My girlfriend is a nurse. 7-7 shifts, days and nights, it alternates.
She’s gotten used to it, isn’t sore from the work anymore. Make sure you have good shoes. Do some research, ask your coworkers - having the right shoes makes a big difference when you’re on your feet for 13-14 hours straight. Add some electrolytes to your water bottle. Doesn’t need to be high in sugar unless you also aren’t eating much too. Moving and standing and being active all day takes energy and hydration. Having some simple electrolytes and enough calories will also make a huge difference in how you feel at the end of the day. You’re basically on a 12 hour hike every shift.