FACTS ASSOCIATED WITH THE CONCEPT OF
THE KINETIC LINK PRINCIPLE














Kinetic link principle is applicable to physical activities in which the goal is to
achieve maximum angular velocity of a distal segment (e.g., throwing, and striking
activities).
Proximal segments of the human body are more massive than distal segments and
therefore tend to have a greater moment of inertia.
Muscles that are attached to proximal segments tend to be bigger and stronger than
muscles attached to distal segments.
Relatively large and strong muscles that are attached to proximal segments contract to
increase the angular velocity of these segments.
Even though stronger muscles are attached to proximal segments, it is difficult to
produce high angular velocity in these segments because of their relatively large
moments of inertia.
After muscular contraction achieves maximum angular velocity in proximal
segments, these muscles relax.
Sequentially, muscles attached to more distal segments should initiate contraction at
the point of maximum angular velocity and zero angular acceleration of the preceding
segment.
It is difficult for muscles attached to distal segments to apply large torques to these
segments, because of the a) smaller size and strength of these muscles and b) force
velocity relationship of muscular contraction (i.e., as velocity of contraction
increases, the potential force of contraction decreases).
Muscles attached to distal segments may only be able to contribute little or no torque
because of an ever increasing angular velocity of more distal segments.
In addition to the angular velocity generated by torques associated with muscular
contraction, there is an increase in angular velocity from proximal to distal segments
because of the principle of conservation of angular momentum.
When more massive proximal segments (i.e., segments with relatively large moments
of inertia) slow down, they give up their angular momentum to less massive distal
segments (i.e., segments with relatively small moments of inertia).
If angular momentum is conserved from the more massive proximal segments, this
results in a dramatic increase the angular velocity of the distal segments.
Maximum angular velocity of the distal segment should be achieved at a critical point
in time (e.g., release in throwing activities and impact in striking activities).
From a coaching perspective, this kinetic link chain of events may be temporally out
of sequence and the coach may suggest that the athletes “timing is off.”
Dr. Eugene W. Brown
Department of Kinesiology
Michigan State University
Kineticlink.doc