Biomechanics Introduction - Linear Kinematics and Introduction to Kinesiology
Welcome back to another article in the series I have been posting on the introduction to Biomechanics. In this article, we are going to move into some more depth with Linear Kinematics and provide a further discussion on Kinesiology, providing details on what it is.
Feel free to head back to part 1 and 2 of this introduction at:
Kinematics is the way we describe motion in physics. It includes two types that are Osteokinematics, which is specifically human movement, and Arthrokinematics which is the movement of joints.
Translation or linear motion includes Rectilinear motion which is a perfect and straight line, this is like movement of someone running forward down a track. While Curvilinear motion is a motion along a curved line or (angular) motion around an axis.
Rotary motion is angular motion and this is similar to the motion of a joint. General Plane motion is combination of rotary and curvilinear motion, this is where we could combine the movement of two joints together, to move something forward.
The motion of an object without regards to the forces that cause motion is Kinimatics.
Measuring and describing motion
Position is described in the XYZ cartesian coordinates which would usually be plotted in a graph, with change in position being Displacement and Distance.
Displacement is a vector quantity describing a change in position in a straight line from the initial position with no regards to path. For example, if you run around an athletics track, start and end point is in the same place, so displacement will be 0.
Distance on the other hand is a Scalar and refers to the sum of all movements in any direction. The full distance around the athletics track, will be instead 400m.
Velocity is a vector quantity ratio of displacement over time, or can be shown in the following formula, where velocity is equal to displacement, over change in time.
v=d/Change In t
Speed is a scalar quantity, and is the actual distance over time.
Velocity is very important for instantaneous speed. We can use the example of a 100m runner where they complete 100m in 10 seconds.
100m Sprinter = 10 seconds
= average velocity 10m per second
With tools like video capture and motion capture, we can see where the athlete is several times a second. From this we can see the speed at different points in the 100m race and decide different things like, does the sprinter need to improve their start, their max speed, or are they getting fatigued toward the end of the race.
Acceleration is a vector quantity demonstrating the rate of change of an object’s velocity. The formula below can describe acceleration where it is equal to change in velocity over change in time.
a = ChangeIn v/ChangeIn t
Remember, you can still be moving at a high velocity and your acceleration may be zero. If your speed is constant, your acceleration will be zero, because there is no change in velocity, while at the same time, if you are slowing down, you acceleration will be negative.
Deceleration is a negative acceleration.
Discussing forces as causing change in acceleration is now the subject of Kinetics.
Objects change momentum or velocity, by forces acting on that object.
Kinesiology is the scientific study of human movement, typically involving the analysis of physical activity and exercise. It is an important part of biomechanics as it helps us define the position of the body and how the body moves.
When discussing how the body moves, we start with the anatomical position, which is the body in standing position with the feet and head straight ahead and the palms of the hands facing forward. Sometimes the anatomical neutral position is used, which is exactly the same as the anatomical position, but the palms of the hands are facing each other.
Now that we know the anatomical position, we can now discuss the anatomical movement descriptors. The descriptors are in pairs as you will see from the list below:
- anterior/posterior - Anterior towards the front of the body, posterior to wards the back
- superior/inferior - Superior is above a reference point, your eyes are superior to your nose, inferior is below the reference point.
- medial/lateral - Medial is towards in middle of the body, lateral is away from the body
- proximal/distal - Proximal is closer to a reference point, while distal is away
- bilateral/unilateral - Bilateral is both sides, unilateral is only one side
- superficial/deep - Superficial is close to the surface, while deep is deep
- cephalic/caudal - Cephalic is towards the head, caudal is towards the tail
- prone/supine - Prone is on your stomach, supine is on your back
Bone movement or Osteokinematics, describe the movement of the skelton in three dimensional space, which are:
- Sagital plan is forward and backwards
- Frontal plan would be out to the side
- Horizontal plan cuts the person in half and includes twisting movements
It is necessary to identify the correct plane of motion, because the plan is dominant and this is how we describe movement
We described how the skeleton movements through different plans. we then refer this to the Anatomical Axis of Motion.
- Longitudinal axis matches up with the horizontal plan, the movement is perpendicular to the axis of rotation. Your arm stretched out and moving in a horizontal motion
- Anterial Posterior matches up with frontal, like your arm flapping
- Coronal movement, is through the sagital plan, like bending at the hips
Any movement in the Sagital plane is referred to as flexion and extension, where extension is a straightening movement, increasing the angle between the joints, eg elbow straightening, flexion is the reverse
Movement in the Anterial Posterior plan is referred to as abduction and adduction movement. Adduction is away from the midline of the body, abduction is towards the midline.
Finally, we need to define external/lateral rotation and internal/medial rotation. External rotation is an outward turning of the anterior surface, while lateral rotation is an internal rotation.
Another big brain dump of information here, but hopefully it has brought a little more clarity on Kinematics as well as Kiniseology.
About The Author
I am a DevOps Engineer, Endurance Athlete, Biomechanics Student and Author. We can all achieve amazing things, it's just a matter of trying, I want to change the world, one run at a time.
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