Saturday, September 29, 2012

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.

There are three joint torques that are responsible for creating upward speed of your whole body when you leave the ground for a vertical jump: hip extension torque, knee extension torque, and ankle plantar flexion torque.

The hip extension torque will create hip extension rotation.  The hip extension rotation will result in angular velocity of the torso body segment and the upper leg segment. The angular velocity of the upper leg segment will create upward linear speed at the hip joint, all spinal vertebral joints, both shoulder joints, both elbow joints, and both wrist joints.  The angular velocity of the torso body segment will create upward linear speed at all spinal vertebral joints, both shoulder joints, both elbow joints, and both wrist joints.  

The knee extension torque will create knee extension rotation.  The knee extension rotation will result in angular velocity of the upper leg segment and the lower leg segment. The angular velocity of the lower leg segment will create upward linear speed at the knee joint, hip joint, all spinal vertebral joints, both shoulder joints, both elbow joints, and both wrist joints.  The angular velocity of the upper leg segment will create upper linear speed at the hip joint, all spinal vertebral joints, both shoulder joints, both elbow joints, and both wrist joints.

Finally, the ankle plantarflexion torque will create ankle plantarflexion rotation.  The ankle plantarflexion rotation will result in angular velocity of the lower leg segment and the foot segment. The angular velocity of the foot segment will create upward linear speed at the ankle joint, knee joint, hip joint, all spinal vertebral joints, both shoulder joints, both elbow joints, and both wrist joints.  The angular velocity of the lower leg segment will create upper linear speed at the knee joint, hip joint, all spinal vertebral joints, both shoulder joints, both elbow joints, and both wrist joints.

When a jump sequence is performed correctly, all of these upward linear speeds are summed (added) together creating whole body upward speed when you leave the ground .  Now it's time look at the vertical jump video clip and see if you can see this principle being used.


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