The hamstrings (posterior thigh muscles) are made up of 3 long muscles that start at the bottom of your pelvis extending down the back of your thigh and along either side of your knee, to your shin bones.
Lie faceup with your heels in the TRX's foot cradles, legs extended and arms straight out to sides in a "T," palms on floor. Lift hips so body is aligned from shoulders to heels. Bend knees, pulling handles toward you. Extend legs to starting position.