When we run.........?

Raise the arm that's opposite the raised leg. This is for better balance, joint-order, inertia, point at takeoff and will help you run better, it's a more advanced movement that same arm-same leg.

People normally are pumping the opposite arm of the foot being raised. Most animals do. I'm sure it has to be a natural phenomena that relates to balance. Horses can be taught to run left front/left back, right front/right back. It looks kinda strange, and it takes a lot of time and patience by the horse trainer.

Most people run with their one arm up and the opposite side of the body's leg up and vice versa. I think its better momentum when you run like that because you are basically working the muscles on both sides of your body at the same time and its easier for you to run that way.

I think I lift my right arm when my left foot is raised, so opposites. I think it all has to do with balance and momentum while running or walking.

Usually it's the opposite hand that's raised. My guess is for balance

opposite. Its all about balance. Your arm works as a counter weight for your foot. Try running with each foot/hand in sync and see how weird it feels.

We have natural, instinctive "opposite" arm and leg movements. It provides the body with balance. Try to walk or run deliberately moving same side arm and leg...It's like being a waddling penguin. - very unnatural!

Its on the opposite. Its mainly for balance. Your body loves balance so you do it without noticing. Next time check that the faster you run, the more your arms move. If you move your arms more, your legs try to go faster. Its all about balance

stand up straight, relax your shoulders. when you walk the opposite arm and leg go forward. It is a matter of balance. it is the same when you run. If you had the same arm and leg forward you would twist and not be able to run forward in a straight direction.

if you don't concentrate on moving your arms they will swing correctly.

It's to balance our speed. That way our body is moving at a relatively constant speed, as opposed to a jerky one that would really not be good at all for running.