You don't have to walk away from and back to the squat rack when doing lunges, that is only one version. And trying to copy Coleman & Branch is not always the best idea. In fact you could put one foot in front of you and do 12 reps at a time and than altenate to the other foot for another 12 reps. Than , without rest, do 12 more reps on the foot you started out with, etc. Most people alternate each foot position after one rep but this gives too much rest, during the exercise, to the leg/hip/ham's in my view.When using walking lunges (as you do) each rep is not always the same distance as the last, usually shorter steps are taken as the walking distance increases. As you become tired/weaker the knee is not always in correct line with the body and could cause concern about injury. Lunges are not so much a quad movement as they are a ham & glute/hip exercise. Might consider step-ups, Bugarian one legged squats or other forms of quad/hip/ ham/glute movements if the lunges are not helping you meet your goals. Good Luck.