Muscles in Focus: Quadriceps for Stronger Sexier Legs
Reverse lunges beat forward lunges since they require you to move slowly and virtually guarantee you will not put undue strain on your knee.
Simply hold a bar or railing and lunge back with one leg, with the other foot planted firmly on the floor. Try and not quite touch the floor behind you with the leg you lift up and to hold the leg just a hair off the floor for one or two full breaths before pulling you leg back to center. Better yet, take the trailing leg and lift it up towards your shoulder as you come forward by bending your knee such that the leg never touches the floor for the duration of the exercise.