Antonyms for "puts one's feet up" include staying active, working hard, being on the go, and keeping oneself busy. These phrases indicate an opposite action to the act of stopping work or relaxing. Other antonyms to "puts one's feet up" involve being tense, anxious or restless, like "sitting on the edge of your seat" or "on the edge of your chair" that shows an opposite behavior to reclining or lounging easily. So, if you must keep going, remain alert keep active, and stay on top of it, if you want to avoid putting your feet up and unwinding.