to pull up the sleeves and stretch out the arms, to strike with bare fists
揎 centers on a forceful, exposed arm action: pulling up sleeves to stretch out the arms, or striking with bare fists. Both meanings share the idea of baring the arms for a direct, physical motion.
揎 combines 扌 (hand) with 宣, which likely contributes the sound. The exact historical development is uncertain, but the hand radical fits the meanings of pulling up sleeves and striking.
The left hand 扌 beside 宣 suggests a hand performing a bold, exposed action. Picture someone rolling up their sleeves with a hand, then stretching out the arm or striking with a bare fist.
For セン, imagine a person pulling up their sleeves to send a powerful bare-fisted punch: send -> セン, and the hand 扌 delivers the strike.