How to do: Lying Prone Quadriceps

Step-by-step instructions

1. 1Lay face down on the floor with your partner kneeling beside you. Flex one knee and raise that leg off the ground, attempting to touch your glutes with your foot. Your partner should hold the knee and ankle. This will be your starting position.
2. 2Attempt to extend your knee while your partner prevents any actual movement.
3. 3After 10-20 seconds, relax your muscles as your partner gently pushes the foot towards your glutes, further stretching the quadriceps and hip flexors.
4. 4After 10-20 seconds, switch sides.

Photos & base instructions from the open-source Free Exercise DB (public domain).