The lunge is a weight training exercise that is used to strengthen the quadriceps muscles, gluteal muscles and the muscles comprising the "hamstrings", the semitendinosus, the semimembranosus, and the biceps femoris. A long lunge emphasizes the glutes whereas a short lunge emphasizes the quadriceps.
To perform the lunge, the individual stands with their feet shoulder-width apart, and then steps forward, landing with the heel first. The knee should be exactly at 90 degrees and directly above the toes no over. The motion is continued until the back knee is nearly touching the ground. Then they return to their starting position by driving upward forward with the front leg, and repeat the exercise by stepping forward with their other leg.
There are several variations on this basic structure, with regard to both form and resistance in addition to varying the step length as mentioned above. The exercise is sometimes performed on an incline or on a bench to increase the difficulty. The walking lunge, as the name suggests, is performed by walking with lunging steps as described above. Sometimes the stationary lunge is performed without alternating the legs on each rep, in order to focus the effort more intensely.
The lunge can be performed without weights (i.e, bodyweight). However, weight trainers usually seek to increase the difficulty using either dumbbells (held in each hand) or a barbell with weights on it (held atop the neck and shoulders). Advanced trainers may find that grip strength is an issue with the dumbbell lunge, and therefore prefer the barbell lunge.