A self-reported group of old runners can apparently walk more efficiently than a self-reported group of old walkers...but the runners were fit enough to run and sustain running to begin with!!
So older people who were fit enough to sustainably run for 6+ months were fitter than older folks who (were possibly not as fit) but choose to walk?
Horrible study...randomly assign fit older people to one or other group, let them run or walk for 6+ months - measure. Reverse the groups again measure.