The Flaw: Leaning forward at the torso.
The Fix: As you lunge, concentrate on pushing your chest out so your torso stays perpendicular to the floor. Keeping your eyes facing forward (not down) will help, too. The objective with lunges is similar to that of squats: You want to keep the weight back and over your heels to take stress off the lower back and maximize tension on the glutes and quads.
The Flaw: Not stepping out far enough.
The Fix: Taking short steps while lunging leads to the knees traveling over the toes at the bottom of each rep. Over the long term, this can wreck the connective tissue in your knees. Step out far enough so your heel hits the floor first. To get the stride length right, do a few practice reps with no weight before adding the barbell.
The Flaw: Going too fast.
The Fix: Yes, you’re moving forward and covering ground with every rep, but this is not a race. If you’re going to lunge for time à la CrossFit, we recommend using only your bodyweight. When there’s a barbell resting across your back, keep the pace moderate and focus on strict form.