How to Perform the Reverse Lunge
The reverse lunge is an excellent exercise for those with a muscle size and strength imbalance between the quadriceps muscles on each leg. Compared to forward lunges you should notice exceptionally less stress and sheer force on knees as well as increased engagement of the hamstrings and gluteus muscles.
While most people prefer to perform the forward lunge using a walking motion, up and down the gym, you should perform the reverse lunge in-place. Walking backwards in a crowded gym environment can be extremely challenging and dangerous. The reverse lunge is best performed after a compound movement like squats or in-lieu of leg curls or other machine-based exercises.
The reverse lunge targets the quadriceps, a muscle group comprised of four heads (Rectus Femoris, Vastus Lateralis, Vastus Intermedius, and Vastus Medialis (Internus).  This exercise engages the gluteus maximus, adductor magnus (inner thigh), and soleus (calf) to assist in completing the movement. The hamstrings, gastrocnemius (calf), erector spinae, gluteus medius and minimus, and quadratus lumborum (lower back) and act as stabilizers during the exercise. 
If you're looking to trigger serious quadriceps balance and growth while willing to endure serious delayed onset muscle soreness (DOMS) then you must include the reverse lunge in your routine.
MTS Nutrition CEO Marc Lobliner shows you how to perform the reverse lunge, aka the step back.
How to Perform the Reverse LungeYou can perform the reverse lunge using a barbell, dumbbells, kettlebells, Smith Machine, or cable apparatus. Although this walkthrough will focus on the performing the reverse lunge with a barbell you can apply the general form and tips to all setup variations.
Approach the barbell rack and adjust the pins so that the barbell is around mid-chest height. Select the appropriate working weight, ensuring you add an even amount of weight to both sides of the bar. don't place 25lbs on one side and 45lbs on the other side of the machine; doing so won't improve your gains and will likely lead to an injury.
Intermediate and advanced trainees can power clean the barbell from the floor and on to the upper back. If this is your first time performing the exercise then pick a conservative weight that you can safely lift for 8 to 12 repetitions.
Once you've selected the appropriate working weight approach the rack and grasp the bar with a traditional pronated grip (thumbs wrapped around the knuckles and palms facing away from you) slightly outside of shoulder width. If you have shoulder flexibility issues then widen your grip so it's comfortable.
With your hands on the bar take a hip width stance with your toes pointed forward and the barbell in-line with your mid foot. Keeping your feet planted pull your elbows towards your side and move your torso under the bar so that the barbell is resting on your trapezius and upper back muscles.
Keeping your chest high, shoulder down, and squeezing your shoulder blades down and together, dismount the barbell from the rack and take a few small steps backwards. At this point your feet should be hip-width and toes should be facing forward. This is your starting position.
After setting your starting position take a deep breath, brace your abdominals for impact, and take a moderate step back backwards with one your left leg. An excessively short or long step backwards will change the range of motion and target muscle group emphasis. At this point you should have you right foot firmly planted on the ground and your left foot should only have its toes in contact with the ground.
Begin moving left knee towards the ground by breaking at the knees and hips in the right leg. Continue descending until the right thigh and shin are almost horizontal and perpendicular, respectively, with the ground. At this point the left knee should being touching or slightly above the ground.
Once you hit the desired depth hold for 0 to 5 seconds. After holding the bottom position for the desired duration initiate the return to the starting position by pushing through the heel of your supporting right foot and toes of your left foot. As you return to the starting position your right leg should extend at the hips and knee and left knee should move away from the ground.
Both knees should extend (but not hyperextend) until both legs are straight, in-line with each other, and hip width apart. The movement pattern for the pushing portion should be the exact reverse of the lowering portion.
Complete for the desired number of repetitions and then switch legs. Perform the same number of repetitions and sets for both legs. Alternatively you can alternate legs for each repetition. Some lifters choose to exhale while lunging back to the starting position or in between in each repetition. Choose a breathing pattern that feels the most natural and comfortable for you.
This exercise can be performed using straight sets, pre-exhaust sets, drop sets, rest-pause sets, supersets, trisets, giant sets, paused reps, partial reps, forced reps, or slow negatives. As with any exercise, the two most important components are high-quality form and progression. Progression can take a variety of forms (e.g. more weight, sets, or reps, decreased rest period, improved rep quality, etc...) but strive to improve every time you walk in to the gym.
Reverse Lunge Form TipsSwitch Up Your Step Distance - To emphasize glute and hamstring involvement take a longer step backwards. To emphasize quadriceps involvement take a shorter step backwards. Regardless of what stance tweaks you make, aim to perform full range-of-motion reps with knees pointing in the same direction as your toes.
Switch Up Your Foot Height - Increase the intensity of the reverse lunge by placing the stationary forward foot on an elevated platform. You increase the movement's range of motion by increasing the distance the leg stepping backwards needs to travel to touch or stop slightly above the ground. This increased range of motion will also further stretch your hips and challenge your midsection to stay tight and upright.
Avoid Half Reps - The reverse lunge provides maximum benefit if performed using full range-of-motion reps. Partial reps place additional stress on the knees, reinforces poor movement patterns, and doesn't provide as much stimulus to the target and supporting muscle groups. Ensure the knee of the leg stepping backwards touches or is slightly above the ground at the bottom of the repetition.
Pause at the Bottom - Pausing at the bottom of the rep increases the intensity by extending the duration of the set and time under tension as well as stretches the adductors (inner thigh muscles) and hips. Pauses minimize you're likelihood of bouncing the knee off the ground and out of the bottom position to complete the rep.
Keep Your Torso Upright - Maintaining an upright torsos throughout the entire reverse lunge movement is crucial for ensuring the stress stays on the quadriceps, hamstrings, glutes, and abdominals rather than the lower back. If you have trouble maintaining an upright torso then focus on stretching your hip flexors and strengthening your abdominals and upper back.
ReferencesGriffing, James, et al. "Quadriceps." ExRx.net. N.p., 2015. Web.
Griffing, James, et al. "Barbell Rear Lunge." ExRx.net. N.p., 2015. Web.