The most common and most likely answer to this crossword clue is the 5 letter word AVAIL
I've seen this crossword clue in The Times
A
V
A
I
L
More clues leading to the result AVAIL
- Sort of lamp I plugged in picked up as benefit
- Be suffering? Take on the Bible for help
- A curtain said to be useful
- A bottle with contents switched is to be of use
- Use excellent line with King James Bible
- A bit of vehicle trouble could result in exercise
- Blocking the rejection of hot stuff, I am useful
- Use of a covering for the ears?
- Benefit from circulating hot stuff around island
- Use a mask, we are told
Buddy explains!

The straight part
We know that "exercise" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case exercise = avail.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 AVAIL mean?
AVAIL noun- Effect in achieving a goal or aim; purpose, use (now usually in negative constructions).
- Proceeds; profits from business transactions.
- An advertising slot or package.
- A press avail.
- Non-binding notice of availability for work.
- A readily available stock of oil.
- Benefit; value, profit; advantage toward success.
- Effort; striving.
- To turn to the advantage of.
- To be of service to.
- To promote; to assist.
- To be of use or advantage; to answer or serve the purpose; to have strength, force, or efficacy sufficient to accomplish the object.
- To provide; to make available.