heavy work; manual labour
Refers to physically demanding work that relies on strength rather than skill or machinery.
This job is heavy manual labour, so it suits people confident in their physical strength.
feat of strength
An impressive display of physical power, often in a competitive or showy context.
He showed off a feat of strength by lifting a heavy rock.
力仕事 is a common synonym for heavy manual work, but 力業 can also imply a specific impressive act of strength.
Standard kanji spelling.
Irregular kanji usage; 技 is not standard for this reading but is sometimes seen.
Kana spelling used for clarity or when the kanji are not needed.
Compound of 力 (chikara, 'strength') and 業 (waza, 'work' or 'act'). The irregular spelling 力技 uses 技 (waza, 'technique') instead of 業, likely by analogy with similar compounds.