crawl, cripple
躄 centers on impaired movement: crawling or being crippled, where the legs cannot support normal walking.
躄 combines 足 (foot/leg) with 辟, which likely contributes the sound and may relate to the idea of being bent or impaired. The exact historical development is uncertain.
The bottom 足 (foot) is crushed under the heavy 辟 on top, leaving the person unable to walk and forced to crawl like a cripple.
For ヘキ, imagine a crippled person crawling to a heckling crowd: heckle -> ヘキ, and the jeering makes the crawling even more pitiful.