I continued my exchanges with Paul Boardman, and presented the following:

Some believe that the excessive 'swivel' of the hips is the result of inappropriate arm swing.  However, the foot at top speed among elites is on the ground eight hundredths of a second.  And force actually peaks in about five hundredths of a second.  When I do a SiliconCoach biomech analysis of my sprinters (top guys running about 9.1 meters per second) the actual amplitude of arm swing (during the time the foot is in contact with the ground) is so minimal (nineteen degrees) as to make make me question whether there is any 'time' for awkward swinging arms to cause the trunk to rotate to the point that it would dissipate force.

Here was Paul's response:

Energy dissipated must be so "lost" in doing work on a body or system.  Rotationally, that work is the applied Torque (T) to cause the moment (rotational movement) multiplied by the angular displacement (rotational "distance") (theta) measured in radians through which the body rotates.  Time is not a factor in this calculation.  However, time for rotation may limit the amplitude of the rotation (theta) and therefore require a much larger torque to dissipate a given amount of energy imparted to the system whether from impact or other applied forces.

1.) Consider the source of the Torque that is rotating the hips; is it from the foot impact?  If not, then it is irrelevant to the question.  If energy from the impact is NOT the source of the rotational work done on the hips, then energy from the impact is NOT dissipated by their rotation.  

 Is the applied Torque from the arm swing?  If so, then this brings us back to the closed system where the sum of the moments must be zero.  If the hip rotation is counter (opposite) to the arm swing then the Torques are internally generated and their net sum is zero to maintain the rotational "equilibrium" of the body about that axis! The vertical axis (horizontal moments); from what I can tell from your description. These countering and balancing moments need have no effect on the foot impact energy transfer (nor the energy storage and return in the stretch reflex).

2.) Now, if you are saying that the integrity of the elastic chain for stretch reflex is compromised by (say for instance) internal loss of tension in the core due to rotational deviation in the horizontal plane (about the vertical axis), then I suppose that could be a factor. So to speak a compromise in the energy storage and return mechanisms brought about by alterations in the orientation of the body as a whole with respect to the plane of action through which the impact energy is stored and returned.  (sounds guru-esque; but its not.)

 Contrarily, if you are saying that some of the impact energy is utilized to torque the hips counter to the arm swing due to poor running mechanics (active posture?), then the question I would ask is; "do the hips snap back in time with the stride impact duration?  In other words, the core rotations driven or forced by the impact might just be part of the holistic energy storage in the body and whatever energy dissipated in the hip-arm swing isn't necessarily dissipated at all IF the arms and hips return with the same timing as the stride impact. That rotational deviation and return could then just be part of the energy storage and return of the system as a whole.  I can't visualize a hip-arm swing cycle that would NOT be in cycle time with the stride impact and return!  I keep seeing a "spastic" collapse of the runners' core stability and a humorous and embarrassing collapse of the entire running mechanics system with the result being a hazardous impact and slide along the track.......... :)

 3.) Finally, any unnecessary rotation might be the result of a weakness in the athlete's core ability to withstand the tensions of high impact.  Certainly, even elite athletes have limits. Some energy might NOT get returned under those stipulations and that would lessen the efficiency of the stretch-reflex in maintaining the driving ground contact force necessary to sustain velocity.  But!  That loss (and I would think it would not be substantial) would simply have to be made up with each stride in the tension production and transmission in the lower extremities.  A lower efficiency of energy return would be taxing over the long haul and is a weakness that the athlete must try to correct with appropriate weight training and plyometrics, of course.

Ken Jakalski