One of the lessons in the online Lingoni German course is about body parts (Körperteile). One of the body parts is der Po. The example sentence using der Po is:
Sie trainiert ihren Po.
and the translation given is:
She is training her bottom.
As a native English speaker, I'm sure that whatever the German sentence means, it does not match the translation given! The various uses of "to train", include training someone or something to do something:
He trains his dog to stand on its hind legs,
training a non-human inanimate thing into a particular form
She is training the climbing-rose over the archway
He is training a bonsai elm tree (i.e., training an elm-tree into a bonsai form)
and training with some sort of prepositional object
She is training for the marathon.
I assume that "she" is not doing any of these things, and that the given German sentence actually corresponds to something like:
She is strengthening her glutes (i.e. gluteal muscles)
She is in training to strengthen her glutes. / Note: NOT She is training her glutes.
However, the example sentence is devoid of context other than Körperteile. Have I guessed the meaning of the sentence correctly, or is something else intended? Potty training of a young girl?