Pump it Up

Pumping your arms, according to Mike Belfiore,  ensures that your arms counterbalance with your legs. This helps improve your running form an keeps everything in sync. Without pumping your arms, your legs would be working against your arms instead of with them!

Now just because your arms are working by swinging, doesn't mean they are supposed to be stiff and adding an extra workout on your body. Doing this will surely slow you down. One way to be sure you're still pumping your arms but not giving yourself an extra workout is make semi-loose fist with your elbows bent. If this doesn't work for you, you can always keep your hands straight while keeping your elbows bent.

Hopefully the mystery behind the arm has been solved and you'll now able to pump those babies with confidence. Your body will in sync ensuring your legs and arms are working together.