SETUP: You can hold a weight if you wish, but this exercise works very well without. Stand next to a rowing machine and place your closest foot on the seat of the machine. I like to keep my hands up in front of chest & shoulders, as this encourages you to maintain proper posture (chest up & shoulders back).
REP: Step back by pushing the seat along the track, taking yourself down into a lunge position. Your grounded foot will be flat, and you can drive yourself back up to the starting point by pushing down into the floor as you slide the seat back to where you were.
TIP: Notice how I keep my body weight over my grounded foot, even as I move down into the lunge. This keeps all the tension on the working leg, and is exactly what we want. If you’re not keeping the tension here, you’ll feel the top of your back leg burning like mad.