The most common and most likely answer to this crossword clue is the 8 letter word EXERTING
E
X
E
R
T
I
N
G
Buddy explains!

The straight part
We know that "Using" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case using = exerting.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 EXERTING mean?
EXERTING verb- To put in vigorous action.
- To make use of, to apply, especially of something non-material.