It feels overwhelming at first, and will remain that way until you figure out how best to utilize your time and how to work your lanes efficiently.
After a while you will be able to better judge which lanes to focus on and which you can "ignore".
Will it get easier? Yes and no, the job is always demanding but you get in better shape and learn to prioritize.
If you keep a good diet then yes you will loose weight. If you drink soda and eat poorly then maybe not.
Some people enjoy outbound as its one of the functions If you do your job no one comes to bother you all day. If you hate it speak to hr before just quitting, they might be able to transfer you to a different department. Worst case just put in enough time to put in a transfer to a different department.
Forgot to add, getting trained on equipment helps as well as you get taught to sort noncon and get a break from lanes.
I guess I should also add, if you are really concerned you could go to hr about it now. Just share your concerns that you know warehouse work is by default a physical job but that you have read outbound is considered the most demanding dept in the facility and your just worried that you won't be able to keep up. Be honest with them, tell them you need the job and just don't want to be set up for failure.