I have seen a study where the muscle growth (of rectus femoris and vastus lateralis) were compared for (smith machine) squats vs leg extensions (see summary of the study here. One result was that the leg extension was significantly better in developing the rectus femoris than the squat.
Now there are other exercises that might on the first view lead to a similar development of the rectus femoris as the leg extension:
- Traditional sissy squats
- Spanish squats
- Somersault Squats
- Brignole Cable Squats
- Smith Machine Hack squats/ Landmine Back Hack Squat
Maybe also some Lunge variations, Step ups or Split Squats.
So is there any data (muscle growth or EMG) which compares those movements to the leg extension? What are the results? Which exercises come close or are even better than the leg extensions for rectus femoris development? Are there exercises in the list above which I wrongly listed as candidates for this (why)?