The secret to perfect running arms
There are almost as many running styles out there as there are runners. Yours is unique to your body but little tweaks can make you more efficient. Who wouldn't want to be a little faster and go a little farther with the same effort?
You are a lover, not a fighter
Next time you head out for a run imagine there is a dotted line straight down the middle of your body separating the left and right sides. Now look at your arms as they swing. Are your hands crossing that line? Do you look more like you are boxer fighting an invisible foe?
If so, you are taking useful energy and throwing it away. Try to aim your hands and forearms so they are parallel with your body as they swing. You should look more steam engine than a boxer.
Time to be a clock
Next look at your knuckles. Are they pointed toward the sky? Do they stay close to the same position as you run? If so, you are running with your elbows. Drop your forearms until they are roughly at a 90 degree angle to your upper arms. I'm stressing "roughly parallel" because some people naturally angle their forearms up or down to compensate for their unique body mass distribution. Do what feels right for you as long as your forearms and hands are swinging like clock pendulums as you run.
But too much is too much
Remember, you aren't running the 100 meter dash so you shouldn't feel like you are pumping your arms. We are going for efficiency. At this point, your arms are not crossing the invisible line and are roughly at the right angle but be careful not to overextend them with your new ex-boxer steam engine clock enthusiasm. Don't punch the air with your fists and you shouldn't look like you are trying to elbow people behind you. If your elbows are passing your ribcage in the front you are swinging too far forward. If your wrists are passing the back of your ribcage you are swinging too far backward. Keep it gentle, rhythmic and feeling natural.
But what is natural? After you check on your adjustments, stop paying attention to your arms for a while then check again. As long as they aren't crossing your invisible line, pulled up against your chest like a praying mantis or punching and elbowing people around you may have found your own sweet spot.
And by the way, unclench those fists. That energy should be going to your legs. They'll appreciate it more.