The issues raised by Klas in his comments on my recent post on Usain Bolt’s sprinting style have led me to wonder just what it is that determines peak sprinting speed and what a runner might do to increase sprinting speed.
The key relevant scientific study is the investigation of 33 physically active adults (aged between 18 and 36) of varying sprinting ability, published by Peter Weyand and colleagues from Harvard University in Journal of Applied Physiology (J Appl Physiol, 89: 1991–1999, 2000). They measured characteristics such as cadence, time on stance, swing time and ground reaction force observed across a range of speeds up each individual’s top sprinting speed. The range of top speeds extended from 6.2 metre/sec up to 11.1 m/sec. They observed that the faster sprinters exerted a stronger push on the ground while on stance and concluded ‘runners reach faster top speeds not by repositioning their limbs more rapidly in the air, but by applying greater support forces to the ground’.
I agree with their conclusion, but closer inspection of their data leads me to a slight modification that might have important implications for how a runner should train to increase speed.
Limb repositioning time
First let us consider the time taken to reposition the swinging leg from its position behind the centre of gravity (COG) at lift-off from stance, to a position a little ahead of the COG at foot-fall. This is the swing time. It embraces two airborne intervals and a period of stance on the other leg. Perhaps surprisingly, the swing time at top speed varies very little between runners of markedly different sprinting ability. The average swing time of the 33 runners was 0.38 seconds with only weak evidence that faster runners have a shorter swing time. For comparison, the average swing time of the three medal winners in the male 100m at the 1996 Olympics was 0.33 sec. However, there is little evidence of a consistent trend across the range of sprinting ability. For example, the slowest of the 33 individuals studies by Weyand had a swing time of 0.34 sec despite running only a little faster than half the speed of the fastest runners.
Although faster runners spend less time on stance, because their speed is greater, the foot gets left further behind during stance. Typically, a slow runner has to move the foot forward by about 85 cm relative to the COG during the swing, while the fastest runners have to move the foot forwards by about 105 cm. Thus, the faster runners do swing their foot forwards a little faster. For an elite sprinter it is worthwhile expending some effort on improving swing dynamics, for example by flexing the knee to create a short lever arm at mid-swing. However, this is only fine tuning – perhaps it might make the difference between a gold medal and fourth place, but it is not likely to produce the magnitude of improvement that might encourage a recreational distance runner to choose to become a sprinter instead.
It is interesting to wonder why swing time at top speed varies so little between elite sprinters and non-athletes. It appears that most of the gain a faster sprinter derives from increased ability to reposition the foot rapidly relative to the COG is required to compensate for the modest increase in the range of the swing required at higher speed. It appears to be impossible to get swing time appreciably below a third of a second. Although the swinging leg is not merely a passive pendulum it is hard to drive it much faster than its natural swinging rate
Time on stance
The strongest predictor of top sprinting speed is ability to get off stance rapidly. In Weyand’s study, the slowest sprinters spent 0.135 sec on stance while the fastest spent about 0.09 sec on stance. Furthermore, there was a very consistent trend for decreasing time on stance to predict faster top speed, across the full range of sprinting ability. The correlation between stance time and top speed was 0.76.
Shorter time on stance is associated with stronger push against the ground. The average vertical ground reaction force (vGRF) during stance increased from 1.9 times body weight to 2.4 times body weight, although the relationship was not quite so consistent across the range of top speeds. The correlation between average push and top speed was 0.62. Thus the average vGRF while on stance was not quite such a reliable predictor of top speed as stance time.
It is of interest to note that because stance time decreases as strength of push increases, the impulse delivered (product of force by time for which the force acts) varies relatively little between the slower sprinters and the fastest. The vertical impulse was 2.49 newton-sec at a top speed of 6.2 m/sec and 2.25 newton-sec at a top speed of 11.1 m/sec. As the vertical impulse determines how much upward momentum is imparted to the body, it determines how high the COG is elevated between mid-stance and mid-flight. .The peak elevation of the COG was marginally lower in the fastest spinters. The precise gain in elevation from a given impulse depends on the shape of the relationship between force and time while on stance. . For a forefoot runer it is approximaltey sinusoidal and in this case, the range of vertical oscillation of the COG was 5 cm at 6.2 m/sec and 4.3 cm at 11.1 m/sec.
Estimated values for slowest and fastest runners based on linear trends across the group of 33 runners. *The calculation of peak vGRF and elevation assumes a sinusoidal variation of vGRF with time during stance – typical of a forefoot runner
Conclusion
These observations indicate that if one wants to sprint faster, one should aim to increase push and decrease time on stance. Although these two variables are related, in fact the decrease in time on stance is a stronger predictor of peak speed than the magnitude of the push. This is not surprising because decreased time on stance directly reduces braking, which leads not only to increased fuel efficiency, as discussed in my post on 16th January, but also to more efficient utilization of peak power.
It is necessary to have strong leg muscles to get off stance quickly, so it is worthwhile training so as to increase leg strength. As eccentric contraction is required, plyometrics are potentially helpful. However, the fact that the ability to get off stance quickly is the strongest predictor of top speed, suggests that one requires not only adequate strength but also good coordination of the muscles so as to capture impact energy as elastic energy and then release that energy in a smoothly coordinated way. This conclusion is similar to that reached on the basis of considering the style of Usain Bolt. If I want to increase my sprint speed I should focus not only on increasing my strength, but also my coordination.
I suspect that genes and development during infancy play a large part in determining how quickly a person can get off stance. Nonetheless, the fact that top speed decreases with age demonstrates that top speed is not fixed, and suggests that a training program aimed at producing changes opposite to those produced by aging might produce an increase in sprinting speed.
How might I increase my coordination? Plyometrics are likely to increase coordination in addition to increasing strength, though they are risky, and should be performed in moderation. A more direct focus on coordination might be worthwhile. Coordination depends on proprioception (the ability to sense where ones limbs are) and the ability to send messages from the central nervous system to the muscles with the appropriate precise timing. I believe that drills such as ‘change of stance’ are likely to be an effective way to achieve this
Canute's Efficient Running Site 
March 16, 2012 at 4:17 am |
Very interesting analysis. I agree with most of it. I suspect one reason why swing is slow is that we cannot actively use the powerful hip flexor rectus femoris if we want the knee to fold efficiently. Nowadays all sprinters seem to let the foot swing up almost to the hip. There used to be some that had more of a knee drive, which resulted in the foot not swinging up much. More power, but less efficient pendulum.
Regarding the ability to get off stance, I would describe it differently.
It is worth considering how the experiement was done. In order to study top speed independently of the effort of acceleration, the runners would lower themselves from the handrails onto the treadmill at top speed, with a harness to avoid falling.
If they were able to take eight steps without support, it was considered successful at that speed. They would then rest and make another attempt at a higher speed.
Imagine what happens beyond their top speed. They are not able to produce the impulse required for proper repositioning. However, I suspect that stance time in this weak push-off is the same as for a runner who succeeds at this speed.
At top speed, stance is like a window of opportunity. The push-off can only happen while the support point of the belt is within the range of hip extension.
The difference is the ability to produce enough impulse during that time, so that proper repositioning will allow the runner to land in a balanced way.
I don’t think the greater push-off gives a shorter stance time at top speed.
March 16, 2012 at 11:37 am |
Klas, I think I agree 🙂
March 17, 2012 at 12:34 am |
Klas,
Thanks for you comment.
I am still not sure of the basis for your opinions regarding stance time. As far as I can see there is no evidence for your belief that when Weyand’s runners fail to achieve a given speed they have short stance time. It appears that you reject the importance of attempting to minimise stance time because you see short stance time as an inevitable consequence of other variables. Variables such as cadence, airborne time, swing time, stance time and vGRF are all related to another. The question of which one in the key variable depends on the question you are asking.
If one asks what is the factor that sets the upper limit to human running speed, the tight limit on swing time is probably an important factor. However I am addressing the question of what a runner might do to improve their sprinting speed. Because there is little difference in swing time between fast and slow sprinters, working on swing time is unlikely to be very productive. Weyand’s study demonstrates that the strongest predictor of top sprinting speed is short stance time, and it therefore seems sensible to attempt to produce a short stance time. This raises the important question of whether or not we can train in a way that improves our ability to get off stance more quickly. As I have mentioned previously, the observation that some Pose runners are able to get off stance very quickly suggests that Pose drills might facilitate this.
You place strong emphasis on the ability to generate adequate impulse. The observation that slow sprinters generate greater impulse at top speed than fast sprinters suggests that ability to generate impulse is not the important factor. Too much impulse will cause excessive elevation. It is of interest to note that slow sprinters have a slightly greater vertical oscillation than faster sprinters. The ability to generate a strong push within a narrow time window is more important than the ability to generate impulse
Overall, the evidence suggests that fast sprinting is achieved by high cadence, strong push, and short time on stance. I think it makes sense to work on all three of these. While I believe it is valuable to develop leg strength, unless neuromuscular coordination is good enough to ensure that the push is delivered within a narrow time window, neither high cadence nor strength alone will not produce very fast sprinting.
March 17, 2012 at 2:03 am
Canute, let the push happen. Just focus on a quick but strong stabile support 🙂
March 17, 2012 at 2:58 am
Canute,
I feel like you often over-interpret my statements as if they were made out of context. It is probably my fault, so I will try to explain more again.
I think you can agree that the slower runners are most likely generating a weaker impulse at 11 m/s than the faster runners. No? That was my statement.
I’m sure they can take a few steps and then they will lose balance, rescued by the harnes. Why? Because they are not able to push enough to generate enough impulse during the short time available for support at that speed.
After all, it is the impulse that propels the runner up in the air, which is what we need.
One thing I wrote before is that it is easier to generate too much impulse the slower we run, because there is more time available for stance.
Weyand found that most runners reduced their impulse when they approached top speed (Fig 2). I don’t think it was deliberate.
My guess is that the faster runners generated more impulse at slow speed than the slow runners, simply because they can. But we don’t have that data.
Thank you for your patience.
March 17, 2012 at 3:16 am
I should clarify my last statement. It refers to your observation that the slowest runners had greater impulse (2.49) at their slow top speed (6m/s) than the faster runners (2.25) at 11m/s (it is not clear to me how you derived that). My explanation is that they have much more time available for support 6 m/s. And my guess is that the faster runners probably had even greater impulse at 6m/s.
Do you agree with my point that there is less time available for support/stance at higher speed?
March 17, 2012 at 3:30 am
One further clarification that might help. My statement “I don’t think the greater push-off gives a shorter stance time at top speed.” By top speed here I mean 11 m/s. The faster runners have a stronger push, so they can generate a stronger impulse at 11 m/s and thus be able to keep running. The slower runners are not strong enough to generate enough impulse during the short time available at 11m/s, so they lose balance. But before they lose balance at 11m/s, I suspect their stance time is as short as that of the faster runners, simply because their support window disappears by the momentum.
March 17, 2012 at 1:02 pm |
Klas
Thank for your continuing clarification of the issues.
With regard to what happens when a slow sprinter is dragged at a faster speed that he/she can maintain, it seems to me there several possibilities. One possibility is that they will attempt to increase stride length, resulting in over-striding. This will cause them to land with the foot further in front of the COG which will give them the opportunity to generate a strong impulse, but at the price of excessive braking. While they on the ground, the harness will pull on the torso and generate a forward rotation which will cause over balancing. However I think there is no more evidence for my proposal than your proposal that they spend too short a time on stance.
With regard to my computation that demonstrated that slower runner generate greater vertical impulse than faster runners at top speed, I multiplied average vGRF on stance by stance time. (Note that because estimating the values of vGRF and stance time for each runner from figure 5 could be inaccurate, I employed Weyand’s equations for the linear trend of vGRF and stance time as top sped increases, given in the caption of figure 5.
With regard to your point that there is less time available for support/stance at higher speed, if we accept that swing time is constrained within fixed limits, then cadence is the variable that determines time available for stance, since time available for stance is the time for two steps (determined by cadence) minus swing time. Insofar as most runners increase cadence as they increase speed, it is true that there will be less time available for stance at higher speed. So I do not disagree with you, but I think that if when addressing the question of what we can do to increase top speed, I think it is more logical to focus on the fact that if we can decrease time on stance, we make it possible to achieve higher cadence and faster speed.
A short stance time must be associated with a strong push to get airborne. Some elite sprinters (eg Usain Bolt) consciously focus on achieving the strong push. I believe this works well for Bolt because he is very well coordinated. For runners who are less well coordinated, I believe it is best to focus on getting off stance quickly while racing, and to focus on improving coordination during training.
March 17, 2012 at 3:39 pm
Thanks, I think you get my point now, and I appreciate your feedback. Our view of what happens seems to be the same.
When a slow runner attempting 11 m/s ends up overstriding, I would say he has already lost balance.
I agree with you that a sprinter should maximize the push at top speed.
I don’t believe that this should be done below top speed, but that is another debate which belongs elsewhere.
BTW, is it your experience that focus on pulling adds value at top speed? I find that it works at slower speed, but not at top speed. I suspect that Bolt’s focus on high knee would work better at top speed, but I have not tried it. (I ruptured by calf skiing a couple of weeks ago, so I can’t try now )-:
March 18, 2012 at 12:48 am
Klas, I find that when going near top speed a focus in releasing my body/posture most valuable. Pulling for me is very ingrained at this point.
March 17, 2012 at 7:00 pm |
Klas,
It is good that we agree on the main points, although I am intrigued by the fact that in summarising our agreement, you place more emphasis on pushing than on getting off stance. Nonetheless your question about whether I find it helpful to focus on pulling at top speed shifts the spot-light to getting off stance.
I usually use a term such a getting off stance rather than pulling because the action depends more on pushing than pulling. However as I have mentioned on previous occasions I do not think that consciously thinking of pushing is helpful unless you have very good coordination. Therefore I think of neither pushing nor pulling. When running at top speed I visualise the foot taking off quickly, and I find that this helps. When I use the word visualise, even this is not quite accurate: it is a bodily sensation as much as a visual image, but the visual image is a good way to establish the pattern. I leave it to my non-conscious brain to work out exactly what muscle action is required.
I find it is also helpful to visualise the foot taking off quickly when I am aiming for a fluent pace in the vicinity of the anaerobic threshold (for example during races in the range 5Km to 16 Km). During training in the aerobic zone I focus more on posture and cadence , though some of the time I visualise the foot lifting rapidly from the ground.
March 18, 2012 at 1:16 am
Klas,
What makes you think HIGH KNEES focus would be better than pulling for top speed?
March 18, 2012 at 11:20 am
Jeremy, my reasoning is the following. The two legs must counter-rotate for the torso to remain stable. At top speed, the support leg has maximal backward rotation, so the swing leg must have maximal forward rotation. This happens largely instinctively. However, failure to maximize this ability will probably limit the top speed. So it might be useful to focus on it. This will in effect also result in a stronger push, which is necessary at top speed.
In the interview, Bolt says that he focuses on high knee. If you look at the slomo video of his run I think you might see what I mean.
However, it is important not to think in terms of a knee drive. The knee should swing up with folded knee. But we probably want it to swing up as high as possible at top speed.
March 18, 2012 at 12:27 pm |
Klas,
I certainly think our knees will be at there highest point when we are at top speed but I still can’t agree that it can’t be accomplished via pulling. My experience of running and practicing drills tells me otherwise.
March 18, 2012 at 1:17 pm
I did not say that it can’t be accomplished by pulling. It is just my personal feeling. An explanation is that stance time is so short anyway. But when it comes to mental focus, the effect is often indirect, so whatever works for a person is good.
March 18, 2012 at 6:30 pm
Klas, each person indeed needs to to what he/she feels is best.
March 16, 2012 at 11:51 am |
Canute,
I really like how your topics encourage and convince me of my current thought and practice of running technique. The really interesting part is how we seem to disagree about one key aspect yet it doesn’t seem to change the overall way that we think we need to train for running fast. I am a big fan of plyometrics and of course the change of stance/support drill. 🙂
March 17, 2012 at 12:36 am |
Jeremy,
We should celebrate our agreement 🙂
In fact, I have often stated that I consider some of the aspects of the practice of Pose are good, especially for recreational runners. I have been especially interested in Pose for several years because of the evidence that Pose drills appear to encourage good neuromuscular coordination. As you know, I find your videos of Pose drills very helpful.
.
The fact that the theory of Pose violates the laws of physics is only of relatively minor importance for recreational runners. When faced with need to obey either Newton or Dr Romanov, Pose runners in practice obey Newton. At constant speed on a level surface, they do not fall after the pose at mid-stance.
March 17, 2012 at 1:54 am
Canute,
Careful don’t ruin or moment of agreement. Running doesn’t even happen without gravity 🙂
March 17, 2012 at 11:32 am |
Jeremy,
We should indeed celebrate our agreement.
Without gravity, running would be flying, but in fact we do need to push against the ground at least transiently to get up to speed and thereafter, in order to overcome air resistance. So running is a dance with the devil in which we rely on the devil to pull us back from heaven to earth 🙂
March 17, 2012 at 1:53 pm
Canute,
If course we have both vertical movement and muscle efforts while we run. We even have greater muscle efforts as we go from slower to faster. Can’t agree on gravity being the devil.
March 17, 2012 at 2:03 pm |
Jeremy,
I am delighted that we have found so many things on which to agree.
I accept that I am not being entirely fair on gravity. I am tempted to cast gravity as the bad guy because the forceful contact with the ground does carry risks. Provided we recognise the risks, dancing with gravity is more like spending the evening at Rick’s Bar in Casablanca – great fun but you need to keep your wits about you.
March 17, 2012 at 2:13 pm
Canute, gravity sets the rules. When you/we break the rules you/we injure ourselves. Gravity wishes us to run in peace and harmony. 🙂
March 17, 2012 at 7:09 pm |
Jeremy
Despite our approach to harmony, I think we might still have a significant disagreement about the risks associated with repeated foot-fall when running. Whichever running style we adopt there are risks. In particular the forefoot landing illustrated in the ‘Pose Method of Running’ creates a non-trivial risk. As mentioned previously, some UK Pose coaches have clearly recognised this and changed their recommendations regarding foot position during stance. However I am disappointed that they appear reluctant to acknowledge this explicitly.
March 17, 2012 at 8:25 pm
Canute, Poor visual illustrations accompanied with inadequate written context is not ideal and could lead someone indirectly to perform incorrect technique. My recommendation would be for individuals to use caution and look for all possible resources available in order to minimize improper technique.
March 18, 2012 at 12:10 am |
Jeremy,
Thanks.
I certainly agree that a Pose novice is well to advised to seek information from other sources in addition to the book.
However, imperfection in presentation of a running technique in a book is not really the main point. Whatever running style we adopt, repeated impacts with the ground, with vGRF ranging from 2 to 4 times body weight, inevitably impose stress on the body. Whichever style we adopt, it is advisable to be aware of where the stresses are greatest with that technique.
I would hope that coaches who teach a particular technique would be well aware of where the stresses arise with that technique. I would also hope that websites advocating the technique would make balanced and realistic claims about the safety of the technique.
As I have stated before, I think that there are good things about Pose. These include a focus on drills and a recommendation to limit training volume while acquiring the skill. In addition the emphasis on avoiding forceful movement makes Pose relatively safe for recreational runners. However, as I have also stated before, the thing that annoys me about the way Pose is presented is the understatement of risks, not only in the book but also in internet forum discussions. I was also dismayed by the resistance to discussion of risk at the two day Pose clinic which I attended.
March 18, 2012 at 12:40 am
Canute, I hear your concern but based on the current information I have evaluated I don’t see the risk as you do. I imagine that is the case with team posetech.
March 18, 2012 at 7:55 pm
Canute, what we have learned from some studies is that indeed certain stress amounts are placed in certain areas of the body depending on the technique used. However what we can’t possibly know is how much stress each individual can handle and for how long regardless of higher values of vgrf. For this reason I can’t lay caution to this aspect specifically, only general as to avoid to much with inadequate technique.
March 18, 2012 at 11:52 am |
Jeremy,
That is what concerns me, in light of evidence for scientific observations such as the Capetown study, and numerous anecdotal reports of injury that are consistent with biomechanical principles.
I will re-iterate that I consider Pose is relatively safe, but your statement (in response to my post of 11th March) that Pose ‘poses the least risk of all possible running related injuries’ which you later modified to ‘all overuse injuries’, is not justified by evidence, Unfortunately, it is consistent with the resistance to weighing-up evidence realistically that I have encountered with other Pose coaches, including Dr Romanov..
March 18, 2012 at 8:26 pm
Jeremy
The comments have got out of order. Here is my reponse to your commeht of 7:55 pm, which I believe was your repsonse to my comment at 6:22 pm shown below.
Thanks.
I think that approach you oultine in your response at 7:55 pm is very sensible.
I think that you do recognise that each technique produces stresses in particular parts of the body. This is not a reason for blaming either the technique or the runner. But it is reason to watch out for signs of stress in the areas concerned – eg calf or Achilles tendon soreness or pain in the top of the foot (which might be a sign of impending or actual metatarsal stress fracture) and taking appropriate avoiding action.
March 18, 2012 at 12:21 pm |
Canute,
I have seen the evidence/information you are talking about and I don’t interpret it in the same manner as you. I don’t expect you to agree with my decision but just trust that I have atleast thought and evaluated the info you mention.
March 18, 2012 at 1:31 pm |
Jeremy,
I do not doubt the genuineness of your belief. In the absence of rational discussion of the evidence, I do question your judgment.
March 18, 2012 at 2:58 pm
Canute, discuss away I am all ears 🙂
March 18, 2012 at 3:42 pm |
Canute,
As I said, the evidence to my rational thought does not suggest that proper execution of pose technique would increase a runners risk of getting a stress fracture.
March 18, 2012 at 5:18 pm
Jeremy,
I consider there are two risks that need to be addressed with any running style which involves forefoot striking:
1) The increased stress around the ankle (demonstrated by the Capetown study of Pose), which increases risk of Achilles and calf injury;
2) Increased loading on the metatarsal; which might increase the risk of stress fracture – a conjecture supported by the evidence of several well publicised instances. One of those was in Pose coach who had been using the Pose style for at least two years. It is possible that an increased training volume was a contributing factor.
I believe both of these risks can be diminished, but not entirely abolished, by allowing the heel to bear some weight during stance. I believe this is the main reason that many coaches and runners now recommend mid-foot landing rather than forefoot. The important question is how the load is distributed between forefoot and heel.
Originally, Pose recommended forefoot landing. Even now, it is difficult to find any clear statement about this issue, though some Pose coaches it appear to address it with obscure phrases such as landing with the weight ‘over the ball of the foot, rather than on the ball of the foot’. I would be interested to know whether or not you consider that the heel should bear a portion of the load during stance, and if so, how you instruct your pupils to achieve a safe loading.
March 18, 2012 at 6:07 pm
Canute, my personal experience is that the heel does not need to bear any weight distribution. It can and even sometimes does depending on speed, terrain and the runners skill of execution of optimal technique. The goal is that the center of mass is over and off the ball of the foot. How that happens safely is thru the correct posture, release and maintenance of that posture, followed by an optimal leg recovery. To safely gain the appropriate skill I recommend frequent drills with short runs. I also advice caution and support along the way. It isn’t typically fast transition to optimal technique as I have seen thru my own running as well as working with others.
March 18, 2012 at 6:22 pm
Jeremy,
It is indeed sensible to allow for a slow transition. That is one of the desirable features of good Pose coaching.
I would be interested to know if you have evidence that you can avoid the additional stress at the ankle observed with Pose (compared with midfoot and heel-striking) in the Capetown study. If so, what are the aspects of the foot action on stance that achieve this reduction in stress?
March 18, 2012 at 4:41 pm |
This is largely a theoretical discussion. Pose recommends minimal push and minimal time on stance. Those are actually conflicting criteria. It becomes a matter of interpretation how to handle the conflict.
Jeremy has often been criticized by other Posers of having a long time on stance. He probably gives priority to the minimal push, and then lets the time on stance be reduced by the range of motion resulting from speed. This is the best compromise if we want to minimize force. (And I suspect it is also most efficient.)
March 18, 2012 at 5:12 pm
Klas,
You state that it is probably best to let the time on stance be reduced by the range of motion resulting from speed rather than by exerting force.
If cadence is constant, then there is a fixed relationship between time on stance and vGRF that is independent of speed, because mean vGRF/Kg multiplied by time on stance must be equal to g multiplied by the duration of a step. Thus at fixed cadence, decreased time on stance must be associated with increased force. If you mean that Jeremy achieves short time on stance with a relatively weak push by virtue of increasing cadence, I agree that this is possible and in fact desirable. However, there are limits to the optimal increase in cadence.
March 18, 2012 at 5:31 pm
I did not state “rather than by exerting force”. Shorter time on stance requires more force.
However, as long as we only reduce time on stance as much as what is dictated by the constraint of range of motion, we are still minimizing the force for that speed.
March 18, 2012 at 5:49 pm
I’m stating this of course in the context of having the same (high) cadence at the given speed.
March 18, 2012 at 5:54 pm
Klas,
Average vGRF/Kg is determined by cadence and time on stance, irrespective of speed. I do not undertand how time on stance can be ‘reduced by the range of motion resulting from speed’ without increasing vGRF, unless it is done by increasing cadence. .
If that is what you mean, we are in agreement, but there are limts to the optimal increase in cadence.
However your most recent post implies you do not mean an increase in cadence. It is not possible to decrease time on stance at constant cadence without an increase in average vGRF
March 18, 2012 at 7:37 pm
Again, I did not state that at all. I explicitly stated that shorter time on stance requires more force, at the same cadence. That is a given.
I have explained before how it works, and you seemed to agree then. When we increase speed, range of motion increases and the body passes more quickly over support. Both constrain time on stance. (A constraint is not a cause.)
So, it is absolutely necessary regardless of technique to reduce time on stance, and increase force, when speed increases. This happens instinctively.
At any given speed and cadence, it is possible to further reduce time on stance by applying even more force, as you believe is more efficient. You are warning against the dangers of doing that. I’m saying that Jeremy probably does not interpret the conflicting recommendations of Pose the same way you do.
March 18, 2012 at 8:55 pm |
Klas,
I am sorry if I appear to be over-interpreting your statements but I am doing my best to make sense of them.
You stated above:
‘Jeremy has often been criticized by other Posers of having a long time on stance. He probably gives priority to the minimal push, and then lets the time on stance be reduced by the range of motion resulting from speed. This is the best compromise if we want to minimize force. (And I suspect it is also most efficient.)
You also stated that you are assuming a constant cadence.
We agree that at fixed cadence the only way time on stance can be decreased is by increasing average vGRF. As stated several times, average vGRF/Kg multiplied by time on stance must equal step time (determined by cadence) multiplied by g
.
At fixed cadence and fixed vGRF, there is no way time on stance can be decreased by increasing speed.
I do not know what you mean by the statement that Jeremy ‘lets the time on stance be reduced by the range of motion resulting from speed. This is the best compromise if we want to minimize force.’
You accept that this entails an increase in force. I consider that the increase in force is what allows the decrease in time on stance, not the increased speed. Alternatively, one might say: decreasing time on stance requires an increase in force. Whichever of these ‘causal’ relationships apply, the decrease in time on stance is not due to speed.
March 18, 2012 at 9:28 pm
I’m sorry if I expressed myself too briefly. I thought I could since we already cover this before.
Speed itself will of course not directly _cause_ time on stance to be short. It constraints time on stance to be short. Indirectly there is a causal chain as well, as I have explained before, but this discussion is not about that.
What I’m saying is that Jeremy is probably not increasing the force more than what is necessary for the speed. You can’t really accuse Pose of causing higher force unless it is more than that.
March 18, 2012 at 11:01 pm
Klas,
I think that all along we have had a different understanding about the causal relationships between the variables speed, cadence, time on stance, and vGRF. I hope that at some future time we will reach agreement.
However, if you simply mean that J uses the minimum force necessary to run at a particular speed, I doubt that this is true, except at maximal speed when it becomes a statement with little information content. At submaximal speed, using the minimum force necessary to achieve that speed would use energy inefficiently though it might minimize the risk of injury. (This was the point of my post on 16th Jan.) By the time he reaches his maximum sprinting speed he will be using the maximum force he can muster, unless he has decreased his time on stance so much that he is in the region where muscle contraction speed is so fast that the conversion of metabolic to mechanical energy is impaired. Weyand’s data suggest this is unlikely. Weyand’s runners achieved their peak speed at peak force. I suppose you might also say this maximum force is also the minimum required to run at that speed, but this seems a rather uninformative statement.
March 21, 2012 at 7:21 pm
I did not mean literally minimal – that would be walking. My point is that Pose does not only advocate minimal time on stance. It also advocates no active push. Based on videos of Jeremy, it looks like he places more emphasis on reducing the push than he does on reducing the stance time. So Pose has a built-in safety mechanism against the danger of minimizing stance.
We should have a thorough discussion of how speed impacts stance time via relaxed knee and range of motion. But that is another topic.
BTW, how can you draw any conclusions about metabolic to mechanical conversion from Weyand’s data? It seems intuitively obvious to me that our muscles are less efficient near their max force. I would guess that lifting 50 kg twice requires less energy than lifting 100 kg once.
March 21, 2012 at 11:17 pm
Klas,
Thanks for your comments.
As you say, Pose recommends avoiding conscious push, but also recommends a short time on stance. We agree that short time on stance must be associated with strong push. I accept that it is possible that J places a strong emphasis on avoiding push and a small emphasis on achieving a short time on stance. If so, he will suffer some loss of efficiency, but he will probably have a lower risk of injury. I think a runner who wants to achieve his peak performance needs to recognise the potential risk associated with a strong push and prepare himself for dealing with the risk.
The point I was making about efficiency of metabolic to mechanical conversion was related to speed of contraction. Muscles lose their efficiency when speed of contraction exceeds the optimum value. This can be shown from studies of isolated animal muscles. When the muscle is required to contract very rapidly against light resistance, it is less efficient that when it contracts more slowly against strong resistance. The point I made was that I do not think that at top speed sprinters contract their muscle so quickly that they exceed the contraction speed at which efficiency is greatest. I think this could only happen if top speed was achieved by means of a very rapid swing (against light resistance) instead of by a strong push against the ground. However Weyand’s data indicate that strong push is the main factor that produces high sprinting speed.
With regard to our apparently differing views about the causal relationships between the variables speed, cadence time on stance, vGRF, you state that when we increase speed, range of motion increases and the body passes more quickly over support. Both constrain time on stance. I believe it is more meaningful to say that time on stance and speed constrain the range of motion of the foot relative to the COG.
I consider that there are three variables that can be adjusted by training and/or conscious intention: cadence, vGRF and time stance. They are mutually related so that once two been determined the third is fixed. I think cadence is the most easily modified by conscious control. Time on stance can be modified by adjusting the tension in our tendons and muscles. This is less easy to do consciously while running, though we can increase time on stance by deliberately over-striding, and also by deliberately running with a relaxed muscles (I think this is what you believe that J does). Irrespective of how we make the adjustment of cadence, vGRF and time on stance, I regard distance travelled while on stance (and therefore, the range of motion of the foot relative to the COG) is a by-product of the adjustments to these three variables.
March 25, 2012 at 9:15 am
Canute, thanks.
It is not at all clear that shorter time on stance for J would be more efficient. It depends on metabolic conversion and on the constraint on stance imposed by speed. I would like to dig more deeply into that constraint, i.e. the relationship between vGRF, stance time, and cadence. I agree with you about their inter-dependency. But I think our views might differ of what comes first. However, that discussion belongs better in your post “Further reflections on running efficiency” of Feb 27. I will try to explain my reasoning about the relationship more clearly in a comment there.
You wrote:
“I do not think that at top speed sprinters contract their muscle so quickly that they exceed the contraction speed at which efficiency is greatest. I think this could only happen if top speed was achieved by means of a very rapid swing (against light resistance) instead of by a strong push against the ground. ” I would like to understand your reasoning here. Are you saying that if the rapid push off is not efficient, then it would be more efficient to swing more quickly? I guess the problem is that a more rapid swing would be even less efficient. It seems reasonable to assume that sprinters are making the most efficient trade-off for their speed, but I see no reason to assume that our muscles are designed to be efficient at that speed.
March 26, 2012 at 11:21 pm
Klas,
The reason I referred to a very rapid swing was not to recommend it but rather, it was to illustrate a possible scenario in which a sprinter might exceed the contraction speed at which efficiency is greatest. However I do not think that sprinters do this in practice. I believe, in accord with Weyand, that the sprinters achieve their top speed by pushing against the ground, However the observation that swing time is only slightly less in elite sprinters than in sprinters whose top speed is only around 6 m/sec does make me wonder whether in fact at top speed we are near the limit beyond which any further increase in contraction speed would result in less efficiency of conversion of metabolic to mechanical energy. Overall, because something appears to set fairly tight constraint on the fastest achievable swing time, I do not think that trying to decrease swing time is a high priority.
March 27, 2012 at 9:02 pm
I still don’t understand why you think that elite sprinters don’t exceed the contraction speed at which efficiency is greatest.
They need to make the least inefficient trade-off between GRF and swing speed, but they don’t need to stay within the most efficient contraction speed.
Their prime concern is top speed, and the limit of top speed is the ability to generate a high force quickly.
If an elite sprinter can generate higher vGRF at the expense of efficiency, he will be able to reach a higher top speed and win.
March 27, 2012 at 11:30 pm
Klas,
A muscle achieves its peak force at a very slow contraction rate. A slow strong contraction is not maximally efficient (where efficiency refers to power output for a given rate of metabolic energy consumption). If you examine the force-velocity curve for an isolated skeletal muscle (from an animal) you will see that it generates it peak power output at a relatively low force – typically around one third of the force it could generate in an isometric contraction. I suspect that at mid-stance a sprinter’s leg muscles develop a force at least half of their peak force, and probably substantially more. It would be wasteful to develop a muscle so strong that it could achieve the required push while exerting only a minor fraction of its maximal force. Thus at mid-stance the speed of muscle contraction is likely to be slower than the contraction speed that would give maximum efficiency of conversion of metabolic to mechanical energy. The sprinter probably sacrifices efficiency to allow him to generate a stronger push. (We agree that the sprinter is probably not maximally efficient – but I do not think this is because the contraction is too fast.)
Maybe in the final instant before lift-off, as force decrease, the speed of muscle contraction might approach the point where efficiency is greatest and perhaps at lift-off it might actually even exceed the limit, but the force exerted at this time is small and any inefficiency would be trivial.
March 18, 2012 at 2:14 pm |
HI Canute,
I like to keep things simple and for me the thing that increased my top speed the most was doing downhill strides on a nice grass surface, 6-=10 efforts with a full recovery.
I guess this is a Lydiard leg speed session.
It works and you can see a good max speed increase within a few weeks.
March 18, 2012 at 2:59 pm |
Rick, increasing your top speed for what distance?
March 18, 2012 at 6:42 pm
Hi, I think you will find if you can improve your top speed it will filter down into all your running distances.
Steve Magness has done some good articles on this.
March 19, 2012 at 12:19 am
Rick, I have never regularly used down hill running to improve speed. From a theoretical stand point I don’t think it would be of great value over other methods, however if I were a sprinter seeking top speed for short distances I wouldn’t be opposed to trying it sometimes.
March 18, 2012 at 3:14 pm |
Rick,
Thanks for that comment. A few years ago when I started running again after a long break I was dismayed at how slow I was. I did downhill 7/10 effort strides on grass (about 1/20 slope) once a week, and I was very pleased with progress. Although I did not assess my sprint speed, within a few months, I was covering 10K on trails in about 41 minutes, which I considered wasn’t too bad for a 60 year old. I think it helped improve my neuromuscular coordination.
Unfortunately, since then I have had several illnesses and I would struggle to do 10K in 50 minutes at present, so I think maybe I should try the down-hill strides again. The main problem is I do not have a well-grassed 1/20 slope nearby any longer, but I will try to find something suitable.
March 18, 2012 at 6:45 pm
Hi Canute, if you can find a nice piece of parkland it would be well worth your effort.
March 19, 2012 at 4:50 am |
Interesting post and comments. Fascinating about the similarities and differences between the average and elite sprinters.
I’d second Rick’s idea about fast downhill strides on a gentle grassy slope – also the Brad Hudson style short (10 sec) sprints up a very steep hill to build leg strength. For improving coordination, you could probably find many examples of running drills to help with that — like the ‘ladder’ drills. A similar one we used to do was 2 or 3 steps in each lane crossing the track aiming for fast cadence/spring off the ground. That might be safer than plyometrics.
March 19, 2012 at 6:38 am |
Ewen
Thanks for your comment. Yes I agree there are many drills that can improve coordination. In making the choice between them, it is necessary to consider the balance between likely effectiveness and safety with regard to risk of injury from eccentric contraction.
I think that change of stance might be effective because it involves an action that has similarities to actual running. I am impressed by the speed of getting off stance achieved by some Pose runners. I also think change of stance is fairly safe.
I think running down hill might be even more effective because it is even more similar to running. I am pleased Rick reminded me of this, especially as I myself have used this strategy with apparent sucess in the past. However I think running down hill is a little bit more risky (as is also the case with plyometrics) so it should be done cautiously on a gentle slope.
Running uphill is also helpful. I think that is mainly because it increases the relevant strength, thereby allowing us to get off stance quickly. Running uphill also presents only a low risk of injury from eccentric contraction, provided one avoids getting too far up on ones toes. Bounding up hll, as advocated by Lydiard is possibly even more effective, but might be a bit riskier.
At present I will stick with regular CoS togehter with less frequent, running down a gentle slope and some uphill sessions. I also do trampolining as a form of gente plyometrics but I am not sure how effective this is.
March 19, 2012 at 1:38 pm |
Canute, are you performing any strength training for your legs? If so what lifts and how much weight can you lift?
March 19, 2012 at 4:41 pm |
Jeremy
Not at present. I had been about to move from body weight resistance exercise to weights when I suffered a relapse of arthritis two yeas ago. My left wrist and knee are still a little troublesome now, especially the left wrist, so for the time being I am defering weights. I still do a small about of body weight resistance exercise, mainly exercise that involve standing on one leg to improve balance as much as strength, and a small amount of core work. Because of the left knee, I am cautious about plyometrics at present; iI do some hopping..Mainly I bounce on the trampoline – but I am not sure how effective this is. I see it as preparation for more demanding plyometrics.
What plyometric exercises and resistance work do you do?
March 19, 2012 at 5:01 pm
Canute, currently I do once a week full body strength routine which for the legs consist of: squats(both machine and Olympic squat), good mornings, deadlift, lying hamstring curls, standing glute kick backs, box step ups, walking lunges and isolation wall hold squats. As for the weight I do it depends on my consistency and racing schedule. I can do 350lbs machine squat and walking Lunges with 100lbs on my shoulders currently.
March 19, 2012 at 7:50 pm |
Jeremy
Thanks. Maybe your workouts are primarily focused on more immediate goals, but I think the really big reward might be in the future. You are still relatively speaking a youngster, but you are putting money in the bank by being proactive in preventing (or even merely minimizing) the loss of strength that is one of the frustrations of the veteran athlete. The other major frustration for the veteran is diminished cardiac output –determined largely by the ill understood but seemingly inexorable decrease in maximum heart rate. It is very difficult to know how to minimize the decrease in maximum heart rate, but maintaining skeletal muscle mass will at least ensure that you have enough muscle to extract a high proportion of the oxygen from the blood that the heart can pump. So I think you are building a solid foundation. Good luck both with your short term goals but also for the day when you will call yourself a veteran.
March 19, 2012 at 7:59 pm
Canute, my main reason for lifting is current strength and long-term health and secondarily for benefiting my running.
March 20, 2012 at 7:46 pm |
Hi Canute,
I don’t know if my own personally experiences would help in under things. I was a national class cross country runner as a teenager but my sprinting ability was rather poor – worse than average in my own class, let alone at district or national level. No matter how much effort I put into sprinting I just couldn’t go faster – my 100m PB is 15 seconds, yet my 400m PB is 59 seconds! Clearly I’m one blessed with lots of slow rather than fast twitch fibres…
Fast forward to today and while out cycling a couple of days ago I decide to a VO2 max interval, I accelerated and got to top speed but couldn’t get any faster, it wasn’t lack of strength at over coming drag as it felt that the peddles weren’t pushing back harder than I could push, rather it felt like I simply couldn’t accelerate my foot downwards any quicker. I’m guessing I just couldn’t shorten my quads any quicker to achieve a faster cadence due to not enough fast twitch fibres, or perhaps what ones I do have are just out of condition..
To me it seems like my lack of sprinting ability and my experience with going flat out for a short interval on the bike is closely associated and to do far more with my inability to shorten my muscles quick enough to generate rapid toe off and turnover required rather than my lack of ability to generate the power required.
As I’m training for an ultra right now I can’t say I care too much about lack of sprinting ability. In training I’ve started adding hill sprints which I can do pretty well, but this is all about power output rather than rate of shortening of muscles.
I would expect adding strength exercise might help my power output but not my ability to shorten my muscles any quicker. I have never tried plyometrics so really don’t know whether it’d help with my sprinting ability, I suspect I might well be close to maxed already given all the sprint intervals I did as kid when training but never bettered my sprinting PBs.
Robert.
March 20, 2012 at 9:11 pm |
Robert,
Thanks for your comment.
That is very interesting. A 15 sec PB for 100m and 59sec for 400m implies that acceleration was a problem. Acceleration in a 100m relies heavily on type 2B fibres. Genes and early development are the main factors influencing the proportion of type 2B fibres. Maybe as youngster, there was little scope for further development of these fibres.
However, you can improve the proportion of type 2A fibres (aerobic fast twitch fibres). As you grow older it is also important to minimise atrophy of the type 2B. I think plyometrics and/or uphill running will help with development of type 2A and sustaining type 2B.
For ultras , you rely very largely on type 1 fibres, though maybe type 2A’s and B’s play some role in avoidance of injury when running on uneven surfaces – such as parts of the West Highland Way, including the descent from Conic Hill. As you imply, you main priority at present is maximising endurance, but maybe after the Highland Fling it might be worth considering some work on the type 2 fibres.
Canute
March 24, 2012 at 6:21 pm |
Hi Canute,
My 100m and 400m PBs show that I had a real problem with accelerating out the blocks. My top speed wasn’t that high either which points to have few fast twitch fibres relative slow twitch fibres. Perhaps my fast twitch fibres tend to be of the aerobic type. Is there any ways to estimate the proportion of fibres?
I did plenty of hill sprints and flat sprint intervals in training when I was aged between 11-14 when I was training with the Athletic club but never improved my sprinting ability, but my stamina and speed endurance were stella, year on year I just got faster and faster at long distances. I suspect even now if I concentrated on improving my sprinting ability I’d soon max out.
However, perhaps this is an advantage… if my slow twitch and aerobic fast twitch fibres are having to do all the work then I’ll be able to stress them all with high intensity training as I won’t have worry about bulking out on non aerobic fast twitch fibres. I haven’t been back into running long enough to access what type of training effects me in what ways so it’s just something I’ll need to experiment with.
I see that others have been suggesting running downhill, I do quite a bit of this as I’m surrounded by hills and mountains here in the Trossachs, most too steep and rough to really hammer it going down safely, but there is few that I can get to around 4 min/mile pace. I don’t know if it helps with my sprint ability but it sure is fun!
March 26, 2012 at 10:44 pm
Robert,
Quantifying fibre type is only possible using biopsy techniques.
I agree that from your description of hill running etc as a youngster, you had probably reached somewhere near your limit in developing fast twitch fibres. Maybe it might have been possible to produce some further limited improvement in sprinting by employing drills focussed on improving proprioception and coordination.
Because age related muscle loss affects the fast twitch most, it is sensible for a veteran runner to make sure that they do enough type 2 development work to minimise the loss. I do not think that bulking out the anaerobic type 2 fibres is much of a problem for any elderly runner and in your case it certainly does sound like there is any risk of too much anaerobic type 2 development. I think the hill work that you do is great. Clearly, careering downhill on uneven surfaces can be risky, though in my experience, if you do a lot of hill running on uneven surfaces your musculo-skeletal system become well enough conditioned that the risks of injury is fairly small provided you are not unduly tired. At least until after the Fling it seems to me you do not need to do anything about fast twitch fibres, apart from being careful on uneven slopes when tired.
As for the question of whether it is worth typing to improve proprioception and coordination in the future depends on your goals. I think that for any distances up to marathon it is worth spending some effort on improving the ability to get off stance quickly. At this stage, I am inclined to agree with Rick that down-hill running on a gentle grassy slope is one of the best things, though I am still intrigued about the possibility of worthwhile gain through drills. However there is little doubt that the major training effort of an endurance athlete should be devoted to developing aerobic capacity.
March 25, 2012 at 2:31 am |
Balance in all things
Run down hill and up hill fast!
In moderation
and on a surface that is nature to the body!
Have you ever thought about Kenyan type hill efforts?
ie run up a good grassy slope, turn around and run downhill fast then turn around and run uphill again, without stopping!
You can make this into a timed session of say 3 mins or maybe 5 or 10 mins with recovery in between then repeat.
March 26, 2012 at 10:50 pm |
Rick
I am sure that running both up and down the hills is a good way to develop overall strength and resilience, but I am inclined to think that to produce the maximal development of coordination etc from down- hill running it is probably best to avoid exhaustion so that you can maintain a good brisk lift off from stance.
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