Qualitative analysis of Sprinting.
Qualitative analysis of Sprinting
Introduction:
"In sprinting the athlete's objective is to cover a given distance in the least possible time". An athlete's end time is directly related to the distance of event and by the athlete's average speed over that distance (Hay, 1993). Sprinting is a complex movement that depends on an athlete's ability to combine the actions of the legs, arms and trunk into a smoothly co-ordinated whole (Hay, 1993). In this report the movements of legs will be analysed within a sprinting situation. The basic factors involved in sprinting are shown below(Hay,1993).
Biomechanical requirements:
The sprinting action of the legs work like a cycle, the foot lands on the ground, goes under the upper body, and is from the ground in order to move forward for the next landing. The sprinting stride is successively connected to the next stride. The arms and legs undergo rotation while the centre of mass tends to rise and fall within the sprinting cycle. The arms move in opposition to the striding action of the legs. The arms are at about 90 degrees of flexion in order to shorten the moment of the shoulder levers(Hay, 1993). When a sprinter is moving, they can loose velocity in the airborne phase of each stride, so in order to maintain continual motion, a force must be applied by the support leg at take off. The linear and angular motion of a sprinters must operate in conjunction with each other to provide optimum performance of movement patterns. An example of this is the flexion and extension of the lower limbs and how these movements work with the rotation, abduction, adduction of the hips and spine. A lever has a greater potential linear velocity at its end if it is longer, but in sprinting the limbs are shortened to bring them forward with less energy requirement. Newton's third law of motion can be observed with every foot-strike, the landing surface pushes back with a force equal to the impact force, driving the sprinter upward and forward in a direction opposite to that of impact (Martin & Coe, 1991).
The sprinting gait cycle:
The sprinting gait cycle can be divided into a stance and swing phase. The stance phase is subdivided into absorption and propulsion phases, and the swing phase into initial and terminal swing phases. The beginning and end of each swing phase has a period of double float, where neither limb has contact with the ground. Increase in velocity is initially achieved by increasing the step length, and subsequently by increasing the cadence. In sprinting there is a large step length and cadence. The sprinter initially contacts the ground with their toes instead of ...
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The sprinting gait cycle:
The sprinting gait cycle can be divided into a stance and swing phase. The stance phase is subdivided into absorption and propulsion phases, and the swing phase into initial and terminal swing phases. The beginning and end of each swing phase has a period of double float, where neither limb has contact with the ground. Increase in velocity is initially achieved by increasing the step length, and subsequently by increasing the cadence. In sprinting there is a large step length and cadence. The sprinter initially contacts the ground with their toes instead of the mid or hindfoot (Thordarson, 1997). The sprinting gait cycle is shown below(Thordarson, 1997):
The relationship of stride length and stride frequency:
Sprinting speed can be increased in three ways(Hay, 1993):
1) by increasing the number of steps per period of time (stride frequency),
2) by increasing the distance between each step (stride length),
3) by increasing both the length and frequency of strides:
) Stride Frequency
The number of strides per second is stride frequency. It is primarily genetically determined by muscle fiber type distribution patterns. Individuals with a high percentage of fast-twitch muscle fibers (type IIb) in the muscles acting on the hip and knee joints will typically have larger stride frequencies. Since it is primarily genetically determined, there is little potential for increasing stride frequency.
2) Stride Length
The horizontal distance covered by each stride is known as stride length. It is determined primarily by the force of the contractions of the muscles that act on the hip and knee joints (primarily the hamstrings, glutes, and quadriceps). The greatest potential for increasing sprinting is to increase the stride length.
Maximum velocity = Stride length x Strike frequency (Hay, 1993)
Sprinting at a constant speed can be performed at an optimum combination of stride length and frequency. This optimum is largely dependent on the person's mechanics or style of running. The length of each stride a runner takes is considered of the sum of three separate distances: the takeoff, the flight and the landing distances. The takeoff distance is the horizontal distance that the center of gravity is forward of the toe of the takeoff foot at toe off. The flight distance is the horizontal distance that the center of gravity travels while the runner is in the air. Finally the landing distance is the horizontal distance that the toe of the leading foot is forward when initial contact occurs (Hay, 1993).
The most dominant factor in sprinting is stride length, this determines the velocity of the sprinter and is determined by the length of the leg, the range of motion in the hip and the power of the leg extensors, these factors contribute to driving the whole body forward (Hay, 1993). Sprinters want to increase their stride length to the maximum possible without having a detrimental effect on performance(McArdle et al, 1996). A sprinter can put in maximal effort for the short distance and energy requirements are met regardless of the stride length.
As velocity increases there is an increase in both stride frequency and stride length. Sprinters, increase their stride length when moving faster, there is also a larger increase in stride frequency than in stride length. This is because an individual has a physical limit to how much stride length can increase in order to sprint faster, therefore stride frequency should be increased(McArdle et al, 1996).
The actual sprinting movement
A sprinters lower appendage movements can be broken down into four basic positions: pull and support phase, C position, A position, and B position. The movements can be viewed in terms of a wheel as illustrated below.
Figure 1 shows an elite sprinter with the correct technique. Figure 2 shows an amateur sprinter with an incorrect technique. The pull and support phase features the foot and ankle movements in proximity of the ground. An efficient pull and support phase is present in all successful sprinting (Kraini, G 1996). Elite sprinters stride length and frequency is a function of a superior pull and support phase. The pull and support phase is shown below figure 1 and 2.
In figure 1 when the left foot leaves the ground, the leg flexes and the heel kicks up to buttock level. In figure 2, the heel kick is not close enough to the buttock level.
The C position requires flexibility to allow the lower leg to move close to the butt. The quadricep muscle group must be flexible enough to allow the full range of lower leg flexion. In figure 1, the right heel is close to the buttock level, and the knee lift is higher than in figure 2. The right leg needs to be driven through to a higher level as in figure 1. The C position is shown below in figure 1 and 2:
The A position features high knee action. The A position of the upper leg is determined by the co-ordinated opposite action of the pull/support phase. Figure 1 shows the sprinter with a high knee action, this increases stride length and ultimately overall forward velocity. The A position is shown below in figure 1 and 2:
The B position requires the lower leg to extend towards the ground and away from the body. The B position of the lower leg helps determine stride length and requires the hamstring muscles to be flexible. In figure 1 the right leg extends to near full extension. In figure 2 the right leg needs to be extended more. The B position is shown below figure 1 and 2:
In the C position the lower leg moves closer to the buttock level, this reduces the inertia (I) of the sprinters leg which increases angular velocity(?) and keeps angular momentum (H) constant (Hay, 1993).
The angular momentum equation is:
H = I?
(Hay, 1993)
An increase in angular velocity allows the to swing through faster and the sprinter provides less effort which increases overall velocity(Hay, 1993).
Elite athletes have better balance and co-ordination, their movements are much smoother. This stops energy from being lost unnecessarily(Kreighbaum, E. & Barthels,K.1996). The flexion of the knee and elbow joints during running is an example of reducing energy loss.
The rotational inertia(I) equation is:
A body's rotational inertia (I) = mass (m) ? radius 2
I = mr2
r = length of lever (Kreighbaum, E. & Barthels.,K.1996).
Rotational inertia or moment of inertia is a measure of a body's resistance to angular acceleration. In this instance r is used as the length of lever. The mass of a body is directly proportional to the rotational inertia, so if the mass was doubled, then the rotational inertia would double. But the length of the lever is doubled, this quadruples its rotational inertia . Therefore, if the length of the limb is halved, (by flexing the limb 90 degrees or more) the rotational inertia can be quartered. This has the effect of allowing the athlete's limb to move with greater velocity, and thus alters stride frequency (Kreighbaum, E. & Barthels.,K.1996).
References:
Hay, James G.. - The Biomechanics of sports techniques. - 4th ed.. - Englewood Cliffs; (Hemel Hempstead) : Prentice-Hall, 1993.
Kreighbaum, E. & Barthels, K.M.(1996)- Biomechanics: A Qualitative approach for studying Human Movement - 4th ed - Allyn and Bacon
Kraini, G (1996) - http://www6.ios.com/~jkraini9/leg_action.html
Martin, D., & Coe, P. (1991). Training Distance Runners. Champaign, IL: Human Kinetics.
McArdle D., Katch F., Katch V. (1996), Exercise Physiology, Fourth edition, Williams and Wilkins Publishers, USA.
Thordarson D. (1997), Running Biomechanics, Clinics in Sports Medicine; Vol.16: No. 2, April, pp239-247.
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