For Coaches Biomechanics 101

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ACoach78

Coach
Coach
Feb 22, 2007
112
USA
From the responses in the vaulting thread, I thought that I'd begin a series of posts that talks about basic biomechanics and will provide some examples of breaking down the mechanics of some skills. This post will focus on terminology.

Biomechanical analysis is divided into two components. First, there is the analysis of movement through description. This is called kinematics. Next, there is the study of the forces that causes motion. This is known as kinetics.

Kinematics = Describing motion

Kinetics = What is causing the motion (forces)


Before I get into further discussion on these two concepts, let's talk briefly about scalar v. vector quantities. This is important to understand as I discuss the terms associated with kinematics and kinetics.

A scalar quantity is a quantity that is just a magnitude (how big? how far?). A vector quantity is a quantity that has a magnitude and a direction associated with it.

For example, the definition of speed is just distance/time. There is no direction associated with it. Speed is an example of a scalar quantity.

In contrast, velocity is a vector quantity. Velocity has a direction associated with it. For example, when I was discussing the velocity after contacting the table, I discussed the "vertical velocity." If I had just said "velocity" and did not indicate a direction (vertical or horizontal), my terminology would have been improper. To go even further, I should have said "positive" vertical velocity so that you knew that the gymnast was moving in the positive (upwards) vertical direction. By just stating "vertical velocity," it could very well have been negative (in which the gymnast would be going downwards). Of course, as coaches, I knew that you understood what I was talking about. But, just stating vertical velocity with no "positive" or "negative" associated with it would not "fly" with the science community, especially if they were not knowledgable of gymnastics.

So, let's talk briefly about some key kinematics terms.

Position - Position is just where you're at in space. In biomechanics, we break
everything into (x,y) coordinates for 2-dimensional analysis and
(x,y,z) coordinates if we're analyzing in 3-dimensions. This is how
we track movement. Basically, the fancy software we use
references everything into a grid system and as the body moves,
those coordinates obviously change. That's the basics.
For 2-dimensions, the math is actually pretty easy, while it gets
nastier for 3-dimensions. Fortunately, the software does all of that
these days.

Displacement - This refers to a change in position in a particular DIRECTION.
So, displacement is a vector. It has a direction associated with
it. (i.e. positive horizontal displacement) The equation is:

final position - initial position (change in position)


Distance is a scalar quantity. It's just a magnitude (how far?)
with no regard for direction.

Here's an example. If I run from one end of the football field to
another, my displacement would be 100 yards. A straight line
from start to finish is always 100 yards. However, my distance
could be well beyond that if I ran a zig-zag the entire length of
the field and not a straight line. So, maybe now I've run 200
yards. Make sense?

Displacement is always measured in meters by the way.


Velocity - This refers to how long it took you to change position. So, there is
a time component. The equation for velocity is the following:

displacement / change in time

So, if I ran in a straight line for 60m and it took me 10s, my
velocity would be 6 m/s. So, in a single second, I was able
to cover 6 meters. (My initial position was 0 and my initial
time was 0)


Acceleration - This refers to how long it took to change in velocity. Or, in other
words, it is the rate of change of velocity. So, did I speed up or
slow down?

change in velocity / change in time

So, if I were moving at a constant velocity of 6 m/s at the start
and increased to 8 m/s after 10s, then my acceleration would
be 0.2 m/s/s.

Velocity at finish = 8 m/s
Velocity at start = 6 m/s
Change = 2 m/s

Time at finish = 10/s
Time at start = 0
Change in time = 10s

So, 2 m/s / 10s = 0.2 m/s/s

This would mean that during each second, I increased my velocity
by 0.2 m/s. So, this is the acceleration or the rate of change in
velocity. And, again, acceleration can be positive or negative and is direction dependent. So, if I throw a ball up into the air, it may be going upwards, but it will slow down as it approaches the top before it comes back down. So, the ball is actually experiencing a negative acceleration. It is slowing down even though it is moving in a positive direction. On the flip side, it will actually be positively accelerating on the way down even though it is moving in a negative direction.

Now, you don't have to be able to calculate this to apply it to gymnastics coaching. But, understanding the concepts is important when you happen to come upon a research article that is actually quantifying these things. You will have the tools to understand the concepts being talked about and you'll be able to put them into coaching concepts and a practical sense.

So, these terms all describe what the body is doing. They are kinematic variables. In my next post, I'll talk more about kinetics. Then, we'll get into angular kinetics and angular kinematics, projectile motion, and eventually move into more gymnastics-specific content.

Let me say, however, that most gymnastics skills are extremely complex and extremely hard to analyze. Few skills have been analyzed because of their complexity. So, if you ask me to analyze a skill, I cannot fully guarantee that I can completely explain why a particular skill is/has to be performed a particular way, but I will do my best to provide some insight and a mechanical rationale.
 
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ryantroop

Member
Sep 21, 2008
423
Illinois
I dont think anyone would ask you to break down a skill...

Ask most physicysts and we shouldnt be able to twist while in air.

Im with you so far, Im curious to see how you apply your understanding to coaching - the human body is capable of so much, it's a wonder we don't see multiple technuiqes for similar skills internationally... I think we did in the past (but not so much anymore), and that's part of what used to make everything exciting at the olympics (for me, anyway), but that's an entirely different topic.

Good stuff, keep it coming!
 

ACoach78

Coach
Coach
Feb 22, 2007
112
USA
Alright, well let's talk about the angular (rotational) equivalents to the linear kinematic concepts that I discussed previously.

Angular Displacement

Basically, this is nothing more than the change in angular position. Let's imagine that I have a pendulum and it swings from say a 9 o'clock position to a 3 o'clock position and stops at 6 o'clock. If 9-3 is 180 degrees, what is the angular displacement?

Even though the pendulum went all the way to 3 o'clock and then came back to 6 o'clock, the angular displacement is only 90 degrees because it's a matter of "what is the displacement from where it started to where it precisely finished" with no regard to how it got there.

Now, if we were looking at angular DISTANCE, the distance it covered would be 270 degrees because it traveled from 9 to 3 (180 degrees) and from 3 back to 6 (90 degrees).

I'm using the clock reference since I don't have a picture for you to observe.

Since displacement is a vector (magnitude + direction), we need to classify its direction in some capacity. This is accomplished by referencing the clock of all things. Typically, the counter-clockwise direction is denoted as being positive (+) while the clockwise direction is negative (-).

So, in my example, if I moved from 9 to 3, I would be rotating in a counter-clockwise (+) direction. When I arrived at 3 and went back to 6, I would be moving in a clockwise (-) direction. Now, with that said, since my displacement was really from 9 to 6, I would say that pendulum was angularly displaced in a counter-clockwise (+) or positive direction 90 degrees.

Displacement is measured in degrees, radians, or revolutions. Typically, in science you tend to see the radian used most often. A radian is equal to 57.3 degrees.


Angular Velocity

Angular velocity is nothing more than the change in angular position (displacement) / change in time. It represents how long it took to change position over a given period of time and in which direction.

Angular speed is the change in distance / time.

The typical measure of angular velocity is degrees/second, radians/second, revolutions/second, or revolutions per minute (RPM).

So, let's stick with my clock example...

If the second hand of a clock moves from the 12 to the 6, let's calculate the angular velocity. For simplicity, we'll keep everything in degrees. I think most can relate to this unit, best.

First off, how far did it travel in degrees? 180 degrees
Over what time frame did this occur? Well, it's the second hand and from 12 to 6, we're talking about 30s.

Now, it displaced in a clockwise direction, so it's really a -180 degrees. So, the displacement = -180 and the change in time is 30s.

So, -180 degrees / 30 seconds = -6 degrees/second (angular velocity)


Angular Acceleration

Now, just like the linear acceleration, angular acceleration is nothing more than the change in angular velocity / change in time. So, again, it's the rate of change of angular velocity. Did the rotating object speed up or slow down in its rotation?

Angular acceleration is measured in either degrees/second/second, radians/second/second, or revolutions/second/second.

Let's say that the clock is malfunctioning and its angular velocity changes from -6 degrees/second to -10 degrees per second before it gets to the 6. So, the time has not changed, only the angular velocity.

So, the change in angular velocity is -6 deg/s to - 2 deg/s over a 30s time period.

So, -2 degs/sec - (-4) = +2 degs/second / 30 seconds

= .066 deg/sec/sec

On the way from the 12 to the 6, the second hand of the clock accelerated
.066 deg/sec/sec. Since it was moving in a negative (clockwise) direction and it was a positive acceleration, this indicates that the second hand is experiencing a decrease in angular velocity or it is slowing down slightly.

(Hopefully, I didn't get that backwards...this always confuses me a bit and I have to think about it for a second)

Anyway, I'm just trying to toss out these terms so that when I start explaining skills, you'll understand what I'm talking about conceptually.

In my next post, I'll talk about the relationship between angular and linear acceleration.
 

dunno

Well-Known Member
Coach
Former Gymnast
Proud Parent
Club Owner
Apr 28, 2009
9,292
From the responses in the vaulting thread, I thought that I'd begin a series of posts that talks about basic biomechanics and will provide some examples of breaking down the mechanics of some skills. This post will focus on terminology.

Biomechanical analysis is divided into two components. First, there is the analysis of movement through description. This is called kinematics. Next, there is the study of the forces that causes motion. This is known as kinetics.

Kinematics = Describing motion

Kinetics = What is causing the motion (forces)


Before I get into further discussion on these two concepts, let's talk briefly about scalar v. vector quantities. This is important to understand as I discuss the terms associated with kinematics and kinetics.

A scalar quantity is a quantity that is just a magnitude (how big? how far?). A vector quantity is a quantity that has a magnitude and a direction associated with it.

For example, the definition of speed is just distance/time. There is no direction associated with it. Speed is an example of a scalar quantity.

In contrast, velocity is a vector quantity. Velocity has a direction associated with it. For example, when I was discussing the velocity after contacting the table, I discussed the "vertical velocity." If I had just said "velocity" and did not indicate a direction (vertical or horizontal), my terminology would have been improper. To go even further, I should have said "positive" vertical velocity so that you knew that the gymnast was moving in the positive (upwards) vertical direction. By just stating "vertical velocity," it could very well have been negative (in which the gymnast would be going downwards). Of course, as coaches, I knew that you understood what I was talking about. But, just stating vertical velocity with no "positive" or "negative" associated with it would not "fly" with the science community, especially if they were not knowledgable of gymnastics.

So, let's talk briefly about some key kinematics terms.

Position - Position is just where you're at in space. In biomechanics, we break
everything into (x,y) coordinates for 2-dimensional analysis and
(x,y,z) coordinates if we're analyzing in 3-dimensions. This is how
we track movement. Basically, the fancy software we use
references everything into a grid system and as the body moves,
those coordinates obviously change. That's the basics.
For 2-dimensions, the math is actually pretty easy, while it gets
nastier for 3-dimensions. Fortunately, the software does all of that
these days.

Displacement - This refers to a change in position in a particular DIRECTION.
So, displacement is a vector. It has a direction associated with
it. (i.e. positive horizontal displacement) The equation is:

final position - initial position (change in position)


Distance is a scalar quantity. It's just a magnitude (how far?)
with no regard for direction.

Here's an example. If I run from one end of the football field to
another, my displacement would be 100 yards. A straight line
from start to finish is always 100 yards. However, my distance
could be well beyond that if I ran a zig-zag the entire length of
the field and not a straight line. So, maybe now I've run 200
yards. Make sense?

Displacement is always measured in meters by the way.


Velocity - This refers to how long it took you to change position. So, there is
a time component. The equation for velocity is the following:

displacement / change in time

So, if I ran in a straight line for 60m and it took me 10s, my
velocity would be 6 m/s. So, in a single second, I was able
to cover 6 meters. (My initial position was 0 and my initial
time was 0)


Acceleration - This refers to how long it took to change in velocity. Or, in other
words, it is the rate of change of velocity. So, did I speed up or
slow down?

change in velocity / change in time

So, if I were moving at a constant velocity of 6 m/s at the start
and increased to 8 m/s after 10s, then my acceleration would
be 0.2 m/s/s.

Velocity at finish = 8 m/s
Velocity at start = 6 m/s
Change = 2 m/s

Time at finish = 10/s
Time at start = 0
Change in time = 10s

So, 2 m/s / 10s = 0.2 m/s/s

This would mean that during each second, I increased my velocity
by 0.2 m/s. So, this is the acceleration or the rate of change in
velocity. And, again, acceleration can be positive or negative and is direction dependent. So, if I throw a ball up into the air, it may be going upwards, but it will slow down as it approaches the top before it comes back down. So, the ball is actually experiencing a negative acceleration. It is slowing down even though it is moving in a positive direction. On the flip side, it will actually be positively accelerating on the way down even though it is moving in a negative direction.

Now, you don't have to be able to calculate this to apply it to gymnastics coaching. But, understanding the concepts is important when you happen to come upon a research article that is actually quantifying these things. You will have the tools to understand the concepts being talked about and you'll be able to put them into coaching concepts and a practical sense.

So, these terms all describe what the body is doing. They are kinematic variables. In my next post, I'll talk more about kinetics. Then, we'll get into angular kinetics and angular kinematics, projectile motion, and eventually move into more gymnastics-specific content.

Let me say, however, that most gymnastics skills are extremely complex and extremely hard to analyze. Few skills have been analyzed because of their complexity. So, if you ask me to analyze a skill, I cannot fully guarantee that I can completely explain why a particular skill is/has to be performed a particular way, but I will do my best to provide some insight and a mechanical rationale.

most gymnastics skills may be complex but are very easy to analyze. thousands of skills have been analyzed because of their complexity and broken down into small part components. it seems with the amount of knowledge you are armed with, you should be able to explain insight and biomechanical rationale to a reasonable degree. gymnastics is not as intimidating as forensic science but a bit more complicated than most sports.
 

blantonnick

Coach
Coach
Former Gymnast
Judge
Club Owner
Apr 17, 2007
174
USA
'Analysis to Paralysis' - A very pertinent metaphor for the utilisation of biomechanics in gymnastics. While I do feel there is a place for Biomechanical analysis in gymnastics, I do feel that sometimes coaches get involved into biomechanics for a 'tell all - end all' prerequisite for teaching.

I coach very close in proximity to one of the leading biomechanical universities in the world - Loughborough University in the United Kingdom. Some of the research that is specifically studied there in relation to gymnastics is very profound. The University is pioneering a degree catered for gymnastics research, a mecca if you will for sports science directly pioneered for gymnastics biomechanics.

Some of the papers they have produced are certainly interesting from a gymnastics perspective, however as a coach, there are certain principles that can infringe on the overall pedogological approach from a coaching standpoint. One example of this infringement is a paper written that discusses horizontal bar dismounts and the ideology that a 'Wind up' or 'Chinese Tap' into dismounts is less efficient from a biomechanical standpoint than a traditional giant swing.

This paper is fascinating reading, as well as being a perfectly researched article. However, as a coach there is a deeper meaning for teaching a 'Chinese Tap' before a dismount. One being the timing of this type of tap swing allows a gymnast a greater degree of maximising the opportunity of hitting an optimal release point at the end of a routine when fatigue and even dizzyness may be an accompanying factor in performance.

This type of contradiction occurs frequently in biomechanical research in relation to gymnastics performance. Coaches must be careful on how much research they allow into their coaching pedogogy.

I am in no way advocating that biomechanics are not important to gymnastics - in fact quite the contrary. What I am stating is that 'Analysis to Paralysis' does occur and coaches must be privy to where the infringement may interrupt practical application of technique into day in and day out performance.
 

Valentin

Coach
Coach
Nov 12, 2007
376
USA
That is a good point blantonnick, and i agree with you on the fact that people need to questions all the time what they read, and critically analyze its value.

Regarding that paper about the giant however i think you might have miss interpreted its significance or conclusion. The paper posses the question
"Which is the better technique?"
The answer draw from the their examination is
"If only the maximum amount of angular momentum is the criterion, then the
global optimum solution is better than the local optimum solution. The global solution is
closest to the traditional circling technique. Why then might gymnasts favour the 'scooped'
technique? Perhaps more strength was needed, or perhaps the total energy cost for the
gymnast was higher for the global technique. Interestingly the gymnast was found always to be working well within his strength limits in the previous calculations and only on the final action leading up to release did the joint torques approach values close to the gymnast's maxima. The simulations were run again with the gymnast's strength reduced by 25%. This time the global optimum solution was found to be the scooped technique rather than the traditional technique. It would therefore appear that both techniques are good and perhaps when a gymnast is tired towards the end of the routine there is a case for using the scoopedtechnique should be as effective at generating angular momentum. For example, the principle of 'staying as long for as long as possible' on the downswing does not appear to have been adhered to. Closer examination of the scooped technique however shows that extra horizontal acceleration by the gymnast as he passes over the bar, bends the bar more in the backwards direction and moves his mass centre further from the neutral bar position than the body shape alone would indicate. Simple mechanics can therefore sometimes"

Anlong with that they mention that
" whilst it would be possible to determine the best possible technique for an individual gymnast, it is likely that the two techniques already in use are individual interpretations of optimum solutions and the absolute best solution is probably going to remain a theoretical one."

Thus the authors conclusions point out that really the technique of choice is gymnast dependent, and i think dismount dependent as well, because most tend to use the regular giant technique in doing a triple back dismount, however just about everyone uses the scooped technique to do a double double.
Anyways my point is critical analysis is the coaches best friend when reading biomechanical literature. Take from it what you need and apply it in a way to work for you and your gymnast.


http://www.chalkbucket.com/forums/members/blantonnick.html
 

Geoffrey Taucer

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Jan 21, 2007
4,075
Baltimore, MD
Country
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Thus the authors conclusions point out that really the technique of choice is gymnast dependent, and i think dismount dependent as well, because most tend to use the regular giant technique in doing a triple back dismount, however just about everyone uses the scooped technique to do a double double.
A very good point; after all, looking at the two best triple backs I've seen off high bar, one was from a chinese tap (Legendre) and one was from a regular giant (Liuken)
 

blantonnick

Coach
Coach
Former Gymnast
Judge
Club Owner
Apr 17, 2007
174
USA
Regarding that paper about the giant however i think you might have miss interpreted its significance or conclusion. The paper posses the question
"Which is the better technique?"
The answer draw from the their examination is
"If only the maximum amount of angular momentum is the criterion, then the
global optimum solution is better than the local optimum solution. The global solution is
closest to the traditional circling technique.
Valentin, I did not misinterpret the significance nor the conclusion of the paper. It is very obvious from the statement above that the global optimum solution - meaning the traditional circling technique - is better than the local optimum solution, if one only takes into account maximum amount of angular momentum. <---This is the point I am referring to...

In that case, that principle could be an infringement on coaching principles from a pedogological standpoint, something that the authors understand and went on to further clarify in their explanation of the paper. I am not trying to state that the authors are one sided in their approach which is something that you may think I was trying to imply. I have read many of the papers that Loughborough produces as well as being very close to one of the researchers at the facility, once again they are very involved with the sport of gymnastics and understand the positives and negative consequences of some of their research on practical application.

The prime biomechanical conclusion was that the traditional circling technique whilst performing giants into dismount can provide the most amount of angular momentum. That conclusion is what I am warning others of with regards to biomechanical principles...They are not 'a tell all end all' reference for teaching.
 

Valentin

Coach
Coach
Nov 12, 2007
376
USA
Sorry blantonnick, i didn't mean draw conclusions for you, i should have worded my post better.

My conclusions to that paper is that
Its is really dependent on the reader to how the interpret the paper. My interpretation is purely on the facts of the paper.
1- This paper draws its results from the optimisation model of 1 gymnast, based on his athropometrics
2- It suggests that for this particular gymnast given his athropometrics and strength the tradidional giant is the most effective technique to generate angular momentum (the primary critical mechanical factor form performing high level dismounts), but its not necessarily so for everyone.
3- The authors state that if the gymnast was a little weaker the scooped giant is definitely the technique of choice.

What i as a coach get from reading this paper is that teaching a scooped giant to weaker gymnasts can help them in working their dismounts, the type of giant used to dismount should be considered on an individual basis. Given the way the CoP is going routines are going to be a little shorter (as only 8 elements count), thus maybe won;t be as tiring (maybe not). The scooped giant at the end of a routine has significant advantages because it requires less energy, and it can be just as effective.

That is what i gather when read that paper, and not that one technique is better than the other. For those interested this is the paper in questions "Swinging in Gymnastics".
 
Last edited:

ACoach78

Coach
Coach
Feb 22, 2007
112
USA
'Analysis to Paralysis' - A very pertinent metaphor for the utilisation of biomechanics in gymnastics. While I do feel there is a place for Biomechanical analysis in gymnastics, I do feel that sometimes coaches get involved into biomechanics for a 'tell all - end all' prerequisite for teaching.

I coach very close in proximity to one of the leading biomechanical universities in the world - Loughborough University in the United Kingdom. Some of the research that is specifically studied there in relation to gymnastics is very profound. The University is pioneering a degree catered for gymnastics research, a mecca if you will for sports science directly pioneered for gymnastics biomechanics.

Some of the papers they have produced are certainly interesting from a gymnastics perspective, however as a coach, there are certain principles that can infringe on the overall pedogological approach from a coaching standpoint. One example of this infringement is a paper written that discusses horizontal bar dismounts and the ideology that a 'Wind up' or 'Chinese Tap' into dismounts is less efficient from a biomechanical standpoint than a traditional giant swing.

This paper is fascinating reading, as well as being a perfectly researched article. However, as a coach there is a deeper meaning for teaching a 'Chinese Tap' before a dismount. One being the timing of this type of tap swing allows a gymnast a greater degree of maximising the opportunity of hitting an optimal release point at the end of a routine when fatigue and even dizzyness may be an accompanying factor in performance.

This type of contradiction occurs frequently in biomechanical research in relation to gymnastics performance. Coaches must be careful on how much research they allow into their coaching pedogogy.

I am in no way advocating that biomechanics are not important to gymnastics - in fact quite the contrary. What I am stating is that 'Analysis to Paralysis' does occur and coaches must be privy to where the infringement may interrupt practical application of technique into day in and day out performance.
My apologies for not continuing with this post. I will attempt to in the near future. I have been busy with life - working on a thesis, studying for a certification examination, coaching, attending conferences, planning to intern at a performance enhancement facility, etc.

Secondly, I agree with you blantonnick. With that said, I'd contend that many coaches without a specific sport science or sport pedagogy degree are not exposed to the basic tenets of biomechanics and teach as they were taught with a limited understanding of scientific principles. Thus, my goal was simply to provide the basics of biomechanics and then offer up some specific examples to allow coaches from a variety of backgrounds a little insight into how to break down and begin to understand skills.

Once you have that background, you have to be able to distinguish the usefulness and/or practicality of the research. But, that is true of all research, whether its the modeling of gymnastics skills or something else. Every study has limitations and it is important to read related studies and use the information along with that of anecdotal "research" from personal experience to determine whether or not the study offers anything useful.

Again, I apologize for my failure to continue on with this post. I will do my best to do so in the near future.
 
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