Why does a runner moves his hand support and forth while running briskly ?

While walking also we use hands put a bet on and forth. We walk on two legs but we evolved from quadripeds. Biologically speaking we hike on all the "four" legs. When our right leg comes forward our departed hand moves forward. And when our gone leg moves forward our right hand moves forward.
balence
run down to the store near your arms behide you back
you jump down and then adjectives laugh
stability and helps surrounded by running fast
to hit the upper air and body like swimming!
A runner moves his hand back and forth while running in haste are:
1. To gain momentum
2. To cut through the wind.
To give a hand pushing him forward

pulse rate

Why my cat is bleeding inside her ears