This month's theme speaks for itself. The subject choice is yours as long as it broadly fulfils the definition of macro photography. Usually the subject or part of the subject is very small, with the image you take being bigger than life size.
Strength can mean different things to different people. Not just the weightlifter on his podium, but sometimes the tiny ant carrying three times its weight, or a small umbrella, bravely holding its own against the wind. What comes to mind when you think of strength?