Quadriceps, hip flexors.
Sit on your heals. Stretch one leg out in front of you. Find a comfortable position for your foot on the bent leg, meaning you can keep your foot under your buttocks, or next to your outer hip (picture). Slowly start to rest back into your arms. If this is enough, stay there. Some people find a stretch when seated, so no need to rest back on your arms. If you do want to rest on your arms or back, feel free to play with it. Place a bolster under your spine, or some pillows for support. The leg that is not the target area, meaning the leg that is stretched out – play with a position for your leg that supports you in feeling the target area(s) in the bent leg. You can keep it straight, or bent, or allowing that leg to drop to the side (picture).
There´s not one way to do this pose. Feel the target area, and modify the pose until you feel the target area, and can allow your muscles to relax.
Stay around 2-5 minutes. Then slowly ease out of the pose and relax a moment before you shift leg.