This combines three lunge variations – reverse, forward, and walking – into one seamless motion. It starts with a reverse lunge using the lead leg, transitions into a walking lunge using the other leg, and then finishes with a forward lunge using the lead leg all over again.
The kicker is that the "finish" isn't much of a finish at all. Instead, both legs have to continue to work in alternating fashion with hardly any rest. The result is a monster lunge variation that creates nasty amounts of metabolic stress and simultaneously crushes both legs.
Moreover, the brief period of perceived instability that occurs when the leg travels all the way forward to all the way back (and vice versa) targets hip flexor strength, trains deceleration and acceleration, and challenges joint stability throughout the lower half.
Try plugging in 2-3 sets as a finisher to cap off a lower-body day, doing it either for distance (20-25 yards) or for a high number of reps.