They are two commonly used words in English, so here is a worksheet on differentiating the use of the nouns regime and regimen–two nouns that look a lot alike, but mean different things, indeed quite different things. So, if you want to start with a new exercise regimen, don’t call it a regime, which better applies where politics and government are concerned.
If you find typos in this document, I would appreciate a notification. And, as always, if you find this material useful in your practice, I would be grateful to hear what you think of it. I seek your peer review.