Gait: A bottom up process (mostly).

"Bottom up" process of running ? Support that it is not "top down".

"These results support a passive arm swing hypothesis for upper body movement during human walking and running, in which the trunk and shoulders act primarily as elastic linkages between the pelvis, shoulder girdle and arms, the arms act as passive mass dampers which reduce torso and head rotation, and upper body movement is primarily powered by lower body movement."
"Angular acceleration of the shoulders and arm increased with torsion of the trunk and shoulder, respectively, but angular acceleration of the shoulders was not inversely related to angular acceleration of the pelvis or arm."

At The Gait Guys have been saying this for years in our writing based off of the research we have consumed that coaching changes in arm and shoulder swing and posture is not the way the system works, or the way to go with coaching running, not without possible ramifications to the athlete by overriding how the system is wired for locomotion. The arm motor patterns are neurologically driven by the lower limbs. It is a bottom up process as we have always said. The arms are largely subservient to the legs, the work as a team, the but quarterback is the pelvis and legs. Obliquity of the pelvis and the antiphasic principles hold true once again in this study. And monkeying with the shoulders and arm swing has a direct effect on the COM, and can thus impact the brains initial choice of optimal step width in any given contact period. Driving more arm movement can over ride inherently hard wired locomotion processes and that can lead to coaching compensatory patterns that should be first driven by lower limb mechanical changes, or coaching recommendations/exercises.
We have discussed that the arms are ballasts, they are there for balance, but also can assist in producing power, but should not be part of the mainstay and dominantly trained process. The process is only "top down" neurologically, meaning the brain is the CPU.

Control and function of arm swing in human walking and running.
J Exp Biol. 2009 Feb;212(Pt 4):523-34. doi: 10.1242/jeb.024927.
Pontzer H1, Holloway JH 4th, Raichlen DA, Lieberman DE.
J Exp Biol. 2009 Mar;212(Pt 6):894. Holloway, John H 3rd [corrected to Holloway, John H 4th].

In this study the authors
" investigated the control and function of arm swing in human walking and running to test the hypothesis that the arms act as passive mass dampers powered by movement of the lower body, rather than being actively driven by the shoulder muscles. We measured locomotor cost, deltoid muscle activity and kinematics in 10 healthy adult subjects while walking and running on a treadmill in three experimental conditions: control; no arms (arms folded across the chest); and arm weights (weights worn at the elbow). Decreasing and increasing the moment of inertia of the upper body in no arms and arm weights conditions, respectively, had corresponding effects on head yaw and on the phase differences between shoulder and pelvis rotation, consistent with the view of arms as mass dampers. Angular acceleration of the shoulders and arm increased with torsion of the trunk and shoulder, respectively, but angular acceleration of the shoulders was not inversely related to angular acceleration of the pelvis or arm. Restricting arm swing in no arms trials had no effect on locomotor cost. Anterior and posterior portions of the deltoid contracted simultaneously rather than firing alternately to drive the arm. These results support a passive arm swing hypothesis for upper body movement during human walking and running, in which the trunk and shoulders act primarily as elastic linkages between the pelvis, shoulder girdle and arms, the arms act as passive mass dampers which reduce torso and head rotation, and upper body movement is primarily powered by lower body movement."