How to do a rfess (rear foot elevated split squat)
Disclaimer: please consult your physician before attempting any exercise.
Place one leg on an elevated surface (I.E. chair, couch, bench, etc.) behind you with the other leg in front.
Back leg on an elevated surface (chair)
Lower yourself until your quad (thigh) of the leg in front is parallel to the ground.
Upper leg (thigh/ quad) parallel to the ground
Press through the heel of your front foot to bring yourself to the starting position.
Return to starting position.
Caution: if you feel in intense stretch or strain in the elevated leg you are relying too much on the back leg, and/or you have tight hip flexors.
To correct this, simply lower the elevated surface and focus on putting the majority of your weight on the front leg. You may use a stick or other support to assist with this process.
You may also bend forward at the waist. This shortens the stretch on the opposing hip flexors.
Details: try to keep your shin (tibia) vertical. If you have knee issues please begin with a basic split squat until your form cleans up.
Vertical tibia (shin) will help avoid knee strain. Although, if you have apparently healthy knees a vertical shin doesn't matter.