The most common and most likely answer to this crossword clue is the 5 plus 5 letter word BENCH PRESS
I've seen this crossword clue in The Times
B
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Buddy explains!

The straight part
We know that "form of exercise" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case form of exercise = bench press.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BENCH PRESS mean?
BENCH PRESS verb- To press the weight of a barbell away from one's body while lying on a bench.