In this month's "Journal of Biomechanics" some researchers from U. Colorado set out to study the effects of reduced arm swing in elderly adults by comparing them to young adults. Just for the heck of it, they also had the young adults mimic reduced arm swing. No surprise, it increased metabolic demand at the same rate as in the seniors. Their hypothesis was that the increased energy cost was the lack of stability that went along with the decrease in the arm swing.
The arm swing in running becomes even more important. Ask your athletes to run with their hands folded across their chest & watch them weeble wobble across the floor. The arm swing blocks rotation in all 3 planes and helps create kinetic energy in the fascial system.
I believe skipping is a great way to train this effect-and not only in running. There are skips to warmup & enhance throwing, hitting, even swimming.