The most common and most likely answer to this crossword clue is the 14 letter word CLEAN-AND-JERK
I've seen this crossword clue in Independent
C
L
E
A
N
-
A
N
D
-
J
E
R
K
Buddy explains!
The straight part
We know that "It requires strength" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it requires strength = clean-and-jerk.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.