The bats are the only mammals that have managed to perfect flight. They have managed to develop wings, but have started to have a nocturnal life, so in order to be more effective, they have developed their senses like the smell and hearing better, and also developed something new, echolocation. Because the eyesight was not really needed, the bats became almost blind, having very bad eyesight. The echolocation replaced their eyesight though, and it has proven as a very effective adaptation. It is an adaptation that manages to locate objects, food source, be it insects or flowering plants, as well as caves for shelter from predators and cold weather.
you are using your shoulder muscle. The reason you are using this muscle is when you put your arm strait up there is no reason to use a bicep or tricep muscle.
