The backrest will help transfer some energy from paddle, through the body, and into the boat. A footrest helps even more.
It’s adjustable. The rail attached to the boat’s bottom has 5 10-24 nuts spaced along its length and epoxied into recesses. The footrest itself can be moved along the rail to the desired positioned and fastened down with the knob which, of course, holds a 10-24 threaded rod. Making it from white ash was straightforward. Drilling holes for fastening into the bottom of the boat offered a bit of tension.
This was the last structural component. Finishing is next.