The best replacement for hip extension is flexion.

The best alternatives to hip extension are rated as following:
★★★★★  flexion
★★  back extension
★  hyperextension
  knee flexion
  hip flexion

Your alternative for hip extension is not listed? Suggest!
Speaking about hip extension, one probably shouldn't forget about leg curl.

Other search terms related to hip extension and their ratings are:
★★★★★ leg curl
You have in mind a companion for hip extension and it is not yet here? Propose!



Google Trends

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hip extension
flexion
back extension