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.

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The Angular Velocity - Linear Speed Principle states the following:

If you increase a joint's angular velocity, any point that is part of, or connected to, the rotating body segment will experience an increase in linear speed.  In addition, the greater the radius of rotation to any point that is part of  the rotating body segment, the greater the linear speed of that point.  Finally, points that are connected to, but not part of, the rotating segment will move with the same speed as the attachment point with the body segment.

Note: radius of rotation is defined as the distance from the joint to the point of interest on the rotating body segment.

Real-World Example (Vertical Jumping)

When a jumper extends his knees during the execution (upward) phase, a knee extension torque causes a knee extension angular velocity.  This knee extension angular velocity causes all points that are part of the rotating body segment (the upper leg including the hip joint), or connected to the rotating body segment (the torso and the arms), to rotate around the joint.  The points on the body segment closer to the knee joint rotate with the smallest linear speeds.  The points on the body segment farther away from the knee joint (i.e., the hip joint) will have the greatest linear speeds.  The knee extension angular velocity will also cause all joints that are connected to the hip joint to move at the same linear speed as the hip joint.  This includes all of the spinal vertebral joints and all of the upper extremity joints (shoulders, elbows, and wrists).

To put as simply as possible, when the knee joint extends, the hip joint and all joints attached to the hip joint (spinal vertebral joints and all upper extremity joints) will move at the same linear speed.