to be applied to the ground from the toes, reacting in a greater reaction. This will in turn propel the athlete further forward in a slightly more rapid extension. 

Figure 13: This image exaggerates the torso lean applied at the finish line.


BIOMECHANICS MOVEMENT PHASES COMBINED

Figure 14: This clip combines all the key biomechanical movement phases mentioned throughout this blog. 

HOW ELSE CAN WE USE THIS INFORMATION

This investigation on optimal biomechanics for sprinting provides an in depth knowledge on how athletes can improve their running efficiency, which will in turn increase their speed. This information is not only useful for people that participate in sprint running, it can be transferred into many other sporting fields. In most sporting events or fields there is some form of sprint running involved. Two particular sporting field that would find this information very useful could be athletes looking to develop their speed in rugby league and union. Speed is a key attribute in these fields, as players want to invade their opponents by running past them and into the try zone.

Carlin Isles is a former USA 100m sprinter and has recently transferred into the field of rugby league. In figure 15 below there is footage of him absolutely obliterating his opponents as no one can catch him. Therefore the transferal of these biomechanics has already been studied in different sporting fields.

Other sports such as Australian Rules Football are starting to look at transferring athletes from other athletic events as well. They have recently drafted a former Steeplechaser called Mark Blicavs, which is an event that requires some important sprinting mechanics. He has excelled in the sport and is leading the Geelong football clubs best and fairest. In summary sprinting biomechanics is a very transferable study, which can be very useful in many sporting fields. With a large range of different sporting codes starting to become aware of this, some particular sporting fields are going to develop some magnificent athletes.

Figure 15: Carlin Isles showing his athletic ability after transferring from 100metre sprinting to rugby league (Rugbyplease, 2012).

REFERENCE:

Armando La Posta, (2008, April 14) Asafa Powell start. [video file]. Retrieved from:https://www.youtube.com/watch?v=h0aoWI2EARM&list=PL74674E0CE7EFF67B

Blazevich, A. (2010). Sports biomechanics, the basics: Optimising human performance. A&C Black. 2^nd ed. 1 – 246

Howcast, (2013, August 10). How to have proper foot strike| sprinting. [video file]. Retrieved from: https://www.youtube.com/watch?v=p0sAZgqoozI

Jordan Kenny, (2015, May 20). Biomechanics sprint start analysis [video file].

Retrieved from: https://www.youtube.com/watch?v=Iooapls-8Ys

Mac, B. 2015. Biomechanics. Sports coach. Retrieved from:

http://www.brianmac.co.uk/biomechanics.htm

Nicholas Eckett, (2012, March 2). Sprint form slow motion. [video file]. Retrieved from: https://www.youtube.com/watch?v=PH-3cHxXAK0

Nick Warren, (2012, March 29). Sprint technique applied to biomechanics [video File]. Retrieved from: https://www.youtube.com/watch?v=TreDUJnTjaI

Mart Muru, (2014, February 10). Michael Johnson analyzes Usain Bolt’s sprinting. [video file]. Retrieved from https://www.youtube.com/watch?v=oZ3c8zhMoWI

Rugbyplease, (2012, December 9). ‪Carlin Isles olympic dream. [video file]. Retrieved from: https://www.youtube.com/watch?v=gA5bwqVN5LM

TV Athletic, (2012, August 9). Usain Bolt sprint analysis English subtitle. [video file]. Retrieved from: https://www.youtube.com/watch?v=Og3DahGtKXU

Wood, R. 2010. Biomechanics & physics of sport. Topend Sports. Sports biomechanics and kinesiology. 1-2