How can I animate the arms without the torso staying still?

[GIEGO04 (GEGO)]

I find a game where when equipping a weapon, the torso still does the running animation how he does that?

• The Game I Found :
  robloxapp-20220807-0722070.wmv

• My Game :
  robloxapp-20220807-0722441.wmv

And no, I didn’t animate the torso in my idle animation.

It’s practically just that.

Please Help