Lunging is a functional exercise as it is a vital action for properly retrieving items off of the floor and for people themselves, being able to get up off of the floor after a fall.
I confess that I do not prescribe this exercise to patient's and I didn't know why until I visited a hotel gym the other day and was watching someone perform lunging exercises.
The way a traditional lunge is taught places excessive pressure on their lower back.
This occurs due to the relationship between the hips, pelvis, sacrum and lumbar spine.
When a human extends their hip past 30 degrees of extension, they should begin to have movement into extension at their lumbar spine. The majority of people, however begin to extend their lumbar spine well before (I have tested people who begin to extend their spines at as little as 2 degrees of hip extension).
A traditional lunge requires about 60 degrees of hip extension thus mandating the lumbar spine to move into extension.
The goal of patients with lower back pathology and those who are at risk for lower back pathology (everyone) is to stabilize their spine's and increase motion in the lower quadrant rather than feed into a pathological motion of premature extension of the lumbar spine.
In my experience Lumbar extension is the most common overused compensation for a lack of hip extension and pelvic motion in younger people.
I would suggest rather that keeping the shoulders back and trunk upright during a lunge, that a person hinge at their their hips forward at least 30 degrees and keep the spine in neutral alignment during both the forward and backward lunge. (As shown in the picture above)
Additionally I suggest that a person bring their opposite arm (with respect to the leg) forward and backward. (Not shown in the picture above)
