If you work up the enthusiasm or courage to do something, you succeed in making yourself feel it. Your creative talents can also be put to good use, if you can work up the energy
If you work yourself up, you make yourself feel very upset or angry about something. She worked herself up into a bit of a state Don't just lie there working yourself up, do something about it. see also worked up
If you work up something such as a piece of writing, you spend time and effort preparing it. I sketched the layout of a prototype store and worked up a business plan
If you work up a sweat or an appetite, you make yourself sweaty or hungry by doing exercise or hard work. You can really work up a sweat doing housework