JD Welch Anna Reponen PE 483 – Final Project 3/14/2009 Introduction An analysis is a “separation of a whole into its component parts” according to the Merrian‐Webster dictionary. So the analysis of a sprint start is the separation of all the components that make it up. This can be viewed as the separation of the sprint start into different phases and doing that it can also be further analyzed through the use of different methods. The different methods incorporate timing of the different phases, anatomical breakdowns by determining which muscles are being used in the phases, as well as determining joint angles and body positions during those phases. The sprint start has always made an athlete a competitor in a race. Starting out of the blocks in a lighting fast manner allows for least time lost and optimal acceleration. The different phases of the sprint start are the “On Your Mark”, “Set”, “Go” and “First Step/Front Leg Extension”. In the “On Your Mark” phase the major joint contributions are primarily the shoulders due to having to hold the pressure from the legs against the hands. “Set” phase uses the hips, knees and shoulders. The hips and knees press the pelvis upwards while the hands and arms support the upper body. The major joints being used in the “Go” phase are the rear knee and ankle as well as the extension of the rear hip. The final phase utilizes the ankle, knee and hip of the front leg and the lower back is used to pull the body upwards. The
Transcript
JD Welch Anna Reponen
PE 483 – Final Project 3/14/2009
Introduction
An analysis is a “separation of a whole into its component parts” according to
the Merrian‐Webster dictionary. So the analysis of a sprint start is the separation of
all the components that make it up. This can be viewed as the separation of the
sprint start into different phases and doing that it can also be further analyzed
through the use of different methods. The different methods incorporate timing of
the different phases, anatomical breakdowns by determining which muscles are
being used in the phases, as well as determining joint angles and body positions
during those phases.
The sprint start has always made an athlete a competitor in a race. Starting
out of the blocks in a lighting fast manner allows for least time lost and optimal
acceleration. The different phases of the sprint start are the “On Your Mark”, “Set”,
“Go” and “First Step/Front Leg Extension”. In the “On Your Mark” phase the major
joint contributions are primarily the shoulders due to having to hold the pressure
from the legs against the hands. “Set” phase uses the hips, knees and shoulders.
The hips and knees press the pelvis upwards while the hands and arms support the
upper body. The major joints being used in the “Go” phase are the rear knee and
ankle as well as the extension of the rear hip. The final phase utilizes the ankle, knee
and hip of the front leg and the lower back is used to pull the body upwards. The
shoulders and arms are now only supporting the arms weight as well as all inertia
created by a motion. All videos were watched and analyzed through YouTube.com.
Breaking down a sprint start is easier done with the understanding of what is
essential for an efficient start. Literature on sprint starts helped determine what
phases were used for the rest of the project.
The information I read came from Gerry Carr’s second edition of Sport
Mechanics for Coaches. In this he describes the forces that are going on in a sprint
start. He says that in a sprinting start block situation, the sprinter gives a muscular
force against the blocks to create an action and then the reaction is the push back
that comes from the earth in an equal and opposite force against the athlete. The
force created by a sprinter allows them to move forward by overcoming the inertia of
their body mass. A sprinter’s body mass is directly related to how much muscle force
that can be created by them, thus the less massive the sprinter the faster they will
accelerate. Also, the more force a sprinter applies the faster their acceleration will
be. This is an example of Newton’s law of acceleration, force = mass x acceleration.
Carr gives a wonderful example to illustrate the relationship between a sprinter and
the earth. He describes the movement by compressing a spring between a heavy
shot put ball and a tennis ball. The shot put is the earth, the spring is the sprinter’s
muscles and the tennis ball is the sprinter. When you let go of both balls, the tennis
ball shoots out and the shot put stays relatively stationary. This explains why the
sprinter shoots out in one direction and the earth moves in an immeasurable amount
in the opposite direction.
The book Applied Kinesiology has a section in it that covers the topic of
overcoming inertia from stationary positions in sprint blocks. It describes the body as
being in an inclined position in the anticipated direction of the movement so that the
center of gravity may be quickly shifted off balance in that direction. As the sprinter
comes out of the blocks in a start they use short and powerful strides in order to
accelerate rapidly. Some of the reasons for the short strides are that their base must
be re‐established because of the extreme forward body lean to begin with and also
so that the leg joints can experience their optimum mechanical advantage through
just a small range of motion. Hip rotation is limited because hips should be flexed
during acceleration and as the sprinter comes to the erect running position the hips
should be less flexed thus, allowing the sprinter to have longer running strides. A
sprinter’s arms are also important to their acceleration because the momentum of
the arm movement is transferred to the body to help with acceleration through hard
driving actions of the arms. The correct arm action should be more forward and less
diagonal during the acceleration of a sprint start. Also they note that adequate
friction between the running surface and the sprinter’s feet is essential for fast starts.
After understanding what is needed to ensure an efficient sprint start they
next step is to create new techniques and exercises to increase the speed in which
the sprinter can achieve.
Introduction of new practice strategies are introduced into every sport it is
essential to understand the reasoning for the new practice strategies that had been
created. One of these new strategies is to use weights while doing sprints. The use
of weights while doing moderate activities has been essential in the conditioning of
the body with the general understanding that the body will adapt to the change and
become strong enough to carry the weight. The use of weights has been overlooked
in sprinting due to the decrease in velocity for the individual.
The researchers chose 24 participants that were enrolled in the physical
education program at the university in which the study was being performed. The
participants were all male and averaged the age of 20. Regular physical activities
were being performed by the participants as well as extra curricular sporting
activities that were considered games, combat or middle distance running. (R, R., M,
K., D, U., D, M., & S, J. 1998)
A recent study performed measured the amount of velocity in sprinting by
either loading the arms or legs. The participants had to hold” …0, 1, 2, or 3 short lead
rods…” in their hands or had “…load belts of 0, 0.6, 1.2, or 1.8 kg [that] were
fastened above the ankle joint of each leg.” (R, R., M, K., D, U., D, M., & S, J. 1998)
The subjects were asked to use their weight for a 4 week period to allow for their
body to adapt to the change and asked to “…emphasis on all‐out acceleration and
maintenance of the maximal running velocity.” (R, R., M, K., D, U., D, M., & S, J. 1998)
The results of this study showed that the higher the amount of weight applied
to the legs the slower the velocity. The stride length did not change but the rate of
stepping did change. With the application of weight to the arms there was no
change in rate of stepping or stride length but there was a decrease in velocity.
When training for an event or sport there is always optimal strategies that can
be performed. The one thing that seems that has trainers at ends is what resistance
training should be done to increase explosiveness. Some type of training regiment
that will increase the “acceleration phase”. Specifically the “acceleration phase” of a
sprint starts. Lifting weights will build the muscle and increase its size and thus
decreases the speed in which the action can be performed. So is the trick to create
an exercise that doesn’t increase the size of the muscle to allow for retention in
speed or is it that lifting takes place at such a slow rate that the muscles then become
slow.
At the University of New Brunswick in Canada researchers concocted a plan to
establish what lifts will encourage an increase in the “acceleration phase” of
sprinting. The first things that the researchers established was which lifts are most
like the action being performed. In this case it ended up being “…a traditional and
split technique, at a range of external loads from 30–70% of one repetition
maximum.” (Sleivert, Taingahue, 2004) The squats weren’t lifting as much weight as
the participant could though. The squats were “…concentric jump squats.”(Sleivert,
Taingahue, 2004)
This study came to find that both squat types encouraged an increase in 5 m
sprint times. The utilization of jump squats focused on explosiveness with weight
resistance compared to body weight. The jumping action relates to the start off the
blocks in which the body is being accelerated away from feet placement. This means
that lifting in a manner in which there is resistance down, that is greater than regular
body weight, that the body will compensate and adapt to the challenge and increase
the rate in which the body accelerates.
The journal article I read investigated the effects of muscle‐tendon length on
the joint movement and power during maximal sprint starts. For their methods, the
researchers had nine male sprinters perform their maximal sprint starts from blocks
that were adjusted to either forty degrees or to sixty‐five degrees horizontally. They
recorded the ground reaction forces and the kinematics of the sprinters with a
camera. Then they analyzed the joint movements and forces. The muscles‐tendons
they analyzed were the gastrocnemius, soleus, vastus medialis, rectus femoris, and
the biceps femoris. Their results showed that the block velocity was greater in the
forty degree than in the sixty‐five degree block angle. They also noted that the initial
lengths of the gastrocnemius and soleus of the front leg and the rear leg at the
beginning of the force phase to the middle of the phase was longer in the forty
degree than in the sixty‐five degree block. However, the initial lengths of the rectus
femoris and the vastus medialis of the front leg were longer in the sixty‐five degree
than in the forty degree block. Also the peak ankle joint and power for the front and
rear legs were greater in the forty degree block and the peak knee joint moment of
the rear leg was greater in the sixty‐five degree block. Based upon their results, they
found that the longer the initial muscle‐tendon lengths of the gastrocnemius and the
soleus in the starting blocks at the beginning of the force production can create a
greater peak ankle joint causing a greater velocity during a sprint start.
The website I found described a few sprint starting drills that can be done to
help an athlete perform the correct form during their sprint start. They placed the
emphasis of the start because it is what allows the sprinter to achieve their best
sprinting form the quickest. The first drill is a low standing start where the sprinter
stands with their feet about one and a half to two foot lengths from the starting line,
bend over at the waist and letting their arms dangle downward toward the starting
line. Then they slowly shift their weight forward until they begin to lose balance. The
second drill is called a four‐point start. They do the same routine as they did in the
low standing start except, both hands, on their fingertips, are placed on the track
behind the starting line. The third drill is the block placement drill where they place
the blocks so the front block is one and a half to two foot lengths from the starting
line and place the rear block so it is two and a half to three foot lengths from the
starting line and then practice coming out of the blocks. The last drill is the “on your
marks” command. The sprinter places their feet against the blocks as they crouch
into them. Their hands are approximately shoulder width apart and behind the
starting line and their weight is evenly distributed between their hands, the foot of
the front leg and the knee of the rear leg. Also, their head is relaxed while their
whole body is being kept in balance as they practice this stance with the appropriate
starting commands. These drills should help a sprinter become more efficient at
performing their sprint starts out of the blocks.
After determining what types of exercise and training techniques needs to be
implemented they trainers need now look at how the body is affected at a cellular
level.
The article I reviewed had a research goal to identify the metabolic factors
that influence the energy cost of running during prolonged exercise runs and
triathlons. They proposed that there is a physiological comparison of running and
triathlons and the relationship between running economy and performance. The
term running economy can be synonymous with oxygen cost or metabolic cost or
energy cost of running or oxygen consumption. Marathons and triathlons modify
biological constraints of athletes and have an influence on their running efficiency.
The factors that may influence the energy cost of running are environmental
conditions, participant specificity, and metabolic modifications. They found that the
various energy cost of prolonged running may only be explained by combined
physiological and biomechanical processes. For exercises lasting more than two
hours the running economy is more pronounced at the end of a long run compared
to a triathlon lasting the same time due to the elevated levels of free fatty acids and
circulating glycerol. They suggest that further studies should be done to understand
the mechanisms behind endurance efforts.
Watching the Olympics is the best way to see the best of the best in many
different events. There are team events in which all participants come together to
create a team of gold medalists or individuals that race against other individuals to
determine who comes out on top. Some events always bring in more publicity than
others and there fore seem to have more importance to who wins and who loses.
Probably the most popular event, per say, is the 100 m sprint.
In the 100 m sprint there are 8 individuals competing against each other so see
who comes out on top. One issue that has come up in the past is lane placement and
if this has any impact on how fast one might be. Now the question of why would
lane placement matter. It matters because the runners on the inside of the track, the
ones closest to the starting pistol, hear the “Go” shot earlier than the participants in
the furthest lane. The “Go” shot dB level or loudness was also greatest with the
participants that were closest to the starting pistol.
This research article looked at the reaction times of the 2004 Olympic Games
to see if the participants’ reaction times correlated with the hypothesis of the
researchers. What they found was that the participants that were closest to the
starting pistol had significantly lower reaction times than the participants that were
in the furthest lane. (Brown, Kenwell, Maraj, Collins, 2008) Once the researchers
established that the reaction times differed a study was then conducted to measure
reaction times specifically but also force produced in relation to dB level of the “Go”
signal.
The study came to the same conclusion of the 2004 Olympics data dealing
with lane assignment and further added to the data by including that an increase in
dB level or volume of “Go” signal decreases reaction time.
Observing a particular task by watching someone perform the task or by
watching a video of that task being performed by the best is always a great way to
analyze what needs to be improved upon. When watching that task in slow motion it
is even easier to break down the task and eliminate unwanted movements in the
task. Then when looking for a video of a task and finding one in slow motion of
someone that is the best then all that is needed to do is relate the two videos of the
participants and reference to the participant with the better technique.
Asafa Powell has set numerous world records by breaking his own and others.
When looking for a video one would imagine that Asafa Powell would be a great
example to view. The video shows Powell in his ready position on the blocks to full
extension of the leading leg and him moving out of the screen. The first motion that
Asafa Powell makes is that his body moves slightly forward before his hands begin to
lift off the ground. From this position his body begins to move upwards at his hips.
His legs begin to extend pushing his body forward as well as his arms begin to move
to their starting position.
As his body continues to extend forward his back leg finishes its extension
phase then begins to move forward to a hip flexion and knee flexion position. The
leading leg is now pushing to accelerate the body forward. His trunk has now moved
to a placement in which it is lining up with his pelvis and creating a straight line
between his skull and pelvis. Powell’s arms are now in a position that is typical of a
running posture.
As his body is at 45 degree angle to the ground his leading leg is now fully
extended behind him and slightly off the blocks where as his other leg is fully flexed
and about to begin to extend for the next stride required for running. His torso and
hind leg are lined up with each other.
Our next step in the pursuit of the understanding of what’s happening during
a sprint start was to determine what muscles are being used in each phase. The
muscles used in each phase determine velocity and acceleration for the sprinter.
To demonstrate the velocity/acceleration of a sprint start we had two
sprinters each perform a thirty meter sprint out of the sprinting blocks. We timed
each sprinter at five meter intervals, a total of six, to show how they accelerated
thorough out their sprint. The following explains our methods and the results we
found through our study. Next thing to do was to determine how fast our sprinters
where going through each phase.
The idea behind our phase timing analysis was to video tape two different
athletes sprint starts out of sprinting blocks. We wanted to see what differences
there were, using the number of frames, between each sprinter in each of the four
phases of the sprint start. The phases were determined due to the nature in the
posture and arrangement of body parts for the sprinter.
Once all the times were determined for each the sprint start phases for the
participants their efficiency needed to be evaluated. Such as the unwanted motions
that waste time and energy, its the little things that make all the difference.
The video kinematics analysis we created is a motion tracking analysis, joint
angle measurement and a segment inclination measurement. The motion tracking
was done at each phase with a stick figure representing the sprinters movement out
of the blocks. For our joint angle measurement we chose to measure the knee angle
of the front leg of the sprinter in each phase. Finally, we decided to do a segment
inclination measurement of the hip movement of each phase.
Methods
We will be comparing two different videos of track starts that we obtained
through YouTube.com. One of the videos is of an Olympic sprinter that held the
world record in the 100‐m sprint. The other videos that we used to compare are of a
college track athlete and a high school track athlete.
The literature reviews were used in the understanding of how the sprint starts
were to be performed.
With the understanding of the sprint start we then needed to look at the
muscles being used in each phase. The anatomical analysis helped to determine what
muscles were being used during each phase. This was done by creating a
spreadsheet with each phase having its own heading and a table devoted to it. In the
tables each major joint section was determined and each muscle was listed and its
appropriate joint action and position, the muscles that were active and the
contraction type associated with that muscle.
In the velocity, acceleration profile we prepared the track, at Western Oregon
University, for our two sprinters by sectioning off the different performance
distances into six equal subsections. We designated a 30 meter straight stretch of
the track were the runners would have the wind (if there was any) at their backs and
then we placed orange cones at equal five meter intervals. There were a total of six
different marks that we measured the time with a video camera when each sprinter
crossed that mark. The participants warmed themselves up to a comfortable level in
which they felt safe to perform before they were asked to perform their sprint. After
we recorded each sprinters “split times” we then calculated the average section
velocity (Δ d/ Δ t) and the average section acceleration (Δ v/ Δ t).
The phase timing analysis was done by using a Panasonic PV‐DV73 camera, to
record to a mini DV tape, to video tape the sprinters. The software program used
was Sony Vegas Movie Studio Platinum with a playback frame rate of thirty (29.97 to
be specific) frames per second (f/p/s). Two different male athletes were utilized in
which both with very different athletic backgrounds. Sprinter one was a middle
distance to long distance runner in high school track and field. Now he is an 800
meter runner at the collegiate level. Sprinter two was a 100 meter sprinter in high
school track and field as well as a competing in a few throwing competitions. Now
sprinter two is strictly a hammer thrower in the collegiate level at Western Oregon
University. We told each sprinter to simply do a sprint start out of the sprinting
blocks while we gave the commands “On Your Marks,” “Set,” “Go.” We only had the
sprinters run approximately ten meters out of the blocks. We video recorded each
sprinter’s start out of the blocks and then analyzed both there sessions.
For our methods of the video kinematics we used the computer program
Microsoft Publisher to create all of the stick figures for each different analysis. The
motion tracking analysis we took a screen shot of each phase of the sprinter from our
recorded video and then copied the photo into publisher. Next we applied the
appropriate line segments over each body segment of the copied photo in order to
create the sprinter. This process was continued for each of the four total phases. We
represented each joint with small circles.
Since we already had created a stick figure for each of the four phases of the
sprint start, it was a lot easier to complete the joint angle measurements. We
decided to measure the angle of the knee of the front leg of the sprinter because it is
a critical joint movement for this particular skill. We took the stick figures from our
motion tracking analysis and measured the appropriate knee angle of each of the
four phases.
The segment inclination measurement was also created using publisher. We
used the same four screen shots from the video to determine the position and angle
of the hips. Both sprinters were used for comparison of the orientation in which the
hips moved through space. A triangle was used to represent the hips and the base of
the triangle is supposed to represent the crest of the hips. At each phase we
observed where the hips were and how they were tilted and moved the triangle to
best represent this. A dotted line was then used to show the path the hips moved
between phases. A parallel line was then placed at the lowest point of the base of
the triangle to help determine the angle at which the hips are at in that particular
phase. Though we determined with great accuracy where the hips where and their
angle proportionate to a determined horizontal position there was still room for
error in the measurements.
Results Phase description and Critical Features Checklist
Sprint Start Mechanics Checklist Phase
1 "On Your Marks" Olympic College High School
Feet placed in blocks 5 5 5
Front knee is even with the starting line but off the ground 5 5 5
Rear knee is rested on the ground 5 5 5
Body is leaned forward with shoulders over the starting line 5 5 5
Hands placed in proper alignment behind the line 5 5 5
Phase 2 "Set" Front leg creates a 90° angle 5 4 4 Rear leg creates approximately 120° 5 4 1 4
Body is leaning forward with most of the body weight on hands 5 5 5
Arms are straight at a 75° over starting line 5 4 5 Hips come up higher than shoulders 5 5 5
Phase 3 "Go" Extension of the rear leg 5 2 2 5 5 Arms come off the ground 5 5 3 5 Body is parallel to ground 5 4 5 Head is tucked 5 4 4 2
Phase 4
"First Step/Front Leg Extension"
Front foot pushing off the block 5 5 5 Front leg in full extension 5 5 5 Rear foot flexed towards shin 5 2 4 Rear leg flexed 5 5 5 Straight line between foot and head along body 5 4 3 6 Body is at a 40° angle to the ground 5 5 4 Front arm is at 90° between upper and lower arm 5 5 5 Rear arm is at a 180° and extended above body 5 5 3 7 Head is tucked 5 4 3
Key
1 Incomplete
2 Almost
Incomplete
3 Near
Complete
4 Almost
Complete 5 Complete
Subscripts are critiques that are in the discussion.
Sprint Start Beginning/Ending Point Phase 1 "On Your Marks"
Beginning Feet and hands are placed and knees are touching the ground.
End When the body becomes motionless waiting for the "Set" signal.
Phase 2 "Set" Beginning Knees and hips are pressed upwards at "Set" Signal
End Body becomes motionless waiting for the "On Your Marks" Signal
Phase 3 "Go"
Beginning Body begins accelerating in a linear motion on the "Go" signal
End The rear foot leaves the block. Phase 4
"First Step/Front Leg Extension"
Beginning Rear leg is in a forward motion. Front arm is in a forward motion.
End Front leg is fully extended. Rear arm is extended above body.
The performers that were evaluated and compared ranged from an Olympic
athlete, a college athlete and a high school athlete. When we evaluated the Olympic
athlete we ranked them with all “5s” due to the expertise and precise execution of all
determined aspects of each phase. Based on our checklist we couldn’t determine
any deviations. We fund that our college athlete wasn’t as proficient as the Olympic
athlete and therefore didn’t rank as high. The high school athlete lacked in some key
aspects of each phase. We assumed that this is due to the lack of experience.
After evaluating our videos we determined that our checklist was very
comprehensive on all of the key elements of a sprint start. However, there were a
few things that we could have been more specific on. Such as, in the “Set” phase we
should have specified that the athlete should have been on their finger tips. Another
is in the “Go” phase. We needed to specify that when the arms come off the ground
that they stay in the sagittal plane.
The positive and negative critiques that we found from all three athletes are as
follows:
For the Olympic athlete we found no negative critiques though we did notice
some very positive key aspects of certain phases. In every phase we noticed that the
athletes head was tucked and in phase 4 we noticed that his body was in a very
excellent alignment between head and front foot.
The college athlete on the other hand had a few negative critiques.
1. Rear leg creates about a 100° angle instead of a 120° in phase 2.
2. Rear leg is pulled forward with no extension in phase 3.
3. Arms move in the frontal plane away from the body in phase 3.
4. Head pops up and then becomes tucked in phase 3.
A positive critique for the college athlete was that they had a 40° angle to the
ground with their body in phase 4. Then they also had great extension of front leg
off the blocks in phase 4.
The high school athlete had less negative critiques than the college athlete
though they didn’t perform as well overall.
5. Presses with rear leg and locks knee before they even moved forward in
Phase 3.
6. Back is arched forward in Phase 4.
7. Arm is actually more at a 110° angle than a 90° which it is supposed to be in
Phase 4.
Positive critiques of the high school student are that they have most of their
weight forward on their hands in phase 2 along with great extension of the front leg
in Phase 4.
The literature review gave us background information on sprint starts and the
recent work that has been done. It was a starting point for this project.
The anatomical analysis allowed us to see what was happening at the skeletal
level to the body. Determining the differences between phases allowed for a better
understanding of what each limb was doing while creating opposing moments of
inertia to stabilize the body.
Using phase timing for our first sprinter we noticed that his speed increased
over each interval. This lets us believe that this is a very well trained and well
conditioned sprinter. We believe from the data that the thirty meters might not have
been long enough for him to reach top speed. From the data and film there is
nothing that we can critique with sprinter one. He had great form out of the blocks
and he progressively decreased his split times. He could always practice starting out
of the blocks to increase his efficiency and speed.
With our second sprinter we noticed that his intervals decreased as he
progressed down the track. Between the fourth and fifth cones he slowed down
showing that within those five meters he reached his top speed and began to slow.
A critique for sprinter two would be to keep his head down out of the blocks. One
thing that we noticed was that his hips dropped a little between the second and third
phase and we believe that this is due to how close his feet are in the blocks. If he
were to increase the distance between the feet placement platforms his hips could
be dropped to the same height that he runs at. A training technique that sprinter
two could use would be to do 200 to 400 sprints to increase his aerobic
endurance/muscle glycogen stores.
We found that Sprinter one was quicker out of the blocks over all with a total
time of 3.80 seconds compared to Sprinter two of 4.03 seconds. It took him 67
frames, or 2.23 seconds, to finish phase one where as Sprinter two took 68 frames, or
2.27 seconds. Phase two was quicker with Sprinter one with 36 frames, or 1.20
seconds, where as Sprinter two took 42 frames, or 1.40 seconds. The third phase was
much closer between the two sprinters with only a one frame difference. In the last
phase Sprinter two was quicker by a frame, though over all had a slower time.
Over all our subjects had very close results, in terms of frames per second,
though hundredths of a second can separate first from last.
From observing the three different video kinematic analyses we were able to
have a better understanding of the sprint start. In turn this enables us to help
sprinters and us in explaining the most efficient method for a sprint start. The
motion tracking analysis allowed us to see the critical movements of each phase the
sprinter goes through. With this we then helped critique the sprint start of our
subjects to increase their overall efficiency in their start. The knee joint angle
measurement allowed us to measure the knee angles and then fine tune the sprinters
start for maximum acceleration. Where as the segment inclination measurement of
the hip allowed us to watch how the hip traveled in each phase. With this we were
able to determine if there was any inefficient movement of the hips such as
downward movement before acceleration. Knowing the angle of the hip allowed us
to determine the orientation of the torso which showed where the center of gravity
was during the acceleration portion of the sprint start. All three of these analyses
came together to help us, and the sprinters, learn more about the sprint start and to
critique the efficiency of each of the specific different phases.
The three kinematic analyses show the motion the sprinters bodies move to
from phase to phase. The direction in which the body moves is determined by many
different things but one that is very essential is the force which the legs create to get
the body moving. Many different biomechanical principals can be applied to a sprint
start.
Newton’s first law of motion is the law of inertia. Inertia is the resistance an
object has to change direction. This means that if an object is moving in a certain
direction and velocity that it will resist any change to its direction or speed. This can
also be looked at as anything resting will resist any change. All athletes and objects
have mass, which is the amount of matter an object has, and therefore have the
potential for inertia. Mass is directly related to inertia because the more mass an
object has the more inertia it has. Therefore, if someone who possesses mass and is
moving in a particular direction and speed they will resist any change. So when a
sprinter moves from one phase to another. The mass of the body resists the change
but once a particular body part is moving in a desired direction they try to obtain the
highest amount of velocity for that segment. The push of the thighs from the blocks
to move the body forward is the change of mass and inertia.
One can easily demonstrate a sprint start through the use of Newton’s second
law of motion, which is the law of acceleration represented in the simple formula
force = mass x acceleration. In the sprint start, the sprinter extends their legs to push
against their mass as well as against the Earth through the use of the blocks. The
sprinter accelerates in a forward direction while the Earth moves a negligible amount
in the opposite direction of the sprinter. The sprinter accelerates because the force
produced by the sprinter’s muscles overcomes the inertia of the sprinter’s mass. To
demonstrate Newton’s second law of motion one can take two sprinters of the same
mass and have them apply a force for the same amount of time. The sprinter who
applies the greater amount of force will accelerate quicker than the sprinter who
applies less force.
Newton’s third law of motion is the law of action and reaction. When an
athlete exerts a force on a second object, the latter will exert a reaction force on the
first that is both equal and opposite in direction. The action and reaction of a sprint
start is shown when the sprinter applies a muscle force by extending their legs, or
exerting force, against the starting blocks. The action is the force, or push, that the
sprinter applies against the blocks. The reaction to the sprinter is the equal and
opposite force that the Earth applies to push back against the sprinter or the Earth’s
ground reaction force. Since the Earths’ potential force is greater than what the
sprinter can produce the sprinter is then the object that moves.
The center of gravity is the point at which the mass of an athlete are balanced
in all directions and the point where the gravitational forces are centralized. The
sprint start is used at a stable position that is used to get the sprinter out of the
blocks as soon as possible. In the “set” command position of the sprint start the
center of gravity is low to the ground and outside of the body. The base of support is
wide and long and the line of gravity is shifted close to the forward edge of the
supporting base. This stance allows the sprinter’s legs to be in a powerful thrusting
position and gets them into the closest position to the finish line just prior to the
start. As the sprinter enters the “go” phase their base of support, or center of
gravity, becomes unstable when they lift their hands off the ground. At first the
sprinter uses purely gravity to give them a forward motion without using muscle
contractions. This happens because the center of gravity is outside and forward of
the body which pulls the torso forward and down. After they have increased velocity
for the fraction of a second the sprinter begins to accelerate as they begin to use
their muscles for movement.
The sprint start is also a great example to show the impulse‐momentum
relationship. Momentum is the quantity of motion that occurs with the simple
formula being momentum = mass x velocity. Momentum occurs when the athlete
starts their movement out of the blocks. If a sprinter increases their mass and/or
velocity, they will increase their momentum. Once the momentum is initiated the
impulse of the sprint start will require a massive force to be applied over a short
distance and a short time frame. An impulse is the force multiplied by the time
during which the force acts. A strong and flexible sprinter can apply more force over
a greater time frame than a weak and less flexible sprinter. The flexible sprinter
allows for a greater range of motion. This motion can be translated into the greater
amount of time in which the motion is being preformed. A less flexible sprinter has a
shorter distance in which they can perform the task.
An energy efficient movement can be created if all the training techniques,
equipment, and surfaces work together in a harmonious manner. Optimal
techniques are designed to decrease the amount of energy loss. The main purpose
of these techniques is to decrease deformation of the body, equipment, and surfaces
as well as to decrease the amount of impact upon the body. With proper use of
these techniques all extraneous movements are eliminated. Deformation of the
body is decreased in knee and foot flexion with proper placement of the blocks.
Deformation of equipment is decrease with the utilization of stiff, very thin soled,
and very light shoes. Deformation of surface occurs with the spikes of the shoes.
The spikes create more traction for the sprinter by penetrating the track and
decreasing friction because of the surface area of the spikes and the material the
spikes are made from. Impact is increased due to the decreased amount of sole of
the shoes but is combated with the track material. Having a tucked head, arms
moving in the sagittal plane, and having flexed hips and knees are all ways to
decrease extraneous movements.
We gained an immense amount of knowledge about the sprint start and if
time allowed much more could have been obtained. Strengths of this project were
that in this modern age all the different technology that are available to us made it
possible to evaluate the sprint start in a much more efficient manner than could have
otherwise been done. A weakness of this project was that since the movement was
so fluid it was hard to make a clear determination when we were creating our phase
descriptions. Future investigations could use the unclear correlation between phases
to more precisely create phase descriptions by possibly extending the distance in
which the start is measured. We can use the knowledge learned from this project to
help athletes with their sprint start. The next step is to create an optimal energy
efficient sprint start for all our participants.
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