**Sum of Joint Linear Speeds Principle**. This principle states that the linear speed of any point on the human body is the summation of linear speeds at that point caused by individual joint angular velocities. In general terms, any joint angular velocity will cause all points on a rotating body segment connected at the joint, and all points on any body segment attached to that rotating body segment, to move with linear speed. A second or a third joint's angular velocity will do the same. The linear speed of any common body segment will then be sum (addition) of the linear speeds of segment caused by each individual joint's angular velocity.

Click on "read more" to view my description of the Real-World Application of the Sum of Joint Linear Speeds principle to the Running and Walking Biomechanical Model for Minimum Movement Time.

Specifically, for running and walking, hip extension angular velocity will cause all points on the torso segment, and all points on any body segment attached to the torso segment, to move with linear speed. Knee extension angular velocity will cause all points on the upper leg segment, and all points on any body segment attached to the upper leg segment (i.e., the torso segment), to move with linear speed. Ankle plantar flexion angular velocity will cause all points on the lower leg segment, and all points on any body segment attached to the lower leg segment (i.e., the upper leg segment and the torso segment), to move with linear speed. Since all three joint angular velocities will cause a common body segment (i.e., the torso segment) to move with linear speed, the Summation of Linear Speeds Principle tells us the total linear speed of the torso segment (i.e., the linear speed of the body) is the sum of the torso's linear speed due to hip extension angular velocity added to the torso's linear speed due to knee extension angular velocity added to the torso's linear speed due to ankle plantar flexion angular velocity.

Below is a graphical representation the Sum of Joint Linear Speeds Principle

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