One's lifted with ground-breaking strength (5)
I believe the answer is:
sinew
'strength' is the definition.
(I know that sinew is a type of strength)
'one's lifted with ground-breaking' is the wordplay.
'one's' becomes 'I's' (Roman numeral).
'lifted' says the letters should be written in reverse (going up in down clue).
'with ground breaking' becomes 'new' (I can't explain this - if you can you should believe this answer much more).
'is' reversed gives 'si'.
'si'+'new'='SINEW'
Can you help me to learn more?
(Other definitions for sinew that I've seen before include "Force" , "Tendon - ligament" , "Tough connective tissue" , "Inelastic tissue" , "It indicates strength" .)