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.
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.