The most common and most likely answer to this crossword clue is the 7 letter word BARBELL
I've seen this crossword clue in The Guardian
B
A
R
B
E
L
L
More clues leading to the result BARBELL
- Boozer to call jerk this?
- Jerk lifts this, omitting source of 8
- Weightlifter’s companion and I might ring last orders
- Bishop visits Andalusian city naked, displaying piercing
- Ken’s girlfriend, 1 down, starts to lift large weight in gym
- Fish with line that has weights, attached to rod
- Fish on line — it builds arm muscles
- Heavy load signals last drinks?
- It augments strength of pub whisky no end
Buddy explains!

The straight part
We know that "jerk this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case jerk this = barbell.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 BARBELL mean?
BARBELL noun- A wide steel bar with premeasured weights affixed to either end, with the central span open for the hands of the weightlifter.