noun
tremendous strength; strength of a hundred people
Idiomatic expression emphasizing great physical or mental power, as if one person had the strength of a hundred.
彼が手伝ってくれるなら百人力だ。
If he helps, it'll be like having the strength of a hundred people.
応援の言葉が百人
The words of encouragement gave me tremendous strength.
千人力 means 'strength of a thousand people', an even stronger expression than 百人力.
Compound of 百 (hundred), 人 (people), and 力 (strength). The exact historical derivation is uncertain, but the expression is conventionally associated with the idea of multiplying one's power.