The most common and most likely answer to this crossword clue is the 7 letter word AEROBIC
I've seen this crossword clue in Independent
A
E
R
O
B
I
C
More clues leading to the result AEROBIC
- Writer propping up bar as a kind of exercise
- I love caber-tossing as a form of exercise
- Like some exercise? I carried back some French wine bottles
- A drill set up since regularly requiring oxygen
- Old boy, somehow I race around — is the exercise this?
- Writer’s block previously related to exercise
- A sort of exercise — one carried back in a carriage, to begin with
- Type of workout song, sung by disrobed Robin and Charlie
- Caber one tossed outside circle, as form of exercise
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 = aerobic.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 AEROBIC mean?
AEROBIC adjective- Living or occurring only in the presence of oxygen e.g. aerobic bacteria.
- Of exercise, performed while maintaining a sufficient supply of oxygen to meet bodily energy needs.
- Of or relating to aerobics.