The Basics 08: Biomechanical Modeling

Up to this point, I have posted some unique ideas related to Biomechanics (see The Basics 01, 02, 03, and 07).  I am not aware of any other Biomechanist who has written about these ideas.  I have also posted some very traditional Biomechanical concepts (see The Basics 04, 05, and 06).  However, I do believe my interpretations of these traditional concepts is unique.  I will finish this introduction to The Basics with the following statement:

No matter what kind of movement (linear or angular) you are performing, the seven basics I have posted so far WILL be a part of every explanation on how to achieve your desired movement outcome.

Of all my ideas, this statement is the most unique aspect of my understanding of Biomechanics.  It implies that their is a key set of Biomechanical Principles that are relevant to the creation of all human movements. To demonstrate my rationale for making this statement, I need to introduce an organizational tool I call Biomechanical Modeling.  As I go through the analyses of many types of movements, I will utilize this tool to show the cause and effect relationship between Biomechanical Principles and desired movement outcomes.  Through these analyses of movement, it will become apparent why I made the statement above.

Click on "read more" to learn about Biomechanical Modeling. 

The Basics 07: The Sum of Joint Linear Speeds Princiiple

In The Basics 06, you learned that the Angular Velocity - Linear Speed Principle tells us that joint angular velocities will cause all points on a rotating body segment, and all points on any body segment attached to a rotating body segment, to move with linear speed.  If two joints are rotating, then the linear speeds of any common points due to each individual joint's angular velocity are summed (added) together.  If a third joint rotates, the linear speed of any common point would increase again.  This  represents The Summation of Joint Linear Speeds Principle.

Click on "read more" to view my description of the Real-World Application of the Sum of Joint Linear Speeds principle to the vertical jumping for maximum height.

The Basics 06: The Angular Velocity - Linear Speed Principle

After reading The Basics 04 and 05, you now know that joint torque, application time of joint torque, and angular inertia are the three modifiable factors that can increase joint angular velocity.  The Angular Velocity - Linear Speed Principle explains the relationship between joint angular velocity and the linear speeds of points that are part of, or connected to, the rotating body segment.

Click on "read more" to learn more about The Angular Velocity - Linear Speed Principle.

The Basics 05: The Angular Impulse - Momentum Principle

If you read the Basics 04, you know that joint torques create joint rotations; and, you would be correct to conclude that stronger joint torques create faster joint rotations (i.e., faster  angular velocities).  But, is joint torque the only factor that creates faster angular velocities?  According, to the Angular Impulse - Momentum Principle, joint torques are not the only factor that creates faster angular velocities.

The Basics 04: Joint Torques

The human angular motion machine uses joint torques to create joint rotations. A joint torque is create by a muscle pulling on body segments on each side of a joint. For example, when the brachialis muscle contracts, it pulls equally on the distal, anterior surface of the humerus (it's origin) and on the coronoid process of the ulna (it's insertion).  If you connect a line between a muscle's origin and it's insertion, you will have drawn the muscle force's line of pull.  Since, the brachialis muscle's line of pull is located anterior to (i.e., in front of ) the elbow joint, a contraction of this muscle will create a torque that results in elbow flexion. The magnitude (i.e., size) of a joint torque is directly proportional to the magnitude of the muscle force (i.e., if muscle force increases, the joint torque increases) and to the perpendicular distance (i.e., the moment arm) from the joint to the line of pull of the muscle (i.e., if the moment arm increases, the joint torque increases).  For the vertical jumping example, three joint torques must be created:

• a hip extension torque 
• a knee extension torque
• a ankle plantar flexion torque

Vertical Jump - Here is what I see

Now that you have had a chance to look at a vertical jump.  Let's compare notes.  This is what I see.

The start times for the hip extension, knee extension, and ankle plantarflexion torques are as follows:

• Hip extension torque starts at time stamp 0:06.439
• Knee extension torque starts at time stamp 0:07.907
• Ankle plantarflexion torque starts at time stamp 0:08.775

I selected the frame at time stamp 0:06.439 as the start of the hip extension torque because the jumper's hip joint and his head begin to move upward.  Now, the hip joint and the head moving upward could be caused by a hip extension torque, a knee extension torque, or an ankle plantar flexion torque.  So, why did I conclude this was the beginning of the hip extension torque?  To answer this question, you have to look at the three joints.  Only the hip joint is moving upward.  The knee joint and the ankle joint are stationary.  If there was an ankle plantarflexion torque all three joints, as well as the head, would all be moving upward.  If there was a knee extension torque, the knee and hip joints, as well as the head, would be moving upward.  The only torque that can cause only the hip joint and the head to be move upward is a hip extension torque.

Vertical Jump - High Speed Video (2)

I noticed on couldn't see the video on my iPad.  I'm trying this link to YouTube instead.

Jump Video on YouTube

Success! It works.  As an added bonus, it plays back with better resolution.  I'll post future videos both ways.  As an embedded video on the blog and as a YouTube link.  Enjoy.

Vertical Jump - High Speed Video

In the post titled "The Basics 03", I provided you the written description of how the human angular motion machine creates a vertical jump.  Watch the video below and see if you can "see" what I described in words.

The Basics 03: The Angular Motion Machine

So, what do I mean when I say the "Human Body is an Angular Motion Machine that creates Linear and/or Angular Motion Outcomes"?

The human body is comprised of joints that function as points of rotation for the bones that are connected at the joint.

• Each wrist joint allows the carpals and the radius and ulna to rotate relative to each other.
• Each elbow joint allows the humerus and the radius and ulna to rotate relative to each other.
• Each shoulder joint allows the humerus and the scapula to rotate relative to each other.
• The thoracic and lumbar spinal joints allow the shoulder girdle (the bones connecting the right and left shoulder joints - 2 scapulae and two clavicles) and the pelvis to rotate relative to each other.
• Each hip joint allows the pelvis and the femur to rotate relative to each other.
• Each knee joint allows the femur and the tibia to rotate relative to each other.
• Each ankle joint allows the tibia and the tarsals to rotate relative to each other

Every joint can allow one to three joint rotations (i.e., angular motions).  These joint rotations are caused by joint torques (i.e., muscle forces pulling on bones on either side of a joint which cause the bones to rotate relative to each other).  Some joint rotations cannot occur because there are no muscles that cross the joint in the correct orientation to cause the joint rotation (e.g., there is no abduction at the elbow because there are no muscles that connect the lateral side of the humerus to the radius and there is no adduction at the elbow because there are no muscles that connect the medial side of the humerus to the ulna).  Even if a joint torque can be created, some joint rotations are not permitted because of bony structural limitations (e.g., the elbow has a maximum extension of approximately 180 degrees; this is because the olecranon process of the ulna collides with the olecranon fossa of the humerus).

The Basics 02: Human Motion Outcomes

Angular Motion vs. Linear Motion: It's determined by the movement of the torso.

If the torso rotates, then the ''body'' is performing angular motion.

Most human angular motion movements rotate around an axis that is parallel to the spine (i.e., a longitudinal axis). When the body is not in contact with the ground, the longitudinal axis is the spine. When the body is in contact with the ground, the longitudinal axis is most often the long axis of the supporting leg. However, the axis of rotation can also be the spine. Examples are throwing a baseball, hitting a golf ball, kicking a soccer ball, and hitting a tennis forehand.

Movements like a somersault, a cartwheel or spiking a volleyball are examples of movements that cause the torso to rotate around different axes. A somersault is a torso rotation around a medial-lateral axis. A cartwheel is a torso rotation around an anterior-posterior axis.  Spiking a volleyball is torso rotation around a medial-lateral axis.

This makes explaining linear motion movements pretty easy. They are movements that do not cause the torso to rotate. Examples are jumping, running, walking, and riding a bicycle.

The Basics 01: How Human Motion is Created

The Basics are posts that present the fundamental concepts related to understanding how human motion is created.

The Basics 01:  The human body is an angular motion machine that creates linear and/or angular motion outcomes.