The phrase "weakest part" means the part or aspect that is the least strong or not as powerful as other parts.
Sentences with «weakest part»
This is perhaps the only weak part of the book. (bookbrowse.com)
The screen is the really the only weak part of the whole set - up. (pocket-lint.com)
The marriage of these two types of efforts plus supplemental lifts that assist or strengthen weaker parts of a lift truly results in stronger one rep max lifts. (bodytribe.com)