בְּכֹשֶׁר (בְּכֹּשֶׁר)
We may tend to think of the Hebrew word כשר as meaning edible by observant Jews – in other words, kosher. And indeed, כשר means fit to be consumed or done.
So it makes sense that the word for fitness is כושר. Likewise, to be in shape is להיות בכושר, or in more colloquial pronunciation, להיות בכּושר.
For example:
אתה מתנשף! אתה לא בכושר!
You’re gasping for breath! You’re not in shape!
Mind you, he’s got an answer to this accusation, which you’ll find in the conversation associated with this dose.