Stand between two very low pulleys with shoulder width or narrower stance. Squat down and grasp stirrup attachments to each side. Stand upright with arms straight down to sides.
Step back with one leg while bending supporting leg. Plant forefoot far back on floor. Lower body by flexing knee and hip of supporting leg until knee of rear leg is almost in contact with floor. Return to original standing position by extending hip and knee of forward supporting leg and return rear leg next to supporting leg. Repeat movement with opposite legs alternating between sides.
Keep torso upright during lunge; flexible hip flexors are important. Forward knee should point same direction as foot throughout movement. A long lunge emphasizes Gluteus Maximus; short lunge emphasizes Quadriceps. See Cable Rear Step-down Lunge for similar exercise.