sprint analysis 1 - analysis of sprint models by alexander michalow m.d

8/12/2019 Sprint Analysis 1 - ANALYSIS OF SPRINT MODELS by Alexander Michalow M.D.

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ANALYSIS OF SPRINT MODELS

RESEARCH PROPOSAL - DETAILS

Alexander Michalow M.D.

1255 Tower Rd, Bourbonnais, IL 60914

[email protected]

This section explains the proposed research project. The basis of the study deals with the forward

propulsion theory vs. the spring model theory and their roles in sprinting. The reason for the study is to

settle a disagreement between the two camps on their differing theories as to the best manner by which to

train an athlete for improving top sprinting speed.

There has been debate in the sprint training circles with regards to the terms forward propulsion

(propulsion theory) and the spring mechanism (spring-model proponents) as to their relative importance in

determining top running speed. Almost everyone agrees that forward propulsion is needed in the

acceleration phase of a sprint. Once peak velocity is attained, the spring model suggests that the runner

moves forward solely due to the momentum that was generated during the acceleration phases, and that

terminal velocity requires no further forward propulsion.

Forward propulsion theory suggests that, even when the sprinter has reached peak and terminal velocity, aforward directed force is required in order to maintain that terminal velocity. Forward propulsion theory

does not rule out the fact that the spring effect is an essential component of terminal velocity phase,

however, the spring model essentially rules out a significant role for forward propulsion, once the runner is

in peak/terminal velocity phase. Furthermore, there is debate as to whether the hip flexors play a

significant role in top running speed.

The spring model was first proposed by Tom McMahon in the 1970s. Several studies have supported the

basic concepts of the spring model. Furthermore, a Harvard study in 1995 concluded that top running

speed was determined by ground forces and not by more rapid leg movements.

Forward propulsion is related to strength. Many studies have demonstrated that the fastest sprinters have

the greatest strength. However, it has been shown that simply performing strengthening exercises, such as

lifting weights, will not improve running speed in the well-trained athlete. This suggests that a specificmanner by which to improve strength is needed. There is no consensus by which manner to best improve

forward propulsion strength.

In addition, EMG (electromyography relates to level of muscle activity) studies have demonstrated that

the hip flexor muscles may play a primary role in achieving top running speed. Because the hip flexors act

to thrust the thigh forward, hence they aid in thrusting, or propelling, the body forward, their action is

consistent with the propulsion theory. Their importance is felt to be minimal by spring model proponents.

The first question to be answered by the research project is to determine whether one can improve top

sprinting speed by improving forward propulsion.

The hypothesis is that an athlete can improve top sprinting speed, ie. improve 100m sprint time, by

improving sport specific strength of those muscles that are responsible for horizontal propulsion (this

includes primarily the hip flexor and extensor muscles, and secondarily the calf muscles). The hypothesisincludes the thought that acceleration, peak velocity and terminal velocity will all be improved with the

appropriate training method, because all phases of a 100m sprint are dependent on propulsion, to some

extent. (This is consistent with forward propulsion theory, but is refuted by spring model proponents.)

This will be demonstrated by comparing sprint times at different intervals along a 100m track before and

after the training program.

The second hypothesis is that a faster horizontal running speed is reflected by an increased horizontally-

directed ground force. This will be demonstrated by measuring horizontal-directed ground forces prior to

and after the training program. The hypothesis goes on to say that the horizontally-directed forces will be


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increased after training of these propulsive muscles, and these increased horizontal forces will be

associated with a faster sprinting speed.

The second question to be answered by the research project is to determine whether one can improve top

sprinting speed by improving the strength of the human spring.

The hypothesis is that an athlete can improve sprinting speed, especially terminal velocity, ie. improve

100m sprint time, by improving sport specific strength of those muscles that are responsible for generating

the spring effect, that occurs at each ground contact during the entire sprint. Because the spring effect

becomes most significant once peak velocity is reached, the hypothesis further implies that training the

spring will improve maintenance of peak and/or terminal velocity, more so than improving the athletes

acceleration or absolute peak velocity. (Maintenance of peak / terminal velocity is important because it

has been shown that, in a group of comparable sprinters, the fastest 100m sprinters don't necessarily have a

greater peak velocity, but they do maintain their speed at or near peak velocity for a longer duration of the

sprint than do slower sprinters. In other words, faster sprinters decelerate less than slower ones in the final

40-50 meters of a 100m sprint.)

The second hypothesis, with respect to training the spring, is that the increased speed achieved with this

training program will be demonstrated by an increased vertically-directed ground force and that this

increased force will be noted during the peak and terminal velocity phases of a 100m sprint.

MY THOUGHTS

A. INTRODUCTION

I essentially agree with the basic concept of the spring model theory, which is that passive force is a key

ingredient that allows a runner to maximize running velocity. When an athlete is in a distance event, the

spring model does a very good job in explaining what are the most important factors that maximize

running speed, for a distance event. However, my research has led me to the conclusion that the spring

model cannot explain all of what occurs when an athlete is sprinting at top running speed. The research

demonstrates that, in addition to being important during the acceleration phase of a sprint, forward

propulsion is a necessary factor that determines top sprinting speed even while the athlete is in the peak

and terminal velocity phases of a sprint.

I further believe that the hip flexor muscles play a role in top sprinting speed, although their role is not anisolated one (the details of which will be explained shortly). These views are contrary to the spring model

and spring model proponents, who state that forward propulsion and/ or hip flexion are not significant

factors, which determine top sprinting speed once an athlete reaches peak velocity. Finally, the middle

distance races are more complex, but will be discussed in some detail later.

In order to understand the forward propulsion component of sprinting it is necessary to understand the

biomechanics of running because these biomechanics will demonstrate which muscles are of primary

importance for each phase of running. [ To better understand the biomechanics I have written a

manuscript, which is included with this letter. In it the biomechanics of running are explained in great

detail. The manuscript also includes additional information, which is relevant to the running athlete and

the track coach. ]

The biomechanics will be briefly discussed in this following section. Before these are discussed one needsto define STRIDE. Total stride is defined as the distance traveled from one toe-touch to the next,

contralateral, toe-touch. This is equal to the distance traveled by the center of gravity (CG) of the body.

B. SR AND SL, and the PROPULSION vs SPRING MODEL THEORIES

With regards to biomechanical factors, Stride rate (SR) and Stride Length (SL) are the two factors, which

determine top sprinting speed. It is a well-accepted concept that faster runners (F) achieve a greater top

sprinting speed than do slower runners (S) because, in general, F runners have both a faster SR and a

greater (longer) SL.


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Why do F runners have a greater SR? The primary reason for this is due to the fact that stance phase time,

or ground contact time (GCT), is shorter for F than S runners.

_____________________________________________________________________________________

ASIDE

In order to better understand the above one has to understand the following facts. :

Total stride is equal to the distance that the CG travels during stance phase plus the distance

that the CG moves during air phase. :

Stride (total) = Stride (stance) + Stride (air)

Because this is true, one can also say that the total stride time is equal to time spent in stance

phase plus time spent in air phase. :

Stride Time (total) = Stride Time (stance) + Stride Time (air)

Next, it has been shown that Stride Time (air), or aerial phase time, is equal between F and S

runners, when they are running at their top running speed. If Stride Time (air) is equal and if

Stride Time (stance) is shorter for F runners, then the conclusion is that Stride Time (total) is

shorter for F than S runners. Because Total Stride Time is less in F runners this simply meansthat stride frequency (ratio: 1/Time) is greater for F runners.

_____________________________________________________________________________________

The conclusion is that F sprinters have a greater SR, or greater stride frequency, than do S sprinters, and

they do this because they have a shorter GCT.

In addition, it has been demonstrated that the length of the stride during stance phase is not different

between F and S sprinters. [The stride length during stance phase is called contact length (CL).] This is

true only when one compares same sex individuals. Men, in general, run faster than women. They also

have a greater contact length. However, when one compares a group of equally-sized men in a 100m

sprint, the fastest ones will have equal CLs when compared to the slowest ones. For a 6 ft male CL is @

1 meter long, and again, this length does not vary much between different level sprinters at their top

running speed.

What do the above facts tell you? Because contact lengths are equal between F and S sprinters and

because F sprinters accomplish this in a shorter period of time (shorter ground contact time GCT) this

tells you that F sprinters move their bodies center of gravity (CG) at a faster pace, or faster rate, than do

slower ones. In other words, the F sprinters move a greater distance per unit time during stance phase.

Furthermore, because rate of body movement is equal to average rate of leg movement one can also say

that F sprinters move their legs at a faster (average) rate than do S sprinters. Conclusion - In order to sprint

faster, one way that this may be accomplished is by moving the legs at a faster rate during stance phase.

Summarizing all of the above, one can say that one reason that F sprinters are able to achieve greater top

running speed is because they have a greater SR. This greater stride rate means that their legs are moving

back and forth at a faster pace during the stance phase than are the S sprinters legs. Furthermore, the F

sprinters are able to move their legs faster during stance phase because they are able to achieve a shorterstance phase time.

What allows a sprinter to achieve a shorter GCT? The F sprinters have the sport specific strength, which

allows them to achieve short GCTs, ie. < 0.1 sec. The reason is that, the shorter the GCT, the greater is the

force that the sprinter needs to recoil in order to keep from falling and to maintain top speed. This is why

the fastest sprinters have the greatest strength. Their greater strength allows them to run with a shorter

GCT, which results in a faster running speed.


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The fact that ground forces are increased is consistent with both propulsion theory and the spring model

theory. The difference is that spring model proponents suggest that the major ground forces are vertical in

nature, repelling the force of gravity on the body. They further suggest that horizontal ground forces are

small, thus horizontal forces are not significant. If horizontal ground forces are not significant then this

supports the belief by Spring Model proponents that training for horizontal propulsion is not necessary for

achieving faster top running speeds.

Propulsion theory agrees with the fact that ground forces are increased with increased running speed. Thedifference is that propulsion theory is consistent with the notion that horizontally-directed ground forces

are significant, and because they are significant, they need to be trained, strengthened appropriately, in

order to achieve a faster top running speed.

Why do F runners have a greater SL? Essentially, the fact that F runners, in general, have a greater SL has

been demonstrated to be true in numerous studies, and confirmed by spring model proponents (Harvard

study).

Thus, the propulsion theorists and spring model proponents all agree that SL is increased for F runners.

The disagreement between the two groups is with respect to how the greater SL is generated. Spring

model proponents state that it is simply a matter of increasing ground forces, which act to improve SL.

They further state that these greater ground forces are primarily vertically-directed forces, whereas

horizontal forces are small and not significant. Horizontal propulsion theory states that a horizontally-directed propulsive force is necessary to improve SL.

In addition, propulsion theory is consistent with the fact that the F sprinters are able to move their legs at a

faster rate during the swing phase than do the S sprinters. Spring model theory, based on the Harvard

study, concludes that faster top running speed is NOT reached by more rapid leg movements. However,

the following more detailed analysis of this tells us that F sprinters do indeed move their legs at a more

rapid rate. In other words in the following paragraphs it will be shown that faster top running speeds are

achieved by more rapid leg movements, including during the swing phase of the sprint. Of interest is that

data from the Harvard study itself is used to demonstrate the fact that more rapid leg movements are

important, which contradicts their own conclusion that rapid leg movements are not important for top

running speeds :

1. Simply put, if SL total is the distance traveled from one toe-touch to the contralateral toe-touch, then: SL total = SL stance + SL air

The Harvard study agrees with the fact that F runners have a greater SL total than do S runners. In

addition, that study also shows that SL stance is equal between F and S runners. Based on the above

formula, then, the conclusion has to be that SL air is greater for F runners than for S runners, who are

running at the top speed.

2. Next, one can define the length of the stride (for one leg) that occurs during swing phase:

SL swing = (SL air + SL stance + SL air)

Because it was just demonstrated that SL air is greater for F sprinters, and we know that SL stance is equal

between F and S sprinters, the conclusion has to be that SL swing is greater for F as compared to S

sprinters.

3. Next, the ratio: SL Swing/ Swing Time is defined as Swing Rate (rate = distance/ time)

If SL swing is greater in F runners, but swing time is equal (The Harvard study demonstrated the fact that

swing times are equal between F and S sprinters when they are running at their top speeds.) between F and

S runners then this ratio is greater for F runners. Thus, this simply explains as to why swing rate is greater

for F runners. If swing rate is faster in F sprinters the conclusion is that F sprinters move their legs more

rapidly during swing phase than do S sprinters.


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__________________________________________________________________________________

ASIDE

The above creates confusion, because SL swing is greater than SL total. IF:

SL total = SL stance + SL air, and if:

SL swing = SL air + (SL stance + SL air), then:

SL swing = (SL stance + SL air) + SL air then:

SL swing = SL total + SL air then:

SL swing is actually greater than SL total, for one lower extremity. Thats because SL swing

includes SL total (for one leg) plus part of the SL (SL air) of the other lower extremity. In

other words, SL swing overlaps with the contra-lateral leg swing phase, the air phase portion.

This is demonstrated by the following, which is what occurs with respect to both lower

extremities when the athlete runs :

(_ R leg swing _) (_ R leg swing _)

(air] + stance-L + [air) + stance-R + (air] + stance-L + [air) + stance-R + _

.. ._ ] [_ L leg swing _] [_ L leg swing _

What one notices is that there is an overlap between each legs swing phase and this occurs at

each air phase.

____________________________________________________________________________________

Spring model proponents have argued that stride length during the air phase cannot be increased because,

they say, no propulsion could occur during air phase. They state that any propulsion that occurs could only

happen during stance phase.

But this argument is not entirely accurate as to what actually occurs. One has to realize that the increased

SL during air phase is due to the enhanced forward propulsion that occurred in the preceding contra-lateral

stance phase. Propulsion occurs only in stance phase and that increased propulsion is reflected by an

increased SL that occurs during the air phase portion of swing phase.

Remember that swing is a combination of Air phase + Stance phase + Air phase. :

SL swing = (SL air + SL stance + SL air)

The forward thrust that occurs is generated in the in-between part (stance phase) and does not occur during

one of the air phases.

To completely understand this, one needs to understand the biomechanics of swing phase. Briefly, thereare 3 parts to swing phase: (1) Air phase 1, (2) stance phase (3) and air phase 2. Thus, there are two air

phases. In the following section I am going to discuss what occurs in each 1/3rd(they are not perfectly

equal thirds) of swing phase. :

1. In air phase 1 the swinging-leg hip is extending, not flexing forward, thus during this early swing phase

the mechanics are such that no forward propulsion occurs during this air phase. But, during early swing

the ipsi-lateral trunk is rotating forward (see manuscript for details, including Biomechanics of Horizontal

Component and Kinetic Chain sections) while the hip is rotating backward (or extending). This trunk

action involves the transfer of energy and is part of the kinetic chain. As the trunk rotates forward it places


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the hip in a more favorable position for the following contra-lateral stance portion of swing, which gives

the hip a better alignment in order to allow it to generate forward thrust.

2. In contra-lateral stance phase the swinging-leg hip changes direction from extension to flexion (one

could call this a stretch-shortening). The hip flexion that follows the change of direction is the forward

acceleration, or forward thrust of the thigh. It is due to a combination of: (a) passive forces, due to the

stretch-shortening, plus (b) an active concentric contraction of the hip flexors. In other words part of the

hip flexion energy is supplied by the trunk rotators, which the hip flexors absorbed during early swingphase. They absorbed this energy because the hip flexor muscles were undergoing an eccentric contraction

in early swing phase. Some of this absorbed energy is recoiled during the subsequent hip flexion thrust.

This energy transfer is not perfect, so a concentric contraction of the hip flexors needs to be supplied in

order to add some energy to the system, that energy which was lost as heat during the stretch (eccentric)

phase.

The forward thrust of the thigh does not and can not occur alone. It can only be generated against a

counter force, which is generated by the contralateral hip extensor and calf muscles (when I refer to a

muscle I really mean the musculotendinous unit, including active and passive forces), which occurs during

contralateral stance phase. This counter-force acts to propel/ accelerate the body forward, in addition to

providing the counter-force to the swinging-leg hip flexors, which thrusts the ipsi-lateral thigh forward.

3. In the second air phase of swing phase the forward accelerating thigh needs to slow down. In this airphase no forward propulsion occurs. Here, late swing phase, the hip extensor muscles (musculo-tendinous

unit) undergo an eccentric contraction in order to slow down the rapidly accelerating thigh. These hip

extensors undergo a stretch-shortening during late swing phase, because a change of direction occurs. The

rapid hip flexion changes to hip extension. Thus, the hip begins to extend prior to toe-touch. ETC (The

manscript describes the above in more detail. Refer to it as needed and use the pictures for more

clarification.)

CONCLUSIONS ON SR and SL:

From the above discussion it can be said that F sprinters run at a faster top running speed, as compared to S

runners, because they have a greater SR and a greater SL.

The greater SR means that the F runners have a faster stride frequency. The greater SR is due primarily to

a shorter GCT for the F sprinters. They are able to achieve a shorter GCT than S runners because they

have the sport specific strength capability to accept the higher ground forces, which are associated with

the shorter GCTs. Second, because F sprinters move their legs an equal length over a shorter GCT than do

S runners, they have a more rapid rate of leg movement during the stance phase of a sprint.

Next, F sprinters run at a faster top running speed, as compared to S runners, because they have a greater

SL during swing phase. Because swing time is equal between F and S runners, the rate of swing (or rate of

leg movement during swing phase) is faster for F runners. Therefore, F sprinters have more rapid leg

movements during swing phase, in addition to more rapid leg movements during stance phase.

Spring model proponents claim that the greater SR, and hence shorter GCT, and SL are due to the spring

effect against the ground and that this force is primarily in the vertical direction, and is due primarily to

passive recoil forces. Propulsion theory suggests that the greater SR and SL are due to greater horizontal

propulsive forces in F runners, including during the peak/ terminal velocity phase of a sprint, and itrequires an active muscle contraction in conjunction with the passive forces.

C. SPRING MODEL CLAIMS

Spring model proponents claim that all speed after peak velocity is reached is due to the spring effect.

Essentially, once a runner reaches top running no more forward propulsion is needed to maintain that

forward velocity. Spring model proponents state that peak velocity can be analogous to a ball bouncing on

the ground. Once the ball is propelled forward it simply bounces, springs, forward with no further

forward propulsion.


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But is the bouncing ball an accurate analogy to the human spring? If one looks at the mechanics of a

super ball one realizes that its bounce is very efficient. That is, at each ground contact, at each bounce,

there is very little energy loss. The human spring is inherently inefficient. Spring model proponents

themselves state that the efficiency of the human ankle-foot articulation is likely no better than 50%. This

means that there is a 50% energy loss at each ground contact.

Furthermore, spring model theory assumes that air friction is minimal and could be ignored. It has been

shown that 15-18% of the energy for running is utilized in order to counteract air friction. If one adds the

above two together then at least 2/3rds of the energy is lost at each stance phase. In order to maintain a

constant peak velocity one would have to add this energy back to the system, otherwise the sprinter

would slow down to a walk in a matter of steps, once peak velocity was reached. Thus, the energy that

needs to be put back into the system is the propulsion force that is needed, in order for the sprinter to

maintain as high a peak velocity as possible.

Furthermore, the concept of horizontal breaking (HB) is well known and well accepted by all. HB is

essentially a deceleration that occurs at each ground contact, or stance, phase of a sprint. If the body

decelerates at each stance, then in order to maintain a relatively constant average peak velocity, it requires

that an equal acceleration also occur at each stance phase. An acceleration is essentially a propulsion,

thus this lends further support to the notion that forward propulsion is needed, even when the sprinter has

reached peak velocity. Spring model theory does not explain how the deceleration and acceleration ispossible. The bouncing ball does not decelerate, nor does it accelerate at each stance phase, thus it is felt

to be a poor analogy to the human spring.

One of the Harvard studys conclusions, that more rapid leg movements are not a factor in determining top

running speeds, is used by spring model proponents to support their beliefs. Rapid leg movements are

actually caused by forward propulsive muscles. Thus the conclusion that more rapid leg movements is

not important is another way of saying that training forward propulsion muscles will have no effect on

peak and/ or terminal velocity. What was just demonstrated above is that the above Harvard conclusion is

not correct, because F runners do indeed have more rapid leg movements. The distinction between the two

is important, because if forward propulsion muscles do cause more rapid leg movements, and these more

rapid leg movements are needed to achieve greater top running speeds, then training of the forward

propulsion muscles is indeed important in order to run faster.

There are additional studies, used by spring model theorists to support their conclusion.

The following is a study that Owen Anderson mentioned inRunning Research Newsback in May of '99:

Legendary Finnish researcher Heikki Rusko and his colleagues worked with 18 highly competitive

endurance runners over a nine-week period (post-season) The athletes in the study were young, fit,

and experienced. During the study, running workouts generally lasted from 30 minutes to two

hours, and there were nine workouts per week, which added up to nine weekly hours of training.

Sixteen percent of the athletes' running mileage was conducted at an intensity above lactate

threshold, with the other 84% below LT.

Ten of the runners in the experimental group spent 32 percent of their training time, about three

hours per week, carrying out explosive strength training. The explosive strength session lasted for

anywhere from 15 to 90 minutes and consisted of sprints (five to ten reps of 20 to 100 meters) andjumping exercises (alternative jumps, bilateral countermovements, drop and hurdle jumps, and one-

legged five-jump tests) Sometimes these jumps were carried out without additional weight; at other

times a barbell was held on the shoulders. In addition, the experimental group completed leg-press,

knee extensor, and knee flexor exercises with low resistance and close-to-maximal movement

velocities.

Results:


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Contact time during the 5Ks decreased from appoximately 210 milliseconds to about 195

milliseconds. Running economy improved by 8.1 percent. The explosive trained athletes also

improved their 20 second sprint speeds, and upgraded their 20 meter sprint times by 3.6 percent.

In the 5K itself, explosively trained runners improved their times by an average of a little over 30

seconds, while the control group was stagnant.

Note the control group did not do hip flexor training.

Does the above study support the spring model theory and does it negate the need for training horizontal

propulsion in order to improve running speed? Use of the above study is essentially saying that the

runners ran faster after training for ground forces, whereas they did no horizontal propulsion training, thus

implying that if the goal is to improve running speed training for horizontal propulsion is not needed.

What the study does in fact support is that distance runners could run faster if they incorporate a more

explosive training method to their program. The training method is consistent with the spring model

theory for distance runners.

I completely agree with the fact that distance runners will improve their running times if they train for the

ability to recoil ground forces. The biomechanics of running are different in a sprint vs. a long distance

run. The horizontal propulsive forces are only significantly important in acceleration and peak/ terminal

velocity during a sprint, which is a distance that is less than 300m, (at 300m the lactic acid build-up is highsuch that further sprinting is not possible.) This study, therefore, does nothing to either support, nor does it

refute the importance of propulsive forces in an all-out sprint, ie. 100m sprint.

Because the biomechanics of sprinting and distance running are completely different, one cannot use this

study, which relates to distance runners, and extrapolate the findings to sprinters. In other words, the

above study does not either support nor does it refute the fact that horizontal propulsion is needed for top

sprinting speeds.

Finally, when I listen to many arguments by spring model theorists, there is a common use of distance

data, which is extrapolated to sprinting mechanics. Thus, although I agree with the fact that the spring

model explains what occurs during a long distance run, it is a combination of the spring effect and

horizontal propulsion that explains what occurs during an all-out sprint. The following section discusses

the biomechanics of sprinting briefly and the studies, which demonstrate that horizontal propulsion is anecessary factor, when the goal is to improve top sprinting speed.

D. SUPPORT FOR HORIZONTAL PROPULSION AT PEAK VELOCITY

Forward propulsion during running can be compared to a wheel. In this model the spokes of the wheel are

analogous to the lower extremities (see figure). The spokes of the wheel move around an axle in the

direction of the arrow. The speed of rotation of the wheel is determined by the power input at its axle.

Just as power input at the axle of a wheel determines speed of its rotation, the power input at the axle of

lower extremity rotation, the hip joint, determines speed of leg rotation hence leg speed, hence running

speed. Thus, the muscles acting at the hip joint are most responsible for determining forward running

speed. This is consistent with the above findings that F runners move their legs more rapidly during stance

and swing phases. This faster leg movement is due to the hip flexor and extensor muscles.


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There have been three independent EMG studies that have suggested that the hip flexors may be the

primary muscles in determining top sprinting velocity. Although I believe that the hip flexors are

important, especially because they act to increase stride length (SL) during swing phase, they do not and

cannot act alone. The hip flexors act to thrust the thigh forward in the middle part of swing phase, during

contra-lateral stance phase. But in order for the hip flexors to be able to thrust the thigh forward requires

that a counter-force be generated in opposition to the hip flexor thrust. This counter-force is generated by

the contralateral hip extensors and calf muscle during stance phase.

----------------------------------------------------- end of part 1 ----------------------------------------------

sprint analysis 1 - analysis of sprint models by alexander michalow m.d

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