[Lisa~]

I hope you'll keep this exercise and not hunt for a replacement for it. Instead, work to figure out proper execution. Reaching lunges of all varieties are a staple of athletic workouts.

This reaching lunge targets the hip of the forward leg (the side that's up on the box). When you reach, your spine should remain neutral and if it does you will not feel much of anything in your low back. The low back doesn't even have to stabilize all that much. The goal is to lengthen the glute, not just by getting the hip lower than the knee, but by also moving the torso forward. The back leg's knee should bend, coming lower than the box. Now, when you return to standing you're doing it from a very low position. Think about those high step-ups we do. This is similar but slightly different. Drive off the forward heel, contracting that glute forcefully.

This movement is going to strengthen the working hip through a very big ROM. It has to contract from a very lengthened position with enough power to lift your whole body upward. This exercise will strengthen your squat and deadlift.