Thanks for the references i’m going to try to locate them, i’m especially interested in EMG study by Mann, Roger and al.
Concerning the second point : i made this point because your initial point was about sprinting speeds only. There’s no point to debate that the knee lift occurs when the athletes comes from walking to running to sprinting.
Comparing individuals, regardless questions related to “style”, permit to think about what is limiting factor and what is not. If we find such a range of hip flexions in elite sprinters, while all show similar hip extensions, it’s possible to guess which is the more important.
Attached pictures taken around top speed at take-off for Davidson Ezinwa (in Athens’97 10.11) and Georgios Theodoridis (In Ghent’00 6.53).
tc0710, i agree with your post. Everybody knows how to come from walk to jog to run to sprint, and adapt their technique unconscienciously. What an effort would it be if we had to think about lifting the knee when we try to catch the bus in the street! Baby learn to walk, but the parent never tell them to put a foot ahead of the other. Elite athletes’ body have the ability to adapt stride mechanics, heart beat and breathing patterns in accordance to the effort in order to spend the minimum energy. But they don’t think about it. I’m always perplexed when it comes to teach sprint technique to elite ones with oral advices… It doesn’t work. Train everyday with Maurice Greene and it will help your technique more than any technical advice will.
Hip Extension push-off force against the ground occurs throughout stance phase, probably maximal in mid-stance. Contralateral hip flexion also occurs throughout stance, with the majority early and mid-stance phase. This is reflected by both analysis of leg positioning during sprinting and the EMG studies that I quoted in the above PierreJean forum letter (Mann and Montgomery references).
The propulsion is similar during acceleration and terminal velocity phases of a sprint in that the hip extensors are the primary muscles responsible for the actual push-off and forward propulsion (but the contra-lateral hip flexors aid in this push-off by providing a stabilizing force)
The difference relates to ground contact time (GCT). In early acceleration there is a relatively long GCT. As late acceleration and terminal velocity phases are approached the GCT time becomes shorter and shorter. Also, in early acceleration the forces are more concentric in nature, whereas as late acceleration and terminal velocity are approached there are greater eccentric (really stretch-shortening) forces. Thus, although the muscles (Hip flex/ext m.) are the same the types of contraction progresses form a primarily concentric to a primarily stretch-shortening type of contraction.
Ground Reaction Force studies (I will have to find the references) demonstrate both an increase in vertical and horizontal GRFs as speed increases. So, yes the push-off portion of the GRF is increased as one increase sprinting speed (ie., progresses from acceleration to terminal velocity).
It would be difficult to measure hip force directly, especially during a sprint. But EMG studies (ie. Mann, Roger, et al., Amer J Sports Med, 14(6); 501-510, 1986 and Montgomery, et al., Amer J Sports Med, 22(2)-272-278, 1994) demonstrate significantly increased hip flexor activity with increasing sprinting speed. Increased EMG activity is associated with greater muscle activation. Greater muscle activation indicates a greater muscle force that is generated.
How does one ever know what is ‘enough’ strength? When you do squats and plyos for the quads you don’t really have a definite endpoint for how much strength you are trying to obtain. You merely individualize each athelte so that each athlete maximizes his/her own abilities or strength capabilities.
Yeah, I agree, it is not a perfect analogy. But the basic principle is that a countering force against which the desired force can contract, will improve the strength of that force. For a sprinter the hip extensors in stance phase push off against the ground, but this push off against the ground will also act to extend the torso. The contra-lateral hip flexion counterbalances this tendency for torso extension.
So, although the hip extensors have the ground against which they generate a force, because the hip extensors also extend the torso, one needs to also stabilize against this action, which is accomplished by the contra-lateral hip flexors.
First of all, the stance phase of sprinting has two functional components, deceleration and acceleration. During the first half of stance phase only deceleration occurs, and this occurs for both the vertical downward momentum and the horizontal forward momentum. The acceleration portion occurs in the second half of stance phase. In siimple terms the hip extension acceleration in stance has a pull-push effect. The hip extensors first pull the leg back, which moves the body (center of mass of the body) forward. An instant later in time the hip extension then pushes the body COM forward. Thus a rapid pull-push effect.
Stronger = Faster. That is my contention. You have to have stronger hip extension strength (ie., dynamic explosive strength) in order to be able to move the hip extensors faster, especially because this extension is occurring against the ground.
I cannot demonstrate that in this forum. e-mail me at alexmicha@aol.com and I will demonstrate this to you with a lengthy more detailed explanation and diagrams.
You are absolutely correct. Finally, we agree. Let me repeat that: NET propulsion force is zero.
But remember that, at each ground contact there is initially a deceleration (both vertical and horizontal deceleration). This deceleration means that energy is lost (absorbed, etc.). If energy is lost, then the net force is also decreased. So this means that at each ground contact there is a loss of forward directed force (momentum derived force). If there is a loss of forward directed force, but net force is zero then the only way that this is possible is if you put energy, or force, back into the system. Otherwise the net force would be negative (and not zero) because of the lost force during deceleration.
Where does that force input come in? It comes in during the subsequent acceleration phase (ie., 2nd half of ground contact). An acccleration is really a propulsion.
This tells you that at each ground contact there is first a loss of forward directed force (deceleration), which is followed by a gain in forward-directed force (acceleration, or propulsion).
The conclusion is that you have to have a propulsion at each ground contact in order to maintain a net force of zero. This propulsion comes from the hip extensors, which is aided by the contralateral hip flexors.
Finally, let me know your e-mail and I will send you some diagrams on hip flexion strengthening, along with additional biomechanical data on the hip flexors.
The buttocks (ie., glutes) is a single joint muscle with little or no tendon. The iliopsoas muscle has a significant tendon for stretch-shortening. It is the two-joint hamstrings which have greater hip extension activity during a sprint than do the glutes.
The iliopsoas, although considered to be a single joint muscle, is functionally a two joint muscle. In other words it has two flexion functions. It first flexes the torso forward (small degree) and second it flexes the hip. This is important in its role in the kinetic chain of events that occurs during sprinting.
See the diagram in: http://www.charliefrancis.com/commu...ght=hip+flexors
This demonstrates in a simple, yet instructional, manner on how the hip flexors stabilize against the torso extension that occurs due to hip extension muscle firing.
Your first statement is in error. I believe that you got that information from ‘spring’ theory proponent, because I have heard them say the say thing.
Hip flexion IS NOT due to a rebound from the ground contact phase. This is absolutely wrong.
To explain this requires that one discusses the biomechanics of sprinting, specifically how and when certain leg/joint motions occur.
At toe-off the air phase (double-legged air phase) is begun. During this first portion of air phase the hip that was extending during the ground contact phase actually continues to extend very slightly. It then changes to hip flexion immediately prior to the contralateral toe touch. With contralateral toe touch there is a much greater hip flexion force that is now generated actively, which occurs during early to mid stance phase of the contralateral ground contact leg.
Now, if the extending hip continues to extend in early air phase then it would be impossible to say that the hip flexion that follows was due to the ground rebound effect.
But this does not negate energy conservation. During the stance phase (and very early toe off when) while the stance phase hip is extending the passive structures (ie., iliopsoas tendon) is absorbing some of the extension energy. This absorption of energy in the iliopsoas tendon is then released during the hip flexion (forward, single-legged swing) phase that immediately follows.
Thus the transfer of energy to the hip flexors comes from two sources. First, energy is transferred from the torso (abdominal muscles) because of the kinetic chain effect. Second, energy from the hip extension is transferred to the ipsi-lateral hip flexors in a stretch-shortening phenomenon.
At faster sprinting speeds the ground reaction forces (GRF) are indeed increased. But GRF have two components, vertical and horizontal (and actually lateral, which are less significant). So this means that one has to train to train both those muscles that are responsible for vertical motion as well as those responsible for horizontal motion in order to improve sprinting speed.
From my viewpoint, elite athletes likely would benefit more from focusing on the hip flexors and extensors in a dynamic/explsoive training method. Likely they already have very good sport specific (ie., sprint specific) quad and calf strength.
Less well trained individuals actually improve no matter what you do. Thus, an un-conditioned individual will improve running speed even if you do completely nonpspecific exercises, such as swimming exercises. The better trained an athlete is, the more focus that needs to be placed on sport specific strengthening training methods.
First I would like to apologize for the late response, as I have just become a member of this forum.
I would like to express here that the Harvard/ Weyand study is incorrect in its conclusion regarding rate of leg movement. That study demonstrates that the time spent in swing phase is equal for fast (F) and slow (S) runners. The study states that, because the TIME spent repositioning the legs is equal between F and S runners, the conclusion is that the RATE of leg movement is no different between F and S runners. The error is that one cannot convert data on time to data on rate of movement.
What the Harvard study does demonstrate is that the swing times during double-legged swing are equal between F and S sprinters. The Harvard authors erroneously concluded that swing ‘rates’ are equal because swing ‘times’ are equal.
The data in that study confirms that the time spent in swing phase (air phase) is equal for F and S runners. (I agree with that finding.) The authors state that, because F runners do not spend more ‘time’ repositioning their legs in swing phase (air phase) then F runners do not have a greater ‘rate’ of leg movement. (Notice how the authors erroneously switch from time to rate, which are two separate issues.) But this reasoning is based on erroneous principles. This is due to the fact that swing ‘rate’ and ‘time’ are two different issues.
Swing time (as I am using it here) refers to double-legged swing phase. Double-legged swing phase time is really air phase time.
AIR PHASE TIME IS DEPENDENT SOLELY ON VERTICAL DISPLACEMENT AND HAS NO BEARING ON FORWARD MOVEMENT OF AN OBJECT, OR ATHELTE.
Another manner of looking at this statement is that, when one describes forward speed and tries to relate that to air phase time then it is wrong.
This fact is based on simple physics. For example, if you throw an object up and wait for it to come down, then the amount of time in the air (ie., air phase time) is dependent only on vertical displacement (which is the distance that it goes up and down). Nothing else determines air phase other than vertical displacement. We can carry out this example further to clarify my point even more.
Let’s say that you have two balls. Let’s then say that you throw one ball up and down and a little distance forward, and that it moves exactly 1 meter in vertical distance and it moves forward 1 meter. Then you throw the second ball 10 meters forward and you do it in a way that its vertical displacement during that throw is exactly 1 meter. With this scenario both balls have equal vertical displacements, 1 meter. Because they both have equal vertical displacements it will take equal amount of time (ie., equal air phase time) for them to go up and down.
But this tells you nothing of forward movement. The 1st ball moves 1 meter in x time, whereas the 2nd ball moves 10 meters in x time. The second ball has greater horizontal speed because it moves 10 meters in x period of time, whereas ball one only moved 1 meter in x period of time. Greater horizontal speed for ball 2 means that its COM has greater speed than ball 1 even though both balls have equal air phase times (equal vertical displacements). This is analogous to S and F sprinters. S and F sprinters have equal vertical displacements, but the F sprinters have greater SL (ie., SL in air phase], which means that they have greater horizontal movement. Because F runners’ horizontal movement is greater and it occurs in an equal time period it means that rate of movement COM is greater for F sprinters. Because movement of the COM is dependent on, and determined by leg movement, one can conclude that the rate of leg movement is also greater for F sprinters during Swing phase, or air phase (and Stance phase as was discussed above).
More on the above. I think that we all can agree with the fact that Stride Length is not the same for F and S runners. The Harvard study itself demonstrates that SL is greater during double-legged swing phase (air phase) for F runners as compared to S runners. And, because F runners have a greater SL in air phase, and this occurs during equal time periods (ie., equal swing phase times for F and S runners) then the ‘rate’ of movement has to be faster for the F runners. (Rate = distance/ time and because distance is greater for F runners and because time is equal, then rate of leg movement is also greater.)
In a different way the same is true for F runners during stance phase. During stance phase both F and S runners (with the same height) have equal stride lengths (also called contact length, CL). F runners have shorter ground contact times (GCT). If F and S runners have equal CL, and that length is traveled during a shorter GCT, then this means that the F runners’ COM (center of mass), and hence the F runners’ leg movement, is greater than for S runners. (Again, Rate = distance/ time. Because distance, CL, is equal and because time, GCT, is shorter for F runners then the ratio d/t is greater for F runners, which means a greater rate of COM movement, which means a greater rate of leg movement for F runners.)
What this means is that RATE of leg movement (or leg repositioning), which is determined by the hip flexor and extensor muscles, is indeed important.
This does not negate the need for sprinters to increase force against the ground in order to improve sprint speed.
I do not have the 1987 biomechanics article, but I have read something along the lines that vertical GRF (ground reactive force) is 10 times greater then the horizontal force. But this is based on constant running at a relatively slow pace. I have seen a (? Japanese study, I will have to find the reference) which demonstrates that horizontal GRFs are roughly 1/3rd those of vertical GRF. Even though a 1/3rd GRF is small it is still significant and needs to be dealt with if one wants to maximiza sprint speed. What this means is that one cannot ignore the horizontal GRFs - simply focusing on verticla GRFs will not allow maximization of sprinting speed.
I would like to finish by repeating that the Harvard study came about an erroneous conclusion. In other words, LEG REPOSITIOINING RATES are important. The rate of hip rotation is an important factor that determines sprinting speed.
I am repeating this not to sound gallant or denounce the study or the authors. The study brings out many important points. However, when sprint coaches are told that the rate of leg movement, or the rate of hip rotation is unimportant then it is a disservice not to set the record straight.
I am a proponant of the theory that ground reaction is significantly involved in the hip return. Whether it is direct via GRF or indirect, via energy stored in tendons, as you suggest, matters little in the end result.
I would prefer to discuss swing phase from personal experience/feeling while sprinting (which, in my case, may be bordering on ancient history/archiology).
My feeling, in moving from average (10.5) to good (10.1) sprinting for my day was that swing time overall likely remained the same BUT that the rate varied more, meaning more/faster action at the hip flexors later in the swing phase, with seemingly way more time to prepare in mid-flight and perceptably less time on the ground.
In addition, it was obvious that there was far more hip movement about all possible planes, and that the hip began “turning under” preceding the knee raise portion, something that had never been perceptable before.
Whatever the case may be, I did hip flexor exercises with light to moderate resistance and found them helpful and would advocate them.
As for the specificity arguement, you’re right as far as you go, but the ultimate specificity is in the correct sprint action itself, and it may be necessary, at some very advanced point, to move away from exercises that too closely compete for the same muscular and nervous resources.
Alex did you get my email I sent to the AOL address?
So, I read that you half believe in the spring mass model. I didn’t know that people researched only half of it? So, do you believe or no?
Where is the knee in elite sprinters at mid stance? Can you provide a photo or picture demonstrating this? Is this a controlable process?
Vern Gambetta once mentioned that one of the biggest faults of the “A” series of exercises is that emphasis on knee lift at the expense of impulse off the ground. Are you saying this analysis is incorrect?
I like what you wrote. I’ve got to admit I’m confused about the process having read so many conflicting interpretations stated with such authority on opposing sides of this debate.
I agree with your thoughts and I wonder if it matters: I still like the idea of “training the movement not the muscles”…how can you separate the muscles in firing sequence and between the main muscle(s) at work from it’s synergists in such a way as to be able to specifically isolate them for the purposes of targeting them for training?
Better to develop the mechanism in toto, rather than to attempt to deconstruct and risk wrecking the lot, perhaps by setting up imbalances and even initiating an adverse firing sequence (by emphasising knee lift).
Stretch Reflex
“The stretch reflex acts similarly to loading a ‘Y’ sling shot, or forcked sling shot. Before shooting the projectile, it remains poised in the stretched elastic, just as the hip flexors remain stretched before the recovery phase. When the sling shot elastic is released, it pops back into original form, sending away the projectile. … The sling shot release parallels the leg recovery phase: the knee cycles through because the hip flexor pops back into normal position from its stretched position. Therefore, the knee coming through occurs naturally and does not necessitate an athlete’s conscious effort. Furthermore, consciously lifting the knee high while sprinting inhibits the legs’ natural timing during the recovery phase. Consciously creating a high knee lift or normal knee lift is like stretching back a sling shot winth projectile and helping push the projectile with the hand while the elastic is releasing. The action would cause a reduction of elastic force, resulting in slower movement with the sling shot as well as with sprinting.” (Tom Tellez)
Your last statement about being confused, well when I first started looking into sprinting biomechanics over 10 years I too was very confused. I am in the process about putting together a detailed manuscript on the biomechanics of sprinting to hopefully make it more understandable. As per the forum note above, I shall send a lot of this information to the CF web site. It is too detailed to put into the forum itself. Hopefully I’ll have it organized by tomorrow.
As far as your other questions:
I do believe in the spring model, but only part of it. The ‘spring’ theory is correct, but in many instances I have seen it applied it incorrectly. For example, many ‘spring’ theorists use distance running data and make recommendations for sprinters. But you can’t do that because the biomechanics are different. Hopefully, some of this becomes more clear in the follow up e-mail to the CF web site.
The knee in stance phase of a sprinter goes from @ 30 degrees flexion at toe-touch, to @ 50 degrees of flexion at toe-off. What does this tell you? The knee only undergoes flexion during stance phase. Because it only flexes, then the quadriceps m., which controls this knee flexion, can only undergo an eccentric contraction. If the knee only flexes and the quadriceps contraction is purely eccentric in stance phase the conclusion is that the quadriceps do not add to vertical lift at toe-off.
If the quads don’t supply vertical lift than what muscles do? Well the hip extensors are in the wrong angle so any lift from these muscles is likely very little. The only muscle left is the gastro-soleus. If you analyze the detailed biomechanics of sprinting you will see that virtually all, or at least 90% (that’s an educated guess) of vertical lift is due to the gastro-soleus muscle group. Thus, the gastro-soleus muscle-tendon unit, along with the quadriceps, absorbs vertical downward momentum in the first half of stance, and the ‘spring’ effect, or upward momenteum in the second half of stance phase is due mainly to the gastro-soleus muscle-tendon group with absolutely no help from the quads. (Does that make sense?) [I’ll supply pictures in the later CF submission]
With regards to knee lift.
I personally feel that the athlete should focus on bringing the thigh/ knee FORWARD as rapidly as possible during a maximal sprint. I actually tried this on my own. If you focus on the pushing part, what happens is that you tend to increase ground contact time (GCT). For the first few steps of a 100m sprint such a focus is ok, but in later acceleration phase, and especially during terminal velocity (TV, which usually occurs at @ 50-60m in a 100m sprint), if you focus too much on pushing off then GCT is increased. [An increased GCT is not what you want to sprint faster.]
I also feel that the athlete should focus more on moving the thigh/knee forward rather than upward. By focusing too much on bringing the leg upward what happens is that you may be bringing it up too much, ie., too much flexion. From athlete to athlete there is a variable amount of hip flexion that is present at toe-off. (See the picture on this page submitted by pierrejean and it demonstrates this point). By focusing on moving the thigh forward rapidly it is amazing, but you actually will feel that there is a simultaneous greater push-off effect, and this occurs at a shorter GCT than if you focus on getting a greater push-off per se.
In other words by focusing on moving the thigh forward as rapidly as possible during swing phase, the overall effect is a greater push-off, which occurs with a shorter ground contact. {Some may not agree but the biomechanics would support this, and if you try this on your own and/ or with your athletes I think that you will find this out for yourself.}
So in response to the Vern Gambatta question, I feel that you may compromise push-off force if you focus on moving the hip into too much flexion, but you won’t compromise it if you focus on rapid hip flexion. Thus, I agree and disagree, depending on how you apply the forward hip thrust.
If you try this yourself and with your athletes, what you will note is that the rapid hip flexion will just end up with a natural end-point of optimal hip flexion, and this will likely differ slightly from athlete to athlete. More hip flexion is not necessarily better for any individual athlete. It likely would take some training to optimize this effect.
In summary, I agree with Vern Gambatta, if the wrong focus is followed, ie., focus too much on obtaining a large degree of hip flexion. Again, I feel that if the focus is on obtaining rapid hip flexion and letting ‘natural’ processes determine the endpoint for maximal degree of hip flexion then the athlete will maximize push-off force, and at the same time, will develop a short GCT.
Theone i couldn’t agree more on Tellez quote, conscious actions usually slow down things ask pianists how they can move their fingers so fast.
I don’t understand these numbers, knee flexion is usually around 150°. Could you explain the measurement?
Your point can be illustrate with this photosequence, which shows the transition between a 90% race to a 100% race which is 11.3m/s (he had 10m to make this transition in effort - not speed of course). See how fast the swing knee comes back forward (at touch down, swing knee is forward support leg’s knee). Honestly, i don’t know what is a cause of this (story of egg and chicken), however, i know this is not a conscient action from him, nor a technical advice from me. It is just a “natural” thing. Before and after this transition zone, the technical pictures would be similar, and the technical changes are only noticable in this transition zone when the sprinter is organizing himself for the change in speed regime. Coordination seems to be a critical point here.
I do believe in the spring model, but only part of it. The ‘spring’ theory is correct, but in many instances I have seen it applied it incorrectly. For example, many ‘spring’ theorists use distance running data and make recommendations for sprinters. But you can’t do that because the biomechanics are different. Hopefully, some of this becomes more clear in the follow up e-mail to the CF web site.
The study that Peter did was not at all done with distance guys?? You either believe it or you don’t? This model has been used in lots of other locomotion research…it is really alive and doing quite well. You would be in the minority saying it’s only half right? Must have been four or five famous biomechanists who made a mistake then huh? The large iliopsoas tendon you speak of is perfectly consistent with what the boys from Harvard have written in the paper and hypothesized for a long time. As a rule in nature, long tendons (like the Achilles in humans) are found at joints in which elastic energy is important and active muscle power is not. (Hmm Spring anyone) Your “stretch-shortening” is exactly what Peter and the Harvard bunch has proposed. Why disrupt it? So it’s kind of weird, you talk about the elastic energy, and then you change and say it can be pulled forward faster. Is it spring like or no? And does it fit for every one? And don’t forget in the study the limbs were not pulled through faster!
I totally agree. The other thing I’d like to add from personal experience is that the faster I got, the easier it was to bring the knees through and the less I noticed how high they were getting (others told me). This was particularly true in the 200m, where it became easier to maintain form.