Shapes

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ALTIS

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Previously, we reviewed the rules of acceleration and upright sprinting. We have also discussed our framework to help us make decisions on how we can improve our players. Before we decide how, we need to know what it is specifically we want to change. We need to assess — or analyze.

In this 40 minute session, you will learn to discern the difference between sprinting shapes, making value judgments upon them — i.e. you can recognize a high quality shape from a low quality shape. This will be our first step in analyzing how our players sprint.


“Thinking back to when I first began actively watching sprinting – and still how I observe today – my eyes naturally gravitated towards the shapes that I saw, how these shapes connected in time, and how quickly and efficiently athletes moved between these shapes.  It is how we probably see most movements, and it is how we teach many movements as well.” – Coach Stuart McMillan.


With little effort, we unconsciously recognize literally thousands of different shapes we come into contact with every day; we know that a dog is a dog, a car is a car, and a tree is a tree, no matter the size, and no matter the angle at which we view them – simply through observing their shape. 

Although there is likely to be a moderate amount of variability amongst athletes in how they sprint, the topological characteristics (the global geometrical properties, based on relative limb motions, that define shape) are likely to be preserved.​1​

It’s simply a matter of identifying these shapes. 

It is thought that we identify these shapes through their internal ‘skeletons’;​2​ all trees have a general skeletal invariance that allows us to recognize a tree as a tree, a dog as a dog, and a car as a car. 

It is the same in sport.  The longer we have been coaching – the more shapes we have seen, the more able we are to recognize the skeleton of them quickly, and eventually – automatically.  

Consider the following video: at which number do you recognize the shape?  

 

Chances are, if you played baseball, or work in baseball, you will recognize the shape at either picture 1 or 2.  Even if you know nothing about baseball, you probably recognized that it was a human swinging a bat as quickly as picture 3 – and almost certainly no later than picture 4.  

Let’s have a look at another one:

 

How did you do with that one?  At what number did you recognize the shape?  What did you first recognize? How did you recognize it?

Let’s try one more:

 

This one was pretty easy, right?  Easier than the first two, and you probably know why — simply because you have seen more people run than you have people who have thrown a punch or hit a baseball.  You are better at recognizing a running shape than you are a boxing or baseball shape.  

Did you make any value judgments on the running shape, and if so, at what point did you do this?  What process did you go through?

We go through our lives constantly recognizing shapes – trees, dogs, cars, etc. – but how do we go about recognizing which kinds of shapes?  Which kinds of trees, dogs, cars, etc.?

At a basic level, we learn to recognize shapes very quickly and easily, but what happens at more subordinate levels?  How do we discern a dachshund from a Doberman?  Or a Porsche 911 from a Honda Civic?  

A good sprint from a bad sprint? A good squat from a bad squat?

Let’s consider the following two shapes: 


Figure A: two ‘squat shapes’ — can you identify the good from the bad?

If we have spent enough time in a weight room, we quickly recognize them as squat shapes, but what do we recognize next?  And how did we go about recognizing this? 

Is this something we know innately, or did we learn it?  

What about this series of shapes?


Figure B: sequence of an Olympic weightlifter performing a snatch.  What are the stable shapes within this sequence?

What stands out?  Are they ‘good’?  What makes them so? And how do we know?  Is this something that was taught to us, or do we know these are good shapes for some other reason?


LEARNING TO ANALYZE

In this session, we will learn to discern the difference between sprinting shapes — make value judgments upon them — i.e. recognize a high quality shape from a low quality shape. This will be our first step in analyzing sprinting, as well as teaching players how to be faster.

Remember – shape refers to the positions an athlete occupies in space during the course of a movement.

It is the ‘first step’ in the ALTIS Coaching Framework.  Shapes form the foundational content of how an athlete solves a movement problem.


 

Dave Collins talks on the first step in his ‘5As’ approach – Analysis. Are there any considerations that you were not expecting?


QUALITY

As coaches, we are generally able to discriminate between good shapes and bad shapes – even in sports we are not already familiar with.  Those of us who are involved in sport have generally been exposed to so many different types of movers, in so many different types of sports, that we can discern the quality of a movement – often just through simply observing a single shape within the movement.  


Consider the following examples (Figure C, below).  

We may not know much about a rugby conversion, baseball batting, golfing, boxing, or ballet dancing – but it’s pretty clear that these are effective shapes – right?  

But what is it about them that we are drawn to? 


Figure C: even in sports we know little about, most coaches can discern a good shape from a bad shape

What is it about these shapes that makes us think they are good? Can we verbalize this?  Or is it just a ‘feeling’ we get from them?

One way we like to differentiate between the quality of a shape is through using more descriptive terminology, rather than simply good and bad. For example, it might be more useful to discern between good and bad sprinting shapes — simply by asking ourselves “does this shape look ugly, or elegant”?

Consider the following 5 shapes of different athletes at the full-support frame.  


Figure D: one of these shapes is of an elite sprinter — can you tell which one?  What about the other shapes? Where do your eyes go first?  Where do your eyes go on the other shapes?

Can you recognize the shape of the sprinter?

What is it about the sprinter’s shape that you recognize, specifically?  Is it just an overall feel, or are there mechanical positions that you are looking at?

Which shape is the most-elegant?  Which is the ugliest?  

How do you go about making qualitative judgements upon them?  Which of the remaining four is the most-elegant?  Which shape is the ugliest?  Does it depend?  If so – upon what? Can you make any inferences on which sports they play?  

Can you make assumptions on how you would train them, even?  

For example, let’s consider shape #4: if you know anything about sprinting, you would probably agree that there is a lot to admire about this shape.  If you don’t know much about sprinting, what do you think?  Can you tell that it is a better (i.e. more elegant) shape than numbers 1, 2, and 3?

Technically – her posture looks pretty good, her swing-leg knee is in front of her stance-leg knee, she has a nice upright torso, and her swing-leg foot is tucked underneath her glutes — overall, pretty good mechanics!  But what about that stance-leg knee angle?  It is very flexed at this point.  Can we make any inferences as to why this might be from this single frame? 

Can we assert that she has poor lower body ‘stiffness’ abilities, for example?  Perhaps she has excessive ankle range of motion? Maybe she is simply young and weak?

Tough to say – but regardless of the reason for this, it is most-definitely performance-limiting, and is something we can address with our training.  


Before we move on to the first practical, check out a pro tip from Nick Winkelman, as he shares his opinion on the trap we fall into with our choice of language.

So one of the most common myths let’s say, in speed development is that to teach something technical, we need to be technical. And what I mean by that is to teach something technical I need to teach using technical language. I want to challenge that notion as a thought experiment for everyone, and that is when you pick up your iPad or your iPhone do you need to have an understanding of the inner workings, the inner mechanics of the processor chip or the motherboard or even how the structure of the devices designed to use it or benefit from it? A hundred percent you say no. Oftentimes we abandon that viewpoint and abandon that core intuition when it comes to teaching movement.  And that is we assume that motor control and motor learning is somehow dependent on our athletes understanding of it, and the reality couldn’t be further from the truth.”

Dr Nick Winkelman, ALTIS Interview, April, 2020

Watch some video of 3-5 athletes doing a task you are not overly familiar with, and make value judgements on them. Maybe you work primarily in football, and have never watched ice hockey, for example. Can you identify the fundamental shapes of skating, and pick out the better skaters from the shapes they create?

What terms other than ugly and elegant can you use to describe a good and bad sprint shape?  What kind of shape are you looking for, and how can you describe this to your athletes? 

We find that coaching through these ‘mood words’ (or motoric words) are extremely powerful coaching tool, as we will describe in more detail later on


Now let’s back up a little.

In the last task, how did you decide which shapes to analyze?  

Did you stop the video at specific points in time?  How did you decide which points to stop at?

Some shapes are more ‘fundamental’ than others, and these form the foundation of our coaching analysis.  When analyzing movement, coaches can identify the fundamental (most-stable) shapes at key points in time during the execution of the movement.  

Consider the following five movement tasks — can you identify the fundamental shapes within them?  How many shapes within the task are fundamental?  How did you come to your decisions?

  1. Barbell back squat
  2. Full Olympic snatch 
  3. Basketball free throw
  4. Kicking a soccer ball
  5. Throwing a football

Chances are, you were able to identify the fundamental shapes of the first one quite easily.  Perhaps you had a little more trouble with the second one, and then more difficulty with each of the last three.  

What about sprinting?

Let’s look at acceleration first. 


ACCELERATION

During acceleration (see Figure E, below), the fundamental shapes occur at ‘toe-off’ and ‘touch-down’.  These are the shapes that tend to be the most-stable (the attractors, if you recall from Book II), and are the positions that coaches tend to identify the most-easily, the most-automatically, and the most-effectively. 


Figure E: the toe-off and touch-down shapes of the accelerative steps of an elite sprinter, a youth soccer player, a Major League Baseball player, and an NFL football player

While the shapes are seemingly quite varied, there are some obvious commonalities (the invariance).  

A reminder of these:

  1. Forward-oriented torso
  2. Neutral pelvis
  3. Scissoring thighs
  4. Push back (‘acute’ shin angles)
  5. Flexed ankles

These are the five RULES (see Figure F, below); the non-negotiable fundamental shapes we should expect to see whenever an athlete is accelerating effectively and efficiently.  In track & field, we would add “align the head with the spine” and “counter-balancing arm swing” to this list, but this is not necessarily appropriate for team sports, where the head has to be up, the eyes scanning, and-or perhaps holding off an opponent, or carrying an implement. 


Figure F: a 2-frame kinogram depicting the two stable states of an acceleration position, and showing the 5 ‘rules of acceleration’: 1) forward-oriented torso;; 2) neutral pelvis; 3) scissoring thigh action; 4) push-back (positive shin angles); and 5) flexed ankles

It should also be noted that there are situations when team sport athletes accelerate maximally without a significant amount of forward torso orientation.  While this is not ideal – as a more vertically-oriented torso will affect all other ‘rules’ – we accept that this is a reality of team sport. 


Click here to review the Key Terms used in the upcoming section

Toe-off (TO): the first frame in which the foot has visibly lost contact with the ground.

Touchdown (TD): the first frame in which the foot is visibly in contact with the ground following the flight phase.

Touchdown distance (TDd): the horizontal distance between the x-coordinate of the CoM and the x-coordinate of the CoM of the stance foot at the point of touchdown.

Toe-off distance (TOd): the horizontal distance between the x-coordinate of the CoM and the x-coordinate of the CoM of the stance foot at the point of toe-off.

Mid-stance (MS): the frame in which the x-coordinate of the CoM is directly above the x-coordinate of CoM of the stance foot. Also referred to as ‘full-support’


AN OVERVIEW OF ACCELERATION MECHANICS

By James Wild

Appropriate shapes at initial ground contact will position an athlete favorably to translate their center of mass horizontally in the forward direction. For example, in a study by Wild and colleagues (2018)​3​ the touchdown distance (horizontal distance between the toe of the stance foot and the center of mass at the instant of touchdown) during the first three steps of sprinting was significantly less in trained sprinters compared with professional rugby union players (see Figure G, below for example). 

A significant difference was also shown between rugby playing positions whereby rugby backs were also shown to achieve smaller touchdown distances compared with rugby forwards.​3​ These results suggest that faster athletes (i.e. track sprinters were faster than the rugby players, whereas rugby backs were faster than rugby forwards) typically touchdown with their foot more posterior relative to their center of mass during the initial steps of a sprint.


Figure G: touchdown distances (TDd) for 4 types/levels of athlete.  Note the TDd of the elite sprinter compared to the other athletes.  Because the foot initially contacts the ground underneath the CoM, there is significantly less ‘braking’.  Note also the youth soccer player with better TDd than the professional team sport athletes, denoting a more efficient shape

A foot positioned more posterior relative to the center of mass at touchdown has been shown to be associated with an increase in the ratio of force during the simulated first step of an elite sprinter,​4​ decreased ground contact time during the first 4 steps of professional rugby backs​5​ and a decrease in the braking impulse at the 15m mark of track & field and team sport athletes.​5​ 

These features are often cited by coaches and researchers as being beneficial to sprint performance and support the ‘rules of acceleration’ at touchdown, and may explain why faster athletes at a group level tend to exhibit smaller touchdown distances. A more posterior foot position relative to the center of mass at touchdown has been shown to be achieved with more forward-oriented trunk and shank angles (acceleration rules 1 and 4) and an increased angular velocity of the hip at the instant of touchdown (a result of rule 3) in professional team sport athletes.​6​  

While favorable shapes at touchdown set the athlete up to direct their center of mass horizontally when ‘pushing’ during ground contact, the shapes identified at toe-off are essentially a function of an effective ‘push-off’ during the stance phase. 

The horizontal position between the stance foot at toe-off and the athlete’s center of mass (‘toe-off distance’ – see Figure H, below) characterizes the whole body forward leaning position during initial sprint acceleration, and is often considered the hallmark of this sprint phase. 


Figure H: note the difference in toe-off distance (TOd) between the elite sprinter (left) and the youth soccer play (right)

Achieving a larger horizontal distance between the stance foot and center of mass at toe-off has been shown to relate to the initial sprint acceleration performance of professional rugby backs and trained sprinters during the first three steps.​3​ This feature has also been associated with higher propulsive impulse during the first step of physical education students​7​ and is likely achieved through an appropriate set-up at touchdown and as an outcome of the rules of acceleration, as shown in Figure F. 

Toe-off distance is predominantly explained by the magnitude of leg extension of the stance leg and the center of mass trajectory angle at toe-off. Large amounts of stance-leg extension at toe-off affords an athlete the ability to take advantage of the longer contact times during the initial steps of a sprint relative to later stages of acceleration and during maximum velocity. 

Pushing for ‘longer’ may be advantageous during the ground contact phase in initial sprint acceleration since it has been observed during these initial steps that performance is more associated with the magnitude of horizontal propulsive ground reaction force produced towards the mid-late stance phase (Colyer, Nagahara, & Salo, 2018), compared with the horizontal ground reaction forces produced earlier in the stance phase. 

While sizeable leg extension at toe-off may be desirable, the coach ought to be cautious about ‘chasing’ this single technical feature without recognition of how it may affect other technical features.

For example, it is not uncommon for athletes to direct their center of mass more vertically when focusing on increasing their leg extension at toe-off. This will likely result in higher vertical forces and possibly greater flight phases which may delay subsequent steps and consequently center of mass acceleration. 

Another consideration is the effect that increasing leg extension, and toe-off distance, may have on contact time. 

For example, as alluded to already, Wild et al. (2018)​3​ found a greater horizontal distance between the stance foot and CoM at toe-off was correlated to better initial sprint acceleration performance in professional rugby athletes and trained sprinters. However, this relationship could not be repeated in later research within a larger cohort of professional rugby backs.​6​

Essentially, it was found that similar levels of initial sprint acceleration performance could be achieved with different magnitudes of toe-off distance, but the extent of this performance was also influenced by the contact times achieved. 

To put it simply, while some athletes were achieving large degrees of leg extension at toe-off, and a foot position substantially more posterior relative to their CoM compared with other athletes, it took them ‘too long’ to reach this extended position (i.e. they produced lengthened contact times which negatively affected their acceleration performance). Different combinations of contact time and toe-off distance observed in the rugby backs were shown to result in similar initial sprint acceleration performance, without an optimal combination resulting in higher sprint acceleration performance. 

This finding was also observed across other team sport athletes (professional male soccer players and international female lacrosse players). 

As an example of the importance of considering technical features in combination, rather than in isolation, consider Figure H.

The picture to the left shows a rugby player at the instance of touch-down and toe-off during the first step of a sprint. The horizontal distance between the vertical red dashed lines represents the toe-off distance achieved by this athlete. From this picture it is intuitive to see how changing leg extension and angle of center of mass trajectory will alter toe-off distance.


Figure H: visualization of three different kinematic factors for three different runs of a professional rugby player.  This visualization shows how contact time, leg extension range, and CoM trajectory relate to each other

To the right of the picture a radar plot depicts 3 technical features for this athlete during the first step across three different sprint efforts (colored triangles). The closer the corners of the triangles are to the outer corners of the radar plot, the more ‘extreme’ the technical features are. For example, the outermost point for contact time depicts a very short contact time. The outermost point for leg extension range depicts ‘maximal’ leg extension at toe-off, while the outermost point for center of mass trajectory would represent a perfectly horizontal trajectory of the center of mass. 

The red triangle shows the magnitude of the three technical features during his first ‘un-prompted’ sprint effort. Here we can see that his leg extension range is limited, his contact times are short and his center of mass trajectory is ‘reasonably’ horizontal. 

In his second sprint effort, he has been encouraged to achieve more forceful leg extension in an attempt to achieve greater leg extension range and we can see (shown by the yellow triangle) that while he has achieved greater leg extension, he has increased his contact time significantly (i.e. it has taken him longer to reach his toe-off position) and he has also directed his center of mass more vertically. 

This is clearly not desirable in terms of sprint acceleration performance during the initial steps. However, it can serve as part of the learning strategy of the athlete. For example, he now has a ‘feel’ for what a more exaggerated pushing action feels like. 

In the third effort (green triangle) he was then encouraged to try and find a middle ground between the first two sprint efforts, and we can see an increased amount of leg extension compared to his first sprint effort, and whilst contact time has increased somewhat compared to his first effort, a more horizontal trajectory is evident. 

The challenge for the coach and athlete is to find the most appropriate balance of these three variables during the initial steps to maximize horizontal acceleration of the individual during the initial steps.

Although different combinations in toe-off distance and contact time may result in similar initial sprint acceleration performance, one thing for sure is that a small horizontal distance between the stance foot and the centre of mass at toe-off combined with long contact times will certainly lead to poor acceleration performance. A reasonable amount of leg extension is therefore desirable, but not if it results in contact times which are deemed ‘too long’. 

This highlights the importance of rule 3, where the intent to scissor the thighs rapidly and with intent should not just be considered a key action when in flight. 

For instance, towards the end of the stance phase, the intent to recover the stance-leg forward in an attempt to attenuate leg extension will likely help to reduce contact time. Rule 3 may be an effective focus therefore for team sport athletes who achieve substantial leg extension at toe-off, but do so with long contact times.

To summarize, the instants of ‘touch-down’ and ‘toe-off‘ during acceleration provide ideal timepoints where coaches can analyze the shapes of team sport athletes. The ‘rules of acceleration’ are likely to result in the production of favorable shapes at ‘touch-down’ and ‘toe-off’ for effective horizontal acceleration of the center of mass. 

While this information is useful, the coach also ought to consider the effect of the combination of variables and avoid ‘chasing’ single technical features without an understanding of how this approach may affect other factors of interest.


Do the differences in starting position effect acceleration? Click here to learn more on on Team Sport starting positions, in this 2 minute read, by James Wild.

One of the factors typifying the often unpredictable nature of team sports is the conditions under which athletes are required to begin accelerating maximally. Sprint efforts will frequently commence from a variety of different positions, after a rolling start or following actions which position the athlete in a less favorable position to begin sprinting in the direction required next. 

Regardless of these starting conditions, the shapes adopted by team sport athletes at the point they begin sprinting linearly with maximal intent will be similar to those as outlined in Figure G. 

For example, following the push-off from a standing two-point start, team sport athletes will be traveling at a velocity of approximately 3-4 m/s.​3​ This is a similar velocity to that which team sport athletes are often required to accelerate from maximally (i.e. a rolling start) in a game situation. Observing the team sport athletes in Figure G at the first touchdown we can see body positions and shapes that would clearly be recognizable on the field of play when sprinting from a relatively slow rolling start. 

The faster the team sport athlete is traveling on the field of play before accelerating maximally, the more aligned their body position, and the shapes they adopt, will be with those achieved in later steps when sprinting from a standing start (i.e. steps 2, 3, 4 and so on), akin to that practiced during typical linear sprint training. This is because body position at touch-down (and toe-off) is largely governed by the velocity an athlete is traveling at. 

Although it is worth noting that ‘standing starts’ still feature in many team sports, fundamental track-style sprint training may not always mimic the starting conditions under which team sport athletes sprint from during a game. However, the shapes that follow the initial push off, and adopted for the remaining distance covered during the sprint efforts undertaken, will always be relevant to the team sport athlete who is required to sprint during their sport.


UPRIGHT SPRINTING

During upright sprinting, the stable shapes are slightly harder to identify (Figure I, below), as upright sprinting is a more complex task than acceleration. 


Figure I: full 5-frame upright kinograms of 3 different athletes 

‘What are the fundamental shapes of upright sprinting?  Are they simply the same as acceleration – touch-down and toe-off?’

Think back to our previous Skills Practice. 

  • How did you go about identifying the fundamental shapes? 
  • Did the number of shapes you identified depend upon the task? 
  • What did it depend upon, specifically?  

If we compare the back squat to the full snatch, for example, it is clear that the back squat has two fundamental shapes – the top position and the bottom position.


Figure J: back squat shapes.  Would you identify any of other shapes during a squatting movement? 

What about the snatch? Let’s check out the snatch sequence once again:


Figure K: snatch sequence: elegant or ugly?

We can probably agree that shapes 1 and 7 are fundamental.  What about the others?  Think back to our discussion around attractors and fluctuations from Book II.  Which of these shapes would we expect to see the most-stability?  Which are more variable?  A good way to answer this question is to ask which shapes will be consistent regardless of the load on the bar?   We can perhaps argue then, that the fundamental shapes are numbers 1, 3 and 7.  These are the shapes that all other shapes depend upon.  These are the most-stable – the ones which we really should be focusing most of our energy on – and most of our coaching cues on.  


Figure L: snatch sequence.  Stable shapes at ‘address’, ‘beginning of second pull’, and ‘catch’

Let’s go back to upright sprinting. 

Using the same rules as described above – can you identify the most-stable shapes in the sequence? 


Figure M: what are the stable shapes within this 5-frame sprinting kinogram?

Right away, we would probably say shape #1 (toe-off) is fundamental, and we can probably eliminate shapes #2 and #3 – but what about shapes #4 and #5?

Let’s consider what these three shapes – toe-off, touch-down and full-support – look like between groups (Figure N, below): 


Figure N: 3-frame kinograms of 6 different athletes 

The increased complexity of this task, relative to acceleration, potentially leads to more variance in execution from athlete to athlete – especially between athletic populations.  

If we consider only more efficient movers, however, the variance is reduced quite a bit, and we can identify the stable shapes more easily (Figure O, below). 


Figure O: The upright kinograms in this graphic depict three athletes ‘playing by the rules’, and three athletes who are not

The three shapes as depicted above are what we would recognize as the most-stable during the sprint cycle – but we must always ask if we can simplify further? 

In the ALTIS Kinogram Method eBook, our friend Dr. Nick Winkelman shares his justification for looking exclusively at these two shapes, which we fully agree with — the question of appropriate selection of frames as it relates to prioritization and simplicity, 

“is to identify the lowest number of technical landmarks that, if changed, have the largest impact on the entire technique; therefore: 1) toe-off, and 2) full-support. Interestingly, toe-off precedes the primary horizontal change in force-motion (i.e., back to front) and full-support precedes the primary vertical change in force-motion (i.e., down to up). I feel that these force-motion shifts (i.e., eccentric to concentric) carry the variability that echoes through the coordination that connects these space-time points. Thus, good coaching can be directed at these time points, with physical development working on the neuromuscular factors that need to deliver the coordinative message.”

So in upright sprinting then, you can argue that the stable shapes are full-support and toe-off (see Figure P, below).  Every other shape is a direct result of the positions the athlete is in at these two shapes.  


Figure P: a full 5-frame Kinogram of an elite sprinter, with the two stable shapes depicted in pink

As an aside – an athlete’s individual shapes are subject to inherent variability, and it is unwise to identify a single shape that is ideal for all athletes. All athletes have unique bodies, and all move in unique ways, and thus, there is a bandwidth of variability around what can be described qualitatively as ‘good shapes’.  

In addition, just because an athlete is not moving in how we would feel is an effective and efficient way does not necessarily mean that that technique should be changed.  


Think back to what you have read thus far — which of the below ‘bad’ techniques would you most-likely try to change in some way, and how might you go about doing it? 

Figure Q: 2-frame upright kinograms of three athletes.  What do you think of these shapes?  

What more information do we require to answer these questions, or can we make recommendations based only upon these shapes?  

Let’s recall the rules of upright sprinting (see Figure R, below).  There are once again 5 — and they are not significantly different from the rules of acceleration (you may recall the various mechanical similarities from Dr. Clark’s presentations in Book II). 

  1. Stacked torso
  2. Neutral pelvis
  3. Scissoring thighs
  4. Strike from above (vertical shin)
  5. Flexed ankles

Figure R: 2-frame kinogram depicting the two stable shapes at full-support and toe-off, and the five rules of upright sprinting: 1) stacked torso; 2) neutral pelvis; 3) scissoring thighs; 4) strike from above (vertical shin); and 5) flexed ankles

Again, there will be variability around these shapes, but we will not maximize sprinting speed without abiding by these five rules. 


OVERVIEW OF UPRIGHT SPRINTING BIOMECHANICS

By James Wild

Recall from earlier in this Session that initial sprint acceleration performance in the first few steps appears to be related to the magnitude of horizontal propulsive ground reaction force produced towards the mid-late stance phase. 

With each successive step the phase of the ground contact which ground reaction forces are most related to sprint performance appears to change until maximum velocity is reached. 

For instance, later in the acceleration phase, associations between horizontal ground reaction force production and performance are more evident towards the earlier phase of ground contacts,​8​ where horizontal braking ground reaction forces likely become more problematic as a sprint progresses. That is, athletes who produced smaller horizontal braking ground reaction forces achieved better sprint performance during those steps in the late acceleration phase.​8,9​

It should be noted at this stage, we can’t rule out that attempts to actively reduce braking ground reaction forces during the early stance phase may decrease the ability to generate high propulsive forces during the later stance phase, which are particularly important during the initial steps.

However, as ground contact times reduce with each successive step, the ability to mitigate horizontal braking ground reaction forces is important as an athlete approaches their maximum velocity and, as already discussed by Dr. Clark in Book II, the ability to produce large vertical forces in short time frames earlier within the stance phase also appears to become more important during full upright sprinting (e.g. Clark & Weyand, 2014).


Figure S: the force signature for speed – elite sprinters demonstrate a fast rising edge with lots of vertical force loaded in the first 25-50% of ground contact, whereas team sport athletes have the upside down U shape that is representative of the ‘spring-mass model’.  Refer back to Dr. Clark’s presentations in Book II for more  information on this

As the mechanical constraints change as the sprint progresses towards maximum velocity, so too do the shapes an athlete adopts. As ground contact times shorten, the whole body of the athlete becomes progressively more upright, since it is simply not possible to keep ‘pushing’ in a forward leaning position in an attempt to achieve high levels of acceleration (i.e. at maximum velocity, athletes are no longer accelerating). 

In this upright position a neutral pelvis (rule 2) provides an appropriate ‘anchor’ from which the lower limb muscles can transmit force to the ground. 

A relatively ‘high-knee’ position at toe-off facilitates the downwards acceleration of the foot into the ground, where a relatively vertical shin position (rule 4) assists the athlete to direct their ground reaction force in a more vertical direction compared with acceleration. 


Figure T: a relatively vertical shin at initial ground contact may allow for both greater whole-body stiffness and a relatively more vertical application of force earlier in the ground contact phase, which has been shown to be a determining factor of sprint speed 

At the point of touchdown, the horizontal distance between the athlete’s foot and their center of mass (touchdown distance – see Figure U, below) will be at its greatest (i.e. with each step taken from the start of a sprint, the foot moves progressively further forward relative to the center of mass and ‘peaks’ when an athlete reaches their maximum velocity).  However, the further forward the foot touches down, the greater the braking forces are likely to be. Since braking forces are likely detrimental to performance in the later stages of acceleration and maximum velocity (Colyer, Nagahara, & Salo, 2018; Morin et al., 2015), this technical feature (touchdown distance) is arguably of more interest to these phases of the sprint compared to the initial steps in acceleration. 


Figure U: the horizontal distance between the athlete’s foot and their centre of mass is termed the touchdown distance (TDd)

However, simply minimizing touchdown distance could potentially just result in a decreased step length if the athlete does not possess the strength-related qualities necessary to achieve the vertical force required in what would likely be a shorter contact time. Consequently, when looking to reduce the extent to which an athlete’s foot is forward of their center of mass at touchdown, the coach ought to determine whether more ‘strength-related’ factors or ‘technical’ features are limiting the athlete’s ability to do so without sacrificing step length and overall velocity.

Provided appropriate ‘pre-activation’ of the leg muscles has been achieved prior to touchdown, and that the athlete exhibits high levels of ‘whole-body stiffness’ (a function of both leg and trunk stiffness – the latter assisted by ‘stacking’ of the torso: rule 1), an efficient and effective short ground contact is achievable. 

How an athlete ‘terminates’ the ground contact phase through appropriate hip mechanics is also important to aid with efficient recovery of the leg in preparation for the next step. As the hip extends during the initial contact phase a net hip extensor moment is evident. However, by toe-off, the hip moment changes to a flexor moment in order to reduce the rate of extension at the hip joint. The point at which the dominance switches from extensor to flexor takes place during latter stages of the stance phase.​10​ The exact stage this switch takes place will vary among athletes, and may be due to individual ability and differences in technique. 

For example, athletes capable of producing more powerful hip extensor muscle contractions (‘hip-extensor dominant’), may require an earlier switch to flexor dominance in order to prevent the duration of the stance phase increasing. 

As alluded to when discussing ‘shapes’ during acceleration, this highlights the importance of the intent to scissor the thighs (rule 3) at the end of the stance phase (not just during the aerial phase) in order to abbreviate ground contact and facilitate an efficient leg recovery action, culminating in the touch-down and full support positions evident in Figure V, below.


Figure V: In elite sprinting at full-support (or ‘mid-stance’), the swing-leg knee will be in front of the stance-leg knee, and the swing-leg shin will be parallel to the ground, forming a ‘figure 4’ position (see elite sprinter).  Generally, the further behind the swing-leg knee is from the stance-leg knee, the less-effective the position is (see 16yr old male and elite soccer).  While team sport sprinting rarely will afford this full figure 4 position, we like to see at least a ‘knees-together’ shape at full-support (see 12yr old female, NFL football, and MLB baseball).

Together, these four shapes (2 acceleration + 2 upright), and the combined ten rules, underpin the basic mechanics of effective sprinting. There really is little else that is important.  

Even with our elite sprinters — these ten rules form the totality of the foundation of their technique. Very rarely will we talk to them about anything at a deeper level.  

Now – that said, knowing the rules, and coaching athletes to move in accordance with them are two different things entirely.  Stay tuned – as we detail this a little later!

In addition, while the invariance of these shapes is important for us to understand, we also need to appreciate how the intention of an action relates to the outcome of that action.  


INTENTION-OUTCOME

The shapes we observe are the outcome of the movement ‘problem’, and are not necessarily the intention.  The distinction between outcome and intention is an important one for coaches to appreciate. Any interpretation of a movement is dependent upon the intent of the movement. Only through acknowledging the athlete’s intention as it relates to the movement task, can we identify any error in the execution of the task.  

“A coach’s role is not only to observe a movement, but also to interpret it.”

-Stuart McMillan

Once we identify the error in the movement, we can move on to classifying whether it is related to the behavior (attention), or the biomechanics (a morpho-functional aberration), and thus designate the appropriate solution strategy.  

As our friend Shawn Myszka states, “it is important to respect that the coordination of the eventual movement outcome involves a multi-level integration of the human movement solution”, involving:

  • Behaviors/perception
  • Brain/intention
  • Biomechanics/action

We can see this in the real world every day as we walk down a busy street:  

Either watch how the person in front of you is walking, or pay attention to how you, yourself, are walking.  Along with a host of other mechanical aberrations, chances are there will be some degree of external rotation of one or both feet through the forward swing of the leg, or at touch-down (or both).  This external rotation is the ‘artifact’ – the gap between the intention (in this case walking in a straight line with our feet pointed forward – because why would we purposefully – consciously – walk externally rotated?) and the outcome (in this case walking with our feet externally rotated).  

If we observe closely, we will also see that every individual has a slightly unique way of walking – despite the intention being the same.  The fact that we all solve the innate task of walking in varying ways, but expect that we can all solve a much more complex task the same way is totally illogical.   

Consider the shapes (Figure W, below) of the first couple of steps of a youth soccer player, an elite sprinter, a Major League Baseball player, and an NFL player.  


Figure W: despite the intention being the same (here – accelerate maximally), the outcome shapes of the first few steps of different athletes can be quite different.  

In this case, while all athletes may have a similar intention (i.e. accelerate maximally), the mechanical outcome differs between them. This outcome is ultimately governed by two sets of factors:

  • ‘Internal factors’: the athlete’s personal (organismic) constraints
  • ‘External factors’: the athlete’s technical understanding of the movement objectives, the specifics of the task itself, and the environment in which it is performed

These two sets of factors will lead to athletes creating fairly distinct shapes – even though they may have the same intention.  

For example, ‘scissoring thighs’ will manifest in a variety of differing outcomes, with varying degrees of extension and flexion at varying magnitudes and angles of projection.  

In acceleration, for example, sprint athletes will generally project at lower angles than team-sport athletes, who may not be as technically adept at this skill.  In addition, the shapes of more-experienced, and stronger athletes will differ from less-experienced, weaker athletes, as the increased ability to display force allows for greater angles and magnitudes of projection. 

The above holds true even in a more homogeneous population, as seen in Figure X, below:


Figure X: 2-frame kinogram of 1st step of four elite sprinters 

Each of the above sprinters have run 100m in under 10 seconds (including the world-record holder — can you pick him out?).  Each of them have the exact same intention at this point of the race.  Yet, the outcomes of these intentions are quite different. 

That said – can you recognize the consistency in the rules?

Similarly, the chaos of team sport means that no two movement outcomes will ever look alike – but that does not mean that the intention varies significantly, as it relates to the fundamental shapes. 

Whether you are a winger knocking the ball past a fullback and accelerating around her, a baseball player running out an infield single, a basketball point guard on a fast break, or a running back attacking the line, your torso will almost certainly be oriented forward, you are still forcefully extending your stance-thigh, flexing the free-leg thigh forward and upward, and flexing your free-leg ankle in anticipation of ground contact (Figure Y, below).  


Figure Y: whether you’re a sprinter trying to win a gold medal, a football player trying to hold off a defender, or a baseball player attempting to steal a base, the foundational ‘rules of sprinting’ are essentially the same

Part of our job as coaches is to understand these shapes relative to the entirety of the skill (i.e. in context), the variable bandwidth of them relative to each individual athlete, develop teaching methods that work to maximize the stability of the shapes, and understand the gap between the movement intention and outcome.  

“Make sure that if you identify a problem off the pitch, in the weight room, on the track, in a training scenario, you actually confirm that it’s a genuine issue on the field.”

– Dave Collins, ALTIS Interview, August, 2020

Once an athlete learns to stabilize these few shapes, they become part of their movement repertoire – manifesting in more contextual-demanding situations.  They learn to better connect these shapes together in space and time, in effective and efficient ways. 


COORDINATION

The consideration of an athlete’s shapes at touch-down and toe-off provides coaches with essential information on some of the technical features adopted by players.  However, it is not possible to derive a full understanding of their movement coordination from only these two discrete time-points, since substantial information is still missing within the step cycle.

For us to interpret the totality of the movement task, we need to understand how the player controls their body through the patterns of movement they create in space and time. 

In sprinting, coordination has been defined as the emergent, self-organizing process of pattern formation describing how elements interact with each other –  working together to realize an objective – in this case, ‘sprinting’

In this sense, coordination is viewed from a ‘systems perspective’; i.e. the interaction of component parts of the motor system, and its subsystems (muscles, joints, connective tissue, etc.). 

This is similar to Bernstein’s definition in his text ‘’Dexterity & It’s Development’,​11​ where he described coordination as “overcoming excessive degrees of freedom of our movement organs, that is, turning the movement organs into controllable systems.” 

This begs the question, however, of at what level of the system are we describing? Is it just the athlete system, or does it include the interactions with the information present in the task and environment?  

At the athlete-system level, these descriptions are very ‘motor-centric’ – i.e. they do not include the interaction with the information in the environment – a fact alluded to by Bernstein later in the same text:  

“coordination is realized with the help of so-called sensory corrections that is, the processes of continuous correction of movement based on information”

Following Newell’s lead, we describe coordination as the first step* in becoming a skilled mover – simply learning how to coordinate our limbs in space to create the appropriate shapes required of a task.  Most of us have enough coordination to be able to sprint.  That does not, however, mean we can sprint very fast, or efficiently, within a number of varying environments.  

Simply, the question we are answering through any demarcation is posed by our friend Shawn Myszka:

“What exactly are we coordinating? And what exactly are we coordinating in response to (or with)?”

We can think of this initial coordination stage as the stabilization of fundamental shapes; the development of the underpinning technical properties of a movement. 

To improve efficiency – and performance – however, an athlete has to learn how to control their limbs in both space and time. Less about individual component-parts of the system, control is how these parts interconnect to produce patterns of movement — and this is the topic of the next session.  

*You will recall that Newell’s model differed from earlier models in that it is not unidirectional, as described by Newell:

“An important implication of the preceding analysis is that the concepts of coordination, control and skill reflect an embedded hierarchy. This implies that the early stage of motor learning primarily consists of acquiring the appropriate topological characteristics of the body and limbs. Further practice leads to refined scaling of the relative motions with optimal scaling reflecting a skilled performance. Coordination does not precede control but rather coordination is the organization of control. However, the acquisition of the structural or behavioral unit requires the development of the appropriate set of relative motions.”


In this 10 minute read, Coach Pfaff addresses Myths surrounding 'Knee Drive'

“If one were to spend any amount of time around a track or a sport session where sprinting was involved, the topic of knee lift or knee drive would surely appear in the feedback given to athletes involved. While commendable to note that fast athletes generally exhibit a unique landmark position and movement expression pathway during the recovery phase of gait, how one obtains that position and what the bandwidth is for that position is not as common in discussions. The bandwidth of knee positions and/or movement pathways have inter-linkages with the athlete’s mobility abilities, postural position on that specific phase of the run, power expression levels, coordinative abilities at various speeds, negative interference from previous coaching/training items, and unique sport specific demands that will influence movement tactics. The biggest issue I have witnessed in this mis-step in coaching is the lack of appreciation or understanding of these variables in determining successful movement expression.

Seldom do we see athletes arrive at the knee lift or knee drive position early or too high. It is more common to note lack of, inconsistent, or late arrival trends in most of the athlete populations we work with. A frequent solution for this is the prescription of drills over emphasizing this position or movement path. A second solution attempt is often over-cueing or over demanding the athlete find a way to get there. It is also quite prevalent to see coaches suggesting the solution of increased hip flexor strengthening exercises and schemes. 

“Seldom do we see athletes arrive at the knee lift or knee drive position early or too high. It is more common to note lack of, inconsistent, or late arrival trends in most of the athlete populations we work with.”

Many movement expressions are reflexive in nature and utilize various ECM and elastic mechanisms to do work. It is our findings, that isolatory, slow movement menu items if done to excess, bias athletes to volitional recruitment and mental strategies. For example, if you ask an athlete to do a “high knee lift” drill over 50m, you will see a compromise in movement expressions after about 10-20m, you will note postural compromises and a net decline in force outputs. On the other hand, if you ask an athlete to do a “marching A skip” exercise, they can execute this easily over the 50m distance with very limited reduction in movement expressions. The reason is during the skip, the athlete gets out of the way and lets the free leg rebound to its desired position via these elastic strategies using less biochemical substrates and it is relatively subconscious. The knee lift drill is voluntary, volitional, and demands a totally different energy response. 

Many of our general athletic preparation exercise schemes reinforce volitional, non-reflexive movement expressions. These are done at very reduced horizontal speeds and translations through space so one must question their transfer to sport power rating. 

“Many of our general athletic preparation exercise schemes reinforce volitional, non-reflexive movement expressions.”

Most applied sport physiologists include the following as major contributors to hip flexion:

As you can see there are a lot of players in this action and it is a symphony of contributions that affect both global and specific movement expressions. There are also antagonistic muscle systems that supply stability and coordination of these activities.

  • So can isolatory or biased training plans really address this complexity of movement?
  • How do antagonistic systems inhibit excitatory expression during stabilization moments? 
  • How do upstream or downstream ECM and muscle systems interplay during both general motor literacy tasks and sport specific tasks? 

Many questions left unanswered by dogmatic polemicists on both sides of the argument.”


BREAKDOWN

  • List the variables linked to successful movement expression
  • What are some facets of movement expression contrasted in a ‘high knee lift drill’ versus an ‘A skip drill’?
  • What are your thoughts on the questions posed?

For Coach Pfaff’s references, please see the full series of ‘Myth Busters’ in the Appendix.


  • List some key considerations that will help you with your ability to analyze
  • How do you discern ‘similar’ shapes? What makes a shape ‘ugly‘ or ‘elegant’?
  • Does analyzing shapes help in deciding how you are going to coach? If so – in what way?
  • In our next session, we look at patterns. This is a long session – around 60 minutes – so you might want to take a break halfway through

Prior to continuing on, we encourage you now to take some time to think about what coordination means to you.  

  • How do you define it?
  • How does this definition compare to others’? 
  • Call a Team Talk with a few of your colleagues to chat about this important concept of coordination

  • PDP#1 – consider creating a slide that summarizes the rules and consistent shapes in your sport
  • Repeat the task for patterns and rhythm over the next two sessions

REFERENCES

  1. 1.
    Newell K. Coordination, Control and Skill. In: Goodman D, Wilberg I, Franks I, eds. Advances in Psychology. Vol 27. North-Holland; 1985:295-317.
  2. 2.
    Ayzenberg V, Lourenco SF. Skeletal descriptions of shape provide unique perceptual information for object recognition. Sci Rep. Published online June 27, 2019. doi:10.1038/s41598-019-45268-y
  3. 3.
    Wild JJ, Bezodis IN, North JS, Bezodis NE. Differences in step characteristics and linear kinematics between rugby players and sprinters during initial sprint acceleration. European Journal of Sport Science. Published online July 11, 2018:1327-1337. doi:10.1080/17461391.2018.1490459
  4. 4.
    Bezodis NE, Trewartha G, Salo AIT. Understanding the effect of touchdown distance and ankle joint kinematics on sprint acceleration performance through computer simulation. Sports Biomechanics. Published online April 3, 2015:232-245. doi:10.1080/14763141.2015.1052748
  5. 5.
    Hunter JP, Marshall RN, McNair PJ. Relationships between Ground Reaction Force Impulse and Kinematics of Sprint-Running Acceleration. Journal of Applied Biomechanics. Published online February 2005:31-43. doi:10.1123/jab.21.1.31
  6. 6.
    Wild ., Bezodis ., North ., Bezodis . The biomechanics and motor control of team sport athletes during initial sprint acceleration, PhD thesis in preparation. Published online 2020.
  7. 7.
    Kugler F, Janshen L. Body position determines propulsive forces in accelerated running. Journal of Biomechanics. Published online January 2010:343-348. doi:10.1016/j.jbiomech.2009.07.041
  8. 8.
    Colyer SL, Nagahara R, Takai Y, Salo AIT. How sprinters accelerate beyond the velocity plateau of soccer players: Waveform analysis of ground reaction forces. Scand J Med Sci Sports. Published online October 10, 2018:2527-2535. doi:10.1111/sms.13302
  9. 9.
    Morin J-B, Slawinski J, Dorel S, et al. Acceleration capability in elite sprinters and ground impulse: Push more, brake less? Journal of Biomechanics. Published online September 2015:3149-3154. doi:10.1016/j.jbiomech.2015.07.009
  10. 10.
    BEZODIS IN, KERWIN DG, SALO AIT. Lower-Limb Mechanics during the Support Phase of Maximum-Velocity Sprint Running. Medicine & Science in Sports & Exercise. Published online April 2008:707-715. doi:10.1249/mss.0b013e318162d162
  11. 11.
    Bernstein N. Resources for Ecological Psychology. Lawrence Erlbaum Associates, Inc.; 1996.

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