With the Olympics being one of the worlds biggest sporting events, the 100m sprint particularly the men’s race, is one of the most prestigious events in the tournament. Usain Bolt (Jamaica) currently holds the Olympic record for the 100m sprint, running it in 9.69 seconds at the 2008 Beijing Olympics. He also holds the current world record overall, running a 9.58 second 100m at the world series in 2009 (IAAF, 2015). It’s often speculated now can this time be beaten, or is Usain Bolt superhuman? Whilst admiring Usain’s technique, we will walk through and unpack the biomechanics of sprinting, using an amateur South Australian sprinter, while looking at Usain Bolt’s technique. This in turn will assist in aiming to improve their max velocity during the race through altering the biomechanical principles.
“”Sprinting” is a term used to express the relative intensity of effort in running.” (Watts, Coleman and Nevill, 2012, p. 1085). An elite 100m track sprint can be broken down into various phases in order to understand the optimal technique and biomechanics required to produce the fastest run. These phases involve beginning with the block start and progressing through the driving phase, transition phase and speed maintenance phase (Arbuckle, 2010). In South Australia the most common competition with the South Australian Athletics League (SAAL) is run on grass and has numerous short distances. The phases can be transferred across to these races. This blog aims to provide an understanding of how the biomechanical principles of sprinting can assist in improving maximum velocity. This will be shown through unpacking Ben Hardy’s (an amateur sprinter with SAAL) technique, which will be compared and contrasted with Usain Bolt’s highly regarded technique.
Background of Ben Hardy:
- Began running with South Australian Athletic League (SAAL) in 2010
- Most common distance run: 70m and 120m
- Has won 3 race meets since beginning (one 70m race and two 120m races)
- Personal trainer and level 2 strength and conditioning coach
- Background in football, weightlifting and softball
The photos and videos of Ben’s technique and speed throughout this blog were filmed on June 2, 2015. This is during his running ‘off season’ which may decrease his maximum velocity as he is not specifically training for races. For the purposes of this blog, to see if we can alter and implement the optimal biomechanical principles in order to increase his maximum velocity during the race, being in off season won’t impede in the way we understand the biomechanical principles of sprinting.
In order to conduct this investigation Ben was filmed sprinting a 70m run multiple times to assess, address and enhance the biomechnical sprinting techniques of his run. This distance was chosen as this is what he now predominantly runs in season. It was measured out using a measuring wheel and was marked out clearly using agility poles as the start line and ‘finish gate’. The app Coaches Eye was used to slow down the video and look closely at the technique. His maximum velocity was measured at 42m into the run using the app Speed Clock (Speed M). This distance was based on England Athletics breakdown of Usain Bolt’s 100m run (figure 1). Usain reaches his peak velocity at 60m into his 100m run (60%, 60% of 70m is 42m). This velocity peak may alter for different athletes, but Usain Bolt is being used as an example of the optimal technique throughout this understanding, making his race the most efficient style.
FIGURE 1: This is a graph composed by England Athletics, 2010 that shows Usain Bolt’s velocity throughout his world recording winning run in Berlin, 2009. His maximum velocity comes about 60 meters into the race. It shows the break down of phases in his run and at what stages he is at his maximum velocity as a percentage.
VIDEO 1: At the start of a race the marshal tells the athletes to get on their blocks. This short clip shows the set up that Ben takes in order to get his block position correct.
Most amateur and elite sprinters use starting blocks during short races (anywhere between 70m and 400m) in order to gain more power and acceleration at the start of their race. Athletes are told to get on their blocks. This involves first placing the balls of feet on the blocks. The tip of the toes should be just touching the ground and the heels peeling back off the top of the block (Digital Track and Field, 2015). Ben demonstrates this perfectly in picture 1. Every athlete tailors their starting blocks to their desire. Those with their feet starting closer together require more power from the legs to drive the back leg forward. The further the feet are apart generally the longer the levers. Those with longer levers are able to take a further initial step forward and gain more distance in the take off. Ben’s feet are relatively close together as seen in picture 1, he is quite short in height, but is also able to produce a lot of power in his legs. Compared to Usain Bolt, his feet are also positioned relatively close (picture 2) considering he is 6ft, 5. This means Bolt is able to produce a lot of power and drive from his legs. Once the feet are set the knees come down, resting on the ground. The hands are then set by measuring an elbow to hand length away from the back knee and then placing the hand on the ground just outside shoulder width. The fingers should be facing outwards, with the thumb and index finger parallel along the line, making an arch in the middle. It’s now important for the athlete to straighten the back by tightening the abdominals. Ben emphasises this in video 1 at 17 seconds into the clip. The head should align by looking down in order to assist in having a straight connection from the head to hips.
PICTURE 1: Ben is demonstrating his crouched block position. He has set himself up using the most optimal technique in preparation for the set position.
PICTURE 2: Usain’s feet are quite close together for such a tall athlete. Compared to Ben the distance between both feet is relatively similar, but Ben is much shorter than Usain.
When the marshal calls out ‘set’ this is when the hips rise higher than the shoulders (Digital Track and Field, 2015), putting pressure through the balls of the feet and hands as seen in picture 3. The center of mass should stay over the middle of the body, the athlete should feel as though they would fall forward if they were to retract their arms. This is often hard for beginning athletes to grasp as putting weight through the hands and pushing away from the blocks is difficult to balance out. Arms are fully extended without locking the elbows and head position shouldn’t change from the crouch as this helps to maintain the straight back. The head should not drop at any stage otherwise it will encourage the back to round and the hips to drop. The athlete is now ready to take off.
PICTURE 3: Ben demonstrates here his hips have risen higher than his shoulders, ready to react to the gun to take off. His elbows aren’t locked out but arms are straight ready to push off.
VIDEO 2: Ben taking off from set position
The driving phase is understood to be the first 10 meters in the race. The take off is one of the most important aspects as this is where 75% of the acceleration is achieved (England Athletic, 2010). Acceleration is the rate of change of velocity (Blazevich, p. 7, 2010). The faster the velocity changes the higher the acceleration. During the take off the skill cues athletes are looking for are triple extension from the foot through to the shoulder (extension at the knees, hips and shoulders of forward leg) picture 4, arms should be stretched as far as possible, back (driving) leg comes through, the front leg then slightly scrapes the ground to reduce inertia and the head position stays down until fully balanced.
PICTURE 4: In the first frame here we can see Ben achieving the triple extension. This starts by propelling the arms and flexing the shoulders together. The hip is extended alike the knee. This means more force is able to be produced in the take off. In the second frame it shows slight elevation of the foot, before the third and fourth frame shows the foot scraping the ground which reduces the gravitational force and moment of inertia that occurs when bringing the leg forward.
When stationary in the set position Ben has no velocity but is considered to have inertia. Newton’ first law states: “An object will remain at rest or continue to move with constant velocity as long as the net force equals zero” (Blazevich, 2010). In order to change his velocity status this can be understood using Newton’s second law: “The acceleration of an object is proportional to the net force acting on it and inversely proportional to the mass of the object, F = ma” (Blazevich, 2010). The force produced by the legs during the take off, is acting against the gravitational forces attempting to push Ben downwards. As Ben’s velocity status increases, inertia is reacting against gravity, assisting in propelling him forward. He stays low to the ground and pushes himself forward rather than directly upwards. This initial effort in turn is how he accelerates. His acceleration action can be seen in video 2.
As the gun goes off Ben brings his knee up, flexing as much as possible at the hip, knee and ankle joint. The other leg is fully extended to achieve the triple extension. The arms extend apart from each other. By performing both these movements they exert a high amount of force. This force production is reinforced by Newton’s third law that states “for every action, there is an equal and opposite reaction” (Blazevich, 2010). There are two ways of explaining this. Firstly, as Ben’s driving leg propels forward this forces the arms to split with the opposite arm spreading forward to the back leg. As the legs rotate through, the arms swap as well. Another way to explain opposite reaction is when the foot hits the ground, a force in applied downward. An opposite reaction force is exerted through the ground; this is called a ground reaction force. In this case it prevents the foot from sinking into earth. If this force is strong enough to overcome the inertia that is in the foot has a result of gravity forcing it downward, horizontal and vertical propulsion occurs. This propulsion is described in further detail when maintaining speed.
The center of mass is very important to get right. As mentioned earlier in the set position the weight of the body should be distributed evenly between the arms and legs, making Ben’s center of mass situate around his hips. If this is not distributed properly athletes may slip or fall forward when taking off (Parker, nd). Throughout the driving phase this center of mass shouldn’t change.
If we look at Usain Bolt’s technique in the take off action and driving phase in video 3, Ben’s is much the same. Due to Usains longer levers he is able to take a further first step. They both achieve triple extension and the split of the arms. Although, Usain is able to push further back with his back arm propelling him forward. The amount of power and force exerted can’t be measured from looking at videos, but going by Usain’s world record time we can infer he exerts more ground force in order to gain more momentum and acceleration to prepare him for the rest of the race
VIDEO 3: Usain Bolt slow motion start; he is able to take a long stride in his first step due to his long levers and the power produced from the back leg. His front leg does not leave the block until he is fully extended. (0.00 – 0.46s)
In the transition phase the athletes are reaching peak acceleration and are beginning to straighten their torso upright and look down the track. This is where maximum velocity is reached. Measuring Ben’s velocity at 42 meters, of the three times showed he had a maximum velocity of 16.8m/s (fastest of the 3), which is slightly slower than expected but there are many constraints (environmental, physical and personal) that may impact this. These include the weather conditions were slightly cooler than what he would normally run in, he usually wears clothing of a tight nature during SAAL races, shoes used during this run are sneakers rather than running spikes, no perceived pressure of other competitors (running for no purpose of his own), preparation was minimal and he is in off season for running making his training and preparation not specific to sprinting.
PICTURE 5: A screenshot from the app SpeedClock showing Ben running a velocity of 16.8m/s, 42m into a 70m run on June 2, 2015.
SPEED MAINTENANCE PHASE
It’s physically impossible to maintain maximum velocity for a prolonged period of time. After maximum velocity is reached, generally at the end of the transition phase, the runner is now attempting to conserve force and power in order to maintain high speed. Although the body can not produce enough energy to do so for the whole race, there are ways to conserve momentum through specific biomechanical understandings.
VIDEO 4: In this video we can see Usain Bolt’s foot contacts the ground under his center of mass and his ability to maintain high velocity in his upper half allows him to be able to take longer strides, producing more power and propelling himself forward faster.
Foot position is important when aiming to conserve speed and momentum. In order to maintain and increase force gained from every step it’s essential to get the right balance between the time the foot spends on the ground and how the foot contacts the ground. As Ben’s foot touches the ground he uses the mid to fore front of his foot. This is optimal as demonstrated by the impulse-momentum relationship. Although in picture 6 we can see Ben’s foot is slightly in front of his hips. The optimal technique is to contact the ground with the foot under the hips (center of mass), because immediately prior to this occurring the foot should have already begun to move backwards slightly before contacting the ground under the hips. In this state the foot contacts the ground and elicits forward force onto the ground. The ground then reacts producing an equal and opposite braking force against the runner (Blazevich, 2010). Once the center of mass has moved past the foot, the force is now being applied in a backward motion, pushing away from the ground causing a propulsive impulse. Usain Bolt demonstrates this optimally in video 4. We can see his foot-ground contact is when the hips are over the foot and then he pushes off and drives the hip up. His stride length is very long giving him a greater time to produce propulsive impulses. The trade off to this, as we can see in Ben’s video 5 he takes quite long stride length but his upper body can not keep up. For amateur sprinters they often aren’t able to attain high speeds propelling their top half forward faster. Whilst taking long strides they spend longer with their foot in contact with the ground waiting for their hips and top half to come forward. This is not optimal as it slows them down and they need more power to be produced in the legs to accelerate them forward again.
PICTURE 6: The green circle on Ben’s hips show his center of mass. His foot should contact the ground under this to reduce the amount of time spent in contact with the ground, therefore reducing the ground reaction force that occurs. The straight white line shows where the foot has contacted and where his center of mass should be over. Being so far away means the length of his stride is too long and his upper body half can not keep up with this speed.
VIDEO 5: This is a video of Ben’s speed maintenance phase. His upper body isn’t quite keeping up with his legs, meaning his stride length is too long for his velocity causing him to spendmore time with his foot in contact with the ground.
Tying in with the impulse-momentum relationship, understanding angular kinetics can help explain how to swing the legs forward quicker in order to increase the speed of the run. During the swing phase of leg movment (moving the leg backwards from the front of the body) the runner needs to overcome the moment of inertia placed on the leg as a result of it normally moving forward then resisting the change in motion. Ben’s technique of the swing and recovery phase when unpacked slowly is optimal and can be compared alike Usain Bolt’s. The distance between the muscle and joint is called the moment arm. Both bring athletes are able to bring the knee upward to form a 90 degree angle at the hip joint at the start of the swing phase. This produces more torque in preparation to resist the moment of inertia when propelling down before foot-ground contact. As the leg rotates through an angle it gains angular momentum, through adopting angular velocity. In order to conserve this angular momentum both runners have a solid leg mass close to the center of rotation (at the hips). This decreases the moment of inertia the leg encounters during the swing phase by having the ability to produce high amounts of force at center of rotation.
As the leg leaves the ground in the swing phase, the recovery phase begins. An efficient recovery phase is just as important as having an optimal swing phase. In order to do so we need to increase the angular velocity during this time and decrease the legs moment of inertia. With the hip being the center of rotation and producing high amounts of torque from the muscles closer to the hip joint during the swing phase, having lighter muscles further down the leg encourages a faster angular velocity. Flexing at the knee promotes the foot to come under the leg, minimizing the moment of inertia, therefore increasing angular velocity. In saying this, the calves and muscles in the foot need to be able to embrace the force and assist in maintaining good foot alignment and posture to give the leg muscles the best chance and producing the most torque. Noticeably both athletes have skinnier bottom legs, but a lean amount of muscle surrounding the calves. This beneficial in adopting the optimal technique.
Although the legs play a major role in propelling the body forward and gaining momentum, the arms are most important when conserving this momentum. The arms naturally swing in the opposite direction to the legs. This is an example of Newton’s third law of for every action, there is an equal and opposite reaction (Blazevich, 2010). At the foot contact with the ground the arm should be lengthened by extending at the elbow to produce angular momentum, alike in. As the foot progresses to behind the body, in order to conserve angular momentum during the rotation of legs the arms should flex at the elbow. When lengthening downward it’s important for the arms to produce a great amount of force to vigorously whip and accelerate the upper half of the body forward.
In order for Ben to improve his maximum velocity there are some small changes that can be made to his technique. Ben’s block position is optimal. His feet are positioned appropriately on the blocks, his arms aren’t locked out, the fingers are parallel to line making an arch between the thumb and index finger, his back straightens up ready for the set position and his head is aligned well in order to keep the back straight. As he enters the set position the head doesn’t change and the hips rise above the shoulders. In the driving phase Ben adopts Newton’s three laws of motion by producing force in order to flex the hip forward and upward, lunging the leg forward and through the first step. Opposing to this his other leg and arms are providing triple extension, optimal for the next step in the driving phase. As he transitions into the speed maintenance phase his foot position is the main aspect that can be improved and is targeted in order for Ben to increase his maximum velocity. In order to get Ben to position his foot to contact the ground under his hips (center of mass) he needs to take shorter strides. This means he is contacting the ground with his foot already beginning to slightly move backward, making less forward force and more propulsive impulses. Ben is able to conserve a lot of angular momentum through the recovery phase by flexing his hip to 90 degrees and flexing at the knee so the foot comes behind the body. His arms could extend more as he is vigorously propelling them down, but they have a great flex during the recovery phase.
After identifying the aspects that Ben can improve on he was filmed and measured 2 weeks later to see if any improvements were made. His training was more specific to adjusting these aspects. It involved a higher number of leg sessions in order to strengthen the upper leg muscles and block starts were included in the cardio sessions. During this testing the weather conditions were a lot cooler, the ground was slipperier, there was a slight head wind and more clothing was worn. He measured a 12.2m/s velocity at 42m into the 70m run, 4.6m/s slower than the initial test. As noticeable in picture 7 his foot is still contacting the ground before his center of mass as a result of him over striding. Although being such a great gap in the measurements from the first time and the second, there may be error in the equipment being used. This could be app processing, distance tracking error or lighting issues.
PICTURE 7: A screenshot from the app SpeedClock showing Ben running a velocity of 12.2m/s, 42m into a 70m run on June 18, 2015.
After conducting the investigation there are biomechanical principles that can be altered on Ben in order to improve maximum velocity throughout the race. Although this was not proven in the measurements after specific training and competitive races could assist in this process. Having run races and used the technique he has been taught for 5 years now, it’s unlikely to be able to change this learnt behaviour in two weeks. Usain Bolt demonstrates optimally correct technique and his body physique and type also assists his ability to produce high amounts of force in order to propel his body forward and sustain a high velocity throughout the race.
HOW ELSE CAN WE USE THIS INFORMATION
All of the information and biomechanical principles discussed here can be used and transferred to other sports. For example cricketers need to accelerate fast when leaving their crease line to swap ends with the other batter to make runs. Although having an implement (bat) will already slow them down they can use their other arm to propel them forward by extending it vigorously backwards and flexing it slower forwards. This may only increase their time by a few hundredths of a seconds but this could be the difference between being run out and being safe.
In football, chasing your opponent and laying a tackle when they have the ball could be the difference between winning and loosing. If you’re able to reach your opponent with the ball faster this reduces the distance they’re able to gain going forward towards their goals. Having stronger muscles higher in the leg assists the force produced and speed that can be achieved in catching you opponent. This strong muscle is also beneficial for the kick. While taking a kick the more power that can be generated the further the ball will travel, provided correct technique of kicking is used. Having strong hip flexors will also benefit when tackling as you’re able to hold a strong body position and pull your opponent down.
Sprinting is useful for many sports. It can be transferred across a wide variety of team sports in order to gain distance or momentum in the game. The biomechanical principles explained in this blog can provide; a lot of run and carry in football, faster running between wickets in cricket, being able to break tackles by having stronger upper legs in rugby and use angular momentum in order to increase the velocity of the ball in a tennis serve
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